EP4347447A2

EP4347447A2 - Autonomous transport vehicle

Info

Publication number: EP4347447A2
Application number: EP22812388.1A
Authority: EP
Inventors: Akram ZAHDEH; Edward Macdonald; Todd Kepple
Original assignee: Symbotic Inc
Current assignee: Symbotic Inc
Priority date: 2021-05-26
Filing date: 2022-05-26
Publication date: 2024-04-10
Also published as: WO2022251864A4; CA3220397A1; WO2022251864A3; WO2022251864A2; KR20240013809A

Abstract

An autonomous transport vehicle, for transporting items in a storage and retrieval system, includes a frame, a controller, at least two independently driven drive wheels mounted to the frame, and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torque to the at least one caster wheel assisting castering of the at least one caster wheel. The controller is communicably connected to the castering assistance motor and configured to effect via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

Description

AUTONOMOUS TRANSPORT VEHICLE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a non-provisional of and claims the benefit of United States provisional patent application numbers 63/193,188 filed on May 26, 2021; 63/213,589 filed on June 22,

2021; and 63/241,893 filed on September 8, 2021 the disclosures of which are incorporated herein by reference in their entireties.

BACKGROUND

1. Field

[0002] The disclosed embodiment generally relates to material handling systems, and more particularly, to transports for automated storage and retrieval systems.

2. Brief Description of Related Developments

[0003] Generally, autonomous transport vehicles in logistics/warehouse facilities are manufactured to have a predetermined form factor for an assigned task in a given environment. These autonomous transport vehicles are constructed of a bespoke cast or machined chassis/frame that is generally heavy and costly to produce. The other components (e.g., wheels, transfer arms, etc.) are mounted to the frame and are carried with the frame as the autonomous transport vehicle traverses along a traverse surface. The mass of the autonomous transport vehicle, in part from the cast or machined frame, calls for appropriately sized motors and suspension components to drive and carry the mass of the autonomous transport vehicles. These motors and suspension components may also increase the cost and weight of the autonomous transport vehicle.

[0004] In addition, conventional autonomous transport vehicles in automated storage and retrieval systems (such as in warehouses or stores) generally are supported on wheels that are fixed (e.g., hard mounted) to a frame of the autonomous transport vehicle. With the conventional wheel configuration the trajectory of the autonomous transport vehicle along a transport path may be altered with a traversal of the autonomous transport vehicle over uneven portion of a deck or aisle on/along which the autonomous transport vehicle traverses. Vibrations may also be induced to the storage structure of the automated storage and retrieval system with traverse of the autonomous transport vehicle over on/along the deck or aisle, which vibrations may induce movement of case unit (s) held on racks of the automated storage and retrieval system structure.

[0005] One or more wheels of the conventional autonomous transport vehicles are drive wheels that drive the autonomous transport vehicle on/along the deck and aisle. In some circumstances the drive wheels may lose traction with the deck or aisle causing the drive wheel to slip. This drive wheel slippage may cause create odometry/localization challenges with respect to locating the autonomous transport vehicle within the automated storage and retrieval system structure. Some conventional autonomous transport vehicles employ a direct drive for driving the drive wheels which may increase the odometry/localization challenges due to, for example, a large inertia ratio between the wheel drive motors and the chassis of the autonomous transport vehicle. In some instances the wheel slip of the direct drive motors may more than about 90° of wheel slip/rotation before controls of the autonomous transport vehicle begin to mitigate the wheel slip. The above-mentioned wheel slip may create discrepancies with respect to localization/positioning of the autonomous transport vehicles within the storage structure.

[0006] Generally the automated storage and retrieval systems employ the autonomous transport vehicles to transport cased goods or case units to and from storage locations in a storage array. These autonomous transport vehicles generally travel along decks that provide unconstrained travel of the autonomous transport vehicle. The decks provide access to picking aisles (along which case units are stored), in which picking aisles the travel of the autonomous transport vehicles is constrained (i.e., guided) by rails. Generally, these autonomous transport vehicles include casters on one (e.g., front) end and differentially driven drive wheels on the opposite (e.g., rear) end of the autonomous transport vehicle. These casters and drive wheels are also located on outer extents (e.g., the outer periphery and away from a center of mass of the autonomous transport vehicle) of the autonomous transport vehicle to effect transfer of case units to and from the autonomous transport vehicle. [0007] Where the autonomous transport vehicle is constrained within a storage aisle, reversal of a direction of travel of the autonomous transport vehicle means that the casters rotate based on a direction of trail of the caster wheel. Here, a reversal of travel direction causes the caster wheel to rotate about a caster pivot axis about 180 degrees so that the caster wheel trails the direction of travel; however, there is no control over which direction the caster wheels rotates about the caster pivot axis (e.g., whether the caster wheels rotate towards or away from a respective rail on which the autonomous transport vehicle is travelling). Rotation of the caster wheel towards the respective rail may cause the autonomous transport vehicle to become wedged within the picking aisle and travel of the autonomous transport vehicle along the picking aisle may be prevented. To overcome this problem locking casters have been employed to lock rotation of the caster wheel about the caster pivot axis; however, the locking mechanism of the locking casters increases the mechanical complexity and cost of the autonomous transport vehicle. The performance of the autonomous transport vehicle may also be impacted by unlocking the rotation of the caster wheel about the caster pivot axis.

[0008] Placement of the drive wheels away from the center of mass of the autonomous transport vehicle increases an amount of drive wheel torque required for differential steerinq of the autonomous transport vehicle (compared to drive wheel torque required for differential steering with drive wheels placed at the center of mass). This additional torque requirement increases the size and cost of the drive motors and associated electronics, as well as increases frictional requirements between the drive wheels and driving surface. Frictional scrubbing of the caster wheels when rotating about the caster pivot axis during turning of the autonomous transport vehicle also increases amount of drive wheel torque required for differential steering of the autonomous transport vehicle as well as decreases a service life of the caster wheels and riding surfaces on which the caster wheels travel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The foregoing aspects and other features of the disclosed embodiment are explained in the following description, taken in connection with the accompanying drawings, wherein:

[0010] Fig. 1 is a schematic block diagram of an exemplary automated storage and retrieval system incorporating aspects of the disclosed embodiment;

[0011] Fig. 2 is a schematic perspective illustration of an autonomous transport vehicle of the automated storage and retrieval system of Fig. 1 in accordance with aspects of the disclosed embodiment;

[0012] Fig. 2A is a schematic perspective illustration of the exemplary autonomous transport vehicle of the automated storage and retrieval system of Fig. 2 in a first configuration in accordance with aspects of the disclosed embodiment; [0013] Fig. 2B is a schematic perspective illustration of the exemplary autonomous transport vehicle of Fig. 2 in a second configuration in accordance with aspects of the disclosed embodiment;

[0014] Fig. 2C is a schematic elevation illustration of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0015] Fig. 3A is a schematic exploded illustration of a portion of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0016] Fig. 3B is a schematic plan view of a portion of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0017] Fig. 3C is a schematic perspective illustration of a portion of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0018] Fig. 4 is a partial exploded illustration of a portion of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0019] Fig. 5A is a schematic perspective illustration of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment; [0020] Fig. 5B is a schematic perspective illustration of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0021] Fig. 6 is a perspective illustration of a portion of the exemplary autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0022] Fig. 7 is an exemplary block diagram of a method in accordance with aspects of the disclosed embodiment;

[0023] Fig. 8 is an exemplary block diagram of a method in accordance with aspects of the disclosed embodiment;

[0024] Fig. 9A is a schematic elevation view of an end of the autonomous transport vehicle of Fig. 2 in a first state in accordance with aspects of the disclosed embodiment;

[0025] Fig. 9B is an elevation view of an end of the autonomous transport vehicle of Fig. 2 in a second state accordance with aspects of the disclosed embodiment;

[0026] Fig. 10A is a schematic elevation view of an end of the autonomous transport vehicle of Fig. 2 in a first state in accordance with aspects of the disclosed embodiment;

[0027] Fig. 10B is an elevation view of an end of the autonomous transport vehicle of Fig. 2 in a second state accordance with aspects of the disclosed embodiment; [0028] Fig. IOC is a schematic perspective illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0029] Fig. 11A is a schematic plan illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0030] Fig. 11B is a schematic plan illustration of a portion of the autonomous transport vehicle of Fig. 2 in a first state in accordance with aspects of the disclosed embodiment;

[0031] Fig. 11C is a schematic plan illustration of a portion of the autonomous transport vehicle of Fig. 2 in the first state in accordance with aspects of the disclosed embodiment;

[0032] Figs. 11D and HE are schematic plan illustrations of a portion of the autonomous transport vehicle of Fig. 2 in a second state in accordance with aspects of the disclosed embodiment;

[0033] Fig. 12A is a schematic perspective illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0034] Fig. 12B is a schematic partial section view of the portion of the autonomous transport vehicle of Fig. 12A in accordance with aspects of the disclosed embodiment;

[0035] Fig. 13A is a schematic elevation view of the portion of the autonomous transport vehicle of Fig. 12A in a first state in accordance with aspects of the disclosed embodiment; [0036] Fig. 13B is a schematic elevation view of the portion of the autonomous transport vehicle of Fig. 12A in a second state in accordance with aspects of the disclosed embodiment;

[0037] Fig. 14A is a perspective illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0038] Fig. 14B is a cross-sectional illustration of the portion of the autonomous transport vehicle shown in Fig. 14A in accordance with aspects of the disclosed embodiment;

[0039] Fig. 15A is a schematic elevation view of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0040] Fig. 15B is a schematic elevation (end) view of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0041] Fig. 16 is an exemplary graph illustrating a wheel slip event in accordance with aspects of the disclosed embodiment;

[0042] Fig. 17 is a schematic block diagram of a traction control system of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0043] Fig. 18 is a schematic block diagram of a portion of the traction control system of Fig. 17 in accordance with aspects of the disclosed embodiment; [0044] Fig. 19 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0045] Fig. 20 is an exemplary plan illustration of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0046] Fig. 21 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0047] Fig. 22 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0048] Figs. 23A and 23B are exemplary plots illustrating tuning of a transient response of the autonomous transport vehicle of Fig. 2 unloaded (not carrying payload) in accordance with aspects of the disclosed embodiment;

[0049] Figs. 24A and 24B are exemplary plots illustrating tuning of a transient response of the autonomous transport vehicle of Fig. 2 loaded (carrying payload) in accordance with aspects of the disclosed embodiment;

[0050] Fig. 25 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0051] Fig. 26 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0052] Fig. 27 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment; [0053] Fig. 28 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment; and

[0054] Fig. 29 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment;

[0055] Fig. 30 is a schematic plan illustration of autonomous transport vehicle traverse in a picking aisle in accordance with aspects of the disclosed embodiment;

[0056] Fig. 31 is a schematic plan illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0057] Fig. 32 is a schematic plan illustration of a portion of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment;

[0058] Fig. 33 is a schematic illustration of an exemplary control architecture of the autonomous transport vehicle of Fig. 2 in accordance with aspects of the disclosed embodiment; and

[0059] Fig. 34 is an exemplary flow diagram of a method in accordance with aspects of the disclosed embodiment.

DETAILED DESCRIPTION

[0060] Fig. 1 illustrates an exemplary automated storage and retrieval system 100 in accordance with aspects of the disclosed embodiment. Although the aspects of the disclosed embodiment will be described with reference to the drawings, it should be understood that the aspects of the disclosed embodiment can be embodied in many forms. In addition, any suitable size, shape or type of elements or materials could be used.

[0061] The aspects of the disclosed embodiment provide an automated storage and retrieval system with a modular autonomous transport robot vehicle 110 (referred to herein as an autonomous transport (or guided) vehicle or bot). The autonomous transport vehicle 110 includes selectable modular chassis, motor, and case unit handling components, the selection of which configures (or reconfigures) the autonomous transport vehicle 110 with different case handling characteristics (e.g., chassis length, chassis width, payload area size, case unit lift height, suspension spring preload, suspension spring rate, chassis rigidity characteristics, etc.) that may depend on a size/weight of the case units being handled and/or storage characteristics (e.g., shelf height, multiple shelves serviced from a common rolling surface/deck) of the automated storage and retrieval system 100 storage structure 130. The modular chassis components (described herein) may be fabricated at least in part from readily available bar stock, tubing stock, channel stock, etc. so as to reduce manufacturing/machining costs compared to conventional autonomous transport vehicles having bespoke chassis/frames. At least the modular chassis components contribute to a reduced weight compared to the conventional autonomous transport vehicles having bespoke chassis/frames. The reduced weight may provide for less wear on the rolling surfaces along which the autonomous transport vehicle 110 travels as well as less wear on the wheels of the autonomous transport vehicle 110.

[0062] The aspects of the disclosed embodiment provide for synergistic dynamic response of an autonomous transport vehicle 110 (of the automated storage and retrieval system 100) in transit through the automated storage and retrieval system 100. In accordance with the aspects of the disclosed embodiment, the autonomous transport vehicle 110 (also referred to herein as an autonomous transport robot) includes a fully independent suspension system and traction control system that synergistically provide a dynamic response of the autonomous transport vehicle 110 in transit that effects superior localization (from wheel odometry) of the autonomous transport vehicle within the automated storage and retrieval system 100 when compared to conventional autonomous transport vehicles whose position/location is determined with wheel odometry. For example, the fully independent suspension 280, 780 (see Fig. 2) is configured to maintain a substantially steady state contact patch CNTC (see Fig. 3A) between wheels of the autonomous transport vehicle 110 and a rolling surface 395 (see Fig. 2) of the storage and retrieval system 100 (e.g., the wheel is in substantial steady state/continuous contact with the rolling surface) over each rolling surface transient 395T (see Fig. 4B) throughout traverse of the wheel(s) over the rolling surface 395. It is noted that the minimized unspring mass of the drive wheels 260A, 260B may at least in part contribute to maintaining the substantially steady state contact patch CNC as there is less unsprung mass to influence wheel hop off the rolling surface 395 (e.g., where the greater the unsprung mass the greater the wheel hop off the rolling surface). The substantially steady state contact patch CNTC provides for accurate wheel odometry (e.g., as determined by wheel position sensors/encoders 1080W of the sensors 1080 - see Fig. 10) determination of the autonomous transport vehicle 110 with the respective wheels in transit on the rolling surface 395 and over any transients 395T (Fig. 4B - such as joints, debris, etc.) that may exist on the rolling surface 395 and that would otherwise cause the wheels to lift away from (e.g., affecting inaccuracies in wheel odometry) the rolling surface 395. The traction control system 1000 (see Fig. 10) is configured with a low latency that mitigates wheel slippage to less than about 1° of wheel slip/rotation, that along with the maintaining of the substantially steady state contact path CNTC synergistically provides the autonomous transport vehicle with superior localization (from wheel odometry) within the automated storage and retrieval system 100 compared to conventional autonomous transport vehicles.

[0063] In accordance with the aspects of the disclosed embodiment, the fully independent suspension system and the traction control system 1000 provide a dynamic response of the autonomous transport vehicle 110 in transit that effects superior takt times for fulfilling product orders. For example, the fully independent suspension is configured to provide the autonomous transport vehicle with a substantially constant/steady state ride height RHT (see Fig. 8A) at which case units CU are held. The fully independent suspension also reduces vibration of the autonomous transport vehicle (due to traverse of the autonomous transport vehicle through the storage structure) that may otherwise cause movement of the case unit(s) within a payload bed 210B (see Fig. 2) of the autonomous transport vehicle. As noted above, the traction control system 100 has a low latency for resolving wheel slip and may substantially prevent yawing of the autonomous transport vehicle that may otherwise cause movement of the case unit(s) within a payload bed 210B of the autonomous transport vehicle. Here, the synergistic dynamic response of the autonomous transport vehicle 110 in transit provides for ungripped/released manipulation of case unit (s) CU within the payload bed 210B substantially simultaneously with start and stop traverse motions of the autonomous transport vehicle 110 along the rolling surface as described herein, which effects the superior takt times compared to conventional autonomous transport vehicles whose traversal along a surface is stopped prior to releasing the case unit(s) for manipulation.

[0064] The fully independent suspension system of the autonomous transport vehicle 110 may also effect locating the ride height RHT at a minimized height from the rolling surface. Minimizing the ride height RHT provides for placement of case unit support surfaces of case unit holding locations closer to the rolling surface 395, which may increase a vertical storage density of the automated storage and retrieval system 100.

[0065] The aspects of the disclosed embodiment also provide for an automated storage and retrieval system 100 that includes a non- holonomic differential drive type autonomous transport vehicle 110 that has two degrees of freedom (i.e., linear and rotational motion). The aspects of the disclosed embodiment address one or more of the deficiencies noted above with respect to conventional autonomous transport vehicles. For example, the autonomous transport vehicle 110 includes independently controllable caster wheels 250 (also referred to as a caster) that are configured as independently controllable motorized caster wheels 600M (Fig. 2) (e.g., caster wheels that include motors capable of driving rotation of a wheel 610 of the caster wheel 250 about a caster pivot axis 691 - see, e.g., Fig. 3A). The motorized caster wheels 600M provide for pivoting of the wheel 610 about the caster pivot axis 691 at least prior to forward or reverse translation of the autonomous transport vehicle 110 to prepare the autonomous transport vehicle for a turn which may provide about a 20% faster turn of the autonomous transport vehicle 110 compared to turning with differential drive wheel 260A, 260B steering alone. As will be described herein, the motorized caster wheels 600M provide for pivoting of the wheel 610 about the caster pivot axis 691 with translation of the autonomous transport vehicle 110 (i.e., with the autonomous transport vehicle 110 in motion) to one or more of maintain a steady state orientation of the wheel 610 and to assist with steering of the autonomous transport vehicle 110. A feed forward control is applied to each of the motorized caster wheels 600M to independently control a turning/steering angle of the motorized caster wheels 600M relative to a travel/turn path of the autonomous transport vehicle 110 so that the motorized caster wheels 600M provide substantially zero scrub (e.g., substantially zero lateral frictional forces are exerted on the wheel 610 by a travel surface along which the caster traverse) along the travel/turn path.

[0066] In accordance with the aspects of the disclosed embodiment, the substantially zero scrub caster wheel 250 movement along the travel/turn path of the autonomous transport vehicle 110 minimizes an amount of energy exerted by drive units 261 of the autonomous transport vehicle 110 drive wheels 260 (see, e.g., Fig. 2) when making a turn by about 20%, compared to making a turn with caster scrub (e.g., with caster scrub the amount of energy needed to turn is increased such that some of the energy is used in overcoming frictional forces due to scrubbing of the caster wheel on the travel surface). Minimizing the amount of energy needed to drive/turn the autonomous transport vehicle 110 provides for optimization of the drive motors 261M of the drive units 261 for linear inertial changes of the autonomous transport vehicle rather than being configured for generating moments large enough to induce castering of the caster wheels 250. Here optimization of the drive motors 261M, and the drives 261 in general, includes at least a reduction in drive motor 261M (see, e.g., Fig. 2) size (and a reduction in size of the associated electronics for driving the drive motor 261M) as well as a reduction in frictional requirements between the drive wheels 260 and the travel surface (which reduces wear of the wheels and wear of the travel surfaces on which the wheels traverse). The aspects of the disclosed embodiment also provide for decreasing a weight and cost of the autonomous transport vehicle 110 by virtue of the reduction in size of the drive motors 261M and associated electronics. [0067] It is noted that the modular chassis components, the independent suspension components and the zero scrub motorized caster wheels may be employed on the autonomous transport vehicle 110 in any suitable combination. For example, the autonomous transport vehicle 110 may include the modular chassis alone or in combination with any one or more of the fully independent suspension and the zero scrub motorized caster wheels; the autonomous transport vehicle 110 may include the fully independent suspension alone or in combination with one or more of the modular chassis and the zero scrub motorized caster wheels; or the autonomous transport vehicle 110 may include the zero scrub motorized caster wheels alone or in combination with any one or more of the modular chassis and fully independent suspension.

[0068] The automated storage and retrieval system 100 in Fig. 1, in which the autonomous transport vehicle 110 operates, may be disposed in a retail distribution center or warehouse, for example, to fulfill orders received from retail stores for replenishment goods shipped in cases, packages, and or parcels. The terms case, package and parcel are used interchangeably herein and as noted before may be any container that may be used for shipping and may be filled with case or more product units by the producer. Case or cases as used herein means case, package or parcel units not stored in trays, on totes, etc. (e.g. uncontained), and/or a tote of individual goods that are of a common or mixed goods type.. It is noted that the case units CU (also referred to herein as mixed cases, cases, and shipping units, or payload) may include cases of items/unit (e.g. case of soup cans, boxes of cereal, etc.) or individual item/units that are adapted to be taken off of or placed on a pallet. In accordance with the exemplary embodiment, shipping cases or case units (e.g. cartons, barrels, boxes, crates, jugs, shrink wrapped trays or groups or any other suitable device for holding case units) may have variable sizes and may be used to hold case units in shipping and may be configured so they are capable of being palletized for shipping. Case units may also include totes, boxes, and/or containers of one or more individual goods, unpacked/decommissioned (generally referred to as breakpack goods) from original packaging and placed into the tote, boxes, and/or containers (collectively referred to as totes) with one or more other individual goods of mixed or common types at an order fill station. It is noted that when, for example, incoming bundles or pallets (e.g. from manufacturers or suppliers of case units arrive at the storage and retrieval system for replenishment of the automated storage and retrieval system 100, the content of each pallet may be uniform (e.g. each pallet holds a predetermined number of the same item - one pallet holds soup and another pallet holds cereal). As may be realized, the cases of such pallet load may be substantially similar or in other words, homogenous cases (e.g. similar dimensions), and may have the same SKU (otherwise, as noted before the pallets may be "rainbow" pallets having layers formed of homogeneous cases). As pallets leave the storage and retrieval system, with cases or totes filling replenishment orders, the pallets may contain any suitable number and combination of different case units (e.g. each pallet may hold different types of case units - a pallet holds a combination of canned soup, cereal, beverage packs, cosmetics and household cleaners). The cases combined onto a single pallet may have different dimensions and/or different SKU's.

[0069] The automated storage and retrieval system may be generally described as a storage and retrieval engine 190 coupled to a palletizer 162. In greater detail now, and with reference still to Fig. 1, the storage and retrieval system 100 may be configured for installation in, for example, existing warehouse structures or adapted to new warehouse structures. As noted before the system 100 shown in Fig. 1 is representative and may include for example, in-feed and out-feed conveyors terminating on respective transfer stations 170, 160, lift module(s) 150A, 150B, a storage structure 130, and a number of autonomous transport vehicles 110 (also referred to herein as robots, "bots," or autonomous transport robots). It is noted that the storage and retrieval engine 190 is formed at least by the storage structure 130 and the bots 110 (and in some aspect the lift modules 150A, 150B; however in other aspects the lift modules 150A, 150B may form vertical seguencers in addition to the storage and retrieval engine 190 as described in United States patent application number 17/091,265 filed on November 6, 2020 and titled "Pallet Building System with Flexible Sequencing, " the disclosure of which is incorporated herein by reference in its entirety). In alternate aspects, the storage and retrieval system 100 may also include robot or bot transfer stations (not shown) that may provide an interface between the bots 110 and the lift module(s) 150A, 150B. The storage structure 130 may include multiple levels of storage rack modules where each storage structure level 130L of the storage structure 130 includes respective picking aisles 130A, and transfer decks 130B for transferring case units between any of the storage areas of the storage structure 130 and a shelf of the lift module(s) 150A, 150B. The picking aisles 130A are in one aspect configured to provide guided travel of the bots 110 (such as along rails 130AR, 800 - see also Fig. 30) while in other aspects the picking aisles are configured to provide unrestrained travel of the bot 110 (e.g., the picking aisles are open and undeterministic with respect to bot 110 guidance/travel). The transfer decks 130B have open and undeterministic bot support travel surfaces along which the bots 110 travel under guidance and control provided by bot steering (as will be described herein). In one or more aspects, the transfer decks have multiple lanes between which the bots 110 freely transition for accessing the picking aisles 130A and/or lift modules 150A, 150B. As used herein, "open and undeterministic" denotes the travel surface of the picking aisle and/or the transfer deck has no mechanical/physical restraints/guides (such as guide rails) that delimit the travel of the autonomous transport vehicle 110 to any given path along the travel surface. It is noted that while the aspects of the disclosed embodiment are described with respect to a multilevel storage array, the aspects of the disclosed embodiment may be equally applied to a single level storage array that is disposed on a facility floor or elevated above the facility floor.

[0070] The picking aisles 130A, and transfer decks 130B also allow the bots 110 to place case units CU into picking stock and to retrieve ordered case units CU. In alternate aspects, each level may also include respective bot transfer stations 140. The bots 110 may be configured to place case units, such as the above described retail merchandise, into picking stock in the one or more storage structure levels 130L of the storage structure 130 and then selectively retrieve ordered case units for shipping the ordered case units to, for example, a store or other suitable location. The in- feed transfer stations 170 and out-feed transfer stations 160 may operate together with their respective lift module(s) 150A, 150B for bi-directionally transferring case units CU to and from one or more storage structure levels 130L of the storage structure 130. It is noted that while the lift modules 150A, 150B may be described as being dedicated inbound lift modules 150A and outbound lift modules 150B, in alternate aspects each of the lift modules 150A, 150B may be used for both inbound and outbound transfer of case units from the storage and retrieval system 100.

[0071] As may be realized, the storage and retrieval system 100 may include multiple in-feed and out-feed lift modules 150A, 150B that are accessible by, for example, bots 110 of the storage and retrieval system 100 so that one or more case unit(s), uncontained (e.g. case unit(s) are not held in trays), or contained (within a tray or tote) can be transferred from a lift module 150A, 150B to each storage space on a respective level and from each storage space to any one of the lift modules 150A, 150B on a respective level. The bots 110 may be configured to transfer the case units between the storage spaces 130S (e.g., located in the picking aisles 130A or other suitable storage space/case unit buffer disposed along the transfer deck 130B) and the lift modules 150A, 150B. Generally, the lift modules 150A, 150B include at least one movable payload support that may move the case unit (s) between the in-feed and out-feed transfer stations 160, 170 and the respective level of the storage space where the case unit(s) is stored and retrieved. The lift module(s) may have any suitable configuration, such as for example reciprocating lift, or any other suitable configuration. The lift module(s) 150A, 150B include any suitable controller (such as controller 120 or other suitable controller coupled to controller 120, warehouse management system 2500, and/or palletizer controller 164, 164') and may form a seguencer or sorter in a manner similar to that described in United States patent application number 16/444,592 filed on June 18, 2019 and titled "Vertical Sequencer for Product Order Fulfillment" (the disclosure of which is incorporated herein by reference in its entirety).

[0072] The automated storage and retrieval system may include a control system, comprising for example one or more control servers 120 that are communicably connected to the in-feed and out-feed conveyors and transfer stations 170, 160, the lift modules 150A, 150B, and the bots 110 via a suitable communication and control network 180. The communication and control network 180 may have any suitable architecture which, for example, may incorporate various programmable logic controllers (PLC) such as for commanding the operations of the in-feed and out-feed conveyors and transfer stations 170, 160, the lift modules 150A, 150B, and other suitable system automation. The control server 120 may include high level programming that effects a case management system (CMS) 120 managing the case flow system. The network 180 may further include suitable communication for effecting a bi directional interface with the bots 110. For example, the bots 110 may include an on-board processor/controller 1220. The network 180 may include a suitable bi-directional communication suite enabling the bot controller 1220 to request or receive commands from the control server 180 for effecting desired transport (e.g. placing into storage locations or retrieving from storage locations) of case units and to send desired bot 110 information and data including bot 110 ephemeris, status and other desired data, to the control server 120. As seen in Fig. 1, the control server 120 may be further connected to a warehouse management system 2500 for providing, for example, inventory management, and customer order fulfillment information to the CMS level program of control server 120. A suitable example of an automated storage and retrieval system arranged for holding and storing case units is described in U.S. Patent No. 9,096,375, issued on August 4, 2015 the disclosure of which is incorporated by reference herein in its entirety.

[0073] Referring now to Fig. 2, the autonomous transport vehicle or bot 110 (which may also be referred to herein as an autonomous guided vehicle or robot) includes a chassis or frame 200 (which may also be referred to as a chassis bus) with a payload support or bed 210B (which may be integral to the frame 200). The frame 200 has a front end 200E1 and a back end 200E2 that define (and between which extends) a longitudinal axis or axis of symmetry LAX of the autonomous transport vehicle 110. The frame 200 may be a space frame 200S (see, e.g., Fig. 2A) and may be constructed (e.g., formed) of any suitable material (e.g., including but not limited to steel, aluminum, composites, etc.). [0074] As will be described herein, and referring briefly to Fig. 2A, the space frame 200S has predetermined modular coupling interfaces (see, e.g., interfaces 3070-3075 - Fig. 3A) that have known locations relative to each other and include datums for positioning/locating components of the autonomous transport vehicle relative to each other as described herein. Each of the modular coupling interfaces is disposed for removably coupling, as a modular unit, a corresponding predetermined electronic and/or mechanical component module of the autonomous transport vehicle 110 to the chassis 200 so that the autonomous transport robot vehicle 110 has a modular construction. The predetermined modular coupling interfaces include at least one of at least one caster wheel module coupling interface 3074, 3075, at least one drive wheel module coupling interface 3072, 3073, and at least one payload support module coupling interface 3070, 3071. As described herein, the corresponding predetermined electronic and/or mechanical component modules include, but are not limited to, ride wheel modules (e.g., at least one drive wheel module 260M and at least one caster wheel module 250M), payload support module 210M, control module 1220M, etc. The drive wheel module 260M has a drive wheel 260A, 260B removably coupled as a module unit to the chassis 200 with a corresponding drive wheel module coupling interface 3072, 3073. The caster wheel module 250M has a caster wheel 250A, 250B removably coupled as a module unit to the chassis 200 with a corresponding caster wheel module coupling interface 3074, 3075. The payload support module 210M has a payload support contact surface 210BS removably coupled as a module unit to the chassis 200 with a corresponding payload support module coupling interface 3070, 3071.

[0075] Referring again to Fig. 2, the autonomous transport vehicle 110 also includes a case handling assembly or payload support 210 configured to handle cases/payloads transported by the autonomous transport vehicle 110. The case handling assembly 210 may be provided as the payload support module 210M and is removably connected to the chassis 200 (e.g., with mechanical fasteners) and is dependent therefrom. The case handling assembly 210 includes at least any suitable payload support contact surface or bed 210B on which payloads are placed for transport and/or any suitable transfer arm 210A connected to the frame and configured for autonomous transfer of payload(s) to and from the frame 200 (e.g., transfer of payload(s) between the autonomous transport vehicle 110 and a payload holding location, such as any suitable payload storage location, a shelf of lift module 150A, 150B, and/or any other suitable payload holding location). The transfer arm 210A is configured to extend laterally in direction LAT and/or vertically in direction VER to transport payloads to and from the payload bed 210. Examples of suitable payload beds 210B and transfer arms 210A and/or autonomous transport vehicles to which the aspects of the disclosed embodiment may be applied can be found in United States pre-grant publication number 2012/0189416 published on July 26, 2012 (United States patent application number 13/326,952 filed on December 15, 2011) and titled "Automated Bot with Transfer Arm"; United States patent number 7591630 issued on September 22, 2009 titled "Materials-Handling System Using Autonomous Transfer and Transport Vehicles"; United States patent number 7991505 issued on August 2, 2011 titled "Materials-Handling System Using Autonomous Transfer and Transport Vehicles"; United States patent number 9561905 issued on February 7, 2017 titled "Autonomous Transport Vehicle"; United States patent number 9082112 issued on July 14, 2015 titled "Autonomous Transport Vehicle Charging System"; United States patent number 9850079 issued on December 26, 2017 titled "Storage and Retrieval System Transport Vehicle"; United States patent number 9187244 issued on November 17, 2015 titled "Bot Payload Alignment and Sensing"; United States patent number 9499338 issued on November 22, 2016 titled "Automated Bot Transfer Arm Drive System"; United States patent number 8965619 issued on February 24, 2015 titled "Bot Having High Speed Stability"; United States patent number 9008884 issued on April 14, 2015 titled "Bot Position Sensing"; United States patent number 8425173 issued on April 23, 2013 titled "Autonomous Transports for Storage and Retrieval Systems"; and United States patent number 8696010 issued on April 15, 2014 titled "Suspension System for Autonomous Transports", the disclosures of which are incorporated herein by reference in their entireties.

[0076] Referring to Figs. 2 and 2A, as will be described in greater detail herein, the chassis 200 includes ride wheels dependent from the chassis 200, proximate opposite end corners 200E1C1, 200E1C2, 200E2C1, 200E2C2 of the chassis 200, on which the autonomous transport vehicle 110 rides so as to traverse a traverse surface TS of the storage and retrieval system 100 storage structure level 130 on which the autonomous transport vehicle 110 is disposed. The ride wheels 250, 260 include at least one idler or caster wheel 250A, 250B and at least one drive wheel 260A, 260B supporting the chassis 200 from the traverse surface TS. For example, one or more idler wheels 250A, 250B are disposed adjacent the front end 200E1 (e.g., a pair of caster wheels 250A, 250B are illustrated in the figures for exemplary purposes) and one or more drive wheels 260A, 260B (e.g., a pair of drive wheels 260A, 260B are illustrated in the figures for exemplary purposes) are disposed adjacent the back end 200E2.

[0077] As will also be described herein, the ride wheels 250, 260 and chassis 200 in combination form a low profile height LPH (Fig. 2C) that is a minimum height from the traverse surface TS to atop 200T the chassis 200, where chassis height 200H and ride wheel height (e.g., one or more of ride wheels heights 250H, 260H) are overlapped (coextensive) at least in part and a payload support contact surface 210BS of the payload support 210B (on which contact surface 210BS a payload, e.g., such as case unit CU, resting on the payload support 210B is seated) is nested within (e.g., between and within the height of at least one of) the ride wheels 250, 260 (see Fig. 2C). Here, the payload support contact surface 210BS disposed atop the chassis 200. The payload support contact surface 210BS may be disposed at a height LPH2 from the traverse surface TS that is substantially the same as the low profile height LPH, while in other aspects the height LPH2 may be greater than the low profile height LPH while still being nested within the ride wheels 250, 260 (see Fig. 2C). [0078] Still referring to Fig. 2, the frame 200 includes at least one idler wheels 250 (also referred to as casters or caster wheels) mounted to the frame and disposed adjacent the front end 200E1. The frame also includes at least two independently driven drive wheels 260 mounted to the frame and disposed adjacent the back end 200E2. In other aspects, the position of the at least one idler wheel 250 and drive wheels 260 may be reversed (e.g., the drive wheels 260 are disposed at the front end 200E1 and the idler wheels 250 are disposed at the back end 200E2). It is noted that in some aspects, the autonomous transport vehicle 110 is configured to travel with the front end 200E1 leading the direction of travel or with the back end 200E2 leading the direction of travel. In one aspect, idler wheels 250A, 250B (which are substantially similar to idler wheel 250 described herein) are located at respective front corners of the frame 200 at the front end 200E1 and drive wheels 260A, 260B (which are substantially similar to drive wheel 260 described herein) are located at respective back corners of the frame 200 at the back end 200E2 (e.g., a support wheel is located at each of the four corners 200E1C1, 200E1C2, 200E2C1, 200E2C2 of the frame 200 - see Fig. 2A) so that the autonomous transport vehicle 110 stably traverses the transfer deck(s) 130B and picking aisles 130A of the storage structure 130. Here, the caster wheel(s) 250A, 250B and the drive wheel(s) 260A, 260B roll, on a rolling surface 395 effecting autonomous transport vehicle 110 traversal over the rolling surface 395. [0079] Referring to Figs. 2A, 2B, 2C, 3A, and 3B, the chassis 200, as noted herein, is a space frame 200S having a modular configuration/construction such that selection of chassis components from a number of different selectable chassis components configures and/or reconfigures the autonomous transport vehicle 110 for one or more of case transfer operations, employment in different storage and retrieval systems having different physical requirements for the autonomous transport vehicles 100, and/or different operational requirements of the autonomous transport vehicles 100 (e.g., suspension travel, case lift heights, ground clearance, automated charging configurations, etc.). The modular configuration of the chassis 200 also facilitates modular repair and/or maintenance of the autonomous transport vehicle 110 so as to reduce downtime (i.e., increase in- service time) of the autonomous transport vehicle 110. The space frame 200S is configured so that the chassis 200 is substantially rigid with predetermined rigidity characteristics, with a shape and form that provide the minimum low profile height LPH from the traverse surface TS to atop 200T the chassis 200. Examples of predetermined rigidity characteristics include, but are not limited to, generating a predetermined transient response of the chassis/payload support contact surface 210BS from one or more of bot traverse transient loads (as described in United States provisional patent application number 63/213,589 filed on June 22, 2021 (having attorney docket number 1127P015753-US (-#2)) and titled "Autonomous Transport Vehicle with Synergistic Vehicle Dynamic Response," the disclosure of which is incorporated herein by reference in its entirety), static and dynamic loads generated by actuation of the transfer arm/end effector 210A, and loading/unloading payloads to/from the payload bed 21B and payload transfers. The space frame 200S configuration resolves both predetermined rigidity characteristics (as to imparted loads) and the minimum low profile height LPH of the chassis 200 from the traverse surface TS to atop 200T the chassis 200. As described herein, the chassis 200 has a selectably variable configuration, selectable from different configurations each having different chassis form factors (e.g., selectably variable lengths and/or widths). The predetermined rigidity characteristics include torsional rigidity of the space frame 200S along the longitudinal axis (e.g., twisting of the chassis about the longitudinal axis), bending rigidity of the space frame 200S along the lateral direction (e.g., from side to side), and bending rigidity of the space frame 200S along the longitudinal direction (e.g., from front to back). The predetermined rigidity characteristics result in deflection, with respect to the payload carried by vehicle 110, that is negligible/indiscernible for a given payload weight (e.g., such as payloads of up to about 60 lbs or more). The deflection is negligible/indiscernible with respect to the seating of the payload across a contact surface between the payload bed (or transfer arm) of the vehicle 110 and the payload such that the payload remains in substantially contact with the contact surface throughout travel of and/or a range of motion of the vehicle 110.

[0080] Referring also to Figs. 3A and 3B, the chassis 200 includes longitudinal hollow section beams 3010 that are arrayed to form longitudinally extended sides (or lateral sides) 200SS1, 200SS2 of the space frame 200S. The chassis 200 also includes a respective front lateral beam or crossmember 3000 and a respective rear lateral beam or crossmember 3050 closing opposite ends 200E1, 200E2 of the space frame 200S. As described herein, at least one of the longitudinal hollow section beams 3010, the front lateral beam 3000, and the rear lateral beam 3050, is/are selectable from a number of different selectably interchangeable respective longitudinal hollow section beams 3010A-3010n, front lateral beams 3000A-3000n, and rear lateral beams 3050A-3050n, each with different predetermined mechanical characteristics. Examples of the difference predetermined mechanical characteristics include, but are not limited to, material, cross-section, etc. Here, selection of the at least one of the longitudinal hollow section beams 3010, the front lateral beam 3000, and the rear lateral beam 3050 from the number of different selectably interchangeable respective longitudinal hollow section beams 3010A-3010n, the front lateral beams 3000A-3000n, and the rear lateral beams 3050A- 3050n determines the selected variable configuration of the chassis 200.

[0081] In one or more aspects the chassis includes the transfer arm 210A that extends/retracts laterally relative to the payload support 210B where the transfer arm 210A may be movable in the vertical direction VER in any suitable manner by any suitable distance so that the transfer arm 210A is above/clears the chassis 200 when the transfer arm 210A is extended/retracted. The transfer arm 210A may be provided as a part of the payload support module 210M as described herein. In some aspects, the payload support 210B and transfer arm 210A are coupled to at least one payload support stanchion module 211, 212 (also referred to as a payload support stanchion) as described herein, where in some aspects the payload support stanchions 211, 212 are configured to move one or more of the payload support 21B and transfer arm 210A in vertical direction VER. In other aspects, the payload support 210B may be a static payload support 210SPS (Fig. 2C) without an actuated transfer arm 210A (and without vertical movement provided by the payload support stanchions 211, 212, although in some aspects vertical movement may be provided). In some aspect, the payload support stanchion modules 211, 212 may also be provided as a part of the payload support module 210M or as separate modules to which the payload support module 210M is coupled.

[0082] The front lateral beam 3000 and the rear lateral beam 3000 extend laterally in direction LAT. The longitudinal hollow section beams 3010 extend longitudinally in direction LON. The longitudinal hollow section beams 3010 are substantially similar to each other so that either longitudinal hollow section beam 3010 can be installed on either lateral side of the autonomous transport vehicle by reorienting (e.g., rotating by about 180 degrees) the longitudinal hollow section beams 3010 about a respective longitudinal axis RAX; however, in other aspects the longitudinal hollow section beam 3010 may be differently configured depending on which lateral side of the autonomous transport vehicle 110 the longitudinal hollow section beams 3010 are installed. Each longitudinal hollow section beam 3010 includes a first end 3010E1 configured to couple to the front lateral beam 3000 in any suitable manner (such as mechanical fasteners). The first end 3010E1 includes at least one datum surface 3091 that is configured to seat against a corresponding datum surface 3092A, 3092B of the front lateral beam 3000. Each longitudinal hollow section beam 3010 also includes a second end 3010E2 configured to couple to the rear lateral beam 3050 in any suitable manner (such as mechanical fasteners). Each second end 3010E2 has at least one datum surface 3093 that is configured to seat against a corresponding datum surface 3094A, 3094B of the rear lateral beam 3050. The longitudinal distance between the datum surface 3091 and the datum surface 3093 of each longitudinal hollow section beam 3010 is predetermined so that with the front lateral beam 3000 and the rear lateral beam 3050 coupled to the longitudinal hollow section beams 3010, e.g., to form the chassis 3099 having a longitudinal length 3099L and a lateral width 3099 , the components (e.g., sensors, actuators, etc.) of the front lateral beam 3000 and the rear lateral beam 3050 have a known positional/spatial relationship relative to each other. The chassis 3099 is illustrated in Fig. 3B without sub-components (e.g., wheels, electronics, etc.) thereon for clarity. In some aspects, the longitudinal hollow section beams 3010 include identifying indicia (radio frequency identification tags, etc.) that inform the controller 1220 of the length (between datum surfaces 3091, 3093) of the respective longitudinal hollow section beam 3010. The identifying indicia are read by suitable sensors of the controller 1220 of the autonomous transport vehicle 110 to effect a plug and play positional/spatial relationship between the autonomous vehicle components by the controller 1220 as described herein. In other aspects, the length (between datum surfaces 3091, 3093) of the respective longitudinal hollow section beam 3010 may be input to the controller 1220 manually through any suitable user interface of the autonomous transport vehicle 110.

[0083] In one or more aspects, the length 3099L and/or width 3099W of the chassis 3099 is selectable from a number of different lengths and/or widths (e.g., effected through a selection of different longitudinal hollow section beam 3010A-3010n having different lengths LRl-LRn and/or a selection of different front and rear lateral beams 3000A-3000n, 3050A-3050n having different widths CWl-CWn, DWl-DWn) so as to enlarge or reduce payload capacity of the autonomous transport vehicle 110. For example, the length 3099L is increased or decreased depending on, for example, a maximum length of case units handled by the autonomous transport vehicle 110. Similarly, the width 3099W is increased or decreased depending on, for example, a maximum width of case units handled by the autonomous transport vehicle 110. The length 3099L and/or width 3099W may also be increased or decreased so as to increase the wheel base WB and/or wheel track WT (see Fig. 4) depending one or more of, for example, structural size constraints imposed on the autonomous transport vehicle 110 by structure of the storage and retrieval system 100 (e.g., picking aisle width, turning radius, etc.), ride quality of the autonomous transport vehicle (e.g., longer wheel base provides less jostling of goods being transported), and transport speeds (e.g., wider wheel track provides greater stability in turns). In other aspects, the length 3099L and/or width 3099 may be increased or decreased for any suitable reasons. The length 3099L of the chassis 3099 is selected through a selection of a number of different longitudinal hollow section beam 3010A-3010n each having a respective length LRl-LRn (where "n" is an integer denoting a maximum number for the selection).

[0084] The width 3099W of the chassis 3099 is selected through a selection of a number of different front lateral beams 3000A- 3000n each having a respective width CWl-CWn and a corresponding one of a number of different rear lateral beams 3050A-3050n each having a respective width DWl-DWn. In some aspects, the front and rear lateral beams 3000, 3050 each include identifying indicia (radio frequency identification tags, etc.) that inform the controller 1220 of at least the width (between datum surfaces 3072D, 3073D or 3074D, 3075D - Fig. 3A) of the respective front and rear lateral beams 3000, 3050. The identifying indicia are read by suitable sensors of the controller 1220 of the autonomous transport vehicle 110 to effect a plug and play positional/spatial relationship between the autonomous vehicle components by the controller 1220 as described herein. In other aspects, the width (between datum surfaces 3072D, 3073D or 3074D, 3075D) of the respective front and rear lateral beams 3000, 3050 may be input to the controller 1220 manually through any suitable user interface of the autonomous transport vehicle 110.

[0085] While the rear lateral beams 3050A-3050n are illustrated as having the drive wheels 260A, 260B installed thereon, in one or more aspects the drive wheels 260A, 260B may be installed, as drive wheel modules 260M, on the rear lateral beams 3050A-3050n prior to coupling of the rear lateral beams 3050A-3050n to the longitudinal hollow section beam 3010. In other aspects, the drive wheels 260A, 260B may be installed, as drive wheel modules 260M, on the rear lateral beams 3050A-3050n post coupling of the rear lateral beams 3050A-3050n to the longitudinal hollow section beam 3010.

[0086] In one or more aspects, the rear lateral beams 3050A- 3050n are provided as selectable modular assemblies that include the drive wheels 260 (which may themselves be provided as drive wheel module 260M sub-assemblies that are selected from a number of different modular drive wheel assemblies 260Al-260An, 260B1- 260Bn and installed to the selectable modular rear lateral beam assembly), electronics (controllers, electronic busses, wire harnesses, sensors, etc.), and auxiliary equipment (e.g., charging interfaces, switches, interface ports, etc.). For example, as can be seen in Figs. 2A, 2B and 3C the rear lateral beam 3050 includes one or more of any suitable power source 3035 (e.g., ultra capacitor, battery, etc.), drive wheels 260, any suitable controller 1220 (and associated electronics), guide rollers 3052, one or more suitable navigation sensors 3067 (e.g., line following sensors, vision sensors, sonic sensors, etc.), and charging interface 3033 (e.g., side-mount bus bar contact pad 3033A and/or under-mount charging pads 3033B). The longitudinal hollow section beam 3010 and/or payload support stanchions 211, 212 are mechanically coupled to the cross member 3050 assembly as described herein.

[0087] The front lateral beam 3000 is, in one or more aspects, provided as an assembly that includes one or more of the caster wheels 250 (which may themselves be provided as modular sub- assemblies that are selected from a number of different modular caster wheel assemblies 250Al-250An, 250Bl-250Bn), electronics (sub-controllers, electronic busses, wire harnesses, motors, sensors, etc.), and/or auxiliary equipment (e.g., charging interfaces, switches, interface ports, etc.) For example, as can be seen in Figs. 2A, 2B and 3C the front lateral beam 3000 includes idler wheels 250, a drive motor 290 for moving a carrier 290 of the payload support stanchions 211, 212 in direction VER (such as where the payload support 210B is an actuated payload support), guide rollers 3051, one or more suitable navigation sensors 3066 (e.g., line following sensors, vision sensors, sonic sensors, etc.), and/or any suitable couplings that facilitate a substantially plug-and-play connection of the components of the front lateral beam 3000 to at least the controller 1220 of the rear lateral beam 3050. In other aspects, the front lateral beam 3000 may also include a charging interface substantially similar to charging interface 3033. In still other aspects, the caster wheels 250, electronics, and/or auxiliary equipment may be coupled to the front lateral beam 3000 after the front lateral beam 3000 is coupled to the longitudinal hollow section beam 3010 and/or payload support stanchions 211, 212. While the front lateral beam 3000 is described above as a module including the caster wheels 250A, 250B, in one or more aspects the drive caster wheels 250A, 250B may be installed on the front lateral beam 3000 prior to or post coupling of the front lateral beam 3000 to the longitudinal hollow section beam 3010. [0088] The at least one payload support stanchion 211, 212 is/are coupled to chassis 3099 so that each payload support stanchion 211, 212 is removed from and installed to the chassis 3099 in a modular manner. In the example illustrated in Figs. 2A, 2B, there is one payload support stanchion 212 disposed at or adjacent end 200E2 of the chassis 200 and another payload support stanchion 211 disposed at or adjacent end 200E1 of the chassis 200; however, in other aspects there may be one payload support stanchion or more than two payload support stanchions. Referring to Figs. 2A, 2B, 3A, and 3B, the payload support stanchions are substantially similar to each other such that payload support stanchion 212 may be coupled to the chassis 3099 at or adjacent end 200E1 and payload support stanchion 211 may be coupled to the chassis 3099 at or adjacent end 200E2. In one or more aspects, rotation of the payload support stanchions about a respective (vertical) axis TAX facilitates placement of the either payload support stanchion 211, 212 at either one of ends 200E1, 200E2. The payload support stanchions 211, 212 are coupled to the chassis 3099 by inserting the payload support stanchions 211, 212 into corresponding receptacles/interfaces 3070, 3071 of a respective front lateral beam 3000 and rear lateral beam 3050. The receptacles 3070, 3071 of the front lateral beam 3000 and the rear lateral beam 3050 form datum surfaces that are in a known spatial relationship with one or more of the datum surfaces 3091, 3093 so as to position the respective payload support stanchion 211, 212 (and payload support contact surface 210BS coupled thereto) in a known predetermined location relative to the components (e.g., actuators, sensors, etc.) of the front lateral beam 3000 and the rear lateral beam 3050. As may be realized, the receptacles 3070, 3071 position the payload support contact surface 210BS at the height LPH2 described herein. The receptacles 3070, 3071 are configured to orient the respective payload support stanchion 211, 212 so that the payload support stanchions 211, 212 extend substantially parallel with each other in the lateral direction LAT and so that the payload support stanchions 211, 212 extend substantially parallel with each other in the vertical direction VER. The payload support stanchions 211, 212 are coupled to a respective one of the front lateral beam 3000 and rear lateral beam 3050 in a removable manner, such as by mechanical fasteners; however, in other aspects, the payload support stanchions 211, 212 are coupled to the longitudinal hollow section beam 3010 and serve as additional frame cross members (e.g., increasing torsional stiffness of the chassis 200); while in still other aspects the payload support stanchions 211, 212 are coupled to both the respective one of the front lateral beam 300 and the rear lateral beam 3050 and the longitudinal hollow section beam 3010.

[0089] The payload support stanchions 211, 212 are selectable from a number of different payload support stanchions 212A-212n each having a respective height THl-THn and width TWl-TWn, where the widths TWl-TWn of the payload support stanchions 212 correspond with (and are selected depending on) the widths of the number of different front lateral beams 3000A-3000n and the number of different rear lateral beams 3050A-3050n. The height THl-THn of the number of different payload support stanchions 212A-212n is selected depending on, for example, heights of case unit holding locations/shelves of the storage and retrieval system 100 at which the autonomous transport vehicle 110 transfers case units.

[0090] The payload support stanchions 211, 212 are, in one or more aspects, provided as modular assemblies. For example, referring to Figs. 2A, 2B, and 3A, each payload support stanchion includes a tower frame 300F. The tower frame 300F includes a base 305, vertical guides 306, 307, and a cross brace or brace 308. The carrier 290 extends laterally between and is guided in vertical movement by the vertical guides 306, 307. The carrier 290 moves vertically in direction VER between the base 305 and brace 308 under motive force of any suitable drive motor 390 that is coupled to the carrier 290 by any suitable flexible transmission 330 (e.g., such as a drive shaft, gear box, belts, chains, and/or cables and associated pulleys/sprockets, etc.) where the transmission is coupled to an axle PXL tower frame 300F. In one aspect, the drive motor 390 is a rotary motor coupled to the carrier 290 through the flexible transmission 330; while in other aspects the drive motor 390 may be a linear motor (e.g., any suitable electric, hydraulic, and/or pneumatic linear actuator) coupled to the carrier 290 for moving the carrier 290 in direction VER. As described herein, the carrier 290 is coupled to and supports the payload support 210 and the transfer arm 210A of the payload support 210 for movement in direction VER.

[0091] Referring to Figs. 2A, 2B, and 6 the payload support 210 is a modular unit/assembly (e.g., the payload support module 210M) that includes at least the payload bed 210B. Where the payload support 210 comprises the static payload support 210SPS the payload support 210 is coupled substantially directly to the chassis 200 in a manner similar to that described above with respect to the payload support stanchions 211, 210 (e.g., where the static payload support is received into the receptacles 3070, 3071) or statically coupled to the payload support stanchions 210, 211 (e.g., the payload support stanchions do not include vertical actuation). In other aspects, the static payload support 210SPS may be coupled to the payload support stanchions 211, 212 for vertical travel in direction VER in a manner substantially similar to that described herein with respect to active payload support 210ACT. The static payload support 210SPS is configured for a passive transfer of case units CU to and from the payload bed 210B. For example, the passive transfer, in one or more aspects, is with respect to the payload bed 210B (e.g., no lateral extension of the payload bed/arm to effect a transfer of the payload). The passive transfer with respect to the payload bed 210B is effected with an extending support (e.g., extendable slatted shelf that is separate and distinct from the vehicle 110) that interfaces with the raised payload bed so that lowering of the payload bed transfers the payload to the extending support (e.g., the payload bed is configured so that the extending support, or a portion thereof, passes through (such as in an interdigitated manner) the payload bed 210B upon lowering of the payload bed 210B. Here, the raised payload bed may be positioned relative to extended support in any suitable manner, such as with a traverse motion of the vehicle 110 in direction LON along a picking aisle or transfer deck so that the extendable support extends to intervene between the raised payload bed 210B and the chassis 200 (where lowering the payload bed passively transfers the payload to the extended support). In one or more aspects, the drive wheels of the vehicle 110 may be omnidirectional wheels that are configured (in combination with rotation or yawing of the caster wheels) to move the vehicle 110 in a lateral traverse motion (e.g., in direction LAT). Here, the lateral traverse motion of the vehicle 110 provides for the raised payload bed 210B to be positioned over a static support (i.e., the support is fixed in place and does not move) by at least the lateral traverse motion of the vehicle 110 in direction LAT such that the static support intervenes between the raised payload bed 210B and the chassis 200 (where lowering the payload bed passively transfers the payload to the extended support). As may be realized, passive transfer of payload to the vehicle 110 may occur in an opposite manner to that described above.

[0092] Where the payload support 210 is an active payload support 210ACT (Fig. 6), the payload support 210 includes transfer arm 210A. In this aspect, the payload bed 210B is coupled to the at least one payload support stanchion 211, 212. The at least one payload support stanchion is configured to move the payload bed 210B and/or transfer arm 210A in direction VER; while in other aspects substantial vertical movement of the payload bed 210B and/or transfer arm 210A may not be provided in direction VER. The transfer arm 210A is movably coupled to the payload bed 210B for lateral movement in direction LAT.

[0093] The payload bed 210B includes a payload bed frame 210BF that forms a payload area in which case units CU carried by the bot 110 are disposed for transport throughout the storage and retrieval system 100. The payload bed frame 210BF includes longitudinal ends 210BE1, 210BE2 that are each coupled to a respective one of the at least one payload support stanchion 211, 212. Here the at least one payload support stanchion 211, 212 includes payload support stanchion 211 disposed at or adjacent the front end 200E1 of the chassis 200 and payload support stanchion 212 disposed at or adjacent the back end 200E2 of the chassis 200. Here, each payload support stanchion 211, 212 includes the movable carrier 290 to which a respective one of the longitudinal ends 210BE1, 210BE2 is fixedly coupled in any suitable manner such as mechanical or chemical fasteners (i.e., so that as the movable carrier 290 moves the payload bed frame 210BF moves with the movable carrier 290). The payload support 210 is coupled to and removed from the carriers 290 of the payload support stanchions 211, 212 in any suitable manner, such as by any suitable mechanical fasteners.

[0094] As noted herein, the payload support 210 is provided as a modular assembly (e.g., payload support module 210M) that is selected from a number of different interchangeable payload support modules 610A-610n (it is noted that while Fig. 6 illustrates an active payload support 210ACT assembly it should be realized different modular static payload support 210SPS may also be provided), each payload support module having a different predetermined payload support module characteristic (e.g., active case transfer (payload bed with end effector/transfer arm), passive case transfer (payload bed without actuated end effector/transfer arm as described herein), lift capability, length, width, different size payload actuators for different sized payload, etc.). The different payload support modules 610A- 610n have longitudinal lengths CHL and lateral widths CHW that correspond with the longitudinal length 3099L and a lateral width 3099W of the chassis 3099 (as effected through selection of the front lateral beams 3000A-3000n, the rear lateral beams 3050A- 3050n, the longitudinal hollow section beams 3010A-3010n, and the payload support stanchions 212A-212n). In this manner one of the payload support modules 610A-610n is selected depending on a predetermined chassis configuration for installation to the chassis 3099 in a modular manner (i.e., the selected payload support 210 is coupled to the carriers 290 substantially without modification to either the payload support 210, the payload support stanchions 211, 212, and the chassis 3099). The different payload support modules 610A-610n may also be selected depending on whether the autonomous transport vehicle 110 is to be configured for active or passive case transfer CU to and from the payload bed 210B.In one or more aspects, the payload support stanchions 211, 212 form a portion of a respective different interchangeable payload support modules 610A-610n, where the payload support stanchions 211, 212 are pre-assembled to the longitudinal ends 210BE1, 210BE2 (see Fig. 6) of the payload bed frame 210BF so that the payload support stanchions 211, 212 form a modular unit with the payload support 210. Here, the modular combination of the payload support stanchions 211, 212 and the payload support 210 are selected from the different interchangeable payload support modules 610A-610n and coupled to the chassis 3099 as a payload support modular unit. [0095] The transfer arm 210A includes one or more fingers 210AF that are each cantilevered from a finger support rail 273 of the transfer arm 210A. It is noted that while three fingers 210AF1- 210AF3 are illustrated for exemplary purposes only, in other aspects there may be more or fewer than three fingers spaced apart from one another (with any suitable spacing) along the finger support rail 273. The finger support rail 273 of the transfer arm 210A is movably coupled to the payload bed frame 210BF in any suitable manner so that the transfer arm 210A (inclusive of the finger support rail 273 and the one or more fingers 210A1-210A3) moves relative to the payload bed frame in direction LAT. Movement of the transfer arm 210A in direction LAT extends and retracts the one or more fingers 210AF for picking and placing payloads to and from the payload bed 210B.

[0096] Referring to Figs. 2A, 2B, 3A, 3C and 4, as described above, the ride wheels 250, 260 include the drive wheels 260A, 260B and idler wheels 250A, 250B. Each of the drive wheels 260A, 260B and idler wheels 250A, 250B are provided as modular components (e.g., drive wheel modules 260M and idle/caster wheel modules 250M) that can each be independently removed from and installed to the chassis 200 as respective modular units in a plug-and-play manner so as to be swapped with other selectable drive wheels 260 and idler wheels 250. For example, idler wheel 250A is selectable from a number of different idler wheels 250Al-250An each having a different characteristic or combination of characteristics (e.g., wheel diameter, ride height, wheel tread pattern, wheel material, motorized (steerable) casters, non-motorized (passive) casters, suspension preload (which may be preset at different levels before mounting to configure the vehicles 110 with different payload capacities), etc.)· Idler wheel 250B is similarly selectable. Drive wheel 260B is selectable from a number of different drive wheels 260Bl-260Bn each having a different characteristic or combination of characteristics (e.g., wheel diameter, ride height, wheel tread pattern, wheel material/friction coefficient, motor horsepower, motor operational speed, suspension preload (which may be preset at different levels before mounting to configure the vehicles 110 with different payload capacities), etc.).

[0097] The idler wheels 250A, 250B are coupled to the front lateral beam 3000 at a respective coupling interface 3074, 3075 in a removable manner such as with mechanical fasteners. Each of the coupling interfaces 3074, 3075 include a datum surfaces 3074D, 3075D at which the idler wheels 250A, 250B are coupled to the space frame 200S in a repeatable and known location relative to the sensors, actuators, etc. of the front and rear crossmembers 3000, 3050 (and the components of the interchangeable payload support modules 610A-610n). For example, the datum surfaces 3074D, 3075D of the space frame 200S seat against and locate mating datum surfaces 250DS of the respective idler wheel 250A, 250B relative to the space frame 200S (see Fig. 3A) so that the idler wheels 250A, 250B can be coupled to and removed from the space frame 200S in a plug-and-play manner.

[0098] The drive wheels 260A, 260B are coupled to the rear lateral beam 3000 at a respective coupling interface 3072, 3073 in a removable manner such as with mechanical fasteners. Here, there are separate and distinct interfaces 3072, 3073 for respective separate and distinct drive wheel modules 260M of each different drive wheel 260A, 260B of a pair of drive wheels. Each of the coupling interfaces 3072, 3073 include a datum surfaces 3072D, 3073D at which the drive wheels 260A, 260B are coupled to the space frame 200S in a repeatable and known location relative to the sensors, actuators, etc. of the front and rear crossmembers 3000, 3050 (and the components of the interchangeable payload support modules 610A-610n). For example, the datum surfaces 3072D, 3073D of the space frame 200S seat against and locate mating datum surfaces 260DS of the respective drive wheel 260A, 260B so as to locate the drive wheels 260A, 260B in the known predetermined location relative to the space frame 200S (see Figs. 3A and 4) so that the drive wheels 260A, 260B can be coupled to and removed from the space frame 200S in a plug-and-play manner. It is noted that while the drive wheel module 260M is illustrated in Fig. 4 as being sans suspension components, in other aspects the drive wheel module 260M may include at least part of suspension system 280 (e.g., control arm(s) and shock absorber mounted to a datum plate that is coupled to the rear crossmember 3050).

[0099] Here, the chassis 200 includes one or more idler wheels 250 disposed adjacent the front end 200E1. In one aspect, an idler wheel 250 is located adjacent each front corner of the chassis 200 so that in combination with the drive wheels 260 (the drive wheels 310 being disposed at each rear corner of the chassis 200) the chassis 200 stably traverses the transfer deck 130B and picking aisles 130A of the storage structure 130. Each idler wheel 250 comprises any suitable un-motorized/passive caster or a motorized caster that is configured to actively pivot the wheel 610 in direction 690 about caster pivot axis 691 (see Fig. 4) to at least assist in effecting a change in the travel direction of the autonomous transport vehicle 110. Each drive wheel 260 comprises a drive unit 261 (see, e.g., Fig. 4) that is independently coupled to the chassis 200 by a respective independent suspension system 280 (see Figs. 3C, 5A and 5B), so that each drive wheel 260 is independently movable (e.g., independently driven by a respective drive motor of a respective drive unit) in a wheel travel direction SUS relative to the chassis 200 and any other drive wheel(s) 260 that is/are also coupled to the chassis 200.

[0100] As described herein the drive wheels 260, the idler wheels 250, and payload support 210 are provided as modular components (e.g., the drive wheel modules 260M, the idler/caster wheel modules 250 , and the payload support module 210M) that can each be independently removed from and installed to the chassis 200 as respective modular units in a plug-and-play manner so as to be swapped with other selectable the drive wheels 260, the idler wheels 250, and payload support 210. For example, the autonomous transport vehicle 110 includes any suitable onboard communications backbone such as a controller area network (CAN) that communicably couples the controller 1220 to the electronic components (e.g., sensors, motors, and other suitable sensors/actuable components) of the autonomous transport vehicle 110. The controller area network is configured such that each of the modular drive wheels 260, the modular idler wheels 250 (such as where the idler wheels include actuable components such as steering motors, locks, etc.), and modular payload support 210 releasably plug into the controller area network (e.g., so that electronic components thereof are in communication with the controller 1220) and include any suitable identification protocol (e.g., digital signature) that is communicated to the controller 1220 over the controller area network upon connection of the modular drive wheels 260, the modular idler wheels 250, and modular payload support 210 to the controller area network. The identification protocol may identify types of sensors, motors specifications, actuator travel limits (such as for lifting case units), and/or any other suitable operation specifications that effect operation of the respective one of the modular drive wheels 260, the modular idler wheels 250, and modular payload support 210 coupled to the controller 1220 through the controller area network. The identification protocol also identifies the position at which the modular drive wheels 260, the modular idler wheels 250, and modular payload support 210 are coupled to the chassis, where the controller 1220 determines the location of the sensors, actuators, etc. of the modular components based on the location of the respective datum surfaces of the respective coupling interfaces 3070, 3071, 3072, 3073, 3074, 3075 and data obtained from the modular components in the identification protocol. The controller 1220 is configured (e.g., through suitable non-transitory computer program code) to receive the identification protocol from the modular drive wheels 260, the modular idler wheels 250, and/or modular payload support 210 and effect operation of the modular drive wheels 260, the modular idler wheels 250, and/or modular payload support 210 based, at least in part, on the operational data embodied in the identification protocol.

[0101] Referring to Figs. 2A-2C, 3A-3C, 6, and 7 an exemplary method will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the chassis 200 (forming the space frame 200S), payload support 210, and ride wheels 250, 260 (Fig. 7, Block 7700). As described herein, the ride wheels 250, 260 and chassis 200 in combination form the low profile height LPH from the traverse surface TS to atop 200T the chassis 200, where chassis height 200H and ride wheel height 250H, 260H are overlapped at least in part and the payload support 210 is nested within the ride wheels 260 (e.g., between the ride wheels 250, 260 such that the low profile height LPH is smaller than one or more of the ride wheel height 250H, 260H). A corresponding electronic and/or mechanical component module (e.g., ride wheel modules (e.g., at least one drive wheel module 260M and at least one caster wheel module 250M), payload support module 210M, control module 1220M, etc., as described herein) are removably coupled, as a modular unit, to the space frame 200S (Fig. 7, Block 7710) with the predetermined modular coupling interfaces 3070, 3071, 3072, 3073, 3074, 3075 described herein.

[0102] Referring to Figs. 2A-2C, 3A-3C, 6, and 8 another exemplary method will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the chassis bus (also referred to as chassis) 200 (Fig. 8, Block 8800), where the chassis bus 200 includes the predetermined modular coupling interfaces 3070, 3071, 3072, 3073, 3074, 3075 described herein. Corresponding predetermined component modules of the autonomous transport vehicle 110 are removably coupled, as a module unit, to the chassis bus 200 (Fig. 8, Block 8810) so that the autonomous transport vehicle 110 has a modular construction. Here, the predetermined component modules include at least one of: a payload support module 210M with a payload support contact surface 210BS removably coupled as a module unit to the chassis bus 200 with a corresponding payload support module coupling interface 3070, 3071; a caster wheel module 250M with a caster wheel 250A, 250B removably coupled as a module unit to the chassis bus 200 with a corresponding caster wheel module coupling interface 3074, 3075; and a drive wheel module 260M with a drive wheel 260A, 260B removably coupled as a module unit to the chassis bus 200 with a corresponding drive wheel module coupling interface 3072, 3073.

[0103] Referring again to Fig. 2, the autonomous transport vehicle 100 includes a drive section 261D connected to the frame 200. The drive section 261D has at least a pair of traction drive wheels 260 (also referred to as drive wheels 260 - see drive wheels 260A, 260B) astride the drive section 261D. As described herein, the drive wheels 260 have a fully independent suspension 280 (also referred to as a (fully) independent multi-link suspension system) coupling each drive wheel 260A, 260B of the at least pair of drive wheels 260 to the frame 200, with at least one intervening pivot link (e.g., the upper and lower frame links 310, 311 described herein) between at least one drive wheel 260A, 260B and the frame 200 configured to maintain a substantially steady state traction contact patch CNTC (Fig. 9A - noting that a similar substantially steady state traction contact patch may be maintained for each caster wheel 250A, 250B by the respective fully independent suspension 80 (described herein) thereof) between the at least one drive wheel 260A, 260B and rolling surface 395 (also referred to as autonomous vehicle travel surface 395) over each rolling surface transient(s) 395T (see Fig. 10B, e.g., bumps, debris located on the rolling surface, surface transitions such as transitions between picking aisles and the transfer deck, transitions between transfer deck floor panels, transitions between different rail portions of the picking aisles, etc.) throughout traverse of the at least one drive wheel 260A, 260B over the rolling surface 395.

[0104] The fully independent suspension 280 of drive wheel 260A is independent from the independent suspension 280 of drive wheel 260B. Each fully independent suspension 280 of each drive wheel 260A, 260B is also independent from the fully independent suspension 780 (described herein) of each other of the at least one caster wheel 250A, 250B. As described herein, the caster wheel(s) 250A, 250B and the drive wheel(s) 260A, 260B of the, and the respective fully independent suspension 780, 280 thereof, are disposed on the frame 200 astride the integral payload support or bed 210B so that the payload seat surface 210AFS at the payload datum position PDP is disposed at a minimum distance MIND above the rolling surface 395 as described herein.

[0105] The substantially steady state traction contact patch CNTC is disposed at a predetermined reference position (see Fig. 9A) of the at least one drive wheel 260A, 260B throughout traverse of the at least one traction drive wheel 260A, 260B over the rolling surface 395. As an example, the predetermined reference position of the substantially steady state traction contact patch CNTC is a designed for position (e.g., such as effected by suspension geometry) located at the bottom of the at least one traction drive wheel 260A, 260B. In accordance with the exemplary embodiment, the substantially steady state traction contact patch CNTC is located at the predetermined reference position of the at least one drive wheel 260A, 260B throughout transient (e.g., reactive short term movement of the wheel effected by fully independent suspension 280 of the autonomous transport vehicle 110) of the at least one drive wheel 260A, 260B due to traverse of the at least one drive wheel 260A, 260B over the rolling surface 395 transients 395T. The fully independent suspension 280 may also effect the substantially steady state traction contact patch CNTC being disposed at the predetermined reference position of the at least one drive wheel 260A, 260B substantially independent of the transients of the at least one drive wheel 260A, 260B due to traverse of the at least one drive wheel 260A, 260B over the rolling surface transients 395T.

[0106] As will also be described herein, the fully independent suspension 280 includes at least one intervening pivot link between the at least one drive wheel 260A, 260B and the frame 200 and is configured to generate a substantially linear (see Figs. 9B and 10B) transient response to the drive wheel 260A, 260B, to rolling over surface transients 395T of the autonomous vehicle travel surface 395 in a linear wheel travel direction SUS throughout each transient, where the linear wheel travel direction SUS is substantially normal to a major plane MP of the frame 200 (see Figs. 9B and 1OB).

[0107] In one aspect, A drive unit 261 for each drive wheel 260 is coupled to the frame 200 in any suitable manner (such as by, for example, a respective fully independent multi-link suspension system 280 or with a rigid coupling.) Where each drive unit 261 is coupled to the frame 200 with the respective fully independent multi-link suspension system 280, each drive wheel 260 is independently movable in a wheel travel direction SUS relative to the frame and any other drive wheel(s) 260 that is/are also coupled to the frame as will be described in greater detail herein. Here, each drive wheel 260 moves in the wheel travel direction SUS relative to the frame 200 independent of movement of the other drive wheel(s) 260 in the wheel travel direction SUS. It is noted that each drive unit 261 comprises any suitable drive motor 261M and a wheel 261W. Each of the drive motors 261M is coupled to and rotationally drives a respective wheel 261W so as to propel the autonomous transport vehicle 110 in a travel direction. Here the motors 261M of two drive wheels 260A, 260B may be operated at the same time and at substantially the same rotational speed to propel the autonomous transport vehicle 110 in a substantially straight line path of travel. In other aspects, the motors 261M of the two drive wheels 260A, 260B may be operated at the same time (or at different times) and at different rotational speeds to generate a vehicle yaw to propel the autonomous transport vehicle 110 along an arcuate path of travel or to pivot the autonomous transport vehicle in direction 294 about vehicle pivot axis 293. The vehicle pivot axis 293 may be located at an origin 900 (see Fig. 31) of the autonomous transport vehicle 110 that is about midway between the two drive wheels 260A, 260B and positioned on the axis of symmetry LAX. The differential operation of the motors 261M of the respective drive wheels 260A, 260B that effects turning and/or pivoting of the autonomous guided vehicle 110 as described above is referred to herein as differential drive wheel steering which, in accordance with the disclosed embodiment, may be aided/supplemented by castering assistance of the at least one caster wheel 250.

[0108] Referring to Figs. 2, 9A, 9B, 5A, and 5B, in one aspect, referring to drive wheel 260B for explanatory purposes only (noting drive wheel 260A is substantially similar), each independent multi-link suspension system 280 includes an upper frame link 310, a lower frame link 311, and a biasing member 312 (also referred to herein for exemplary purposes as a shock absorber). The upper frame link 310 has a first end 310E1 (Fig. 5A) pivotally coupled to the frame at upper frame pivot axis 320. The upper frame link 310 also has a second end 310E2 (Fig. 5A) pivotally coupled to a motor housing 621MH of the motor 621M about upper motor pivot axis 321. The lower frame link 311 has a first end 311E1 (Fig. 9B) pivotally coupled to the frame at lower frame pivot axis 322. The lower frame link 311 also has a second end 311E2 (Fig. 9B) pivotally coupled to the motor housing 621MH about lower motor pivot axis 323. It is noted that while the upper frame link 310 and the lower frame link 311 are each illustrated as being monolithic, in other aspects there may be more than one upper frame link 310 and/or more than one lower frame link 311. The lower frame link 311 and the upper frame link 310 are akin to or otherwise form a double wishbone suspension system.

[0109] A distance 391U between the longitudinal axis LAX of the autonomous transport vehicle 110 and the upper frame pivot axis 320 may be substantially the same as another distance 391L between the longitudinal axis LAX and the lower frame pivot axis 322. A distance 399U between the upper frame pivot axis 320 and the upper motor pivot axis 321 (e.g., the length of the upper frame link 310) may be substantially the same as another distance 399L between the lower frame pivot axis 322 and the lower motor pivot axis 323 (e.g., the length of the lower frame link 311). The substantially equal distances 391U, 391L and the substantially equal distances 399U, 399L provide for a substantially camber free movement of the drive wheel 260B in the wheel travel direction SUS, where "camber" is the angle between vertical axis of a wheel WV and a vertical axis of the vehicle VV when viewed from the front or rear of the vehicle (see Fig. 9A and 9B). For example, as can be seen by comparing Figs. 9A and 9B, the wheel 261W (shown in Fig. 9A) is substantially perpendicular to the autonomous vehicle travel surface 395 (and the vertical axis of the wheel WV is substantially parallel with the vertical axis of the vehicle VV) with the wheel in substantial contact (e.g., at the substantially steady state traction contact patch CNTC) with the autonomous vehicle travel surface 395. The wheel 261W (shown in Fig. 9B) remains substantially perpendicular to the autonomous vehicle travel surface 395 (and the vertical axis of the wheel WV remains substantially parallel with the vertical axis of the vehicle VV) with the wheel lifted off of the autonomous vehicle travel surface 395 by any suitable distance 398 (i.e., the camber of the wheel does not change with movement of the wheel in the wheel travel direction SUS). In other aspects, the distances 399U, 399L, 391U, 391L may be any suitable distances to effect the substantially camber free movement of the drive wheel 260B in the wheel travel direction SUS.

[0110] The wheel 261W is biased towards the autonomous vehicle travel surface 395 by the shock absorber 312. A first end 312E1 of the shock absorber 312 is pivotally coupled to the frame 200 about shock absorber pivot axis 366 and a second end 312E2 of the shock absorber 312 is connected to, for example, the lower frame link 311 by a connecting link 311C. It should be understood that employment of the shock absorber 312 is exemplary and in other aspects any suitable biasing member such as a torsion bar may be coupled to the connecting link 311C for biasing the wheel 261W as described herein. In one aspect, the connecting link 311C is integrally formed with or otherwise coupled to the lower frame link 311 so that an angle a between the lower frame link 311 and the connecting link 311C is substantially constant and does not change. The connecting link 311C extends from the lower frame link 311 so that a free end of the connecting link 311C is pivotally coupled to the second end of the shock absorber 312 about a connecting link pivot axis 325. In this manner, as the wheel 261W travels in the wheel travel direction SUS the lower frame link pivots about lower frame pivot axis 322 to cause the connecting link to push on the shock absorber 312 in shock absorber compression/extension direction 376 so that movement of the wheel 261W in the wheel travel direction SUS is damped by the shock absorber 312 and the wheel is biased by the shock absorber 312 against the autonomous vehicle travel surface 395. As shown in Figs. 5A and 5B the shock absorber 312 extends in a substantially horizontal direction (e.g., substantially parallel with the autonomous vehicle travel surface 395 or substantially perpendicular to a direction of articulated wheel travel direction SUS provided by the upper and lower frame links 310, 311) that is substantially transverse to the longitudinal axis LAX. In this aspect, an angle b (Fig. 5A) of a longitudinal axis 312X of the shock absorber 312 relative to the vertical axis of the vehicle VV may range from being about perpendicular to the vertical axis of the vehicle VV to an angle of more than about 45° relative to the vertical axis of the vehicle VV.

[0111] While the shock absorber 312 is described as being coupled to the lower frame link 311, in other aspects the shock absorber 312 may be coupled to the upper frame link 310 in a manner substantially similar to that describe above by moving the shock absorber 312 closer to a bottom of the frame 200 (e.g., adjacent the autonomous vehicle travel surface 395). In still other aspects, respective dampers may be coupled to both the upper frame link 310 and the lower frame link 311 in a manner substantially similar to that described above, such as to increase the bias on the wheel 261W depending on a weight of payload carried by the autonomous transport vehicle 110. The shock absorber 312 may be a hydraulically damped coil over shock, a gas spring, an undamped coil over shock, a damper with an internal spring, or any other suitable shock absorber. Further, while the shock absorber 312 is illustrated as a unit that includes both a damper 312D and spring 312S (see Fig. 5A) in other aspects the shock absorber 312 may include a damper that is separate and distinct from the spring where each of the spring and damper are coupled to the frame and the lower frame link 311 independent of each other (e.g., such as in a side-by-side or one-over-the-other spatial relationship, rather than an in-line relationship).

[0112] Referring to Figs. 2, 10A, 10B, and IOC, in one aspect, referring to drive wheel 260A for explanatory purposes only (noting drive wheel 260B is substantially similar), the drive wheel 260 is coupled to the frame 200 by an independent multi-link suspension system 280 substantially similar to that described above with respect to Figs. 5A, 5B, 9A, 9D. However, in this aspect the shock absorber 312 is arranged in a substantially vertical orientation rather than a substantially horizontal orientation. In this aspect, an angle Q of the longitudinal axis 312X of the shock absorber 312 relative to the vertical axis of the vehicle VV may range from being about parallel with the vertical axis of the vehicle VV to an angle of less than about 45° relative to the vertical axis of the vehicle VV.

[0113] In this aspect, the first end 312E1 of the shock absorber 312 is coupled to the frame 200 at shock absorber pivot axis 466. The shock absorber pivot axis 466 is disposed adjacent to or coaxially with the upper frame pivot axis 320 so as to orient the longitudinal axis 312X of the shock absorber 312 substantially vertically (see Fig. 10B). In this aspect, the connecting link 311C of the lower frame link 311 extends towards the wheel 261W so as to be disposed adjacent to or coaxial with the lower motor pivot axis 323, again so that the longitudinal axis 312X of the shock absorber 312 has a substantially vertically orientation (see Fig. 10B). In other aspects, the shock absorber pivot axes 466, 325 may have any suitable spatial relationship relative to the pivot axes 320, 322, 323, 321 that effects orienting the shock absorber in the substantially vertically orientation while biasing the wheel 261W towards the autonomous vehicle travel surface 395.

[0114] Referring to Figs. 2, 9A, 9B, 5A, 5B, 10A, 10B, and IOC, a height profile WHT of the drive wheel 260A, 260B and a height profile SHT of the fully independent suspension 280 (see Figs. 9A and 10A), inclusive of the intervening pivot link of the fully independent suspension 280, define a minimum height profile MHP. Here, the minimum height profile MHP is a height profile where the fully independent suspension 280 does not extend above the height profile WHT of the respective drive wheel 260A, 260B.

[0115] Referring now to Figs. 2, 15A, and 15B, each drive wheel 260A, 260B has a height profile or envelope WHT relative to the rolling surface 395. The height profile WHT is substantially the same for each drive wheel 260A, 260B. Here, the drive wheels 260A, 260B are disposed so that a payload datum position PDP, defined by a case unit support surface 210AFS (also referred to herein as a payload seat surface), of the transfer arm 210A fingers 210AF is at a minimum distance MIND above the rolling surface 395. Here, the minimum distance MIND at which the payload datum position PDP is located is defined by the lowermost position of the case unit support surface 210AFS (e.g., relative to the rolling surface 395) that is allowed by the structure of the autonomous transport vehicle 110 that intervenes between the fingers 210AF of the transfer arm 210A and the rolling surface 395. The lowermost position of the case unit support surface 210AFS (e.g., relative to the rolling surface 395) that is allowed by the structure of the autonomous transport vehicle 110 is such that the minimum distance MIND and the payload datum position PDP extends within the height profile WHT of the traction drive wheels 260A, 260B (e.g., the minimum distance MIND is lower than the top or height of the drive wheels 260A, 260B). It is noted that the payload datum position PDP is coincident with and defined by the case unit support surface 210AFS of the fingers 210AF (also referred to as tines) of the transfer arm 210A (also referred to as an end effector) with the transfer arm 210A retracted into the payload bed 210B and lowered to its lowermost position - see Fig. 15A).

[0116] Referring now to Figs. 2, 11A, 11B, 11C, and 11D, in one aspect the autonomous transport vehicle 110 includes a suspension lockout system 500 configured to stop movement of (e.g., lock) the independent multi-link suspension system 280 of one or more of the drive wheels 260A, 260B, e.g., the lockout system 500 is configured to lock one or more of the independent multi-link suspension system 280 for a respective drive wheel 260A, 260B in a predetermined position relative to the frame 200. For example, in one aspect, the independent multi-link suspension system 280 of drive wheel 260A may be locked from movement by a lock (described herein) of the suspension lockout system 500 while the independent multi-link suspension system 280 of the drive wheel 260B remains operable (or vice versa). In another aspect, the independent multi-link suspension system 280 of both drive wheels 260A, 260B may be automatically locked, such as by controller 1220) from movement by respective locks (described herein) of the suspension lockout system 500. Locking movement of one or more of the drive wheels 260A, 260B may facilitate transfer of payloads to and from the autonomous transport vehicle 110 by preventing rolling of the autonomous transport vehicle 110 about the longitudinal axis LAX due to, for example moments induced by cantilevered loads on the autonomous transport vehicle 110 that may compress the fully independent suspension on a side of the autonomous transport vehicle 110 from which the transfer arm 21A extends. Here the suspension may be automatically locked by the controller 1220 (e.g., with commands from the controller that effect actuation of the lock) while transferring loads to and from the autonomous transport vehicle 110 and automatically unlocked by the controller 1220 (e.g., with commands from the controller that effect release of the lock) while the autonomous transport vehicle is traversing the transfer deck 130B and picking aisles 130A. As an example, the controller 1220 is configured to receive sensor signals from any suitable sensor (e.g., transfer arm position sensor 888 (see Figs. 8A, 8B, and 20) or any other suitable sensor(s) that are configured to sense/detect extension and/or retraction of the transfer arm 210A) and based on the position of the transfer arm 210A (as determined from the sensors signals) effect automatic actuation of the lock/suspension lockout system 500 of a respective fully independent suspension 280 with extension of the transfer arm 210A from frame 200 (e.g., extension from the payload bed 210B and/or from the payload datum position PDP), and effect automatic release of the lock/suspension lockout system 500 of the respective fully independent suspension 280 with retraction of the transfer arm 210A into the frame 200 (e.g., retraction into the payload bed 210B and/or to the payload datum position PDP).

[0117] For exemplary purposes only the suspension lockout system 500 will be described with respect to the substantially vertically oriented shock absorbers, but it should be understood that the aspects of the suspension lockout system 500 are equally applicable to the substantially horizontally oriented shock absorbers described herein (see Fig. 5A). The suspension lockout system 500 includes a brake or lock 510 on the shock absorber 312 for each drive wheel 260. When the brake 510 is engaged, movement (e.g., extension and/or retraction) of the respective shock absorber 312 is prevented. When the brake 510 is released, the shock absorber 312 may extend and retract freely (e.g., uninhibited by the brake 510) to effect movement of a respective drive wheel 260 in the wheel travel direction SUS. The controller 1220 is in one or more aspects configured to automatically actuate the brake(s) 510 to prevent movement of the respective shock absorber 312 upon extension of the transfer arm 210A to transfer case units to and from the payload bed 210B. For example, any suitable sensors 888 (see Fig. 15A, e.g., motor current sensors, proximity sensors, etc.) may be provided on the autonomous transport vehicle 110 that detect extension of the transfer arm 210A. The sensors 888 send sensor signals to the controller 1220 and based on the sensor signals the controller 1220 actuates the brake(s) 510 so that the transfer arm extension substantially does not cause tilting/tipping of the frame 200 (e.g., tilting such as from compression of the fully independent suspension described herein due to cantilevered loading of the frame 200). In other aspects, the brake(s) 510 may be locked at any suitable time to effect any suitable autonomous transport vehicle 110 operation.

[0118] Referring also to Fig. IOC, the shock absorber 312 includes a shock housing 312H and a piston 312P that extends from and reciprocates relative to the shock housing 312H (or vice versa depending on which end of the shock absorber is held stationary). In this example the piston 312P includes the first end 312E1 of the shock absorber 312 and the shock housing 312H includes the second end 312E2. As described above, the first end 312E1 (and hence the piston 312P) is coupled to the frame 200 about shock absorber pivot axis 466 where the shock absorber pivot axis 466 remains stationary (i.e., in a fixed unmovable position) relative to the frame 200. The second end 312E2 of the shock absorber 312 is coupled to the lower frame link 311 about the connecting link pivot axis 325, where the connecting link pivot axis 325 moves relative to the frame 200 as the wheel 261W moves in the wheel travel direction SUS. As will be described in greater detail below, the brake 510 engages the shock housing 312H (e.g., the reciprocating portion of the shock absorber 312) so as to prevent movement of the shock housing 312H and hence, prevents movement of the respective independent multi-link suspension system 280. It should be understood that in other aspects, such as where the piston 312P reciprocates relative to the shock housing 312H (such as in Fig. 5A and 5B) the brake may engage the piston 312P so as to prevent movement of the shock housing 312H and hence, prevents movement of the respective independent multi-link suspension system 280.

[0119] Still referring to Figs. 11A, 11B, 11C, and 11D, the brake 510 includes a frame 510F, a motor 550 (Fig. 11A), lock links 560, 561, and brake levers 570, 571. The configuration of the brake 510 illustrated is exemplary and in other aspects may have any suitable configuration. The motor 550 may be any suitable motor including but not limited to a stepper motor, a servo motor, linear actuator, etc. The motor 550 is coupled to the frame 510F in any suitable manner, such as with mechanical fasteners. A shaft collar 552 is coupled to an output shaft 551 of the motor 550, such as by friction or in any other suitable manner, so that the output shaft 551 drives rotation of the shaft collar 552. The shaft collar includes eccentric lock link pivots 553, 554, each having a respective lock link pivot axis 553X, 554X. Each lock link 560, 561 has a substantially "U" shaped configuration which includes a first end 560E1, 561E1 a second end 560E2, 561E1, and a base portion 560B, 561B that connects the respective first end 560E1, 561E1 to the respective second end 560E2, 561E2, where the first end 560E1, 561E1 and second end 560E2, 561E2 project from a common side of the respective base portion 560B, 561B to form the substantially "U" shaped configuration. In other aspects, the lock links 560, 561 may have any suitable configuration.

[0120] In one aspect, the first end 560E1 of the lock link 560 is coupled to eccentric lock link pivot 554 so as to pivot about lock link pivot axis 554X. The second end 560E2 of the lock link 560 is coupled to a first end 570E1 of brake lever 570 about a first brake lever pivot axis 570X1 so that the brake lever 570 pivots relative to the lock link 560. A second end 570E2 of the brake lever 570 is coupled to the frame 510F so as to pivot about second brake lever pivot axis 570X2.

[0121] Similarly, the first end 561E1 of the lock link 561 is coupled to eccentric lock link pivot 553 so as to pivot about lock link pivot axis 553X. The second end 561E2 of the lock link 561 is coupled to a first end 571E1 of brake lever 571 about a third brake lever pivot axis 571X1 so that the brake lever 571 pivots relative to the lock link 561. A second end 571E2 of the brake lever 571 is coupled to the frame 510F so as to pivot about fourth brake lever pivot axis 571X2. In other aspects, a linear actuator may extend between the pivot axes 570X1, 571X1 such that extension and retraction of the linear actuator effects movement of the brake levers 570, 571 to lock and release the brake 510.

[0122] Each of the brake levers 570, 571 include a friction pad 570P, 571P that are arranged relative to one another in an opposing relationship so as to grip and release shock housing 312H. As described above, the second ends 570E2, 571E2 of the brake levers 570, 571 are coupled to the frame 510F about a respective one of the second brake lever pivot axis 570X2 and the fourth brake lever pivot axis 571X2 so that a distance 598 between the second brake lever pivot axis 570X2 and the fourth brake lever pivot axis 571X2 is fixed and does not change. Rotation of the shaft collar 552 by the motor 550 causes an eccentric rotation of the lock links 560, 561 so that the lock links 560, 561 push or pull (depending on a direction of rotation of the shaft collar 552) the first end 570E1, 571E1 of the respective brake lever 570, 571 so that a distance between the first brake lever pivot axis 570X1 and the third brake lever pivot axis 571X1 increases or decreases (depending on a direction of rotation of the shaft collar 552). For example, the brake 510 is shown in a released configuration in Figs. 11B and llC where the friction pads 570P, 571P are not in contact with the shock housing 312H (i.e., the respective independent multi-link suspension system 280 is free to move). The brake is shown in a locked configuration in Fig. 11D where the friction pads 570P, 571P are in contact with the shock housing 312H (i.e., the respective independent multi-link suspension system 280 is locked to stop wheel travel in wheel travel direction SUS). In the unlocked configuration the distance between the first brake lever pivot axis 570X1 and the third brake lever pivot axis 571X1 is distance 599R. In the locked configuration the distance between the first brake lever pivot axis 570X1 and the third brake lever pivot axis 571X1 is distance 599C, where the distance 599C is less than the distance 599R. [0123] To lock the brake 510 from the unlocked configuration the shaft collar 552 is rotated in direction 580 (Fig. 11D) so that the lock links 560, 561 move the first ends 570E1, 571E1 of the brake levers 570, 571 towards each other to reduce/decrease the distance between the first brake lever pivot axis 570X1 and the third brake lever pivot axis 571X1 to distance 599C so that the friction pads 570P, 571P contact the shock housing 312H. For example, when the shaft collar 552 is rotated in direction 580, the lock link 560 moves the first end 570E1 of the brake lever 570 in direction 507 while lock link 561 moves the first end 571E1 of the brake lever 571 in the opposite direction 508.

[0124] To unlock the brake 510 from the locked configuration the shaft collar 552 is rotated in direction 581 (Fig. 11B) so that the lock links 560, 561 move the first ends 570E1, 571E1 of the brake levers 570, 571 away from each other to increase the distance between the first brake lever pivot axis 570X1 and the third brake lever pivot axis 571X1 to distance 599R so that the friction pads 570P, 571P are not in contact with the shock housing 312H. For example, when the shaft collar 552 is rotated in direction 581, the lock link 561 moves the first end 571E1 of the brake lever 571 in direction 507 while lock link 560 moves the first end 570E1 of the brake lever 570 in the opposite direction 508.

[0125] As can be seen in Fig. 11D, the "U" shaped configuration of the lock links 560, 561 provide for an over-center locking of the brake levers 570, 571 in the locked configuration substantially without aid of force by the motor 550. For example, referring to Figs. 11D and HE with the brake 510 in the locked configuration, the friction pads 570P, 571P are compressed against the shock housing 312H which causes force FI to be exerted by the brake lever 571 on the second end 561E2 of lock link 561 at the third brake lever pivot axis 571X1 (a similar force is exerted on the second end 560E2 of lock link 560 by brake lever 570). The force FI on the lock link 561 in turn generates force F2 at the lock link pivot axis 553X (a similar force is generated at lock link pivot axis 554X). As can be seen in Fig. 11E the forces FI, F2 may be substantially egual in magnitude and are located on opposite sides of the center (e.g., axis of rotation 551X) of the drive shaft 551 / shaft collar 552 (i.e., over-center) such that a moment generated about axis of rotation 551X by force F2 cancels out another moment generated about axis of rotation 551X by force FI so as to maintain the brake 510 in the locked configuration substantially without aid from the motor 550. The motor 550 provides sufficient torque to overcome the over-center locking so as to move the brake levers 570, 571 between the locked and unlocked configurations.

[0126] As described above, the frame 200 includes one or more idler wheels 250 disposed adjacent the front end 200E1. In one aspect, an idler wheel 250 is located adjacent each front corner of the frame 200 so that in combination with the drive wheels 310 disposed at each rear corner of the frame 200, the frame 200 stably traverses the transfer deck 130B and picking aisles 130A of the storage structure 130. Referring to Figs. 2, 12A, and 12B, in one aspect, each idler wheel 250 comprises any suitable caster 600. In one aspect, the caster 600 is an un-motorized or passive caster 600P (see Fig. 2) where the wheel 610 of the caster 600P pivots passively in direction 690 about caster pivot axis 691 in response to changes in a travel direction of the autonomous transport vehicle 110. In other aspects, the caster 600 is a motorized caster 600M (see Figs. 2, 12A, and 12B) that is configured to actively pivot the wheel 610 in direction 690 about caster pivot axis 691.

[0127] Regardless of whether the caster 600 is a passive caster 600P or a motorized caster 600M the caster 600 may include an articulated fork 740 suspension system as described herein; while in other aspects, the caster 600 may be sans suspension (see Figs. 14A and 14B). The articulated fork caster 600S in combination with the drive wheels 260, coupled to the frame by the respective independent suspension system 280, provide the autonomous transport vehicle 100 with independent suspension at all four corners of the frame 200 to effect the stable traverse of the frame 200 along/on the transfer deck 130B and picking aisles 130A of the storage structure 130 as described in greater detail herein.

[0128] In one or more aspects, where the casters 600 are motorized casters 600M, each motorized caster 600M includes a frameless motor 670 (also referred to as castering assistance motor) that is integrated into a caster frame 650and includes a caster pivot shaft 630. The caster pivot shaft 630 is rotatably coupled to the caster frame 650 by any suitable bearings 666 and is driven in rotation about axis 691 by the frameless motor 670. The frameless motor 670 may be a servo motor, a stepper motor, or any other suitable type of motor configured to provide controlled intermittent bi-directional rotation of the articulated fork 740

(and the wheel 610 coupled to the articulated fork 740) about the pivot axis 691.

[0129] As described herein, the castering assistance motor 670 engages the at least one wheel 610 so as to impart castering assistance torque to the at least one caster wheel 250 assisting castering of the at least one caster wheel 250. Here, the castering assistance motor 670 imparts a bias force BF (Fig. 14B) to the caster wheel 250 at each castering position (e.g., at each rotation position of the wheel 610 relative to a respective caster pivot axis 691) of the caster wheel 250. The bias force BF substantially negates, as described herein in a manner similar to a commanded castering assistance torque led, one or more of castering resistance (e.g., torque induced about the caster pivot axis 691) imparted to the at least one caster wheel 250 from castering scrub (as described herein) and resistance (e.g., moments or torque generated by castering scrub that acts about the origin 900 and is counter to drive motion torque id - see Fig. 31 - is substantially negated) from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels 260A, 260B.

[0130] Each motorized caster wheel 600M is configured to actively pivot its respective wheel 610 (independent of the pivoting of other wheels of other motorized casters) in direction 690 about caster pivot axis 691 to at least assist (e.g., assist the differential steering) in effecting a change in the travel direction of the autonomous transport vehicle 110 as will be described in greater detail herein. The motorized caster wheel(s) 600M may provide for faster steering response compared to, for example, the conventional steering of an autonomous transport vehicle with differential drive wheel steering alone where the autonomous transport vehicle includes passive (e.g., non- motorized) casters (i.e., referred to differential drive wheel steering paired with passive casters). The motorized caster wheel(s) 600M may also provide for, when used in combination with the differential drive wheel steering, a lesser torque being applied by the drive wheels to differentially steer the autonomous transport vehicle 110 (e.g., from rest (such as for a zero-radius turn/pivoting of the autonomous transport vehicle about its origin 900 or to initiate a arcuate trajectory from rest) or while in motion) compared to the differential drive wheel steering paired with passive casters. Here each of the motorized caster wheel(s) 600M may be operated in one or more of a torque assist mode and a steering mode. In the torque assist mode the motorized caster wheel(s) 600M are used in conjunction with differential drive wheel steering to reduce the torque required by the drive wheels to differentially steer the autonomous transport vehicle 110 as noted above. In the steering mode the motorized caster wheel(s) 600M provide for steering of the autonomous transport vehicle 110 substantially without differential drive wheel steering. It is noted that while the motorized casters 600M include motors 670 for driving rotation of a respective wheel 610 about a respective pivot axis 691, the motor/caster is configured such that when motor torque is not applied for rotating the wheel 610 about pivot axis 691, the wheel 610 is in one or more aspects free to pivot about the respective axis 691 (i.e., in a manner substantially similar to that of a passive/un-motorized caster); while in other aspects the motor/caster is configured to bias the wheel 610 against castering about the pivot axis 691 and maintain the caster wheel 250 in a predetermined steady state position (e.g., relative to the pivot axis and/or the axis of symmetry LAX) with the autonomous transport vehicle 110 in motion as will be described herein.

[0131] Referring to Figs. 14A and 14B, each motorized caster 600M includes a caster mount housing 620 (also referred to herein as a caster housing) that is configured to house the castering assistance motor 670. The castering assistance motor 670, is in one or more aspects, a frameless motor 670F that is integrated in the caster housing 620. For example, the frameless motor 670F (also referred to as motor 670) is integrated into a caster frame 650 of the caster housing 620; however, in other aspects the motorized casters 600M may include any suitable motors for driving rotation of the respective wheel 610 about the respective pivot axis 691. The frameless motor 670 may be a servo motor, a stepper motor, or any other suitable type of motor configured to provide controlled intermittent bi-directional rotation of the wheel 610 about the pivot axis 691. Generally, the frameless motor 670F includes a motor rotor 631 and a motor stator 625 that are both built into a machine assembly (such as the caster assembly) to transmit torque to drive rotation of the wheel 610 of the motorized caster 600M. The motor stator 625 is coupled to the caster housing 620 (so as to be integrated with the caster housing 620). For example, the motor stator 625 is disposed against and supported by the caster housing 620. The motor rotor 631 is disposed against a caster pivot shaft 630, where the caster pivot shaft 630 pivotally joins at least one wheel 610 to the caster housing 620. Here the motor rotor 631 is coupled to the caster pivot shaft 630 so as to be integrated with the caster pivot shaft 630. The caster pivot shaft 630 is rotatably coupled to the caster frame 650 of the caster housing 620 by any suitable bearings 666, where caster housing 620 houses at least a portion of the caster pivot shaft 630 and the caster pivot shaft 630 is driven in rotation about axis 691 by the frameless motor 670. As will be described herein, the wheel 610 is mounted to a wheel fork 640 that is in turn coupled to or integral with the caster pivot shaft 630 (see Figs. 14A and 14B) in any suitable manner for rotation, with the caster pivot shaft 630, about axis 691. The caster wheel 610 is coupled to the wheel fork 640 about an axis of rotation 692 of the wheel fork 640. The wheel fork 640 is coupled to, or in other aspects is formed integrally with, the caster pivot shaft 630 so as to rotate with the caster pivot shaft 630 as a single unit about pivot axis 691.

[0132] The caster 600 having the articulated fork 740 is illustrated in Figs. 13A and 13B (see also Figs. 12A and 12B) as a motorized caster 600M for exemplary purposes only; however, in other aspects the caster 600 having the articulated fork 740 may be the passive caster 600P described above. As noted above, the caster 600 (whether motorized or passive) in combination with the drive wheels 260 provide the autonomous transport vehicle 110 with four-wheel fully independent suspension (i.e., an independent suspension at each of the four corners of the frame 200). The four-wheel fully independent suspension is configured for autonomous transport vehicle handling/vehicle drive dynamics with different/variable suspension geometries at the front end 200E1 (and at each corner of the front end 200E1) and at the rear end 200E2 (and at each corner of the rear end 200E2) of the autonomous transport vehicle 110. The different/variable suspension geometries effect synergism in autonomous transport vehicle 110 handling/vehicle drive dynamics between each of the articulated fork casters 600S and drive wheels 260 as well as wheel compliance (e.g., relative to the rolling or vehicle travel surface 395 - see Figs. 9A and 9B) in wheelbase (i.e., wheel compliance between the front end 200E1 and the back end 200E2), wheel compliance in wheel track (i.e., wheel compliance between the lateral sides 200LS1, 200LS2 - see Fig. 2), and diagonal wheel compliance (i.e., wheel compliance between opposite front and back corners FC1, RC2 and wheel compliance between opposite front and back corners FC2, RC1 - see Fig. 2). The articulated fork casters 200S in combination with the drive wheels 260 provide the autonomous transport vehicle 110 with and maintains a stable platform when the autonomous transport vehicle 110 picks and places case units CU and traverses the rolling surface 390.

[0133] Referring to Fig. 14B, to detect the rotation angle of the respective wheel 610 about the pivot axis 691 each motorized caster 600M includes any suitable feedback device 681, such as a rotary encoder 682 or other suitable sensor. For example, a rotary encoder track 682T may be affixed to (or integral with) the caster pivot shaft 630 in any suitable manner (so as to rotate as a unit with the caster pivot shaft 630 and the caster wheel 610 about the axis 691). A sensor 682S configured to read the encoder track may be mounted to the frame 650 at a fixed location of the frame 650. The feedback device 681 is coupled to one or more of the controller 1220 and an electronic motor drive 688 for providing feedback signals that embody a wheel rotation position relative to a predetermined (e.g., a home, zero, or starting position) wheel orientation about axis 691, wheel rotation direction about axis 691, and a wheel rotation speed about the axis 691. The feedback device 681 is configured to determine one or more of an absolute and incremental position of the caster pivot shaft 630 (and hence the wheel 610) about the axis 691.

[0134] The motor 670 of the motorized caster 600M is configured to (e.g., under control of controller 1220 - see, e.g., Fig. 1) apply a variable amount of torque along the pivot axis 691 for rotating the caster wheel 610. Here, each motorized caster 600M is driven by the electronic motor drive 688 that is configured receive motor current/torque commands from the controller 1220 (see Figs. 1 and 33) and implement those motor current/torque commands (e.g., to the motor 670) to effect rotating the wheels 610 about the respective axis 691. The electronic motor drive 688 is configured so as to receive frequently updated motor currents/torques (e.g., substantially real time updates to the motor currents that are commanded by the controller 1220 and that are processed by the electronic motor drive 688 in the order of milliseconds). [0135] Here, each motor 670 is sized to provide a sufficient amount of torque for rotating a respective caster wheel 610 about axis 691 in a predetermined direction (e.g., with the autonomous transport vehicle stationary or not traversing the travel surface 394, of the transfer decks 130B and inclusive of the rails 800 in the picking aisles 130A), which sufficient amount of torque is matched to an amount of traction/friction between the caster wheels 610 and the travel surface 395. The controller 1220 is configured to apply a castering assistance torque ic (also referred to as torque ic), with the motor 670, to the at least one wheel 610 biasing the at least one wheel 610 in a castering direction to a predetermined skew orientation (as described herein with respect to Figs. 31 and 32) with the autonomous transport vehicle 110 at rest or in motion.

[0136] As an example, referring also to Fig. 30, the autonomous transport vehicle 110 may be travelling along rails 800 within the picking aisles 130A in direction 810 and is to reverse the travel direction so as to travel in direction 820. The controller 1220 is configured to issue commands to the electronic motor drive 688 for each motorized caster 600M so that the respective wheel 610 is rotated in a direction 830, 831 away from the sides 800S of the picking aisle 130A (i.e., the wheels are rotated towards a center of the picking aisle 130A) so that the wheels 610 are not wedged against the sides 800S of the rails 800. Here, torque is applied by the motor 670 of the motorized caster wheel 600M when the autonomous transport vehicle 110 changes the direction of travel within the picking aisle 130A so that the trail of the caster wheel 610 flips or turns about 180 degrees. The torque is applied by the motor 670 to the caster pivot shaft 630 (and hence to the wheel 610) in direction 830, 831 so that the wheel 610 rotates inwardly towards a center of the picking aisle 130A as described above. It is noted that the wheel 610 behaves in a manner similar to that of an inverted pendulum and only a minimal bias (e.g., amount of torque) is needed from the motor 670 to initiate inward rotation of the caster wheel 610 about caster pivot axis 691 in combination with the autonomous transport vehicle 110 traverse along the picking aisle 130A. Here, caster locking mechanisms and special autonomous transport vehicle behaviors (e.g., slowing down to unlock the caster wheel, reduce pre-loads, and manage caster wheel wear) are substantially eliminated.

[0137] As another example, Referring to Fig. 32, where the autonomous transport vehicle 110 is disposed on a non- deterministic surface such as the, flat and open transfer deck 130B, the autonomous transport vehicle 110 may be at rest (i.e., not traversing in a travel direction), where the autonomous transport vehicle is to initiated a turn from rest so as to pivot about its origin 900. In other aspects, the autonomous transport vehicle 110 is travelling along the transfer deck 130B and is to initiate a turn while in motion. Here, in one or more aspects, the controller 1220 is communicably connected to the castering assistance motor 670 and is configured to effect via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels 260A, 260B, and castering assistance of the at least one caster wheel 250A, 250B with the autonomous transport vehicle 110 in motion with a predetermined kinematic state (e.g., vehicle trajectory 10667 - Fig. 32 - which trajectory defines the kinematics of the autonomous transport vehicle 110 along a given path). In one or more aspects, the controller 1220 is communicably connected to the castering assistance motor 670 and is configured to effect, via castering assistance torque ic from the castering assistance motor 670 assisting castering input from vehicle yaw generated by differential torque from the at least two independently driven drive wheels 260A, 260B, substantially scrubless castering of the at least one caster wheel 250 with the autonomous transport vehicle 110 in motion with a predetermined kinematic state (e.g., vehicle trajectory). In one or more aspects, the controller 1220 is communicably connected to the castering assistance motor 670 and is configured to effect castering of the at least one caster wheel 250 with the autonomous transport vehicle 110 in motion with a predetermined kinematic state via combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels 260A, 260B, and castering assistance torque ic, from the castering assistance motor 670, where the castering assistance torque ic is developed to substantially negate resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle 110. For example, the controller 1220 may apply a castering assistance torque ic to the caster wheels 250A, 250B so that each respective wheel 610A, 61B is biased in a castering direction to a respective skew orientation (e.g., respective zero-scrub angles 51, 52. Biasing the wheels 610 to the respective skew orientation may reduce an amount of power (e.g., of the drive wheel motors 261M) that differentially drives the drive wheels 260A, 260B to initiate turning (e.g., traverse along an arcuate path) of the autonomous transport vehicle 110 from rest or with the autonomous transport vehicle 110 in motion as described herein. In one or more aspects, the controller 1220 is configured to determine the torque ic as a supplemental torque that supplements castering input to the at least one caster wheel 250, from the vehicle yaw, to effect scrubless castering of the at least one caster wheel 250.

[0138] It is noted that the castering assistance motor 670 is configured so that a maximum castering assistance torque icm (Fig. 31) is a motor rated (full-load) torque (i.e., the torque required to produce the rated power of the motor at full-load speed without the motor overheating) of the motor 670. It is also noted that a commanded castering assistance torque red (Fig. 31, see also the motor torque commands in Fig. 33) is configured wherein resistance from castering scrub at each predetermined kinematic state (e.g., of the autonomous transport vehicle 110) is substantially negated so as to effect a substantially scrubless castering of the caster wheel 250 along and throughout each vehicle path, such as vehicle path 10666 (see Fig. 32) via the commanded castering assistance torque led, substantially independent of the vehicle path 10666 and the kinematic state. As described herein, in one or more aspects, the commanded castering assistance torque icd for each respective caster wheel 250A, 250B, of the at least one caster wheel 250, is determined independently for each respective caster wheel 250A, 250B so as to effect substantially scrubless castering of each respective caster wheel 250A, 250B substantially independent of the vehicle path and the kinematic state. In one or more aspects, as described herein, the commanded castering assistance torque icd for each respective caster wheel 250A, 250B, of the at least one caster wheel 250, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein the castering assistance torque ic respectively commanded for each corresponding caster wheel 250A, 250B varies between corresponding caster wheels 250A, 250B of the at least one caster wheel 250 based on turn radius (e.g., an instantaneous turn radius or a steady state turn radius - see Fig. 32 where the castering assistance torque ica for caster wheel 250A may be greater than the castering assistance torque icb for caster wheel 250B to achieve the respective zero-scrub angles dΐ, d2). The commanded castering assistance torque Ted substantially negates one or more of castering resistance (e.g., torque) imparted to the at least one caster wheel 250 from castering scrub and resistance (e.g., moments) from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels 260A, 260B.

[0139] Referring to Figs. 14B and 31, when the torque ic is applied to the castor pivot axis 691 by the motor 670 (e.g., based on the commanded torque led), a proportional torque/moment (referred to herein as moment ib) is applied to an origin 900 of the autonomous transport vehicle 110, where the moment lb applied origin 900 depends on the angle sΐ, s2 of the caster wheel pivot point 941 (i.e., the point of contact (or a center of contact area/patch) between the caster wheel 610A, 610B and the travel surface 395). The origin 900 being located at a center point W/2 (e.g., about half the width W of the autonomous transport vehicle - e.g., substantially on the axis of symmetry LAX) between the two drive wheels 260A, 260B and along an axis 971 defined by and extending between the rotation axis of each drive wheel 260A, 260B. For example, the moment ib at the origin 900 is expressed by the following:

[0141] where, ic is the torque applied at the castor pivot axis 691, TA is the length of the caster pivot arm (e.g., the caster trail - see Figs. 14A, 14B, and 31), Px and Py are the components (e.g. distances) of the vector from the origin 900 to the caster wheel pivot point 941, and s is the angle ol or s2 of the caster wheel 610A or 610B. A linear force fb applied at the origin 900 and along a centerline or longitudinal axis LAX of the autonomous transport vehicle 110 as a result of the torque ic applied to the castor pivot axis 691 by the motor 670 is expressed by the following:

[0143] It is noted that the ratio Px/TA that results from an angle s of the caster wheel pivot point 941 of about 0 degrees or about 180 degrees (see Fig. 31) is a moment multiplier that results from a "small" trailing arm TA compared to the distance Px of the caster wheel pivot point 941 from the drive wheels). As an example, for the geometry of the autonomous transport vehicle 110 illustrated in the figures (e.g., exemplified by Fig. 31) the ratio of Px/TA results in the torque lb applied about the origin 900 (as a result of caster wheel 610 pivoting) being about forty-eight times greater than the torque ic applied at the caster pivot axis 691. In comparison, the torque id applied at the origin 900 (as a result of differential steering with the drive wheels 260A, 260B) is about four times greater than the torque applied to the drive wheels 260A, 260B. As may be realized from the above, initiating a turn of the autonomous transport vehicle 110 (e.g., with the caster wheels 610 at the about 0 degree or about 180 degree angular orientation, either from rest or with the autonomous transport vehicle in motion) by applying torque ic at the caster pivot axis 691 of each motorized caster 600M is more efficient than initiating the turn with only differential torque applied to the drive wheels 260A, 260B. Here, by initiating the turn of the autonomous transport vehicle 110 with the motorized casters 600M a reduction in the size of the drive motors 261M and associated electronics (e.g., electronic motor drives, amplifiers, etc.) is effected as the torque lb supplements torque id. As may also be realized from the above, the larger moments generated at the origin 900 by the motorized casters 600M (e.g., with the caster wheels 610 at the about 0 degree or about 180 degree angular orientation) provide for a faster steering response when compared to the moments generated at the origin 900 by the drive wheels 260A, 260B and the steering response provided thereby. [0144] Referring to Figs. 1 and 30, as noted above, the motorized casters 600M may be employed for autonomous transport vehicle 110 travel in the picking aisles 130A and along the transfer deck 130B. For example, as described above, torgue ic is applied to the caster wheels 610 by the respective motor 670 to bias rotation of the caster wheels 610 inwards towards a center of the picking aisle to effect a change in travel direction of the autonomous transport vehicle 110 along the rails 800 of the picking aisle 130A. It is noted that other than the bias torgue to initiate rotation of the caster wheel 610 about the caster pivot axis 691 in an inward direction, no torque is applied to the caster pivot shaft 630 by the motor 670 during autonomous transport vehicle 110 traverse along the picking aisle (e.g., the caster wheels 610 are allowed to rotate freely so as to naturally align, due to caster wheel trail, with a direction of movement along the picking aisle 130A rails 800).

[0145] For autonomous transport vehicle 110 travel along the transfer deck 130B the motorized casters 600M are employed to one or more of reduce an amount of differential torque applied by the drive wheels to effect autonomous transport vehicle travel along the transfer deck 130B and assist in aligning the caster wheels 610 with their nominal trailing position to minimize scrubbing of the caster wheels 610 on the travel surface 395 (Figs. 14A and 14B). Here, the controller 1220 is configured to position the castering assistance motors 670 so as to bias a respective one of the at least one caster wheel 250 against castering and maintain the at least one caster wheel 250 in a predetermined steady state position (e.g., to effect travel of the autonomous transport vehicle 110 along a substantially straight line travel path or along an arcuate travel path) with the autonomous transport vehicle 110 in motion.

[0146] Referring to Figs. 2, 14B, and 32, in an exemplary operation of autonomous transport vehicle 110 travel on the transfer deck 130B, the controller 1220 independently controls each of the motorized casters 600M (e.g., casters 250A, 250B) so that the wheel 610A, 610B (similar to caster wheel 610) of the caster wheels 250A, 250B is rotated to a zero-scrub angle 51, 52. The zero-scrub angle 51, 52 is the rotation angle about the caster pivot axis 691 that results in the wheel 610A, 610B pivoting about its contact patch with the travel surface, substantially without lateral friction forces induced on the wheel 610A, 610B by the travel surface) given a current/present angle of the caster wheel 610A, 610B (as measured by, e.g., feedback device 681 for any given instant of time at which the angle measurement is employed by controller 1220 for controlling the angle ol, s2 of the caster wheel 610A, 610B) and a desired velocity vector of the autonomous transport vehicle 110 (e.g., a rotation angle of the caster wheel 610A, 610B about a respective caster pivot axis 691, at which rotation angle substantially zero lateral frictional forces - substantially zero scrub - are exerted on the caster wheel by a travel surface along which the caster wheel traverses). As described in greater detail herein, the zero-scrub angle 51, 52 is a predetermined skew orientation of the at least one caster wheel 250 that is employed by the controller 1220 as a feed-forward term to drive rotation of each wheel 610A, 610B towards the respective zero-scrub angle dΐ, d2 while balancing an amount of steering torque ic. It is noted that where sufficient traction exits between the caster wheel 610A, 610B and the travel surface 395 (Figs. 14A and 14B), the direction of torque ic (Fig. 31) for turning the caster wheel 610A, 610B is generally in the same direction as the torque for steerinq the autonomous transport vehicle 110; however, in other aspects there may be instances where the direction of torque re (Fig. 31) for turning the caster wheel 610A, 610B is in an opposite direction as the torque for steerinq the autonomous transport vehicle 110.

[0147] As can be seen in Fiq. 32, the zero-scrub angle dΐ, d2 for the different caster wheels 250A, 250B and the torque ic applied to the different caster wheels 250A, 250B may be different for any qiven turn radius R of the autonomous transport vehicle 110; however, at least the zero-scrub angle dΐ, d2 may be the same for the different caster wheels 250A, 250B with the autonomous transport vehicle 110 travelling along a substantially straight line path. Here, the controller 1220 independently calculates and controls the scrub angle for each of the caster wheels 610A, 610B. It is noted that at a steady state (e.g., a constant turn radius R (path) and constant velocity along the path (trajectory)) the zero-scrub angle dΐ, 52 is substantially perpendicular to the line from the caster wheel pivot point 941 and a center RC of the turn radius R (again noting that the turn radius R is measured or otherwise defined from the origin 900 of the autonomous transport vehicle 110. Here, the controller 1220 is configured to apply the castering assistance torque ic, with the motor 670, to the at least one caster wheel 250 biasing the at least one caster wheel 250 in a castering direction (e.g., as shown in Figs. 31 and 32) to the predetermined skew orientation/zero-scrub angle 51, 52 of the at least one caster wheel 250, which predetermined skew orientation/zero-scrub angle 51, 52 forms a bias angle (see also angles ol, s2) between the at least one caster wheel 250, in the predetermined skew orientation, and the axis of symmetry LAX of the autonomous transport vehicle.

[0148] Referring to Figs. 2, 14B, 31, 32, and 33, as described above, the autonomous transport vehicle 110 is a non-holonomic differential-drive type robot that has but two degrees of freedom (e.g., with respect to travel of the autonomous transport vehicle along a travel surface and exclusive of case unit pick/place features of the autonomous transport vehicle 110). Here the two degrees of freedom for travel of the autonomous transport vehicle 110 along a travel surface 395 (Figs. 14A and 14B) are linear and rotational motion, which two degrees of freedom correspond to two dimensions of travel motion forces (e.g., net (or summation of) drive motion torque id and net (or summation of) drive motion force fd) applied at the origin 900 by the motors 261M of the drive wheels 260A, 260B and the motors 670 of the motorized casters 600M. It is noted that torque lb generated by the motorized casters 600M may be a component of (i.e., supplements) the net drive motion torque id and the force fb generated by the motorized casters 600M may be a component of (i.e., supplements) the net drive motion force fd (see Fig. 31). With the two drive wheels 260A, 260B, and but two dimensions of travel motion forces, the drive motor 261M torque for each drive wheel 260A, 260B is defined by a desired force and desired moment to move the autonomous transport vehicle 110 along a predetermined travel path; however, in accordance with aspects of the disclosed embodiment the motorized casters 600M provide the autonomous transport vehicle 110 with four motors (rather than the conventional two motors) that contribute to the net drive motion force fd and the net drive motion torque id effecting an under-constrained drive system of the autonomous transport vehicle 110. Here, the generation of the drive motion force fd and torque id is distributed over the four motors 670, 261M of the drive wheels 260A, 260B and the caster wheels 250A, 250B. This provides for the motors 261M of the drive wheels 260A, 260B to be optimized (e.g., is size, power, etc. as described herein) for linear inertial changes of the autonomous transport vehicle 110 motion rather than being configured for generating moments (e.g., about the origin 900) of the autonomous transport vehicle 110 that induce castering of the at least one caster wheels 250 (e.g., the motors 261M do not have to be sized to generate moments about the origin 900 that effect castering of the caster wheels 250, which moments are greater than those moments needed to effect only linear inertial changes in autonomous transport vehicle motion).

[0149] Fig. 33 is an exemplary control architecture of the autonomous transport vehicle 110 that effects one or more of substantially zero-scrubbing of the caster wheels 610A, 610B and a dynamic distribution of the drive motion force fd and torque id over the four motors 670, 261M of the drive wheels 260A, 260B and the caster wheels 250A, 250B. In accordance with the aspects of the disclosed embodiment, the controller 1220 includes any suitable velocity controller 1111 and optimization solver 1112. The velocity controller 1111 is configured to, based on a commanded task (e.g., case unit transport task, traverse task, etc.), determine and output (e.g., to the optimization solver 1112) a predetermined drive motion force fpd and/or predetermined drive motion moment ipd for moving the autonomous transport vehicle along a travel path for completing the commanded task. The optimization solver 1112 is configured to, using feedback from one or more of the caster wheels 250A, 250B and drive wheels 260A, 260B minimize an optimization function 1113 such that the net drive motion force fd and the net drive motion torque id from the four motors 261M, 670 of the caster wheels 250A, 250B and drive wheels 260A, 260B meets constraints defined by the output of the velocity controller 1111 and the maximum available torque from each of the motors 261M, 670. The optimization function 1113 may any suitable optimization function including, but not limited to, a balancing of the forces/moments fd, id between the four motors 261M, 670, minimizing the maximum torque applied to any given wheel 260A, 260B, 610A, 610B, and/or minimizing energy waste due to heat loss in the motor windings (i.e., minimize the sum of I²R, where I is current and R is resistance) across the four motors 261M, 670.

[0150] The above-noted constraints may be expressed as linear equality or inequality constraints, and the optimization function 1113 may correspondingly be quadratic. Here, the optimization solver is configured with, for example, any suitable quadratic programming solution method; however, in other aspects any suitable solution method for effecting a determination of motor torgue commands for effecting traverse of the autonomous transport vehicle 110.

[0151] To effect the substantially zero scrubbing of the wheels 610A, 610B of the caster wheels 250A, 250B, the feed-forward control described herein is employed to provide feedback/input to the optimization solver 1112. Here, the controller 1220 calculates the zero-scrub angle 51, 52 for each of the caster wheels 250A, 250B in the manner described above for the commanded travel path and velocity of the autonomous transport vehicle 110. The controller 1220 also receives the current/present angle sΐ, s2 (as measured by, e.g., feedback device 681) for each of the wheels 610A, 610B (see Fig. 31). The controller 1220 is configured to determine a difference between the zero-scrub angle 51 and the current angle ol of the caster wheel 610A to determine a caster angle error 1160. The caster angle error 1160 is processed through a proportional gain 1120 of the controller 1220, where the output of the proportional gain is employed by the controller 1220 to constrain an available amount of torque for the motor 670 of the caster 250A so as to determine constrained caster torque 1161. It is noted that as the caster angle error 1160 increases, the caster torgue of caster 250A is further constrained to push the caster wheel 610A towards the zero-scrub angle 51. Similarly, the controller 1220 is configured to determine a difference between the zero-scrub angle 52 and the current angle o2 of the caster wheel 610B to determine a caster angle error 1162. The caster angle error 1162 is processed through a proportional gain 1121 (which may be same as or different from proportional gain 1121) of the controller 1220, where the output of the proportional gain is employed by the controller 1220 to constrain an available amount of torque for the motor 670 of the caster 250B so as to determine constrained caster torque 1163. It is noted that as the caster angle error 1162 increases, the caster torque of the caster 250B is further constrained to push the caster wheel 610B towards the zero-scrub angle 52.

[0152] Generally, where traction is maintained between the wheels 610A, 610B and the travel surface 395 (see Figs. 14A and 14B), the constrained caster torque 1161, 1163 does not create additional constraints on the optimization solver 1112, because the sign (i.e., direction) of the torque needed to maintain the zero-scrub angle 51, 52 is the same sign (i.e., direction) as the steering torque. Where traction between the caster wheels 610A, 610B and the travel surface 395 is lost, the caster angle error 1160, 1162 increases and can be of opposite sign (e.g., direction) than the steering torque. Here, the torque is redistributed from the casters 250A, 250B to the drive wheels 260A, 260B so that the predetermined drive motion force fpd and/or predetermined drive motion moment ipd are satisfied, while also pushing/driving the caster wheels 610A, 610B back to the zero-scrub angle 51, 52. It is noted that where the caster angle error 1160, 1162 is of opposite sign (e.g., direction) than the steering torque, the proportional gain 1120, 1121 is configured to effect a balance between obtainment of the zero-scrub angle 51, 52 and obtainment of torque distribution between the wheels 610A, 610B, 250A, 250B. Here a dynamic redistribution of drive motion force and or drive motion moment between the casters 250A, 250B and the drive wheels 260A, 260B provides for caster-heavy steering, while still providing for zero-radius turns with the differential drive of the drive wheels 260A, 260B.

[0153] With the predetermined force fpd, the predetermined moment ipd, motor torques DWMTA, DWMTB from drive wheels 260A, 260B (determined by any suitable sensors in communication with the controller 1220), and the constrained caster torques 1161, 1163 known to the optimization solver 1112, the optimization solver determines present/real-time motor commands (e.g., present force frt and present moment irt) for driving the motors 670 of one or more of the casters 250A, 250B and/or motors 261M of one or more of the drive wheels 260A, 260B so as to effect travel of the autonomous transport vehicle 110 along a predetermined path and having a predetermined kinematic state. In one or more aspects, the constrained caster torques 1161, 1163 may be larger than a maximum torque available to the caster 250A, 250B, in which case the constrained caster torques 1161, 1163 are clipped to the maximum torque available. Similarly, the constrained caster torques 1161, 1163 may be less than a minimum torque available to the caster 250A, 250B, in which case the constrained caster torques 1161, 1163 are clipped to the minimum available torque. As described herein, the above-noted control is performed in a real time loop so that the motor torque commands (e.g., present force frt and present moment irt) are updated in real-time so as to maintain the caster wheels 610A, 610B at the respective zero-scrub angle dΐ, d2 with the autonomous transport vehicle 110 travelling along a substantially straight and/or curved path(s).

[0154] Referring to Fig. 34 as well as to Figs. 1, 2, 14B, 30, 31, 32, and 33 an exemplary method for driving an autonomous transport vehicle 110 in the storage and retrieval system 100 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided (Fig. 34, Block 12110). The autonomous transport vehicle 110 includes, as described herein, a frame 200, a controller 1220, at least two independently driven drive wheels 260A, 260B mounted to the frame 200, and at least one caster wheel 250 mounted to the frame 200 and having a castering assistance motor 670. A castering assistance torgue ic is imparted (Fig. 34, Block 12120), with the castering assistance motor 670 engaged to the at least one caster wheel 250, so as to assist castering (e.g., rotation of the wheel 610 about the caster pivot axis 691) of the at least one caster wheel 250. As described herein, the autonomous transport vehicle 110 traverses both the transfer deck 130B and the picking aisles 130A. With the autonomous transport vehicle 110 on the transfer deck 130B, the controller 1220 effects castering of the at least one caster wheel 250 (Fig. 34, Block 12130), via a combination of vehicle yaw, generated by differential torgue from the at least two independently driven drive wheels 260A, 260B, and castering assistance torque ic from the castering assistance motor 670. Here, the castering of the at least one caster wheel 250 is performed with the autonomous transport vehicle 110 in motion with a predetermined kinematic state; however, the controller 1220 may also effect application of the castering assistance torque ic to the at least one caster wheel 250 biasing the at least one caster wheel in a castering direction to the predetermined skew orientation dΐ, d2 with the autonomous transport vehicle 110 at rest (such as to initiate a turn or arcuate path of motion from rest as described herein). The autonomous transport vehicle 110 traverses the transfer deck 130B (Fig. 34, Block 12140) under control of controller 1220 where directional changes of the autonomous transport vehicle on the transfer deck are effected at least by application of castering assistance torque ic to the at least one caster wheel 250.

[0155] With traverse of the autonomous transport vehicle 110 along the transfer deck 130B, the controller 1220, in one or more aspects, positions the castering assistance motor 670 so as to bias the at least one caster wheel 250 against castering and maintains the at least one caster wheel 250 in a predetermined steady state position with the autonomous transport vehicle 110 in motion along the transfer deck 130B so as to maintain traverse of the autonomous transport vehicle 110 along a predetermined path with a predetermined kinematic state (e.g., velocity vector). The controller 1220 effects application of the castering assistance torque ic (as described herein with the autonomous transport vehicle 110 at rest or in motion) to the at least one caster wheel 250 biasing the at least one caster wheel 250 in a castering direction to a predetermined skew orientation dΐ, d2 of the at least one caster wheel 250, which predetermined skew orientation 51, 52 forms a bias angle (see angles sΐ, s2) between the at least one caster wheel 250 (e.g., the wheel 610), in the predetermined orientation, and an axis of symmetry LAX of the autonomous transport vehicle 110.

[0156] As described herein, with traverse of the autonomous transport vehicle 110 along the transfer deck 130B, the controller determines, independently for each respective caster wheel 250A, 250B, the commanded castering assistance torque ic for each respective caster wheel 250A, 250B, of the at least one caster wheel 250, so as to effect substantially scrubless castering of each respective caster wheel 250A, 250B substantially independent of vehicle path and kinematic state. As illustrated in Fig. 32 and as described above, the controller 1220 determines, independently for each respective caster wheel 250A, 250B, the commanded castering assistance torque icd for each respective caster wheel 250A, 250B to effect substantially scrubless castering of each respective caster wheel 250A, 250B, wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels 250A, 250B based on turn radius.

[0157] With the autonomous transport vehicle 110 in a picking aisle, the controller 1220 effects castering of the at least one caster wheel 250 (Fig. 34, Block 12150), via a combination of linear vehicle motion, generated by torque from the at least two independently driven drive wheels 260A, 260B, and castering assistance torque ic from the castering assistance motor 670. Here, the castering of the at least one caster wheel 250 is performed with the autonomous transport vehicle 110 making a change in direction within the picking aisle (such as from travel in direction 810 to travel in direction 820 - see Fig. 30). The castering of the at least one caster wheel 250 is performed at least in part with the autonomous transport vehicle in motion with a predetermined kinematic state (e.g., travelling along the picking aisle with a predetermined velocity vector). Here, the controller 1220 initiate castering of the at least one caster wheel 250 by effecting application of the castering assistance torque ic to the at least one caster wheel 250 biasing the at least one caster wheel in a castering direction (e.g., towards a center of the picking aisle 130A as described herein) with the autonomous transport vehicle 110 at rest (such as to initiate the change in direction within the picking aisle 130A). The autonomous transport vehicle 110 traverses the picking aisle 130A (Fig. 34, Block 12160) under control of controller 1220 as described herein with, in one aspect, substantial no castering assistance torque ic being applied to the at least one caster wheel 250 during traverse along the picking aisle; while in other aspects, a castering assistance torque ic being applied to the at least one caster wheel 250 so as to bias the at least one caster wheel 250 against castering and maintain the at least one caster wheel 250 in a predetermined steady state position with the autonomous transport vehicle 110 in motion along the picking aisle 130A.

[0158] While the operation of the castering assistance motor 670 was described herein with respect to the motorized caster 600M of Figs. 14A and 14B (e.g., sans suspension), it should be understood that the operation of the castering assistance motor 670 is substantially similar to that described herein with the motorized caster 600M equipped with the fully independent suspension 780 illustrated in Figs. 12A, 12B, 13A, and 13B.

[0159] As noted above, referring again to Figs. 12A, 12B, 13A, and 13B, where each of the casters 600 includes a fully independent suspension 780 the articulated fork 740 is to the caster pivot shaft 630 (or in other aspects a caster pivot shaft of the passive caster 600P) in any suitable manner, such as with any suitable mechanical and/or chemical fastener 777. The articulated fork 740 includes a fork frame 741 and a fork pivot arm 742. The fork frame 741 includes a leading end 778 that leads travel of the articulated fork caster 600S. The fork frame 741 also includes a trailing end 779 that trails travel of the caster 600. The fork frame 741 defines a pivot axis 792 adjacent the leading end 778 where the fork pivot arm 742 is coupled to the fork frame 741 for rotation about pivot axis 792. The wheel 610 is coupled to the fork pivot arm 742 about axis of rotation 692 so that the wheel 610 and fork pivot arm 742 rotate about axis 792 as a unit.

[0160] The rotational (or pivoting) motion between the fork frame 741 and the fork pivot arm 742 is biased against a stop, so that the autonomous transport vehicle 110 frame 200 is substantially level with the rolling surface 395 (see Figs. 9A, 9B, 15A and 15B). For example, the rotational (or pivoting) motion between the fork frame 741 and the fork pivot arm 742 is limited by a suspension travel stop 790 that extends from the fork pivot arm 742 so as to substantially contact or otherwise engage, adjacent the trailing end 779, a stop surface 710 of the fork frame 741. In the example illustrated in Figs. 12A, 12B, 13A, and 13Bthe suspension travel stop 790 forms an "open boxed frame" with an aperture 790A (Fig. 12A) defined thereby. The fork frame 741 extends into the aperture 790A so that the stop surface 710 of the fork frame 741 engages one or more corresponding stop surfaces 721 of the suspension travel stop 790. The stop surfaces 721 are one or more protruding surfaces (e.g., ends of pins 791 integrally formed with or otherwise coupled to and forming a part of the suspension travel stop 790) that extend from the "open boxed frame" towards the stop surface 710; however, in other aspects the one or more surfaces 721 have any suitable configuration for contacting/engaging the stop surface 710 of the fork frame 741.

[0161] As can be seen in Figs. 12A, 12B, 13A, and 13B, the suspension travel stop 790 is configured to arrest rotational movement of the fork pivot arm 742 in direction 792A (Fig. 12A) relative to the fork frame 741. It is noted that the configuration of the suspension travel stop 790 is exemplary and in other aspects the suspension travel stop may have any suitable configuration for arresting rotational movement of the fork pivot arm 742 in direction 792A (Fig. 12A) relative to the fork frame 741.

[0162] The caster 600 includes a biasing member 750 disposed between the fork frame 741 and fork pivot arm 742. The biasing member 750 is illustrated as a compression spring; however, in other aspects the biasing member 750 may be a torsion spring or bar disposed to apply biasing torque in direction 792A against the fork pivot arm 742 at the axis of rotation 792 or any other suitable resilient member configured to bias rotation of the fork pivot arm about axis of rotation 792 in direction 792A.

[0163] The caster 600 includes one or more seats 711, 722, e.g., spring seats or other receiving members configured to receive ends of the biasing member 750 and restrain movement of the ends of the biasing member 750 relative to a respective one of the fork frame

741 and fork pivot arm 742. For example, one end of the biasing member 750 is retained within a seat 722 of the pivoting fork arm

742 so as to be restrained from movement in the directions LON, LAT, VER (see Figs. 12A, 12B). The seat 722 is coupled to the fork pivot arm 742 in any suitable manner or is integrally formed with the fork pivot arm 742.

[0164] The other end of the biasing member 750 is retained within a seat 711 that is movably coupled to the fork frame 741 so as to reciprocate in a direction VER, where the direction VER extends along the caster pivot axis 691. For example the seat includes a recess that receives an adjustment member 711 (e.g., screw or other movable post) so that the adjustment member 711 restrains movement of the seat 721 in direction LAT and in direction LON while effecting movement of the seat 722 in direction VER. For example, the fork frame 741 includes a threaded aperture (shown in Fig. 12B) through which the adjustment member 711 extends and to which the adjustment member is threadably engaged (e.g., the adjustment member 711 includes threads that mate with the threads of the threaded aperture). Rotation of the adjustment member 711 about its axis of rotation drives adjustment member 711 and the seat 721 (against the biasing force of the biasing member 750) in direction VER to compress or relax the biasing member 750 so as to set a preload exerted by the biasing member 750 on the fork pivot arm 742. In one or more other aspects, the seat 721 is fixed to the fork frame 741 so as to be stationary, relative to the fork frame 741, in directions LON, LAT, VER where the preload of the biasing member 750 is set (not-adjustable) by (or with) a configuration of the biasing member (e.g., a length of the biasing member, a number of coils, a spring rate, biasing member wire thickness, etc.).

[0165] As may be realized, the autonomous transport vehicle carries case units CU having different weights and sizes (e.g., for exemplary purposes only the case units CU may weigh up to about 60 lbs or more). Here the weight/mass supported by the autonomous transport vehicle 110 suspension varies depending on the case unit CU being transported. The casters 600 are configured to resist any moments induced on the frame 200 when picking and placing the case units CU. For example, to transfer case units to and from the autonomous transport vehicle 110, the transfer arm 210A is extended and retracted as shown in, for example, Fig. 15B. With the transfer arm 210A extended, fingers 210AF of the transfer arm 210A and any case unit CU held on the fingers 210AF are cantilevered from the frame 200, where the cantilevered fingers 210AF and case unit CU create a moment 893 (see Fig. 15B) about, for example, a center of gravity CG of the autonomous transport vehicle 110. This moment 893, left un-countered, would cause the autonomous transport vehicle 110 to tilt/tip and become un-level relative to the rolling surface 395 and any case unit holding location 866 to and from which case units CU are picked/placed. Here, the spring rate and spring preload of the at least the biasing member 750 of each caster 600 is configured so that when the heaviest case unit CU expected to be handled by the autonomous transport vehicle 110 is being held by the cantilevered fingers 210AF (such as during a pick/place action of the transfer arm 210A), the stop surface 710 of the fork frame 741 is substantially engaged with (e.g., in substantial contact with) the one or more corresponding stop surfaces 721 of the suspension travel stop 790 and the autonomous transport vehicle 110 remains level relative to the rolling surface 395 and any case unit holding location 866 to and from which case units CU are picked/placed.

[0166] In addition to maintaining the autonomous transport vehicle 110 level, the casters 600 are configured to maintain a consistent ride height RHT (which is coincident with the payload datum position PDP) of the autonomous transport vehicle 110. To maintain the consistent ride height RHT (e.g., so the ride height does not change regardless of the case unit weight/mass held by the autonomous transport vehicle 110) the spring rate and the spring preload of at least the biasing member 750 of each caster 600 is sized so that when the heaviest case unit CU expected to be handled by the autonomous transport vehicle 110 is being held by the autonomous transport vehicle 110, the stop surface 710 of the fork frame 741 is substantially engaged with (e.g., in substantial contact with) the one or more corresponding stop surfaces 721 of the suspension travel stop 790. As may be realized, the shock absorber 312 of the multi-link suspension system 280 (see Figs. 5A, 5B, and 10A-10C) is configured with a spring rate and spring preload that is sized so that when the heaviest case unit CU expected to be handled by the autonomous transport vehicle 110 is being held by the autonomous transport vehicle 110, the ride height RHT is maintained.

[0167] Referring also to Figs. 2, 15A, and 15B, the frame 200 includes wheel interfaces 222A-222D. Each of the drive wheels 260 is coupled to the frame 200 at a respective interface 222A, 222B, where the interface 222A, 222B couples the drive wheel 260 to the frame 200 at a known location on the frame 200. The interfaces 222A, 222B, in one or more aspects, include the multilink suspension system 280 link-to-frame mounting points (axes) described herein; while in other aspects, the drive wheels 260 and multilink suspension system 280 are provided as a modular unit, where the modular unit has a frame mount configured to couple with the interface 222A, 222B. Each of the casters 260 is coupled to the frame 200 at a respective interface 222C, 222D, where the interface 222C, 222D couples the caster 260 to the frame 200 at a known location on the frame 200. The interfaces 222C, 222D includes coupling features (e.g., threaded holes, locating pins, recesses, stop surfaces, etc.) that mate with the corresponding coupling features (e.g., recesses, locating pins, fastener through holes, stop surfaces, etc.) of the caster frame 650.

[0168] Mounting the casters 600 and the drive wheels 620 to the frame at known locations in combination with known suspension geometry of each of the casters 600 and drive wheels 620 facilitates setting the ride height RHT of the autonomous transport vehicle 110. For example, with respect to the casters 600, the biasing member 750 biases the one or more stop surfaces 721 of the fork pivot arm 742 against the stop surface 710 of the fork frame 741 to set an angle Y between the axis of rotation 792 of the fork pivot arm 742 and the axis of rotation 692 of the wheel 610, where the angle Y is measured relative to a datum DAT1 that is defined by an axial direction of extension of the caster pivot axis 691 (see Fig. 13A). This angle Y at least in part sets a ride height RHT of the autonomous vehicle 110 relative to the rolling surface 395.

[0169] The multi-link suspension system 280 of each drive wheel 260 is also configured to have a predetermined extension that at least in part sets the ride height RHT. For example, the shock absorbers 312, in one or more aspects, include integral stops 555 (such as between the piston 312P and the shock housing 312H - see Fig. 11A) that limit the extension of the shock absorber to a known length SAL (see Fig. IOC); while in other aspects the extension travel of the shock absorbers 312 (and of the multi-link suspension system 280) is limited in any suitable manner, including but not limited to, bump stops 556 (see Fig. 11A) mounted to the frame 200 that interface with and arrest travel of one or more suspension links of the multi-link suspension system 280.

[0170] As can be seen in Figs. 15A and 15B, the ride height RHT (and payload datum position PDP) of the autonomous transport vehicle 110 is measured from the rolling surface 395 to a case unit support surface 210AFS (also referred to herein as a payload seat surface) of the transfer arm 210A fingers 210AF; however, in other aspects the ride height RHT can be measured from the rolling surface 395 to any suitable location on the autonomous transport vehicle 110 (such as the bottom of the frame 200 or any other suitable location. Here the ride height RHT is set so that the transfer arm 210A can access (i.e., pick and place) case units CU at each case unit holding location accessible from the transfer deck 130B and picking aisles 130A. For example, as illustrated in Fig. 15B the ride height RHT corresponding to the case unit support surface 210AFS of the fingers 210AF is lower than a height SHT of a case unit support plane CUSPH of case unit holding location 866 so that the transfer arm 210A is raised and lowered for picking and placing case units from and to the case unit holding location 866.

[0171] As described herein, the ride height RHT (which is coincident with the payload datum position PDP) is at a minimum distance MIND above the rolling surface 395. The minimized distance of the ride height RHT from the rolling surface 395 effects placement of the case unit support plane CUSPH of the case unit holding location 866 (e.g., such as a shelf of a storage rack in a picking aisle or other suitable location of the storage structure 130) closer to the rolling surface 395 compared to conventional storage and retrieval systems. Here, the vertical storage density of storage structure 130 (and of the storage and retrieval system 100) may be increased based on the minimized ride height RHT of the autonomous transport vehicle 100. [0172] In accordance with the aspects of the disclosed embodiment, referring to Figs. 2, 5A, 5B, 12B, and 20 the fully independent suspension of the autonomous transport vehicle is tuned (such as by adjusting the preload as described herein) to minimize transient vibration induced to the storage structure (e.g., which vibrations may cause movement/migration of case units from predetermined locations on a storage shelf or other case unit holding location) by traverse of the autonomous transport vehicle 110 over the rolling surface 395 of the transfer deck 130B and/or picking aisle 130A, as well as to minimize transient vibrations of the autonomous transport vehicle 110 as the autonomous transport vehicle traverses the rolling surface 395. The frame 200 of the autonomous transport vehicle 110 has a predetermined rigidity characteristic 289 (e.g., a vibrational characteristic of the frame) that defines a transient response of the frame 200 from transient loads imparted to the frame 200 via at least one of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B.

[0173] The predetermined rigidity characteristic 289 is set (e.g., tuned) based on a predetermined transient response characteristic (e.g., one or more of response frequency, impact G- force in the X, Y, and/or Z directions, and acceleration in the X, Y, and/or Z directions) of the fully independent suspension 780, 280 of at least one of the at least one caster wheel 250A, 250B and the at least one traction drive wheel 260A, 260B and/or the a predetermined transient response characteristic of the fully independent suspension 780, 280 of at least one of the at least one caster wheel 250A, 250B and the at least one traction drive wheel 260A, 260B is set (e.g., tuned) based on the predetermined rigidity characteristic 289 of the frame 200. The predetermined rigidity characteristic 289 may also be set/tuned based on a predetermined transient response characteristic e.g., one or more of response frequency, impact G-force in the X, Y, and/or Z directions, and acceleration in the X, Y, and/or Z directions) of the frame 200 determining the transient response of the frame 200 from transients of the at least one caster wheel 250A, 250B and at least one drive wheel 260A, 260B rolling on the rolling surface 395. The predetermined rigidity characteristic 289 of the frame 200 determines the frame 200 as being substantially rigid relative to the fully independent suspension of at least one caster wheel 250A, 250B and least one drive wheel 260A, 260B of the drive wheels 260A, 260B rolling on the rolling surface 395. The predetermined rigidity characteristic 289 may also be set based on a predetermined transient response characteristic of the frame 200 with the autonomous transport vehicle carrying a payload and/or without carrying a payload (e.g., unloaded).

[0174] For example, each of the biasing members 312, 750 at each corner of the autonomous transport vehicle 110 are preloaded with a respective preload PI, P2, P3, P4 that depends on one or more of a mass of the autonomous transport vehicle 110 and a payload (e.g., case units CU) to be carried by the autonomous transport vehicle 110. The preloads PI, P2, P3, P4 have, in some aspects, substantially similar values while in other aspects one or more of the preloads PI, P2, P3, P4 may be set to a different value than other ones of the preloads PI, P2, P3, P4. The preloads PI, P2, P3, P4 may also be set to provide any suitable weight distribution of the autonomous transport vehicle 110 (e.g., to set a portion of the weight of the autonomous transport vehicle and payload carried by each wheel).

[0175] As an exemplary preload arrangement, as noted herein, the preload PL1, PL2 of the casters 250A, 250B may each be set to a weight of the heaviest case unit CU transported by the autonomous transport vehicle so that as the transfer arm 210A is extended to transfer case units CU to and from the payload bed 210B the frame 200 remains substantially level (e.g., parallel) with the rolling surface 395 and, with the transfer arm 210A at its lowermost position within the payload bed 210B, at a predetermined height (e.g., the ride height RHT) set by the suspension travel stops 790. The preload PL3, PL4 of the drive wheels 290A, 260B may also be set to the weight of the heaviest case unit CU transported by the autonomous transport vehicle so that as the transfer arm 210A is extended to transfer case units CU to and from the payload bed 210B the frame 200 remains substantially level (e.g., parallel) with the rolling surface 395 and, with the transfer arm 210A at its lowermost position within the payload bed 210B, at the ride height RHT set by the stops 555, 556.

[0176] In other aspects, one or more of the preloads PL1, PL2, PL3, PL4 of the autonomous transport vehicle 110 may be set to a different value than one or more other preloads PL1, PL2, PL3, PL4. For example, the preloads PL1, PL3, PL4 may be set to a weight of the heaviest case unit CU transported by the autonomous transport vehicle 110 while preload PL2 is set to a load/weight less than the heaviest case unit CU transported by the autonomous transport vehicle 110. Setting the preload PL2 to a load/weight that is less than the heaviest case unit CU transported by the autonomous transport vehicle 110 may reduce peak vibrations/forces between the autonomous transport vehicle 110 and the rolling surface 395 such as where the autonomous transport vehicle 110 traverses a transient (e.g., a step, joint, debris, etc.) on the transport deck 130B and picking aisles 130A.

[0177] The preloads PL1, PL2, PL3, PL4 may be set so that the autonomous transport vehicle has about a 40% (front) to about a 60% (rear) weight distribution with the weight distribution, with the autonomous transport vehicle unloaded (e.g., not carrying a payload) between the pick side and non-pick side being substantially the same. It should be understood that while exemplary preloads and weight distributions have been described in other aspects any suitable preloads and weight distribution may be provided to effect minimization of vibration of the autonomous transport vehicle and effect minimization of induced vibrations to the storage structure from the traverse of the autonomous transport vehicle 110 over the rolling surface 395.

[0178] Figs. 23A and 23B are exemplary plots/graphs illustrating tuning of predetermined rigidity characteristic of the autonomous transport vehicle 110 with the autonomous transport vehicle unloaded (e.g., not carrying a payload/case unit (s)). Fig. 23A illustrates the transient response (as G-force (i.e., force per unit mass due to gravity) and vibrational frequency) of a portion of the frame 200 in response to a transient 395T on the rolling surface 395 that is reacted by the fully independent suspension 780, 280 with the preloads PL1, PL3, PL4 of the fully independent suspension 780, 280 set to substantially the same value (such as set to the weight of the heaviest case unit carried by the autonomous transport vehicle) while preload PL2 is set to a lesser value than preloads PL1, PL3, PL4. Fig. 23B illustrates the transient response and vibrational freguency of the same portion of the frame 200 in response to the transient 395T on the rolling surface 395 that is reacted by the fully independent suspension 780, 280 with the preloads PL1, PL2, PL3, PL4 of the fully independent suspension 780, 280 set to substantially the same value (such as set to the weight of the heaviest case unit carried by the autonomous transport vehicle). As can be seen in Figs. 23A and 23B both forward traverse (with end 200E1 leading the direction of traverse) and rearward traverse (with end 200E2 leading the direction of traverse) transient load responses of the frame 200 are illustrated with the autonomous transport vehicle 110 traversing over transient 395T on the rolling surface 395. As also can be seen in the transient load response of the frame 200 illustrated in Fig. 23B with the preload PL1, PL2, PL3, PL4 being substantially the same is less than the transient load response of the frame 200 illustrated in Fig. 23A with the preload PL2 being less than the preloads PL1, PL3, PL4. As may be realized, the tuning illustrated in Figs. 23A and 23B is exemplary only and that the preloads PL1, PL2, PL3, PL4 of each fully independent suspension at each corner of the frame 200 may be set to any suitable value to reduce/minimize the transient response of the frame to the transient loads imparted to the frame 200 by/through the at least one of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B for a given payload carried by the autonomous transport vehicle 110.

[0179] Figs. 24A and 24B are exemplary plots/graphs illustrating tuning of predetermined rigidity characteristic of the autonomous transport vehicle 110 with the autonomous transport vehicle loaded (e.g., carrying a payload/case unit (s)). Fig. 24A illustrates the transient response (as G-force (i.e., force per unit mass due to gravity) and vibrational frequency) of the same portion of the frame 200 (as in Figs. 23A and 23B) in response to the same transient 395T on the rolling surface 395 that is reacted by the fully independent suspension 780, 280 with the preloads PL1, PL3, PL4 of the fully independent suspension 780, 280 set to substantially the same value (such as set to the weight of the heaviest case unit carried by the autonomous transport vehicle) while preload PL2 is set to a lesser value than preloads PL1, PL3, PL4. Fig. 24B illustrates the transient response and vibrational freguency of the same portion of the frame 200 in response to the transient 395T on the rolling surface 395 that is reacted by the fully independent suspension 780, 280 with the preloads PL1, PL2, PL3, PL4 of the fully independent suspension 780, 280 set to substantially the same value (such as set to the weight of the heaviest case unit carried by the autonomous transport vehicle). As can be seen in Figs. 24A and 24B both forward traverse (with end 200E1 leading the direction of traverse) and rearward traverse (with end 200E2 leading the direction of traverse) transient load responses of the frame 200 are illustrated with the autonomous transport vehicle 110 traversing over transient 395T on the rolling surface 395. As also can be seen in the transient load response of the frame 200 illustrated in Fig. 24B with the preload PL1, PL2, PL3, PL4 being substantially the same is less than the transient load response of the frame 200 illustrated in Fig. 24A with the preload PL2 being less than the preloads PL1, PL3, PL4. As may be realized, the tuning illustrated in Figs. 24A and 24B is exemplary only and that the preloads PL1, PL2, PL3, PL4 of each fully independent suspension at each corner of the frame 200 may be set to any suitable value to reduce/minimize the transient response of the frame to the transient loads imparted to the frame 200 by/through the at least one of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B for a given payload carried by the autonomous transport vehicle 110.

[0180] As can be seen in comparing Figs. 23A and 23B with a respective one of Figs. 24A and 24B, with the tuning of the fully independent suspension 280, 780 the predetermined rigidity characteristic 289 can be set/tuned (with the autonomous transport vehicle loaded and/or unloaded) so that the predetermined rigidity characteristic 289 is substantially the same when the autonomous transport vehicle is loaded and unloaded. In some instances the predetermined rigidity characteristic 289 may be set so that the G-Force and vibrations are less with the autonomous transport vehicle 110 loaded compared to the G-Force and vibrations with the autonomous transport vehicle 110 unloaded. The tuning of predetermined rigidity characteristic 289, as illustrated in Figs. 23A-24B, minimize low frequency vibratory responses and minimize the G-forces such that the payload (e.g., case unit(s) CU) carried by the autonomous transport vehicle 110 remain in a substantially constant location when held on the payload bed 210B (or transfer arm 210A) in an un-gripped or released state as described herein.

[0181] The tuning of the fully independent suspension of the autonomous transport vehicle is such that peak vibrations/forces and durations of the vibrations are minimized (e.g., frame settling times are minimized). The tuning of the fully independent suspension provides for a substantially constant autonomous transport vehicle 110 ride height RHT (and smoothness of motion that maintains the substantially constant ride height) that effects autonomous transport vehicle 110 start/stop traverse motion along the rolling surface 395 substantially simultaneously with the one or more of: placing case units CU to the payload bed 210B, securing (e.g., gripping with any suitable gripping/justification features such as case pushers, fences, etc.) case units CU in the payload bed, and unsecuring (e.g., releasing from grip) case units CU in the payload bed. Here, the tuning of the fully independent suspension provides for "pre processing" case units CU (e.g., prior to placement of a case unit) or "post processing" case units CU (e.g., after picking a case unit) within the payload bed 210B with the autonomous transport vehicle 110 in motion, traversing along the rolling surface.

[0182] Pre-processing of the case units CU with traverse of the autonomous transport vehicle 110 along the rolling surface 395 may include, the release of the case unit(s) CU from grip and justification of the case unit (s) CU to a predetermined position of the payload bed 210B for transfer of the case unit(s) CU from the payload bed to any suitable case unit holding location. Post processing of the case units CU with traverse of the autonomous transport vehicle 110 along the rolling surface 395 may include, lowering the transfer arm 210A to place the case unit (s) CU at the payload datum position PDP (described herein), justification of the case unit(s) CU within the payload bed 210B, and securing of the case unit (s) CU within the payload bed 210B. Respectively pre-processing and post-processing the case unit (s) CU substantially simultaneously with the start traverse and stop traverse motions of the autonomous transport vehicle 110 provides for superior takt times (e.g., for fulling product orders) compared to conventional storage and retrieval systems where the autonomous transport vehicles are not traversing along a rolling surface during operation of the transfer arm/end effector and justification features for case unit pick and place operations.

[0183] Referring to Figs. 2, 16, 17, and 18 the autonomous transport vehicle 110 includes a traction control system 1000 that effects autonomous transport vehicle 110 navigation through the transfer deck 130B and picking aisles 130A. As described herein, the traction control system synergistically operates with the fully independent suspension to provide the autonomous transport vehicle 110 with superior wheel odometry for localization of the autonomous transport vehicle 110 within the storage and retrieval system 100. [0184] As described herein, the autonomous transport vehicle 110 includes a differential drive system (e.g., independently operable drive wheels 260A, 260B) with direct drives (e.g., the output of the drive motors 261M is coupled substantially directly, without gear reduction, to the respective drive wheels 261W) so as to reduce or minimize the "unsprung mass or structure" (e.g., the weight not carried by the fully independent suspension described herein) of the autonomous transport vehicle 110. The drive section 261D is configured so that each traction drive wheel 261W of the at least a pair of traction drive wheels 261W is separately powered by a corresponding traction motor 261M closely coupled with the respective traction drive wheel (i.e., directly driven with a low moment of inertia drive, with near instant motor applied torque). The traction motor 261M for a respective traction drive wheel 261W is distinct and separate from each other traction motor 261W of the drive section 261D corresponding to each other traction drive wheel 261W. Each traction drive wheel 261W of the drive section 261D has the corresponding traction motor 261M separately powering the traction drive wheel 261W closely coupled with the respective traction drive wheel 261W.

[0185] In the aspects of the disclosed embodiment, there is a large effective inertia ratio between the autonomous transport vehicle 110 "sprung" structure (i.e., the structure of the autonomous transport vehicle carried by the fully independent suspension - e.g., the frame 200, transfer arm 200, controls, etc.) and the drive motors 261M (e.g., the inertia of the sprung structure is larger than the inertia of the drive motors 261M and the respective wheels 261W). Here, loss of traction between the drive wheels 261W and the rolling surface 395 during acceleration of the autonomous transport vehicle 110 (i.e., a slip event) may result in a rapid acceleration of the drive motors 261M and respective wheels 261W.

[0186] The traction control system 1000 of the aspects of the disclosed embodiment mitigates slip events by minimizing a slip angle between drive wheels 260A, 260B to an amount that is less than about 1° of relative wheel slip (e.g., upon loss of traction the amount of relative rotation between the wheels 261W of the drive wheels 260A, 260B is less than about 1°). To effect the less than about 1° of relative wheel slip the traction control system 1000 is configured, as described herein, with sufficient bandwidth so as to have a very low latency (e.g., on the order of about less than 2 milliseconds (ms)) from a start of the slip event to a control reaction that mitigates the slip event given a position feedback system that includes noise in the feedback signal. For example, Fig. 16 is a graphical representation of a slip event where the wheel 261W loses (some or all) traction at about t=lms and the wheel accelerates beyond the velocity at which the frame 200 is travelling in any given traverse direction. The controller, such as the controller 1220 of the autonomous transport vehicle 110, reacts to reduce the wheel 261W velocity so that the wheel 261W velocity substantially matches (i.e., is synchronized with) the frame 200 velocity. Here, the traction control system 1000 is configured to operate the motors 261M to apply full peak available motor torgue in reaction to the slip event. [0187] The traction control system 1000 has a multi-loop architecture that includes a velocity estimation and control and control loop that provides for very fast (e.g., less than about 2 ms data sampling rate) velocity estimation and control. The multi^¬ loop architecture of the traction control system 1000 also includes other loops that operate at a slower (e.g., about less than 10 ms) sampling rate. For example, referring to Fig. 17, the traction control system 1000 (which may be incorporated in the controller 1220 or any other suitable controller onboard the autonomous transport vehicle 110) is communicably coupled to the drive wheels 260A, 260B through, for example, a controller area network (CAN) Bus interface 1070 of the autonomous transport vehicle 110. The traction control system 1000 includes any suitable sensors (e.g., line following sensors, vision systems, accelerometers, wheel encoders, current sensors, etc.) that effect a state determinations (e.g., at least position and acceleration) of the autonomous transport vehicle 110. The traction control system 1000 also includes a communications (e.g., "comms") interface 1010, a trajectory handler 1015, a position estimator 1020, a position controller 1025, a velocity estimator 1030, and a velocity controller 1035. In other aspects, the traction control system 1000 may have any suitable configuration and the configuration shown and described herein is exemplary. In the example provided, the communications interface 1010, trajectory handler 1015, position estimator 1020 and position controller 1025 may operate with a sampling rate of less than about 10 ms (in other aspects the sampling rate may be about 10 ms or more) while the sensors 1080, velocity estimator 1030, and velocity controller 1035 operate at a sampling rate of less than about 2 ms (in other aspects, the sampling rate may be about 2 ms or more).

[0188] The sensors 1080 are configured to sense/detect and provide spatial positioning data (e.g., line following positions, visual position data, wheel odometry, etc.) to the position estimator 1020. The sensors 1080 are also configured to sense/detect and provide inertial measurements of the autonomous transport vehicle 110 (e.g., including at least accelerations) to the velocity estimator 1030. The velocity estimator 1030 receives wheel encoder data (e.g., from any suitable wheel encoders 1080W of the drive wheels 260A, 260B, where the wheel encoders 1080W effect wheel odometry determinations) and measured current (e.g., of the motors 261M of the drive wheels 260A, 260B as measured by any suitable current sensors) over the CAN Bus interface 1070. The velocity estimator 1030 provides a velocity estimate to the position estimator 1020. The position estimator 1020 determines a position estimate from the spatial positioning data and the velocity estimate and provides the position estimate to one or more of the trajectory handler 1015 and the position controller 1025. The trajectory handler 1015 is configured to receive waypoint/navigation data from the communications interface 1010 and determines a trajectory of the autonomous transport vehicle 110 based on the waypoint/navigation data and the positon estimate. The position controller 1025 receives the trajectory from the trajectory handler 1015 and determines velocity targets of the autonomous transport vehicle 110 based on the trajectory and position estimate. [0189] The velocity estimator 1030 also provides the velocity estimate to the velocity controller 1035. The velocity controller 1035 receives the velocity targets from the position controller 1025 and determines current targets (e.g., for the motors 261M of the drive wheels 260A, 260B) based on the velocity targets and the velocity estimate. The motors 261M of the drive wheels 260A, 260B are operated/driven based on the current targets from the velocity controller 1035.

[0190] As described herein, the wheel encoder data and measured current (as well as any other sensor data from the sensors 1080) have noise in the respective feedback data signals employed for control of the drive wheels 260A, 260B. To effect the low latency (e.g., less than about 2 ms) response time of the traction control system 1000 with the presence of noise in the feedback signals the velocity controller 1035 and the velocity estimator 1030 are each configured as multi-input and multi-output controllers that, rather than explicitly detect and react to occurring slip events, are configured to resolve incipient slip (e.g., near instantaneous slip resolution so that wheel slip effectively does not occur (e.g., relative rotation of the drive wheels 261 is limited to less than about 1°) and address multiple control objectives (i.e., achieving a predetermined velocity of the autonomous transport vehicle frame 200 while also matching the wheel velocity to the frame velocity). An exemplary configuration of the velocity controller 1035 and velocity estimator 1030 is illustrated in Fig. 18. [0191] The multi-input/multi-output velocity controller 1035 is configured to determined, based on time optimal autonomous transport vehicle trajectory, a predetermined kinematic characteristic (e.g., velocity gradient, acceleration, etc.) of the autonomous transport vehicle 110, and modulates motor applied torque (as described herein) to the traction drive wheel 261W (e.g., from a predetermined applied torque, such as a maximum available applied torque, for optimal trajectory, i.e. modulate motor applied torque from bang-bang control input) to match traction drive wheel 261W rotation with the predetermined kinematic characteristic of the autonomous transport robot within a predetermined wheel slip characteristic of the traction drive wheel 261W relative to the rolling surface 395. The predetermined wheel slip characteristic of the traction drive wheel 261W results in near instantaneous (with respect to the autonomous transport vehicle trajectory path) traction drive wheel 261W rotation modulation resolving wheel slip of the traction drive wheel 261W based on modulated applied torque commanded by the multi input/multi-output velocity controller 1035. Here, as described herein, the near instantaneous traction drive wheel 261 modulation is less than about 10 ms, and about less than 2 ms. The multi-input/multi-output velocity controller 1035 is configured to determine modulation of applied torque in response to wheel position data from the wheel position sensor 1080W, and to determine relative incipient slip of the traction drive wheel 261W to the rolling surface 395 based on the wheel position data. [0192] In accordance with the aspects of the disclosed embodiment, the velocity estimator 1030 includes (left and right) wheel velocity estimators 1030W1, 1030W2 and a chassis (or frame) velocity estimator 1030C. The velocity controller 1035 includes (left and right) wheel velocity (sub-)controllers 1035W1, 1035W2 and a chassis (or frame) velocity (sub-)controller 1035C that operate in parallel with each other. The output of each wheel velocity controller 1035W1, 1035W2 is summed with the output of the chassis velocity controller 1035C for determining a respective net torque for each of the (left and right) drive wheels 260A, 260B.

[0193] The wheel velocity estimators 1030W1, 1030W2 provide respective wheel 261W velocity estimates (e.g., velocity vectors) to the respective wheel velocity controller 1035W1, 1035W2 based on the wheel encoder measurements of the respective wheel 261W. The wheel velocity estimators 1030W1, 1030W2 are configured to estimate the respective wheel velocity by differentiating the respective wheel encoder data and passing it through a low pass filter with minimal (e.g., within the less than about 2 ms sampling rate) delay. It is noted that a low pass filter may be integrated into the respective wheel velocity estimators 130W1, 130W2.

[0194] The chassis velocity estimator 1030C provides frame or chassis 200 velocity estimates (e.g. velocity vectors) to the chassis velocity controller 1035 based on the wheel encoder measurements (e.g., for both drive wheels 260A, 260B) and the inertial measurements of the autonomous transport vehicle 110. The chassis velocity estimator 1030C is also configured to transform the frame 200 velocity estimates to nominal wheel velocities (e.g., wheel velocities that would result from the wheels being synchronized with the frame velocity without the presence of wheel slip) for each wheel 261W of the drive wheels 260A, 260B where the nominal wheels speeds are provided to the respective wheel velocity controller 1035W1, 1035W2.

[0195] As noted above, the chassis velocity controller 1035C receives the chassis velocity estimates (or vectors) as well as a target velocity (e.g., velocity vector) of the frame 200. The chassis velocity controller 1035C may have any suitable configuration that outputs (left and right) motor 261M torques for each of the (right and left) drive wheels 260A, 260B, which motor torques impart forces/moments on the frame 200 to achieve the target chassis velocity. The wheel velocity controllers 1035W1, 1035W2 receive the nominal wheel velocities and velocity estimates for the respective wheel 261W of the respective drive wheel 260A, 260B. Each wheel velocity controller 1035W1, 1035W2 is configured with and employs a non-linear control law.

[0196] The non-linear control law is configured to minimize an amount of encoder differentiation noise that may be amplified by the wheel velocity controllers 1035W1, 1035W2 and the chassis velocity controller 1035C. The non-linear control law also configures the traction control system 1000 so that the output of the wheel velocity controller 1035W1, 1035W2 is small where error (e.g., difference) between the wheel velocity estimate and the nominal wheel velocity is small; however, the output of the wheel velocity controller 1035W1, 1035W2 increases rapidly as the error between the wheel velocity estimate and the nominal wheel velocity increases. Here, in accordance with the aspects of the disclosed embodiment, the contribution of the wheel velocity controllers 1035W1, 1035W2 to the drive wheel torque commands (e.g., the net wheel torques) is minimized where wheel slip is substantially not present; however, where wheel slip is present the contribution of the wheel velocity controllers 1035W1, 1035W2 to the drive torque commands dominates the drive wheel control output (e.g., the contribution of the wheel velocity controllers to determination the net wheel torques dominates the contribution of the chassis velocity controller to the determination of the net wheel torques). An example of the non-linear control law of the wheel velocity controllers 1035W1, 1035W2 is as follows:

[0197] Torque = K_p * e² * sin(e)

[0198] where e is the error between the nominal wheel velocity and the estimated wheel velocity and K_p is a gain that can be tuned to select how much the velocity controller 1035 prioritizes achieving the target wheel velocities versus the target chassis velocity.

[0199] Referring to Figs. 1, 17, 18, and 19, an exemplary application of drive wheel 260A, 260B traction control employing the above non-linear control law will be described. The autonomous transport vehicle 110 chassis velocity controller 1035C issues commands to the drive wheels 290A, 260B so that each motor 261M applies a maximum torque (i.e., a maximum available torque as per motor specifications) to the respective wheel 261W (Fig. 19, Block 1200) to accelerate the autonomous transport vehicle 110 along a given trajectory on the transfer deck 130B or along a picking aisle 130A. Here, the wheels 261W and the frame 200 accelerate proportionately and the respective velocities are synchronized (e.g., no slipping of the wheels 261W). The drive wheel 260A, 260B control commands from the chassis velocity controller 1035C dominate in determining (e.g., in the respective summing of the torgues from each of the wheel velocity controllers 1035W1, 1035W2 with the chassis velocity controller 1035C - see Fig. 18) the respective (left and right) net drive wheel torques such that the wheel velocity controllers 1035W1, 1035W2 (also referred to as wheel slip controllers) have little to no effect on the respective (left and right) net drive wheel torques when wheel slip is not present.

[0200] At the occurrence of a wheel slip event (e.g., one or more of the wheels 261W of the drive wheels 260A, 260B slips/loses traction on the rolling surface) the slipping wheel(s) 261W begins to accelerate at a faster rate than the acceleration of the autonomous transport vehicle 110 frame 200. The slipping/loss of traction of the one or more wheels 261W results in a difference between the drive wheel velocity of the slipping drive wheel(s) 260A, 260B and the velocity of the frame 200. A respective one or more of the wheel velocity controllers 1035W1, 1035W2 (employing the non-linear control law) issues respective drive wheel 260A, 260B torque commands that counteract the torque commands of the chassis velocity controller 1035C so that the drive wheel 260A, 260B torque commands issued by the one or more of the wheel velocity controllers 1035W1, 1035W2 begins to dominate or dominates in determining (e.g., in the respective summing of the torgues from each of the wheel velocity controllers 1035W1, 1035W2 with the chassis velocity controller 1035C - see Fig. 18) the respective (left and right) net drive wheel torques for the slipping drive wheel(s) 260A, 260B (Fig. 19, Block 1210) such that the chassis velocity controller 1035C has a diminished (or in some instances, depending on the amount of wheel slip, no affect) on the net drive wheel torque for a slipping drive wheel 260A, 260B when wheel slip is present. As the torque commands issued by the one or more of the wheel velocity controllers 1035W1, 1035W2 decrease the wheel 261W velocity of the slipping drive wheel(s) 260A, 260B and the velocity of the slipping drive wheel 260A, 260B approaches the nominal wheel velocity, the influence of the torque commands issued by the one or more of the wheel velocity controllers 1035W1, 1035W2 on the respective net drive wheel torque(s) decreases and the torque commands issued by the chassis velocity controller regain dominance in determining the net drive wheel torque(s) (Fig. 19, Block 1220).

[0201] The traction control system 1000 continuously monitors for available traction of the drive wheels 260A, 260B by applying the maximum available motor torque of the respective drive wheels 260A, 260B until a point the respective wheel 261W begins to slip, at which point the non-linear control law drives the velocity of the slipping drive wheel 260A, 260B back to its nominal wheel velocity (e.g., so that the wheel velocity and chassis velocity are substantially synchronized as described herein). With the loss of traction of the drive wheel(s) 260A, 260B mitigated, the chassis velocity controller employs the maximum available motor torque of the drive wheels 260A, 260B to effect traverse of the autonomous transport vehicle along the transfer deck 130B and/or picking aisle 130A. As described above, the low latency of the traction control system 1000 and the limits the wheel slip to about less than 1° relative rotation between the wheels 261W of the drive wheels 260A, 260B. In accordance with the aspects of the disclosed embodiment, the traction control system 1000 described herein substantially eliminates the explicit detection and reaction to a slip event. Rather, the traction control system 1000 substantially continuously reacts to wheel slip events where the magnitude of reaction by the traction control system varies with and depends on the magnitude of the slip event.

[0202] In accordance with the aspects of the disclosed embodiment, and as noted herein, the fully independent suspension system and the traction control system 1000 provide a dynamic response of the autonomous transport vehicle 110 in transit that effects superior takt times for fulfilling product orders. For example, with the fully independent suspension maintaining a substantially constant/steady state ride height RHT (see Fig. 15A) and reducing vibration of the autonomous transport vehicle (due to traverse of the autonomous transport vehicle through the storage structure), the traction control system resolves any wheel slip that may otherwise cause yawing of the autonomous transport vehicle. The reduced vibrations, steady state ride height RHY, and the substantial prevention of wheel slip (e.g., bot stability smoothness effected by synergism of the fully independent suspension, chassis/suspension tuning, and traction control system) provide for a stable case unit holding platform that substantially maintains a position (e.g., without jostling/movement) of the case unit(s) on the case unit support surface 210AFS with the case unit(s) substantially un gripped/unrestrained. Here, the predetermined rigidity characteristic 289 of the frame 200 is set so that transient loads, from transients (e.g., induced from rolling over transients 395T on the rolling surface 395) of the at least one of the at least one caster wheel 250A, 250B and the at least one traction drive wheel 260A, 260B, imparted to the payload (e.g., case unit(s) CU) on the payload seat surface 210AFS via the frame 200, are minimized. The transient loads are minimized so that the payload unrestrained pose on the payload seat surface 210AFS is substantially constant (in at least one degree of freedom, e.g., at least one of X, Y, Q - see Fig. 20) in response to the transient loads with the autonomous transport vehicle 110 rolling on the rolling surface 395 (for a predetermined kinematic state such as an acceleration and/or deceleration of the autonomous transport vehicle 110). Here, the synergistic dynamic response of the autonomous transport vehicle 110 in transit provides for ungripped/released manipulation of case unit (s) CU within the payload bed 210B substantially simultaneously with start and stop traverse motions of the autonomous transport vehicle 110 along the rolling surface as described herein, which effects the superior takt times compared to conventional autonomous transport vehicles whose traversal along a surface is stopped prior to releasing the case unit(s) for manipulation.

[0203] Referring to Figs. 2, 5A, 5B, 9A-15B, and 21, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the frame 200, the transfer arm 210A, and the drive section 261D (Fig. 21, Block 1400). As described herein, the frame 200 has an integral payload support (e.g., also referred to as the payload support bed 210B); the transfer arm 210A provides autonomous transfer of payload (e.g., case units CU) to and from the frame 200; and the drive section is connected to the frame 200 and has a pair of traction drive wheels 260A, 260B astride the drive section 261D. In the method a substantially steady state traction contact patch CNTC is maintained (Fig. 21, Block 1410), with a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, between the at least one traction drive wheel 260A, 260B and a rolling surface 395 over rolling surface transients 395T throughout traverse of the at least one traction drive wheel 260A, 260B over the rolling surface 395, wherein the fully independent suspension has at least one intervening pivot link (e.g., the upper and lower frame links 310, 311) between at least one traction drive wheel 260A, 260B and the frame 200.

[0204] Still referring to Figs. 2, 5A, 5B, 9A-15B, and also to Fig. 22, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the frame 200, the transfer arm 210A, and the drive section 261D (Fig. 22, Block 1500). As described herein, the frame 200 has an integral payload support (e.g., also referred to as the payload support bed 210B); the transfer arm 210A provides autonomous transfer of payload (e.g., case units CU) to and from the frame 200; and the drive section is connected to the frame 200 and has a pair of traction drive wheels 260A, 260B astride the drive section 261D. In the method a substantially linear transient response is generated (with the at least one intervening pivot link, e.g., the upper and lower frame links 310, 311) to at least one traction drive wheel (Fig. 22, Block 1510), to rolling over surface transients of a rolling surface in a linear direction substantially normal to the frame throughout each transient, wherein the at least the pair of traction drive wheels have the fully independent suspension coupling each wheel 261W of the at least the pair of traction drive wheels 260A, 260B to the frame 200, with the at least one intervening pivot link between at least one traction drive wheel 260A, 260B and the frame 200.

[0205] Referring to Figs. 2, 5A, 5B, 9A-15B, and 25, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the frame 200 (Fig. 25, Block 1800), the transfer arm 210A (Fig. 25, Block 1810), the caster wheel(s) 250A, 250B (Fig. 25, Block 1820), and the drive section 261D (Fig. 25, Block 1830). The at least one caster wheel 250A, 250D and at least one traction drive wheel 260A, 260B of the pair of traction drive wheels 260A, 260B are disposed on the frame 200 (Fig. 25, Block 1840) astride the integral payload support 210B so that the payload seat surface 210AFS at the payload datum position PDF is disposed at a minimum distance above the rolling surface 395, wherein the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B of the pair of traction drive wheels 260A, 260B roll, on a rolling surface effecting autonomous transport vehicle 110 traversal over the rolling surface 395, and each of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B of the pair of traction drive wheels 260A, 260B having a fully independent suspension 780, 280.

[0206] Referring to Figs. 2, 5A, 5B, 9A-15B, and 26, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport vehicle 110 is provided with the frame 200 (Fig. 26, Block 1900), the transfer arm 210A (Fig. 26, Block 1910), the caster wheel(s) 250A, 250B (Fig. 26, Block 1920), and the drive section 261D (Fig. 26, Block 1930). The predetermined rigidity characteristic 289 is set (Fig. 26, Block 1940) based on a predetermined transient response characteristic of the fully independent suspension 780, 280 of at least one of the at least one caster wheel 250A, 250B and the at least one traction drive wheel 260A, 260B.

[0207] Referring to Figs. 2, 5A, 5B, 9A-15B, and 27, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport robot is provided with a frame 200, a transfer arm 210A, at least one caster wheel 250A, 250B, and a drive section 261D (Fig. 27, Block 2000). The frame 200 has an integral payload support 210B. The transfer arm 210A is connected to the frame 200 and is configured for autonomous transfer of payload (e.g., case units CU) to and from the frame 200. The at least one caster wheel 250A, 250B is mounted to the frame 200, and a drive section 261D has at least a pair of traction drive wheels 260A, 260B astride the drive section 261D. The drive section 261D is connected to the frame 200, where the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B of the pair of traction drive wheels 260A, 260B roll, on a rolling surface 395 effecting autonomous transport vehicle traversal over the rolling surface 395. Each of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B having a fully independent suspension 780, 280. A predetermined rigidity characteristic 289 of the frame 200 is set (Fig. 27, Block 2010) based on a predetermined transient response characteristic of the frame 200 determining the transient response of the frame 200 from transients of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B of the pair of traction drive wheels 260A, 260B rolling on the rolling surface 395, where the predetermined rigidity characteristic 298 defines a transient response of the frame 200 from transient loads imparted to the frame 200 via at least one of the at least one caster wheel 250A, 250B and at least one traction drive wheel 260A, 260B. [0208] Referring to Figs. 2, 5A, 5B, 9A-15B, and 28, an exemplary method for the autonomous transport vehicle 110 will be described in accordance with aspects of the disclosed embodiment. In the method the autonomous transport robot is provided with: a frame 200 and a drive section 261D (Fig. 28, Bock 2100). The frame 200 has an integral payload support 210B, and the drive section 261D has at least a pair of traction drive wheels 260A, 260B (e.g., see wheels 261W) astride the drive section 261D. The drive section 261D is connected to the frame 200 and is configured so that each traction drive wheel 260A, 260B of the at least the pair of traction drive wheels 260A, 260B is separately powered by a corresponding traction motor 261W closely coupled with the respective traction drive wheel 260A, 260B, and distinct and separate from each other traction motor 261M of the drive section 261D corresponding to each other traction drive wheel 260A, 260B. Each traction drive wheel 260A, 260B of the at least the pair of traction drive wheels 260A, 260B is separately powered, with the drive section 261D, (Fig. 28, Block 2110) by a corresponding traction motor 261M closely coupled with the respective traction drive wheel 260A, 260B, and distinct and separate from each other traction motor 261M of the drive section 261D corresponding to each other traction drive wheel 260A, 260B. The multi-input/multi- output (velocity) controller 1035, determines based on optimal robot trajectory a predetermined kinematic characteristic of the autonomous transport vehicle 110, and modulates motor applied torque to the traction drive wheel 260A, 260B (Fig. 28, Block 2120) to match traction drive wheel rotation with the predetermined kinematic characteristic of the autonomous transport vehicle 110 within a predetermined wheel slip characteristic of the traction drive wheel 260A, 260B relative to the rolling surface 395.

[0209] Referring to Figs. 2, 5A, 5B, 9A-15B, and 29, an exemplary method for an autonomous transport vehicle 110 will be described in accordance with one or more aspects of the disclosed embodiment. In the method, the autonomous transport robot with is provided a frame (Fig. 29, Block 2200), a transfer arm 210A (Fig. 29, Block 2210), and a drive section (Fig. 29, Block 2220). The frame 200 has the integral payload support 210B. The transfer arm 210A is connected to the frame 200 and configured for autonomous transfer of payload (e.g., case units CU) to and from the frame 200. The drive section 261D is connected to the frame 200 and has at least a pair of traction drive wheels 260A, 260B astride the drive section 261D, where the at least the pair of traction drive wheels 260A, 260B has a fully independent suspension 280 coupling each traction drive wheel 260A, 260B of the at least the pair of traction drive wheels 260A, 260B to the frame 200. The fully independent suspension 280 is locked in a predetermined position relative to the frame 200 with a lock/suspension lockout system 500 that is releasably coupled to the fully independent suspension 280 (Fig. 29, Block 2230). As described herein the controller 2330 automatically effects actuating the lock 500 of a respective fully independent suspension 280 with extension of the transfer arm 210A (e.g., from the datum payload position PDP), and releasing the lock 500 of the respective fully independent suspension 280 with retraction of the transfer arm (e.g., to the datum payload position PDP). [0210] In accordance with one or more aspects of the disclosed embodiment, an autonomous transport robot vehicle for transporting a payload is provided. The autonomous transport robot vehicle comprises: a chassis that is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame; a payload support connected to the chassis and dependent therefrom; and ride wheels dependent from the chassis, proximate opposite end corners of the chassis, on which the autonomous transport robot vehicle rides so as to traverse a traverse surface, the ride wheels include at least one caster wheel and a pair of drive wheels supporting the chassis from the traverse surface, and wherein the ride wheels and chassis in combination form a low profile height from the traverse surface to atop the chassis, where chassis height and ride wheel height are overlapped at least in part and the payload support is nested within the ride wheels; and wherein the space frame has predetermined modular coupling interfaces, each disposed for removably coupling, as a module unit, a corresponding predetermined electronic or mechanical component module of the autonomous transport robot vehicle to the chassis.

[0211] In accordance with one or more aspects of the disclosed embodiment, the predetermined modular coupling interfaces include at least one of at least one caster wheel module coupling interface, at least one drive wheel module coupling interface, and at least one payload support module coupling interface. [0212] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel is selectable from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

[0213] In accordance with one or more aspects of the disclosed embodiment, drive wheels of the pair of drive wheels are selectable from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

[0214] In accordance with one or more aspects of the disclosed embodiment, the payload support is selectable from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

[0215] In accordance with one or more aspects of the disclosed embodiment the at least one drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules of each different drive wheel of the pair of drive wheels.

[0216] In accordance with one or more aspects of the disclosed embodiment, the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame are mechanically fastened to each other.

[0217] In accordance with one or more aspects of the disclosed embodiment the payload support comprises a payload support contact surface on which a payload resting on the payload support is seated, the payload support contact surface is disposed atop the chassis.

[0218] In accordance with one or more aspects of the disclosed embodiment, the space frame is configured so that the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from the traverse surface to atop the chassis.

[0219] In accordance with one or more aspects of the disclosed embodiment, the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from the traverse surface to atop the chassis.

[0220] In accordance with one or more aspects of the disclosed embodiment the chassis has a selectably variable configuration, selectable from different configurations each having different chassis form factors.

[0221] In accordance with one or more aspects of the disclosed embodiment at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam, is selectable from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

[0222] In accordance with one or more aspects of the disclosed embodiment selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

[0223] In accordance with one or more aspects of the disclosed embodiment, an autonomous transport robot vehicle for transporting a payload is provided. The autonomous transport robot vehicle comprises: a chassis bus with predetermined modular coupling interfaces, each disposed for removably coupling, as a module unit, corresponding predetermined component modules of the autonomous transport robot vehicle to the chassis bus so that the autonomous transport robot vehicle has a modular construction; and wherein the corresponding predetermined component modules include at least one of: a payload support module with a payload support contact surface removably coupled as a module unit to the chassis bus with a corresponding payload support module coupling interface; a caster wheel module with a caster wheel removably coupled as a module unit to the chassis bus with a corresponding caster wheel module coupling interface; and a drive wheel module with a drive wheel removably coupled as a module unit to the chassis bus with a corresponding drive wheel module coupling interface.

[0224] In accordance with one or more aspects of the disclosed embodiment, the caster wheel module is selectable from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic. [0225] In accordance with one or more aspects of the disclosed embodiment, the drive wheel module is selectable from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

[0226] In accordance with one or more aspects of the disclosed embodiment, the corresponding drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules.

[0227] In accordance with one or more aspects of the disclosed embodiment, the payload support module is selectable from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

[0228] In accordance with one or more aspects of the disclosed embodiment the chassis bus is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame.

[0229] In accordance with one or more aspects of the disclosed embodiment, the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame are mechanically fastened to each other.

[0230] In accordance with one or more aspects of the disclosed embodiment, the space frame is configured so that the chassis bus is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from a traverse surface to atop the chassis.

[0231] In accordance with one or more aspects of the disclosed embodiment, the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from a traverse surface to atop the chassis.

[0232] In accordance with one or more aspects of the disclosed embodiment at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam, is selectable from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

[0233] In accordance with one or more aspects of the disclosed embodiment selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

[0234] In accordance with one or more aspects of the disclosed embodiment the autonomous transport robot vehicle includes at least one caster wheel module and at least one drive wheel module, the at least one caster wheel module and the at least one drive wheel module are dependent from the chassis bus, proximate opposite end corners of the chassis, where the autonomous transport robot vehicle rides on at least a caster wheel of the at least one caster wheel module and at least one drive wheel of the at least one drive wheel module so as to traverse a traverse surface.

[0235] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel, the at least one drive wheel, and the chassis bus in combination form a low profile height from the traverse surface to atop the chassis, where: the at least one drive wheel comprises a pair of drive wheels and the at least one caster wheel comprises a pair of caster wheels, a chassis height and a height of the at least one drive wheel are overlapped at least in part, and the payload support contact surface, on which a payload resting on the payload support module is seated, is nested within the pair of drive wheel and the pair of caster wheels.

[0236] In accordance with one or more aspects of the disclosed embodiment the payload support contact surface, on which a payload resting on the payload support module is seated, is disposed atop the chassis bus.

[0237] In accordance with one or more aspects of the disclosed embodiment the chassis bus has a selectably variable configuration, selectable from different configurations each having different chassis form factors.

[0238] In accordance with one or more aspects of the disclosed embodiment a method comprises: providing the autonomous transport robot vehicle with: a chassis that is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame, a payload support connected to the chassis and dependent therefrom, and ride wheels dependent from the chassis, proximate opposite end corners of the chassis, on which the autonomous transport robot vehicle rides so as to traverse a traverse surface, the ride wheels include at least one caster wheel and a pair of drive wheels supporting the chassis from the traverse surface, and wherein the ride wheels and chassis in combination form a low profile height from the traverse surface to atop the chassis, where chassis height and ride wheel height are overlapped at least in part and the payload support is nested within the ride wheels; and removably coupling as a module unit, with predetermined modular coupling interfaces of the space frame, a corresponding predetermined electronic or mechanical component module of the autonomous transport robot vehicle to the chassis.

[0239] In accordance with one or more aspects of the disclosed embodiment, the predetermined modular coupling interfaces include at least one of at least one caster wheel module coupling interface, at least one drive wheel module coupling interface, and at least one payload support module coupling interface.

[0240] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting the at least one caster wheel from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic. [0241] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting drive wheels of the pair of drive wheels from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

[0242] In accordance with one or more aspects of the disclosed embodiment, the method further comprises selecting the payload support from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

[0243] In accordance with one or more aspects of the disclosed embodiment the at least one drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules of each different drive wheel of the pair of drive wheels.

[0244] In accordance with one or more aspects of the disclosed embodiment, the method further comprises mechanically fastening the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame to each other.

[0245] In accordance with one or more aspects of the disclosed embodiment the payload support comprises a payload support contact surface on which a payload resting on the payload support is seated, the payload support contact surface is disposed atop the chassis. [0246] In accordance with one or more aspects of the disclosed embodiment, the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from the traverse surface to atop the chassis.

[0247] In accordance with one or more aspects of the disclosed embodiment, the space frame resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from the traverse surface to atop the chassis.

[0248] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting a selectably variable configuration of the chassis from different configurations each having different chassis form factors.

[0249] In accordance with one or more aspects of the disclosed embodiment, the method further comprises selecting at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

[0250] In accordance with one or more aspects of the disclosed embodiment selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis. [0251] In accordance with one or more aspects of the disclosed embodiment a method comprises: providing the autonomous transport robot vehicle with a chassis bus with predetermined modular coupling interfaces; and removably coupling as a module unit, with the predetermined modular coupling interfaces, corresponding predetermined component modules of the autonomous transport robot vehicle to the chassis bus so that the autonomous transport robot vehicle has a modular construction; wherein the predetermined component modules include at least one of: a payload support module with a payload support contact surface removably coupled as a module unit to the chassis bus with a corresponding payload support module coupling interface, a caster wheel module with a caster wheel removably coupled as a module unit to the chassis bus with a corresponding caster wheel module coupling interface, and a drive wheel module with a drive wheel removably coupled as a module unit to the chassis bus with a corresponding drive wheel module coupling interface.

[0252] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting the caster wheel module from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

[0253] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting the drive wheel module from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic. [0254] In accordance with one or more aspects of the disclosed embodiment, the drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules.

[0255] In accordance with one or more aspects of the disclosed embodiment, the method further comprises selecting the payload support module from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

[0256] In accordance with one or more aspects of the disclosed embodiment the chassis bus is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame.

[0257] In accordance with one or more aspects of the disclosed embodiment, the method further comprises mechanically fastening the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame to each other.

[0258] In accordance with one or more aspects of the disclosed embodiment, the space frame is configured so that the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from a traverse surface to atop the chassis.

[0259] In accordance with one or more aspects of the disclosed embodiment, the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from a traverse surface to atop the chassis.

[0260] In accordance with one or more aspects of the disclosed embodiment, the method further comprises selecting at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

[0261] In accordance with one or more aspects of the disclosed embodiment selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

[0262] In accordance with one or more aspects of the disclosed embodiment the autonomous transport robot vehicle includes at least one caster wheel module and at least one drive wheel module, the at least one caster wheel module and the at least one drive wheel module are dependent from the chassis bus, proximate opposite end corners of the chassis, where the autonomous transport robot vehicle rides on at least caster wheel of the at least one caster wheel module and at least one drive wheel of the at least one drive wheel module so as to traverse a traverse surface. [0263] In accordance with one or more aspects of the disclosed embodiment the caster wheel, the drive wheel, and the chassis bus in combination form a low profile height from the traverse surface to atop the chassis, where: the at least one drive wheel comprises a pair of drive wheels and the at least one caster comprises a pair of caster wheels, a chassis height and a height of the at least one drive wheel are overlapped at least in part, and the payload support contact surface, on which a payload resting on the payload support module is seated, is nested within the pair of drive wheel and the pair of caster wheels.

[0264] In accordance with one or more aspects of the disclosed embodiment the payload support contact surface, on which a payload resting on the payload support module is seated, is disposed atop the chassis bus.

[0265] In accordance with one or more aspects of the disclosed embodiment the method further comprises selecting a selectably variable configuration of the chassis bus from different configurations each having different chassis form factors.

[0266] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

[0267] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0268] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0269] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients. [0270] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0271] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0272] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0273] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0274] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to generate a substantially linear transient response to the at least one traction drive wheel, to rolling over surface transients of a rolling surface in a linear direction substantially normal to the frame throughout each transient.

[0275] In accordance with one or more aspects of the disclosed embodiment the least one intervening pivot link between the at least one traction drive wheel and the frame is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over the rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface; and the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0276] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0277] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0278] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0279] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0280] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile. [0281] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0282] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided, the method comprising: providing the autonomous transport robot with: a frame, the frame having an integral payload support, a transfer arm connected to the frame, the transfer arm providing autonomous transfer of payload to and from the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, where the drive section is connected to the frame; and maintaining, with a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface, wherein the fully independent suspension has at least one intervening pivot link between at least one traction drive wheel and the frame.

[0283] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface. [0284] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0285] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0286] In accordance with one or more aspects of the disclosed embodiment the further comprises defining a payload datum position with a payload seat surface of the integral payload support, wherein the payload datum position determines a predetermined payload position relative to the autonomous transport robot, and the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0287] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel. [0288] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0289] In accordance with one or more aspects of the disclosed embodiment the method further comprises locking, with a lock of the fully independent suspension, the fully independent suspension in a predetermined position relative to the frame.

[0290] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided. The method comprising: providing the autonomous transport robot with: a frame, the frame having an integral payload support, a transfer arm connected to the frame, the transfer arm providing autonomous transfer of payload to and from the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, where the drive section is connected to the frame; and generating a substantially linear transient response to at least one traction drive wheel, to rolling over surface transients of a rolling surface in a linear direction substantially normal to the frame throughout each transient, wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame.

[0291] In accordance with one or more aspects of the disclosed embodiment the method further comprises: maintaining, with the least one intervening pivot link between the at least one traction drive wheel and the frame, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over the rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface; wherein, the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0292] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0293] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0294] In accordance with one or more aspects of the disclosed embodiment the method further comprises defining a payload datum position with the integral payload support, wherein the payload datum position determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0295] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0296] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0297] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0298] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support that has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension, and are disposed on the frame astride the integral payload support so that the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0299] In accordance with one or more aspects of the disclosed embodiment the autonomous transport robot has fully independent suspension at each of the at least one caster wheel and each traction drive wheel.

[0300] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0301] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0302] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0303] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0304] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

[0305] In accordance with one or more aspects of the disclosed embodiment the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0306] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel. [0307] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0308] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0309] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel, the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel.

[0310] In accordance with one or more aspects of the disclosed embodiment the predetermined transient response characteristic of the at least one of the at least one caster wheel and the at least one traction drive wheel is set based on the predetermined rigidity characteristic of the frame.

[0311] In accordance with one or more aspects of the disclosed embodiment the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

[0312] In accordance with one or more aspects of the disclosed embodiment the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

[0313] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0314] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0315] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0316] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0317] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition. [0318] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0319] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0320] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0321] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0322] In accordance with one or more aspects of the disclosed embodiment the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel with the autonomous transport robot carrying a payload.

[0323] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided, the method comprising: providing the autonomous transport robot with a frame having an integral payload support, the integral payload support having a payload seat surface and defining, with the payload seat surface a payload datum position that determines a predetermined payload position relative to the autonomous transport robot; providing a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; providing at least one caster wheel mounted to the frame; providing a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; and disposing the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels on the frame astride the integral payload support so that the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, and each of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels having a fully independent suspension.

[0324] In accordance with one or more aspects of the disclosed embodiment the autonomous transport robot has fully independent suspension at each of the at least one caster wheel and each traction drive wheel.

[0325] In accordance with one or more aspects of the disclosed embodiment the method further comprises, maintaining, with the fully independent suspension of the at least one traction drive wheel, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0326] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0327] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0328] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient. [0329] In accordance with one or more aspects of the disclosed embodiment the method further comprises, disposing the fully independent suspension on the frame to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

[0330] In accordance with one or more aspects of the disclosed embodiment the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0331] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0332] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0333] In accordance with one or more aspects of the disclosed embodiment the method further comprises locking the fully independent suspension in a predetermined position relative to the frame. [0334] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided, the method comprising: providing the autonomous transport robot with a frame having an integral payload support; providing a transfer arm connected to the frame, the transfer arm being configured for autonomous transfer of payload to and from the frame; providing at least one caster wheel mounted to the frame; providing a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension, and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel; and setting the predetermined rigidity characteristic based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel.

[0335] In accordance with one or more aspects of the disclosed embodiment the predetermined transient response characteristic of the at least one of the at least one caster wheel and the at least one traction drive wheel is set based on the predetermined rigidity characteristic of the frame. [0336] In accordance with one or more aspects of the disclosed embodiment the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel with the autonomous transport robot carrying a payload.

[0337] In accordance with one or more aspects of the disclosed embodiment the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

[0338] In accordance with one or more aspects of the disclosed embodiment the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

[0339] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0340] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0341] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0342] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0343] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition. [0344] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0345] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0346] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0347] In accordance with one or more aspects of the disclosed embodiment the method further comprises locking the fully independent suspension in a predetermined position relative to the frame.

[0348] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel, the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the frame determining the transient response of the frame from transients of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels rolling on the rolling surface.

[0349] In accordance with one or more aspects of the disclosed embodiment the predetermined rigidity characteristic of the frame determines the frame as being substantially rigid relative to the fully independent suspension of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels rolling on the rolling surface.

[0350] In accordance with one or more aspects of the disclosed embodiment the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from the transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

[0351] In accordance with one or more aspects of the disclosed embodiment the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

[0352] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0353] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0354] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0355] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0356] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

[0357] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0358] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0359] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0360] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0361] In accordance with one or more aspects of the disclosed embodiment the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the frame with the autonomous transport robot one or more of carrying a payload and unloaded.

[0362] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; a multi-input/multi-output controller coupled to the drive section; and wherein the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; wherein the multi-input/multi-output controller is configured to determined, based on optimal robot trajectory, a predetermined kinematic characteristic of the autonomous transport robot, and modulates motor applied torgue to the traction drive wheel to match traction drive wheel rotation with the predetermined kinematic characteristic of the autonomous transport robot within a predetermined wheel slip characteristic of the traction drive wheel relative to the rolling surface.

[0363] In accordance with one or more aspects of the disclosed embodiment the predetermined wheel slip characteristic results in near instantaneous wheel rotation modulation resolving wheel slip of the traction drive wheel based on modulated applied torque commanded by the multi-input/multi-output controller.

[0364] In accordance with one or more aspects of the disclosed embodiment the near instantaneous wheel rotation modulation is less than about 10 ms, and about less than 2ms.

[0365] In accordance with one or more aspects of the disclosed embodiment multi-input/multi-output controller is configured to determine modulation of applied torque in response to wheel position data from the wheel position sensor, and to determine relative slip of the traction drive wheel to the rolling surface based on the wheel position data.

[0366] In accordance with one or more aspects of the disclosed embodiment each traction drive wheel of the drive section has the corresponding traction motor separately powering the traction drive wheel closely coupled with the respective traction drive wheel.

[0367] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

[0368] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0369] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0370] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0371] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0372] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0373] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile. [0374] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0375] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot for transporting a payload is provided, the method comprising: providing the autonomous transport robot with: a frame having an integral payload support, a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame, at least one caster wheel mounted to the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and setting a predetermined rigidity characteristic of the frame based on a predetermined transient response characteristic of the frame determining the transient response of the frame from transients of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels rolling on the rolling surface, where the predetermined rigidity characteristic defines a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel. [0376] In accordance with one or more aspects of the disclosed embodiment the predetermined rigidity characteristic of the frame determines the frame as being substantially rigid relative to the fully independent suspension of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels rolling on the rolling surface.

[0377] In accordance with one or more aspects of the disclosed embodiment the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from the transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

[0378] In accordance with one or more aspects of the disclosed embodiment the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

[0379] In accordance with one or more aspects of the disclosed embodiment the method further comprises maintaining, with the fully independent suspension of the at least one traction drive wheel, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

[0380] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0381] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0382] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

[0383] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition. [0384] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0385] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0386] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0387] In accordance with one or more aspects of the disclosed embodiment the method further comprises locking the fully independent suspension in a predetermined position relative to the frame.

[0388] In accordance with one or more aspects of the disclosed embodiment the method further comprises setting the predetermined rigidity characteristic based on a predetermined transient response characteristic of the frame with the autonomous transport robot carrying a payload. [0389] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided, the method comprising: providing the autonomous transport robot with: a frame with an integral payload support, and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; separately powering, with the drive section, each traction drive wheel of the at least the pair of traction drive wheels by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; and determining, with a multi-input/multi-output controller, based on optimal robot trajectory, a predetermined kinematic characteristic of the autonomous transport robot, and modulating motor applied torque to the traction drive wheel to match traction drive wheel rotation with the predetermined kinematic characteristic of the autonomous transport robot within a predetermined wheel slip characteristic of the traction drive wheel relative to the rolling surface.

[0390] In accordance with one or more aspects of the disclosed embodiment the predetermined wheel slip characteristic results in near instantaneous wheel rotation modulation resolving wheel slip of the traction drive wheel based on modulated applied torque commanded by the multi-input/multi-output controller.

[0391] In accordance with one or more aspects of the disclosed embodiment the near instantaneous wheel rotation modulation is less than about 10 ms, and about less than 2ms.

[0392] In accordance with one or more aspects of the disclosed embodiment the multi-input/multi-output controller determines modulation of applied torque in response to wheel position data from the wheel position sensor, and to determines relative slip of the traction drive wheel to the rolling surface based on the wheel position data.

[0393] In accordance with one or more aspects of the disclosed embodiment each traction drive wheel of the drive section has the corresponding traction motor separately powering the traction drive wheel closely coupled with the respective traction drive wheel.

[0394] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame, the method further comprising maintaining, with the fully independent suspension a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

[0395] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0396] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0397] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0398] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface. [0399] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0400] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

[0401] In accordance with one or more aspects of the disclosed embodiment the method further comprises locking the fully independent suspension in a predetermined position relative to the frame.

[0402] In accordance with one or more aspects of the disclosed embodiment an autonomous transport robot for transporting a payload is provided, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section connected to the frame and having at least a pair of traction drive wheels astride the drive section, the at least the pair of traction drive wheels has a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame; and a lock releasably coupled to the fully independent suspension, the lock being configured to lock the fully independent suspension in a predetermined position relative to the frame.

[0403] In accordance with one or more aspects of the disclosed embodiment the autonomous transport robot further comprises a controller, the controller is configured to automatically effect: actuation of the lock of a respective fully independent suspension with extension of the transfer arm, and release of the lock of the respective fully independent suspension with retraction of the transfer arm.

[0404] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension coupling has at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

[0405] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0406] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0407] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0408] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0409] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0410] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof define a minimum height profile. [0411] In accordance with one or more aspects of the disclosed embodiment a method for an autonomous transport robot is provided, the method comprises: providing the autonomous transport robot with a frame, the frame having an integral payload support; providing the autonomous transport robot with a transfer arm, the transfer arm being connected to the frame and configured for autonomous transfer of payload to and from the frame; providing the autonomous transport robot with a drive section, the drive section being connected to the frame and having at least a pair of traction drive wheels astride the drive section, the at least the pair of traction drive wheels has a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame; and locking, with a lock releasably coupled to the fully independent suspension, the fully independent suspension in a predetermined position relative to the frame.

[0412] In accordance with one or more aspects of the disclosed embodiment the method further comprises, with a controller, automatically effecting: actuating the lock of a respective fully independent suspension with extension of the transfer arm, and releasing the lock of the respective fully independent suspension with retraction of the transfer arm.

[0413] In accordance with one or more aspects of the disclosed embodiment the fully independent suspension has at least one intervening pivot link between at least one traction drive wheel and the frame, the method further comprising maintaining, with the fully independent suspension, a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

[0414] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

[0415] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

[0416] In accordance with one or more aspects of the disclosed embodiment the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

[0417] In accordance with one or more aspects of the disclosed embodiment the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

[0418] In accordance with one or more aspects of the disclosed embodiment the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

[0419] In accordance with one or more aspects of the disclosed embodiment the height profile of the at least one traction drive wheel and fully independent suspension thereof define a minimum height profile.

[0420] In accordance with one or more aspects of the disclosed embodiment an autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle comprises: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torgue to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect via a combination of vehicle yaw, generated by differential torgue from the at least two independently driven drive wheels, and castering assistance torgue from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

[0421] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torgue is configured wherein resistance from castering scrub at each predetermined kinematic state is substantially negated so as to effect substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

[0422] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

[0423] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius. [0424] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub.

[0425] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

[0426] In accordance with one or more aspects of the disclosed embodiment the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

[0427] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

[0428] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

[0429] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

[0430] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

[0431] In accordance with one or more aspects of the disclosed embodiment the caster assistance motor is at least one of a servo motor and a stepper motor.

[0432] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion. [0433] In accordance with one or more aspects of the disclosed embodiment an autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle comprises: a frame;

[0434] a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel, of a non-holonomic steering system, is mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torque to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect, via castering assistance torque from the castering assistance motor assisting castering input from vehicle yaw generated by differential torque from the at least two independently driven wheels, substantially scrubless castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

[0435] In accordance with one or more aspects of the disclosed embodiment the controller is configured to determine the castering assistance torque as a supplement torque supplementing castering input to the at least one caster wheel, from vehicle yaw, to effect scrubless castering of the at least one caster wheel.

[0436] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torque is configured wherein resistance from castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

[0437] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

[0438] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

[0439] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub. [0440] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

[0441] In accordance with one or more aspects of the disclosed embodiment the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

[0442] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

[0443] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest. [0444] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

[0445] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

[0446] In accordance with one or more aspects of the disclosed embodiment the caster assistance motor is at least one of a servo motor and a stepper motor.

[0447] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

[0448] In accordance with one or more aspects of the disclosed embodiment an autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle comprises: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torgue to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state via a combination of vehicle yaw, generated by differential torgue from the at least two independently driven drive wheels, and castering assistance torgue, from the castering assistance motor, the castering assistance torque being developed substantially negating resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle.

[0449] In accordance with one or more aspects of the disclosed embodiment the controller is configured to determine the castering assistance torque as a supplement torque supplementing castering input to the at least one caster wheel, from vehicle yaw, to effect scrubless castering of the at least one caster wheel.

[0450] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torque is configured wherein the resistance from the castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

[0451] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

[0452] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

[0453] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from the castering scrub.

[0454] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates resistance from the castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels. [0455] In accordance with one or more aspects of the disclosed embodiment the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

[0456] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

[0457] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

[0458] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing. [0459] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

[0460] In accordance with one or more aspects of the disclosed embodiment the caster assistance motor is at least one of a servo motor and a stepper motor.

[0461] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

[0462] In accordance with one or more aspects of the disclosed embodiment an autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle comprises: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance electromagnetic actuator that engages the at least one caster wheel so as to impart a bias force to the at least one caster wheel at each castering position of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance electromagnetic actuator and configured to effect castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and bias force, from the castering assistance electromagnetic actuator, that is commanded so as to bias the at least one caster wheel to a corresponding castering position that substantially negates resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle.

[0463] In accordance with one or more aspects of the disclosed embodiment the commanded bias force substantially negates castering resistance imparted to the at least one caster wheel from the castering scrub.

[0464] In accordance with one or more aspects of the disclosed embodiment the commanded bias force substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

[0465] In accordance with one or more aspects of the disclosed embodiment the controller is configured to determine a castering assistance torque of the castering assistance electromagnetic actuator as a supplement torque supplementing castering input to the at least one caster wheel, from the vehicle yaw, to effect scrubless castering of the at least one caster wheel. [0466] In accordance with one or more aspects of the disclosed embodiment the castering assistance electromagnetic actuator is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance electromagnetic actuator, and commanded castering assistance torque is configured wherein the resistance from the castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

[0467] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

[0468] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius. [0469] In accordance with one or more aspects of the disclosed embodiment the controller is configured to position the castering assistance electromagnetic actuator so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

[0470] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply a castering assistance torque, with the castering assistance electromagnetic actuator, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

[0471] In accordance with one or more aspects of the disclosed embodiment the controller is configured to apply the castering assistance torque, with the castering assistance electromagnetic actuator, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

[0472] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing and the castering assistance electromagnetic actuator is a frameless motor, the frameless motor being integrated in the caster mount housing. [0473] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance electromagnetic actuator, a stator of the caster assistance electromagnetic actuator being disposed against and supported by the caster mount housing, and a rotor of the castering assistance electromagnetic actuator being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

[0474] In accordance with one or more aspects of the disclosed embodiment the caster assistance electromagnetic actuator is at least one of a servo motor and a stepper motor.

[0475] In accordance with one or more aspects of the disclosed embodiment the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

[0476] In accordance with one or more aspects of the disclosed embodiment a method for driving an autonomous transport vehicle in a storage and retrieval system is provided. The method comprises: providing an autonomous transport vehicle having a frame, a controller, at least two independently driven drive wheels mounted to the frame, and at least one caster wheel mounted to the frame and having a castering assistance motor; imparting castering assistance torgue, with the castering assistance motor engaged to the at least one caster wheel, so as to assist castering of the at least one caster wheel; and effecting, with the controller communicably connected to the castering assistance motor, via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

[0477] In accordance with one or more aspects of the disclosed embodiment a maximum castering assistance torque of the castering assistance motor is a motor rated torque of the castering assistance motor, and resistance from castering scrub at each predetermined kinematic state is substantially negated by commanded castering assistance torque so as to effect substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

[0478] In accordance with one or more aspects of the disclosed embodiment the method further comprises determining, independently for each respective caster wheel, the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

[0479] In accordance with one or more aspects of the disclosed embodiment the method further comprises determining, independently for each respective caster wheel, the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel to effect substantially scrubless castering of each respective caster wheel, wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

[0480] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub.

[0481] In accordance with one or more aspects of the disclosed embodiment the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

[0482] In accordance with one or more aspects of the disclosed embodiment the method further comprises, positioning, with the controller, the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

[0483] In accordance with one or more aspects of the disclosed embodiment the method further comprises applying, under control of the controller, the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

[0484] In accordance with one or more aspects of the disclosed embodiment the method further comprises applying, under control of the controller, the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

[0485] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

[0486] In accordance with one or more aspects of the disclosed embodiment the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing. [0487] In accordance with one or more aspects of the disclosed embodiment the caster assistance motor is at least one of a servo motor and a stepper motor.

[0488] It should be understood that the foregoing description is only illustrative of the aspects of the disclosed embodiment. Various alternatives and modifications can be devised by those skilled in the art without departing from the aspects of the disclosed embodiment. Accordingly, the aspects of the disclosed embodiment are intended to embrace all such alternatives, modifications and variances that fall within the scope of any claims appended hereto. Further, the mere fact that different features are recited in mutually different dependent or independent claims does not indicate that a combination of these features cannot be advantageously used, such a combination remaining within the scope of the aspects of the disclosed embodiment.

[0489] What is claimed is:

Claims

1. An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torque to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

2. The autonomous transport vehicle of claim 1, wherein the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torque is configured wherein resistance from castering scrub at each predetermined kinematic state is substantially negated so as to effect substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

3. The autonomous transport vehicle of claim 2, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

4. The autonomous transport vehicle of claim 2, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

5. The autonomous transport vehicle of claim 2, wherein the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub.

6. The autonomous transport vehicle of claim 2, wherein the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

7. The autonomous transport vehicle of claim 1, wherein the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

8. The autonomous transport vehicle of claim 1, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

9. The autonomous transport vehicle of claim 8, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

10. The autonomous transport vehicle of claim 1, wherein the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

11. The autonomous transport vehicle of claim 1, wherein the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

12. The autonomous transport vehicle of claim 1, wherein the caster assistance motor is at least one of a servo motor and a stepper motor.

13. The autonomous transport vehicle of claim 1, wherein the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

14. An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel, of a non-holonomic steering system, is mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torque to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect, via castering assistance torque from the castering assistance motor assisting castering input from vehicle yaw generated by differential torque from the at least two independently driven wheels, substantially scrubless castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

15. The autonomous transport vehicle of claim 14, wherein the controller is configured to determine the castering assistance torque as a supplement torque supplementing castering input to the at least one caster wheel, from vehicle yaw, to effect scrubless castering of the at least one caster wheel.

16. The autonomous transport vehicle of claim 14, wherein the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torque is configured wherein resistance from castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

17. The autonomous transport vehicle of claim 16, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

18. The autonomous transport vehicle of claim 16, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

19. The autonomous transport vehicle of claim 16, wherein the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub.

20. The autonomous transport vehicle of claim 16, wherein the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

21. The autonomous transport vehicle of claim 14, wherein the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

22. The autonomous transport vehicle of claim 14, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

23. The autonomous transport vehicle of claim 22, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

24. The autonomous transport vehicle of claim 14, wherein the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

25. The autonomous transport vehicle of claim 14, wherein the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

26. The autonomous transport vehicle of claim 14, wherein the caster assistance motor is at least one of a servo motor and a stepper motor.

27. The autonomous transport vehicle of claim 14, wherein the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

28. An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance motor that engages the at least one caster wheel so as to impart castering assistance torgue to the at least one caster wheel assisting castering of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance motor and configured to effect castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque, from the castering assistance motor, the castering assistance torque being developed substantially negating resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle.

29. The autonomous transport vehicle of claim 28, wherein the controller is configured to determine the castering assistance torque as a supplement torque supplementing castering input to the at least one caster wheel, from vehicle yaw, to effect scrubless castering of the at least one caster wheel.

30. The autonomous transport vehicle of claim 28, wherein the castering assistance motor is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance motor, and commanded castering assistance torque is configured wherein the resistance from the castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

31. The autonomous transport vehicle of claim 30, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

32. The autonomous transport vehicle of claim 30, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

33. The autonomous transport vehicle of claim 30, wherein the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from the castering scrub.

34. The autonomous transport vehicle of claim 30, wherein the commanded castering assistance torque substantially negates resistance from the castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

35. The autonomous transport vehicle of claim 28, wherein the controller is configured to position the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

36. The autonomous transport vehicle of claim 28, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

37. The autonomous transport vehicle of claim 36, wherein the controller is configured to apply the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

38. The autonomous transport vehicle of claim 28, wherein the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

39. The autonomous transport vehicle of claim 28, wherein the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

40. The autonomous transport vehicle of claim 28, wherein the caster assistance motor is at least one of a servo motor and a stepper motor.

41. The autonomous transport vehicle of claim 28, wherein the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

42. An autonomous transport vehicle for transporting items in a storage and retrieval system, the autonomous transport vehicle comprising: a frame; a controller; at least two independently driven drive wheels mounted to the frame; and at least one caster wheel mounted to the frame and having a castering assistance electromagnetic actuator that engages the at least one caster wheel so as to impart a bias force to the at least one caster wheel at each castering position of the at least one caster wheel; wherein the controller is communicably connected to the castering assistance electromagnetic actuator and configured to effect castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and bias force, from the castering assistance electromagnetic actuator, that is commanded so as to bias the at least one caster wheel to a corresponding castering position that substantially negates resistance from castering scrub in each predetermined kinematic state of the autonomous transport vehicle.

43. The autonomous transport vehicle of claim 42, wherein the commanded bias force substantially negates castering resistance imparted to the at least one caster wheel from the castering scrub.

44. The autonomous transport vehicle of claim 42, wherein the commanded bias force substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

45. The autonomous transport vehicle of claim 42, wherein the controller is configured to determine a castering assistance torque of the castering assistance electromagnetic actuator as a supplement torque supplementing castering input to the at least one caster wheel, from the vehicle yaw, to effect scrubless castering of the at least one caster wheel.

46. The autonomous transport vehicle of claim 45, wherein the castering assistance electromagnetic actuator is configured so that a maximum castering assistance torque is a motor rated torque of the castering assistance electromagnetic actuator, and commanded castering assistance torque is configured wherein the resistance from the castering scrub at each predetermined kinematic state is substantially negated so as to effect the substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torque, substantially independent of vehicle path and kinematic state.

47. The autonomous transport vehicle of claim 46, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is determined independently for each respective caster wheel so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

48. The autonomous transport vehicle of claim 46, wherein the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, is independently determined to effect substantially scrubless castering of each respective caster wheel, and wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

49. The autonomous transport vehicle of claim 42, wherein the controller is configured to position the castering assistance electromagnetic actuator so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

50. The autonomous transport vehicle of claim 42, wherein the controller is configured to apply a castering assistance torque, with the castering assistance electromagnetic actuator, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

51. The autonomous transport vehicle of claim 50, wherein the controller is configured to apply the castering assistance torque, with the castering assistance electromagnetic actuator, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

52. The autonomous transport vehicle of claim 42, wherein the at least one caster wheel has a caster mount housing and the castering assistance electromagnetic actuator is a frameless motor, the frameless motor being integrated in the caster mount housing.

53. The autonomous transport vehicle of claim 42, wherein the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance electromagnetic actuator, a stator of the caster assistance electromagnetic actuator being disposed against and supported by the caster mount housing, and a rotor of the castering assistance electromagnetic actuator being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

54. The autonomous transport vehicle of claim 42, wherein the caster assistance electromagnetic actuator is at least one of a servo motor and a stepper motor.

55. The autonomous transport vehicle of claim 42, wherein the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

56. A method for driving an autonomous transport vehicle in a storage and retrieval system, the method comprising: providing an autonomous transport vehicle having a frame, a controller, at least two independently driven drive wheels mounted to the frame, and at least one caster wheel mounted to the frame and having a castering assistance motor; imparting castering assistance torgue, with the castering assistance motor engaged to the at least one caster wheel, so as to assist castering of the at least one caster wheel; and effecting, with the controller communicably connected to the castering assistance motor, via a combination of vehicle yaw, generated by differential torque from the at least two independently driven drive wheels, and castering assistance torque from the castering assistance motor, castering of the at least one caster wheel with the autonomous transport vehicle in motion with a predetermined kinematic state.

57. The method of claim 56, wherein a maximum castering assistance torgue of the castering assistance motor is a motor rated torque of the castering assistance motor, and resistance from castering scrub at each predetermined kinematic state is substantially negated by commanded castering assistance torque so as to effect substantially scrubless castering along and throughout each vehicle path via the commanded castering assistance torgue, substantially independent of vehicle path and kinematic state.

58. The method of claim 57, further comprising determining, independently for each respective caster wheel, the commanded castering assistance torque for each respective caster wheel, of the at least one caster wheel, so as to effect substantially scrubless castering of each respective caster wheel substantially independent of vehicle path and kinematic state.

59. The method of claim 57, further comprising determining, independently for each respective caster wheel, the commanded castering assistance torgue for each respective caster wheel, of the at least one caster wheel to effect substantially scrubless castering of each respective caster wheel, wherein castering assistance torque respectively commanded for each corresponding caster wheel varies between corresponding caster wheels of the at least one caster wheel based on turn radius.

60. The method of claim 57, wherein the commanded castering assistance torque substantially negates castering resistance imparted to the at least one caster wheel from castering scrub.

61. The method of claim 57, wherein the commanded castering assistance torque substantially negates resistance from castering scrub imparted against vehicle yaw moment generated by the differential torque from the at least two independently driven drive wheels.

62. The method of claim 56, further comprising, positioning, with the controller, the castering assistance motor so as to bias the at least one caster wheel against castering and maintain the at least one caster wheel in a predetermined steady state position with the autonomous transport vehicle in motion.

63. The method of claim 56, further comprising applying, under control of the controller, the castering assistance torque, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to a predetermined skew orientation of the at least one caster wheel, which predetermined skew orientation forms a bias angle between the at least one caster wheel, in the predetermined orientation, and an axis of symmetry of the autonomous transport vehicle.

64. The method of claim 63, further comprising applying, under control of the controller, the castering assistance torgue, with the castering assistance motor, to the at least one caster wheel biasing the at least one caster wheel in a castering direction to the predetermined skew orientation with the autonomous transport vehicle at rest.

65. The method of claim 56, wherein the at least one caster wheel has a caster mount housing and the castering assistance motor is a frameless motor, the frameless motor being integrated in the caster mount housing.

66. The method of claim 56, wherein the at least one caster wheel has a caster mount housing, the caster mount housing houses the castering assistance motor, a stator of the caster assistance motor being disposed against and supported by the caster mount housing, and a rotor of the castering assistance motor being disposed against a caster pivot shaft of the at least one caster wheel, the caster pivot shaft pivotally joining the at least one caster wheel to the caster mount housing.

67. The method of claim 56, wherein the caster assistance motor is at least one of a servo motor and a stepper motor.

68. The method of claim 56, wherein the castering assistance motor effects optimization of drive wheel motors of the at least two independently driven drive motors so that the drive wheel motors are optimized to effect linear inertial changes in autonomous transport vehicle motion.

69. An autonomous transport robot vehicle for transporting a payload, the autonomous transport robot vehicle comprising: a chassis that is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame; a payload support connected to the chassis and dependent therefrom; and ride wheels dependent from the chassis, proximate opposite end corners of the chassis, on which the autonomous transport robot vehicle rides so as to traverse a traverse surface, the ride wheels include at least one caster wheel and a pair of drive wheels supporting the chassis from the traverse surface, and wherein the ride wheels and chassis in combination form a low profile height from the traverse surface to atop the chassis, where chassis height and ride wheel height are overlapped at least in part and the payload support is nested within the ride wheels; and wherein the space frame has predetermined modular coupling interfaces, each disposed for removably coupling, as a module unit, a corresponding predetermined electronic or mechanical component module of the autonomous transport robot vehicle to the chassis.

70. The autonomous transport robot vehicle of claim 69, wherein the predetermined modular coupling interfaces include at least one of at least one caster wheel module coupling interface, at least one drive wheel module coupling interface, and at least one payload support module coupling interface.

71. The autonomous transport robot vehicle of claim 70, wherein the at least one caster wheel is selectable from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

72. The autonomous transport robot vehicle of claim 70, wherein drive wheels of the pair of drive wheels are selectable from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

73. The autonomous transport robot vehicle of claim 70, wherein the payload support is selectable from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

74. The autonomous transport robot vehicle of claim 70, wherein the at least one drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules of each different drive wheel of the pair of drive wheels.

75. The autonomous transport robot vehicle of claim 69, wherein the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame are mechanically fastened to each other.

76. The autonomous transport robot vehicle of claim 69, wherein the payload support comprises a payload support contact surface on which a payload resting on the payload support is seated, the payload support contact surface is disposed atop the chassis.

77. The autonomous transport robot vehicle of claim 69, wherein the space frame is configured so that the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from the traverse surface to atop the chassis.

78. The autonomous transport robot vehicle of claim 69, wherein the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from the traverse surface to atop the chassis.

79. The autonomous transport robot vehicle of claim 69, wherein the chassis has a selectably variable configuration, selectable from different configurations each having different chassis form factors.

80. The autonomous transport robot vehicle of claim 69, wherein at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam, is selectable from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

81. The autonomous transport robot vehicle of claim 80, wherein selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

82. An autonomous transport robot vehicle for transporting a payload, the autonomous transport robot vehicle comprising: a chassis bus with predetermined modular coupling interfaces, each disposed for removably coupling, as a module unit, corresponding predetermined component modules of the autonomous transport robot vehicle to the chassis bus so that the autonomous transport robot vehicle has a modular construction; and wherein the corresponding predetermined component modules include at least one of: a payload support module with a payload support contact surface removably coupled as a module unit to the chassis bus with a corresponding payload support module coupling interface; a caster wheel module with a caster wheel removably coupled as a module unit to the chassis bus with a corresponding caster wheel module coupling interface; and a drive wheel module with a drive wheel removably coupled as a module unit to the chassis bus with a corresponding drive wheel module coupling interface.

83. The autonomous transport robot vehicle of claim 82, wherein the caster wheel module is selectable from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

84. The autonomous transport robot vehicle of claim 82, wherein the drive wheel module is selectable from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

85. The autonomous transport robot vehicle of claim 84, wherein the corresponding drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules.

86. The autonomous transport robot vehicle of claim 82, wherein the payload support module is selectable from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

87. The autonomous transport robot vehicle of claim 82, wherein the chassis bus is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame.

88. The autonomous transport robot vehicle of claim 87, wherein the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame are mechanically fastened to each other.

89. The autonomous transport robot vehicle of claim 87, wherein the space frame is configured so that the chassis bus is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from a traverse surface to atop the chassis.

90. The autonomous transport robot vehicle of claim 87, wherein the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from a traverse surface to atop the chassis.

91. The autonomous transport robot vehicle of claim 87, wherein at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam, is selectable from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

92. The autonomous transport robot vehicle of claim 91, wherein selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

93. The autonomous transport robot vehicle of claim 82, wherein the autonomous transport robot vehicle includes at least one caster wheel module and at least one drive wheel module, the at least one caster wheel module and the at least one drive wheel module are dependent from the chassis bus, proximate opposite end corners of the chassis, where the autonomous transport robot vehicle rides on at least a caster wheel of the at least one caster wheel module and at least one drive wheel of the at least one drive wheel module so as to traverse a traverse surface.

94. The autonomous transport robot vehicle of claim 93, wherein the at least one caster wheel, the at least one drive wheel, and the chassis bus in combination form a low profile height from the traverse surface to atop the chassis, where: the at least one drive wheel comprises a pair of drive wheels and the at least one caster wheel comprises a pair of caster wheels, a chassis height and a height of the at least one drive wheel are overlapped at least in part, and the payload support contact surface, on which a payload resting on the payload support module is seated, is nested within the pair of drive wheel and the pair of caster wheels.

95. The autonomous transport robot vehicle of claim 82, wherein the payload support contact surface, on which a payload resting on the payload support module is seated, is disposed atop the chassis bus.

96. The autonomous transport robot vehicle of claim 82, wherein the chassis bus has a selectably variable configuration, selectable from different configurations each having different chassis form factors.

97. A method comprising: providing the autonomous transport robot vehicle with: a chassis that is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame, a payload support connected to the chassis and dependent therefrom, and ride wheels dependent from the chassis, proximate opposite end corners of the chassis, on which the autonomous transport robot vehicle rides so as to traverse a traverse surface, the ride wheels include at least one caster wheel and a pair of drive wheels supporting the chassis from the traverse surface, and wherein the ride wheels and chassis in combination form a low profile height from the traverse surface to atop the chassis, where chassis height and ride wheel height are overlapped at least in part and the payload support is nested within the ride wheels; and removably coupling as a module unit, with predetermined modular coupling interfaces of the space frame, a corresponding predetermined electronic or mechanical component module of the autonomous transport robot vehicle to the chassis.

98. The method of claim 97, wherein the predetermined modular coupling interfaces include at least one of at least one caster wheel module coupling interface, at least one drive wheel module coupling interface, and at least one payload support module coupling interface.

99. The method of claim 98, further comprising selecting the at least one caster wheel from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

100. The method of claim 98, further comprising selecting drive wheels of the pair of drive wheels from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

101. The method of claim 98, further comprising selecting the payload support from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

102. The method of claim 98, wherein the at least one drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules of each different drive wheel of the pair of drive wheels.

103. The method of claim 97, further comprising mechanically fastening the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame to each other.

104. The method of claim 97, wherein the payload support comprises a payload support contact surface on which a payload resting on the payload support is seated, the payload support contact surface is disposed atop the chassis.

105. The method of claim 97, wherein the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from the traverse surface to atop the chassis.

106. The method of claim 97, wherein the space frame resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from the traverse surface to atop the chassis.

107. The method of claim 97, further comprising selecting a selectably variable configuration of the chassis from different configurations each having different chassis form factors.

108. The method of claim 97, further comprising selecting at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

109. The method of claim 108, wherein selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

110. A method comprising: providing the autonomous transport robot vehicle with a chassis bus with predetermined modular coupling interfaces; and removably coupling as a module unit, with the predetermined modular coupling interfaces, corresponding predetermined component modules of the autonomous transport robot vehicle to the chassis bus so that the autonomous transport robot vehicle has a modular construction; wherein the predetermined component modules include at least one of: a payload support module with a payload support contact surface removably coupled as a module unit to the chassis bus with a corresponding payload support module coupling interface, a caster wheel module with a caster wheel removably coupled as a module unit to the chassis bus with a corresponding caster wheel module coupling interface, and a drive wheel module with a drive wheel removably coupled as a module unit to the chassis bus with a corresponding drive wheel module coupling interface.

111. The method of claim 110, further comprising selecting the caster wheel module from a number of different selectably interchangeable caster wheel modules, each with a different predetermined caster wheel module characteristic.

112. The method of claim 110, further comprising selecting the drive wheel module from a number of different selectably interchangeable drive wheel modules, each with a different predetermined drive wheel module characteristic.

113. The method of claim 112, wherein the drive wheel module coupling interface includes separate and distinct interfaces for respective separate and distinct drive wheel modules.

114. The method of claim 110, further comprising selecting the payload support module from a number of different interchangeable payload support modules, each with a different predetermined payload support module characteristic.

115. The method of claim 110, wherein the chassis bus is a space frame formed of: longitudinal hollow section beams, arrayed to form longitudinally extended sides of the space frame, and respective front and rear lateral beams closing opposite ends of the space frame.

116. The method of claim 115, further comprising mechanically fastening the longitudinal hollow section beams and the respective front and rear lateral beams of the space frame to each other.

117. The method of claim 115, wherein the space frame is configured so that the chassis is substantially rigid with predetermined rigidity characteristics, with a shape and form that provides a minimum height from a traverse surface to atop the chassis.

118. The method of claim 115, wherein the space frame configuration resolves both predetermined rigidity characteristics and a minimum low profile height of chassis from a traverse surface to atop the chassis.

119. The method of claim 115, further comprising selecting at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from a number of different selectably interchangeable respective longitudinal hollow section beams, front lateral beams, and rear lateral beams each with different predetermined mechanical characteristics.

120. The method of claim 119, wherein selection of the at least one of the longitudinal hollow section beams, the front lateral beam, and the rear lateral beam from the number of different selectably interchangeable respective longitudinal hollow section beams, the front lateral beams, and the rear lateral beams determines the selected variable configuration of the chassis.

121. The method of claim 110, wherein the autonomous transport robot vehicle includes at least one caster wheel module and at least one drive wheel module, the at least one caster wheel module and the at least one drive wheel module are dependent from the chassis bus, proximate opposite end corners of the chassis, where the autonomous transport robot vehicle rides on at least caster wheel of the at least one caster wheel module and at least one drive wheel of the at least one drive wheel module so as to traverse a traverse surface.

122. The method of claim 121, wherein the caster wheel, the drive wheel, and the chassis bus in combination form a low profile height from the traverse surface to atop the chassis, where: the at least one drive wheel comprises a pair of drive wheels and the at least one caster comprises a pair of caster wheels, a chassis height and a height of the at least one drive wheel are overlapped at least in part, and the payload support contact surface, on which a payload resting on the payload support module is seated, is nested within the pair of drive wheel and the pair of caster wheels.

123. The method of claim 110, wherein the payload support contact surface, on which a payload resting on the payload support module is seated, is disposed atop the chassis bus.

124. The method of claim 110, further comprising selecting a selectably variable configuration of the chassis bus from different configurations each having different chassis form factors.

125. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

126. The autonomous transport robot of claim 125, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

127. The autonomous transport robot of claim 125, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

128. The autonomous transport robot of claim 125, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

129. The autonomous transport robot of claim 125, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

130. The autonomous transport robot of claim 125, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

131. The autonomous transport robot of claim 130, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

132. The autonomous transport robot of claim 125, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

133. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to generate a substantially linear transient response to the at least one traction drive wheel, to rolling over surface transients of a rolling surface in a linear direction substantially normal to the frame throughout each transient.

134. The autonomous transport robot of claim 133, wherein: the least one intervening pivot link between the at least one traction drive wheel and the frame is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over the rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface; and the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

135. The autonomous transport robot of claim 134, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

136. The autonomous transport robot of claim 134, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

137. The autonomous transport robot of claim 133, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

138. The autonomous transport robot of claim 133, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

139. The autonomous transport robot of claim 139, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

140. The autonomous transport robot of claim 133, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

141. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with: a frame, the frame having an integral payload support, a transfer arm connected to the frame, the transfer arm providing autonomous transfer of payload to and from the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, where the drive section is connected to the frame; and maintaining, with a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface, wherein the fully independent suspension has at least one intervening pivot link between at least one traction drive wheel and the frame.

142. The method of claim 141, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

143. The method of claim 141, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

144. The method of claim 141, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

145. The method of claim 141, further comprising defining a payload datum position with a payload seat surface of the integral payload support, wherein the payload datum position determines a predetermined payload position relative to the autonomous transport robot, and the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

146. The method of claim 141, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

147. The method of claim 146, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

148. The method of claim 141, further comprising locking, with a lock of the fully independent suspension, the fully independent suspension in a predetermined position relative to the frame.

149. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with: a frame, the frame having an integral payload support, a transfer arm connected to the frame, the transfer arm providing autonomous transfer of payload to and from the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, where the drive section is connected to the frame; and generating a substantially linear transient response to at least one traction drive wheel, to rolling over surface transients of a rolling surface in a linear direction substantially normal to the frame throughout each transient, wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame.

150. The method of claim 149, further comprising:

Maintaining, with the least one intervening pivot link between the at least one traction drive wheel and the frame, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over the rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface; wherein, the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

151. The method of claim 150, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

152. The method of claim 150, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

153. The method of claim 149, further comprising defining a payload datum position with the integral payload support, wherein the payload datum position determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

154. The method of claim 149, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

155. The method of claim 154, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

156. The method of claim 149, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

157. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support that has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension, and are disposed on the frame astride the integral payload support so that the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

158. The autonomous transport robot of claim 157, wherein the autonomous transport robot has fully independent suspension at each of the at least one caster wheel and each traction drive wheel.

159. The autonomous transport robot of claim 157, wherein the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

160. The autonomous transport robot of claim 159, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

161. The autonomous transport robot of claim 159, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

162. The autonomous transport robot of claim 159, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

163. The autonomous transport robot of claim 157, wherein the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

164. The autonomous transport robot of claim 157, wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

165. The autonomous transport robot of claim 157, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

166. The autonomous transport robot of claim 165, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

167. The autonomous transport robot of claim 157, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

168. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel, the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel.

169. The autonomous transport robot of claim 168, wherein the predetermined transient response characteristic of the at least one of the at least one caster wheel and the at least one traction drive wheel is set based on the predetermined rigidity characteristic of the frame.

170. The autonomous transport robot of claim 168, wherein the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

171. The autonomous transport robot of claim 170, wherein the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

172. The autonomous transport robot of claim 168, wherein the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

173. The autonomous transport robot of claim 172, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

174. The autonomous transport robot of claim 172, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

175. The autonomous transport robot of claim 172, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

176. The autonomous transport robot of claim 168, wherein the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

177. The autonomous transport robot of claim 168, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

178. The autonomous transport robot of claim 177, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

179. The autonomous transport robot of claim 178, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

180. The autonomous transport robot of claim 168, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

181. The autonomous transport robot of claim 168, wherein the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel with the autonomous transport robot carrying a payload.

182. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with a frame having an integral payload support, the integral payload support having a payload seat surface and defining, with the payload seat surface a payload datum position that determines a predetermined payload position relative to the autonomous transport robot; providing a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; providing at least one caster wheel mounted to the frame; and providing a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; and disposing the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels on the frame astride the integral payload support so that the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, and each of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels having a fully independent suspension.

183. The method of claim 182, wherein the autonomous transport robot has fully independent suspension at each of the at least one caster wheel and each traction drive wheel.

184. The method of claim 182, further comprising, maintaining, with the fully independent suspension of the at least one traction drive wheel, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

185. The method of claim 184, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

186. The method of claim 184, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

187. The method of claim 184, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

188. The method of claim 182, further comprising, disposing the fully independent suspension on the frame to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

189. The method of claim 182, wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

190. The method of claim 182, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

191. The method of claim 190, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

192. The method of claim 182, further comprising locking the fully independent suspension in a predetermined position relative to the frame.

193. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with a frame having an integral payload support; providing a transfer arm connected to the frame, the transfer arm being configured for autonomous transfer of payload to and from the frame; providing at least one caster wheel mounted to the frame; and providing a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension, and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel; and setting the predetermined rigidity characteristic based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel.

194. The method of claim 193, wherein the predetermined transient response characteristic of the at least one of the at least one caster wheel and the at least one traction drive wheel is set based on the predetermined rigidity characteristic of the frame.

195. The method of claim 193, wherein the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the fully independent suspension of at least one of the at least one caster wheel and the at least one traction drive wheel with the autonomous transport robot carrying a payload.

196. The method of claim 193, wherein the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

197. The method of claim 196, wherein the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

198. The method of claim 193, wherein the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

199. The method of claim 198, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

200. The method of claim 198, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

201. The method of claim 198, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

202. The method of claim 193, wherein the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

203. The method of claim 193, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

204. The method of claim 203, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

205. The method of claim 204, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

206. The method of claim 193, further comprising locking the fully independent suspension in a predetermined position relative to the frame.

207. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; at least one caster wheel mounted to the frame; and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame; wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and wherein the frame has a predetermined rigidity characteristic defining a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel, the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the frame determining the transient response of the frame from transients of the at least one caster wheel and at least one traction wheel of the pair of traction drive wheels rolling on the rolling surface.

208. The autonomous transport robot of claim 207, wherein the predetermined rigidity characteristic of the frame determines the frame as being substantially rigid relative to the fully independent suspension of the at least one caster wheel and at least one traction wheel of the pair of traction drive wheels rolling on the rolling surface.

209. The autonomous transport robot of claim 207, wherein the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from the transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

210. The autonomous transport robot of claim 209, wherein the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

211. The autonomous transport robot of claim 207, wherein the fully independent suspension of the at least one traction drive wheel is configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

212. The autonomous transport robot of claim 211, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

213. The autonomous transport robot of claim 211, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

214. The autonomous transport robot of claim 211, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

215. The autonomous transport robot of claim 207, wherein the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

216. The autonomous transport robot of claim 207, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

217. The autonomous transport robot of claim 216, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

218. The autonomous transport robot of claim 216, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

219. The autonomous transport robot of claim 207, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

220. The autonomous transport robot of claim 207, wherein the predetermined rigidity characteristic is set based on a predetermined transient response characteristic of the frame with the autonomous transport robot one or more of carrying a payload and unloaded.

221. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; a multi-input/multi-output controller coupled to the drive section; and wherein the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; and wherein the multi-input/multi-output controller is configured to determined, based on optimal robot trajectory, a predetermined kinematic characteristic of the autonomous transport robot, and modulates motor applied torque to the traction drive wheel to match traction drive wheel rotation with the predetermined kinematic characteristic of the autonomous transport robot within a predetermined wheel slip characteristic of the traction drive wheel relative to the rolling surface.

222. The autonomous transport robot of claim 221, wherein the predetermined wheel slip characteristic results in near instantaneous wheel rotation modulation resolving wheel slip of the traction drive wheel based on modulated applied torque commanded by the multi-input/multi-output controller.

223. The autonomous transport robot of claim 221, wherein the near instantaneous wheel rotation modulation is less than about 10 ms, and about less than 2ms.

224. The autonomous transport robot of claim 221, wherein multi-input/multi-output controller is configured to determine modulation of applied torque in response to wheel position data from the wheel position sensor, and to determine relative slip of the traction drive wheel to the rolling surface based on the wheel position data.

225. The autonomous transport robot of claim 221, wherein each traction drive wheel of the drive section has the corresponding traction motor separately powering the traction drive wheel closely coupled with the respective traction drive wheel.

226. The autonomous transport robot of claim 221, wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

227. The autonomous transport robot of claim 226, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

228. The autonomous transport robot of claim 226, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

229. The autonomous transport robot of claim 226, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

230. The autonomous transport robot of claim 226, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

231. The autonomous transport robot of claim 226, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

232. The autonomous transport robot of claim 231, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

233. The autonomous transport robot of claim 226, wherein the fully independent suspension has a lock configured to lock the fully independent suspension in a predetermined position relative to the frame.

234. A method for an autonomous transport robot for transporting a payload, the method comprising: providing the autonomous transport robot with: a frame having an integral payload support, a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame, at least one caster wheel mounted to the frame, and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, wherein the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels roll, on a rolling surface effecting autonomous transport robot traversal over the rolling surface, each having a fully independent suspension; and setting a predetermined rigidity characteristic of the frame based on a predetermined transient response characteristic of the frame determining the transient response of the frame from transients of the at least one caster wheel and at least one traction drive wheel of the pair of traction drive wheels rolling on the rolling surface, where the predetermined rigidity characteristic defines a transient response of the frame from transient loads imparted to the frame via at least one of the at least one caster wheel and at least one traction drive wheel.

235. The method of claim 234, wherein the predetermined rigidity characteristic of the frame determines the frame as being substantially rigid relative to the fully independent suspension of the at least one caster wheel and at least one traction wheel of the pair of traction drive wheels rolling on the rolling surface.

236. The method of claim 234, wherein the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and the predetermined rigidity characteristic is set so that transient loads, from the transients of the at least one of the at least one caster wheel and at least one traction drive wheel, imparted to the payload on the payload seat surface via the frame, are minimized.

237. The method of claim 236, wherein the transient loads are minimized so that the payload unrestrained pose on the payload seat surface is substantially constant in response to the transient loads with the bot rolling on the rolling surface.

238. The method of claim 234, further comprising maintaining, with the fully independent suspension of the at least one traction drive wheel, a substantially steady state traction contact patch between the at least one traction drive wheel and the rolling surface over each rolling surface transient throughout traverse of the at least one traction drive wheel over the rolling surface.

239. The method of claim 238, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

240. The method of claim 238, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over the each rolling surface transient.

241. The method of claim 238, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the each rolling surface transient.

242. The method of claim 234, wherein the fully independent suspension is disposed to maintain each of the at least one caster and each of the at least one traction drive wheel in a steady state position relative to the frame during one or more of transients of the transfer arm and with the integral payload support in a loaded and unloaded payload condition.

243. The method of claim 234, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

244. The method of claim 243, wherein the at least the pair of traction drive wheels are disposed so that the payload datum position, defined by the integral payload support, is at the minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

245. The method of claim 244, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

246. The method of claim 234, further comprising locking the fully independent suspension in a predetermined position relative to the frame.

247. The method of claim 234, further comprising setting the predetermined rigidity characteristic based on a predetermined transient response characteristic of the frame with the autonomous transport robot carrying a payload.

248. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with: a frame with an integral payload support, and a drive section with at least a pair of traction drive wheels astride the drive section, the drive section being connected to the frame, the drive section being configured so that each traction drive wheel of the at least the pair of traction drive wheels is separately powered by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; separately powering, with the drive section, each traction drive wheel of the at least the pair of traction drive wheels by a corresponding traction motor closely coupled with the respective traction drive wheel, and distinct and separate from each other traction motor of the drive section corresponding to each other traction drive wheel; and determining, with a multi-input/multi-output controller, based on optimal robot trajectory, a predetermined kinematic characteristic of the autonomous transport robot, and modulating motor applied torque to the traction drive wheel to match traction drive wheel rotation with the predetermined kinematic characteristic of the autonomous transport robot within a predetermined wheel slip characteristic of the traction drive wheel relative to the rolling surface.

249. The method of claim 248, wherein the predetermined wheel slip characteristic results in near instantaneous wheel rotation modulation resolving wheel slip of the traction drive wheel based on modulated applied torque commanded by the multi-input/multi output controller.

250. The method of claim 248, wherein the near instantaneous wheel rotation modulation is less than about 10 ms, and about less than 2ms.

251. The method of claim 248, wherein the multi-input/multi- output controller determines modulation of applied torque in response to wheel position data from the wheel position sensor, and to determines relative slip of the traction drive wheel to the rollinq surface based on the wheel position data.

252. The method of claim 248, wherein each traction drive wheel of the drive section has the corresponding traction motor separately powering the traction drive wheel closely coupled with the respective traction drive wheel.

253. The method of claim 248, wherein the at least the pair of traction drive wheels have a fully independent suspension coupling each wheel of the at least the pair of traction drive wheels to the frame, with at least one intervening pivot link between at least one traction drive wheel and the frame, the method further comprising maintaining, with the fully independent suspension a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

254. The method of claim 253, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

255. The method of claim 253, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

256. The method of claim 253, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

257. The method of claim 253, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

258. The method of claim 253, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

259. The method of claim 258, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof, including the intervening pivot link, define a minimum height profile.

260. The method of claim 253, further comprising locking the fully independent suspension in a predetermined position relative to the frame.

261. An autonomous transport robot for transporting a payload, the autonomous transport robot comprising: a frame with an integral payload support; a transfer arm connected to the frame and configured for autonomous transfer of payload to and from the frame; a drive section connected to the frame and having at least a pair of traction drive wheels astride the drive section, the at least the pair of traction drive wheels has a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame; and a lock releasably coupled to the fully independent suspension, the lock being configured to lock the fully independent suspension in a predetermined position relative to the frame.

262. The autonomous transport robot of claim 261, further comprising a controller, the controller is configured to automatically effect: actuation of the lock of a respective fully independent suspension with extension of the transfer arm, and release of the lock of the respective fully independent suspension with retraction of the transfer arm.

263. The autonomous transport robot of claim 261, wherein the fully independent suspension has at least one intervening pivot link between at least one traction drive wheel and the frame configured to maintain a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

264. The autonomous transport robot of claim 263, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

265. The autonomous transport robot of claim 263, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

266. The autonomous transport robot of claim 263, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

267. The autonomous transport robot of claim 261, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

268. The autonomous transport robot of claim 261, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

269. The autonomous transport robot of claim 268, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof define a minimum height profile.

270. A method for an autonomous transport robot, the method comprising: providing the autonomous transport robot with a frame, the frame having an integral payload support; providing the autonomous transport robot with a transfer arm, the transfer arm being connected to the frame and configured for autonomous transfer of payload to and from the frame; providing the autonomous transport robot with a drive section, the drive section being connected to the frame and having at least a pair of traction drive wheels astride the drive section, the at least the pair of traction drive wheels has a fully independent suspension coupling each traction drive wheel of the at least the pair of traction drive wheels to the frame; and locking, with a lock releasably coupled to the fully independent suspension, the fully independent suspension in a predetermined position relative to the frame.

271. The method of claim 270, further comprising, with a controller, automatically effecting: actuating the lock of a respective fully independent suspension with extension of the transfer arm, and releasing the lock of the respective fully independent suspension with retraction of the transfer arm.

272. The method of claim 270, wherein the fully independent suspension has at least one intervening pivot link between at least one traction drive wheel and the frame, the method further comprising maintaining, with the fully independent suspension, a substantially steady state traction contact patch between the at least one traction drive wheel and a rolling surface over rolling surface transients throughout traverse of the at least one traction drive wheel over the rolling surface.

273. The method of claim 272, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout traverse of the at least one traction drive wheel over the rolling surface.

274. The method of claim 272, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel throughout transient of the at least one traction drive wheel due to traverse over rolling surface transients.

275. The method of claim 272, wherein the substantially steady state traction contact patch is disposed at a predetermined reference position of the at least one traction drive wheel substantially independent of transients of the at least one traction drive wheel due to traverse over the rolling surface transients.

276. The method of claim 270, wherein the frame is configured so the integral payload support has a payload seat surface defining a payload datum position that determines a predetermined payload position relative to the autonomous transport robot, and wherein the payload seat surface at the payload datum position is disposed at a minimum distance above the rolling surface.

277. The method of claim 270, wherein the at least the pair of traction drive wheels are disposed so that a payload datum position, defined by the integral payload support, is at a minimum distance above the rolling surface and extends within a height profile of the at least one traction drive wheel.

278. The method of claim 270, wherein the height profile of the at least one traction drive wheel and fully independent suspension thereof define a minimum height profile.