SE2051046A1 - A vehicle chassis - Google Patents

Abstract

A vehicle chassis includes a first frame (no) for receiving a payload of the vehicle, the first frame having at least one undriven wheel (CW2), and a second frame (120) having two coaxial driven wheels (MW1, MW2), one or more undriven wheels (CW1) and a support point (121) for partially supporting the first frame. The support point is joined pitch-rotatably to the first frame. In an embodiment where the support point (121) is aligned with the undriven wheel (CWi) of the second frame (120) with respect to a longitudinal direction (L), the adhesive weight is minimized and made independent of the vehicle’s payload.

Description

A VEHICLE CHASSIS TECHNICAL FIELD id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1" id="p-1"

[0001] The present disclosure relates to a vehicle chassis suitable for a mobile robot or autonomous guided vehicle (AGV).

BACKGROUND id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2" id="p-2"

[0002] For two main reasons, it is attractive to provide a robot with more than three wheels: - To distribute load on more wheels. Specifically, it is cost-efficient to re-direct major part of the load to passive (castor) wheels.

- To create a more stable robot that is less sensitive to tipping-over when accelerating, decelerating and/ or turning. id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3" id="p-3"

[0003] For mobile robots with more than three wheels, special considerationsmust be taken to ensure stability and traction of the robot. It is desirable for thewheels to be always in contact with the ground despite local height variations.Specifically, to achieve traction for acceleration and deceleration/braking, it is crucialthat the active wheels be always in contact with the ground. If this is not addressed,even slightly uneven floors (occasional cables on a floor, endpoints of inclined ramps,etc.) will create a great variation in the individual wheels forces, which in turn may lead to traction or stability issues. id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4" id="p-4"

[0004] Some known active suspension systems address the above problem bydynamically controlling the weight distribution on each wheel, and thus the adhesiveweight of the robot. However, such systems are typically of a considerable complexity and may require frequent maintenance. id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5" id="p-5"

[0005] One problem is to present a cost-efficient and simple solution suitable for robots that achieves reliable traction.

SUMMARY id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6" id="p-6"

[0006] One objective is to make available a passive vehicle chassis in which the influence of the vehicle"s payload on the adhesive weight is reduced or altogether absent. Another objective is to make available a generic vehicle chassis where the loaddistribution between driven and undriven wheels can be controlled by varying adesign parameter. These and other objectives are achieved by a vehicle chassis with the features of claim 1. id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7" id="p-7"

[0007] Generally, all terms used in the claims are to be interpreted according totheir ordinary meaning in the technical field, unless explicitly defined otherwiseherein. All references to "a/ an/ the element, apparatus, component, means, step, etc."are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8" id="p-8"

[0008] The term "driven wheel" is used to describe a wheel having means forapplying a positive and/ or negative torque, so that an accelerating,decelerating/braking or turning action on the vehicle is obtained. This disclosure uses driven wheel and motorized wheel interchangeably. id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9" id="p-9"

[0009] The term "undriven wheel" covers wheels without such means, also knownas trailing wheels. An undriven wheel in this sense may be a castor (caster) wheel, which may or may not be fork-mounted.

BRIEF DESCRIPTION OF THE DRAWINGS id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10" id="p-10"

[0010] Aspects and embodiments of the invention are now described, by way of example, with reference to the accompanying drawings, on which: figure 1 is a cutaway perspective view of a vehicle chassis according to an embodiment;figure 2 is a perspective view of the vehicle chassis in a loaded condition; figures 3 and 4 are longitudinal sections through vehicle chassis according to twoembodiments, to illustrate the effect of design parameter f on the load distribution between driven wheels MW and undriven wheels CW; and figure 5 contains schematic perspective view of two vehicle chassis with four castor wheels, according to two further embodiments of the invention.

DETAILED DESCRIPTION id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11" id="p-11"

[0011] The invention will now be described more fully with reference to theaccompanying drawings, on which certain embodiments are shown. The inventionmay, however, be embodied in many different forms and the embodiments shouldnot be construed as limiting; rather, they are provided by way of example so that thisdisclosure will be thorough and complete, and to fully convey the scope of all aspectsof invention to those skilled in the art. Like numbers refer to like elements throughout this description. id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12" id="p-12"

[0012] Figure 1 shows a vehicle chassis generally composed of a first frame 110 and a second frame 120. id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13" id="p-13"

[0013] The second frame 120 includes one undriven wheel CW1 and two laterallyarranged driven wheels MW1 and MW2 (hidden) on a common rotation axis. Thesecond frame 120 may further include a traction motor, drive circuitry, batteries andother components. Departing from the illustrated basic structure of the second frame120, a designer may utilize his liberty to include and exclude such components inorder to optimize the total weight m2 of the second frame 120. The optimal totalweight may depend on the desired location of the vehicle"s centre of total mass and/ or its desired adhesive weight, as further discussed below. id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14" id="p-14"

[0014] The first frame 110 includes a central beam 111 aligned with a longitudinaldirection L of the chassis and suitable for receiving a payload F of the vehicle. At theright end of the beam 111, there is suspended an undriven wheel CW2. At the left end,the beam 111 rests on a suspension point 121 on the second frame 120. If the properweight of the first frame 110 is m1, the total load on the undriven wheel CW2 and support point 121 is F + m1 g. id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15" id="p-15"

[0015] Preferably, the suspension point 121 is a single point or multiple points atthe same longitudinal coordinate, to permit rotatory movement (pitch). In particular,the suspension point 121 may be constituted by one or more surfaces on a revolutejoint 122 extending transversally and allowing rotatory movement (pitch) betweenthe first frame 110 and second frame 120. The revolute joint 122 may be substantially aligned, in terms of its longitudinal position, with the axle of the undriven wheel CW1. Alternatively, as shown in figure 1, the revolute joint 122 may be longitudinally separated from the undriven wheel CW1. id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16" id="p-16"

[0016] The vehicle chassis shown in figure 1 may be utilized in a differential-drivemobile robot. Here, two of the wheels are active and used to create motion. Steeringof the platform is a result of the two motorized wheels MW1, MW2 running atdifferent speeds, which is the differential aspect. These wheels need only carryenough load (adhesive weight) that the friction relative to the floor prevents slippageat acceleration / deceleration or turning. The rest of the load is preferably directed tothe passive castor wheels CW1, CW2. For this specific case of a small size robot, only two additional castor wheels are used, so that the robot has four wheels. id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17" id="p-17"

[0017] By the introduction of the central beam 111 of the first frame 110, the ve-hicle consists of two connected structural parts, the first 110 and second 120 frames.The second frame 120 forms a three-wheeled carriage with the two motorized wheelsMW1, MW2 and one of the castor wheels CW1. Such carriage is statically self-stablein the sense that all wheels relax into contact with the floor. The first frame is connec-ted similar to a trailer to the second frame 120 through the passive revolute joint 122with its axis horizontal and parallel with the rotation axis of the motorized wheelsMW1, MW2. In this joint 122, preferably, some degree of friction is introduced todampen rotary motion of the system. This friction can be achieved by adding a bolt, nut and washers. The payload F of the vehicle is supported by the central beam 111. id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18" id="p-18"

[0018] If the joint 122 between the first 110 and second 120 frames is placed rightabove the castor wheel CW1, the central beam together with the two castor wheelsCW1, CW2 forms an arch that will carry the full payload, whereas the motorized wheelsMW1, MW2 will carry only a well-defined portion of the weight of the second frame 120. id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19" id="p-19"

[0019] If instead the joint 122 is moved inwardly in the second frame 120, cor-responding to nonzero values of the design parameter ä E [0,1] illustrated in figure 4, a greater share of the payload will be distributed onto the motorized wheels MW1, MW2. More precisely, simple statics reveal that the vertical reaction forces on the wheels indicated in figure 4 are given by: mzg2 fFMW=š(F+m1.9)+ l-fFcw1 =T(F+m1g)+m22gF+mgFcwz :Tl Assuming the second frame 120 is symmetric, the driven wheels MW1, MW2 willnormally receive equal shares of the force F MW. The configuration shown in figure 1 corresponds to f of about 0.25. id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20" id="p-20"

[0020] Figure 3 shows the special case ß = 0, where the suspension point 121 isaligned with the axis of the undriven wheel CW1 of the second frame 120. Then, the above expressions simplify into: m9FMWIZZ _F+(m1+m2)gCW1_ F + m gFcwz = TlThis F MW corresponds to the minimum achievable adhesive weight on the drivenwheels MW1, MW2. It is notable that the adhesive weight is independent of thepayload, which brings the benefit that the vehicle will have identical tractive properties in a loaded and an empty condition. id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21" id="p-21"

[0021] The opposite extreme case ß = 1 (not illustrated) is when the suspensionpoint 121 is aligned with the axis of the driven wheels MW1, MW2. This allocates a maximal share of the payload onto the driven wheels. id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22" id="p-22"

[0022] Figure 2 shows the chassis of figure 1 when carrying a load 130, which restson the first frame 110 via a plate 131. The load 130 may include an operable robot manipulator. id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23" id="p-23"

[0023] Returning to figure 4, optional elements for influencing the dynamics ofthe chassis are illustrated, according to an alternative embodiment. On the one hand,two lateral elastic elements 123 are arranged to limit and dampen lateral movement(yaw) or lateral bending of the central beam 111 relative to the second frame 120. Theelastic elements 123 are preferably located in the vicinity of the second castor wheelCW2. The elastic elements 123 may be a plastic sliding bearing mounted on thesecond frame 120. On the other hand, a compressible structural member 124 is addedbetween the central beam 111 and the bottom of the second frame 120. The structuralmember 124 at some point between the driven wheels MW1, MW2 and the first castorwheel CW1; preferably, it is located closer to the first castor wheel CW1 or in itsvicinity. The structural member 124 may be viscoelastic (e.g., of rubber), whereby itcontributes to the damping of vertical vibrations. Since the structural member 124will act, when compressed, as a further support point on the second frame 120, it will transfer a portion of the payload F onto the driven wheels MW1, MW2. id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24" id="p-24"

[0024] In a further embodiment, as an alternative to differential drive, the vehiclechassis may comprise steerable motorized wheels, which may render the vehicle omni-directional, i.e., steerable in arbitrary directions. id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25" id="p-25"

[0025] Figure 5 illustrates two further embodiments of the invention directed to vehicle chassis with four castor wheels. id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26" id="p-26"

[0026] The aspects of the present disclosure have mainly been described abovewith reference to a few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims (11)

1. A vehicle chassis, including: a first frame (110) for receiving a payload of the vehicle, the first frame having at least one undriven wheel (CW2); and a second frame (120) having two coaxial driven wheels (MW1, MW2), one or moreundriven wheels (CW1) and a support point (121) for partially supporting the first frame, wherein the support point is joined pitch-rotatably to the first frame.

2. The vehicle chassis of claim 1, wherein the support point (121) is comprised,with respect to a longitudinal direction (L) of the vehicle chassis, between the drivenwheels (MW1, MW2) and one of the undriven wheels (CW2) of the second frame(12o).

3. The vehicle chassis of claim 2, wherein the support point (121) is aligned, withrespect to the longitudinal direction (L), with said one of the undriven wheels (CW1) or with a rotation axis common to a plurality of the undriven wheels.

4. The vehicle chassis of any of the preceding claims, wherein the first frame (110) includes a beam (111) oriented in a longitudinal direction (L) of the chassis.

5. The vehicle chassis of any of the preceding claims, wherein the support point(121) is stiff or rigid with respect to the first frame”s yaw and/ or roll relative to the second frame.

6. The vehicle chassis of claim 5, wherein the support point (121) includes arevolute joint (122) rotatable around an axis parallel with the axis of the drivenwheels (MW1, MW2).

7. The vehicle chassis of any of the preceding claims, further including a yaw damper (123) arranged between the first and second frames.

8. The vehicle chassis of claim 7, wherein the yaw damper (123) includes twoelastic members arranged laterally on respective sides of a portion of the first frame (11o).

9. The vehicle chassis of any of the preceding claims, further including a compressible support member (124) arranged to transfer a vertical component from the first frame (110) to the second frame (120), wherein the compressible supportmember is comprised, with respect to a longitudinal direction (L) of the chassis,between the driven wheels (MW1, MW2) and one of the undriven wheel (CW1) of the second frame.

10. The vehicle chassis of any of the preceding claims, wherein the second frame (120) comprises two or more undriven wheels (MW1, MW2).

11. A mobile robot or autonomous guided vehicle, AGV, including the vehicle chassis of any of the preceding claims.