WO2019122930A1

WO2019122930A1 - Load balancing transportation device

Info

Publication number: WO2019122930A1
Application number: PCT/GB2018/053759
Authority: WO
Inventors: Ben BOMFORD; Carson Brown
Original assignee: Uniwheel Limited
Priority date: 2017-12-22
Filing date: 2018-12-21
Publication date: 2019-06-27
Also published as: GB2569657A; GB201721823D0

Abstract

A transportation device adapted to move based on a fore-aft balance of a load with respect to the transportation device. The axis about which the load rotates is offset from the axis about which a ground contacting member of the transportation device rotates, wherein a balance control system is adapted to controllably drive the ground contacting member based on a fore- aft balance of the load. A rotation of the load about the first axis is restricted.

Description

LOAD BALANCING TRANSPORTATION DEVICE

FIELD OF INVENTION

The present invention relates to the field of transportation devices, and in particular to transportation devices which moves based on a fore-aft balance of a load.

BACKGROUND TO THE INVENTION

Powered transportation device for transporting loads, such as packages or individuals, are known. Some such transportation devices aim to maintain a fore-aft balance of the transported load.

Typically, fore-aft balance of the transported load is maintained by arranging the transportation device such that is rotates about a single axis, and providing a balance control system to maintain a fore-aft balance of the transportation device. For example, there is a known concept of a powered self-balancing transportation device comprising a single wheel for positioning between a user’s legs.

Typically, such self-balancing transportation devices comprise electronic and/or mechanical systems that are adapted to control the rotation of a wheel so as to control the fore-and-aft balance of the transportation device and thereby the load. In such devices, such as those described by US Patent Number US 6,302,230, a sensor and an electronic arrangement are provided. Information detected by the sensor and electronic arrangement is passed to a motor, which drives the wheel in the appropriate direction and at suitable speed so as to maintain or preserve fore-and-aft balance.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to a first aspect of the inventive concept, there is provided a transportation device for transporting a load comprising: a load support adapted to support a load and adapted to rotate about a first axis; a ground contacting arrangement comprising: a ground contacting member adapted to rotate about a second, different axis; and a drive arrangement adapted to control a rotation of the ground contacting member; a rotation restricting system adapted to restrict the rotation of the load about the first axis; and a balance control system adapted to control the operation of the drive arrangement based on a fore-aft balance of the load about the first axis.

Embodiments provide a load-balancing transportation device in which a load (e.g. a user) rotates about a different axis of rotation as that of a driven wheel. A rotation of the load about the (first) axis is restricted by a rotation restricting system.

By offsetting the axis about which the load support rotates from the axis about which a wheel is driven, a more stable transportation device is provided. There is also a reduced burden of weight on the driven wheel when compared to conventional self-balancing transportation devices. This may allow for improved weight distribution about the transportation device and for lighter/cheaper wheels to be used.

As the user is also offset from the ground contacting member, any movement which is induced in the ground contacting arrangement (e.g. due to a bump or rough terrain) will have a reduced impact on the user, thereby increasing a ride comfort.

In a conventional self-balancing device, where the user rotates about a same axis as the self-balancing arrangement, a rotation of the user induces a translational movement of the self-balancing device. For example, a forward rotation of the load would unintentionally shift the self-balancing transportation device backwards. This requires a substantial amount of power or energy to maintain a balance of the load (e.g. for the wheel to overcome the force of the translational movement).

This translational force is advantageously avoided by offsetting the axis of rotation of the user from the axis about which the ground contacting member rotates. This is because the rotational force is no longer directly applied to the self-balancing transportation device. Thus, a reduced power is required to balance the user.

The rotation restriction system prevents, limits or discourages the load from over-rotating about the first axis. This prevents the user from exceeding a capability of the drive arrangement to power the ground contacting member (so that they cannot be balanced by the load), to thereby improve a safety of the transportation device.

The rotation restriction system may effectively prevents the load from rotating beyond a first predetermined angle of rotation. In other examples, the resistive force may increase with a rotation of the load, such that the greater the rotation of the load, the greater the resistive force to further rotation. This advantageously provides feedback to a load and acts as a safety feature.

The rotation restriction system may be a physical stop, an electronic stop or an increasing resistance to further rotation. In some examples, the rotation restriction system provides a resistive force that requires an excessive amount of force to overcome, such as a force which is greater than the weight of a load, thereby effectively preventing further rotation of the load about the first axis.

Preferably, the balance control system is adapted to maintain a fore-aft balance of the load about the first axis.

In some embodiments, the rotation restricting system comprises a mechanical stop adapted to prevent rotation of the load support beyond a first predetermined angle of rotation.

A mechanical stop prevents, in the case of a power cut or other failure (which could lead to a sudden deceleration of the device), a load support from unrestrictedly rotating about its axis, which could throw a load from the load support. Rather, there is a maximum rotation of the load support beyond which it is unable to tilt, so that a load is able to brace itself against the mechanical stop, thereby preventing their own over-rotation and preventing themselves from falling forward. In some embodiments, the rotation restricting system comprises a bracing member adapted to engage with the load so as to prevent rotation of the load about the first axis.

The bracing member allows a load to brace against their own over-rotation (e.g. caused by a sudden deceleration of the transportation device due to a power cut). Thus, the load may prevent themselves from falling forward by bracing against the bracing member. The bracing member also provides more precise control for the user over their forward-and- rearward leaning, and thereby over the speed of the transportation device.

The bracing member may connect to or engage with any part of the load, but preferably to a point above the load’s center of mass. This helps prevent unwanted or unintended over-rotation of the load.

Preferably, the bracing member comprises a handle to be held by a user of the transportation device.

In at least one embodiment, the rotation restricting system is adapted to restrict the rotation of the load support about the first axis based on a torque applied by the drive arrangement to the ground contacting member.

Restricting the rotation based on a torque provides a form of feedback to the load. In this way, the load may receive an indication of their speed and/or power output by the drive arrangement. This provides a load with an intuitive indication of the operation of the transportation device. Moreover, restricting based on a torque prevents over-rotation of the load (which could otherwise lead to the load falling forward).

Thus, the load support may not be freely rotatable about the first axis, but rather there may be a resistance to an attempted rotation, which resistance is based upon a torque applied by the drive arrangement to the ground contacting member. By providing a resistance that is based on the torque, a user can intuitively feel (e.g. through their feet) an amount of torque being applied to ground contacting member, and thereby their relative speed. Preferably, there is an increasing resistance to (further) rotation of the load support as a torque applied by the drive arrangement increases or a speed of the transportation device increases. This may be used to limit the maximum speed of the transportation device, as it will become increasingly difficult to rotate the overcome the resistive force. This is of particular advantage in increasing a safety of the transportation device as light loads (e.g. children) may be unable to travel at high speeds, whilst heavier loads (e.g. adults) may be able to provide the necessary force to travel at high speeds. Thus, as a mass and weight of a load increases, a maximum speed of the device may also increase.

The rotation restricting system may, for example, comprise a motor that drives to oppose a tilting of the load support induced by the load based on a torque applied by the drive arrangement (e.g. sensed by a torque monitoring device). In other examples, the rotation restricting system may comprise a linking element that directly controls restricts a rotation of the load support based on a torque applied by the drive arrangement. Other embodiments for a suitable torque-based rotation system will be apparent to the skilled person.

The transportation device may be adapted wherein: the ground contacting arrangement further comprises a central portion rotatable about the second axis and around which the ground contacting member rotates; the balance control system is adapted to control the operation of the drive arrangement so as to maintain a fore-aft balance of the central portion; and the rotation restricting system comprises a linking arrangement adapted to couple the load support to the central portion, such that a rotation of the load support about the first axis causes a rotation of the central portion about the second axis and vice versa.

Thus, the ground contacting arrangement by itself acts as a self- balancing device, where the forward and rearward tilting of the ground contacting arrangement is controlled by the load support via a linking arrangement. This allows existing self-balancing devices to be incorporated into the transportation device, minimizing a complexity of the transportation device. Moreover, this prevents the need for wires or other communication devices (e.g. wireless modules) for communicating information about a rotation of the load support to the ground contacting arrangement. Rather, the rotation of the load support is transferred to the ground contacting member, which then performs its own self-balancing operation.

Such an embodiment provides a simpler and more reliable transportation device, having fewer components and advantageously utilizing existing devices.

Moreover, a linking arrangement provides feedback to a user of the transportation device, as a torque applied to the ground contacting member causes an opposing force in the central portion which is transferred to the load support. This opposing force is perceivable by a user.

The linking arrangement may comprise: a first portion fixedly coupled to the load support; a second portion rotatably coupled to the first portion; and a third portion rotatably coupled to the second portion and fixedly coupled to the central portion.

Such a linking arrangement provides a simple and effective mechanism for transferring the rotation of the load support to a rotation of the central portion of the ground contacting arrangement.

In at least one embodiment, the load support is adapted to rotate about a first axle, and the ground contacting member is adapted to rotate about a second axle, wherein the linking arrangement is adapted to couple the first axle to the second axle.

Coupling an axle of the load support to an axle of the ground contacting arrangement more effectively transfers the rotation of the load support to the central portion of the ground contacting arrangement. In particular, a distance between the axles remains substantially constant and in a same location relative to other parts of the transportation device (such as a frame or chassis). This improves a reliability of the linking arrangement and therefore of the transportation device.

In some embodiments, the diameter of the first axle is different to the diameter of the second axle.

The magnitude or angle of rotation of the load support thereby causes a different angle of rotation in the central portion of the ground contacting arrangement, as well causing a different amount of torque to be applied to the ground contacting member by the drive arrangement. A first axle having a diameter smaller than the second axle allows for more precise or fine control by the load of the rotation of the central portion (and therefore of the device’s speed and the applied torque). A first axle having a diameter larger than the second axle allows for increased responsiveness and/or speed of the transportation device to a rotation of the user.

Preferably, the magnitude of the rotation of the load support about the first axis is proportional to the magnitude of the rotation of the central portion about the second axis.

Thus, a rotation of the load support induces an equal rotation of the central portion. This ensures that the balance control system will control the speed of the transportation device so as to accurately balance the load about the first axis, thereby increasing a safety of the transportation device.

The transportation device may further comprise an inertial measurement unit adapted to determine an angle of a ground surface supporting the transportation device, wherein the balance control system adjusts the operation of the drive arrangement based on the determined angle of the ground surface.

Provision of an inertial measurement unit to determine an angle of the ground surface allows for more precise and accurate control over controlling the speed of the transportation device so as to balance a load provided on the load support. In particular, the transportation device may use the inertial measurement unit to distinguish between an angle of the load support about the first axis due to a shape of the ground surface or due to an intention of the user. The speed of the transportation device may be controlled based on the determined intention of the user.

Preferably, the drive arrangement comprises an outrunner motor, the ground contacting member being coupled to a rotor of the outrunner motor.

An outrunner motor advantageously provides a driven ground contacting arrangement having a high amount of torque with extremely precise control over a speed or torque output by the motor. This allows for improved control over the speed and/or balancing method performed by the transportation device so as to balance a load on the load support.

The load support may comprise a first and second foot support adapted to support a foot of a user.

Thus, the transportation device may be adapted to transport a user or rider. The user may stand on the load support and control the tilt or rotation of the load support using their feet. This provides a simple and intuitive mechanism for controlling the speed of the device.

In other examples, the load support comprises a single support, such as a board or platform, upon which two feet may be placed. The single support may be pivoted about a fulcrum, for example.

Preferably, the transportation device comprises a steering arrangement comprises at least one further ground contacting member and a steering mechanism adapted to steer the at least one further ground contacting member.

Thus, the transportation device may comprise an additional ground contacting member (e.g. wheel, ski, skid-pad, roller, skate or track) which can be steered so as to control a direction of the transportation device.

Using a steering mechanism allows for a greater control over the direction of the transportation device and a reduced turning circle (when compared to a simple leaning of the transportation device, for example).

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 illustrates a transportation device according to a first embodiment;

Figure 2 illustrates a modified version of the transportation device according to the first embodiment;

Figure 3 illustrates a transportation device according to a second embodiment;

Figures 4A and 4B illustrate a ground contacting arrangement of a transportation device according to an embodiment; and

Figure 5 illustrates a transportation device according to a third embodiment.

DETAILED DESCRIPTION

According to a concept of the invention, there is proposed a transportation device adapted to automatically maintain or otherwise control a fore-aft balance of a load with respect to the transportation device. The axis about which the load rotates is offset from the axis about which a ground contacting member of the transportation device rotates, wherein a balance control system is adapted to controllably drive the ground contacting member based on a fore-aft balance of the load. A rotation of the load about the first axis is restricted.

Embodiments are at least partly based on the realization that a feedback of a self-balancing transportation device’s speed may be provided to a load without the need for the load to rotate about the same axis as a ground contacting member (providing the self-balancing). In other words, it has been recognized that an axis of rotation of a load may be offset from an axis of rotation of a wheel which assists in maintaining or controlling a fore- aft balance of the load. With reference now to Figure 1 , a transportation device 10 according to a first embodiment of the invention will be described. The transportation device 10 comprises a load support 11 adapted to support a load 90, a ground contacting arrangement 12, a rotation restricting system 15 and a balance control system 16.

The load support 11 , and thereby load 90, is adapted to rotate about a first axis 11A of rotation. The load support comprises a pair of foot platforms each adapted to support a foot of a user of the transportation device.

The ground contacting arrangement 12 comprises a wheel 13, i.e. a ground contacting member. The wheel is adapted to rotate about a second axis 13A of rotation. The ground contacting arrangement further comprises a drive arrangement (not shown) which controllably drives the wheel. The driver arrangement may be built into the wheel 13, for example, as a hub motor.

The balance control system 16 is adapted to maintain a fore-aft balance of the load about the first axis 11 A. The balance control system 16 may, for example, comprise one or more inertial measurement units, accelerometers or gyrometers adapted to determine a rotation of the load or load support about the first axis. A drive arrangement (not shown) of the ground contacting arrangement is adapted to control a rotation of the wheel about the second axis based on information about the rotation of the load or load support about the first axis.

Rotation of the wheel 13 about the second axis 13A is controlled so as to maintain a fore-aft balance of the load 90 about the first axis 11 A. Thus, the load 90 may be balanced to remain in an upright position. This may be performed, for example, by attempting to maintain the load support 11 in a substantially horizontal (i.e. perpendicular to a gravitational force) direction. The first axis 11A and second axis 13A are offset from one another, such that they do not lie in a same axis. Thus, the balance control system 16 senses forward and backward tilt of the load 90 about the first axis and regulates the drive arrangement accordingly so as to keep the load upright. In this way, the load (e.g. a user) is provided a way of controlling the acceleration and deceleration of the unicycle by varying their rotation about the first axis, for example, by leaning forwards or backwards or applying different pressures with a foot.

The rotation restricting system 15 is adapted to restrict the rotation of the load or load support 11 about the first axis 11 A. The rotation restricting system 15 here comprises a first mechanical stop 17A adapted to prevent rotation of the load support beyond a first predetermined angle of rotation (e.g. in a clockwise-direction). A second mechanical stop 17B similarly prevents a rotation of the load support beyond a predetermined angle of rotation in the opposing direction (e.g. an anti-clockwise direction).

It is recognized that in the event of a power failure or insufficient torque of the drive arrangement, so that the drive arrangement is no longer able to correctly control a rotation of the wheel 13, the load will no longer be balanced by the transportation device. In such a scenario, the first mechanical stop 17A or second mechanical stop 17B will prevent the load support from rotating beyond the (first) predetermined angle, and thereby reduce an impact of the load falling forward, as the load will be unable to rotate beyond the first predetermined angle. This improves a safety of the transportation device.

A direction of travel is controlled at least by leaning or tilting the transportation device sideways. The gyroscopic effect of the lean or tilt will cause the device to begin performing a turn, so as to undergo a banked turn. This well-known phenomenon may also be called precession. In other words, the load (e.g. a user) may steer the device by adjusting their sideways lean (by shifting a body weight of the user). The transportation device 10 also comprises a further ground contacting arrangement 18. The further ground contacting arrangement 18 comprises one or more wheels, tracks or rollers.

The transportation device 10 comprises a frame 19 or chassis coupling the elements of the transportation device 10 together. The load support may be a platform (such as a foot platform) which is tiltable or rotatable about the frame, to provide improved control for the load in controlling a forward and backward speed of the transportation device.

The load support 31 may comprise foot platforms positioned either side of the frame, and connected together by an axle, such that rotation 2 of a first foot platform induces a rotation in the second foot platform.

Figure 2 illustrates a modified version of the first embodiment of the invention. The transportation device 20 further comprises a bracing member 21 adapted to engage with the load so as to prevent or restrict rotation of the load about the first axis.

The bracing member 21 comprise a handle which is adapted to be held by a user (i.e. the load). The handle 21 thereby allows the user to control their own rotation about the first axis by bracing or pushing/pulling the handle to control their rotation. The handle therefore provides a greater amount of control to the load in controlling their rotation.

The bracing member 21 or handle provides a further point of contact for the load to be supported by the transportation device. In the event of a power failure or insufficient torque, as previously described, the load or user may support themselves against the bracing member 21 so as to further assist in preventing their rotation about the first axis.

Thus, in the event of a power failure of a drive arrangement, a user is able to maintain their balance with respect to the transportation device, without falling forward/backward. This improves a safety of a self- balancing transportation device. The bracing member 21 forms a rotation restricting system, and may be used in addition to or instead of the first/second mechanical stops 1 17 A, 17B of the first embodiment of the invention.

Preferably, the bracing member 21 couples to the further ground contacting arrangement 18 and/or the frame 19 in the vicinity of the further ground contacting arrangement. This ensures that the force applied by a load to the bracing member 21 is in the vicinity of a ground contacting portion, to provide greater support to the bracing member.

In at least one embodiment, the bracing member 21 is coupled to the further ground contacting arrangement and controls a direction of the further ground contacting arrangement. Put another way, the bracing member may steer the further ground contacting arrangement.

In one example, the further ground contacting arrangement 18 comprises a wheel which may be steered by the bracing member 21 (e.g. via a steering mechanism). Thus, there may be provided a steering arrangement comprising the bracing member 21 , the further ground contacting arrangement 18 and a steering mechanism which allows the bracing member to control a direction the ground contracting arrangement. For example, the further ground contacting arrangement may be rotatably coupled to the frame 19, the rotation of the ground contacting arrangement about the frame being controlled by the bracing member 21. A steering arrangement provides greater control over the direction of travel of the device, and allows for a tighter turning circle. In particular, a steering arrangement allows for some control over the yaw of the device.

Preferably, the further ground contacting arrangement comprises a single wheel which may be steered by the steering mechanism, which is turn controlled by a user of the transportation device (e.g. using the bracing member as handles).

The bracing member 21 and/or further ground contacting arrangement may comprise a suspension system (not shown), which may be formed of coils, hydraulics and so on. This provides a greater amount of comfort to a user operating the transportation device.

The bracing member 21 and/or steering arrangement may be adapted for use in any embodiment of the transportation device herein described.

The synergistic effect of the first mechanical stop 17A and the bracing member 21 ensures that a user or load of the transportation device will not topple forward if the transportation device comes to a sudden stop (e.g. due to a power failure). In particular, the first mechanical stops the user’s feet from over-rotating, and the bracing member 21 can prevent the user’s body or torso from over-rotating. The combined effect these components prevents over-rotation of the user to a greater extent than a single one alone, as the bracing member 21 will prevent a user from being thrown forward if a rotation of their feet has been prevented by the first mechanical stop.

Figure 3 illustrates a transportation device 30 according to a second embodiment of the invention.

The transportation device 30 comprises a load support 31 adapted to support a load 90, a ground contacting arrangement 32, a rotation restricting system 35 (formed from a linking arrangement 35) and a balance control system 36.

As before, the load support 31 is adapted to rotate about a first axis 31 A.

The ground contacting arrangement 32 comprises an outrunner motor 32B, 32C which acts as a drive arrangement. The outrunner motor is formed of a central stator 32B (or central portion) and an outer rotor 32C coupled to a tire 32D (ground contacting member). The outer rotor 32C (and thereby tire) is adapted to rotate about the central stator 32B, the center of rotation defining a second axis 32A. The speed of rotation of the outer rotor, and thereby of the tire, about the central stator is controlled by a drive arrangement (not shown). The greater the power output by the outrunner motor or drive arrangement, the greater the speed of rotation of the tire and the speed of the transportation device.

The balance control system 36 is adapted to maintain a fore-aft balance of the central stator 32B with respect to a ground surface 95 by controlling an operation of the drive arrangement. Thus, the balance control system 36 senses forward and backward tilt of the central stator 32B about the second axis 32A and regulates the drive arrangement accordingly with the aim of keeping the central stator upright. By way of example, if the central stator 32B rotates in a forward direction, so the balance control system controls the ground contacting arrangement to move the transportation device 30 forward. The angle of the central stator 32B thereby defines a speed of the transportation device 30.

The ground contacting arrangement 32 may itself be considered as a self-balancing transportation device which self-balances about a single axis, such as a self-balancing unicycle or self-balancing wheel.

The load support 31 is coupled to the central stator by a linking arrangement 35, such that a rotation of the load support 31 about the first axis 31 A causes a corresponding rotation of the central stator 32B about the second axis 32A. Rotation of the central stator causes a change in speed of rotation of the tire. In this way, rotation of the load support 31 controls a rotation of the tire 32D, and thereby a speed of the transportation device 30.

The power/torque applied by the drive arrangement (not shown) also results in an opposing resistive force to further rotation of the central stator 32B. Thus, the greater the angle of the central stator 32B, the greater the power/torque applied by the drive arrangement and the greater the corresponding resistive force to further rotation of the central stator about the second axis 32A.

The linking arrangement 35 causes this resistive force to be mirrored/replicated in the load support 31. The linking arrangement 35 thereby acts as a rotation restricting system, restricting rotation of the load support 31 and load 90 about the first axis 31 A (as the balance of the load support will be

maintained) based on the amount of torque applied by the drive arrangement.

The linking arrangement thereby provides a feedback to the user of the force applied by the drive arrangement to the ground contacting member.

The linking arrangement 35 of the second embodiment is adapted to couple a first axle (at a location of the first axis 31 A), of the load support 31 , to a second axle (at a location of the second axis 32A) of the ground contacting arrangement 32. A rotation of the load support causes a complimentary rotation of the first axle. A rotation of the central stator causes a complimentary rotation of the second axle. Rotation of the first axle causes a rotation in the second axle and vice versa. Thus, a rotation of the load support can be replicated or mirrored by the central stator and vice versa.

The linking arrangement comprises: a first portion 35A fixedly coupled to the first axle; a second portion 35B rotatably coupled to the first axle; and a third portion 35C fixedly coupled to the second axle and rotatably coupled to the second portion. Such an arrangement allows a rotation of the first axle to be transferred or mirrored by the second axle and vice versa.

The first axle and the second axle may have different diameters. This will result in a rotation of the first axle inducing a proportional, but not equal, rotation in the second axle. Thus, a rotation of the load support 41 induces a proportional rotation in the central stator 52B. This may be exploited to provide greater precision in the speed of the transportation device (when the first axle is smaller than the second axle) or increase an ease of a user in

attaining a maximum speed of the transportation device (when the second axle is smaller than the first axle). Moreover, such a concept may be used to control the torque and/or speed that needs to be applied by the drive arrangement to the ground-contacting arrangement (i.e. the torque-speed ratio, as a power applied by the drive arrangement will generally be the same). In particular, it is recognized that the greater an attempted rotation of a self-balancing transportation device, the less torque that needs to be applied by the transportation device to maintain a balance of the transportation device.

Thus, if a first axle is larger than the second axle, a greater attempted rotation is induced in the central stator 52B by a rotation of the load support 41. Such a greater rotation results in less torque being required to balance a user.

This concept can thereby allow different motor sizes to be used with the transportation device, increasing a design freedom.

The rotation restricting system of the second embodiments acts as an electrical stop to prevent or restrict rotation of the load support. In some embodiments, the balance control system may be adapted to prevent rotation of the central stator (and thereby of the load support) beyond a predetermined angle of rotation. This may be performed, for example, by virtually adjusting a location about which a fore-aft balance of the central stator is determined, which would adjust an amount of torque (and therefore resistive force) applied by the drive arrangement.

The second embodiment of the invention may comprise any one or more of the elements of any rotation restricting system previously described, such as a mechanical stop or a bracing member.

Other linking arrangements are also envisaged, for example, a chain, belt or other flexible coupling element coupling the first axle to the second axle. Preferably, the flexible coupling element comprises a bracer (e.g. a cog) located between the first and second axle and connecting one side of the element to the other side. This provides a supporting structure to the flexible element and prevents sagging. A flexible element provides a simple, efficient and low-cost solution to a linking arrangement, and may be more reliable that the previously proposed linking arrangement formed of three portions.

Other rotation restricting systems that control can restrict the rotation of the load support about the first axis based on a torque applied by the drive arrangement to the ground contacting member are also envisaged. One example would be a rotation restriction system that comprises a user support motor, adapted to apply a rotational fore-aft force to the load support, and a torque monitoring device, adapted to monitor a torque applied by the drive arrangement to the ground control member (which may be formulated in software). The user support motor may be adapted to drive a rotation of the user support rearwards or forward in response to the monitored torque level (e.g. to increase a resistance in a forward and rearward direction respectively).

In another example, the user support motor may be replaced by an electromagnet which increasingly opposes a forward/rearward rotation based on an amount of torque applied by the drive arrangement to the ground contacting member. Such an electromagnetic may comprise a winding formed around a corresponding ring or annulus of magnets fixed onto the load support, to thereby control a resistance to attempted rotation by the load support.

Figures 4A and 4B illustrate internal components of a drive arrangement 40 for the ground contacting arrangement. Figure 4A is an exploded diagram, whereas Figure 4B is a section view. The drive arrangement 40 is formed of the central stator 32B and the outer rotor 32C (i.e. an outrunner motor). The outer rotor is coupled to the tire (not shown in Figures 4A or 4B), which acts as a ground contacting member.

The central stator 32B comprises a winding arrangement 411 mounted on a central support 412, which couples to an axle 413 at its center. The axle 413 defines a location of the second axis about which the ground contacting arrangement rotates. The outer rotor 32C comprises a permanent magnet ring 421 and a rim 422, which may mount a tire. The rim 422 is formed of two separate rim portions 422A, 422B, which come together to define a single rim upon which a tire may be mounted. The magnet ring 421 may be formed, for example, of two separate magnet rings, each mounted in a respective rim portion. Such a configuration decreases a manufacturing complexity of the drive arrangement, as symmetrical rim portions and magnet rings may be formed.

The outer rotor 32C is coupled to the axle 413 via bearings 431 , so that the outer rotor 32C is able to rotate about the axle 413, and thereby about the central stator 32B. Each rim portion 422A, 422B comprises a hole 423A, 423B through which the axle 413 is threaded. The bearings couple the axle 413 to an inner edge of each hole.

An electrical current through the winding arrangement 41 1 controls a rotation of the magnet ring 421 about the winding arrangement, according to well-known electromechanical principles. As the magnet ring 421 is coupled to the tire via the rim, a speed of rotation of a tire is controlled by the electrical current through the winding arrangement. Control of the self- balancing transportation device’s speed and/or acceleration may thereby be controlled by controlling the current through the winding(s).

The drive arrangement 32B, 32C thereby acts as an outrunner motor, where an outer rotor 32C is driven by a central stator 32B to rotate a tire about the central stator. It has been recognized that such a described outrunner motor provides a greater amount of torque than a conventional (i.e. inrunner) motor.

To use the drive arrangement 40 in a transportation device according to the second embodiment, a balance control system (not shown) is provided and adapted to control the drive arrangement to maintain an orientation of the central stator 32B in a substantially upright position. Thus, the current through the winding arrangement is controlled with the aim of preventing a rotation of the central stator (e.g. with respect to a ground surface) by controlling a speed of the tire. The balance control system may comprise an accelerometer or gyrometer adapted to detect an attempted change in orientation of the central stator, and a control system adapted to control a current through the winding arrangement (and thereby speed of the transportation device) to counteract this change.

Thus, as the load support rotates about the first axis, inducing a rotation of the central stator 32B, the current through the winding arrangement is controlled so as to accelerate/decelerate the transportation device to counteract the rotation of the central stator and thereby the load support.

In particular, the linking arrangement (not shown) may be connected to the axle 413, such that tilting of the load support induces a complimentary tilting of the axle and the central stator. This causes the ground contacting arrangement to accelerate/decelerate in an attempt to maintain the balance of the central stator, and thereby moves the transportation device.

To use the drive arrangement 40 in a transportation device according to the first embodiment, a current through the winding arrangement may be controlled based on a fore-aft rotation of the load about the first axis (e.g. detected by an accelerometer positioned in/on the support). Thus, a balance control system (not shown) is provided and adapted to control the drive arrangement to maintain an orientation of the load or support substantially the same.

A casing for the ground contacting arrangement may also be mounted on the axle 413 and/or the central support 412. A control system may be provided to control the operation of the drive arrangement. Batteries may also be provided (e.g. mounted on casing or located between the rim portions 422A, 422B) to provide power for the drive arrangement.

Other embodiments of a suitable ground contacting arrangement will be readily apparent to the skilled person, such as a friction- driven or belt-driven wheel. Figure 5 illustrates a transportation device 50 according to a third embodiment. The transportation device 50 comprises a load support 51 , a ground contacting arrangement 52, a rotation restricting system 55, a balance control system 56, and a frame 59.

The load support 51 is adapted to support a load 90 thereon and to rotate about a first axis 51 A. The load support thereby rotates about the frame 59.

The ground contacting arrangement 52 comprises, arranged around a second axis 52A: a central stator 52B, an outer rotor 52C and a tire 52D. The outer rotor 52C and tire 52D adapted to rotate about the central stator 52B, having a rotational center at the second axis. The ground contacting arrangement 52 is also adapted to rotate about the frame 59.

The balance control system 56 comprises a first inertial measurement unit (IMU) 56A and second inertial measurement unit 56B.

The first IMU 56A is adapted to detect a fore-aft orientation of the central stator 52B of the ground contacting arrangement 52 (or, alternatively, of the load support 51 ). The second IMU 56B is adapted to detect a fore-aft orientation of the frame 59. As the frame will generally be parallel to the ground surface 95, the second IMU thereby determines an angle of the ground surface relative to gravity.

This allows for more accurate determination of the angle of the central stator 52B with respect to the ground surface 95.

In particular, embodiments allow the balance control system 56 to distinguish between rotation of the load support due to terrain (as a user will naturally wish to remain upright, even on slanted terrain) and rotation of the load support due to a user’s intent to change a speed of the transportation device.

The balance control system 56 may aim to control the speed of the transportation device based on the determined user intent.

In some embodiments, a maximum speed of the transportation device is limited to improve user safety and minimize motor wear. On a substantially level ground surface, the maximum speed may be defined by limiting a maximum torque or power output by the drive arrangement (i.e. the maximum allowable torque or power applied to the ground contacting member or tyre). However, the present invention recognizes that a speed of the transportation device depends upon a function including both torque/power and surface inclination. For example, the steeper a ground surface the slower the speed (for a same torque output).

Calculation of the surface inclination can therefore be used to correctly set a maximum allowable torque or output power threshold to more accurately limit the maximum speed of the transportation device.

As previously described, the balance control system 56 may be adapted to maintain a balance of the load support 51 or central stator 52B.

This is performed by driving the ground contacting member 52D of the ground contacting arrangement 52 appropriately to balance the load support (e.g. maintain it substantially horizontally).

However, the balance control system may be adapted to control an orientation of the load support 51 , for example, to maintain its balance in an off-horizontal position (i.e. not perpendicular to a gravitational force). It is possible to control an orientation or angle of the load support by virtually adjusting a location about which a balance of the load is determined. For example, if transportation device is in motion and a virtual position about which a balance of the load is determined is shifted towards a rear of the transportation device, the transportation device will accelerate and tilt the pedals backwards. This concept is known as tilt-back, and can be used to warn a load of insufficient power (to provide a required torque), low battery, inappropriate usage or faulty operation.

The tilt-back functionality may be used to improve a rider experience when travelling up/down an incline. In particular, the load support may be tilted so as to provide a more natural feeling to a user of the transportation device, and increase rider comfort. The second IMU 56B may be used to determine the orientation of the ground surface. The angle of the load support 51 A may be set, by the transportation device, so as to incline a load to improve their comfort. The amount that a user is tilted depends upon the inclination of the ground surface and may, for example, be in the region of 10-100% of the inclination of the ground surface, and preferably around 10-40%. The inclination may be limited to a maximum of 10°.

By way of example, if the transportation device 50 is moving up an inline of 10°, the pedals may be angled (away from the incline) 1 °. This provide a more natural feeling.

In conceivable embodiments, the motor of the drive arrangement is located at the load support, so as to directly control the orientation of the user thereupon. The drive arrangement may comprise a belt or other flexible connector which couples the motor to the ground contacting member to thereby control a speed of the ground contacting member.

The repositioning of the drive arrangement allows for improved or controlled weight distribution of the transportation device, and for the usage of gearing ratios between the drive arrangement of the wheel. This may allow, for example, a smaller motor or a more efficient motor to be used (as highly- efficient motors typically optimally operate at higher speeds).

In yet another embodiment, a standalone rotation restricting element may be achieved with a twin motor setup, with a first motor controlling an orientation of the load support and a second motor (i.e. the drive arrangement) driving the ground contacting member. The first motor may, for example, comprise an electromagnetic dynamo-meter (for variable damping), the dynamo-meter being paired with a motor. Use of such a motor set-up can improve design constraints. The first motor may be adapted to control an orientation of the load support based on the torque applied by the second motor (i.e. the drive arrangement) that drives the ground contacting member. In some other embodiments, the rotation restricting system comprises a torsion spring adapted to restrict rotation of the load support about the first axis. The torsion spring simulates the rotation restricting system of the second embodiment, and progressively increases a resistance to further rotation as an angle of rotation increases. The torsion spring embodiment provides a low-cost solution to simulating a speed feedback system. Other similar restricting systems are envisaged.

Whilst balance control system comprising inertial-based sensors have been herein described, other sensors for a balance control system (e.g. a proximity sensor positioned in the load support for determining a proximity of the ground to the load support) will be apparent to the person skilled in the art. Other ground contacting members are also envisaged, such as a roller or

track.

As used herein, the phrase “restrict a rotation of the load” means to prevent or dampen a rotation of the load support or load about the first axis, or to provide a resistive force to further rotation of the load beyond a predetermined point. The resistive force preferably increases with an amount of rotation or attempted rotation of the load support.

In any above described examples, the outrunner motor may be replaced by a conventional or inrunner motor. In such examples, the terms ‘central portion’ or‘central stator’ instead refer to the stationary component of the motor (i.e. the stator) which induces a rotation of a second, ground contacting portion (i.e. the rotor), and the embodiments may be modified accordingly.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A transportation device for transporting a load comprising:

a load support adapted to support a load and adapted to rotate about a first axis;

a ground contacting arrangement comprising:

a ground contacting member adapted to rotate about a second, different axis; and

a drive arrangement adapted to control a rotation of the ground contacting member;

a rotation restricting system adapted to restrict the rotation of the load about the first axis;

a balance control system adapted to control the operation of the drive arrangement based on a fore-aft balance of the load about the first axis.

2. The transportation device of claim 1 , wherein the rotation restricting system comprises a mechanical stop adapted to prevent rotation of the load support beyond a first predetermined angle of rotation.

3. The transportation device of any of claims 1 or 2, wherein the rotation restricting system comprises a bracing member adapted to engage with the load so as to prevent rotation of the load about the first axis.

4. The transportation device of claim 3, wherein the bracing member comprises a handle to be held by a user of the transportation device.

5. The transportation device of any preceding claim, wherein the rotation restricting system comprises adapted to restrict the rotation of the load support about the first axis based on a torque applied by the drive arrangement to the ground contacting member.

6. The transportation device of any preceding claim, wherein:

the ground contacting arrangement further comprises a central portion rotatable about the second axis and around which the ground contacting member rotates;

the balance control system is adapted to control the operation of the drive arrangement so as to maintain a fore-aft balance of the central portion; and

the rotation restricting system comprises a linking arrangement adapted to couple the load support to the central portion, such that a rotation of the load support about the first axis causes a rotation of the central portion about the second axis and vice versa.

7. The transportation device of claim 6, wherein the linking arrangement comprises:

a first portion fixedly coupled to the load support; a second portion rotatably coupled to the first portion; and a third portion rotatably coupled to the second portion and fixedly coupled to the central portion.

8. The transportation device of claim 6 or 7, wherein the load support is adapted to rotate about a first axle, and the ground contacting member is adapted to rotate about a second axle, and wherein the linking arrangement is adapted to couple the first axle to the second axle.

9. The transportation device of claim 8, wherein the diameter of the first axle is different to the diameter of the second axle.

10. The transportation device of any of claims 6 to 8, wherein the magnitude of the rotation of the load support about the first axis is proportional to the magnitude of the rotation of the ground contacting member about the second axis.

11. The transportation device of any preceding claim, further comprising an inertial measurement unit adapted to determine an angle of a ground surface supporting the transportation device, wherein the balance control system controls the operation of the drive arrangement based on the determined angle of the ground surface.

12. The transportation device of any preceding claim, wherein the drive arrangement comprises an outrunner motor, the ground coupling member being coupled to a rotor of the outrunner motor.

13. The transportation device of any preceding claim, wherein the load support comprises a first and second foot support each adapted to support a foot of the user.

14. The transportation device of any preceding claim, further comprising a steering arrangement comprises at least one further ground contacting member and a steering mechanism adapted to steer the at least one further ground contacting member.