BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to vehicles, and in particular, an omnidirectional wheelchair base in which the frame provides integral chassis suspension and support for the wheelchair. Description of the Prior Art

Many types of omnidirectional vehicles are known in the art. For example, La in U.S. Patent No. 4,237,990 describes an omnidirectional bumper car for amusement parks. Ziegler in U.S. Patent 3,295,700 describes an omnidirectional vehicle for use in handling radioactive materials. Suitable wheels for such vehicles are described in U. ^* S. Patent 3,789,947" to

Blu rich and U.S. Patent 3,876,255 to Hon.

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These patents typify the prior approaches to omnidirectional vehicles in which size and weight were not significant factors in the design of the vehicle. The ride qualities of these prior art vehicles were determined mainly by the resiliency of the tires or wheels employed. The omnidirectional nature of the vehicle made provision of other suspension systems difficult. In addition, the cumbersome design of these prior art omnidirectional vehicles rendered them inapplicable to wheelchairs, in which all of the propulsion, suspension, and control must be situated in a relatively small area beneath the seat of a chair.

SUMMARY OF THE INVENTION This invention provides an omnidirectional wheelchair base of highly compact design, and in which the suspension and chassis are integral. In a preferred embodiment of the invention, the wheelchair

base includes upper and lower flexible base plates, typically fabricated from fiberglass-reinforced, nylon. The upper and lower plates are separated by a pair of front supports and a single rear support which are used to maintain the plates in parallel alignment at a fixed separation. The axes of rotation of the front wheels, which are mounted on the front supports, are less than 180° apart, while the axis of rotation of the rear wheel is less than 180° from the axis of each of the front wheels.

In the preferred embodiment of the invention, a fourth support is provided to distribute loading equally between the upper and lower plates and to provide a mounting point for a chair and the battery power supply. By control of, the shape and thickness of the upper and lower plates, the suspension qualities of the wheelchair may be controlled without need for cumbersome springs .and shock absorbers or other suspension components.

Typically, each of the wheels includes a frame and a plurality of rollers disposed, about the circumference of the wheel and attached to the frame. The axis of rotation of each roller corresponds to a chord of the circumference of the wheel on which it is mounted. By fabricating each roller in three parts and spacing the center portion from the end portions with bearings, the rollers may be preassembled and then attached to the frame using suitable apparatus. By displacing the axes of the front wheels 14.75° forward of a straight line perpendicular to the axis of the rear wheel, the cosine of the angle of the front wheel axis is 0.25, which simplifies digital processing of ^• control information for driving the wheels.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an perspective view of a sim¬ plified embodiment of the omnidirectional wheelchair base of this invention;

Figure 2 is a top view of the structure of Figure 1 illustrating the omnidirectional nature of the wheelchair base;

Figure 3 is a perspective view of the complete wheelchair including base and chair;

Figure 4 is a perspective view of the base of the chair shown in Figure 3 with cover removed;

Figure 5 is an exploded view of one wheel of the base illustrating its construction;

Figure 6 is a side view of the wheel illus¬ trating the construction of the rollers and their attachment to the wheel frame; and

Figure 7 is a cross-sectional view of the bearing and manner of attachment of it. to the frame of . the wheel.

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DETAILED DESCRIPTION OF THE PREFERRED EMB JIMENT Figure 1 is a perspective view of a simplified version of the omnidirectional wheelchair base 7. The base shown includes an upper flexible base plate 10 and a lower flexible base plate 20. Each plate is generally T-shaped and of desired thickness to provide the requisite softness of suspension while also providing a chassis for the base. In the preferred embodiment each of the upper and lower plates are fiber-reinforced epoxy to provide high strength, low weight, and flexibility.

At the front 12 of the wheelchair base, a pair of front supports 14 and 16 maintain the upper and lower plates 10 and 20 at the desired parallel separa¬ tion. A rear support 18 provides the same function at the rear of the base. Each of the supports -provides a mounting for one of the wheels of the base. Front

support 14 provides a mounting for wheel 22 and driving motor and gearbox 24, while front support 16 provides a mounting for wheel 26. The motor and gearbox which drive wheel 26 is concealed behind support 16 in Figure 1. Finally, rear support 18 provides a mounting for wheel 28 and motor gearbox 30.

Disposed about the periphery of each wheel are a plurality of rollers. For example, disposed about the periphery of wheel 26 are rollers 32 through 37. Each of the other wheels includes similar rollers. The axes of rotation of the rollers correspond to chords of the circumference of the wheels. The rollers enable the omnidirectional base to move in directions other than the axis of rotation of the wheels. For example, if the base shown in Figure 1 is to move directly forward or backward, motor gearbox 30 will not drive rear wheel 28, while the corresponding motors gearboxes for each of wheels 22 and 26 will drive those wheels at an equal sg.eed in the same direction. In this manner back wheel 28 will roll along the ground in the direction of its axis of rotation by virtue of the rotation of the rollers around its periphery.

In a related manner, if the base is to be driven in the direction of arrow 38, each of wheels 22 and 26 will be driven clockwise (as viewed from the exterior side of the wheel) , while wheel 28 will be driven counterclockwise. By driving wheels 22 and 26 at an angular rate sufficient to make the component of their rotation in the direction of arrow 38 equal to the angular rotation of wheel 28, the base will move in the direction of arrow 38. In a like manner, by driving each wheel at the appropriate angular rotation rate, the omnidirectional base can be caused to move in any direction.

The base shown in Figure 1 also includes a fourth support 40 disposed between the upper and lower plates and between the front supports 14 and 16 and the

rear support 18. Support 40 also functions to maintain the upper and lower plates 10 and 20 in a spaced-apart configuration, while providing a convenient attachment point for the chair portion of the wheelchair, as will be explained in conjunction with Figures 3 and 4.

Figure 2 is a top view of the structure shown in Figure 1 illustrating how, by driving each wheel at an appropriate rate, the omnidirectional base can be caused to follow a complicated path. As shown in Figure 2, base 7 may be caused to follow a curved path, for example, to allow an individual seated at a circular table to move to an adjoining place. To achieve the path 42 shown, the rear wheel 28 is driven at a slightly greater angular rate than the sum of the velocity components of the front wheels in direction 42. Thus, the back of base 7 will move further than the front in a given amount of time causing the chair to traverse an arc.

Figure 3 is a perspective view of base 7 after being enclosed in a cover 44. Other covers 46 are disposed over each of the wheels. Rollers 36 and 37 on wheel 26 are shown projecting from beneath cover 46. Covers 44 and 46 prevent an individual using the wheelchair from soiling their clothes or having them become entangled in the rotating wheels, while at the same time protect the motors and other equipment disposed between plates 10 and 20 from the environment. The cover may be a multi-piece configuration as here, or a single piece unit. As shown in Figure 3 a chair 50 is mounted on base 7 on which the operator may sit. The chair includes controls 52 for controlling the height, back tilt, lumbar support, and other features of chair 50. Also mounted on the chair is a joystick 54 which through a suitable control system drives the wheels at necessary rates to move the chair in the desired direction.

Figure 4 is a perspective view showing combination chassis and suspension system 7 in further detail. In the preferred embodiment the axis of rotation of the front wheels is 104.75° forward from the axis of rotation of the rear wheel. In this manner, the cosine of the angle of the front wheels with respect to a line perpendicular to the axis of rotation of the rear wheel is 0.25. This enables more convenient calculation of the necessary rotational rates of the wheels in a microprocessor-based control system.

As shown in Figure 4 the upper plate 10 has been contoured by removal of material from regions 56 and 58 to adjust its stiffness. In addition, the central portion 60 of plate 10 is thicker than in the intervening region separating region 60 from the front 14 and 16 and rear 18 supports. A cylindrical tube 62 extends through the upper plate 10 and -is connected to the lower plate 20 to couple the upper and lower plates together to distribute the loading of the vehicle between them and to provide a connection point for chair 50. In such an embodiment, chair 50 includes a flange on its lower surface to which a cylindrical pipe of smaller diameter than 62 is attached. A slot in the pipe attached to the bottom of chair 50 engages the pin 64 extending through tube 62 to angularly couple chair 50 to base 7 while still enabling removal of the chair for servicing of the base. Batteries 66 are shown mounted from tube 62 to provide a power supply for the motors which drive each wheel. By supporting the batteries from the tube 62, they are shock-isolated, thereby extending their lifetimes. A microprocessor- based control system 68 is suspended from top plate 10 to isolate it from vibration.

In Figure 4, the left front wheel has been removed to show the axle 70, hub 72 and attachment bolts 74 by which the frame of each wheel is secured to

the base 7. The bearing allows axle 70 to rotate in response to signals from the drive motor. The wheels shown in Figure 4 are described in further detail in conjunction with Figures 5 and 6.

Figure 5 is an exploded view of one wheel 22 illustrating the manner in which the wheel is constructed and secured to the base. As shown in Figure 5 the motor gearbox 24 is coupled to support 14 to drive axle 70, thereby rotating hub 72 and wheel 22 attached thereto. The manner in which support 14 is attached to the upper and lower plates 10 and 20 is illustrated. In particular, rigid plates 76 are bolted to the upper and lower surfaces of flexible plates 10 and 20, respectively. The bolts extend through the flexible plates into the support 14. The power amplifier circuitry box 78 is also illustrated.

All ^' three of the motor/gearboxes, their amplifiers and support.members are identical. This simplifies manufacturing and servicing of the wheelchair by providing easier ascension to the economies of scale and a single component for a dealer or service bureau to stock. Furthermore, the supports provide a large, highly thermally conductive heat sinking surface for the power amplifiers, enabling them to run cooler and extending their service life. By including the amplifier on the motor mount/support, each motor assembly is a self-sufficient motive unit requiring only a power source and control signal.

Wheel 22 includes a frame 80, typically aluminum or glass-reinforced nylon. The frame includes a series of projecting members 82, 84, 86 which are adapted to receive bearings in the manner shown in detail in Figure 7. Each roller includes three components, a central portion 88 and end portions 90 which are separated by bearings 92 (shown in Figure 7) . An axle 94 (shown in Figure 6) extends through the two end portions 90 and central portion 88 of each roller

as well as the bearings 92 to provide a completed assembly such as roller assembly 96. The frame/rollers are assembled by bringing the roller assembly 96 into position with respect to projecting frame members 82 and then employing clips 98 to secure the bearings in their proper position in the frame members.

Figure 6 is a side view of wheel 22 illus¬ trating the three large roller assemblies 96 and three smaller roller assemblies 100 coupled to frame 80 in each wheel. The lower roller assembly is shown in cross section to illustrate the central 88 and end portions 90, the axle 94 and bearings 92. Each portion of the roller includes a hub 102 typically comprised of glass-reinforced nylon, aluminum, or other desired material, and an exterior portion 104, typically of synthetic rubber, to provide traction.

The foregoing description of an omnidirectional vehicle base has been made with reference to specific embodiments. It should be

« understood that' these embodiments are provided for purposes of explaining the invention, and are not intended to limit the invention. The invention will be applicable to other vehicles in which a compact integral chassis/suspension system is desired, for example, in materials handling, robots, etc. The scope of the invention may be ascertained from the appended claims.