WO2002046031A1

WO2002046031A1 - Remote-operated multi-directional transport vehicle

Info

Publication number: WO2002046031A1
Application number: PCT/US2000/032908
Authority: WO
Inventors: Eric J. Allard
Original assignee: Allard Eric J
Priority date: 2000-12-04
Filing date: 2000-12-04
Publication date: 2002-06-13
Also published as: AU2001218155A1

Abstract

A multi-directional wheeled transport vehicle for propelling components disposed thereon which has a structural base consisting of a chassis (20) and a top (22) with axles (44, 46 and 48) rotatably affixed to the chassis. A bi-directional wheel (52) is located on each axle with front and rear wheels positioned longitudinally and the intermediate wheel located in a lateral position between the front and rear wheel. Each wheel consists of at least one hub (54), spokes (58) a circumferencial ring (68) attached to the extending end of the spokes and a series of cylindrical rollers (70) and spacers (62) mounted onto the ring. The preferred embodiment consists of four identical hubs and rings etc. making up one complete wheel. A pair of opposed drive trains (74/74') simultaneously rotate each front and rear wheel and an intermediate drive train (98) rotates the lateral wheels permitting the vehicle to move forward and aft and also to one side or the other. The drive trains are preferably powered by electric motors (80/80' and 80') using batteries (104) and control means in the form of propulsion command and guidance controls (106).

Description

REMOTE-OPERATED MULTI-DIRECTIONAL TRANSPORT VEHICLE

TECHNICAL FIELD

The invention pertains to wheeled transport vehicles in general and more particularly, to a remote-operated, transport vehicle platform that utilizes bi-directional wheels driven by electric motors using remote control.

BACKGROUND ART

Remote-operated multi-directional transport vehicles also referred to as mobile robots. Mobile robots have found use in a variety of applications. Aside from the movie industry, which often portrays robots capable of highly agile locomotion, robots are also used for moving material within a manufacturing environment, hazardous waste disposal, handling radioactive components, assisting police bomb squads, working with firefighters, exploring underwater or outerspace environments, acting as a security or military sentry.

A variety of transport systems have been developed to provide mobility to robots. A simple and commonly found transport system comprises an undercarriage or platform upon which the robot is transported, wherein the platform is supported by a row of wheels positioned on either side of the platform. In other configurations, the wheels are replaced by tank tracks. The tank track, is a continuous, flexible tread passing over cogged wheels turning inside the tread. In a more interesting transport system, the tank tracks are substituted by outstretched, articulating legs. The movement of these legs are actuated by a network of springs, solenoids, dampers and the like.

A search of the prior art did not disclose any patents that possess the novelty of the instant invention, however the following U.S. patents are considered related: Patent Number Inventor Issue Date

4,101,004 Oltman Jul. 18, 1978

4,168,468 Mabuchi, et al. Sep.18, 1979

4.335.899 Hiscock Jun. 22, 1982 4,621,562 Carr, et al. Nov. 11, 1986

4.823.900 Farman Apr. 25, 1989 4,993,912 King Feb. 19, 1991 5,323,867 Griffin, et al. Jun. 28, 1994

Oltman in U.S. patent 4,101,004 teaches a drive and steering apparatus for a vehicle having ground engaging wheels or tracks on each side. A shaft is rotatably connected to the frame and rotated by a motor. Each side has a drive assembly using the shaft in conjunction with a clutch and brake. Control is provided to position the clutch and brake, including both a neutral position and a drive position.

Patent No. 4,168,468 issued to Mabuchi, et al. is for a radio control system with a power supply, two electric motors and a transmitter mounted on a model toy for radio control. The transmitter emits a control pulse representing a signal "1" and a control pulse representing a signal "0"with a d-c current supplied to the motors.

Hiscock in U.S. patent 4,335,899 also discloses a wheel drive for a toy vehicle. A rear driving wheel for a pedal car includes a ground engaging portion formed by a plurality of freely rotatable rollers projecting through a circumferential portion of the wheel hub.

The wheel is positioned such that the axis of rotation is at right angles to the axis of rotation of the hub.

Carr, et al. in U.S. patent 4,621,562 teaches a remote-controlled robot vehicle that has two pairs of wheels mounted on a support secured to the vehicle. The wheels are mounted for pivotal movement on a horizontal axis extending longitudinally to the vehicle.

The wheels located on the same side of the vehicle are capable of being driven in synchrony. Patent No. 4,823,900 issued to Farman is for a four-wheeled-driven wheelchair having a frame and seat with rear wheels mounted on opposite sides of the frame. A pair of front compound wheels are also mounted on opposite sides of the frame and are capable of rotating in a plane parallel to the side of the frame and include castor wheels mounted around the perimeter to permit the front end to roll freely from side to side in addition to forward and backward. The wheels are interconnected to turn in unison by differential control using a joy stick.

U.S. Patent No. 4,993,912 of King is directed to a stair climbing robot that includes a chassis with powered opposed front wheels along with two pairs of rear wheels, with each pair rotatably mounted on a beam at opposite ends of the chassis. A drive motor rotates each pair of wheels in the same direction at a predetermined velocity along with the beams. The stair climbing ability includes the steps of rotating the beams in a forward direction while causing each pair of rear wheels to rotate in the opposite direction at the same velocity. In this way forward movement is achieved by action of the front wheels and the rotating beams along with the rotational velocity of the rear wheels relative to the terrain.

Allar and Griffin et al. in U.S. patent 5,323,867 discloses a robot transport platform having a base with three wheels on each side. The two wheels located at the front and rear are omnidirectional and the single wheel that is located in-between is a conventional wheel. The omnidirectional wheels have staggered rows of spherical balls rotatably mounted to the circumference of the wheel's hub. The rollers are mounted to annular shafts that circumscribe the circumference of the hub and are supported in an overlying position over the hub by radially-extending spokes. Torque is transferred to the wheels with gear boxes, chains and cogged drive belts. Controls are furnished by a radio receiver and servo controllers furnish regulation to battery-driven motors, which provide power.

Prior art does utilize robot vehicles and platforms that use omnidirectional wheels, however not exclusively and not with cylindrical rollers which allow bi-directional movement. DISCLOSURE OF THE INVENTION

From the above described prior art it can be plainly seen that a need exists for a highly mobile vehicle or platform that is capable of carrying considerable weight while being agile and capable of maneuvering in extremely close quarters. The invention is an improvement on previously issued Patent No.5,323,867, in which the inventor was a joint participant. While the original invention was successful, there is room for improvement in a number of areas. The applicant's previous patent utilized six wheels in line with three wheels on each side. The front and rear wheels, on each side, are omnidirectional and the middle wheel on each side consists of a conventional type wheel. This linear wheel arrangement functioned properly permitted the transport platform vehicle to be guided in the desired direction by increasing the speed on one side or the other for directional movement, and the vehicle could be turned completely around by reversing rotation of the wheels on opposite sides. The improvement has, however, gone one step beyond this ability in that the middle wheels are not in line with the others; instead they are at right angles to the front and rear wheels, thus permitting the vehicle to move laterally without rotating the platform at all. This feature is particularly useful when maneuvering in extremely close quarters, and with such applications as when a motion picture or television camera is mounted on the platform, since no rotation of the camera is necessary to compensate for the platform's rotation when sharply changing direction. It will be clearly seen that this object of improvement is beneficial in numerous ways, creating an entirely new and useful form of navigational steering. The invention in its improved state may now zig zag or follow a diagonal direction in the same manner as a conventional drive system. For any vehicle to be propelled completely sideways, in combination with conventional steering using separate drives on side wheels, is indeed unique and novel. The right angular movement of the vehicle is accomplished using six wheels of the same construction, having a series of rollers rotatably disposed on a ring held securely with spokes attached to a hub in concert with other like rings and rollers. A pair of front wheels and rear wheels are positioned the same as a conventional vehicle, however, a pair of middle wheels are positioned between the front and rear wheels with each set having their own propulsion system. Since the wheels have rollers that are transverse to the direction of rotation of the wheel, they create a conventional footprint and operate as a normal wheel when the vehicle is propelled longitudinally. When the vehicle is directed to move sharply to the side, the middle wheels create the motivation direction and the front and rear wheels become stationary, with the rollers on the bottom rotating, thereby permitting the vehicle to move sideways under the urging of the middle wheels.

It should also be noted that the maneuverability of the vehicle in its original form has not changed, as it may still rotate completely around in a circle; only an added feature has been developed that expands the utility of the invention. Another change that has been made to accomplish this improvement is that rollers replace balls on the rings that are attached to the spokes. While this feature was originally designed to permit the front and rear wheels to pivot without rubbing when the middle wheels rotate, it has been found that the use of rollers does not effect this functional operation, as the wheel's _; still roll in the appropriate direction. Further the roller shape permits the wheels to maintain traction in their transverse position relative to the wheel's rotation.

An important object of the invention is that not only are the rubber balls replaced with rollers, but the rollers include radial bearings on each end which interface with the ring, thus creating a much more secure mount while allowing minimal friction when the wheel is stationary with the platform moving. The balls in the inventor's previous patent utilized a bushing of a resilient material such as nylon or some other polymer, whereas the bearings in the improvement consist of metallic balls in conventional ball bearing. These bearings are more frictional resistant, have a greater life expectancy have an increased load bearing capability. Another object of the invention is the simplicity of the drive system. In the past there have been two complex motor systems, that have been used to require gear boxes, chain drives etc. These system while the instant invention has three simple belt-driven systems, two of which are duplicated. All three systems utilize conventional synchronous belt drives, which provide positive grip along with smooth and quiet operation.

Still another object of the invention is directed to the ability of the plurality of rollers to create a secure gripping surface over almost any type of terrain, as a number of rollers are in contact with the surface at the same time and their shape with the exposed ends provide an extended surface contact with the ground and bite into the surface easily. If the surface is hard and flat, the wheels also function properly, as the rollers are equally spaced apart each roller is not always parallel with the flat surface but a portion of the extended surface is always touching, thus making a smooth transition between rollers as the wheel rotates.

Yet another object of the invention is that the platform may be shorter in length than other six-wheeled vehicles since the middle wheel is positioned at right angles to the direction of travel. This advantage is easily realized in applications where size is significant and maneuverability is of the utmost importance.

These and other objects and advantages of the present invention will become apparent from the subsequent detailed description of the preferred embodiment and the appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a partial isometric view of the preferred embodiment with the top partially cut away to illustrate elements housed within.

FIGURE 2 is a partial isometric view of the preferred embodiment with the top removed showing the internal elements of the chassis. FIGURE 3 is a front view of the preferred embodiment.

FIGURE 4 is a side view of the preferred embodiment.

FIGURE 5 is a plan view of the preferred embodiment with the top, including its related structure, removed for clarity. FIGURE 6 is a cross-sectional view taken along lines 6-6 of FIGURE 5.

FIGURE 7 is a cross-sectional view taken along lines 6-6 of FIGURE 5.

FIGURE 8 is a partial isometric view of one of the bi-directional wheels completely removed from the invention for clarity.

FIGURE 9 is a cross sectional view taken along lines 9-9 of FIGURE 8. FIGURE 10 is an exploded view of one of the bi-directional wheels completely removed from the invention for clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the invention is presented in terms of a preferred embodiment. The preferred embodiment is shown in FIGURES 1 through 10, and is comprised of a structural base having a chassis 20 and a load bearing top 22. The chassis consists of a bottom 24, a right side 26, a left side 28, a front 30, a rear 32, a forward center bulkhead 34, a rearward center bulkhead 36, and a right partition 38 and a left partition 40 that are at right angles to the bulkheads 34 and 36. FIGURES 2-7 illustrate the construction of the chassis 20, which may be of sheet metal structure with flanged interface joints, welded plates, structural steel or tubular frame with sheet metal panels, fiberglass sheets bonded together, injection-molded thermoplastic or any other conventional mode of fabrication. Further, the load bearing top 22, is attached to the chassis 20 and if it is in a flat configuration, it will contain a plurality of access openings 42 for entry into chassis. If the top 22 is in a different configuration, for example as a camera mount, the structure will be formed in such a manner as to leave spaces for access into the interior of the chassis 20 or would at least have the access openings 42 within the enclosure itself. Since the invention may have many and varied applications, a structure on top of the chassis is designed to fit the type of function required, which could range from a simple flatbed, as illustrated in FIGURE 1, to a complex structure for robotics. A pair of lateral opposed front axles 44, a pair of lateral opposed rear axles 46 and a pair of longitudinal intermediate axles 48 that are between the front and rear axles, are rotatably affixed to the chassis 20. These axles are retained on each end by a flanged pillow block 50 which is attached to each respective side 26 and 28, partition 38 and 40 and bulkhead 34 and 36, as depicted best in FIGURE-5. The flanged pillow blocks 50 are well known in the art and normally have a single row of self-aligning, deep-groove, ball bearings, which are double sealed with a cast iron mono-block housing preferably in the two-bolt flange configuration, as illustrated in FIGURES 1, 2, 5, 6 and 7. While a pillow block 50 is preferred, the four bolt style or any other type may be used with equal ease and dispatch according to the size of the shaft and load requirements. The axles 44, 46, and 48 are preferably a conventional, metallic, round shaft type having keyway's for machine keys held in place with set screws in the pillow blocks 50.

A bi-directional wheel 52 is disposed on each axle 44, 46, and 48 for mobility in two directions: rotational forward and rearward, and also sideways, thereby permitting the transport vehicle to be propelled forward, aft and sideways without turning or rotating the platform. The bi-directional wheel 52 is illustrated in all of the figures, however, FIGURES 8-10 show the wheel by itself in specific detail. Each wheel 52 includes a hub 54 which has a polygonal-shaped outer surface and a internal keyway 56 for interfacing with the respective axles 44, 46, and 48. The preferred embodiment utilizes a centered hexagonal-shape hub 54 for attachment to the axle, as shown in FIGURE 9. A plurality of spokes 58 are connected to and extend from the hub 52 in a radial direction, as shown in FIGURES 9 and 10, and are connected to the hub 52 with a plurality of attaching plates 60 on one end and to a plurality of split spacers 62 on the other. The spokes 58 are formed in mated pairs, with one on each side of the spacer 62, each spoke slips into pockets 64 side by side formed within the hub 54. The spokes 58 are held tightly together by the attaching plates 60 on one end and by threaded fasteners 66 connecting the spokes on opposite sides of the spacers 62.

A circumferencial ring 68 is attached to the extending end of the spokes 58 through the split spacers 62, thus forming the radial portion, or rim, of the wheel 52. The ring 68 is preferably formed of a round, metallic bar that is bent radially into a continuous circle, however, the circumferencial ring 68 is preferably severed in one place to facilitate assembly of the balance of the wheel by springing the ring into an offset position, as shown in FIGURE 10. The open ends of the ring 68 are held together by one of the split spacers 62 after assembly is completed, with the threaded fasteners 66 creating a structural bond.

A plurality of cylindrical rollers 70 are rotatably mounted onto each ring 68 in spaced orientation, as illustrated in FIGURE 9. The rollers 70 may be made of a variety of materials, however, a structural thermoplastic is preferred such as polyurethane which is known to be as strong as steel and as resilient as rubber. While this material is preferred, any other type of wheel material may be used such as mold over sleeve solid granular rubber, solid or mold-on neoprene or even all-forged steel or cast iron. In any case each cylindrical roller 70 has a radial bearing 72 disposed within each opposite end to permit the rollers to freely rotate. These bearings 72 are illustrated in FIGURE 9 and may be any type, with single row ball bearings preferred. It should be noted that the inner race of each bearing 72 is slightly oversized for the diameter of the ring 68 to allow them to slip over the radial ring in tandem with the split spacers 62 in between, as shown.

While one ring 68, with its cylindrical rollers 70, spacers 62, spokes 58 and hub 54 has been described individually, there may be more than one used in concert to make up the bi-directional wheel 52. As the drawings depict, four individual rings 68 with their accompanying elements are preferred, however, it should not be construed as being limiting to this specific number, as others may function equally well in specific applications.

Further, it should be noted that each roller 70 is positioned such that rollers in adjoining rings 68 are spaced apart to preclude alignment with adjacent rollers for gripping surfaces upon which the platform is operating. FIGURES 1-9 illustrate this feature which permits not only gripping of the surface to which the vehicle is operating, but also spreads a load to adjoining rollers and smoothes out the peripheral outline of the wheel.

A pair of opposed drive trains 74 and 74' each simultaneously rotate one front wheel 76 and 76' and one rear wheel 78 and 78 upon demand. Each opposed drive train 74 and 74' consists of an electric motor 80 and 80', including a shaft 82 and 82', with a motor drive pulley 84 and 84' connected to each motor shaft. A motor-driven pulley 86 and 86' is connected to only one front 44/44' or rear axle 46' as shown in FIGURES 5-7. Further, a front shaft pulley 88 and 88' is connected upon each opposed front axle 44 and 44'; and a rear shaft pulley 90 and 90' is connected upon each opposed rear axle 46 and 46'. It may be seen that the drive trains 74 and 74' are identical except they are or mirror images of the other as illustrated best in FIGURE 5.

The motor drive pulleys 84 and 84', along with the motor driven pulleys 86, and 86' are each connected with a first power transmitting belt 92 and 92'. Further the shaft front pulleys 88 and 88', along with the rear pulleys 90 and 90'on each opposed front axles 44 and 44' and rear axles 46 and 46', are each connected with a second power transmitting belt 94 and 94' to transmit rotational torque from the motors 80 and 80' to both wheels 52 simultaneously. A pair of idlers 96 are positioned in line with the pulleys 88/88' and 90/90' for maintaining tension therebetween. An intermediate drive train 98 simultaneously rotates each intermediate bidirectional wheel 100 and 100' upon demand. This intermediate drive train 98 consists of a motor 80" including a shaft 82" with a motor drive pulley 84"on the shaft 82", and a motor-driven pulley 86" positioned on each intermediate axle 48. Further, the driven pulleys 86"on each intermediate axle 48 and 48' are connected together with a third power transmitting belt 102 which includes a pair of idlers 96 for maintaining tension between the driven pulleys 86".

The preferred belt 92/92'and 94/94'and 102 are the synchronous type, which is also known as a timing belt, and the pulleys contain involuted teeth for meshing with the belt to provide a positive non-slip grip. It should be noted however, that other types and styles of drive trains may be employed for motivation of the wheeled transport vehicle. The electric motors may drive the wheels by chains, v-belts, flat belts and the like, or, internal combustion engines may be utilized.

In the preferred embodiment, electrical storage means in the form of a battery 104 may be disposed at a convenient location within the chassis 20 for furnishing electrical power to the drive trains 74/74' and 98. Also, electrical control means in the form of propulsion command and guidance controls 106 are also conveniently disposed within the chassis for furnishing guidance to the drive trains 74/74'and 98 for propulsion.

As previously mentioned, the opposed drive-trains 74 and 74', along with the intermediate drive train 98, may optionally use an internal combustion engine. If this is the case the electrical storage means is a starting battery and the electrical control means comprise an engine on/off ignition system, clutches, brakes and guidance controls. It should be noted that the engine and its auxiliary equipment are not shown since they are so well known in the art and are in common usage throughout the world in conventional motor driven vehicles.

While the invention has been described in complete detail and pictorially shown in the accompanying drawings, it is not to be limited to such details, since many changes and modifications may be made to the invention without departing from the spirit and scope thereof. Hence, it is described to cover any and all modifications and forms which may come within the language and scope of the appended claims.

Claims

1. A remote-operated multi-directional wheeled-transport vehicle for propelling components disposed thereupon comprising: a) a structural base having a chassis and a weight bearing top, b) a pair of laterally opposed front axles, a pair of lateral opposed rear axles and a pair of longitudinal intermediate axles between the front and rear axles with all of the axles rotatably affixed to said chassis, c) a bi-directional wheel disposed upon each axle for mobility, with each bi-directional wheel having, 1) at least one hub for attachment to an axle,

2) a plurality of spokes connected to and extending from the hub in a radial direction,

3) a circumferencial ring attached to the extending end of the spokes, and

4) a plurality of cylindrical rollers rotatably mounted onto each circumferencial ring in spaced orientation, d) a pair of opposed drive trains each simultaneously rotating one front and one rear bidirectional wheel upon demand, e) an intermediate drive train simultaneously rotating each intermediate bi-directional wheel upon demand, f) electrical storage means disposed within the chassis for furnishing electrical power to the drive trains, and g) electrical control means disposed within the chassis for furnishing guidance to the drive trains for propulsion.

2. The transport vehicle as recited in claim 1 wherein said chassis further comprises a bottom, a right side, a left side, a front, a rear, a forward center bulkhead, a rearward center bulkhead, a right partition and a left partition at right angles to the bulkheads.

3. The transport vehicle as recited in claim 2 wherein said weight bearing top is attached to the chassis wherein said weight bearing top further comprises a plurality of access openings for entry into the chassis.

4. The transport vehicle as recited in claim 2 wherein said front axles, rear axles and intermediate axles are retained by a flanged pillow block attached to respective sides, partitions and bulkheads.

5. The transport vehicle as recited in claim 1 wherein said bi-directional wheels permit the transport vehicle to be propelled forward, aft and sideways without turning or rotating the vehicle.

6. The transport vehicle as recited in claim 1 wherein said hub has a polygonal shaped outside surface and are internal keyway to interface with said axle.

7. The transport vehicle as recited in claim 1 wherein said spokes are connected to the hub with a plurality of attaching plates on one end and to a plurality of split spacers on the other.

8. The transport vehicle as recited in claim 1 wherein said circumferencial ring is severed in one place to facilitate assembly of said cylindrical rollers by springing the ring into an offset position.

9. The transport vehicle as recited in claim 1 wherein each cylindrical roller has a radial bearing disposed within each opposite end to permit the rollers to freely rotate.

10. The transport vehicle as recited in claim 1 wherein each roller is positioned such that rollers in adjoining rings are spaced apart to preclude alignment with adjacent rollers for gripping surfaces upon which the vehicle is operating.

11. The transport vehicle as recited in claim 1 wherein each opposed drive train comprises an electric motor, including a shaft, with a motor drive pulley connected upon the motor shaft, a motor driven pulley connected upon only one front or rear axle and a front shaft pulley connected upon each opposed front axle and a rear shaft pulley connected upon each opposed rear axle.

12. The transport vehicle as recited in claim 11 wherein said motor drive pulley and said motor driven pulley is connected with a first power transmitting belt, also both shaft front and rear pulleys on each opposed front and rear axle are connected with a second power transmitting belt to transmit rotational torque from the motors to both wheels simultaneously, further a pair of idlers are positioned in line with the pulleys for maintaining tension therebetween.

13. The transport vehicle as recited in claim 1 wherein said intermediate drive train comprises a motor including a shaft, with a motor drive pulley upon said shaft, and a motor driven pulley upon each intermediate axle.

14. The transport vehicle as recited in claim 13 wherein said drive pulley on each intermediate axle are connected together with a third power transmitting belt including a p air of idlers for maintaining tension therebetween.

15. The transport vehicle^" as recited in claim 1 wherein said electrical storage means is a battery.

16. The transport vehicle as recited in claim 1 wherein said electrical control means further comprises propulsion command and guidance controls.

17. The transport vehicle as recited in claim 1 wherein said opposed drive trains and said intermediate drive train further comprises an internal combustion engine and said electrical storage means is a starting battery with said electrical control means further comprising an engine on/off ignition system, clutches, brakes and guidance controls.

18. A remote-operated multi-directional wheeled transport vehicle for propelling components disposed thereupon comprising: a) a structural base having a chassis and a weight bearing top, b) a pair of lateral opposed front axles, a pair of lateral opposed rear axles and a pair of longitudinal intermediate axles rotatably affixed to said chassis between the front and rear axles, c) a bi-directional wheel rotatably disposed upon each axle, wherein each bi-directional wheel constructed in an identical manner, permitting the transport platform to be propelled forward, aft and sideways without turning the chassis, d) a pair of opposed drive trains each simultaneously rotating one front and one rear wheel upon demand, e) an intermediate drive train simultaneously rotating each intermediate wheel upon demand, and f) means to propel and remotely guide the platform.

19. A remote-operated multi-directional wheeled transport vehicle for propelling components disposed thereupon comprising: a) load bearing means, b) a pair of opposed front axles with bi-directional wheels facing longitudinally, a pair of opposed rear axles with bi-directional wheels facing longitudinally and a pair of intermediate axles with bi-directional wheels facing laterally between the front and rear axles, with each axle rotatably affixed to said load bearing means, c) a pair of opposed drive trains each simultaneously rotating each front wheel and rear wheel, d) an intermediate drive train simultaneously rotating each intermediate wheel, and e) means to propel and remotely guide the platform.

20. The transport vehicle as recited in claim 19 wherein said bi-directional wheels permit the transport vehicle to be propelled forward, aft and -sideways without turning or rotating the vehicle.