WHEELCHAIR AND DEVICE FOR ENABLING THE CONVERSION OF A CHAIR WITH CASTORS INTO A WHEELCHAIR

Abstract: A device for enabling the conversion of a chair (4) with castors (10) into a powered wheelchair comprises a structure (32) for attachment to the chair and, mounted on said structure (32), a pair of drive wheels (52), a pair of motors (70) for driving said drive wheels and a control unit (78) for controlling operation of the motors.

Description: WHEELCHAIR AND DEVICE FOR ENABLING THE CONVERSION OF A CHAIR WITH CASTORS INTO A WHEELCHAIR The present invention relates to a powered wheelchair and to a device for enabling the conversion or adaptation of a chair with castors into a powered wheelchair for the disabled. More particularly, but not exclusively, the invention relates to a highly manoeuvrable powered wheelchair for indoor use. Conventional powered wheelchairs having a pair of large driven rear wheels and two smaller front wheels or castors are generally large and cumbersome and are not comfortable or prolonged periods of use. Also, because the axis of rotation lies centrally between the two rear wheels, the front part of the wheelchair swings round in a large arc upon rotation and may collide with and damage furniture, walls doorways etc. Such chairs are not therefore sufficiently manoeuvrable for use in confined spaces. The style and choice of fabrics also tends to be very limited. Although some custom-built powered wheelchairs are available that are better suited for use indoors, these tend to be very expensive. The seats may also be insufficiently comfortable for prolonged use. It is an object of the present invention to mitigate at least some of the aforementioned disadvantages. According to the present invention there is provided a device for enabling the conversion of a chair with castors into a powered wheelchair. Because chairs suitable for conversion, such as office chairs, are readily available and relatively inexpensive, it is possible to provide a powered wheelchair at much reduced cost. Such chairs are generally ergono ically designed and comfortable for prolonged periods, and are available in many different styles and fabrics to suit the taste of the user. The manoeuvrability of the wheelchair is also very good. Advantageously, said device includes a structure for attachment to the chair and, mounted on said structure, at least one drive wheel, a motor for driving said drive wheel and means for controlling operation of the motor, so as to control the speed and/or direction of the chair. The chair may include a base having a plurality of castors mounted thereon, and said device advantageously includes means for attaching said structure to said base. The base may comprise a plurality of castor arms, said structure advantageously being adapted to engage one or more of said castor arms. The chair may include a central support shaft and said device advantageously includes means for attaching said structure to said shaft and a plurality of castors mounted on said structure. In this form, the original seat base is not used. The device advantageously includes two drive wheels mounted substantially centrally (from front to rear) on opposite sides of the chair. The chair may have a central support shaft and said drive wheels advantageously engage the ground at locations slightly forwards of, or substantially in line with, said support shaft. This ensures very good manoeuvrability and allows the chair to rotate substantially about its central axis. Advantageously, said drive wheels engage the ground at locations that lie within the circle defined by the locations of " the castors. The wheelchair thus occupies minimal floor space. The device advantageously includes resilient biasing means for urging the or each drive wheel into positive engagement with the ground. This allows the wheelchair to traverse irregularities in the floor without the drive wheels losing traction. Alternatively, the device may be provided with 5 resilient (e.g. pneumatic) tyres for the same purpose, or the wheelchair may be provided with sprung castors. According to a second aspect of the invention there is provided a wheelchair including a seat, a support structure 0 for said seat, a plurality of castors attached to said support structure and arranged to support the wheelchair, and at least one drive wheel for driving said wheelchair. The wheelchair may include two drive wheels mounted on 5 opposite sides of the chair. Advantageously, the support structure includes a central support shaft and said drive wheels engage the ground at locations slightly forwards of, or substantially in line 0 with, said support shaft. Advantageously, said castors are arranged substantially equi-angularly around said seat and engage the ground at locations lying substantially on the circumference of an 25 imaginary circle. Advantageously, the or each drive wheel engages the ground at a location lying within said imaginary circle. 30 The wheelchair advantageously includes resilient biasing means for urging the or each drive wheel into positive engagement with the ground. An embodiment, of the invention will now be described, by 3.5 way of example, with reference to the accompanying drawings, of which: Fig. 1 is a side elevation of a chair with castors that has been converted into a powered wheelchair; Fig. 2 is a sectional view of the lower part of the wheelchair, on line II-II of Fig. 1; Fig. 3 is a side elevation, partially in section, on line III-III of Fig. 2; Fig. 4 is a perspective view of one driving wheel, and Fig. 5 is a perspective view showing a detail of the support shaft for the seat. As shown in Figs. 1 and 2, the present invention provides a device 2 for converting an existing chair, for example a standard office chair 4, into a wheelchair. Such a chair 4 typically has a star-shaped base 6 with five arms 8a-8e, each of which has a castor 10 at its outer end, a telescopic central support shaft or column 12 and a seat 14 having a base 16, a back rest 18 and two arms 20. The telescopic column 12 consists of an upper part 12a and a lower part 12b, and conventionally allows for adjustment of the seat height and rotation of the seat about the axis of the column. In the present invention, rotation of the seat is prevented for safety reasons by means of a mechanism 22, which is shown in more detail in Fig. 5. This mechanism 22 consists of a vertical rod 24 that is attached by means of a clamp 26 to the lower part 12b of the column, and which passes through a slot 28 in a second clamp 30 attached to the upper part 12a of the column. Relative rotation of the upper and lower parts 12a,12b is thus prevented, without impeding operation of the height adjustment mechanism. Returning to Figs. 1 and 2, the chair 4 is converted into a powered wheelchair by means of a conversion device 2 comprising a support structure 32 that is securely attached, for example by means of bolts 34, to the arms 8a- 8e of the base 6. The support structure 32 includes a forward part 32a and a rear part 32b that together form a boss 36 in which the column 12 of the chair is received. The forward part 32a of the support structure 32 comprises a first boss segment 36a that surrounds and engages a front portion of the column 12, four arms 38a-d that extend radially from the boss 36 at angles mirroring those of the castor arms 8a-8d and a substantially rectangular frame 40, comprising a front rail 40a and two side rails 40b,40c that connects the arms 38a-d to one another at their outer ends. Each of the arms 38a-d is provided at its outer end with a down-turned leg 42 that stands on one of the castor arms 81-8d and is connected thereto by a bolt 34. A footrest 44 is pivotably connected to the front rail 40a by means of a hinge 46. The rearward portion 32b of the support structure 32 comprises a second boss segment 36b that, with the first segment 36a, completes the central boss 36. A pair of short arms 48a,48b extend radially from the boss 36 at an included angle of approximately 144°, thus mirroring the angle of the two arms 38a, 38d to which the short arms 48a,48b are bolted. Extending rearwardly from the short arms 48a,48b is a small rectangular frame 50. A third arm 38e bisects the angle between the short arms 48a,48b and passes underneath the frame 50. The arm 38e is provided at its outer end with a down-turned leg 42, which stands on the fifth castor arm 8e and is connected thereto by a bolt 34. The support structure 32 is provided on either side with a drive wheel 52, which is shown in more detail in Figs. 3 and 4. The drive wheel 52 is connected to one of the side rails 40b,40c by means of a suspension unit 54 comprising a sliding plate 56 that is mounted for vertical movement in a π-shaped frame 58. A pair of compression springs 60, located around telescoping tubes 62, are provided between the upper edge of the plate 56 and the upper part 58a of the π-shaped frame to urge the drive wheel 52 resiliently into positive engagement with the ground. Downwards movement of the wheel 52 is limited by a pair of stops 64 that engage the lower edge of the plate 56. The axle 66 of the wheel 52 is received in a bearing (not shown) mounted on the plate 56 and is connected to a drive unit 68 comprising an electric motor 70 and a gearbox 72. The two motors 70 are electrically connected, via an electronic controller 74, to a rechargeable electric power source 76, for example a lead-acid battery, that is secured to the small rectangular frame 50. A control unit 78, for example a joystick, is mounted on one of the arms 20 of the wheelchair and is connected by means of a cable 80 to the electronic controller 74, to control the delivery of current to the motors 70, thereby controlling the speed and direction of the wheelchair. In operation, each motor 70 may be driven independently and is controlled by means of the control unit 78. The wheelchair may thus be driven forwards of backwards or, by driving the drive wheels 52 in opposite directions, it may be caused to rotate. Because the axles 66 of the drive wheels 52 are approximately in line with (or slightly in front of) the central column 12, the wheel chair may be rotated virtually about its central axis. The wheelchair is therefore highly manoeuvrable and well-suited for use in confined spaces. Various modifications of the invention are of course possible. For example, the support structure 32 may consist of a single part rather than two separate parts that have to be bolted together, and may take the form of a platform, for example of pressed steel, rather than a frame. This reduces production costs and may also increase the rigidity of the structure. A one piece structure is possible because in most office chairs the column 12 is only an interference fit in the base 6 and the seat 14 and may be removed therefrom simple by tapping the one end of the column 12 with a hammer. The column can then be inserted through the boss 36 in the frame and reinserted into the base 6. The structure may also include a skirt or rubbing strip to prevent objects becoming trapped between the castor arms 8a-e. A further possibility is that instead of attaching the support structure 32 to the base 6 of an office chair, a structure may be provided that replaces the base 6 entirely. The structure would in that case be provided with castors as well as the drive wheels 52, and the boss 36 may be tapered to receive the column 12 of the seat with an interference fit. The mechanism 22 for preventing unwanted rotation of the seat 14 may take different forms. For example, the mechanism may consist of a "goalpost" arrangement comprising two upright members of square-section steel tubing connected to one another at their upper ends by a crossbar of similar tubing. The cross bar would be attached to the upper part of the support shaft underneath the seat 14 and the two uprights would extend downwards through apertures in the support structure 32. The uprights would be able to move vertically through the apertures to allow for height adjustment but would prevent rotation of the seat. An advantage of the "goalpost" arrangement is that an arm could be attached to one of the uprights, to carry the control unit 78. As the control unit 78 would not then have to be attached to one of the arms of the chair 14, the choice of chairs that could be adapted using the conversion kit would be extended still further. For example, as well as standard office type chairs, the device could be used with bespoke chairs designed especially for the needs of particular users. The suspension mechanism 54 may also differ from that shown in the drawings. For example, instead of a sliding plate arrangement, the drive wheels may be mounted on swing arms that are urged into contact with the ground by springs. Other possible suspension arrangements will be apparent to persons skilled in the art. It may be sufficient in some cases for the drive wheels to be provided with pneumatic tyres, which themselves provide a degree of compensation for uneven floor surfaces. It is envisaged that instead of, or as well as, selling a device for converting existing chairs into wheelchairs, wheelchairs having the basic features described above may be manufactured and sold as finished units. The invention is intended to include such wheelchairs. Although the wheelchair is intended primarily for use indoors where the floor surfaces are relatively smooth, it may readily be adapted for outdoor use by incorporating larger castors and drive wheels, a more powerful propulsion unit and a suspension system that allows for an increased range of vertical movement of the drive wheels. Instead of a pair of drive wheels, a pair of driven rollers may be provided, or alternatively there may be a single steerat_e drive wheel or roller. Although the wheelchair may have more or fewer than five castors, that is the preferred number for stability and economy of manufacture.

Claims: CLAIMS 1. A device for enabling the conversion of a chair with castors into a powered wheelchair. 2. A device according to claim 1, said device including a structure for attachment to the chair and, mounted on said structure, at least one drive wheel, a motor for driving said drive wheel and means for controlling operation of the motor. 3. A device according to claim 2, wherein said chair includes a base having a plurality of castors mounted thereon, said device including means for attaching said structure to said base. 4. A device according to claim 3, wherein said base comprises a plurality of castor arms, said structure being adapted to engage one or more of said castor arms. 5. A device according to claim 2, wherein said chair includes a central support shaft, said device including means for attaching said structure to said shaft and a plurality of castors mounted on said structure. 6. A device according to any one of the preceding claims, including two drive wheels mounted on opposite sides of the chair. 7. A device according to claim 6, wherein said chair has a central support shaft and said drive wheels engage the ground at locations substantially in line with, or slightly forwards of, said support shaft. 8. A device according to claim 6 or claim 7, wherein said drive wheels engage the ground at locations that lie within the circle defined by the locations of the castors. 9. A device according to any one of the preceding claims, including resilient biasing means for urging the or each drive wheel into positive engagement with the ground. 10. A wheelchair including a seat, a support structure for said seat, a plurality of castors attached to said support structure and arranged to support the wheelchair, and at least one drive wheel for driving said wheelchair. 11. A wheelchair according to claim 10, including two drive wheels mounted on opposite sides of the chair. 12. A device according to claim 11, wherein said support structure includes a central support shaft and said drive wheels engage the ground at locations slightly forwards of, or substantially in line with, said support shaft. 13. A wheelchair according to any one of claims 10 to 12, wherein said castors are arranged substantially equi- angularly around said seat and engage the ground at locations lying substantially on the circumference of an imaginary circle. 14. A wheelchair according to claim 13, wherein the or each drive wheel engages the ground at a location lying within said imaginary circle. 15. A wheelchair according to any one of claims 10 to 14, including resilient biasing means for urging the or each drive wheel into positive engagement with the ground.

Inventors: WILSON BRIAN, WILSON, BRIAN
Applicants: WILSON BRIAN, WILSON, BRIAN
Application year: 1997
Main classification: A61G5
IPC codes: A61G5