GB2374322A

GB2374322A - Electric wheelchair provided with stabilising means

Info

Publication number: GB2374322A
Application number: GB0108744A
Authority: GB
Inventors: David Oliver Batty; Thomas William Wilson; James William Taylor
Original assignee: Remploy Ltd
Current assignee: Remploy Ltd
Priority date: 2001-04-06
Filing date: 2001-04-06
Publication date: 2002-10-16
Also published as: GB0108744D0

Abstract

A wheelchair, particularly an electric wheelchair, and a stabilising attachment therefor. An electric wheelchair includes, or a frame (1) for attachment to the rear of an electric wheelchair includes, at least one stabilising wheel (2) rotatably mounted about its axis (3); wherein the axis (3) is moveable with respect to the frame (1) or wheelchair. The wheelchair or attachment may include damping means (5) for damping movement of the axis (3). Alternatively the wheelchair or frame (1) may include means (6) for moving the axis (3) from a first position to a second position and means for locating the wheel (2) in the second position.

Description

ELECTRIC WHEELCHAIR AND STABILISING ATTACHMENT THEREFOR The present invention concerns a wheelchair, particularly an electric wheelchair, and a stabilising attachment therefor. Most electrically powered wheelchairs rely upon a control unit through which the disabled occupant manages the operation of the motorised rear drive wheels to control speed, direction and braking of the wheelchair. The contact grip of the driving wheels to the surface over which the wheelchair is travelling is an important condition in maintaining this control. If skidding of the rear drive wheels occurs, occupant control of the wheelchair is adversely affected.

The degree of wheel grip with the surface is often referred to as traction, and is a function of the load carried by the rear drive wheels, the efficiency of the tires, and the co-efficient of friction of the surface which the driving wheels are in contact with. On rear wheel drive electrically powered wheelchairs, optimum traction occurs when the centre of gravity of the occupant and the vehicle is directly over the rear drive wheels.

However, there are other considerations which may take preference over weight positioning for optimum traction of the driving wheels, such as clinical posture, ergonomics, environmental access, and stability, which means that optimum traction is seldom achievable in practice.

The angle of slope which a wheelchair is travelling over can adversely affect traction, and consequently the safe operation of the wheelchair. On rear wheel drive electrically powered wheelchairs, this is as follow :- If the wheelchair is going downhill, the front wheels carry much of the combined vehicle and occupant weight. On

steep slopes, this can have the effect of the rear driving wheels losing grip contact, resulting in loss of occupant control.

If the wheelchair is going uphill, the rear wheels carry much of the combined vehicle and occupant weight. On steep slopes, or when coming into contact with obstacles such as kerbs, this can result in the wheelchair tipping over backwards.

These two conditions occur to a degree in all outdoor environments. Their resolution is a compromise of trying to design a balance between two opposite demands.

A wheelchair which has a long wheel base, with the rear wheels set back for a high degree of rearward stability, will be susceptible to losing drive grip control with the surface the wheelchair is travelling over when going downhill.

Conversely, a wheelchair with a rear wheel position set at the centre of gravity of the vehicle, for optimum traction, will be susceptible to rearward tipping when travelling uphill.

Many outdoor electric wheelchairs are equipped with rear anti-tip stabilisers, which prevent a complete tip over backwards. However, rigidly mounted anti-tip stabilisers can adversely affect other aspects of wheelchair operation.

If anti-tip stabilisers are fitted close to the ground, they do not allow the front leading wheels of the wheelchair to rise over obstacles such as kerbs. Anti-tip stabilisers set to allow the front leading wheels to rise over kerbs cannot assist in controlling angular movement of the chair, pitching and tossing when travelling over uneven

ground, and do not contribute to the comfort of the disabled occupant during normal motion. If anti-tip stabilisers protrude out a long way at the rear of the wheelchair, the turning circle is increased with an adverse affect on manoeuverability in a confined area.

For a wheelchair fitted with anti-tip stabilisers, it is quite possible when climbing and descending kerbs to get into a position where the rear drive wheels become lifted from the ground, leaving the wheelchair and occupant stranded.

The first aspect of the present invention aims to address the above problems.

Traction contact of the rear wheels also functions as a brake, providing the occupant with a means for stopping and parking the wheelchair.

However, there are occasions where it may be convenient or necessary for a parked wheelchair to be manoeuvred quickly into position by a attendant person, not by the disabled occupant. Presently, this is achieved by providing a release mechanism on the motors, so that the attendant can disconnect the drive and the wheelchair can be pushed manually. Wheelchairs of this type have caution labels warning the attendant not to operate the drive release mechanism when there is an occupant in the wheelchair, but this is often ignored for convenience.

There is a potential safety risk in this, if the attendant disconnects the drive and then leaves the wheelchair unattended for a moment, as the disabled occupant may be unable to reach and reconnect the drive to regain control of the wheelchair. Situations such as this can result, for example, in a safety risk, with the wheelchair and its disabled occupant running away out of control downhill, with the disabled occupant unable to stop the wheelchair.

An electrically powered wheelchair is a heavy unit.

Some wheelchairs are fitted with hand-operated parking brakes acting on the rear wheels. These are usually inadequate to prevent the chair from stopping once it has started to move. Parking brakes are also prone to damage, or alternatively if robust enough, can cause a malfunction in another area of the wheelchair, if it is driven inadvertently with them applied, as frequently happens.

The second aspect of the present invention aims to address the above mentioned problems.

According to a first aspect of the present invention, an attachment for an electric wheelchair comprises :- a frame for attachment to the rear of an electric wheelchair; at least one stabilising wheel rotatably mounted about its axis; wherein the axis is moveable with respect to the frame, and wherein the attachment includes damping means for damping movement of the axis with respect to the frame.

The first aspect of the present invention also provides an electric wheelchair comprising :- at least one stabilising wheel rotatably mounted about its axis at the rear of the wheelchair, wherein the axis is moveable with respect to the wheelchair, further comprising damping means for damping movement of the axis with respect to the wheelchair.

In the present invention, the damped moveable stabilising wheel may be depressed under loads as the front wheels of the wheelchair move over obstacles. This prevents lifting of the rear wheels which may leave the wheelchair and occupant stranded. The stabilising wheel

also prevents backwards tipping as the wheelchair moves over obstacles. Overall, the first aspect of the invention allows the rear wheel position to be set safely for optimum drive contact at or around the vehicle centre of gravity, whilst also controlling excess tipping motion at all times, particularly when climbing and descending kerbs.

According to a second aspect of the present invention, an attachment for an electric wheelchair comprises :- a frame for attachment to the rear of an electric wheelchair; at least one stabilising wheel rotatably mounted about its axis; wherein the axis is moveable with respect to the frame, and wherein the attachment includes means for moving the axis from a first position to a second position and means for locating the wheel in the second position.

The second aspect of the present invention also provides an electric wheelchair comprising :- at least one stabilising wheel rotatably mounted about its axis at the rear of the wheelchair, wherein the axis is moveable with respect to the wheelchair, further comprising means for moving the axis from a first position wherein, in normal operation of the wheelchair, the stabilising wheel is not in contact with the ground, and a second position wherein the stabilising wheel is in contact with the ground and the rear wheels of the electric wheelchair are lifted from the ground, and further comprising means for locating the axis of the stabilising wheel in the second position.

According to the second aspect of the invention, a means of allowing the attendant to manually push the wheelchair is provided. The wheelchair may be operated in

a manual mode, wherein the stabilising wheel is pivoted downwards by the attendant person to locate into a position wherein the rear wheels are lifted from the ground and the wheelchair can be manoeuvred manually by the attendant person.

Preferably, a pair of stabilising wheels are provided which are rotatably mounted on a common axis.

Preferably, the axis of the stabilising wheels is moveable by pivoting about a second axis.

Preferably, the damping means comprises spring dampeners. Preferably, gas springs are used, as these are more controllable, but coil springs may also be used.

Preferably, the wheels are moveable from the first position to the second position by means of a lever operated mechanism. Preferably, the lever is positioned such that it may be reached by the wheelchair occupant, at least to release the wheels from the second position.

Preferably, the lever is detachable.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings in which :- Figure 1 shows an attachment for a wheelchair in accordance with the present invention; Figure 2 shows a wheelchair in accordance with the present invention in normal operation; Figure 3 shows a wheelchair in accordance with the present invention mounting a kerb;

Figure 4 shows a wheelchair in accordance with the present invention in normal operation; and, Figure 5 shows a wheelchair in accordance with the present invention in manual push mode.

Figure 1 shows an attachment for an electric wheelchair comprising a frame 1 for attachment to the rear of a standard electric wheelchair, and a pair of stabilising wheels 2a, 2b rotatably mounted about an axis 3. The wheels are further pivotably mounted about an axis 4, and gas springs 5a, 5b are provided to resiliently bias the wheels 2a, 2b towards a rest position. The attachment also includes a lever 6 which is operable to rotate cross strut 9. Rigid link 10 is hinged to the cross strut 9, and on rotation of the cross strut 9, acts to pivot the stabilising wheels 2a, 2b downwards into a second position.

Figure 2 shows the attachment of Figure 1 installed on a standard electric wheelchair 7. The lever 6 is detachable, and, in Figure 2, the lever is shown detached.

The rest position of the stabilising wheels 2 is such that, in the normal travelling position of the wheelchair 7, travelling on a substantially horizontal surface, as shown in Figure 2, the wheels 2 are located slightly above the ground.

Figure 3 shows the wheelchair 7 mounting a kerb. The stabilising wheels 2 come into contact with the ground and are pushed upwards against the force of gas springs 5, and the wheels 2 pivot upwards about axis 4. The stabilising wheels 2 prevent the wheelchair 7 from tipping over backwards whilst travelling over obstacles, as shown in Figure 3. The force of the dampers 5 resiliently biassing the wheels 2 downwards balances the moment of the centre of gravity of the wheelchair and its occupant. Because the wheels 2 are depressable, the rear drive wheels 8 of the

wheelchair 7 do not become lifted from the ground, leaving the occupant stranded.

The position and height of the stabilising wheels 2 in the rest position may be set by adjusting the gas springs 5. Furthermore, the strength of the damping force may be adjusted depending on the weight of the occupant.

Figure 4 shows the wheelchair 7 in its normal position with the lever 6 attached.

Figure 5 shows the wheelchair in manual push mode, wherein the lever 6 is pivoted forwards, such that the stabilising wheels 2 pivot downwards about axis 4 and are located in a second position. When the lever 6 is rotated, the link 10 is extended, causing the wheels 2 to swivel downwards about their axis 4. When the bent link 10 passes an"over centre"point, the swivelling cross strut 9 reaches a stop position. At this point the weight of the wheelchair holds the linkage 10 and wheels 2 in the manual push mode. Although a means may be provided to lock the mechanism in this mode, it is preferable that this position is maintained by the weight of the wheelchair alone, so that the occupant can easily bring the drive wheels back into operation. In the manual push mode the rear drive wheels 8 of the wheelchair are lifted from the ground. Thus, the wheelchair can be pushed manually by an assistant. In this position, the lever 6 is in a position such that it may be reached by the occupant of the wheelchair, so that the occupant may release the wheelchair from manual push mode if required.

Claims

1. An attachment for an electric wheelchair comprising :- a frame for attachment to the rear of an electric wheelchair; at least one stabilising wheel rotatably mounted about its axis; wherein the axis is moveable with respect to the frame, and wherein the attachment includes damping means for damping movement of the axis with respect to the frame.

2. An electric wheelchair comprising :- at least one stabilising wheel rotatably mounted about its axis at the rear of the wheelchair, wherein the axis is moveable with respect to the wheelchair, further comprising damping means for damping movement of the axis with respect to the wheelchair.

3. An attachment for an electric wheelchair comprising :- a frame for attachment to the rear of an electric wheelchair; at least one stabilising wheel rotatably mounted about its axis; wherein the axis is moveable with respect to the frame, and wherein the attachment includes means for moving the axis from a first position to a second position and means for locating the wheel in the second position.

4. An electric wheelchair comprising :- at least one stabilising wheel rotatably mounted about its axis at the rear of the wheelchair,

wherein the axis is moveable with respect to the wheelchair, further comprising means for moving the axis from a first position wherein, in normal operation of the wheelchair, the stabilising wheel is not in contact with the ground, and a second position wherein the stabilising wheel is in contact with the ground and the rear wheels of the electric wheelchair are lifted from the ground, and further comprising means for locating the axis of the stabilising wheel in the second position.

5. An attachment or a wheelchair according to claim 3 or 4, in which the wheels are moveable from the first position to the second position by means of a lever operated mechanism.

6. An attachment or a wheelchair according to claim 5, in which the lever is positioned such that it may be reached by the wheelchair occupant, at least to release the wheels from the second position.

7. An attachment or a wheelchair according to claim 5 or 6, in which the lever is detachable.

8. An attachment or a wheelchair according to any one of the preceding claims, in which a pair of stabilising wheels are provided which are rotatably mounted on a common axis.

9. An attachment or a wheelchair according to any one of the preceding claims, in which the axis of the stabilising wheels is moveable by pivoting about a second axis.

10. An attachment or a wheelchair according to any one of the preceding claims, in which the damping means comprises gas springs.

11. An attachment substantially as described with reference to the accompanying drawings.

12. A wheelchair substantially as described with reference to the accompanying drawings.