Motor vehicles – Special driving device – Stepper
Patent
1987-02-20
1989-01-03
Mitchell, David M.
Motor vehicles
Special driving device
Stepper
180907, 280 526, 280DIG10, 297DIG4, B62B 906
Patent
active
047949996
DESCRIPTION:
BRIEF SUMMARY
In my published International patent application No. WO85/01206, corresponding to my U.S. Pat. No. 4,645,222 dated Feb. 24, 1987, I have disclosed a wheelchair capable of climbing a flight of stairs. The wheelchair comprises a frame, a seat on the frame, front and rear pairs of laterally spaced carriers, three wheels on each of the carriers and an arm pivoted on the frame, the rear carriers being mounted on the arm and rotatable relative thereto about a rear axis, the front carriers being mounted on the frame and relative thereto about a front axis, the front wheels being spaced apart around the front axis and the rear wheels being spaced apart around the rear axis. Drive means for driving the carriers about their respective axes includes means for pivoting the arm relative to the body in such a manner that driving of the rear carriers up the first two stairs of a flight of stairs, whilst the front carriers move a relatively short distance towards the bottom stair, causes the rear carriers to be pivoted upwardly relative to the frame so that the attitude of the seat is not changed unduly. For use on a level floor, there is provided a castor which is disposed between the front carriers and can be lowered into engagement with the floor, raising the wheels of the front carriers from the floor. The wheelchair is then propelled by driving wheels of the rear carriers.
An earlier proposal for a stair-climbing wheelchair is contained in U.S. Pat. No. 3,241,848 of Flory. The Flory wheelchair also has front and rear carriers, each carrying three wheels spaced apart around on axis of rotation of the respective carrier. As in the wheelchair disclosed in my own prior application, the rear carriers are supported by an arm which can pivot relative to the frame of the wheelchair to permit upward and donward movement of the rear carriers. Flory proposes hand-operated screw and nut mechanism for raising and lowering the rear carriers. Thus, there is no automatic raising and lowering of the rear carriers in accordance with differences between rotation of the front and rear carriers, as is provided in the wheelchair disclosed in my prior application.
From a first aspect, the present invention relates to a wheelchair, comprising a seat, front and rear pairs of laterally spaced carriers, a plurality of wheels on each carrier and drive means for driving at least some of said wheels, wherein the front carriers are mounted for turning relative to the seat about a front axis, the rear carriers are mounted for turning relative to the seat about a rear axis, the wheels on each front carrier are spaced apart around the front axis and the wheels on each rear carrier are spaced apart around the rear axis.
The wheelchair is preferably adjustable to vary the distance between the front and rear axes and the drive means may be arranged for effecting such adjustment in response to rotation of either the front carriers or the rear carriers relative to the other carriers. The drive means is preferably arranged for selectively turning the carriers of a first of the pairs about their axis relative to the seat independantly of the carriers of the second pair, such turning being accompanied by variation of the distance between the front and rear axes, or turning the carriers of both the first and second pairs together about respective axes relative to the seat, the spacing between the axes then remaining constant.
According to a second aspect of the invention, there is provided a method of operating a wheelchair according to the first aspect, wherein the wheelchair is turned whilst a respective wheel on each of the front carriers is engaged with the ground and the perpendicular line through the centre of gravity of the wheelchair, including the occupant, is near to, but is to the rear of, a straight line joining the positions where said wheels engage the ground and wherein the geometry of the wheelchair is then adjusted to move the perpendicular through the centre of gravity rearwardly away from said straight line.
During upward and downward movem
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Diederiks, Jr. Everett G.
Mitchell David M.
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