Abstract:
A dual mode wheelchair ( 300 ) providing both a maneuverable indoor mode and a travel mode. The wheelchair ( 300 ) comprises fore wheels ( 104 ) mounted on a fore axis ( 105 ) and rear wheels ( 102 ) mounted on a rear axis ( 103 ). A distance between the fore axis ( 105 ) and the rear axis ( 103 ) defines a wheelbase of the wheelchair ( 300 ). The wheelbase is alterable between a short wheelbase providing a maneuverable mode of the wheelchair ( 300 ) and a long wheelbase providing a travel mode of the wheelchair ( 300 ). The wheelchair ( 300 ) further provides a lowered center of gravity and a reclining position in the travel mode to provide improved stability and occupant security.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority from Provisional Patent Application No. 2004904400 filed on 4 Aug. 2004, the content of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to wheelchairs, and in particular to a dual mode wheelchair having a manoeuvrable mode and a travel mode. 
   BACKGROUND OF THE INVENTION 
   A wide range of wheelchairs are currently available, each type of wheelchair having characteristics which make it suitable for a given application. One type of wheelchair, commonly referred to as an indoor chair, has a seat arranged to place the occupant in an upright seated position, for instance to enable the occupant to eat at a dining table, or work at an office desk or use a computer. The indoor chair, being used in confined indoor environments such as offices and homes, must have dimensions to enable the chair to negotiate doorways, corridors, and tight indoor spaces. Consequently, the wheelbase of such indoor chairs, being the distance between a front wheel axis and a rear wheel axis, is made short to provide a manoeuvrable wheelchair which can be turned within a small floor space. However, such a short wheelbase leads to directional instability should such a wheelchair be used at speed, and so manoeuvrable wheelchairs are unsuited for travel over distance. 
   A second type of wheelchair, commonly referred to as an outdoor wheelchair or a travel wheelchair, has a wheelbase which is significantly longer than that of manoeuvrable wheelchairs, in order to avoid or minimise the directional instability associated with short wheelbase wheelchairs used at speed. Consequently, travel wheelchairs require a large footprint for turning which makes them unsuitable for use in confined indoor environments. Further, travel wheelchairs have a seat arranged to place the occupant in an upright seated position, such a posture being required at the destination. Some travel wheelchairs provide for the seat to be set to a user-selected partially reclined position upon delivery. Further travel wheelchairs provide for reclining positions to be selected or altered during use, however such chairs raise the occupant&#39;s centre of gravity during such reclining, thus decreasing the stability of the wheelchair at speed or on uneven ground. 
   With these and other wheelchairs being applicable to only a subset of activities undertaken by a user, many wheelchair users obtain more than one wheelchair so that a suitable wheelchair is available for each situation encountered by the user in day to day use. Consequently, wheelchair users are faced with the costs of obtaining and maintaining multiple wheelchairs, the need for the user to regularly transfer from one wheelchair to another, and the burden of carrying those unused wheelchairs with them for future use. 
   Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
   Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
   SUMMARY OF THE INVENTION 
   According to a first aspect, the present invention provides a dual mode wheelchair comprising: 
   at least one fore wheel mounted on a fore axis and at least one rear wheel mounted on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the wheelchair; 
   wherein the wheelbase is alterable between a short wheelbase providing a manoeuvrable mode of the wheelchair and a long wheelbase providing a travel mode of the wheelchair. 
   According to a second aspect the present invention provides a dual mode wheelchair comprising: 
   at least one fore wheel mounted on a fore axis and at least one rear wheel mounted on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the wheelchair; 
   wherein the wheelbase is alterable between a short wheelbase providing a manoeuvrable mode of the wheelchair and a long wheelbase providing a travel mode of the wheelchair; 
   and wherein a centre of gravity of the wheelchair when occupied in the manoeuvrable mode is higher than a centre of gravity of the wheelchair when occupied in the travel mode. 
   In preferred embodiments of the invention, in the short wheelbase manoeuvrable mode the wheelbase may be less than substantially 45 centimeters, and more preferably may be less than substantially 40 centimeters. In preferred embodiments of the invention, in the long wheelbase travel mode the wheelbase may be greater than substantially 55 centimeters, and more preferably may be greater than substantially 60 centimeters. 
   In preferred embodiments of the invention the wheelchair provides a reclined seating position in the travel mode, and an upright seating position in the manoeuvrable mode. In such embodiments, in the travel mode the wheelchair is preferably arranged to provide a centre of gravity of the occupant at a smaller distance off the ground than when in the manoeuvrable mode. Such embodiments thus reduce the likelihood of the chair overturning or the occupant being thrown forward during braking or laterally from the chair during cornering or travel over uneven ground in the travel mode. 
   Preferred embodiments of the invention may provide for operation of the wheelchair at one or more intermediate positions between the manoeuvrable mode and the travel mode, thus providing the option of intermediate set-points providing gradually varying amounts of recline and wheelbase extension. 
   The dual mode wheelchair may comprise a sub-frame upon which the at least one rear wheel is mounted, and a seat frame upon which the at least one fore wheel is mounted. In such embodiments, the seat frame is preferably movably mounted to the sub-frame to provide for alteration of the wheelbase between the two modes. The movable mounting of the seat frame to the sub-frame may comprise a sliding mount, wherein the seat frame is slidable relative to the sub-frame to provide for alteration of the wheelbase between the manoeuvrable mode and the travel mode. A sliding mount attachment of the seat frame is preferably proximal to a rear of the seat frame, and the sliding mount preferably provides for the sliding mount attachment of the seat frame to travel forwardly and downwardly when the wheelbase is lengthened from the manoeuvrable mode to the travel mode. Such embodiments provide for a centre of gravity of the wheelchair to be lower when in the travel mode than a centre of gravity of the wheelchair when in the manoeuvrable mode. Such embodiments further provide for the rear of the seat frame to be moved lower relative to a fore portion of the seat frame when in the travel mode, thus providing for a reclined seating position of the wheelchair in the travel mode. 
   Movement of the sliding mount attachment of the seat frame along the sliding mount may be actuated by a motor. For example an electric motor may drive the sliding mount attachment along the sliding mount. Alternatively the movable mount between the seat frame and the sub-frame may be actuated manually, for example by way of a hand-operated threaded winding mechanism. 
   In alternate embodiments, the seat frame may be movably mounted to the sub-frame by at least one pivot arm, the at least one pivot arm adapted to stand upright when in the manoeuvrable mode, and adapted to extend forwardly when in the travel mode, such that a height of the seat frame is less when in the travel mode. 
   The rear wheels may be drive wheels of large diameter to enable an occupant to grasp the drive wheels or appended hand rails. The dual mode wheelchair may comprise a motor to drive the drive wheels. 
   At least one guide wheel may be provided rearward of the rear wheels in order to counteract backwards tipping of the wheelchair. Preferably one guide wheel is provided, which is preferably positioned substantially centrally between the sides of the wheelchair. Such embodiments provide for a guide wheel to be positioned a sufficient distance rearward of the rear wheels to counteract tipping of the wheelchair to the rear, while retaining the ability for the wheelchair to manoeuvre within a small area. 
   The at least one guide wheel may be a castor. 
   In embodiments comprising at least one guide wheel provided rearward of the rear wheels, the wheelchair is preferably articulated in order to retain all wheels in contact with the ground over uneven terrain. Such articulation may be effected by the movable mount between the sub-frame and the seat frame. 
   The at least one fore wheel may be a castor. 
   According to a third aspect the present invention provides a dual mode wheelchair frame comprising: 
   a first frame portion for mounting at least one fore wheel on a fore axis; and 
   a second frame portion for mounting at least one rear wheel on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the dual mode wheelchair frame; 
   wherein the first frame portion is movably mounted to the second frame portion to provide for alteration between a short wheelbase providing a manoeuvrable mode of the wheelchair frame and a long wheelbase providing a travel mode of the wheelchair frame. 
   According to a fourth aspect the present invention provides a dual mode wheelchair frame comprising: 
   a first frame portion for mounting at least one fore wheel on a fore axis; and 
   a second frame portion for mounting at least one rear wheel on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the dual mode wheelchair frame; 
   wherein the first frame portion is movably mounted to the second frame portion to provide for alteration between a short wheelbase providing a manoeuvrable mode of the wheelchair frame and a long wheelbase providing a travel mode of the wheelchair frame; 
   and wherein a centre of gravity of the wheelchair frame when occupied in the manoeuvrable mode is higher than a centre of gravity of the wheelchair frame when occupied in the travel mode. 
   According to a fifth aspect the present invention provides a method of constructing a dual mode wheelchair, the method comprising: 
   providing at least one fore wheel mounted on a fore axis; and 
   providing at least one rear wheel mounted on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the wheelchair; 
   wherein the wheelbase is alterable between a short wheelbase providing a manoeuvrable mode of the wheelchair and a long wheelbase providing a travel mode of the wheelchair. 
   According to a sixth aspect the present invention provides a method of constructing a dual mode wheelchair, the method comprising: 
   providing at least one fore wheel mounted on a fore axis; and 
   providing at least one rear wheel mounted on a rear axis, a distance between the fore axis and the rear axis defining a wheelbase of the wheelchair; 
   wherein the wheelbase is alterable between a short wheelbase providing a manoeuvrable mode of the wheelchair and a long wheelbase providing a travel mode of the wheelchair; 
   and wherein a centre of gravity of the wheelchair when occupied in the manoeuvrable mode is higher than a centre of gravity of the wheelchair when occupied in the travel mode. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Examples of the invention will now be described with reference to the accompanying drawings in which: 
       FIGS. 1   a  to  1   d  illustrate a wheelchair in accordance with a first embodiment of the invention; 
       FIGS. 2   a  and  2   b  illustrate a wheelchair in accordance with a second embodiment of the invention; 
       FIGS. 3   a  to  3   c  illustrate damped support means suitable for application in the first and second embodiments; 
       FIGS. 4   a  to  4   c  illustrate articulation of a wheelchair suitable for use in conjunction with the first and second embodiments; and 
       FIG. 5  illustrates a motorised actuation mechanism for adjusting the wheelchair of the first or second embodiment between a travel mode and an indoor mode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a dual mode wheelchair  100  in accordance with a first embodiment of the present invention. Wheelchair  100  comprises two rear drive wheels  102  mounted to sub-frame  110  on a rear axis  103 , and two fore castor wheels  104  mounted to seat frame  108  on a fore axis  105 . A distance between the rear axis  103  and fore axis  105  defines the wheelbase  106  of the wheelchair  100 . Seat frame  108  is movably mounted to sub-frame  110  by a pivot arm  112  having a pivotal connection  114  to seat frame  108  and a pivotal connection  116  to sub-frame  110 . A fore portion of seat frame  108  is secured to sub-frame  110  by damped support means (not shown in  FIG. 1 ). Sub-frame  110  further comprises a rear castor wheel  118 , positioned rearward of the rear drive wheels  102  and, as shown in  FIGS. 1   c  and  1   d , positioned substantially centrally between the sides of the wheelchair  100 . The provision of rear castor wheel  118  in the present embodiment provides for the torque from the drive wheels  102  to be transmitted to the rear castor wheel  118  rather than to the seat frame  108 . Thus, the castor wheel  118  decreases the tendency for rearward tipovers of the wheelchair  100 , particularly in the travel mode. 
     FIG. 1   a  shows wheelchair  100  in a manoeuvrable mode, in which wheelbase  106   a  is short. In the manoeuvrable mode, seat frame  108  is held high by the pivot arm  112  standing upright, such that seat frame  108  provides for a user to be in an upright seated position, and a centre of gravity of wheelchair  100  when occupied is relatively high providing for an occupant to work at a desk, sit at a dinner table, or the like.  FIG. 1   c  is a plan view illustrating the footprints of wheels  102 ,  104  and  118 , and shows the turning footprint  140  of wheelchair  100  required when wheelchair  100  is in the manoeuvrable mode. As can be seen the footprint  140  is defined by the relative positions of the wheels  102 ,  104  and  108 , and wheelchair  100  requires a small footprint  140  when in the manoeuvrable mode. 
     FIG. 1   b  shows wheelchair  100  in a travel mode, in which wheelbase  106   b  is lengthened sufficiently to provide for directional stability for travel of the wheelchair  100  at speed. In the travel mode, pivot arm  112  extends forwardly and thus holds the rear of seat frame  108  in a lower position in the travel mode than in the manoeuvrable mode, thus lowering a centre of gravity of the wheelchair  100  when occupied and thus improving stability of the wheelchair  100 . As seat frame  108  is substantially rigid, a fore portion of seat frame  108  remains at a similar height in both the travel mode and the manoeuvrable mode, and so the seat frame  108  provides a reclined seating position in the travel mode as illustrated in  FIG. 1   b . Such a reclined seating position is advantageous in reducing the likelihood of an occupant being thrown forward out of the wheelchair  100 . Further, by increasing a percentage of the weight of the user applied to a backrest portion of the seat frame  108 , the reclined seating position increases frictional resistance to a user being thrown laterally from the wheelchair  100 .  FIG. 1   d  is a plan view illustrating the footprint  160  required for turning of the wheelchair  100  in the travel mode, footprint  160  being significantly larger than the footprint  140  required for turning of the wheelchair  100  in the manoeuvrable mode. Such a large wheelbase  160   b  provides for improved stability of the wheelchair  100  when in the travel mode. 
   Movement of pivot arm  112  between the manoeuvrable mode and the travel mode may be effected by a motor (not shown) or manually by a hand operated threaded winding mechanism (not shown). 
     FIG. 2  illustrates a wheelchair  200  in accordance with a second embodiment of the present invention. Wheelchair  200  comprises rear drive wheels  202  mounted to a sub-frame  210  on a rear axis  203 . Wheelchair  200  further comprises fore castor wheels  204  mounted to a seat frame  208  on a fore axis  205 , and a rear guide castor wheel  218  mounted on sub-frame  210 . A sliding mount attachment  212  of seat frame  208  is movably mounted to a sliding mount  214  of sub-frame  210 . The sliding mount  214  is angled thus providing for the sliding mount attachment  212  of the seat frame  208  to travel forwardly and downwardly when the wheelbase  206  is lengthened from the manoeuvrable mode of  FIG. 2   a  ( 206   a ) to the travel mode of  FIG. 2   b  ( 206   b ). Again, a fore portion of seat frame  208  is secured to sub-frame  210  by damped support means (not shown in  FIG. 2 ). 
   Movement of sliding mount attachment  212  between the manoeuvrable mode and the travel mode may be effected by a motor (not shown) or manually by a hand operated threaded winding mechanism (not shown). 
     FIG. 3   a  illustrates a wheelchair  300  in which a fore portion of seat frame  308  is secured to sub-frame  310  by appropriate damped support means  320 . Such a configuration may be applied in either embodiment shown in  FIGS. 1 and 2 . As can be seen in  FIG. 3 , a fore portion of seat frame  308  is maintained a distance off the ground which is roughly the same for both the manoeuvrable mode of  FIG. 3   a  and the travel mode of  FIG. 3   c .  FIG. 3   b  illustrates positioning of the sliding mount at an intermediate set-point so as to provide a range of seat tilt and frame extension allowing for driver preference. The use of damped support means  320  provides for some articulation of the wheelchair  300  to enable travel over kerbs, and uneven ground. 
     FIGS. 4   a  to  4   c  illustrate an articulated wheelchair frame and the ability of such a frame to maintain contact of all wheels on the ground even over uneven terrain. Thus, stability is maintained over convex surfaces ( FIG. 4   a ) or concave surfaces ( FIG. 4   b ), and traction of the drive wheels can be maintained. Further, this allows for the torque from the drive wheels to be transmitted to the rear castor rather than the front frame in the travel mode, thus decreasing the tendency for rearward tipovers. Thus, mainly forward and back motion is transmitted to the seat frame, whereas little or no torque is transmitted to the seat frame from the drive wheels. Still further, as illustrated in  FIG. 4   c , when the wheelchair of the present invention passes over a kerb, minimal seat tilt occurs as a result of such an articulated frame. Such articulation may be implemented in conjunction with the wheelchair of  FIG. 1  or the wheelchair of  FIG. 2 . 
     FIG. 5  illustrates a motorised actuation mechanism  500  for changing a wheelchair between an indoor (manoeuvrable) mode and a travel mode. The mechanism  500  comprises a motor  510  and 90 degree gear drives  512  which pass the drive force to worm drives  514 . The worm drives  514  move a sliding mount attachment  520  of a seat frame (not shown) along slide rails  522  of a sub-frame (not shown), so as to effect transition of the wheelchair from an indoor (manoeuvrable) mode to a travel mode. Also shown is a pivot axis  524  of the seat frame mounted on the sliding mount attachment  520 . As the sliding mount attachment  520  and pivot axis  524  are driven along the slide rail  522 , pivoting of the seat frame may occur about the pivot axis  524  to effect transition of the seat between a low, stable reclined position in the travel mode and a high upright seated position in the indoor (manoeuvrable) mode. The pivot axis  524  further permits articulation of the wheelchair frame to permit travel over uneven terrain while maintaining contact of all wheels upon the ground. 
   It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.