Abstract:
Gentle and substantially linear vertical motion of a wheelchair foot support is expected to provide superior results for maintenance of a wheelchair user&#39;s leg muscle mass&#39; thus reducing atrophy of the wheelchair user&#39;s legs. Additionally, gentle continuous motion of the foot support is expected to aid in maintaining elasticity of the wheelchair user&#39;s leg joint ligaments&#39; thus reducing contractures. Accordingly, an atrophy-reducing wheelchair includes a movable foot support mounted to a linkage that is movably connected to the wheelchair frame. As the wheelchair moves in normal operation, rotation of a wheelchair wheel drives the linkage to provide substantially linear vertical reciprocation of the foot support.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to wheelchairs and, more particularly, to an atrophy-reducing movable foot support apparatus for use on wheelchairs. 
     BACKGROUND OF THE INVENTION 
     Typical wheelchair designs employ a sturdy frame supporting a seat assembly. The seat assembly includes arm rests and push bars to allow the wheelchair to be pushed by an aide. Attached to the rear of the frame is a pair of drive wheels. The drive wheels are typically large diameter wheels attached to a central hub with spokes. Push rims are mounted to the drive wheels to allow the wheelchair occupant to propel the chair using their arms and upper body. A smaller pair of pivoting castor wheels is attached to the front of the frame to provide steerability. Extending down from the lower front of the wheelchair frame is a footrest system to support the lower legs. The footrest system typically includes a pair of bars, one mounted to each side of the frame. Attached to each bar is a footrest, which typically may be pivoted up and out of the way to provide clearance if the occupant so desires. Adjustment mechanisms allow each bar to slide in adjustment relative to the frame to accommodate the differing heights and leg lengths of the wheelchair occupant. 
     One drawback to existing wheelchairs is that the footrest system, once adjusted for the particular size of the occupant, remains locked in a fixed position. As a result, the occupant&#39;s legs are stationary while seated in the wheelchair. Over extended periods of time, a wheelchair occupant who is not able to move their legs on their own may develop atrophy in the leg muscles and contracture of the leg joint ligaments. 
     Muscular atrophy is a decrease in muscle mass resulting from, among other things, lack of use. Muscular atrophy begins within a few days after confinement to a wheelchair, and is a major factor preventing full recovery from leg injuries. Over longer periods of time, muscles in the leg may deteriorate completely. 
     Contracture of ligaments is a loss of elasticity resulting from lack of use. Like muscular atrophy, contracture may begin to set in soon after confinement to a wheelchair, and is a second major factor preventing full recovery from leg injuries. Extremely painful stretching exercises and other physical therapies are required to restore contracted ligaments to anything approaching pre-injury conditions. 
     Efforts have been made to prevent muscle atrophy and contractures by providing continuous motion of a wheelchair occupant&#39;s legs. For example, one prior art solution is provided by U.S. Pat. No. 5,324,060 issued to Van Vooren et al. The &#39;060 patent discloses a wheelchair cycle apparatus that includes a frame to which is attached a connecting device for connecting the frame to a wheelchair. A drive wheel and driven wheel are attached to the frame. A pair of pedals are attached to either the drive wheel or the driven wheel depending upon whether the user can move his/her own legs. A chain connects the drive wheel to the driven wheel. The wheelchair cycle apparatus may be connected to the frame of a wheelchair to produce a wheelchair assembly that enables a disabled individual to exercise his/her own legs while seated in the wheelchair. 
     However, the wheelchair cycle apparatus shown in the &#39;060 patent requires the disabled individual to assume a non-standard position in the wheelchair. Additionally, the forward-protruding cycle frame makes the wheelchair cycle apparatus occupy a larger envelope of space than does a conventional wheelchair. Since building accesses and other public services have been specifically designed to accommodate conventional wheelchairs, these public services may not accommodate the wheelchair cycle apparatus of the &#39;060 patent. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus for use with a wheelchair that produces gentle and substantially linear vertical motion of a movable foot support and is expected to provide superior results for maintenance of a wheelchair user&#39;s leg muscle mass, thus reducing atrophy of the wheelchair user&#39;s legs. 
     According to one aspect of the present invention, a wheelchair is provided with a movable foot support assembly that reduces leg muscle atrophy and ligament contracture. 
     According to another aspect of the present invention, a wheelchair is provided with a movable foot support assembly that reduces leg muscle atrophy without substantially exceeding the dimensions of a conventional wheelchair. 
     According to another aspect of the present invention, a collapsible wheelchair is provided with a movable foot support assembly that reduces leg muscle atrophy without hindering collapsible motion of the wheelchair for storage. 
     In one embodiment of the present invention, an atrophy-reducing wheelchair comprises a movable foot support assembly that is driven by rotation of a rear wheel of the wheelchair. 
     In another embodiment of the present invention, an atrophy-reducing wheelchair includes first and second side frames, each side frame including rigidly connected structural members lying substantially in a corresponding plane, a front wheel bracket pivotally connected to one of the structural members, and a rear wheel mount formed in one or another of the structural members and defining a rear wheel axis, and at least one of the first and second side frames being modified to include a pivot and a journal, each journal defining a journal axis substantially perpendicular to the plane of the corresponding side frame, each pivot defining a pivot axis substantially perpendicular to the plane of the corresponding side frame and also defining horizontal and vertical axes substantially perpendicular to the pivot axis, a front wheel being rotatably mounted to each front wheel bracket, and a rear wheel being rotatably mounted to each rear wheel mount, the rear wheel axis of the second side frame being substantially in registration with the rear wheel axis of the first side frame, and the second side frame being offset from the first side frame along the rear wheel axes. First and second pivotally connected crossbars, having upper and lower ends and together defining a plane substantially perpendicular to the first and second planes, collapsibly connect the first and second side frames, the lower end of the first crossbar being pivotally connected to the second side frame and the upper end of the first crossbar carrying a first longitudinal bar lying substantially in the first plane and slidably connected to the first side frame, the lower end of the second crossbar being pivotally connected to the first side frame and an upper end of the second crossbar carrying a second longitudinal bar lying substantially in the second plane and slidably connected to the second side frame, the crossbars and longitudinal bars cooperating to permit motion of the first and second side frames between an open position in which the second side frame is offset from the first side frame by a seat width and a closed position in which the second side frame is offset from the first side frame by a collapsed width. A sling seat is supported between the first and second longitudinal bars. At least one linkage is movably connected to the modified side frame at the pivot and the journal, the linkage carrying a movable foot support; and a belt flexibly connects the linkage to the rear wheel of the modified side frame, such that rotation of the rear wheel drives the linkage to move the movable foot support. 
     In another embodiment of the present invention, an atrophy-reducing foot support assembly for use on a wheelchair having a modified side frame includes a foot support; a crank arm having a proximal end, a distal end, and a middle segment connecting the proximal and distal ends, the distal end carrying the foot support and the proximal end being pivotally mounted to a pivot of the modified side frame; an axle assembly rotatably mounted in a journal of the modified side frame, having an outer circumferential surface and having a rod pin extending substantially parallel to the journal axis at a radial distance from the journal axis; a push-rod having a driven end and having a driving end, the driven end being pivotally connected to the rod pin; a crank pin pivotally connecting the driving end of the push-rod to the middle segment of the crank arm; a drive wheel fixedly and substantially co-axially mounted to the rear wheel of the first side frame, the drive wheel having an outer circumferential surface; and a belt engaging the outer circumferential surface of the axle assembly and the outer circumferential surface of the drive wheel, thereby flexibly coupling the axle assembly to the drive wheel. When the wheelchair moves forward or backward, motion of the rear wheel of the modified side frame causes oscillating motion of the foot support. 
     In another embodiment of the present invention, an atrophy-reducing foot support assembly for use on a wheelchair having a modified side frame includes a foot support; an axle assembly rotatably mounted in a journal of the modified side frame, having an outer circumferential surface and having a rod pin extending substantially parallel to the journal axis at a radial distance from the journal axis; a push-rod having a driven end, a driving end, and a middle segment connecting the driving and driven ends, the driving end carrying the foot support and the driven end being pivotally connected to the rod pin; a crank arm having a proximal end and a distal end, the distal end being pivotally mounted to the middle segment of the push-rod by a crank pin, and the proximal end being pivotally mounted to a pivot of the modified side frame; a drive wheel fixedly and substantially co-axially mounted to the rear wheel of the modified side frame, the drive wheel having an outer circumferential surface; and a belt engaging the outer circumferential surface of the axle assembly and the outer circumferential surface of the drive wheel, thereby flexibly coupling the axle assembly to the drive wheel. When the wheelchair moves forward or backward, motion of the rear wheel of the modified side frame causes oscillating motion of the foot support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified perspective view of a conventional wheelchair as known in the prior art. 
         FIG. 2  is a simplified perspective view of a wheelchair cycle as known in the prior art. 
         FIG. 3  is a schematic illustration showing a motion envelope for pedals of the wheelchair cycle of  FIG. 2 . 
         FIG. 4  is a simplified partial perspective view of an atrophy-reducing wheelchair according to an embodiment of the present invention. 
         FIG. 5  is a simplified partial perspective view of a belt tensioner and wheel brake for the atrophy-reducing wheelchair of  FIG. 4 . 
         FIG. 6  is a side view showing a motion envelope of a movable foot support for the atrophy-reducing wheelchair of  FIG. 4 . 
         FIG. 7  is a schematic illustration showing exemplary velocities and forces for the movable foot support assembly of  FIGS. 4 and 6 . 
         FIG. 8  is a simplified partial perspective view of an adjustable movable foot support assembly on an atrophy-reducing wheelchair according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , one embodiment of a conventional wheelchair  10  includes a frame  12 , rear wheel assemblies  16  rotatably mounted to the frame  12 , front caster assemblies  18  pivotally mounted to the frame  12 , and a seat assembly  22  and footrests  24  that are fixedly mounted to the frame  12 . 
     The frame  12  includes side frames  26  joined by pivotally connected crossbars  28 . The crossbars  28  have upper and lower ends, the lower end of each crossbar  28  being pivotally connected to a lower horizontal structural member of a corresponding side frame  26  and the upper end of each crossbar  28  being pivotally connected to a longitudinal bar  29  that is slidingly attached to vertical structural members of the other side frame  26 . The side frames  26 , the pivotally connected crossbars  28 , and the longitudinal bars  29  are arranged so as to permit collapsing motion of the side frames  26  toward each other and deploying motion of the side frames  26  away from each other. Each side frame  26  typically is fabricated by bending and fastening together structural members manufactured from extruded metal tubing. The side frames  26  also can be fabricated by stamping, injection molding, composite wrapping, or other known techniques for making strong, durable, and lightweight articles. The crossbars  28  and the longitudinal bars  29  can be made from stamped metal, or by other conventional methods. 
     Each rear wheel assembly  16  conventionally includes a drive wheel  30  and a push rim  32 , which are radially connected to enable a wheelchair occupant to propel the chair using their arms and upper body. The drive wheel  30  is radially connected to a hub  34 . For rotary motion of the rear wheel assembly  16 , the hub  34  is rotatably mounted to the side frame  26 . The drive wheel  30  typically includes a metal or hard polymer rim on which is mounted a soft polymer tire. The push rim  32  typically includes a metal or hard polymer rail extending circumferentially, and optionally includes a soft grip mounted on the rail. 
     Each of the front caster assemblies  18  includes a wheel bracket  38  that is pivotally connected to the side frame  26 . Each of the front caster assemblies  18  also includes a front wheel  40  that is rotatably mounted within the wheel bracket  38 . Accordingly, the front wheel  40  can freely swivel to permit steering the wheelchair  10  without wheel skid. 
     The seat assembly  22  includes conventional elements for supporting the wheelchair occupant such as a seat back supported between upper vertical structural members of the side frames  26 , arm rests supported on upper horizontal structural members of the side frames  26 , and a sling seat that is supported between the longitudinal bars  29 . The seat assembly  22  also includes a push bar to allow the wheelchair to be pushed by an aide. The elements of the seat assembly  22  that extend between the side frames  26  typically are made of fabric or flexible polymer to permit collapsing and deploying motion of the side frames  26 . 
     The footrests  24  are provided at the front of the frame  12  to support the feet and lower legs of the wheelchair occupant. Each footrest  24  typically is pivotally supported on a bar  42  mounted to one of the side frames  26 . The footrests  24  typically may be pivoted up and out of the way around the bars  42  for ease of entering or leaving the wheelchair  10 . However, once lowered for use by the wheelchair occupant, the footrests are fixedly mounted to the frame  12 . As a result, the occupant&#39;s legs are stationary while seated in the wheelchair  10 , leading to the problem of atrophy discussed above. 
     Accordingly, wheelchair cycles have been proposed to provide exercise for a wheelchair occupant. Referring to  FIG. 2 , a wheelchair cycle apparatus  50 , as disclosed by the &#39;060 patent, is provided by connecting a cycle frame  52  to a conventional wheelchair frame  54 . The cycle frame  52  protrudes forward from the wheelchair frame  54 , and supports a forward wheel  56  and a rearward wheel  58 . Pedals  62  are attached to the forward wheel  56 , which defines an approximately horizontal axis of pedal rotation  64  and also defines a vertical axis  66  perpendicular to the horizontal axis  64 . A chain  68  connects the forward wheel  56  to the rearward wheel  58 . A brake (not shown) can be attached to the rearward wheel  58 . When the pedals  62  are attached to the forward wheel  56 , a wheelchair occupant having minimal leg function can exercise his/her legs by pedaling. Optionally, the brake can be attached to the rearward wheel  58  for increased exercise. 
     In operation, the pedals  62  revolve around the horizontal axis  64 , defining an approximate motion envelope  70  as shown in  FIG. 3 . It has been discovered that cycling motion, such as that of the motion envelope  70  in  FIG. 3 , can adversely affect the ligaments and cartilage of a wheelchair occupant&#39;s knees, leading to further deterioration of the wheelchair occupant&#39;s legs. 
     Referring to  FIG. 4 , an atrophy-reducing wheelchair  80 , according to an embodiment of the present invention, includes many elements similar to the conventional wheelchair  10  shown in  FIG. 1 . However, in place of the fixedly mounted footrests  24  shown in  FIG. 1 , the atrophy-reducing wheelchair  80  includes a movable foot support assembly  82  that is mounted to a modified side frame  84  for motion substantially parallel to the modified side frame  84 . 
     In the embodiment shown in  FIG. 4 , the movable foot support assembly  82  comprises a foot support  86  movably connected to the modified side frame  84  and to an axle assembly  88  by a rocker linkage  90 . 
     The modified side frame  84  includes a rear wheel mount (not shown) for receiving an axle of a modified rear wheel assembly  92 . A drive wheel  94  is rigidly mounted to the modified rear wheel assembly  92 . The modified side frame  84  further includes a journal  96  for mounting the axle assembly  88  and a pivot  98  for mounting the rocker linkage  90 . The journal  96  defines a journal axis  100 , while the pivot  98  defines a vertical axis  102  and a horizontal axis  104 . 
     Referring to  FIG. 5 , the rocker linkage  90  includes a push-rod  106  having a driven end and a driving end, and a crank arm  108  having a proximal end and a distal end joined by a middle segment. As shown in  FIG. 5 , the foot support  86  is pivotally mounted on the distal end of the crank arm  108 ; however, the foot support  86  can be pivotally or fixedly connected to either the push-rod  106  or the crank arm  108 . The axle assembly  88  includes an axle  110  that is rotatably mounted in the journal  96 . The axle assembly  88  also includes a driven wheel  112  rigidly mounted to an inner end of the axle  110 , and a belt wheel  114  rigidly mounted to an outer end of the axle  110 . The driven end of the push-rod  106  is pivotally connected to the driven wheel  112  by a rod pin  118 . The driving end of the push-rod  106  is pivotally connected to the middle segment of the crank arm  108  by a crank pin  120 . The crank arm  108  is pivotally mounted to the modified side frame  84  at the pivot  98 . The dimensions of the driven wheel  112 , the push-rod  106 , and the crank arm  108 , and the locations of the rod pin  118 , the crank pin  120 , and the pivot  98  are chosen to provide a “rocker” configuration, whereby rotation of the driven wheel  112  is transformed into reciprocating motion of the distal end of the crank arm  108 . 
     Referring back to  FIG. 4 , a belt  116  engages an outer circumferential surface of the belt wheel  114  to flexibly couple the belt wheel  114  to the drive wheel  94 , thereby transferring rotation from the modified rear wheel assembly  92  to the linkage  90  through the drive wheel  94 , the belt  116 , and the axle assembly  88 . 
     Referring to  FIG. 6 , since it may be desirable to disengage the linkage  90  when the atrophy-reducing wheelchair  80  is not in motion, a belt tensioner  122  is provided for engaging or releasing tension of the belt  116  around the drive wheel  94  and the belt wheel  114 . The belt tensioner  122  can be made part of a wheel brake assembly  124 , so that when the wheel brake  126  is engaged the belt tensioner  122  is released. In one embodiment of the present invention, the wheel brake assembly  124  is movable to an intermediate position whereby both the belt tensioner  122  and the wheel brake  126  are released. 
     Each part of the atrophy-reducing wheelchair  80  can be made from materials well-known in the art. For example, stamped metal, extruded and bent tubing, injection-molded polymers or fiber-resin composites all are suitable materials for the components of the rocker linkage  90 . The belt  116  can be fabricated from vinyl, rubber, leather, cotton, polyethylene, or any combination of flexible and moderately elastic materials having an adequate coefficient of static friction on the materials chosen for the belt wheel  114  and the drive wheel  94 . 
     Referring to  FIGS. 5 and 7 , the rocker linkage  90  provides substantially linear reciprocating motion of the foot support  86  in a plane substantially perpendicular to the journal axis  100 . Specifically, dimensions of the driven wheel  112 , the pushrod  106 , and the crank arm  108 , and locations of the rod pin  118 , the crank pin  120 , the journal  96 , and the pivot  98 , are chosen to provide gentle and substantially linear vertical reciprocation of the foot support  86  when the atrophy-reducing wheelchair  80  is moved forward or backward. In the example shown in  FIGS. 5 and 7 , the atrophy-reducing wheelchair  80  can be moved at approximately a normal walking pace of one meter per second (1 m/s). The foot support  86  reciprocates through a vertical travel  124  of approximately five (5) inches approximately once per second, with a maximum horizontal travel  128  of approximately two (2) inches, and presents a maximum velocity  130  of about eighteen inches per second (18 in/s) and a maximum upward force  132  of about one and one-tenths gravity (1.1 g) to the feet of an occupant seated in the atrophy-reducing wheelchair  80 . 
     It is expected that, for typical wheelchair occupants, the gently vertically reciprocating motion of the foot support  86  will result in reduced rates of leg muscle atrophy and ligament contracture, and also will result in superior longevity of knee joint tissue compared to the wheelchair cycle apparatus  50  shown in  FIG. 2 . 
     Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. 
     For example, since it may be desirable to adjust the motion of the movable foot support to accommodate differing leg lengths of a plurality of potential wheelchair occupants, an atrophy-reducing wheelchair  140  shown in  FIG. 8  can be provided with an adjustable four-bar linkage  142 . The adjustable four-bar linkage  142  includes an adjustable push-rod  144 . Increasing the length of the adjustable push-rod  144  will tend to shift a movable foot support  146  downward. 
     As another example, motion of the foot support  86  could be further varied by mounting the foot support  86  to the push-rod  106  in a Hoekens linkage configuration, rather than to the crank arm  108  as in the rocker linkage  90 . In the Hoekens linkage configuration, selecting appropriate dimensions of the push-rod  106  and the crank arm  108  will result in linear motion of the foot support  86  in one direction and curvilinear motion of the foot support  86  in the other direction. However, the Hoekens linkage configuration can result in somewhat greater forces than are provided by the rocker linkage  90 . To mitigate the effects of rapid acceleration on the wheelchair occupant, an absorbing member such as a gas spring can be included in the Hoekens linkage configuration. 
     As another example, a movable foot support also can be driven by a pantograph linkage that is actuated by a rotary cam directly mounted to a rear wheel of a wheelchair. 
     As another example, while a belt-driven linkage is believed to be simple and easily maintained, a chain-driven linkage could be used by substituting a chain for the belt  116  and substituting a derailleur for the belt tensioner  122 . 
     As a further example, although the present invention has been described with reference to collapsible hand-propelled wheelchair embodiments, adaptation of a hand-propelled embodiment for use on a motor-driven wheelchair would be within the scope of one having ordinary skill in the art. 
     Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above-detailed description, but that the invention will include all embodiments falling within the scope of this disclosure.