Abstract:
A wheelchair includes a seat for supporting an occupant and a frame supporting the seat, where the frame further includes a first pair of wheels and a second pair of wheels connected by a differential for reversibly locking the second pair of wheels such that propulsion of only one of the wheels in the second pair of wheels results in both of wheels in the second pair of wheels moving in an identical direction.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to medical equipment, and more specifically relates to manually operated wheelchairs. 
       BACKGROUND 
       [0002]    Wheelchairs are used by people for whom walking is difficult or impossible due to illness (physiological or physical), injury, or disability. Conventional wheelchairs are propelled either by a motor or manually (e.g., by the seated occupant turning the rear wheels by hand). 
         [0003]    A basic manually-operated wheelchair incorporates a seat, foot rests, and four wheels: two caster wheels at the front and two larger wheels at the back. The two rear wheels are used to propel the chair. Turning both of the rear wheels simultaneously in the same direction (e.g., by the seated occupant using both hands) propels the chair in a straight line, forward or backward. Turning only one of the wheels (e.g., by the seated occupant using only one hand) results in a pivot or circular propulsion of the wheelchair. It is typically not possible to propel a conventional manually-operated wheelchair in a straight line using only one hand. 
         [0004]    Unfortunately, the seated occupant may not have easy use of both hands. For instance, certain illnesses or injuries (e.g., cancer, multiple sclerosis, amputation) may limit an individual&#39;s use of his or her hands and arms. This makes operation of a manually-operated wheelchair difficult, since both hands are typically needed in order to enjoy the full range of motion of the chair as discussed above. 
       SUMMARY OF THE INVENTION 
       [0005]    A wheelchair includes a seat for supporting an occupant and a frame supporting the seat, where the frame further includes a first pair of wheels and a second pair of wheels connected by a differential for reversibly locking the second pair of wheels such that propulsion of only one of the wheels in the second pair of wheels results in both of wheels in the second pair of wheels moving in an identical direction. 
         [0006]    In another embodiment, a wheelchair includes a seat for supporting an occupant and a frame supporting the seat, where frame includes a pair of front wheels, the pair of front wheels including a first front wheel and a second front wheel, a pair of rear wheels, the pair of rear wheels including a first rear wheel and a second rear wheel, and a differential connecting the first rear wheel and the second rear wheel. The differential includes a first planet gear connected to the first rear wheel by a first axle, a second planet gear connected to the second rear wheel by a second axle, and a sun gear connected to the frame, where the sun gear is moveable in a vertical direction to selectively engage the first planet gear and the second planet gear such that propulsion of only one of the first rear wheel or the second rear wheel results in the pair of rear wheels moving in an identical direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  is an exploded, perspective view of a wheelchair, according to embodiments of the present invention; 
           [0009]      FIG. 2  is a perspective view illustrating the differential in the “locked” configuration; 
           [0010]      FIG. 3  is a side view of the differential, in which the differential is unlocked; 
           [0011]      FIG. 4  is a side view of the differential, in which the differential is locked; 
           [0012]      FIG. 5  is an isometric view of the planet gear lever and associated components; and 
           [0013]      FIG. 6  is an isometric view of the assembled wheelchair, in which the differential is locked. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In one embodiment, the present invention includes a manually-operated wheelchair having an integrated differential that allows a full range of motion under one-handed operation. The integrated differential can be selectively engaged by a seated occupant of the wheelchair and locks the rear wheels of the wheelchair such that manual propulsion of one of the rear wheels causes both rear wheels to move in the same direction. Thus, the wheelchair can be propelled in a straight line (e.g., forward or backward) by turning only one of the rear wheels once they have been locked. When the integrated differential is disengaged, the rear wheels are unlocked and can be operated in the conventional manner (e.g., wherein turning of only one rear wheel results in pivoting of the wheelchair). 
         [0015]      FIG. 1  is an exploded, perspective view of a wheelchair  100 , according to embodiments of the present invention. For ease of explanation,  FIG. 1  is somewhat simplified, and components that are known to those of skill in the art are not discussed in detail. 
         [0016]    The wheelchair  100  generally comprises a seat  101 , a frame  107 , a first set of wheels (“front” wheels)  105   a - 105   b,  and a second set of wheels (“rear” wheels)  113   a - 113   b.  The seat  101  is configured to support a seated occupant of the wheelchair  100  and is mounted to the frame  107  (e.g., using screws and/or other fasteners). The first set of wheels  105   a - 105   b  is also mounted to the frame  107 , for example via a leg support  103  that attaches to the frame  107 . The leg support  103  may be configured to support the legs of the seated occupant. The second set of wheels  113   a - 113   b  is mounted to the frame  107  via a set of axels and a differential, as will be discussed in further detail below. 
         [0017]    Whereas the first set of wheels  105   a - 105   b  is used largely to support the wheelchair  100 , the second set of wheels  113   a - 113   b  is used to control the direction of propulsion of the wheelchair  100 . The second set of wheels  113   a - 113   b  is thus larger in diameter than the first set of wheels  105   a - 105   b  and is positioned behind the first set of wheels  105   a - 105   b.  The wheels  105   a  and  105   b  are spaced apart from each other in a parallel manner, on opposite sides of the seat  101 . 
         [0018]    As discussed above, the second set of wheels  113   a - 113   b  is mounted to the frame  107  via a set of axels and a differential. In one particular embodiment, a first support bracket  111  is mounted to a first side of the frame  107 . The first support bracket  111  includes an aperture through which a first axle  109  is inserted. The first support bracket  111  may further include a plurality of bearings  112  (e.g., press fitted ball bearings) that allow the first axle  109  to spin freely. 
         [0019]    One of the wheels  113   a  from the second set of wheels  113   a - 113   b  is mounted to a first end of the first axle  109  (e.g., using washers, nuts, and/or other fasteners), such that the first support bracket  111  is positioned between the wheel  113   a  and the first axle  109 . A gear  115  is mounted to a second end of the first axle  109  and functions as a first planet gear of the differential. One or more spacers  119  may be fitted onto the first axle  109  (e.g., such that one spacer  119  is positioned on either side of the first support bracket  111 ) in order to allow the first planet gear  115  to spin freely. 
         [0020]    A second support bracket  131  is mounted to a second side of the frame  107 , opposite the first support bracket  111 . The second support bracket  131  includes two apertures through which a second axle  127  and a third axle  125  are respectively inserted. The second support bracket  131  may further include a plurality of bearings  132  (e.g., press fitted ball bearings) that allow the second axle  127  and the third axle  125  to spin freely. 
         [0021]    The other wheel  113   b  in the second set of wheels  113   a - 113   b  is mounted to a first end of the second axle  127  (e.g., using washers, nuts, and/or other fasteners), such that the second support bracket  131  is positioned between the wheel  113   b  and the second axle  127 . A gear  117  is mounted to a second end of the second axle  127  and functions as a second planet gear of the differential. A first end of the third axle  125  is mounted to the second support bracket  131 . A gear  133  is mounted to a second end of the third axle  125  and function as a third planet gear of the differential. The third planet gear  133  engages the second planet gear  117 , as illustrated. One or more spacers  129  may be fitted onto the second axle  127  and/or the third axle  125  (e.g., such that one spacer  129  is positioned on either side of the second support bracket  131 ) in order to allow the second planet gear  117  and the third planet gear  133  to spin freely. 
         [0022]    As discussed above, the differential includes the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . In addition, the differential includes a sun gear  153  that is positioned in a perpendicular manner relative to the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . The sun gear  153  is mounted to a first end of a shaft  135 . A second end of the shaft  135  is attached (e.g., using a washer, a nut, and/or other fasteners) to a sun gear lever (which is collectively comprised of at least one handle  205  coupled to an end of a connector  143 ), which in turn is mounted to the frame  107  (e.g., via a first frame bracket  121  and/or second frame bracket  123 ). The shaft  135  fits within a tubular support  149 . Both ends of the tubular support  149  may include bearings  155  (e.g., press fitted ball bearings) to allow the shaft  135  to rotate freely within the tubular support  149 . As discussed above, the sun gear lever includes at least one handle  205  coupled to a connector  143 . The handle  205  allows the sun gear lever to be manually rotated such that the sun gear  153  selectively engages or disengages the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . In one embodiment, one such handle  205  is positioned on either side of the wheelchair  100  (e.g., at opposite ends of the connector  143 ). 
         [0023]    When the sun gear  153  engages the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 , the differential is locked.  FIG. 2 , for example, is a perspective view illustrating the differential in the “locked” configuration. When the differential is locked, both of the wheels  113   a  and  113   b  in the second set of wheels are locked together, such that manual propulsion of one of the wheels  113   a  or  113   b  causes both rear wheels  113   a  and  113   b  to move in the same direction. Thus, the wheelchair  100  can be propelled in a straight line (e.g., forward or backward) by turning only one of the wheels  113   a  or  113   b  when the differential is locked. 
         [0024]    Locking of the differential is reversible by rotating the sun gear lever such that the sun gear  153  is disengaged from the first planet gear  115 , the second planet gear  117 , and the third planet gear  133  (i.e., the differential is unlocked). In this case, both of the wheels  113   a  and  113   b  in the second set of wheels are free spinning and moveable independently of one another, such that manual propulsion of one of the wheels  113   a  or  113   b  causes the wheelchair  100  to be propelled in a circular motion. 
         [0025]    It is further noted that due to the manner in which the axles  109 ,  127 , and  125  are coupled to the respective wheels  113  of the wheelchair  100 , the wheels  113  rotate with the axles  109 ,  127 , and  125 . This stands in contrast to conventional wheelchairs, in which the wheels and their axles typically rotate independently of each other (e.g., at different frequencies). 
         [0026]      FIG. 3  is a side view of the differential, in which the differential is unlocked. In one embodiment, the handle  205  is connected to the connector  143  (not illustrated, but would be normal to the page in  FIG. 3 ), which in turn is connected to a first linkage  301  and a second linkage  303 . Thus, the first linkage  301  is connected directly to the sun gear lever, while the second linkage is connected directly to the sun gear support  149 . The first linkage  301  is connected to the second linkage at a joint  305 . The first linkage  301  and the second linkage  303  are moveable relative to each other about the joint  305 . When the handle  205  of the sun gear lever is in the vertical position, a first angle θ is created between the first linkage  301  and the second linkage  303 , and the sun gear  153  sits at a first height relative to the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . 
         [0027]      FIG. 4  is a side view of the differential, in which the differential is locked. When the handle  205  of the sun gear lever is in the horizontal position, a second angle ω is created between the first linkage  301  and the second linkage  303 . The second angle ω is smaller in degree than the first angle θ, and the first linkage  301  and the second linkage  303  are collapsed or pushed closer together, which raises the sun gear  153  so that it sits at a second height relative to the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . The second height is higher than the first height and is sufficient to engage the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 , thereby locking the differential. Thus, the sun gear  153  is moveable in the vertical direction to selectively engage or disengage the first planet gear  115 , the second planet gear  117 , and the third planet gear  133 . 
         [0028]      FIG. 5  is an isometric view of the sun gear lever and associated components. As discussed above, the sun gear lever may include more than one handle  205  coupled to the connector  143 . In the illustrated example, two handles  205  are coupled to the connector  143  (e.g., via the first frame bracket  121  and the second frame bracket  123 ). Rotation of the handle  205  about the connector  143  causes the first linkage  301  and the second linkage  303  to be collapsed, as discussed above. 
         [0029]      FIG. 6  is an isometric view of the assembled wheelchair  100 , in which the differential is unlocked (as indicated by the vertical position of the handle  205  of the sun gear lever, as discussed above). 
         [0030]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Various embodiments presented herein, or portions thereof, may be combined to create further embodiments. Furthermore, terms such as top, side, bottom, front, back, and the like are relative or positional terms and are used with respect to the exemplary embodiments illustrated in the figures, and as such these terms may be interchangeable.