Abstract:
Attachments for a manual wheelchair are provided for navigating a wheelchair over obstacles and uneven terrain, such as a typical curb on a street. The attachments provide for regulating the movement of the wheelchair as the wheelchair descends the curb and to prevent the wheelchair from flipping over during such movement. The attachments include a front caster wheel slider assembly on each side of the wheelchair, a follower wheel assembly and a track belt damping bar. The front caster wheel slider assembly includes a piston that will quickly push the front caster wheels down after they roll over the top edge of the curb. The follower wheel assembly acts as a sensor that will release the piston in the assembly after the front caster wheels roll over the top edge of the curb. As the back wheels of the wheelchair roll over and down the curb, the track belt damping bar slows the descent of the wheelchair.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This patent application is a division of U.S. patent application Ser. No. 11/697,934, titled “Wheelchair Attachments” that was filed on Apr. 9, 2007, and is now U.S. Pat. No. 7,766,342, which claims priority to U.S. Provisional Patent Application Ser. No. 60/790,596, that was filed on Apr. 7, 2006. Both the 60/790,596 and the 11/697,934 applications are incorporated by reference herein in their entireties. 
    
    
     U.S. GOVERNMENT RIGHTS 
     N.A. 
     COPYRIGHT NOTICE 
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosures, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     Manual wheelchairs, such as the Quickie XTR, Quickie 2, Invacare Xtra and E&amp;J Epic wheelchairs, are typically equipped with two main side wheels and two front caster wheels. The four wheels on most wheelchairs are arranged so that the seat of the wheelchair and the bottoms of the wheels remain even and level when the wheels are in contact with a level, even or flat ground surface. Such an arrangement works well when the wheelchair travels over flat ground and generally provides smooth transportation for a wheelchair occupant. However, when such a wheelchair travels over a curb, e.g., at the edge of a sidewalk onto a street, or otherwise moves from an upper surface to a lower surface, the wheel arrangement can cause the wheelchair to tip when the bottoms of the front caster wheels drop over the curb into a position that is at a different elevation, e.g., lower, than the level of the bottom of the main side wheels. Such tipping can present a potential danger to a wheelchair occupant and can cause accidents which may result in spinal or other injuries to a wheelchair occupant if the chair quickly drops down off the curb. 
     Improvements to manual wheelchairs have been previously proposed for ascending and descending curbs or other uneven surfaces, and navigating obstacles. One example is the device described in U.S. Pat. No. 4,962,942. Another example is a power wheelchair for traversing uneven terrain, such as the wheelchair described in. U.S. Pat. No. 6,554.086. However, those wheelchairs require electrical or computerized components or input from the wheelchair occupant. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention comprise one or more assemblies that are adapted to control a manual wheelchair&#39;s descent from an upper surface to a lower surface, such as a typical curb at the edge of a sidewalk. The assemblies can be provided as one or more standalone attachments for an existing wheelchair, or their functionality and construction can be integrated into a wheelchair, e.g., at the time of manufacture. 
     Manual wheelchairs typically have four wheels: two large main side wheels with hand rails, one on each side of the wheelchair seat, and two smaller front caster wheels located near a wheelchair occupant&#39;s feet. A wheelchair occupant can propel the wheelchair using the hand rails mounted on the two main side wheels. 
     The embodiments described herein are for a manual wheelchair, but may be used with other types of wheelchairs as appropriate. Embodiments of the invention may provide after-manufacture attachments for existing wheelchairs, or the structure and functionality described herein may be included and integrated into a wheelchair structure at the time of manufacture. Embodiments of the invention provide for regulating the movement of the wheelchair as the wheelchair descends from an upper surface to a lower surface, such as from a typical curb at the edge of a sidewalk to street level, or down stairs or other obstacle, which, for example, may be several inches high, and to prevent the wheelchair from tipping over during such movement. Embodiments of the invention provide for keeping the wheelchair level as the wheelchair descends over the curb or obstacle and will maintain the safety of any occupant of the wheelchair. In one embodiment, input or control is not required from an occupant of the wheelchair. In other words, this embodiment operates without input from the wheelchair occupant. Other embodiments may operate manually. Embodiments of the invention may be mounted on most existing wheelchairs in such a manner that will not interfere with any of the wheelchair&#39;s functionality, such as the ability to fold a folding wheelchair, braking capability for wheels, movement of foot pedals, seat or height adjustment, or other functionality. 
     In one embodiment, a front caster wheel slider assembly may be mounted on the front of a wheelchair, one on each side of the chair. The front caster wheel slider assembly extends a caster wheel from an upper surface to a lower surface in such a manner that maintains a level position and safety of a wheelchair occupant. One example of a front caster wheel slider assembly may have a vertically mounted spring loaded or pneumatic damping unit, such as an adjustable gas spring damping unit, which may have a piston pointing downwards that is adapted to connect to the top of a rail mounted in a linear bearing. The bottom of the rail may be connected to a front caster wheel. In some embodiments, the rail may be held in a retracted position by a latch, or other fixation device, during normal operation, e.g., when a wheelchair is on level ground. In one example, as the wheelchair rolls from an upper surface to a lower surface, e.g., down a curb, the latch will retract and allow the piston to extend the rail downwards so that the position of the front caster wheel is lowered until it engages the lower surface of the curb and supports the wheelchair. As the wheelchair continues to roll over and descend the curb being supported by the lowered caster wheel, the weight of the wheelchair (and occupant) will push the extended rail, and thus the piston, upwards until the rail engages the latch and the rail and caster wheel are returned to their original respective locked and retracted positions. One of skill in the art will understand that the aforementioned parts may be replaced with other parts and other arrangements that perform the same functions described herein. 
     In some embodiments, the spring loaded or pneumatic damping unit is constructed in a manner that may allow the wheelchair to descend a curb without any jerking or sudden movements. The damping unit may be constructed in a manner that allows the piston to extend out of the unit quickly when the piston or rail is released. In some embodiments, when the piston is pushed upward into the unit, the unit may exert a damping force that may slow the piston&#39;s movement upward into the unit. Thus, the extension velocity of the piston relative to the wheelchair may be higher than the retraction velocity of the piston. In some embodiments of the invention, the damping unit may be a pneumatic device that is fabricated in such a way to allow air to escape through a groove on a fixed side of the piston, thereby giving differential movement during extension and retraction. 
     In some embodiments, the front caster wheel slider assembly is activated by a sensor that causes the front caster wheels to extend automatically. The sensor may be mounted to the wheelchair frame at one or more points and include a sensing component, such as a follower wheel assembly. The sensor may be adapted to activate the front caster wheel slider assembly at the occurrence of, for example, a change of altitude or attitude of the wheelchair, one or more front caster or rear main wheels losing contact with a surface, such as the ground, contact between a ground surface and a point on the wheelchair, or other occurrence. 
     In some embodiments of the invention, a follower wheel assembly is adapted to act as a sensor to trigger the latches in the front caster wheel slider assembly. In other embodiments, the latch can be operated manually. One example of how a follower wheel assembly may be used is that one or more follower wheel assemblies are connected to and operate one or both latches in each front caster wheel slider assembly. The follower wheel assembly may act as a sensor that detects when the front caster wheels roll over the top edge of a curb and in turn, triggers and releases the latch. The follower wheel may be attached to the wheelchair frame together with a follower wheel assembly so that the follower wheel is positioned in alignment with the wheelchair&#39;s front small caster wheels and the main side wheels. In some embodiments of the invention, the follower wheel is positioned towards the front of the wheelchair relative to the main side wheels. In addition, the follower wheel is positioned at a height that is somewhat higher than the level of the four wheels, so that in normal operation during travel on a flat surface, the follower wheel does not come in contact with the ground surface. A follower wheel positioned at the somewhat higher level would come into contact with the ground when, for example, the wheelchair travels over and descends a curb, or the front wheels and the side wheels are positioned on surfaces of uneven heights. 
     In one example, as the wheelchair rolls over the curb, the follower wheel may engage the upper surface of the curb and temporarily support the wheelchair until the front caster wheels drop down and engage the lower surface, of the curb. When the follower wheel engages the upper surface, the follower wheel may also activate the latch by pulling on a cable attached to the follower wheel assembly and the latch. One of skill in the art will understand the aforementioned parts may be replaced with other parts and other arrangements that perform the same functions previously discussed. 
     In some embodiments of the invention, a track belt damping bar is provided to slow a wheelchair&#39;s descent over a curb, step or other obstacle. In one example, a track belt damping bar may be mounted at the rear of a wheelchair to ease the wheelchair&#39;s descent down a curb. In general, the track belt damping bar may be mounted to the wheelchair frame at a height above the height of the main wheels so it is not in contact with the ground when the wheelchair travels over the ground. In some embodiments of the invention, the track belt damping bar may extend out and up from a point along an axis of the perimeter of the main wheels so the track belt damping bar engages an upper edge of the curb as the wheelchair descends the curb. As the wheelchair moves down the curb, a friction belt made of a durable, non-slippery material may engage the upper edge of the curb and begin to rotate around two or more rollers. Rotational dampers are provided to dampen the rotation of the rollers. Thus, as the belt rotates around the rollers, the rotational dampers dampen the rotation of the rollers and the movement of the belt thereby slowing the descent of the wheelchair. One of skill in the art will understand the aforementioned parts may be replaced with other parts and other arrangements that perform the same functions previously discussed. 
     In some embodiments of the invention, front caster wheel slider assemblies, follower wheel assemblies and track belt damping bars may be used together in combinations of some or all of the assemblies and their respective functionality. In other embodiments, either one of the assemblies or components may be used independently. The use of one or all of the assemblies and bars is a design choice within the purview of one of ordinary skill in the art. For example, one may design the damping unit to have enough damping force to lower a wheelchair down a curb, step or other obstacle without the need for a damping bar. In other eases cases, one may design the damping unit to work in conjunction with a damping bar to lower the wheelchair down the curb, step or other obstacle, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated in the figures of the accompanying drawings which are meant to be exemplary and not limiting, in which like references are intended to refer to like or corresponding parts, and in which: 
         FIG. 1  is a perspective view of a wheelchair with attachments for descending a curb or other obstacle according to an embodiment of the invention; 
         FIG. 2  is a perspective view of a caster wheel slider assembly according to an embodiment of the invention; 
         FIG. 3  is an exploded view of the caster wheel slider assembly of  FIG. 2  according to an embodiment of the invention; 
         FIG. 4  is a perspective view of a linear bearing in the caster wheel slider assembly of  FIG. 2  according to an embodiment of the invention; 
         FIG. 5  is an exploded view of a lower portion of the caster wheel slider assembly depicted in  FIG. 2  according to an embodiment of the invention; 
         FIG. 6  is a perspective view of a follower wheel assembly according to an embodiment of the invention; 
         FIG. 7  is an exploded view of the follower wheel assembly depicted in  FIG. 6  according to an embodiment of the invention; 
         FIG. 8  is a perspective view of a track belt damping bar assembly according to an embodiment of the invention; 
         FIGS. 9A-D  depict a side view of a wheelchair with a front caster wheel slider assembly and follower wheel assembly descending a curb according to an embodiment of the invention; and 
         FIG. 10  is a side view of a wheelchair with the front caster wheel slider assembly, the follower wheel assembly and a track belt damping bar descending a curb according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are described herein with reference to the drawings.  FIG. 1  depicts a manually powered wheelchair  10  that may be any type of wheelchair such as the manual wheelchairs manufactured by, for example, Quickie XTR, Quickie 2, Invacare Xtra and E&amp;J Epic. The wheelchair  10  typically comprises a rigid frame  15  that is constructed in any manner well known in the art. The wheelchair  10  also comprises several components mounted on the frame including; two main side wheels  20  with hand rails  22 , two small front caster wheels  25 , a seat  30 , a seat back  35 , two arm rests  40  and two hand grips  45 . The components can be attached to the frame in any manner well known in the art. In addition, the components of wheelchair  10  may be any appropriate or standard wheelchair component well known in the art, such as any component associated with standard manual wheelchairs including the Quickie XTR, Quickie 2,Invacare Xtra and E&amp;J Epic. 
       FIGS. 2-5  illustrate a front caster wheel slider assembly  100  that can be attached to the wheelchair  10 . The front caster wheel slider assembly  100  is constructed of commonly available parts in manners well known in the art. The front caster wheel slider assembly  100  includes a damping unit  110  that may be an adjustable piston gas spring or pneumatic damping unit. The damping unit  110  is connected to the wheelchair frame with two brackets  115 , one at each end of the damping unit  110 . The damping unit  110  may be a piston gas spring damping device comprising a tube  120  closed at one end  125  and open at the other end  130 , or other damping devices may be used. A piston rod  135  fits into the open end  130  and is able to slide into and out of the tube  120 . Tube  120  is filled with a gas that is well known in the art and that acts as a spring pushing against piston rod  135  as rod  135  moves in and out of the tube  120 . The open end  130  includes a seal (not shown) that surrounds piston rod  135  and keeps the gas inside tube  120 . 
     The damping unit is constructed in a manner that, will cause the piston to quickly extend out of the unit when the piston or rail is released, e.g., by the latch. When the piston is pushed back into the unit, the unit will exert a damping force that will slow the piston&#39;s movement back into the unit. Thus, the extension velocity of the piston relative to the wheelchair will be higher than the retraction velocity of the piston. The damping unit may be a pneumatic device that is fabricated in such a way to allow air to escape through an orifice on a fixed side of the piston, thereby giving differential movement during extension and retraction. 
     The lower end of piston rod  135  is connected to fire upper end of tubular rail  140 . The tubular rail  140  may be of any construction well known in the art such as plastics, metals, composite materials or other lightweight sturdy material. The tubular rail  140  passes through and is able to move back and forth through bracket assembly  145 . 
     Bracket assembly  145  includes an upper mounting plate  150  and a lower mounting plate  155 . The two plates can be of any construction well known in the art. The two mounting plates  150 ,  155  are rigidly connected by two connector rods  160  that may be of any construction well known in the art such as bolts and nuts. For example, the connector rods  160  can be bolts that are affixed in any manner well known in the art to upper mounting plate  150 . The upper and lower mounting plates  150 ,  155  include matching holes  165  through which the bolts can pass and then be secured to the lower mounting plate using nuts  166 . The mounting plates  150 ,  155  may be rigidly affixed to the wheelchair frame  15  in any manner well known in the art. For example, as shown in  FIG. 1 , the lower mounting plate  155  is secured to one portion  50  of the wheelchair frame  15  and one of the connector rods  160  passes through to upper mounting plate  150  of the wheelchair frame  15 . Commonly available foot rest mounts (not shown) may be secured to the upper mounting plate  150  in any manner well known in the art. 
     The bracket assembly also includes a linear polymer bearing  175 . The linear polymer bearing  175  can be of any construction well known in the art such as low friction polymer Iglide® bearings available from Igus, Inc. For example, the linear polymer bearing  175  can be a tube  180  made of aluminum or other lightweight material with a replaceable sleeve insert  185 , which may be plastic or other material. The linear bearing  175  is rigidly affixed to both the upper and lower mounting plates  150 ,  155  in any manner well known in the art. Tubular rail  140  passes through linear bearing  175  and can move back and forth through the linear bearing  175 . 
     The lower end of tubular rail  140  is connected in any manner well known in the art to a washer and thread insert stack  190 . The stack  190  can be any commonly available bearing package and may include, for example, washers  200 , bearings  205  and thrust bearing  210 . 
     Front caster wheel  25  can be a commonly available caster wheel assembly for a wheelchair. Front caster wheel  25  may be mounted in fork  215  in any manner well known in the art so that front caster wheel  25  can rotate about a vertical axle  225 . The vertical axle  225  is mounted to fork  215  in any manner well known in the art. Vertical axle  225  fits into washer and thread insert stack  190  so that it can rotate inside tubular rail  140 . A plate  230  is mounted to vertical axle  225  to limit the extent that the fork  215  can push into tubular rail  140 . 
     Bracket assembly  145  also includes a conventional slam latch  235  that is affixed to upper mounting bracket  150  in any manner well known in the art such as by machine screws  195  that engage corresponding holes  196  in the upper mounting bracket  150 . One end of a cable  405  inside a cable cover  415  of an actuation cable  240  is connected in any manner well known in the art to a latch bar  245  in the slam latch  235 . The latch bar  245  is spring loaded (not shown) to remain extended out of the slam latch housing  250 . When the cable  405  is pulled, the latch  245  will be drawn into the latch housing  250 . The other end of cable  405  is connected to a follower wheel assembly discussed in more detail below. 
       FIGS. 6-7  illustrate a follower wheel assembly  300 . The follower wheel assembly  300  includes a frame  305 . A follower wheel  310  is mounted on the frame  305  in any manner well known in the art. For example, a screw  315  can be placed through a hole  320  in wheel  310  and screwed into a hole  325  on the frame  305 . The follower wheel  310  can be made of neoprene or any other durable material suitable for occasional contact with the surfaces over which the wheelchair  10  will roll. Screw  315  is constructed in such a way to allow wheel  310  to rotate around screw  315 . A washer  330  can be placed on screw  315  and between wheel  310  and frame  305  to allow the wheel  310  to easily rotate. 
     The follower wheel assembly also includes a lower frame bracket  335 . The bracket  335  has screw holes  340  that accept screws  345 . Screws  345  pass through a slot  350  in frame  305 . Washers  355  are placed on screws  345  between the screw heads and the frame  305 . The screws  345  are constructed in such away and positioned in such a manner to allow the slot  350 , and frame  305 , to slide over screws  345 . A bumper  360  is affixed to the frame  305  by a screw  365  that fits into screw hole  370  in frame  305 . The frame  305  also includes a pin  375  that is mounted in hole  380  of frame  305 . One end of a tension spring  385  is attached to pin  375 . The other end of tension spring  385  passes through slot  390  in the lower frame bracket  335  and is affixed to pin  395  that passes through hole  400  and slot  390 . One end of cable  405  is attached to pin  375 . Cable  405  passes through hole  410  in lower frame bracket  335  and then through cable cover  415  of actuation cable  240  to slam latch  235 . 
     The follower wheel assembly  300  is mounted on the wheelchair frame  15  using the lower frame bracket  335  and an upper frame bracket  425 . Lower frame bracket  335  includes a lower receiving channel  420  that is shaped to fit around a portion of frame  15 . The upper frame bracket  425  includes an upper receiving channel  430  that fits around another portion of frame  15  and mates with the lower frame bracket  335 . The upper frame bracket  425  includes holes  435  through which screws  440  pass and engage screw holes  445  in the lower frame bracket  335 . When the screws  440  are tightened, the lower and upper frame brackets  335 ,  425  will compress against frame  15  in a manner well known in the art. 
       FIG. 8  depicts a track belt damping bar  500 . Track belt damping bar  500  includes angled support frames  505  that are constructed in such a manner to support two rollers  510  mounted on axles  515 . Additional rollers may also be used. The rollers  510  and axles  515  may be connected to rotational dampers (not shown) that dampen the rotation of rollers  510 . A friction belt  520  may be mounted around and be adapted to move around rollers  510 . Lower ends  525  of angled support frames  505  are mounted to the wheelchair frame  15  in any manner well known in the art. For example, the lower ends  525  can be shaped to fit around a portion of the wheelchair frame  15  and fasteners  530  pass through the lower ends  525  and the wheelchair frame  15  in such a way to rigidly affix the angled support frames  505  to the wheelchair frame  15 . In general, the support frames  505  are mounted to the wheelchair frame  15  at a location along an axis of the perimeter of the side wheels. Such positioning allows, for example, the support frames  505  to engage a curb when the wheelchair side wheels descend from an upper surface to a lower surface thereby temporarily supporting a portion of the wheelchair during the descent. 
       FIGS. 9A-9D  illustrate the wheelchair  10 , front caster wheel slider assembly  100  and follower wheel assembly  300  in operation as the wheelchair  10  moves from an upper surface  600  to a lower surface  605  over a curb  610 .  FIG. 9A  depicts the wheelchair  10  in a normal operating mode on upper surface  600 . The frame  305  of follower wheel assembly  300  is shown in a lowered position. Referring to  FIGS. 6-7 , the tension spring  385  causes the frame  305  to be pulled down towards the lower frame bracket  335  and into the lowered position. The follower wheel assembly  300  is mounted to a portion of wheelchair frame  15  between the front caster wheel slider assembly  100  and side wheels  20  and is mounted in such a way to prevent the follower wheel  310  from touching the ground during the normal operating mode of the wheelchair, i.e., when the wheelchair is traveling over level surfaces.  FIG. 9A  also depicts the tubular rail  140  of front, caster wheel slider assembly  100  in an tipper upper retracted position. Referring to  FIGS. 2-5 , the tubular rail  140  is held in its upper retracted position by latch bar  245  of slam latch  235 . 
       FIG. 9B  depicts wheelchair  10  after the front caster wheels  25  have traveled over curb  610 . As the wheelchair  10  moves over the curb  610 , the front caster wheels  25  will begin to drop over the edge of curb  610 . As the wheelchair  10  pitches forward, the follower wheel  310  will engage upper surface  600  and the follower wheel assembly  300  will begin to support wheelchair  10  as the wheelchair  10  continues to roll over upper surface  600 . As the wheelchair  10  pitches forward, the slot  350  in frame  305  of the follower wheel assembly  300  will slide over the screws  345  until the bumper  360  touches the lower frame bracket  335 . As the frame  305  pushes upwards, pin  395  on frame  305  will pull cable  405 , which will in turn pull on latch bar  245  of slam latch  235  until the latch bar  245  is in the latch housing  250 . Once the latch bar  245  enters the latch housing  250 , the latch bar  245  will release the tubular rail  140 . Since the upper end of tubular rail  140  is connected to piston rod  135  of damping unit  110 , the gas inside tube  120  of damping unit  110  will eject the piston rod  135  and in turn push the tubular rail  140  down so that front caster wheels  25  will quickly push down to engage and roll over lower surface  605 . As shown in  FIG. 9B , the wheelchair  10  remains in the same level position as it was in  FIG. 9A , when the front caster wheels  25  descend over the curb  610 . 
       FIG. 9C  depicts the wheelchair  10  after the follower wheel  310  moves over curb  610 . When the follower wheel  310  moves past the curb and no longer engages upper surface  600 , the follower wheel assembly  300  no longer supports the wheelchair  10 . Instead, the front caster wheel slider assembly  100  will support the wheelchair  10 . The damping unit  110  has a damping force that prevents the piston rod  135  and tubular rail  140  from moving upwards quickly into a retracted position. After the follower wheel  310  moves over the curb  610 , the spring  385  of the follower wheel assembly  300  will pull on frame  305  so that the slot  350  in frame  305  will slide over the screws  345  until the top screw  345  engages the top of the slot  350 . As shown in  FIG. 9C , the wheelchair  10  remains in the same level position as it was in  FIGS. 9A and 9B . 
       FIG. 9D  depicts wheelchair  10  after the two main side wheels  20  roll over curb  610 . As the two main side wheels  20  roll over curb  610 , the weight of the wheelchair  10  will shift and cause the front caster wheels  25  to push on the tubular rail  140  and on the piston rod  135  in such a fashion that the piston rod  135  is pushed back into the damping unit  110 . The damping unit  110  is adjustable in such a fashion to control the piston rod&#39;s  135  retraction speed back into the damping unit  110 , i.e., so that it retracts slowly to avoid sudden movements. The adjustability of the damping unit  110  can also be used to adjust the pitch of the wheelchair  10  as it moves over and down a curb. When the two main side wheels  20  engage the lower surface  605 , the piston rod  135  and tubular rail  140  will be back in their retracted position and latch bar  245  of slam latch  235  will push back out of latch housing  250  to engage and hold in the retracted position the tubular rail  140 . As shown in  FIG. 9D , the wheelchair  10  remains in the same level position as it was in  FIGS. 9A ,  9 B and  9 C. 
       FIG. 10  illustrates the wheelchair  10  and track belt damping bar  500  in operation as the wheelchair  10  moves from an upper surface  600  to a lower surface  605  over a curb  610 . As shown, the track belt damping bar  500  may be connected to a follower wheel assembly frame  305 , but may also be connected to a wheelchair frame  15  or other location. As the two main side wheels  20  roll over curb  610  and the follower wheel assembly  300  is no longer supporting the wheelchair  10 , a point  620  on the friction belt  520  of the track belt damping bar  500  will engage a point  625  on the curb  610 . As the wheelchair  10  rolls forward, the point  620  of belt  520  will continue to engage point  625  on the curb  610  and cause the belt  520  to roll around, the rollers  510 . As the belt  520  rolls around the rollers  510 , rotational dampers (not shown) will dampen the rotation of the rollers and slow the movement of the wheelchair  10  over the curb  610 . Thus, the wheelchair  10  can slowly and safely move over a curb while maintaining a level position for an occupant of the wheelchair  10 . 
     While the invention has been described and illustrated in connection with preferred embodiments, many variations and modifications as will be evident to those skilled in this art may be made without departing from the spirit and scope of the invention, and the invention is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modification are intended to be included within the scope of the invention.