Patent Publication Number: US-7222881-B1

Title: Stop for an anti-tip wheel for a wheelchair

Description:
TECHNICAL FIELD 
     The present invention relates in general to wheelchairs and specifically to wheelchairs having anti-tip wheels. More particularly, the invention relates to the use of an anti-tip stop for limiting the range of motion the anti-tip wheels. 
     BACKGROUND OF THE INVENTION 
     Wheelchairs are land vehicles that are provided for transporting the physically impaired. Wheelchairs generally include a base frame supported on a supporting surface by a pair of idler wheels and a pair of drive wheels. The drive wheels may be manually driven by a wheelchair occupant or power driven by motors controlled by the wheelchair occupant. The wheelchair may be maneuvered by differentially driving the drive wheels. The idler wheels are generally in the form of casters, typically located in front of the drive wheels. The casters swivel to enhance the maneuverability of the wheelchair. Optionally, the wheelchair may include a pair of anti-tip wheels, typically located to rear of the drive wheels, which function to enhance the stability of the wheelchair. 
     The drive wheels have historically supported a rear portion of the wheelchair base frame while casters have supported a front portion of the wheelchair. However, the drive wheels of late have supported a front portion of the base frame as well. The former wheelchairs are commonly referred to as rear-wheel drive wheelchairs while the later wheelchairs are commonly referred to as mid-wheel drive wheelchairs. The casters of rear-wheel drive wheelchairs are typically located towards the front of the base frame. The casters of mid-wheel drive wheelchairs typically located towards the rear of the base frame. 
     Tipping is a potential problem with wheelchairs, and can occur when accelerating, or traversing obstacles or unlevel terrain. Tipping may also occur in wheelchairs that are provided with reclining seats. Anti-tip wheels are commonly attached to wheelchairs to reduce the risk of wheelchairs tipping over. Anti-tip wheels are usually attached to the rear end of rear-wheel drive wheelchairs and to the front end of mid-wheel drive wheelchairs. The anti-tip wheels are typically fixed in place or limited to a predetermined range of motion. This may have an undesirable affect on the operation of the wheelchair. For example, if the anti-tip wheels are fixed in place the mobility of the wheelchair may be impaired by the limited range of motion of the anti-tip wheels and make maneuverability difficult. Additionally, for example if the anti-tip wheels are limited to a predetermined range of motion and the range of motion is too large then the anti-tip wheels may fail to add stability since they would not provide resistance until after the wheelchair has become unstable. Conversely, if the range of motion is too small then the wheelchair may experience the same problems as when the anti-tip wheels are fixed in place. 
     It would be advantageous if there could be developed an improved anti-tip system that provides stability while maintaining the mobility and maneuverability of a wheelchair. 
     BRIEF SUMMARY OF THE INVENTION 
     An anti-tip adjustable stop for a wheelchair is disclosed. 
     According to the invention there is provided an anti-tip system for a wheelchair including an arm having an attachment end and a distal end, wherein the arm is pivotably mounted at the attachment end on a wheelchair frame. The wheelchair frame includes a wheelchair frame member. An anti-tip wheel is rotatably connected to the distal end of the arm, and a stop for limiting the range of motion of the arm relative to the wheelchair frame member is operably located between the arm and the frame member. 
     According to this invention there is also provided an arm having an attachment end, and a distal end, wherein the arm is pivotally mounted at the attachment end by a resilient hinge on a wheelchair frame, the wheelchair frame including a wheelchair frame member. An anti-tip wheel is rotatably connected to the distal end of the arm, wherein the arm includes a threaded bore. An adjustable stop for limiting the range of motion of the arm relative to the wheelchair frame member is also provided. The stop is operably located between the arm and the frame member, wherein the stop includes a threaded bolt, a lock nut and a resilient bumper, wherein the threaded bolt is disposed in the threaded bore. 
     According to the invention there is also provided a wheelchair having such an anti-tip system. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view in perspective of a wheelchair in accordance with the present invention. 
         FIG. 2  is a side view in schematic of the base frame of the wheelchair of  FIG. 1  with the cover removed. 
         FIG. 3  is an enlarged view of a portion of the base frame of  FIG. 2 . 
         FIG. 4  is an enlarged view of the anti-tip system of  FIG. 3 . 
         FIG. 5  is a view similar to that shown in  FIG. 4 , but with the stop, the arm and the frame member in an operably connected position. 
         FIG. 6  is a view similar to that shown in  FIG. 4 , but showing a first alternative embodiment of the present invention. 
         FIG. 7  is a view similar to that shown in  FIG. 6 , but with the stop, the arm and the frame member in an operably connected position. 
         FIG. 8  is a view similar to that shown in  FIG. 4 , but showing a second alternative embodiment of the present invention. 
         FIG. 9  is a view similar to that shown in  FIG. 4 , but showing a third alternative embodiment of the present invention. 
         FIG. 10  is a view similar to that shown in  FIG. 4 , but showing a fourth alternative embodiment of the present invention. 
         FIG. 11  is a view similar to that shown in  FIG. 4 , but showing a fifth alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  a wheelchair portion  12  includes a base frame  13   a  (as shown in  FIGS. 2 and 3 ), which is mounted for movement on front caster wheels  14  and rear drive wheels  16 . The base portion  12  also includes a cover  13   b . The wheelchair is preferably provided with a drive motor  17   a  and a drive transmission  17   b  (as shown in  FIGS. 2 and 3 ) for each of the drive wheels  16 , and a source of power (not shown) for the drive motors  17   a.    
     The wheelchair  10  includes a seat portion  18 . The seat portion  18  includes a seat frame (not shown), which supports a seat cushion  20  for the support of an occupant. The wheelchair  10  includes a seat back  22 . The seat back  22  includes a back frame  23  and a seat back cushion  23   a , which provide support to the occupant&#39;s body. The wheelchair  10  also includes an optional headrest  24 , which supports the occupant&#39;s head. The occupant&#39;s arms can be supported by armrests  26 . A footrest  30  is provided and optional leg rests (not shown) may be provided. 
     As best seen in  FIGS. 2 and 3 , a pair of rear anti-tip wheels  34  is mounted on arms  38 . It is to be understood that there could be just a single anti-tip wheel. Each arm  38  includes an attachment end  40 , an intermediate portion  42 , and a distal end  44 . The attachment end  40  of the arm  38  is pivotably mounted at a pivot point  48  on the frame member  46 , with the frame member  46  being part of the base frame  13   a . The arm  38  may, however, be mounted at any appropriate frame member. The arm  38  is pivotably mounted so the arm  38  can “swing up”, or pivot in a counter-clockwise direction as illustrated by an arrow  39  in  FIG. 3 , as will be described below. Preferably, the arm  38  is pivotably mounted upon the base frame  13   a  at the pivot point  48  by a resilient hinge connection  48   a.    
     The wheelchair  10  includes an adjustable stop  50 . The stop  50  preferably includes a threaded bolt  52  and a bumper  54  on a first end  56  of the bolt  52 , as shown in  FIGS. 4 and 5 . Preferably, the bumper  54  is a resilient bumper. For example, the bumper  54  may be made of rubber. The bumper  54  may, however, be made of any suitable material. The bumper  54  increases the smoothness of the ride as will be discussed below. 
     As shown in  FIGS. 4 and 5 , the stop  50  is preferably threadably connected to the arm  38  at a threaded bore  60  in the intermediate portion  42  of the arm  38 . Most preferably, the arm  38  includes a plurality of threaded bores  60 , each suitable to receive the threaded bolt  52  of the stop  50 . As shown in  FIG. 4 , the stop  50  is operably located between the arm  38  and a frame member  62 , generally meaning that the stop  50  is in a position between the arm  38  and the frame member  62  suitable to limit the range of motion of the arm  38  relative to the frame member  62 . As shown in  FIG. 4 , there is space between the stop  50  and frame member  62  through the free range of motion of the arm  38 . The frame member  62  can be any portion of the base frame  13   a  that is suitable for the stop  50  to engage. For further example, there is shown in  FIG. 6  an alternative spacing arrangement with space between the sub-components of the stop  50 . 
     When the arm  38  pivots, for example because of unlevel terrain or displacement of the occupant&#39;s weight, the arm  38  will pivot toward the frame member  62  of the base frame  13   a . The arm  38  is pivotably mounted so that the arm  38  can “swing up” or pivot. The arm  38  is preferably pivotably mounted upon the base frame  13   a  at the pivot point  48  by the resilient hinge connection  48   a  so that there will be some resistance or resiliency to the “upward swing” or pivot of the arm  38 . When the arm  38  reaches a predetermined position relative to the frame member  62 , the stop  50  limits the range of motion of the arm  38 , and in turn the anti-tip wheel  34 , relative to the base frame  13   a , thereby providing stability to the wheelchair  10 . Thus, when the stop  50  limits the range of motion, the stop is operably connected to the arm  38  and the frame member  62 . This means that the stop  50  is fully engaged, without space between the arm  38  and the frame member  62 , to limit the range of motion of the arm  38  relative to the frame member  62 . Thus, at some point in the “upward swing” or pivot, the resiliency effect reaches its limit and the arm  38  can pivot no farther. Thus, the stop  50  is operably connected to the arm  38  and the frame member  62 , generally meaning that the stop  50  is in a position between the arm  38  and the frame member  62 , without space there between, and limiting the range of motion of the arm  38  relative to the frame member  62 . When the bumper  54  engages the frame member  62  the bumper  54  allows a small amount of additional travel while providing some resistance. Thus, the bumper  54  increases the smoothness of the ride by providing some resiliency to the stop  50  in addition to the resiliency of the hinge connection  48   a.    
     The limit of the range of motion of the arm  38  relative to the frame member  62  may be adjusted by increasing or decreasing the extent to which the threaded bolt  52  is screwed into the treaded bore  60 . This adjustment decreases or increases the distance of the bumper  54  from the arm  38 , and thus decreases or increases the limit of the range of motion of the arm  38  and the rear anti-tip wheel  34 . The limit of the range of motion may be further adjusted by selecting a different threaded bore  60  for the stop  50  to threadably engage. The use of the stop  50  thus allows the extent of the pivotal movement of the arm  38  to be readily adjusted to meet the needs of a particular wheelchair occupant or user. 
     As shown in  FIGS. 6 and 7 , the threaded bolt  52  of the stop  50  may optionally be threadably connected to the frame member  62 , at a threaded bore  64 . Further, the bumper  54  of the stop  50  may optionally be mounted on a separate part rather than being mounted on the bolt  52 . For example, the bolt  52  can be mounted on the arm  38 , with the bumper  54  mounted on the frame member  62 . Alternatively, the bolt  52  can be mounted on the frame member  62 , with the bumper  54  mounted on the arm  36 . Thus, the bumper  54  can be placed on the one of the arm  38  and the frame member  62  to which the threaded bolt  52  is not connected. As shown in  FIGS. 6 and 7  a plurality of bumpers  54  are connected to the arm  38 . For example, the bumpers  54  may be connected to the arm  38  by adhesive, or by any suitable manner. Preferably, the frame member  62  includes a plurality of threaded bores  64 , each suitable to receive the threaded bolt  52  of the stop  50 . Most preferably, the location of each of the bumpers  54  corresponds to the location of one of the bores  64 . Thus, when the bolt  52  is screwed into any of the bores  64 , the stop  50 , including the threaded bolt  52  and the corresponding bumper  54 , is operably located between the arm  38  and the frame member  62 . The stop  50  may optionally include a lock nut  58  in order to fix the extent to which the threaded bolt  52  is screwed into the frame member  62 . 
     When the arm  38  pivots, for example because of unlevel terrain or displacement of the occupant&#39;s weight, the arm  38  will pivot toward a frame member  62  of the base frame  13   a . As previously discussed, the arm  38  is pivotably mounted so that the arm  38  can “swing up” or pivot and preferably by the resilient hinge connection  48   a . When the arm  38  reaches a predetermined position relative to the frame member  62  the bumper  54  engages the threaded bolt  52 , thus the stop  50  is operably connected to the arm  38  and the frame member  62 . The stop  50  thus limits the range of motion of the arm  38 , and in turn the anti-tip wheel  34 , relative to the base frame  13   a , and provides stability to the wheelchair  10 . 
     As discussed previously, the range of motion of the arm  38  relative to the frame member  62  may be adjusted by increasing or decreasing the extent to which of the threaded bolt  52  engages the treaded bore  64 , in this case, thus decreasing or increasing the amount of the threaded bolt  52  extending from the frame member  62 , and thus decreasing or increasing the range of motion. The limit of the range of motion may be further adjusted by selecting a different threaded bore  64  for the threaded bolt  52  to threadably engage. The lock nut  58  may then be adjusted toward the frame member  62  to secure the threaded bolt  52  in place, relative to the frame member  62 . The use of the stop  50  thus allows the extent of the pivotal movement of the arm  38  to be readily adjusted to meet the needs of a particular wheelchair occupant or user. 
       FIG. 8  is a view of an embodiment similar to that shown in  FIG. 4 , similar elements or components are labeled with similar numbers. Although the preferred embodiment has been described with the threaded bolt  52 , which is a straight bolt, an alternative embodiment includes a bolt  152 , which is curved. 
       FIG. 9  is a view similar to that shown in  FIG. 4 , and similar elements or components are labeled with similar numbers. Although the preferred embodiment has been described with the threaded bolt  52 , an alternative embodiment includes a bolt  252  with a damper  253 . The damper  253  is preferably a hydraulic shock absorber, however it must be understood that the damper  253  may be any suitable damper, such as a mechanical spring assembly or any other suitable damper. 
       FIG. 10  is a view similar to that shown in  FIG. 4 , and similar elements or components are labeled with similar numbers. The bumper  54  is connected to sleeve  359 . The sleeve  359  includes a plurality of holes  361 . The sleeve  359  slidably engages a rod  352 . The rod  352  is preferably permanently fixed in a bore  360  in the arm  38 . That is to say, that substantial damage would occur to either the rod  352  or the arm  38  if the rod  352  were to be removed from the arm  38 . Alternatively, the rod  352  could be removable. The rod  352  includes a plurality of holes  355 . A moveable retainer pin  357 , for example a cotter pin, is disposed in aligned holes  361  and  355  as to secure the sleeve  359  relative to the rod  352 . The limit of the range of motion of the arm  38  relative to the frame member  62  may be adjusted by increasing or decreasing the amount of the sleeve  359  engaging the rod  352 , thus decreasing or increasing the distance of the bumper  54  from the arm  38 , and thus decreasing or increasing the limit of the range of motion. 
       FIG. 11  is a view similar to that shown in  FIG. 4 , with similar elements or components being labeled with similar numbers. A curved plate  452  is disposed in a curved bore  460  in the arm  38 . The curved plate is generally arcuate shaped, but may be any suitable shape. The curved plate  452  includes a plurality of holes  455  and the arm  38  includes a hole  461 . A retainer pin  457 , such as a cotter pin, is disposed in the hole  461  and one of the holes  455  as to secure the curved plate  452  relative to the arm  38 . The limit of the range of motion of the arm  38  relative to the frame member  62  may be adjusted by increasing or decreasing the amount of the curved plate  452  engaging the arm  38 , thus decreasing or increasing the distance of the bumper  54  from the arm  38 , and thus decreasing or increasing the limit of the range of motion. 
     While the invention has been described in its preferred embodiment with rear anti-tip wheels  34 , it must be understood, however, that the anti-tip wheel  34  and the arm  38  may be placed in any suitable location upon the wheelchair  10 . Further, while the invention has been illustrated in its preferred embodiment with the frame member  62  being a vertical frame member, it must be understood, however, that the frame member  62  may be any suitable frame member. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.