Abstract:
A wheelchair leg-rest adapter is configured to attach to a wheelchair using mounting features functionally compatible with those of a leg rest suitable for the wheelchair, and having mounting features functionally compatible with those of a wheelchair suitable for the leg rest. The leg-rest mounting features are pivotally connected to the structure comprising the wheelchair mounting features, so that a leg rest attached to the former can rotate relative to a wheelchair attached to the latter. The adapter further comprises an adjustment mechanism to move an effective pivot point between the leg-rest and wheelchair mounting features at least in a vertical direction, to bring the pivot point near the knee of a user of the wheelchair.

Description:
FIELD 
       [0001]    The invention relates to knee, leg or foot rests for chairs and seats. More specifically, the invention relates to adjustable, pivotally moveable footrests that are connected to the chair or seat for relative movement. 
       BACKGROUND 
       [0002]    Many people suffer from disabilities that affect their life activities. Fortunately, some disabilities can be ameliorated or even alleviated through the use of engineered devices. For example, a cane or walker can help someone with strength or balance problems, while a pacemaker can improve a cardiac patient&#39;s quality of life. 
         [0003]    One common assistive device that is beneficial to both temporarily- and permanently-disabled individuals is the wheelchair. These are available in a wide range of styles, from light-duty, temporary chairs, to racing and cross-country chairs and fully-powered electric models. Although wheelchairs can be useful in a variety of situations, lower-body and leg injuries are disproportionately common among the difficulties faced by a wheelchair user. 
         [0004]    For this reason, many chairs include leg-support structures (generically, “leg rests”) to improve user comfort and convenience. Of course, users&#39; bodies are different sizes and proportions, so it is important for the leg rests (as well as other parts of the chair) to be adjustable, and to be carefully adjusted to fit the user. With respect to leg rests in particular, a problem often encountered is that the rests must be moved, raised and lowered (e.g., to provide suitable ground clearance), and rotated (or swung) up and down (extending the leg) to improve comfort or promote circulation. 
         [0005]    A number of mechanisms for adjustable and extensible leg rests are known in the art, but a common problem is that the effective rotation center of many rests is offset from the leg-rotation (extension) center at the user&#39;s knee, which causes either the flexed or extended leg-rest length to be wrong. (In other words, a leg rest properly adjusted for length in the flexed position, is too short in the extended position; or vice versa.) Mechanisms designed to address this problem are often complex, heavy or prone to breakage. Furthermore, such existing mechanisms are incompatible with standardized, mass-produced, inexpensive leg-rest components that fit many existing wheelchairs. ( FIG. 2  shows an example “universal” leg rest  210 , including the standardized attachment points  220  and  230 , which mate with corresponding points  240  and  250  of compatible wheelchairs This Figure also shows the length adjustment feature of the leg rest  260  and a fold-down foot rest  270 .) 
         [0006]    A new wheelchair accessory that can convert a standard wheelchair and universal leg rest into a length-corrected, extendable leg rest may be of significant value to many wheelchair users. 
       SUMMARY 
       [0007]    Embodiments of the invention add at least one degree of freedom to the adjustment of a wheelchair leg rest so that the rest can be extended and retracted without requiring a compensating adjustment in length. Many embodiments are designed to work with existing non-extendible leg rests. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” 
           [0009]      FIG. 1  shows a general-perspective view of a wheelchair fitted with an embodiment of the invention. 
           [0010]      FIG. 2  shows a prior-art leg rest attached to a wheelchair in the conventional way. 
           [0011]      FIGS. 3A and 3B  are diagrams illustrating the problem to be addressed by embodiments of the invention. 
           [0012]      FIGS. 4A-4D  show several views of an embodiment of the invention with a prior-art length-adjustable “universal” leg rest attached. 
           [0013]      FIG. 5  shows an exploded view of an embodiment of the invention. 
           [0014]      FIGS. 6A-6C  show side views of an embodiment of the invention in flexed, intermediate and extended positions 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the invention provide for adjustment of the location of a pivot point where an elevating leg rest attaches to a wheelchair. Adjusting the pivot point to be closer to the user&#39;s knee allows the foot support of the leg rest to travel in a similar arc as the user&#39;s lower leg and foot, so the foot support remains at a comfortable position, neither too near nor too far from the front of the chair. 
         [0016]      FIG. 1  shows a general-perspective view of a wheelchair  100  fitted with left and right leg rests  110  and  120 , attached to the chair by embodiments of the invention at  130  and  140 . The right leg rest is shown in the lowered position (the user&#39;s leg would be flexed at about 90°) while the left leg rest is shown in the raised (elevated or extended) position, where the user&#39;s lower leg would extend out in front, perhaps supported by a calf pad (not shown). 
         [0017]      FIG. 3A  shows a representative side view of a wheelchair, with key portions of the chair and user identified by reference characters. The heavy horizontal line at  310  indicates the seat of the wheelchair, while line  320  (and short perpendicular line  325 ) represent the leg rest and foot support. The leg rest is rotatably attached to the seat at the seat&#39;s front edge,  330 . 
         [0018]    The user&#39;s thigh is represented by heavy horizontal line  340 , while his lower leg and foot are shown as  350  and  355 . These lines may be thought of as approximating the location and orientation of the bones of the leg and foot: the femur, tibia/fibula, tarsus, metatarsus and phalanges. Rotation of the lower leg relative to the upper leg occurs at the knee  360 . 
         [0019]    As shown in  FIG. 3B , elevating the leg rest and lower leg results in a mismatch  370  between the elevated leg-rest length and the length of the user&#39;s leg. This mismatch occurs because the leg rest and lower leg follow different arcs about their respective pivot points as they are raised. Embodiments of the invention permit the adjustment of the leg rest pivot point to bring it nearer the user&#39;s knee. When so adjusted, the leg rest and lower leg follow similar arcs, and the extended leg-rest length need not be altered to maintain user comfort. 
         [0020]      FIGS. 4A-4D  show top, front, left and perspective views of an embodiment of the invention with a prior-art universal, length-adjustable leg rest in place. Details are most easily indicated in side view  4 C, so that is where most reference characters are placed. However, each of these views was created from a single three-dimensional model, so each shows substantially the same elements, except where one element occludes visibility of another one in a particular view. 
         [0021]    At the left side of  FIG. 4C , the standard universal leg rest is identified generally as  210 . In this view, the length-adjusting holes  260  are apparent, as are mounting bosses  220  and  230 , by which the leg rest may be attached to a compatible wheelchair (see, for example,  FIG. 2 .) The embodiment of the invention comprises a main body tube  400 , curved into roughly horizontal and roughly vertical portions, through which a slidably-adjustable vertical tube  410  passes. At the upper end of the adjustable tube is a pivot mechanism  440 , including a shield  450  against which mounting boss  230  rests (or, in some embodiments, to which it is secured). 
         [0022]    At the right side of the figure, the embodiment&#39;s mounting bosses  420  and  430  are visible. These bosses connect the embodiment to the wheelchair (for example, the upper boss  420  fits into, and the lower boss  430  rests against, a vertical tube of the frame of the wheelchair, indicated in this figure by dashed lines  200 . Vertical adjustment tube  410  can be secured in place by a locking mechanism  470  (in the embodiment depicted here, the locking mechanism comprises a simple slot  460  in the main body  400  to form a split-flange feature, with a thumb-screw adjustable compression ring  470  to hold tube  410  at a desired position. In use, locking mechanism  470  would be released and tube  410  adjusted vertically to bring pivot  430  near the seated wheelchair user&#39;s knee. Then compression ring  470  would be tightened to lock tube  410  and pivot  440  in position. 
         [0023]    In some embodiments, other locking mechanisms may be used. For example, a lever and cam “quick release” may substitute for the thumb-screw adjustable compression ring. Alternatively, for more-permanent installations, a set screw or grub screw may secure the sliding tube. If fine adjustability is not necessary, a five- or six-hole captured-pin or shear-pin adjustment, similar to the length adjuster of the leg rest, may be provided. The important capability of the adjuster is that it allow at least vertical movement and positioning of pivot  440 , to bring the pivot nearer the wheelchair user&#39;s knee. 
         [0024]    It is appreciated that, for best results, the pivot point must be both vertically and horizontally near the user&#39;s knee when viewed from the side (but need not be near the knee medially). The embodiments shown in  FIGS. 1 and 4A  -  4 D only allow pivot adjustment in the vertical direction. This is acceptable for many wheelchair applications because the position of the user&#39;s knee can be moved fore and aft by using existing adjustment features of the wheelchair. Since fore/aft adjustment is available in the chair already, an embodiment of the invention may be constructed more simply, reliably and inexpensively by providing only up-and-down adjustment of the pivot point. However, for use on wheelchairs that lack adequate fore/aft adjustability, an embodiment may allow the pivot point to be adjusted in more than one direction. 
         [0025]      FIG. 5  is an exploded view of the embodiment shown in  FIG. 4 . Since adjustable leg rest  210  has been removed from the embodiment (generally,  500 ), its complete mounting bosses  220 ,  230  are visible. Note that they are functionally interchangeable with the corresponding mounting bosses  420  and  430  on the embodiment, because the embodiment connects to the wheelchair in place of the leg rest. In this exploded view, receptacle  520  is visible. Mounting boss  220  (a cylindrical, expandable plug) fits into this receptacle (just as mounting boss  420  fits into a corresponding receptacle in the wheelchair frame), while mounting boss  230  (a substantially horizontal stay) rests against shield  450 . Shield  450  mostly obscures the pivot point in this figure, so the pivot is not identified with a reference character. Clamping mechanism  570  is visible. 
         [0026]    It is appreciated that the two sets of mounting features of an embodiment (the features that connect to the leg rest assembly, and the features that connect to the wheelchair) may be similar (if the embodiment is to be interposed between a leg rest and a wheelchair for which the leg rest is designed); or different (if the embodiment is to be interposed between a leg rest and a different wheelchair, with which the leg rest could not ordinarily be used). In other words, in addition to allowing adjustment of the elevating leg rest pivot point so that the leg rest length need not be adjusted between the elevated and retracted positions, an embodiment can serve as an adapter to allow one type of leg rest to be used with a different type of wheelchair. As an alternative way of describing this property of an embodiment, note that the two sets of mounting features are complementary. In an embodiment designed for use with a leg rest and the wheelchair for which the leg rest is designed, two instances of the embodiment can be connected together because the leg-rest mounting features of one instance will mate properly with the wheelchair mounting features of the other instance. By contrast, in a “heterogeneous” embodiment (designed to fit between a wheelchair and a leg rest designed for a different, incompatible wheelchair), two instances of the heterogeneous embodiment cannot be connected together because the mounting features are not compatible. 
         [0027]      FIGS. 6A-6C  show side views of an embodiment of the invention as the leg rest rotates from fully-flexed to fully-extended position. Note that rotation occurs generally about the pivot point  430  (which has been adjusted to be near the wheelchair user&#39;s knee). 
         [0028]    The embodiments illustrated in  FIGS. 4-6  only permit adjustment of the leg-rest pivot point in a roughly vertical direction. The main body of an embodiment, e.g. support sleeve  400 , advances the vertical support  410  forward from the frame tube  200 , but the amount of advance is not adjustable. However, differently-dimensioned support sleeves can be provided so that the vertical support  410  is placed closer or further away from the front edge of the seat. Note that the portions of the embodiment that engage the wheelchair frame (e.g., upper plug  420  and midpoint strut  430 ) are designed to emulate (in size and orientation) the corresponding features of the leg rest  210 , while the portions of the embodiment that engage the leg rest (e.g., socket  520  and shield  450 ) similarly emulate corresponding features of the wheelchair frame. Thus, these embodiments can be used to convert a wheelchair with a fixed leg rest (or an elevating leg rest with an incorrectly-positioned pivot point) into a wheelchair with an adjustable, elevating leg rest. The use of standard mounting features and orientations also allows the use of existing replacement parts. 
         [0029]    Embodiments of the present invention have been described largely by reference to specific examples and in terms of particular physical structures to achieve the useful characteristics described. However, those of skill in the art will recognize that adjustable elevating leg rests for wheelchairs can also be constructed using different components and arrangements. Such variations and implementations are understood to be captured according to the following claims.