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 . fig1 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 ). fig3 a 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 . 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 . as shown in fig3 b , 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 . fig4 a - 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 . at the left side of fig4 c , 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 , fig2 .) 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 ). 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 . 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 . 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 fig1 and 4a - 4d 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 . fig5 is an exploded view of the embodiment shown in fig4 . 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 . 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 . fig6 a - 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 ). the embodiments illustrated in fig4 - 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 . 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 .
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 .