referring now to the drawings , particularly fig1 the crutch attachment 10 will be seen to include two basic assemblies , the vertical support assembly 19 and the knee support assembly 29 . the vertical support assembly 19 includes two parallel vertically disposed angle beams or channels 20 joined at the base by a bottom cross brace 28 formed of a substantially &# 34 ; u &# 34 ; shaped member . this vertical support assembly 19 provides the foundation for the mounting and movement of the knee support assembly 29 . the vertical channels 20 according to the preferred embodiment of this invention are each constructed from angled aluminum stock . however , the present invention is not to be limited to this material . the beams 20 are oriented so that the one leg 25 of both angle beams 20 project inwardly in a common plane while the other leg 26 of each beam lies in an individual plane rotated ninety degrees from the common plane in the direction of the crutch . furthermore , the beams 20 are provided with a plurality of holes 21 longitudinally arrayed , to extend downwardly from the upper end and which lie in the side plane 26 of each beam 20 . the holes 21 provide a height adjusting means for attaching the device 10 to the frame elements of a crutch c . longitudinally disposed along the medial portion of the rearward projecting leg 26 of each beam 20 is a slot 22 of such a size as to enable a slidable and rotatable connection , by means of hinge pin 51 , to move within the upper knee support brace 40 . furthermore , the lower end of the slots 22 terminate in a notch 24 which forms a locking area for the sliding mechanism . each notch 24 projects rearward at an angle of approximately ninety degrees with the slot itself . the opposite end of the upper knee support brace 40 is rotatably joined by hinge pin 52 to the upper end of the lower knee support brace 30 while the lower end of the lower knee support brace 30 is , in turn , rotatably affixed by hinge pin 53 to the bottom end of the vertical support beam 20 . the ends of the hinge pin 52 are seated in the upper brace member 40 as at 31 while the ends of the other hinge pin 53 will be seen to be seated in the vertical beams 20 as depicted at 32 . to provide for comfortable engagement by the user &# 39 ; s knee , the knee support brace members 40 are spanned by a suitably cushioned member 42 . the folding , opening , and locking in the open position of the knee support assembly in an open position is accomplished with the aid of the notch 24 and a pair of leaf springs 37 . the lower ends of the leaf springs 37 slide up and down within the interior of the channel cross brace 28 while the upper ends of the leaf springs 37 are affixed to the intermediate portion of the lower knee support braces 30 as will be most readily seen in fig4 at 33 . when the knee support assembly 29 is in the folded position , the lower knee support brace and the upper knee support brace are held by the leaf spring in a substantially vertical position against the vertical support assembly . to move the knee support assembly to the locked open position , the hinge pin 52 which joins the bottom end of the upper knee support brace to the upper end of the lower knee support brace , must be moved in a substantially horizontal and forward direction away from the vertical support assembly . this motion will cause the upper end of the lower knee support brace and the lower end of the upper knee support brace to follow an arcuate path away from the vertical support assembly . this arc is defined by a radius equal to the distance along the lower knee support brace from the bottom hinge pin 53 to the middle hinge pin 52 , and equates to an axis of rotation located at the bottom hinge pin 53 . as the joint defined by the hinge pin 52 moves outward and downward from the stored or folded position , the upper end of the upper knee support brace will move vertically downward , following a path defined by the slot 22 in the vertical support beams 20 . slot 22 of the upper knee support brace , and the lower support brace will work in conjunction with each other to approximate the motion of a sliding crank mechanism . in this respect , the lower knee support brace will function as the crank , the upper knee support brace will function as the connecting rod and the hinge pin 51 will function as the slider with a reciprocating motion along the path defined by the slot 22 . following the sliding crank analogy , and establishing the zero reference angle for the lower knee support brace ( crank ) at its folded position , the maximum angular displacement of the lower knee support brace ( crank ) will occur when the hinge pin ( slider ) reaches the bottom of the slot in the vertical support assembly ( slider path ) and the upper knee support brace ( connecting rod ) is substantially perpendicular to the slot in the vertical support assembly ( slider path ). the knee support assembly may be locked open only in the fully extended position . to lock the knee support in this position , the device 10 should preferably be held in an upright or vertical attitude . when the knee support assembly is opened to the fully extended position and then released , the spring will force the lower knee support brace to rotate back toward the folded position . this , in turn , will move the upper knee support brace in a lateral direction toward the rear of the device forcing the sliding hinge pin to move into the notch at the bottom of the slot in the vertical support beam . thus , the device will be locked in the open position . to release the self - locking mechanism and fold the device , the user must simply push the hinge pin 51 forward out of the notch into the main channel of the slot and raise the pin to the point where the spring no longer exerts any force due to its bending . to install the present invention on an existing crutch , the mounting holes 21 which are located along the top portion of the vertical support beams 20 may be lined up with the existing hand grip attachment holes on the crutch c . the device may then be affixed to the crutch with the aid of a bolt and wing nut . the bolt should be inserted to pass through the holes in the crutch frame and a selected hole 21 in the vertical support beam . a wing nut or the like may then be used to secure the bolt in position . an alternate embodiment of the present invention makes use of a sling 60 in place of the upper knee support brace 40 . several minor structural changes must be made in order to facilitate the use and installation of the sling . referring now to fig5 the alternate embodiment is seen to include a sling 60 which is suspended between a fixed rod 61 on the vertical support beam 20 and a hinge 52 at the upper end of the lower knee support brace 30 . the upper knee support brace has been shortened and moved to a lower position , the lower end of the alternate support brace 62 is hingedly attached to the medial portion of the lower knee support brace , while the upper end of the alternate support brace is affixed to a hinge pin similar to that of the first embodiment . the mechanism functions in a manner similar to a slider crank mechanism , however the slider portion is not captively held or restricted to a simple linear motion as defined by the slot in the first embodiment . the upper end of the alternate support brace 62 simply slides in a vertical plane along the front of the vertical support beams . the maximum angular displacement of the lower knee support brace is dependent on the length of the sling 60 . as the lower end of the alternate support brace 62 is drawn forward away from the vertical support beams , the upper end of the alternate support brace will slide down along the front of the vertical support beam . the alternate support brace 62 will become perpendicular to the vertical support beam 20 just before the fully extended position of the knee support assembly is reached . in the fully extended position of the knee support assembly , the upper end of the alternate support brace will fall past the point where the brace is perpendicular to the vertical support beam and will fall to rest on a brace stop 63 which projects horizontally forward from the vertical support beam .
an attachment for existing crutches includes a foldable mechanism having a knee supporting platform and which is shiftable from a horizontal use position , on the inside of a crutch , to a vertical stowed position . provision is included for vertical adjustment of the platform whereby a user may easily select either mode of the device when transitioning from a walking to a standing , at - rest position . alternate knee supporting platform structure is proposed , to accommodate the desires of the user .