Abstract:
A portable commode, shower, and bath wheelchair apparatus comprising a first support frame, a second support frame, a mechanical interface interconnecting the first support frame to the second support frame thereby forming a first contiguous support rail and a second contiguous support rail. A seat assembly is slidingly attached to both the first contiguous support rail and to the second contiguous support rail.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from a U.S. Provisional Application having Ser. No. 60/821,923 filed Aug. 9, 2006. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a portable commode, shower and bath wheelchair apparatus. 
     BACKGROUND OF THE INVENTION 
     When using prior art apparatus and methods, persons using wheelchairs usually require assistance when using the bathroom, including the toilet and shower. Few prior art devices allow for the seamless transition from bed to toilet to shower or bathtub and back again. These apparatus are typically comprised of a commode chair with a seat that can slide along an adjoining track system, over the barrier of the shower or bathtub, to position the person over the shower or bathtub. 
     The track systems employed have either been fixed to the shower or bathtub or have been supported on one side by the commode chair and on the other side by two support members. Fixation of the track system to the shower or bathtub does not enable the track system to be transported to another location. Reliance on the commode chair to support the track system can present stability problems during the transfer, which can result in injury to the person transferred. 
     SUMMARY OF THE INVENTION 
     The invention comprises a portable commode, shower, and bath wheelchair apparatus, and a method using that apparatus. Applicant&#39;s apparatus comprises a first support frame comprising a first support rail, a second support rail, and four first leg assemblies, a second support frame comprising a third support rail, a fourth support rail, and four second leg assemblies, and a mechanical interface comprising a first interface assembly comprising a fifth support rail, and a second interface assembly comprising a sixth support rail. 
     The first interface assembly can be releasably attached, without using any tools, to the first support rail and to the third support rail, such that the first support rail and the fifth support rail and the third support rail comprise a first contiguous support rail. The second interface assembly can be releasably attached, without using any tools, to the second support rail and to the fourth support rail, such that the second support rail and the fifth support rail and the fourth support rail comprise a second contiguous support rail. A seat assembly comprising a plurality of attachment assemblies can be slidingly attached to both the first contiguous support rail and to the second contiguous support rail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from a reading of the following detailed description taken in conjunction with the drawings in which like reference designators are used to designate like elements, and in which: 
         FIG. 1  is a perspective view showing Applicant&#39;s first support frame, mechanical interface, and second support frame, wherein Applicant&#39;s seat assembly is shown slidingly disposed on the second support frame; 
         FIG. 2  is a perspective view of Applicant&#39;s first support frame, wherein a plurality of leg assemblies are shown in a first configuration wherein those leg assemblies extend outwardly from a set of parallel support members; 
         FIG. 3  is a perspective view of Applicant&#39;s second support frame, wherein a plurality of leg assemblies are shown in a first configuration wherein those leg assemblies extend outwardly from a set of parallel support members; 
         FIG. 4  is a perspective view of Applicant&#39;s mechanical interface; 
         FIG. 5A  is a perspective view of Applicant&#39;s backrest and seat, wherein the backrest is disposed in an upright configuration; 
         FIG. 5B  is a perspective view of Applicant&#39;s backrest and seat, wherein the backrest is disposed in a folded configuration; 
         FIG. 5C  is a perspective view showing additional elements of Applicant&#39;s seat assembly; 
         FIG. 6A  is a top view showing Applicant&#39;s hinge assembly in a locked position; 
         FIG. 6B  is a top view showing Applicant&#39;s hinge assembly in a locked position; 
         FIG. 7A  is a side view showing Applicant&#39;s hinge assembly in an unlocked and folded position; 
         FIG. 7B  shows an aperture formed in the ends of each of the support members disposed in Applicant&#39;s first support frame and second support frame; 
         FIG. 8A  shows the leg assemblies of Applicant&#39;s first support frame disposed in a folded configuration wherein those leg assemblies are disposed within the first support frame; 
         FIG. 8B  shows the leg assemblies of Applicant&#39;s second support frame disposed in a folded configuration wherein those leg assemblies are disposed within the second support frame; 
         FIG. 9  shows the elements of Applicant&#39;s attachment assembly; 
         FIG. 10  shows a shaft passing through the elements of  FIG. 9 ; 
         FIG. 11  is a side view of Applicant&#39;s seat frame; 
         FIG. 12A  is perspective view of Applicant&#39;s seat frame; 
         FIG. 12B  is a bottom view showing Applicant&#39;s seat frame attached to a set of support rails, wherein a set of locking assemblies are in a locked configuration; 
         FIG. 12C  is a bottom view showing Applicant&#39;s seat frame attached to a set of support rails, wherein a set of locking assemblies are in an unlocked configuration; 
         FIG. 13A  is a side view of Applicant&#39;s attachment assembly showing an aggregate arcuate surface formed by a first arcuate surface and a second arcuate surface; 
         FIG. 13B  shows the radius of curvature of the aggregate arcuate surface of  FIG. 13A ; 
         FIG. 13C  shows the radius of curvature of a plurality of Applicant&#39;s support rails; 
         FIG. 13D  shows one of Applicant&#39;s attachment assembly releasably attached to one of Applicant&#39;s support rails. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention is described in preferred embodiments in the following description with reference to the Figures, in which like numbers represent the same or similar elements. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     Referring now to  FIG. 1 , Applicant&#39;s apparatus  100  comprises movable first support frame  110 , second support frame  120 , mechanical interface  130 , and seat assembly  140 . In the illustrated embodiment of  FIG. 1 , first support frame  110  further comprises a first set of parallel rails  111 , comprising support rail  112  and support rail  114 . Interface  130  comprises a second set of parallel rails  131 , comprising support rail  132  and support rail  134 . Second frame assembly  120  comprises a third set of parallel rails  121 , comprising support rail  122  and support rail  124 . As described more fully herein, movable first support frame comprises a plurality of wheels. 
     In the illustrated embodiment of  FIG. 1 , the first set of rails  111 , second set of rails  131 , and third set of rails  121  are aligned such that seat assembly  140  can be moved bidirectionally from the first set of rails  111  to the second set of rails  131 , and bidirectionally from the second set of rails  131  to the third set of rails  121 . Thus, seat assembly  140  can be slideably moved from first support frame  110  across interface  130  and onto second frame  120 . Similarly, seat assembly  140  can be slideably moved from second frame  120  across interface  130  and onto first support frame  110 . 
     Interface  130  is releasably interconnected by a springpin lock mechanism with first support frame  110  such that the first set of rails  111  is aligned with the second set of rails  131 . Moreover, second support frame assembly  120  is releasably interconnected by a springpin lock mechanism with interface  130  such that the third set of rails  121  is aligned with the second set of rails  131 . 
     In certain embodiments, support rail  112  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. By “engineering plastic,” Applicant means a polymeric material comprising a tensile modulus of about 500,000 psi or greater, and/or a flexural modulus of about 500,000 psi or greater. Such polymeric materials include, without limitation, one or more polyamides, one or more polyimides, one or more polyetheretherketones, one or more cured epoxy resins, and the like. 
     In certain embodiments, Applicant&#39;s engineering plastic material comprises a polymeric material in combination with one or more fillers, wherein those one or more fillers comprise, for example and without limitation, continuous glass strands, woven fiber glass mats, chopped glass, and the like. In certain embodiments, Applicant&#39;s engineering plastic comprises a filament wound composite comprising one or more reinforcing fiber matrices such as for example fiber glass, carbon fiber, and the like, in combination with one or more cross-linked polymeric resins such as for example a cured epoxy resin. 
     In certain embodiments, support rail  112  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  112  comprises a tubular member having a length between about 16 inches and about 19 inches. In certain embodiments, support rail  112  comprises a solid member having a circular cross-section. 
     In certain embodiments, support rail  114  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rail  114  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  114  comprises a tubular member having a length between about 16 inches and about 19 inches. In certain embodiments, support rail  114  comprises a solid member having a circular cross-section. 
     In certain embodiments, support rail  122  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rail  122  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  122  comprises a tubular member having a length between about 16 inches and about 19 inches. In certain embodiments, support rail  122  comprises a solid member having a circular cross-section. 
     In certain embodiments, support rail  124  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rail  124  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  124  comprises a tubular member having a length between about 16 inches and about 19 inches. In certain embodiments, support rail  124  comprises a solid member having a circular cross-section. 
     In certain embodiments, support rail  132  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rail  132  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  132  comprises a tubular member having a length between about 11 inches and about 18 inches. In certain embodiments, support rail  132  comprises a solid member having a circular cross-section. 
     In certain embodiments, support rail  134  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rail  134  comprises a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rail  134  comprises a tubular member having a length between about 11 inches and about 18 inches. In certain embodiments, support rail  134  comprises a solid member having a circular cross-section. 
     Referring to  FIG. 2 , first support frame  110  comprises support rail  112 , support rail  114 , bracing member  262 , bracing member  264 , first leg assembly  220 , second leg assembly  230 , third leg assembly  240 , fourth leg assembly  250 , wheel assembly  270   a , wheel assembly  270   b , wheel assembly  270   c , wheel assembly  270   d , hinge assembly  600   a , hinge assembly  600   b , hinge assembly  600   c , and hinge assembly  600   d . In the illustrated embodiment of  FIG. 2 , first leg assembly  220  comprises a first member  222  and a second member  224 . The second member  224  is telescopically received by first member  222 , wherein the length of member  224  extending outwardly from member  222  can be adjusted. 
     Similarly, members  234 ,  244 , and  254 , are telescopically received by second members  232 ,  242 , and  252 , respectively. The length of members  234 ,  244 , and  254 , extending outwardly from members  232 ,  242 , and  252 , respectively, can be adjusted. Because the leg heights of support frame  110  are adjustable by varying the lengths of members  224 ,  234 ,  244 , and/or  254 , it is possible to accommodate seat assembly  140  to match various toilet bowl heights, bathtub/shower stall heights, and the height of other objects, such as, without limitations, bed heights. 
     In certain embodiments, members  222 ,  224 ,  232 ,  234 ,  242 ,  244 ,  252 , and  254 , are formed from a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, members  222 ,  232 ,  242 , and  252  comprise a tubular members having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, members  222 ,  232 ,  242 , and  252 , comprise a tubular member having a length between about 8 inches and about 14 inches. In certain embodiments, members  222   232 ,  242 , and  252  comprise a solid member having a circular cross-section. 
     In certain embodiments, members  224 ,  234 ,  244 , and  254 , comprise a tubular member having an outside diameter between about ¾ inch and about ⅞ inch. In certain embodiments, members  224 ,  234 ,  244 , and  254 , comprise a tubular member having a length between about 6 inches and about 10 inches. In certain embodiments, members  224 ,  234 ,  244 , and  254 , comprise a solid member having a circular cross-section. 
     In certain embodiments, wheel assembly  270   a , wheel assembly  270   b , wheel assembly  270   c , and wheel assembly  270   d  comprise a 4-inch diameter wheel. In other embodiments, wheel assembly  270   a , wheel assembly  270   b , wheel assembly  270   c , and wheel assembly  270   d  comprise a wheel having a diameter less than 4 inches. In yet other embodiments, wheel assembly  270   a , wheel assembly  270   b , wheel assembly  270   c , and wheel assembly  270   d  comprise a wheel having a diameter greater than 4 inches. In certain embodiments, wheel assembly  270   a , wheel assembly  270   b , wheel assembly  270   c , and wheel assembly  270   d  comprise castoring wheel assemblies. 
     In other embodiments, wheel assembly  270   a  and wheel assembly  270   d  comprise 15 inch diameter solid rubber wheels with locking brakes which may be interchanged with other wheel assemblies. In these embodiments, the user can grasp one or both of the wheels while seated, and cause moveable assembly  110  in combination with seat assembly  140  to move forwardly, rearwardly, or pivot in either direction, without the assistance of another. 
     In the illustrated embodiment of  FIG. 2 , vertical leg member  222  and vertical leg member  252  are cambered to provide stability, and to prevent tipping of the first support frame  110 . Vertical leg member  222  and vertical leg member  252  are cambered rearwardly at a substantially 15-degree angle. By “substantially 15-degree angle,” Application means 15 degrees+/−2 degrees. The cambering adds stability to the chair rendering it safer and provides the ability to add “rear lean” affording additional comfort for the user. By “rear lean,” Applicant means the ability for a user to lean backward in the chair by adding length to front vertical leg members  232  and  242  using their telescoping features. 
     In the illustrated embodiment of  FIG. 2 , first set of vertical leg members  220  are pivotally interconnected with support rail  112  by hinge  600   a  described hereinafter. Second set of vertical leg members  230  are pivotally interconnected with support rail  114  by hinge  600   b . Third set of vertical leg members  240  are pivotally interconnected with support rail  114  by hinge  600   c . Fourth set of vertical leg members  250  are pivotally interconnected with support rail  112  by hinge  600   d.    
     In the illustrated embodiment of  FIG. 2 , bracing member  262  and bracing member  264  are substantially perpendicular to set of parallel rails  111 . By “substantially perpendicular,” Applicant means the angle formed between bracing member  262  and support rail  112  is 90 degrees+/−10 degrees. In certain embodiments, first bracing member  262  is interconnected with first set of vertical leg members  220  and second set of vertical leg members  230  by conventional attachment means, such as welding, plastic welding, mechanical fasteners, and the like. In certain embodiments, second bracing member  264  is interconnected with third set of vertical leg members  240  and fourth set of vertical leg members  250  by conventional attachment means, such as welding, plastic welding, mechanical fasteners, and the like. 
     In certain embodiments, first bracing members  262  and  264  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, bracing members  262  and  264  comprise a planar member having a length between about 15 inches and about 18 inches. In certain embodiments, bracing members  262  and  264  comprise a width between about 1.5 inches and about 2 inches. In certain embodiments, bracing member  262  comprises a solid member having a rectangular cross-section. In other embodiments, bracing member  262  comprises a circular or oval cross-section. 
     Referring to  FIG. 3 , second support frame  120  comprises support rail  122 , support rail  124 , bracing member  362 , bracing member  364 , first leg assembly  320 , second leg assembly  330 , third leg assembly  340 , fourth leg assembly  350 , adjustable non-skid glide assembly  370   a , adjustable non-skid glide assembly  370   b , adjustable non-skid glide assembly  370   c , adjustable non-skid glide assembly  370   d , brace bar  380 , hinge assembly  600   e , hinge assembly  600   f , hinge assembly  600   g , and hinge assembly  600   h.    
     In the illustrated embodiment of  FIG. 3 , vertical leg members  222 ,  232 ,  242  and  252  are cambered to provide stability, and to prevent tipping of the second support frame  120 . Vertical leg member  232  and vertical leg member  242  are cambered forwardly at a substantially 15-degree angle. Vertical leg member  222  and vertical leg member  252  are cambered rearwardly at a substantially 15-degree angle. By “substantially 15-degree angle,” Application means 15 degrees+/−2 degrees. The cambering adds stability to the chair rendering it safer and provides the ability to add “rear lean” affording additional comfort for the user. By “rear lean,” Applicant means the ability for a user to lean backward in the chair by adding length to front vertical leg members  232  and  242  using their telescoping features. 
     In the illustrated embodiment of  FIG. 2 , first leg assembly  320  comprises a first member  322  and a second member  324 . The second member  324  is telescopically received by first member  322 , wherein the length of member  324  extending outwardly from member  322  can be adjusted. A glide  370   a  is disposed on the distal end of member  324 . 
     Similarly, members  334 ,  344 , and  354 , are telescopically received by members  332 ,  342 , and  352 , respectively. The length of members  334 ,  344 , and  354 , extending outwardly from members  332 ,  342 , and  352 , respectively, can be adjusted. Glides  370   b ,  370   c , and  370   d , are disposed on the distal ends of members  334 ,  344 , and  354 , respectively. Because the leg heights of support frame  120  are adjustable by varying the lengths of members  324 ,  334 ,  344 , and/or  354 , it is possible to accommodate seat assembly  140  to match various toilet bowl heights, bathtub/shower stall heights, and the height of other objects, such as, without limitations, bed heights. 
     In certain embodiments, members  322 ,  324 ,  332 ,  334 ,  342 ,  344 ,  352 , and  354 , are formed from a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, members  322 ,  332 ,  342 , and  352  each comprise a tubular members having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, members  322 ,  332 ,  342 , and  352 , comprise a tubular member having a length between about 8 inches and about 14 inches. In certain embodiments, members  322   332 ,  342 , and  352  comprise a solid member having a circular cross-section. 
     In certain embodiments, members  324 ,  334 ,  344 , and  354 , comprise a tubular member having an outside diameter between about ⅚ inch and about ⅞ inch. In certain embodiments, members  324 ,  334 ,  344 , and  354 , comprise a tubular member having a length between about 9 inches and about 15 inches. In certain embodiments, members  324 ,  334 ,  344 , and  354 , comprise a solid member having a circular cross-section. 
     In the illustrated embodiment of  FIG. 3 , first set of vertical leg members  320  are pivotally interconnected with support rail  122  by hinge  600   e  described hereinafter. Second set of vertical leg members  330  are pivotally interconnected with support rail  124  by hinge  600   f . Third set of vertical leg members  340  are pivotally interconnected with support rail  124  by hinge  600   g . Fourth set of vertical leg members  350  are pivotally interconnected with support rail  122  by hinge  600   h.    
     In the illustrated embodiment of  FIG. 3 , bracing member  362  and bracing member  364  are substantially perpendicular to set of parallel rails  121 . In certain embodiments, first bracing member  362  is interconnected with first set of vertical leg members  320  and second set of vertical leg members  330  by conventional attachment means, such as welding, plastic welding, mechanical fasteners, and the like. In certain embodiments, second bracing member  364  is interconnected with third set of vertical leg members  340  and fourth set of vertical leg members  350  by conventional attachment means, such as welding, plastic welding, mechanical fasteners, and the like. 
     In certain embodiments, bracing members  362  and  364  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, bracing members  362  and  364  comprise a planar member having a length between about 15 inch and about 18 inch. In certain embodiments, bracing members  362  and  364  comprise a width between about 1.5 inches and about 2 inches. In certain embodiments, bracing members  362  and  364  comprise a solid member having rectangular cross-section. In other embodiments, bracing members  362  and  364  comprise a circular or oval cross-section. 
     In certain embodiments, glides  370   a ,  370   b ,  370   c , and  370   d , each comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, glides  370   a ,  370   b ,  370   c , and  370   d , each comprises a member having a height between about ¼ inch and about ½ inch. In certain embodiments, glides  370   a ,  370   b ,  370   c , and  370   d , comprises a width between about 1 inch and about 1⅛ inches. In certain embodiments, glides  370   a ,  370   b ,  370   c , and  370   d , are sold in commerce by SUPERIOR COMPONENTS. 
     In the illustrated embodiment of  FIG. 3 , brace bar  380  comprises a first and second end. First end of brace bar  380  is attached to support rail  122  and second end of brace bar  380  is attached to support rail  124  by conventional attachment means. Brace bar  380  gives the user of the apparatus  100  more ease when using second frame  120  because the seat assembly  140  will not tip or slide off the end of second frame  120 . 
     In certain embodiments, brace bar  380  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, brace bar  380  comprises a planar member having a length between about 15 inches and about 18 inches. In certain embodiments, brace bar  380  has a width between about ¾ inches and about 1.5 inches. In certain embodiments, brace bar  380  comprises a solid member having rectangular cross-section. In other embodiments, brace bar  380  comprises a circular or oval cross-section. 
     Referring to  FIG. 4 , mechanical interface  130  comprises a set of parallel support members  132  and  134 , in combination with connector  131   a , connector  131   b , connector  133   a , connector  133   b , tab  135   a , tab  135   b , tab  135   c , tab  135   d , tab  135   e , tab  135   f , tab  135   g , and tab  135   h . The elements of mechanical interface  130  can releasably interconnect first support frame  110  to second support frame  120 . 
     In the illustrated embodiment of  FIG. 4 , connector  131   a , connector  131   b , connector  133   a , and connector  133   b  have an outside diameter that is equal to the inside diameter of support rail  112 , support rail  114 , support rail  122 , and support rail  124 . Support rail  112 , support rail  114 , support rail  122 , and support rail  124 , are formed to include apertures to accommodate lock tab  135   a , tab  135   b , tab  135   c , tab  135   d , tab  135   e , tab  135   f , tab  135   g , and tab  135   h . Tab  135   a , tab  135   b , tab  135   c , tab  135   d , tab  135   e , tab  135   f , tab  135   g , and tab  135   h  comprise depressible tabs which extend outwardly from connector  131   a ,  131   b ,  133   a , and  133   b , respectively. Tab  135   a , tab  135   b , tab  135   c , tab  135   d , tab  135   e , tab  135   f , tab  135   g , and tab  135   h  comprise springpin devices known in the art. 
     In certain embodiments, support rails  132  and  134  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, support rails  132  and  134  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, support rails  132  and  134  comprise a tubular member having a length between about 12 inches and about 20 inches. In certain embodiments, support rails  132  and  134  each comprise a solid member having a circular cross-section. 
     In certain embodiments, connector  131   a , connector  131   b , connector  133   a , and connector  133   b , comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, connector  131   a , connector  131   b , connector  133   a , and connector  133   b , comprise a tubular member having an outside diameter between about ⅚ inch and about ⅞ inch. In certain embodiments, connector  131   a , connector  131   b , connector  133   a , and connector  133   b , comprise a tubular member having a length between about 3 inch and about 6 inches. In certain embodiments, connector  131   a , connector  131   b , connector  133   a , and connector  133   b , comprise a solid member having a circular cross-section. 
     Referring now to  FIGS. 5A and 5B , seat assembly  140  comprises seat  530  and backrest  510  which is hingedly attached to seat  530  using hinges  600   i  and  600   j .  FIG. 5A  shows backrest disposed in an upright configuration.  FIG. 5B  shows backrest  510  in a folded configuration. 
     Referring to  FIG. 5C , seat assembly  140  comprises a backrest  510 , a set of armrests  520 , a seat  530 , a first vertical member  542 , a second vertical member  544 , a set of push handles  560  and  561 , a set of armrest acceptor tubes  570 , and a footrest assembly  580 . In the illustrated embodiment of  FIG. 5C , the backrest  510  comprises a rectangular element  512  and a cushion  514  which is releasably interconnected by conventional attachment means for easy replacement. 
     Backrest  510  is interconnected to a set of vertical members  542  and  544  by conventional attachment means. In the illustrated embodiment of  FIG. 5C , the set of armrests  520  comprises a first armrest  522  and a second armrest  524 . In the illustrated embodiment of  FIG. 5C , first armrest  522  and second armrest  524  are shown in a first orientation wherein each armrest is pivotally mounted in a set of acceptor tubes  570 . First armrest  522  and second armrest  524  are releasably interconnected to first acceptor tube  572  and second acceptor tube  574 , respectively. First acceptor tube  572  is mounted to first vertical member  542  by conventional attachment means. Second acceptor tube  574  is mounted to second vertical member  544  by conventional attachment means. 
     In certain embodiments, rectangular element  512  comprises a rigid material selected from a group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, backrest  512  comprises a flat member having a thickness between about ⅛ inch and about ⅝ inch. In certain embodiments, backrest  512  comprises a sheet having a height between about 7 inches and about 10 inches. In certain embodiments, backrest  512  comprises a sheet having a width between about 16 inches and about 18 inches. 
     In certain embodiments, cushion  514  comprises a flexible foam. In certain embodiments, cushion  514  is sold in commerce by Red Central Foams, S.A., Monterrey, N.L., Mexico under the name vinyl-coated foam cushion. In certain embodiments, cushion  514  has a thickness between about ¾ inch and about 1½ inches. In certain embodiments, cushion  514  comprises a width between about 15 inches and about 17 inches. In certain embodiments, cushion  514  comprises a height between about 7 inches and about 10 inches. In certain embodiments, cushion  514  is contoured. Cushion  514  is releasably interconnected to element  512  by a mechanical attachment means for easy replacement. By “mechanical attachment means,” Applicant means hook and loop fasteners, snaps, zippers, or combinations thereof, and the like. Cushions of various shapes and sizes will attach universally to the seat base to accommodate users of varying sizes. 
     In certain embodiments, armrests  522  and  524  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, armrests  522  and  524  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, the distal ends of armrest  522  and armrest  524  extend about 14 inches from the back of seat. In certain embodiments, armrests  522  and  524  comprise a solid member having a circular cross-section. 
     In certain embodiments, acceptor tubes  572  and  574  comprise a rigid material selected from a group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, acceptor tubes  572  and  574  comprise a tubular member having an outside diameter between about 1 inch and about 1.5 inches. In certain embodiments, acceptor tubes  572  and  574  comprise a tubular member having a length between about 2 inches and about 4 inches. In certain embodiments, acceptor tubes  572  and  574  comprise a solid member having a circular cross-section. 
     In the illustrated embodiment of  FIG. 5C , a first vertical member  542  comprises a push pin mechanism at the top of the vertical member  542  so that push handle  560  can be locked into place. The vertical member  542  is interconnected to seat form  530  at the back portion of the seat form  530  at the back two corners by hinge assembly  600  (see  FIGS. 6A ,  6 B,  7 A,  7 B) as to achieve a seat assembly in which a user may sit. Vertical member  542  is connected to backrest  510  by conventional attachment means. 
     In the illustrated embodiment of  FIG. 5C , a second vertical member  544  comprises a push pin mechanism at the top of the vertical member  544  so that push handle  561  can be locked into place. The vertical member  544  is interconnected to seat form  530  at the back portion of the seat form  530  at the back two corners by hinge assembly  600  (see  FIGS. 6A ,  6 B,  7 A,  7 B) as to achieve a seat assembly in which a user may sit. Vertical member  544  is connected to backrest  510  by conventional attachment means. 
     In certain embodiments, vertical members  542  and  544  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, vertical members  542  and  544  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, vertical members  542  and  544  comprise a tubular member having a length between about 15 inches and about 18 inches. In certain embodiments, vertical member  544  comprises a solid member having a circular cross-section. 
     In the illustrated embodiment of  FIG. 5C , seat assembly  530  comprises a cushion  532  and a seat frame  534 . Cushion  532  is releasably attached to seat frame  534  by conventional attachment means for easy replacement. As one skilled in the art would appreciate, the aperture  536  in cushion  532  and seat board  534  allow for ease of use over a toilet. In other embodiments, cushion  532  and seat board  534  comprises a rectangular form. Seat frame  534  is interconnected to hinge mechanism  600  at the back of the seat frame  534  by conventional attachment means. In certain embodiments, frame  534  comprises a rigid material selected from a group consisting of metal, an engineering plastic, wood, or combinations thereof. 
     Referring now to  FIGS. 5 and 12A , in certain embodiments top portion  1201  comprises a flat member having a thickness between about ⅛ inch and about ⅜ inch. In certain embodiments, top portion  1201  comprises a member having a width between about 18 inches and about 20 inches. In certain embodiments, top portion  1201  comprises a member having a width between about 18 inches and about 20 inches. In certain embodiments, top portion  1201  is formed from 0.090″ 5052 grade aluminum sheet. 
     In certain embodiments, cushion  532  comprises a flexible foam. In certain embodiments, cushion  532  is sold in commerce by Red Central Foams, S.A., Monterrey, N.L., Mexico under the name vinyl-coated foam cushion. In certain embodiments, cushion  532  has a thickness between about ¾ inch and about 1.5 inches. In certain embodiments, cushion  532  comprises a sheet having a width between about 17 inches and about 20 inches. In certain embodiments, cushion  532  comprises a sheet having a depth between about 18 inches and about 20 inches. Cushions of various shapes and sizes will attach universally to the seat base to accommodate users of varying sizes. Cushion  532  will be releasably interconnected to cushion  532  by a mechanical attachment means for easy replacement. By “mechanical attachment means,” Applicant means hook and loop fasteners, snaps, zippers, or combinations thereof. 
     In illustrated embodiment of  FIG. 5C , the set of push handles  560  and  561  are releasably interconnected to vertical member  542  and vertical member  544 , respectively. The push handles  560  and  561  allow for a second person to have ease of movement when pushing or pulling from behind. 
     Referring to  FIG. 5C , push handle  560  and push handle  561  can independently move in two positions. The first position is the push/pull position where a second person can grip the handles and push or pull from behind. The second position is an inward position that aligns the push handles with the backrest  510  for ease in folding the wheelchair for storage. 
     In certain embodiments, push handles  560  and  561  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, push handles  560  and  561  comprise a tubular member having an outside diameter between about ¾ inch and about 1 inch. In certain embodiments, push handles  560  and  561  extend between about 4 inches and 6 inches from the backrest  510 . In certain embodiments, push handles  560  and  561  comprise a tubular member with a length between about 9 inches and about 12 inches. In certain embodiments, push handles  560  and  561  are bent at a substantially 90 degree angle. By “substantially 90 degree angle,” Applicant means a 90 degree angle+/−5 degrees. In certain embodiments, push handles  560  and  561  comprise a solid member having a circular cross-section. 
     In the illustrated embodiment of  FIG. 5C , footrest assembly  580  comprises a first attachment member  582   a , second attachment member  584   a , and footrest pad  586 . The second attachment member  584   a  is contoured so as not to have any sharp edges. The first attachment member  582   a  comprises a first end and a second end. The first end of attachment member  582   a  is releasably interconnected with second attachment member  584   a  by a push pin lock mechanism. The first attachment member  582   a  is telescopically received in the first end by second attachment member  584   a . First attachment member  582   a  is releasably extendable by a springpin lock mechanism. Second attachment member  584   a  is attached to seat board  534  by a push pin lock mechanism. 
     In the illustrated embodiment of  FIG. 5C , footrest assembly  580  comprises first attachment member  582   b , second attachment member  584   b , and footrest pad  586 . The second attachment member  584   b  is contoured so as not to have any sharp edges. The first attachment member  582   b  comprises a first end and a second end. The first end of attachment member  582   b  is releasably interconnected with second attachment member  584   b  by a push pin lock mechanism. The first attachment member  582   b  is telescopically received in the first end by second attachment member  584   b . First attachment member  582   b  is releasably extendable by a springpin lock mechanism. Second attachment member  584   b  is attached to seat board  534  by a push pin lock mechanism. 
     Referring to  FIG. 5C , footrest pad  586  comprises a skid-free flat plate  586   c  attached to a first attachment member  586   a  on one end of the skid-free plate and second attachment member  586   b  on the other end by a supporting member  586   d . First attachment member  586   a  is attached to member  582   a  by a push pin lock mechanism. Second attachment member  586   b  is attached to member  582   b  by a push pin lock mechanism. Skid-free plate  586   c  is attached to supporting member  586   d  by conventional attachment means. First attachment member  586   a  and second attachment member  586   b  are attached to supporting member  586   d  by conventional attachment means. 
     In certain embodiments, attachment members  582   a  and  584   a  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, attachment members  582   a  and  584   a  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, attachment members  582   a  and  584   a  comprise a tubular member having a length between about 4 attachment members  582   a  and  584   a  comprise member  582   a  comprises a solid member having a circular cross-section. 
     In certain embodiments, attachment members  582   b  and  584   b  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, attachment members  582   b  and  584   b  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, attachment members  582   b  and  584   b  comprise a tubular member having a length between about 4 inches and about 8 inches. In certain embodiments, attachment members  582   b  and  584   b  comprise a solid member having a circular cross-section. 
     In certain embodiments, attachment members  586   a  and  586   b  comprise a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, attachment members  586   a  and  586   b  comprise a tubular member having an outside diameter between about ⅞ inch and about 1 inch. In certain embodiments, attachment members  586   a  and  586   b  comprise a tubular member having a length between about 1 inch and about 3 inches. In certain embodiments, attachment members  586   a  and  586   b  comprise a solid member having a circular cross-section. 
     In certain embodiments, skid-free plate  586   c  comprises a rigid material selected from a group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, skid-free plate  586   c  comprises a rectangular flat member with a length between about 14 inches and 16 inches. In certain embodiments, skid-free plate  586   c  comprises a width between about 5 inches and 7 inches. The top surface of the plate  586   c  comprises a non-slip surface material selected from the group consisting of metal, an engineering plastic, or combinations thereof. In certain embodiments, skid-free plate  586   c  is oval shaped or the like thereof. 
     In certain embodiments, supporting member  586   d  comprises a rigid material selected from a group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, supporting member  586   d  comprises a flat rectangular member with a length between about 16 inches and about 20 inches. 
     Referring now to  FIGS. 5 and 12A , seat assembly  530  comprises frame  534 , first support member  552 , and second support member  554 . Seat frame  534  comprises a top portion  1201 , and four sides  1203 ,  1205 ,  1207 , and  1209 , attached to top portion  1201  and extending downwardly therefrom to form a 5-sided enclosure. Cushion  532  is removeably attached to top portion  1201 . Side  1203  is formed to include apertures  1212  and  1214  extending therethrough. Side  1207  is formed to include apertures  1216  and  1218  extending therethrough. 
       FIG. 6A  is a side view showing hinge assembly  600  in the locked position. In the illustrated embodiment of  FIG. 6A , hinge assembly  600  comprises pin assembly  610 , assembly  620 , and interconnecting member  605 . In the illustrated embodiment of  FIG. 6A , pin assembly  610  comprises a pin  612  and an aperture  616 . In certain embodiments, pin assembly further includes attachment cable  614  (see  FIG. 6B ). In the illustrated embodiment of  FIG. 6A , horizontal member  112  and vertical member  222  are connected by pin assembly  610 , assembly  620 , and interconnecting member  605 . 
     In the illustrated embodiment of  FIG. 6A , interconnecting member  605  is attached to the top end of vertical member  222  by conventional attachment means. In the illustrated embodiment of  FIG. 6A , the inside diameter of horizontal member  112  and the outer diameter of interconnecting member  605  are equal such that a first end of interconnecting member  605  can be slideably inserted into one end of horizontal member  112 . In the illustrated embodiment of  FIG. 6A , interconnecting member  605  comprises an aperture  628  that is dimensioned such that assembly  620  is movable bidirectionally within interconnecting member  605 . 
     In certain embodiments, interconnecting member  605  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, interconnecting member  605  comprises a tubular member having an outside diameter between about 1 inch and about 1½ inches. In certain embodiments, interconnecting member  605  comprises a tubular member having a length between about 2 inches and about 3 inches. In certain embodiments, interconnecting member  605  comprises a solid member having a circular cross-section. 
     In certain embodiments, pin  612  comprises a rigid material selected from the group consisting of metal, an engineering plastic, wood, or combinations thereof. In certain embodiments, pin  612  comprises a tubular member having an outside diameter between about ⅛ inch and about ¼ inch. In certain embodiments, pin  612  comprises a tubular member having a length between about 1 inch and about 1½ inches. In certain embodiments, pin  612  comprises a solid member having a circular cross-section. In certain embodiments, pin  612  comprises a 1.25 inch grip range. In certain embodiments, pin  612  is stainless steel. In certain embodiments, the optional attachment cable  614  (see  FIG. 6B ) comprises a flexible material. 
       FIG. 6B  is a top view showing hinge assembly  600  in the locked position. In the illustrated embodiment of  FIG. 6B , assembly  620  comprises a bolt  622 , a first nut  624 , a second nut  626 , and opposing apertures  630   a  and  630   b . In the illustrated embodiment of  FIG. 6B , tubular member  112  and interconnecting member  605  have a set of opposing circular apertures  630   a  and  630   b  so that horizontal member  112  and interconnecting member  605  can be releasably attached by bolt  622 , a first nut  624 , and a second nut  626 . 
     In the illustrated embodiment of  FIG. 6B , assembly  610  comprises a pin  612  and opposing apertures  616   a  and  616   b . In the illustrated embodiment of  FIG. 6B , tubular member  112  and interconnecting member  605  have a set of opposing circular apertures  616   a  and  616   b  so that horizontal member  112  and interconnecting member  605  can be locked by pin  612 . 
     In the illustrated embodiment of  FIG. 6B , the horizontal member  112  and the interconnecting member  605  are formed to include opposing apertures  616   a  and  616   b  so that pin assembly  610  can be locked by pushing the pin  612  through apertures  616   a  and  616   b  so that the horizontal member  112  and vertical leg member  222  form a substantially ninety degree angle in the locked position. By “substantially ninety degree angle,” Applicant means a ninety degree angle +/−10 degrees formed between the horizontal member  112  and the vertical leg member  222 . In the illustrated embodiment of  FIG. 6B , interconnecting member  605  is formed to include an opposing oval-shaped apertures  628   a  and  628   b  so that horizontal member  112  and interconnecting member  605  are dimensioned such that a first end of interconnecting member  605  can be slideably inserted into one end of horizontal member  112 . Interconnecting member  605  can be positioned within horizontal member  112  such that apertures  630   a ,  628   a ,  630   b , and  628   b  are aligned. Bolt  622  can be inserted through these aligned apertures. 
     In certain embodiments, bolt  622  comprises a rigid material selected from the group consisting of metal, an engineering plastic, or combinations thereof. In certain embodiments, bolt  622  comprises a tubular member having an outside diameter between about ¼ inch and about ½ inch. In certain embodiments, bolt  622  comprises a tubular member having a length between about 1 inch and about 1½ inch. In certain embodiments, bolt  622  comprises a ¼-20 stainless steel carriage bolt. In certain embodiments, bolt  622  comprises a solid member having a circular cross-section. 
       FIG. 7A  is a side view showing hinge assembly  600  in the unlocked and folded position. In the illustrated embodiment of  FIG. 7A , pin  612  is removed from aperture  616  to allow horizontal member  112  and interconnecting member  605  to separate. Interconnecting member  605  can be slideably moved from within horizontal member  112  and rotated in a downward motion into a folded and portable form by way of aperture  710 , (see  FIG. 7B ). Attachment cable  614  is attached to horizontal member  112  on first end and attached to pin  612  on the second end. When pin  612  is removed from aperture  616 , attachment cable  614  allows pin  612  to hang from horizontal member  112 . By attaching pin  612  to horizontal member  112  there are no loose parts when collapsing apparatus  100  for storage and portability. 
     Referring to  FIG. 7B , horizontal member  112  comprises an aperture  710  dimensioned such that interconnecting member  605  can be rotated in a downward motion into a folded and portable form (see  FIG. 7A ). 
     Referring to  FIG. 8A , support frame  110  is shown in a folded configuration for ease of transport. The upright configuration of  FIG. 2  can be transformed into the folded configuration of  FIG. 8A  by removing a locking pin  612  ( FIG. 7A ) from each of hinge  600   a , hinge  600   b , hinge  600   c , and hinge  600   d , pivoting vertical member  220  inwardly about ninety degrees, pivoting vertical member  230  inwardly about ninety degrees, pivoting vertical member  240  inwardly about ninety degrees, and pivoting vertical member  250  inwardly about ninety degrees. 
     Referring to  FIG. 8B , support frame  120  is shown in a folded configuration for ease of transport. The upright configuration of  FIG. 3  can be transformed into the folded configuration of  FIG. 8B  by removing a locking pin  612  ( FIG. 7A ) from each of hinge  600   a , hinge  600   b , hinge  600   c , and hinge  600   d , pivoting vertical member  320  inwardly about ninety degrees, pivoting vertical member  330  inwardly about ninety degrees, pivoting vertical member  340  inwardly about ninety degrees, and pivoting vertical member  350  inwardly about ninety degrees. 
     Support frame  110  in the folded configuration of  FIG. 8A , support frame  120  in the folded configuration of  FIG. 8B , the elements of mechanical interface  130  ( FIG. 4 ), and seat assembly  140  in the folded configuration of  FIG. 5B , can be easily disposed in, and carried in, a carrying case. Applicants&#39; apparatus  100  may be easily disassembled and reassembled, without the use of any tools. The individual elements of Applicant&#39;s apparatus  100  can be transported in the carrying case enabling the user to travel to places which may be otherwise inaccessible without Applicant&#39;s apparatus. 
     Referring to  FIGS. 5 ,  12 A,  12 B, and  12 C, lock assembly  590   a  comprises a plate-mount, hand retractable spring and ball disposed on front side  1203 . Lock assembly  590 A comprises release member  1242 A which can be disposed in a first position or a second position. In the illustrated embodiment of  FIGS. 12A and 12B , release member  1242 A is shown in a second and locking position wherein locking pin  1244 A extends inwardly from side  1203 . When locking pin  1244 A is inserted into an aperture formed in member  114  or member  124 , seat assembly  140  is prevented from sliding in either direction or disengaging from support frame  110  or support frame  120 , respectively. 
     In the illustrated embodiment of  FIG. 12C , release member  1242 A is shown in a first and unlocked position wherein locking pin  1244 B does extend inwardly from side  1203 . When locking pin  1244 A is not inserted into an aperture formed in member  114  or member  124 , seat assembly  140  may slide in either direction on support frame  110  or support frame  120 , respectively. 
     Referring to  FIGS. 5   12 A,  12 B, and  12 C, lock assembly  590 B comprises a plate-mount, hand retractable spring and ball disposed on rear side  1207  of seat frame  534 . In the illustrated embodiment of  FIGS. 12A and 12B , locking pin  1244 B extends inwardly. When locking pin  1244 B is inserted into an aperture formed in member  112  or member  122 , seat assembly  140  is prevented from sliding in either direction or disengaging from support frame  110  or support frame  120 , respectively. 
     In the illustrated embodiment of  FIG. 12C , release member  1242 B is shown in a first and unlocked position wherein locking pin  1244 B does extend inwardly from side  1207 . When locking pin  1244 B is not inserted into an aperture formed in member  114  or member  124 , seat assembly  140  may slide in either direction on support frame  110  or support frame  120 , respectively. Lock assembly  590   a  and lock assembly  590   b  must be simultaneously placed in an unlocked orientation for seat assembly  140  to be released from either support frame  110  or support frame  120 . 
       FIGS. 12B and 12C  show seat frame  534  slideably mounted on members  124  and  126  using attachment assemblies  1000 A,  1000 B,  1000 C, and  1000 D. Referring now to  FIG. 9 , each attachment assembly  1000  comprises a rotatable member  920  and a fixed member  930 . Rotatable member  920  is formed to include aperture  925  extending therethrough. Fixed member  930  is formed to include aperture  935  extending therethrough. 
     Rotatable member  920  comprises a cylinder  940 , hub  950  attached to and extending outwardly from cylinder  940 , and cylinder  960  attached to and extending outwardly from hub  950 . In certain embodiments, cylinder  940 , hub  950 , and cylinder  960  comprise an integral assembly that is formed by machining a cylindrical block of a rigid plastic, metal, wood, and combinations thereof. In certain embodiments, cylinder  940 , hub  950 , and cylinder  960  comprise an integral assembly that is formed by injection molding an engineering plastic. 
     Cylinder  940  comprises a diameter  945  and cylinder  960  comprises a diameter  965 , wherein the diameter  945  is greater than the diameter  965 . Cylinder  960  comprises a length  970 . 
     Hub  950  comprises a cylinder with an arcuate-shaped wall  954  interconnecting cylinders  940  and  960 , wherein a first end of hub  950  comprises diameter  945  and a second end of hub  950  comprises diameter  965 . Hub  950  further comprises diameter  954  at a point between the first end and the second end, wherein diameter  954  is less than diameter  965 . Surface  952  comprises an arcuate shape comprising a radius of curvature corresponding to the radius of support members  112 ,  114 ,  122 ,  124 ,  132 , and  134 . 
     Fixed member  930  is formed to include a circular aperture  932  extending inwardly from side  936 , wherein circular aperture  934  comprises diameter  925  and a depth  934 , wherein depth  934  equals length  929 . Fixed member  930  further comprises an arcuate surface  938 , wherein arcuate surface  938  comprises a radius of curvature corresponding to the radius of support members  112 ,  114 ,  122 ,  124 ,  132 , and  134 . 
     In the illustrated embodiment of  FIG. 10 , shaft  1220  extends through aperture  925  ( FIG. 9 ) in rotatable member  920 , and through aperture  935  ( FIG. 9 ) in fixed member  930 . Rotatable member  920  is positioned such that cylinder  960  ( FIG. 9 ) is rotatably disposed within aperture  932  ( FIG. 9 ). 
     Referring now to  FIG. 11 , shaft  1220   a  extends through aperture  1212  ( FIG. 12A ) in front  1203  of seat frame  534 , and through aperture  1216  in rear  1207  of seat frame  534 . In certain embodiments, shaft  1220   a  is rotatably disposed in seat frame  534 . Shaft  1220   a  extends through rotatable member  920 A, fixed member  930 A, rotatable member  920 B, and fixed member  930 B. 
     Top  1110 A ( FIGS. 10 ,  11 ) of fixed member  930 A is attached to surface  1202  of seat top member  1201 , and top  1110 B of fixed member  930 B is attached to surface  1202  of seat top member  1201 . Rotatable members  920 A and  920 B are rotatably disposed on shaft  1220 A, but fixed members  930 A and  930 B are not rotatably disposed on shaft  1220 A. 
     Similarly, shaft  1220 B extends through apertures  1214  and  1218  in seat frame  534 . Attachment assembly  1000 C is identical to attachment assembly  1000 A, wherein attachment assembly  1000 C comprises a rotatable member  920  rotatably disposed on shaft  1220 B, and a fixed member  930  attached to surface  1202  of seat top member  1201 . Attachment assembly  1000 D is identical to attachment assembly  1000 B, wherein attachment assembly  1000 D comprises a rotatable member  920  rotatably disposed on shaft  1220 B, and a fixed member  930  attached to surface  1202  of seat top member  1201 . 
     Referring now to  FIGS. 9 ,  10 ,  13 A, and  13 B, in the illustrated embodiment of  FIGS. 13A and 13B , rotatable member  920  is shown having cylinder  960  rotatable inserted into aperture  932  such that arcuate surface  952  having length  1310  abuts arcuate surface  938  having length  1320  to form an aggregate arcuate surface comprising a length  1330  and a radius of curvature  1340 , wherein aggregate length  1330  equals length  1310  plus length  1320 . 
     Referring now to  FIG. 13C , in certain embodiments support members  112 ,  114 ,  122 ,  124 ,  132 , and  134 , comprises tubular members having an outer radius  1360  and an outer circumference  1350 , wherein that outer radius  1360  equals the radius of curvature  1340  ( FIG. 13B ).  FIG. 13D  a support member selected from the group consisting of support member  112 , support member  114 , support member  122 , support member  124 , support member  132 , and support member  134 , releasably attached to attachment assembly  1000 . In certain embodiments, length  1330  of the aggregate arcuate surface formed by arcuate surface  952  and arcuate surface  938  is greater than (0.50) (outer circumference  1350 ). In certain embodiments, length  1330  of the aggregate arcuate surface formed by arcuate surface  952  and arcuate surface  938  is about (0.67) (outer circumference  1350 ). In certain embodiments, length  1330  of the aggregate arcuate surface formed by arcuate surface  952  and arcuate surface  938  is about (0.75) (outer circumference  1350 ). 
     Referring now to  FIGS. 12B ,  12 C, and  13 D, more than fifty percent (50%) of the surface area of support member  122  in contact with attachment assembly  1000 B is encircled by attachment assembly  1000 B. Similarly, more than fifty percent (50%) of the surface area of support member  122  in contact with attachment assembly  1000 D is encircled by attachment assembly  1000 D. In addition, more than fifty percent (50%) of the surface area of support member  124  in contact with attachment assembly  1000 A is encircled by attachment assembly  1000 A. Moreover, more than fifty percent (50%) of the surface area of support member  122  in contact with attachment assembly  1000 C is encircled by attachment assembly  1000 C. 
     Applicant&#39;s attachment assemblies  1000 A,  1000 B,  1000 C, and  1000 D, releasably attach seat assembly  140  to first support frame  110 , second support frame  120 , and mechanical interface  130 . Applicant&#39;s attachment assemblies  1000 A,  1000 B,  1000 C, and  1000 D, snap onto support members  112 / 144 , or  122 / 124 , or  132 / 134 . Once attachment assemblies  1000 A,  1000 B,  1000 C, and  1000 D, are engaged with a set of support rails, seat assembly  140  is both securely and moveably attached to that set of support rails. Seat assembly  140  cannot be inadvertently disengaged from a set of support rails. In order to remove seat assembly  140  from a set of support rails, each of attachment assemblies  1000 A,  1000 B,  1000 C, and  1000 D, must be manually disengaged from one of the two support rails. As a result, if the user leans forwardly or backwardly in seat assembly  140 , that seat assembly  140  will not inadvertently falls off of first support frame  110 , second support frame  120 , or mechanical interface  130 . 
     While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.