Abstract:
A method of constructing a wheelchair that is durable, lightweight, economical and fully adaptable to any end user&#39;s requirements, such as sizing, convertibility, environment and lifestyle, and the resulting wheelchair, is disclosed, made possible by the utilization of specially designed weld-free connector fittings with any desirable or available tubular materials.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention generally relates to wheelchairs, and more specifically to a method of wheelchair construction and resulting wheelchair. 
     2. Description of the Prior Art 
     There are two commonly used wheelchair design—the crossbrace folding wheelchair and the welded rigid frame wheelchair. The typical method of construction for both types of wheelchairs is to weld or braze metal tubes together to form frames and folding members. Unfortunately, the two above-described designs have one major flaw in common—the strength inconsistencies of the welded joints. Breakage of welded or brazed joints is the main cause for structural failure in wheelchairs. Welding or brazing also creates a heat-affected zone weakening the frame tube around the welded or brazed joints and making repairs in most cases impossible. Repairs and maintenance of these wheelchairs are costly and require elaborate service infrastructure. In addition, the welded construction makes it extremely difficult, if not impossible, to adapt the wheelchair to the end user&#39;s changing needs and environment. Conversion from rigid frame to a folding wheelchair is also virtually impossible. 
     It is desirable to have a wheelchair design constructed without welds or brazes. A weld-free wheelchair design would eliminate the shortcomings described above and open the door to endless new design possibilities. 
     Some wheelchair manufacturers build each of the wheelchair types listed above but they are of dedicated, welded construction and, for the aforementioned reasons, do not adapt from one type to another. There are chairs that are modular in design and can change the widths of the wheelchair with little difficulty. There is a design that converts from a user propelled to an assistant propelled wheelchair (U.S. Pat. No. 5,294,141). There is also a wheelchair that converts the riding position from the standard seating position to a recumbent position (U.S. Pat. No. 5,011,175). There is a weld-free folding wheelchair that folds in a non-conventional manner but is not modular (U.S. Pat. No. 4,682,783). Another wheelchair design appears to be a weld-free design that allows the wheelchair to adjust to different needs by use of special shaped bars and plates but is limited to width and depth adjustment (U.S. Pat. No. 5,743,545). There are several U.S. patents that claim to be modular, allowing for different components to be used to build the chair to the user&#39;s needs. Among these is a rigid frame wheelchair (U.S. Pat. No. 5,421,598), but again this wheelchair does not convert or adapt to the extent of this invention. There are several U.S. patents for wheelchairs that have welded or brazed construction. 
     In U.S. Pat. No. 5,253,888, issued to the assignee of the subject invention, a rigid frame weld-free wheelchair is disclosed that utilizes a series of special clamps for clamping tubes to each other. However, such weld-free construction has some disadvantages. A series of specially designed clamps had to be utilized which were not universal to all designs, making further design changes virtually impossible. Also, by virtue of the clamp designs, numerous bolts were required that were clearly visible and detracted from the appearance of the wheelchair. 
     There are no wheelchairs known to exist at this time that are constructed with distortion-free connectors and that can be configured or adapted to the extent of this design. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method of wheelchair construction and resulting wheelchair that do not have the disadvantages inherent in the comparable prior art. 
     It is another object of the invention is to provide a lightweight and economical wheelchair that can quickly and easily be sized, adapted or converted. The weld-free construction allows for considerable increase in strength and durability and minimal maintenance. 
     It is another object of the invention to provide a modular construction wheelchair that can be quickly and easily converted from rigid frame to folding, to sports, to companion chair, etc. 
     It is another object of this invention to provide a wheelchair that has the ability to adapt to virtually any configuration or option required by the wheelchair user. 
     It is yet another object of this invention to provide a wheelchair that can be constructed of non-specific tubular materials (steel, aluminum, stainless steel, titanium) and connector fittings which allows to adapt the wheelchair to any environment. 
     It is another object of this invention to provide a wheelchair built with standardized components which allows it to be shipped in parts and be assembled and customized locally by an unskilled person using simple tools. 
     The resulting wheelchair has a pair of like side frame assemblies spaced from each other and each including a generally horizontal seat tube and a generally horizontal bottom tube below the seat tube. Each of the seat and bottom tubes have front and rear ends. The wheelchair also has a generally vertical backrest tube having a lower end proximate to the rear ends of the seat and bottom tubes and an upper end that extend upwardly of the seat tube and form handgrips. The wheelchair has a caster assembly for each side frame assembly carrying a caster wheel and having a generally upwardly extending shaft portion, at least one failsafe weld-free means for each of the frame assemblies rigidly connecting at least two tubes of the wheelchair to each other and transverse connecting means for extending between and connecting said side frame assemblies to each other. 
     This wheelchair also has footrest supports secured to said seat tube and rear wheels mounted on the side frame assemblies. 
     The typical wheelchair frame is made up of left and right side frame assemblies, two push handle assemblies, upholstery and removable folding or rigid crossbars. There are specially designed failsafe weld-free connector fittings that are used to provide for a secure fastening internally between mating tubes. These fittings are used throughout all assemblies where two or more tubes mate up. These fittings shall be referred to as connector fittings throughout this text. Each side frame assembly is provided with mounting holes to assemble the wheelchair as either folding or rigid. The folding crossbar assemblies have T-type fittings at the lower end which are a sliding fit to the lower side frame assembly tubes. At the top of the crossbars are seat tubes held in place perpendicular to the crossbar by the connector fittings. Each seat tube is assembled with a multi position insert that is used to attach the seat tube to the crossbar and to assemble the seat upholstery. There are holes in the crossbars near the center. These holes are the location where a pair of crossbars are bolted together and act as the pivot point when folding. These crossbars are slid onto the lower frame tube and held in place with retaining rings fastened through holes in the tube. This maintains proper horizontal position. There are also holes near the top of the crossbars that are fastened to links that pivot on the side frame assemblies. The links hold the wheelchair frame assemblies parallel when the chair is in both the open (riding) and folding (storage) positions. When the wheelchair is in the open (riding) position, the seat tubes nest into saddles fastened to each side frame assembly. This nesting along with the tension of the upholstery creates a solid box frame giving the chair the feel and performance associated with rigid frame wheelchairs. 
     Rigid frame type wheelchair use different cross tubes and back assembly. The rigid frame does not use the folding crossbars, links, and retaining rings which are specific to the folding wheelchair. There are two types of rigid crossbars. The lower crossbars are straight tubes. The upper crossbars have a bend at both ends to give clearance at the seat and back upholstery. Each of the rigid crossbars is assembled with the connector fittings. The same seat inserts in the folding design are inserted into the upper frame tubes of the side frame assemblies. The top rigid cross tubes are assembled to each side frame at the appropriate holes with the connector fittings. Inserts are placed into the lower side frame tubes and the lower crossbars are fastened in place. 
     The backrest of the wheelchair may be adjusted to varying heights as may be required by the user or to a folding back for the rigid frame version for ease of transportation and storage. Each side frame has an insert in the back at the seat level that is used to fasten the backrest tubes to the frame. Changing heights can be done by removing two fasteners on either side and the back upholstery and replacing with the new backrest tubes and upholstery. To replace the fixed back with a folding back, the back insert is replaced in the frame with the proper insert for folding. The backrest tube is assembled to the folding hinge plates and all to the frame assemblies are assembled. A reclining back assembly can also be assembled in place of the standard straight back or folding back assemblies. All components are modular allowing for simple alteration of the seat width and depth and back height. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The benefits of the construction herein disclosed will become apparent to those skilled in the art from the following detailed description of a presently preferred embodiment, having reference to accompanying drawings wherein: 
     FIG. 1 is a rear elevation view of a wheelchair assembled with folding crossbars with the failsafe weld-free connectors in accordance with the invention: 
     FIG. 2 is a side elevation view of the wheelchair shown in FIG. 1 with folding crossbars, shown with rear wheels removed: 
     FIG. 3 is a top plan view of the wheelchair shown in FIGS. 1 and 2, with folding crossbars (upholstery removed for clarity); 
     FIG. 4 is a rear elevation view of the wheelchair assembled with rigid cross tubes; 
     FIG. 5 is a side elevation view of the wheelchair shown in FIG. 4 assembled with rigid cross tubes (upholstery removed for clarity); 
     FIG. 6 is a top plan view of the wheelchair shown in FIGS. 4 and 5 assembled with rigid cross tubes (upholstery removed for clarity); 
     FIG. 7 is a fragmentary, exploded perspective view of the connector fitting used in the wheelchair shown in FIGS. 1-6; 
     FIGS. 8 a  and  8   b  are side and top elevation views of optional flip up footplate assemblies; 
     FIG. 9 is an exploded partial side view of a rigid frame wheelchair with optional wheel camber plate; 
     FIG. 10 is a fragmentary exploded perspective view of the caster bearing housing assembly; 
     FIG. 11 is a side elevation view of a wheelchair assembled with a lever drive kit; 
     and FIG. 12 is a side elevation view of a wheelchair assembled with a hand cycle attachment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the figures, in which identical or similar parts are designated by the same reference numerals throughout, and first referring to FIGS. 1,  2  and  3 , a folding wheelchair in accordance with the present invention is generally designated by the reference numeral  10 . 
     The chair  10  has a pair of like side frame assemblies  12  spaced from each other and including a generally horizontal top tube  14  and a generally horizontal bottom tube  16  below the top tube. The top and bottom tubes have front or distal ends  14   a ,  16   a  and rear or proximal ends  14   b ,  16   b . An important feature of the invention is that at least one, and usually all, of the tubes that are joined to each other, such as the top and bottom tubes at front ends  14   a ,  16   a , are joined using connector fittings  20 . The details of the connector fittings are best shown in FIG.  7  and are more fully described at pages 5, 10 and 17 in U.S. patent application Ser. No. 09/442,057, filed simultaneously herewith, for “Distortion-Free Weldless Method of Joining Tubular Elements,” with the same inventor and assignee as the present application. 
     The top tube  14  and the bottom tube  16  are secured to each other at front  14   a ,  16   a  and at the rear  14   b ,  16   b  using connector fittings  20 . The top tube  14  has a row of holes  14   c  for seat attachment when converted to a rigid frame wheelchair. 
     The chair also has like crossbar assemblies  22  including angular crossbar tubes  24  and a generally horizontal seat tube  26 . There is an insert tube  28  located inside of the seat tube which has threaded holes for multiple connections coinciding with holes in the upper frame  14  and seat tubes  26  which include seat to crossbar and seat upholstery on both the folding and the rigid wheelchair. The seat tube  26  and cross tubes  24  are joined at the upper ends of the cross tube  24   a  that is offset from the center of the seat tube  26 . The tubes are attached using connector fittings  20 . The lower ends of the crossbar tubes  24   b  are inserted into T-fittings  30  with the through hole parallel to the seat tube  26 . Each T-fitting has a sliding fit relative to the lower side frame tube  16 . The crossbar assemblies  22  are installed over the lower side frame tube  16  in opposing directions (left side with longer portion of seat tube to rear, right side longer portion to front) with seat upholstery holes  26   a  pointing upward. Each crossbar assembly  22  is held in position by retaining rings  32 . Crossbar links  34  are installed over the top frame tube  14  and held in place with retaining rings  32 . The hole at the small end of the crossbar links  34  are fastened to the opposing crossbar tube  24  at hole  24   a . The crossbar links  34  maintain a parallel relationship between side frame assemblies when the wheelchair is in either the open or folded position. Seat tube saddles  36  are also assembled to the top frame tube  14 . The seat saddles are a snap fit with the seat tubes  26 , when the wheelchair is in the open position the seat tubes rest in the saddles and lock the frame rigidly. The seat upholstery  76  is secured to the seat tube with screws at upholstery holes  26   a.    
     Each side frame assembly  12  has a back tube stiffening insert  40  secured near the top of the vertical component of the bottom frame tube end  16   b  and protruding upward. Back upholstery  78  is assembled over a pair of push handle tubes  38  and secured with screws near the top of each push handle tube end  38   a . Push handles are assembled over the top of the back tube stiffener insert  40  abutting the top of the vertical component of the bottom frame tube  16   b . The assembly is secured with fastener through holes in each tubular member. Hand grips  80  are installed over the top ends of each push handle tube  38 . 
     A caster assembly is generally designated by the reference numeral  42  and includes a downwardly extending open fork member  44  that receives and supports a caster wheel  46  by means of a transverse axle  48 . Extending upwardly from the fork member  44  is a solid shaft portion  50  rotatably supported about its axis in bearings  84 , as will be described below. 
     A caster bearing housing  74  (See FIG. 10) is mounted on the bottom frame tube  16  near the front of the tube  14   a . The caster bearing housing has a threaded hole  74   a  on one end and a slot  74   b  on the opposite side with perpendicular serrations  74   c  crossing the slot. The caster bearing housing is secured to the bottom frame tube. The caster bearing housing  74  is free to rotate vertically about the hole. A mating serrated cam  82  is secured over the slot in the caster bearing housing  74  and when properly placed maintains a vertical posture for the caster fork stem  50 . The caster bearing housing  74  has both an upper and lower bearing pocket  74   d ,  74   e  into which radial bearings  84  are pressed. 
     The vertical solid shaft  50  of the caster assembly  42  is inserted through the bearings  84  pressed into the caster bearing housing  74 . The top of the caster stem is threaded to enable securing to the caster bearing housing with a locking nut. The caster assembly  42  is horizontally rotatable about the bearings and stem. 
     Footrest assembly  52  includes extension tubes  54  that are telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A transverse tube  56  is secured to one extension tube  54  at its lower end and nests into a fitting  58  on the opposite extension tube. A footrest  60  is secured to the transverse tube  56  (FIGS. 2 and 3) by means of footrest clamps  62 . A belt or strap  64  extends between opposing extension tubes  54  and is positioned above the footrest  60  to serve as a foot support and to prevent the legs from slipping rearwardly off the footrest. 
     An alternate footrest assembly  66  is shown in FIG.  8 . This assembly includes extension tubes  68  that are telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A flip up footplate  70  is secured to the lower end of the extension tube  68 . It is free to rotate upward toward the extension tube. The footplate  70  is limited in rotation downward to a position perpendicular to the extension tube  68 . A belt or strap  72  is attached to the inner and outer rear corners of the foot plate  70   a  with a studs  74  (see FIG. 2) and loops around the footrest extension tube  68  positioned above the footplate. 
     The vertical component of the bottom frame tube  16   c  has a series of holes to which are mounted a pair of rear wheel mounting plates  84  and a wheel plate bushing  86  which is captured between the pair of plates. The position of the axle mounting plates on the bottom frame tube determines the wheelchair rear seat height and seat angle. An axle bushing  88  is installed through the wheel mount plates  84  and wheel plate bushings  86  secured on the back side with a nut. Axles  90  (not shown) support the rear wheels  92  and insert into axle bushing  86 . Rear wheels are rotatable vertically about the axles. 
     FIG. 9 shows an optional wheel attachment, which consists of an axle plate tube  94 , mounted between the top frame tube  14  and the bottom frame tube  16  at  14   b ,  16   c . The axle plate tube is secured to the frame tubes with connecting fittings  20  at both ends. Spanning between the axle plate tube  94  and the vertical component of the bottom tube  16  is a generally horizontal axle camber plate  86 . The axle camber plate has a series of holes through which the wheel axle bushing  88  is secured. Positioning of the wheel bushing in the holes in the axle camber plate  86  determine the center of gravity of the wheelchair. Angling the lower edge of the axle camber plate  86  outward creates camber to the rear wheels which aids in stability and performance. 
     Now referring to FIGS. 4,  5  and  6 , a rigid wheelchair in accordance with the present invention is generally designated by the reference  110 . 
     The wheelchair  110  has a pair of like side frame assemblies  120  spaced from each other and including the same components as the previous folding wheelchair side frame assemblies, upper tube  14 , lower tube  16  and connector fittings  20 . 
     To convert the folding wheelchair  10  to a rigid wheelchair  110 , the following components are removed from the folding wheelchair: seat upholstery  76 , crossbar assemblies  22  (including crossbar tubes  24 , seat tube  26  and tee fitting  30 , see FIGS.  1 , 2  and  3 ), crossbar links  34 , seat tube saddles  36  and retaining rings  32 . The insert tubes  28  in the seat tubes are removed and reinstalled in the top tube  14  of the rigid side frame assemblies  120 . The upper frame tubes  14  and lower frame tubes  16  mount to one another with connector fittings  20  at the front at  14   a  and  16   a  and at the rear at  14   b  and  16   c . This allows the top frame  14  to at the same seat height from the floor as the seat tube  26  on the folding frame wheelchair  10 . Threaded inserts  122  are installed into the lower frame tubes  16  at holes  16   d  aligning holes. Straight crossbar tubes  124  are installed at the holes  16   d  and  16   e  with the special connector fittings and screws. Formed cross tubes  126  are installed on the upper frame tubes  14  at  14   d  and  14 e using special connector fittings and screws. The insert  28  has corresponding threaded holes to  14   d  and  14   e  to which the formed cross tubes  126  are attached. An additional formed cross tube  126  is attached to the push handle tubes  38  at  38   b  using special fittings  20  and screws. 
     An optional folding back assembly  130  may be attached to the rigid frame wheelchair  110 . The push handle tubes  38   a  are removed from the side frame assembly  120  by removing the screws at  38   a . The back insert  40  is removed and replaced with a new insert  128 . Insert  134  is added to the bottom of each push handle  38  at holes  38   a . Screws are used to attach back hinge plates  132  to the push handles at  38   a  and to the top frame tube  14  at  14   f . A removable pin through the hinge plates  132  and the top of the lower frame tube  16   b  at hole  16   f.    
     Caster assemblies  42  are the same as used on the folding wheelchair  10 . 
     The footrest assembly  52  or  66  are the same as those used on the folding frame wheelchair  10  or an optional rigid footrest assembly  134  may be used on the rigid frame wheelchair  110 . This assembly consists of a generally u-shaped tubular footrest tube  136 . Each parallel leg  136   a  and  136   b  of the footrest tube has a series of holes through both walls of the tube. Each of the parallel legs is telescopically received within the front ends  14   a  of the top frame tubes  14 , as shown. A footrest  60  is secured to the horizontal potion of the unshaped footrest tube  136  by means of footrest clamps  62 . A belt or strap  64  extends between opposing parallel legs of the footrest tube  136  and is positioned above the footrest  60  to serve as a foot support and to prevent the legs from slipping rearwardly off of the footrest. 
     The above mentioned procedure is to convert a folding wheelchair  10  into a rigid frame wheelchair  110 . The reverse procedure would be used to convert rigid to folding. 
     All frame components are designed to accept parts for both the folding  10  and rigid frame  110  wheelchairs. Tubular components are designed to be easily attached to other members with the special connector fittings  20 . 
     This design offers a simple, lightweight and dependable wheelchair, which can be easily assembled, repaired and maintained by a layman utilizing basic hand tools. The design employs failsafe weld-free connectors to join tubular components. 
     The elimination of welding and brazing provides the following advantages: 
     1. Increased strength and durability; 
     2. Design flexibility: the dimensions of the wheelchair can be easily changed to accommodate the end users&#39; requirements; 
     3. Modular construction providing for quick conversion from rigid frame to folding, to companion chair, to front wheel drive, to lever drive, to hand cycle, etc. 
     4. The possibility of using stainless steel, aluminum, titanium, etc., tubing for control of the weight and cost of the wheelchair; 
     5. The possibility of using noncorrosive materials, warranting a climate proof design; 
     6. Most of the components are standardized, so the wheelchairs can be shipped in kits and assembled locally; and 
     7. The wheelchairs can be manufactured locally using various available materials to adapt to rural, suburban or urban environment. 
     Thus, this wheelchair design: 
     (a) incorporates tubular connector fittings instead of welded or brazed joints for added structural strength and durability; 
     (b) uses tube connector fittings with an internal fastener captured within the fitting by a second fastener creating a failsafe mechanism; 
     (c) uses weld-free tube connectors that allow for the utilization of various hard-to-weld materials such as stainless steel, aluminum, titanium, etc.; 
     (d) has standardized components allowing for modular construction, ease of assembly, repair, maintenance, convertibility, shipping and storage; and 
     (e) is constructed with the ability to adapt to virtually any environment, configuration or option required by the wheelchair user. 
     While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications will be effected within the spirit and scope of the invention as described herein and as defined in the appended claims. Thus, while multiple connector fittings have been used to construct the wheelchair in conjunction with the presently preferred embodiment it should be clear that other methods of joining tubes in a wheelchair can also be used in conjunction with the use of one or more connector fittings of the invention.