Patent Publication Number: US-8991933-B2

Title: Backrest for wheelchair

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of European Patent Application No. 11179221.4, filed on Aug. 29, 2011, which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of backrests. More particularly, the invention pertains to a width adjustable backrest for wheelchair. 
     BACKGROUND OF THE INVENTION 
     There is an increasing need for variable adjustment possibilities in order to adapt the backrest configuration, in particular its width, to the individual requirements of a particular wheelchair user. The requirements can occur from the need of comfort of the user or from the need of accommodation of a variety of health issues and reasons for wheelchair use. 
     Document U.S. Pat. No. 2,534,009 describes a conventional adjustable backrest, which comprises a pair of spaced apart side bars, each side bar having a plurality of spaced transverse bars extending therefrom towards the opposite side bar. The transverse bars of the two side bars comprise each a circular through hole and a slot. Fasteners pass through corresponding hole and slot in order to fasten the transverse bars together, the holes and slots being positioned so that the lateral spacing of the side bars is adjustable. According to this embodiment, the width adjustment of the backrest depends on the lengths of the slots, nevertheless the side bars do not contribute itself to the width adjustment and therefore limit the width adjustment. Moreover, the transverse bars of each side bar are not linked together so that the reliability of the assembly depends essentially on the connection means between the side bars and their transverse bars. 
     Document U.S. Pat. No. 5,564,786 describes an adjustable seat frame. The frame comprises a pair of spaced apart side rail having a plurality of spaced parallel transverse beams extending therefrom towards the opposite rail and a central beam telescopingly engaged between corresponding beams on each rail. Here again, the side rails do not contribute to the width adjustment of the frame and the transverse beams are not linked together. Due to the connections between each central beam and its corresponding transverse beams, this embodiment need two times more fastening means than the embodiment described in U.S. Pat. No. 2,534,009. 
     SUMMARY OF THE INVENTION 
     In line with the invention, it is proposed a backrest intended to be connected to a wheelchair frame comprising a first lateral end, a second lateral end, a front side and a back side, at least one pair of side wings, namely a first side wing and a second side wing, that may be generally vertically oriented when connected to the wheelchair frame, and connectors configured to fixedly connect the first side wing and the second side wing to the wheelchair frame, wherein the first side wing comprises a plurality of vertically spaced first transverse profiles extending therefrom towards the second side wing and the second side wing comprises a plurality of vertically spaced second transverse profiles extending therefrom towards the first side wing and wherein at least one first transverse profile of the first side wing and at least one associated second transverse profile of the second side wing are at least partially mutually embraced in a slidable manner, the at least one first transverse profile and the at least one second transverse profile being dimensioned and configured so that the mutual slidably embracement of the at least one first transverse profile and the at least one second transverse profile is made on a range of distances enabling the width adjustment of the backrest, the mutual embracement of the at least one first transverse profile and the at least one second transverse profile being configured to prevent the side wings from disengaging from each other in a direction other than the slidably direction of the side wings and the first transverse profiles, respectively the second transverse profiles, being at least partially linked together so as to define approximately a continuous surface S c . 
     The invention also concerns a wheelchair having a backrest as defined above. 
     The backrest is adjustable in width and can be connected to a large variety of wheelchair frames. The width adjustable backrest is sustainable and reliable. The connectors are configured to fixedly connect the first side wing and the second side wing to the wheelchair frame. The mutual embracement of the first and second transverse profiles, as well as optionally the hollow buckles and the openings, are configured to prevent the side wings from disengaging from each other in a direction other than the sildably direction of the side wings, in particular to prevent the side wings from disengaging from each other in a direction perpendicular to the transverse profiles. Apart from the connectors, which connect the side wings to the wheelchair frame, additional fasteners fastening the side wings together are unnecessary since the connection of the side wings to the wheelchair frame determines the relative positioning of the side wings in relation to one another and since the mutual embracement of the first and second transverse profiles prevent the disengagement of the side wings. The numbers of connectors and fasteners are therefore minimized. The arrangement for adjusting the width of the backrest are therefore simple and trouble-free and require the use of common and unitary tool. Advantageously, the width adjustment of the backrest is maximized since the entire widths of the side wings contribute to the width adjustment. Moreover, the first transverse profiles, respectively the second traverse profiles, are at least partially linked together so as to define approximately a continuous surface. Therefore, the resultant force applied by the wheelchair user in the backrest is distributed over the backrest surface. The sustainability and the reliability of the backrest are thus strengthened. Advantageously, the side wings are sandwiched between plates, which are connected together with the help of a first fastener. A second fastener is used to firmly fasten the side wings and the plates together in a position of use in which the width of the backrest cannot be changed. This sandwich assembly strengthens the stiffness of the backrest. The first fastener and the second fastener are advantageously positioned on the vertical symmetry axis of the backrest. According to a resultant force applied by a wheelchair user in the symmetry axis of the backrest, no bending stress is applied to the fasteners positioned on the said symmetry axis. There is therefore no risk of accidental undoing or breaking of the fasteners. 
     Further objects, features and advantages of the invention will become apparent to a person skilled in the art upon reading the specification and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which: 
         FIG. 1  depicts an exploded back perspective view of a backrest in accordance with the invention; 
         FIG. 2  depicts a back perspective view of a backrest in accordance with the invention connected to a wheelchair frame; 
         FIG. 3  depicts a front perspective view of one pair of disassembled side wings in accordance with  FIG. 1 ; 
         FIG. 4  depicts a back perspective view of one pair of disassembled side wings in accordance with  FIG. 1 ; 
         FIGS. 5   a ,  5   b , and  5   c  depict three front perspective views of one pair of assembled side wings, respectively in thinnest, middle and widest positions, in accordance with  FIG. 1 ; 
         FIGS. 6   a ,  6   b ,  6   c  depict three back perspective views of one pair of assembled side wings, respectively in thinnest, middle and widest positions, in accordance with  FIG. 1 ; 
         FIG. 7  depicts a back view of a backrest in accordance with  FIG. 1 ; 
         FIG. 7A  is a sectional view taken along the plane indicated by lines A-A in  FIG. 7 ; 
         FIG. 7B  is a sectional view taken along the plane indicated by lines A-A in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the appended  FIGS. 1 to 7 , in which one embodiment of the invention is shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to the person skilled in the art. 
     Varying a backrest width of a wheelchair permits the backrest to suit different users having different body constitutions and varying handicaps. This degree of adjustment also enables the backrest to accommodate a patient&#39;s growth easily. Furthermore, whereas a width adjustable backrest can be connected to a large variety of wheelchair frames, the industrial production of backrests is rationalized. Indeed, the width of the backrest is adjusted at the time of mounting according to the width of the frame. Avoiding the production of backrest of different sizes, the production costs are reduced. Moreover, the supply of such width adjustable backrests reduces the stocks of retailers or specialized institutions and simplifies the management of the said stocks. 
     The design and the proportioning of an adjustable backrest have to provide high degrees of sustainability and reliability. In all situations, the adjustable backrest has to meet the safety needs of the wheelchair user. Moreover, the means for adjusting the width of the backrest should advantageously be uncomplicated and trouble-free and require the use of common and unitary tool to accomplish the width adjustment. The numbers of connectors and fasteners should be minimized. Moreover, in order to maximize the width adjustment of the backrest, the entire widths of the backrest should contribute to the width adjustment. 
     Therefore, there is a need for a backrest for wheelchair fulfilling, respectively avoiding, the above-mentioned requirements and drawbacks. The aim of the present invention is thus to provide a solution to these problems. 
       FIG. 1  depicts an exploded back perspective view of a backrest  1  in accordance with the invention. The backrest  1  comprises a first lateral end  11 , a second lateral end  12 , a front side  13  and a back side  14 , as well as one pair of side wings, namely a first side wing  3  and a second side wing  4 , and connector  10  configured to fixedly connect the first side wing  3  and the second side wing  4  to the wheelchair frame  2 . Optionally, the backrest  1  comprises one pair of plates, namely a first plate  15  and a second plate  16 , disposed on each side of the backrest  1 , respectively in the front side  13  and in the back side  14  of the backrest  1 . The side wings  3  and  4  and the plates  15  and  16  may be generally vertically oriented when connected to a wheelchair frame  2 . For instance, one pair of assembled side wings, which are connected to the wheelchair frame  2 , is shown in  FIG. 2 . 
     The first side wing  3  comprises a plurality of vertically spaced first transverse profiles  5  extending therefrom towards the second side wing  4  and the second side wing  4  comprises a plurality of vertically spaced second transverse profiles  6  extending therefrom towards the first side wing  3 . As described in detail hereinafter, the mutual embracement of the first and second transverse profiles  5  and  6  are configured to allow the backrest  1  to be adjustable in width in a slidable manner. Moreover, the mutual embracement of the first and second transverse profiles  5  and  6  are configured to prevent the side wings  3  and  4  from disengaging from each other in a direction other than the slidably direction of the side wings, in particular to prevent the side wings from disengaging from each other in a direction perpendicular to the transverse profiles  5  and  6 . The mutual embracement of the first and second transverse profiles  5  and  6  should be understood in the way that some portions of the first transverse profiles  5  are configured to embrace some portions of the second transverse profiles  6  and some other portions of the first transverse profiles  5  are configured to be embraced by some other portions of the second transverse profiles  6 . As a definition, “to embrace at least partially” should be understood as to enclose, to surround or to envelop at least partially. Specifically, “at least partially” should be understood in the sense that an embracing element does not necessarily enclose, surround or envelop entirely the cross section of the associated embraced element. 
     The first transverse profiles  5  of the first side wing  3  comprise each a first embracing portion  5   a  and a first embraced portion  5   b , the first embracing portion  5   a  being closer to the first lateral end  11  of the backrest  1  than the first embraced portion  5   b . Respectively, the second transverse profiles  6  of the second side wing  4  comprise each a second embracing portion  6   a  and a second embraced portion  6   b , the second embracing portion  6   a  being closer to the second lateral end  12  of the backrest  1  than the second embraced portion  6   b . The first embracing portions  5   a  of the first side wing  3  and the second embracing portions  6   a  of the second side wing  4  are configured to slidably at least partially embrace respectively the second embraced portions  6   b  of the second side wing  4  and the first embraced portions  5   b  of the first side wing  3 , the first embracing portions  5   a , the second embracing portions  6   a , the first embraced portions  5   b  and the second embraced portions  6   b  being dimensioned and configured so that the slidably embracement of the side wings  3  and  4  is made on a range of distances enabling the width adjustment of the backrest. The connector  10  comprises at least one first clamp  18  disposed at the first lateral end  11  of the backrest  1  and at least one second clamp  19  disposed at the second lateral end of the backrest  1 , the at least one first clamp  18  and the at least one second clamp  19  being adapted for engaging the wheelchair frame  2  in order to connect receptively the first side wing  3  and the second side wing  4  to the wheelchair frame  2 . The at least one first clamp  18  and the at least one second clamp  19  are respectively fixed to the first side wing  3  and to the second side wing  4  with the help of nuts and bolts. Apart from the connectors  10 , which connect the side wings  3  and  4  to the wheelchair frame  2 , additional fasteners fastening the side wings together are unnecessary since the connection of the side wings to the wheelchair frame determines the relative positioning of the side wings in relation to one another and since the mutual embracement of the first and second transverse profiles prevent the disengagement of the side wings. Moreover, the first transverse profiles  5 , respectively the second transverse profiles  6 , are made in one single piece so as to define a continuous surface S c  offering strengthened sustainability and reliability of the backrest. In particular, the first embracing portions  5   a  of the first side wing  3 , respectively the second embracing portions  6   a  of the second side wing  4 , are linked together so as to define approximately a continuous surface S c  offering strengthened sustainability and reliability of the backrest. Indeed, by virtue of the continuous surfaces S c , the resultant force applied by a wheelchair user in the backrest is distributed over the backrest surface. The risk of accidental breaking of the transverse profiles  5  and  6  is therefore reduced. Moreover, the width adjustment of the backrest is maximized since the entire widths of the side wings contribute to the backrest width adjustment. 
     As mentioned above, the backrest optionally comprises one pair of plates, namely a first plate  15  and a second plate  16 , disposed on each side of the backrest  1 , respectively in the front side  13  and in the back side  14  of the backrest  1 . Indeed, the first side wing  3  and the second side wing  4  can advantageously be sandwiched between the first plate  15  and the second plate  16 , the first plate  15  and the second plate  16  being connected together with the help of first fastener  17  (see  FIGS. 7A and 7B ) and at least one of the plates being connected to the side wings with the help of a second fastener  57 . By virtue of the first plate  15  and the second plate  16  sandwiching the side wings  3  and  4 , the stiffness of the backrest  1  is strengthened. The sustainability and the reliability of the backrest  1  are therefore increased. Moreover, the first plate  15  and the second plate  16  protect the side wings  3  and  4  from dust and dirt, which could potentially affect the slidably embracement of the side wings  3  and  4 . The plates  15  and  16  can advantageously offer fixation points to additional backrest elements (not shown) like cushions and storage units as well as width and height adjustable structures like headrests, additional backrest plates or wings and any rest of body limp. In particular, the first plate  15  comprises a plurality of through holes and the second plate  16  comprises a plurality of associated threaded holes distributed along at least the backrest height. The first fasteners  17  comprise a plurality of nuts, each nut being engaged in each through holes and threaded onto the associated threaded hole in order to fasten the first plate  15  and the second plate  16  together. The plurality of through holes and the plurality of associated threaded holes are respectively positioned on the first plate  15  and on the second plate  15  so that the first fasteners can pass through the space between two adjacent transverse profiles of the first and second side wings  3  and  4 . Furthermore, at least some of the plurality of through holes and at least some of the associated threaded holes can advantageously be respectively positioned on the first plate  13  and on the second plate  14  so that the first fasteners  17  are positioned at least partially on the vertical symmetry axis of the backrest. According to a resultant force applied by a wheelchair user in the symmetry axis of the backrest, no bending stress is therefore applied to the first fasteners  17 . The sustainability and the reliability of the backrest are thus increased. Moreover, second fasteners  57  are used to firmly fasten the side wings  3  and  4  and the plates  15  and  16  together in a position of use in which the width of the backrest  1  cannot be changed. At least one of the first plate  15  or second plate  16  advantageously comprises at least one third through hole  59 . Moreover, as shown in  FIG. 1 , two first transverse profiles  5  comprise a plurality of first circular through holes  9   a  and the associated two second transverse profiles  6  comprise a plurality of associated second circular through holes  9   b . The plurality of first circular through holes  9   a  and the plurality of associated second circular through holes  9   b  are positioned on their respective transverse profiles so that at least one of the plurality of the first circular through hole  9   a  and at least one of the plurality of associated second circular though hole  9   b  are placed opposite one another for each desired width configuration of the backrest. The second fasteners  57  may be passed through at least one of the plurality of first circular through holes  9   a , through at least one of the plurality of the associated second circular though holes  9   b  and though at least one of the at least one third through hole  59  in order to firmly fasten the first side wing  3 , the second side wing  4 , the first plate  15  and the second plate  16  together, the first plate  15  and the second plate  16  being connected together with the help of the first fasteners. The second fasteners comprise two pairs of nut and bolt. The two nuts are each engaged in one of the plurality of first circular through holes  9   a , in one of the plurality of the associated second circular through holes  9   b  and in at least one of the at least one third through hole and threaded onto the associated bolt. The plurality of first circular through holes  9   a , the plurality of second circular through holes  9   b  and the at least one third through hole are advantageously positioned on the first transverse profiles  5 , on the second transverse profile  6  and on the first or second plate so that the second fasteners can be positioned on the vertical symmetry axis of the backrest  1  for each desired width configuration. According to a resultant force applied by a wheelchair user in the symmetry axis of the backrest, no bending stress is therefore applied to the second fasteners. There is thus no risk of accidental undoing or breaking of the second fasteners. Moreover, the plurality of first circular through holes  9   a  and the plurality of associated second circular through holes  9   b  are positioned on their respective transverse profiles so that at least one of the plurality of the first circular through hole  9   a  and at least one of the plurality of associated second circular though hole  9   b  are placed opposite one another in the symmetry axis of the backrest for each desired width configuration. Accordingly and with the help of the second fasteners, the first plates  15  and the second plates  16  are centered in the backrest. 
       FIG. 3  and  FIG. 4  depict respectively a front perspective view and a back perspective view of one pair of disassembled side wings of the backrest  1  in accordance with  FIG. 1 . In the illustrated embodiment, the first transverse profiles  5  and the second transverse profiles  6  are parallel with each other. Moreover, each first transverse profile  5 , in particular each first embracing portion  5   a , comprises one hollow buckle  7  in which the associated second transverse profile  6 , in particular the second embraced portion  6   b  of the associated second transverse profile  6 , is intended to be engaged. Furthermore, each second transverse profile  6 , in particular each second embracing portion  6   a , comprises an opening  8  in which the associated first transverse profile  5 , in particular the first embraced portion  5   b  of the associated first transverse profile  5 , is intended to be engaged. Both buckles  7  and openings  8  are used in order to prevent the side wings  3  and  4  from disengaging from each other in a direction other than the slidably direction of the side wings, in particular to prevent the side wings from disengaging from each other in a direction perpendicular to the transverse profiles  5  and  6 . Furthermore, the first embraced portions  5   b  and the second embraced portions  6   b , as well as the first embracing portions  5   a  and the second embracing portions  6   a , are at least partially I-shaped profiles. Once the side wings assembled and according to their mutual embracement, the first embracing portions  5   a  prevent vertical displacements of the second embraced portions  6   b , as well as their horizontal displacement in the direction of the back side  14 . Similarly, the second embracing portions  6   a  prevent vertical displacements of the first embraced portion  5   b , as well as their horizontal displacement in the direction of the back side  14 . Moreover, the buckles  7  prevent horizontal displacement of the second embraced portion  6   b  in the direction of the front side  13 . Similarly, the openings  8  prevent horizontal displacement of the first embraced portion  5   b  in the direction of the front side  13 . Therefore, the mutual embracement of the first and second transverse profiles  5  and  6  mainly allow slidable displacement of the side wings one to each other in the direction of the first and second lateral ends  11  and  12 . Consequently, once each side wing connected to the wheelchair frame  2  with the help of the connectors  10 , the side wings are interdependent and form a stiff assembly due to their mutual embracement. The lengths of the first transverse profiles  5  are respectively equal to the lengths of the associated second transverse profiles  6 . In this particular case, the lengths of the first embracing portions  5   a , respectively of the first embraced portions  5   b , can respectively be equal to the lengths of the associated second embraced portions  6   b , respectively of the associated second embracing portions  6   a.    
     In order to shape the backrest to the back of the user, the first transverse profiles  5  and the second transverse profiles  6  are curved. 
       FIGS. 5   a ,  5   b , and  5   c  depict three front perspective views of one pair of assembled side wings, respectively in thinnest, middle and widest positions, in accordance with  FIG. 1 .  FIGS. 6   a ,  6   b ,  6   c  depict the same but in back perspective views. The mutual embracement of the first and second transverse profiles  5  and  6  are evidenced. In particular, the first embracing portions  5   a  and the second embracing portions  6   a  slidably at least partially embrace respectively the second embraced portions  6   b  and the first embraced portion  5   b . Moreover, in the configuration in which the second embraced portions  6   b  are in contact with the first embraced portions  5   b , the second embraced portions  6   b  slidably at least partially embrace the first embraced portions  5   b . This configuration can be appreciated in  FIGS. 5   b  and  5   c  as well as in  FIGS. 6   b  and  6   c.    
       FIG. 7  depicts a front view of an assembled backrest in accordance with  FIG. 1 .  FIG. 7A  is a sectional view taken along lines A-A in  FIG. 7 .  FIG. 7B  is a sectioned perspective view taken along lines A-A in  FIG. 7 . The respective position of the side wings corresponds to the one of  FIGS. 5   a  and  6   a , namely the assembled side wings in thinnest position. In  FIG. 7B , the embracement between the first embracing portions  5   a  of the first side wing  3  and the second embraced portions  6   b  of the second wings  4  is evidenced. The I-shaped profile of the first embracing portions  5   a  and the I-shaped profile of the second embraced portions  6   b  are proportioned so that they fit tight together. Their respective cross-section does indeed not allow vertical displacement of the second embraced portions  6   b . Moreover, the first embracing portions  5   a  embracing the second embraced portions  6   b , the first embracing portions  5   a , respectively the second embraced portions  6   b , prevent horizontal displacement of the second side wing  4  in the direction of the back side  14 , respectively horizontal displacement of the first side wing  3  in the direction of the front side  13 . 
     The backrest of the invention being adjustable in width, it can be connected to a large variety of wheelchair frames. The width of the backrest can adjusted at the time of mounting according to the width of the frame. Advantageously, the backrest of the invention can be connected to a wheelchair frame which is extendable in width. Such type of width extendable wheelchair frame is known in the prior art. 
     The side wings and the plates are preferably made of plastic. They may each be manufactured as a single piece from injection molded plastic material, advantageously fiber reinforced plastic material. Other materials, without limitations, like metals such as stainless steal, aluminum, titanium, as well as fiberglass or wood may also be used to manufacture the parts. 
     Typical dimensions of the main parts of the backrest are hereafter provided. Each side wing, which is typically 48 cm in height, comprises typically six transverse profiles. The transverse profiles are typically about 27 cm in width and 4 cm in height. The embraced portions are typically about 15 cm in width. The vertical spacing between two adjacent transverse profiles is typically 40 cm. The first and second plates are typically 25 cm in width. 
     The above detailed description with reference to the drawings illustrates rather than limit the invention. There are numerous alternatives, which fall within the scope of the appended claims. For instance, other types of fasteners may also be used without departing from the invention. Moreover, variations of the above-mentioned invention embodiment are hereinafter specified (not shown on Figures). 
     In particular, the first transverse profiles, respectively the second transverse profiles, comprise each a plurality of first embracing portions and a plurality of first embraced portions, respectively a plurality of second embracing portions and a plurality of second embraced portions. On each first transverse profile, the plurality of first embracing portions is closer to the first lateral end of the backrest than the plurality of first embraced portions. Respectively, on each second transverse profile, the plurality of second embracing portions is closer to the second lateral end of the backrest than the plurality of the second embraced portions. At least one of the plurality of first embracing portions and at least one of the plurality of second embracing portions slidably at least partially embrace respectively at least one of the plurality of second embraced portions and at least one of the plurality of first embraced portions. 
     Furthermore, the backrest comprises a plurality of pair of side wings and optionally a plurality of pair of plates. The plurality of pair of side wings intended to be connected to the wheelchair frame can advantageously be connected to each other with the help of second fasteners. Each pair of plates is intended to sandwich each associated pair of side wings. 
     In addition, at least one first transverse profile comprises at least one first embracing portion having at least one hollow buckle in which at least one second embraced portion of the associated at least one second transverse profile is engaged. Similarly, at least one second transverse profile comprises at least one second embracing portion having at least one opening in which at least one first embraced portion of the associated at least one first transverse profile is engaged. Moreover, the positions of the at least one hollow buckle and the at least one opening can be inversed so that the at least one hollow buckle is positioned on the at least one second transverse profile and the at least one opening is positioned on the at the least one first transverse profile. 
     At least one first transverse profile comprises a plurality of first circular through holes and the associated at least one second transverse profile comprises a plurality of associated second circular through holes. The second fasteners may be passed through at least one of the plurality of first circular through holes and through at least one of the associated second circular though holes in order to fasten the side wings together. Moreover, the plurality of first circular through holes or the plurality of associated second circular through holes can be replaced by at least one elongated slot, the second fasteners passing through at least one of the plurality of first or associated second circular through holes and through at least one elongated slot in order to fasten the side wings together. Alternatively, the plurality of first circular through holes and the plurality of associated second circular through holes can be replaced each by at least one elongated slot. The combination of circular through holes and associated elongated slot or the combination of two elongated slots enables an infinite number of width configuration of the backrest whereas the number of width configuration is discrete with the combination of a discrete number of first circular through holes and associated second circular through holes. 
     Other profiles than I-shaped profiles can be used as long as the first embracing portions  5   a  and the second embracing portions  6   a  slidably at least partially embrace respectively the second embraced portions  6   b  and the first embraced portions  5   b . For instance, U-shaped profiles can replace at least partially the I-shaped profiles, the first embracing portions  5   a  and the second embraced portions  6   b  being I-shaped profiles whereas the second embracing portions  6   a  and the first embraced portions  5   b  being for example U-shaped profiles or vice versa. 
     The slidably embracement of the side wings does not require the same orientation of the first transverse profiles, respectively the same orientation of the second transverse profiles. Indeed, the slidably embracement of the side wings does require that each first transverse profile of the first side wing has the same orientation as its associated second transverse profile of the second side wing. 
     
       
         
           
               
            
               
                   
               
               
                 Nomenclature 
               
            
           
           
               
               
               
            
               
                   
                 Element 
                 Reference sign 
               
               
                   
                   
               
               
                   
                 Backrest 
                 1 
               
               
                   
                 First side wing 
                 3 
               
               
                   
                 First transverse profile 
                 5 
               
               
                   
                 First embracing portion 
                  5a 
               
               
                   
                 Buckle 
                 7 
               
               
                   
                 First embraced portion 
                  5b 
               
               
                   
                 First circular through holes 
                  9a 
               
               
                   
                 Second side wing 
                 4 
               
               
                   
                 Second transverse profile 
                 6 
               
               
                   
                 Second embracing portion 
                  6a 
               
               
                   
                 Opening 
                 8 
               
               
                   
                 Second embraced portion 
                  6b 
               
               
                   
                 Second circular through holes  
                  9b 
               
               
                   
                 First plate 
                 15  
               
               
                   
                 Second plate 
                 16  
               
               
                   
                 Wheelchair frame 
                 2