Patent Publication Number: US-6698839-B2

Title: Back of chair

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a back of a chair. 
     2. Background Art 
     Backs having a back frame are known which comprise a U-shaped lower frame part and a plastic bow serving as upper end part. The cover comprises two lateral rand seams or hollow seams which are pushed onto the essentially perpendicular lateral legs of the lower frame part. The cover is secured onto the lower frame part by means of securing pins. On said cover, a central upper bracket is formed which is attached in the upper end bow and tensioned. 
     Furthermore, a back having a back frame is known, said back frame comprising two lateral pipe-shaped stanchions and an upper and a lower transversal stanchion made of flat steel. The lateral stanchions are made of an aluminum profile comprising an undercut longitudinal groove into which rand bars are inserted which are attached onto the side edges of a cover. The cover comprises at its upper and lower edges rand seams into which flat steel stanchions are inserted. Thereafter, the frame is assembled by screws. 
     These known structures require an extraordinarily expensive assembly. 
     DE 197 54 817 A1 describes a back comprising a frame shaped like a reversed letter U being open towards the bottom. The legs of said frame are connected in an articulated manner to the upper transversal stanchion. The cover used is formed in the shape of a sack. The articulated frame is inserted into the cover by swaying the stanchion and one leg accordingly and expanding it with the cover being tensioned. The free lower ends of the frame legs are then attached to the chair. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a back for a chair which is easy to assemble and allows an even tension of the cover in all directions. 
     According to the present invention, this object is achieved in a back of a chair, comprising: a back frame comprising a first and a second frame part each being C-shaped and having two legs and a bar, said frame parts being joined with each other on the free ends of said legs on connecting locations; a cover, comprising four rand seams for receiving said legs and said bar of the first and the second frame parts, at least one insertion opening in a rand seam on a joint location of said frame parts; and two connecting members by means of which said frame parts are connected with each other at the joint locations, and at least one of which covers said at least one insertion opening. The solution according to the present invention results in the fact that the frame parts can be inserted into a rand seam of the pre-fabricated cover through a relatively small opening. The assembly of the two frame parts to form a frame is very simple. The opening formed in the cover is optically hidden completely when the two frame parts are fixed relative to each other. 
     Further features, advantages and details of the invention will become clear from the following description of two example embodiments with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a chair comprising a back according to a first embodiment of the present invention, 
     FIG. 2 shows an exploded view of the frame of the back of the chair shown in FIG. 1, 
     FIG. 3 shows the cover for the back shown in FIGS. 1 and 2, 
     FIG. 4 shows a connecting member for the frame shown in FIG. 2, 
     FIG. 5 shows a chair comprising a second embodiment of a back according to the present invention, and 
     FIG. 6 shows an exploded view of the frame of the back of the chair shown in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The chair shown in FIG. 1 comprises a seat  1  supported on the floor by means of chair legs  2 ,  3  being arranged symmetrically to each other and having chair rollers  4 . Said chair legs  2 ,  3  are each linked to each other in pairs to form an arm rest  5 . Onto the rear ends of said arm rests  5 , a back  6  is attached comprising a rectangular, and in particular square, back frame  7  provided with a cover  8 . 
     As shown in FIG. 2, said frame  7  consists of two essentially similar C-shaped frame parts  9 ,  10  made of metal tubes  11  joined with each other by welding at the corners  12  between one leg  13  or  14 , respectively, and a bar  15 . Said two frame parts  9 ,  10  are connected to each other at the free ends of their legs  13 ,  14  as shown in the exploded view of FIG.  2 . For centering, a centering pin  16  is attached to the end of one leg  13  or  14 , respectively, to be inserted into the respective end of the leg  13  or  14 , respectively, being flush with it. 
     Said frame  7  to be formed by said two frame parts  9 ,  10  is provided with a cover  8  shown in FIG.  3 . Said cover  8  comprises at each of its four longitudinal sides assigned to said bars  15  and said legs  13 ,  14  a hollow rand seam  17 ,  18 ,  19 ,  20 , i.e. a hose-shaped hollow seam. Said cover  8  is made of a knitwear made of natural and/or plastic and/or metal yarn or a suitable mixture of such yams. It may also be manufactured of a fabric having sufficient flexibility. Said rand seams  17  through  20  may be formed during the knitting process or be formed afterwards by sewing or the like. In the center of each of said rand seams  17 ,  19  receiving said legs  13 ,  14  of said two frame parts  9 ,  10 , a small insertion opening  21  is formed, respectively, through which one frame part  9 ,  10 , respectively, is inserted. Due to the flexibility of said cover  8  and a sufficient width of said rand seams  17  through  20  compared with the width of said tubes  11 , said frame parts  9 ,  10  can be inserted. Said cover  8  is tensioned by engaging said legs  13 ,  14  with each other by means of said centering pins  16 . The joints of said legs  13 ,  14  of said frame parts  9 ,  10  are located in the place of said openings  21 . 
     The connection of said back  6  being pre-assembled as described above to said arm rests  5  of the chairs is implemented by connecting members  22  which are shown in particular in FIG.  4 . Said connecting members  22  forming part of said back  6  are formed in a T-shape. Its end bar  23  to be arranged perpendicularly comprises an inner surface  24  adapted to the curve of said tubes  11 . Further, it comprises two bores  25  being flush with two bores  26  formed in said legs  13 ,  14  of said frame parts  9 ,  10  when the latter are joined abut with each other as described above. Screws  27  are inserted into said bores  25  and screwed into said bores  26 . By doing so, said two frame parts  9 ,  10  are tightly connected with each other and with said connecting members  22 . Further, the end bar  23  of each connecting member  22  covers the respective opening  21  formed in said rand seam  17 ,  19  of said cover  8  so that said opening  21  becomes invisible from outside. 
     The respective central bar  28  of each connecting member  22  comprises two supporting pins  29 ,  30  projecting towards each other in parallel for engagement into the two open ends of the two tubes  31 ,  32  forming the chair legs  2 ,  3  and being joined to form an arm rest  5 . Said connecting members  22  are fixed to said tubes  31 ,  32  by means of a screw  33 , respectively, which is screwed from beneath through the respective outermost tube  31  into a bore  34  in the longer supporting pin  29 . This connection bears the leaning force exerted by the user of the chair onto said back  6 . 
     The back frame  7  is formed as an arc, i.e. the horizontal bars  15  are—viewed from said seat  1 —bent to the rear while the perpendicular legs  13 ,  14  are bent towards said seat  1 . 
     The chair shown in FIG. 5 is an office chair the seat  40  of which is mounted on a seat support (not shown) which is attached via a lengthwise adjustable chair column  41  to a foot cross  42  which is supported by chair rollers  43  on the floor. To the seat support, a back support  44  is attached which extends upward behind said seat  40 . It has a cross shape, i.e. it comprises a central bar  45  essentially extending upward and a transverse bar  46  extending essentially in a horizontal direction. Both bars  45 ,  46  are bent towards their ends directed to said seat  40 , i.e. they are concave when viewed from said seat  40  or convex when viewed from the rear side. 
     Onto said back support  44 , a part of a back  47  is attached which—as in the example embodiment described above—comprises a rectangular, in particular an essentially square back frame  48  provided with a cover  49  formed in the same way as said cover  8  described above and shown in FIG. 3 so that reference can be made to the respective description. 
     Said frame  48 , too, consists of two C-shaped frame parts  50 ,  51 , the legs  52 ,  53  of which are arranged horizontally in this example embodiment while the bars  54  are arranged perpendicularly. Said legs  52 ,  53  comprise at their free ends flange bars  55 ,  56  facing each other which are aligned in pairs with each other and then have the same cross-section as said legs  52 ,  53 . They each comprise two bores  57  which flush with each other when both bars  55 ,  56  are laid on each other and which can be brought into coverage with bores  58  formed in support bearings  59 ,  60  of said central bar  45 . Also, in the end of said transverse bar  46 , bores  61  are formed which flush with one bore  62 , respectively, provided in the center of the respective bar  54  when said frame  48  is in contact with said back support  44 . 
     In this embodiment, said frame parts  50 ,  51  are not made of metal tubes but of extruded, fiber-reinforced plastic such as plastic reinforced with graphite fibers. 
     As described above, the assembly is done by firstly inserting a leg  52  and then said bar  54  followed by the other leg  53  of one frame part  50  or  51 , respectively, through an insertion opening  21  of said cover  49  into said rand seams  17 ,  18 ,  19  and then the other frame part  51  in the same manner into said rand seams  17 ,  20 ,  19 . Here, too, said rand seams  17  through  20  are wider than said legs  52 ,  53  and said bars  54  in order to allow insertion. Following this, said flange bars  54 ,  55  cover said openings  21  of said cover  49 . For facilitating the assembly, said frame parts  50 ,  51  are stabilized against each other by pushing an assembly supporting pin (not shown) through central centering bores  63  of said flange bars  55 ,  56 . Thereafter, said back  47  which has been pre-assembled in this manner is laid against said support bearings  59 ,  60  which serve as connecting members, followed by mounting said frame  48  with said cover  49  onto said central bar  45  by screwing screws  64  through said bores  58  in said support bearings  59 ,  60  into said bores  57  of said flange bars  55 ,  56  lying on top of each other, thus also achieving a fixed joint between said frame parts  50 ,  51 . For stabilizing said back  47 , screws  65  are also screwed through said bores  61  in said transversal bar  46  into said bores  62  formed in said bars  54 . 
     In this embodiment, too, said openings  21  of said cover  49  are completely covered by said support bearings  59 ,  60  so as to become invisible. Said screws  65  are screwed through said cover  49 ; no openings need to be provided for them in the cover. In the example embodiment shown in FIGS. 5 and 6, too, said back frame  48  may be arched in its entirety, i.e. said horizontal legs  52 ,  53  are bent rearwards to said back support  44  while said perpendicular bars  54  are bent towards the seat  40 .