Push button adjuster for chair backrest
BACKGROUND OF THE INVENTION 
     Height adjustable backrests are commonly employed on secretarial chairs or the like, and a variety of backrest adjusting and locking mechanisms for such backrests are known in the prior art. In most instances, the prior art adjusters are fairly costly and commonly have protruding knobs, operating levers and the like which are somewhat unsightly and sometimes inconvenient. Some examples of the prior art are shown in the below-listed U.S. patents which are made of record herein to comply with the duty to disclose known prior art under 37 C.F.R. 1.56, U.S. Pat. Nos.: 
     2,054,557 
     3,326,602 
     3,351,379 
     3,526,430 
     3,854,772 
     4,012,158 
     4,043,594. 
     The objective of the invention is to provide a chair backrest adjuster which is entirely free of the above-noted deficiencies of the prior art, and which is considerably less costly to manufacture, more convenient to use, and provides a much better finished appearance on the chair which employs the invention. A further attribute of the present invention resides in a simpler and less costly assembly procedure for the backrest which is equipped with the push button adjuster in accordance with the invention. 
     Other features and advantages of the invention will appear to those skilled in the art during the course of the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear perspective view of a chair backrest equipped with the push button adjuster embodying the invention. 
     FIG. 2 is an enlarged central vertical section taken through the backrest and adjuster on line 2--2 of FIG. 1. 
     FIG. 3 is a fragmentary vertical section through the backrest taken on the plane of line 3--3 of FIG. 2. 
     FIG. 4 is a fragmentary horizontal section taken on line 4--4 of FIG. 3. 
     FIG. 5 is a fragmentary horizontal section taken on line 5--5 of FIG. 3. 
     FIG. 6 is a fragmentary exploded perspective view of the invention, partly in cross section. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings in detail wherein like numerals designate like parts, the numeral 10 designates a fabric covered padded backrest for a secretarial chair which is attached for height adjustment by means of the present invention to an upright backrest support bar 11 carrying an anchor plate 12 at its lower end for attachment to a chair seat, not shown. 
     The backrest 10 comprises separate forward and rear plywood panels 13 and 14, the rear panel 14 being removably attached to the forward panel 13 preferably by three wood screws 15 near the top and bottom edges of the backrest. The forward plywood panel 13 has a vertically extending rectangular slot 16 formed through its lower edge at its transverse center and having an upper horizontal end wall 17 disposed somewhat above the vertical center of the backrest 10. Forwardly of the plywood panel 13, the adjustable backrest has padding 18 of any preferred type and this padding is covered and enclosed by a fabric section 19 which defines the forward face of the backrest 10. The marginal edge of the fabric section 19 extends to the rear face of panel 13 to form a relatively narrow portion 20 which may be stapled to the panel 13. 
     The rear removable plywood panel 14 is covered on its rear face with fabric 21 which is also lapped about the edges and front face of the panel 14 to form a fabric portion 22&#39; facing the portion 20 and stapled to the forward face of panel 14. A finishing bead 22 of fabric extends around the margin of the backrest 10 with extensions 23 thereof clampingly engaged between the two panels 13 and 14. 
     A sturdy metal bracket 24 is utilized to connect the backrest 10 adjustably to the upright support bar 11. This bracket includes a flat forward wall 25 disposed immediately forwardly of the bar 11 and longitudinally spaced pairs of rear flat flanges 26 which lie in a common plane parallel to the wall 25 and spaced rearwardly thereof. The flanges 26 of bracket 24 lap the back of support bar 11 and constitute with the wall 25 and connecting edge portions 27 of the bracket a flattened sleeve body which slidably embraces the bar 11. Opposite side outwardly extending flat tabs 28 on the metal bracket 24 are anchored by screws 29 to the rear face of plywood panel 13. In this manner, the bracket 24 constitutes a support for the entire backrest 10 enabling it to be adjusted upwardly or downwardly on the support bar 11 in a manner to be further described. The upper end wall 17 of the slot 16 in panel 13 provides a limit stop for the downward movement of the backrest 10 on the support bar 11. 
     A plywood bridging strip 30, FIGS. 2 and 5, is preferably placed across the bottom of the rather wide slot 16 and anchored to the front face of panel 13 by a pair of screws 31. This bridging strip 30 provides a ready means of clamping the narrow fabric portion 20 against the forward wall 25 of bracket 24 in the region where such fabric would otherwise be unsupported due to the presence of the slot or cut-out 16. 
     To form the height adjusting means for the backrest 10 according to the main feature of the invention, the support bar 11 is provided with a central vertically elongated adjusting slot 32 having a series of independent cylindrically curved detent recesses 33 formed along its length. These detent recesses 33 provide multiple height adjustment positions for the backrest 10. In cooperation with the adjusting slot 32, a horizontal axis adjusting and locking pin 34 of cylindrical formation is adapted for selective engagement in the detent recesses 33 along the slot 32. The pin 34 is received through an aperture 35 in the wall 25 of bracket 24 and has a flat head 36 which lies immediately rearwardly of the wall 25, FIGS. 2 and 4. The pin 34 has a rearwardly projecting screw-threaded shank 37 of reduced diameter which is threadedly engaged with a push button 38 normally biased by a coil spring 39 into a position where the push button is approximately flush with the rear face of the backrest 10 or protruding slightly therefrom, as shown in FIG. 2. Push button 38 and biasing spring 39 are received within a cylindrical cup 40, which cup is snugly fitted within an opening 41 of the plywood panel 14 and fixed therein along with surrounding fabric 42 by cementing or the like. The cup 40 has a forward end wall 43 which substantially abuts the rear face of support bar 11 and the end wall 43 has a central aperture 44 formed therethrough providing further axial guidance for the adjusting the locking pin 34. The biasing spring 39 normally holds the head 36 of pin 34 in abutment with the bracket forward wall 25. 
     In the use of the adjuster to regulate the height of the backrest 10, it is merely necessary to press the button 38 forwardly into the cup 40 against the spring 39, as illustrated in FIG. 4. This will cause the cylindrical body of pin 34 to move forwardly and out of engagement with the particular detent recess 33 in which it is seated, the axial length of the pin body being about equal to the thickness of the bar 11 plus the thickness of the bracket wall 25. When the pin 34 is thus thrust forwardly, it enters the cushioning material 18 which yields and offers no significant resistance to the movement of the pin. With the pin 34 out of the adjusting slot 32, the backrest 10 can be freely adjusted upwardly or downwardly on the bar 11, the bracket 24 offering smooth guidance of the backrest on the support bar 11. Following the removal of finger pressure on the push button 38, the locking and positioning pin 34 may enter any selected adjustment recess 33 of the bar 11 to securely hold the backrest 10 in the selected adjusted position. 
     It may now be seen that the operation of the backrest adjuster is very simple and convenient. There are no levers to tilt or knobs to turn and no awkward parts of the mechanism protrude from the backrest. A great virtue of the structure is that the bracket 24 and all associated parts other than the push button 38 are concealed internally in the padded backrest, thus making for a very clean and uncluttered appearance which is extremely important in furniture. The construction of the invention is also durable, simplified, virtually foolproof in operation, and economical to manufacture. Its many advantages over the prior art should now be apparent. 
     The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof but it is recognized that various modifications are possible within the scope of the invention claimed.