Patent Publication Number: US-6659554-B2

Title: Adjustment device of a chair backrest

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an adjustment device of a chair backrest, and more particularly, an adjustment device that is easy to use and can firmly fix the chair backrest after the adjustment. 
     Referring to FIGS.  6 ˜ 9 , a conventional adjustment device of a chair backrest includes a fixed member  51 , a movable member  52 , a fixing member  53  and an elastic member  54 . The fixed member  51  is secured to the bottom of the seat of a chair by means of screws passing through holes  511  thereof, and has two opposing lateral parts, which each has a through hole  512  and a curved slot  513 . 
     The movable member  52  also has two opposing lateral parts  521 , which each has a through hole  522 , a connecting hole  524  and a through hole  525 . The movable member  52  further has an insertion hole  523 , through which a supporting rod of a backrest  58  is passed. 
     The movable member  52  is received in, and pivotably connected to, the fixed member  51  with a rod  56  passing through the through holes  522  as well as the through holes  512 . 
     The elastic member  54  is disposed between the lateral parts  521  of the movable member  52 , and has an upper end portion, a middle connecting portion, and lower end hooked portions. The rod  56  is passed through the middle portion of the elastic member  54  such that the upper end portion of same abuts the lower side of the fixed member  51 . A rod  57  is passed into the connecting holes  524  of the movable member  52  and engage the lower end hooked portion of the elastic member  54  such that the rear end of the movable member  52  is biased up by the elastic member  54 . 
     The fixing member  53  is connected to a first one of the through holes  525  by means of a bolt  531  passing through the first through hole  525 , and the corresponding curved slot  513 . 
     Thus, the fixing member  53  can be burned between a loose position for allowing the movable member  52  to be adjusted in respect of the orientation in relation to the fixed member  51 , and a tight position for fixing the movable member  52  to the fixed member  51 . 
     U.S. Pat. Nos. 1,932,618 GABB, 1,263,162 TRAVERS, 2,272,980 MCLELLAN ETAT, 3,709,525 POTHERMEL, 6,220,664 LEE, ITALIAN Patent No. 672,811 NIENBURGER, BRITISH Patent No. 857,525 THOMPSON, and SWEDISH Patent No. 127,140 GABB also have adjustment devices of the same feature, i.e. the curved slots for allowing the movable member to move relative to the fixed member. 
     However, the above mentioned adjustment structure is found to have a drawback that the fixing member  53  can&#39;t firmly fix the movable member  52  after the adjustment because the lateral parts of the fixed member  51  are flat and smooth, and is likely to move relative to the fixing member  53 , especially when a person is sitting onto the chair. Consequently, the orientation of the chair backrest in relation to the seat after adjustment is unwantedly changed. 
     SUMMARY OF THE INVENTION 
     Therefore, it is a main object of the present invention to provide an adjustment device for a chair backrest such that the backrest can be firmly fixed in position after adjustment, without possibility of unwanted change of orientation in relation to the seat. 
     The adjustment device of the present invention includes a fixed member, a movable member, an elastic member, and a fixing member, which takes the form of a spanner. 
     The fixed member is fixed to the bottom of the seat. The movable member is pivoted to the fixed member. The backrest is connected to the rear end of the movable member. The fixing spanner is connected to an outer end of a bolt passing through both a lateral curved slot of the fixed member and a hole of the movable member from a connecting end portion thereof so as to be turnable between an unlocking position for allowing adjustment of the backrest and a locking position for fixing the movable member in position after the adjustment. The elastic member biases the rear end of the movable member upwards. 
     The fixed member further has a curved bump enclosing the curved slot; the bump has a lateral tapering side with an upper portion bigger than a lower portion thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood by reference to the accompanying drawings, wherein: 
     FIG. 1 is an exploded perspective view of the adjustment device of the present invention. 
     FIG. 2 is a cross-sectional view of the adjustment device of the present invention. 
     FIG. 3 is another cross-sectional view of the adjustment device of the present invention. 
     FIG. 4 is a third cross-sectional view of the adjustment device of the present invention. 
     FIG. 5 is a view showing the operation of the adjustment device of the present invention. 
     FIG. 6 is a perspective view of the conventional adjustment device of the present invention. 
     FIG. 7 is a cross-sectional view of the conventional adjustment device of the present invention. 
     FIG. 8 is another cross-sectional view of the conventional adjustment device of the present invention. 
     FIG. 9 is a view showing the operation of the conventional adjustment device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS.  1 ˜ 4 , an adjustment device of a chair backrest of the present invention includes a fixed member  1 , a movable member  2  an elastic member  3  and a fixing member  4 . 
     The fixing member  1  has a horizontal part, and two opposing lateral parts; the horizontal part has through holes  11  thereon, and is fixedly fitted to the bottom of a seat  111  of a chair by means of screws passing through the holes  11 . The lateral parts have opposing through holes  12 , and opposing curved slots  14  and  15  at the rear end portion; a first one of the curved slots  14  is enclosed by a curved bump. The curved bump enclosing the curved slot  14  is shaped such that the upper portion thereof is bigger than the lower portion, i.e. the curved bump tapers off toward the lower portion, as shown in FIG.  2 . 
     The movable member  2  has two opposing lateral parts, which have first opposing holes  21 , opposing connecting holes  22 , and third opposing holes  23  and  24 . A first one of the lateral parts of the movable member  2  has a fourth hole  27 , while the other lateral part has a holding hole  28  facing the fourth hole  27 . The hole  23  is enclosed by a circular bump, having an upper portion which is bigger than the lower portion, i.e. the circular bump tapers off toward the lower portion. The movable member  2  is substantially received in, and pivoted to, the fixed member  1 ; a pivotal rod  13  is passed through a middle portion of the elastic member  3 , and the first holes  21  as well as the through holes  12  of the fixed member  1  such that an upper end portion of the elastic member  3  abuts the bottom of the horizontal part of the fixed member  1 . A connecting rod  221  is passed into the connecting holes  22  of the movable member  2 , and engage lower end hooked portions of the elastic member  3  such that the rear end of the movable member  2  is biased upwards by the elastic member  3 . 
     The fixing member  4  can take the form of a spanner, and has a lower end connecting portion  40 . A bolt  41  is passed through the hole  23  of the movable member  2 , the curved slot  14  enclosed by the curved bump, and screwed into a nut  42  disposed adjacent to the curved bump. The connecting portion of the fixing member  4  is connected to the nut  42  such that it can be turned between an unlocking loose position for allowing adjustment of the orientation of the movable member  2  in relation to the fixed member  1 , and a tight locking position after the adjustment is performed. A covering part  43  is screwed onto the outer end of the bolt  41  to prevent the fixing member  4  from falling out. Another shaft  44  is passed through the hole  24  and the curved slot  15 . 
     The backrest  25  of the chair has a supporting rod  251 , which is passed through the insertion hole  26  of the movable member  2 . A bolt  252  is passed through the fourth hole  27 , the holding hole  28  of the movable member  2 , and a fixing block  254 , and screwed into a tube portion of a knob  253 ; the fixing block  254  is disposed between the lateral parts of the movable member  2  to contact the supporting rod  251  of the backrest  25 . Thus, the knob  253  can be turned loose for allowing the backrest to be adjusted in respect of the height. 
     When the fixing member  4  is turned to the tight position after adjustment of the position of the movable member  2 , the connecting portion  40  thereof will come into contact with the curved bump of the curved slot  14 . 
     From the above description, it can be easily understood that the adjustment device of a chair backrest of the present invention has an advantage that the circular bump, having bigger height at the upper portion, can move slightly down relative to the fixed member  1  when a person is sitting on the chair, thus engaging the same further so as to help the movable member  2  firmly fixed in position after adjustment.