Abstract:
An adjustment device includes a seat brace including lower and upper support plates fixed thereon, respectively. A back brace includes a second end tightly disposed between the lower and upper support plates of the seat brace, with friction generated between the lower and upper support plates and the second end of the back brace, respectively. A locating portion is defined on the second end of the back brace. An adjustment unit includes an end pivotally connected to the seat brace and another end opposite to the actuated element and exposed outside of the adjustment device for use. An actuated element is mounted on the adjustment unit relative to the locating portion and connected to the locating portion.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an adjustment means for a backrest. In particular, the adjustment means can be operated with a single hand and reduces harm to users during adjustment of positions of the backrest. 
   2. Description of the Related Art 
   Referring to U.S. Pat. No. 7,264,312, a conventional chair includes a backrest adjusting mechanism for changing the distance and height of a backrest relative to a seat of a chair at the same time. However, while a user is sitting on the chair and wants to adjust the position of the backrest relative to the seat, he or she has to operate a L-shaped locating gear with his or her hand and push the backrest with his or her back simultaneously. Hence, adjustment of the position of the backrest relative to the seat of said chair with a user&#39;s single-hand is unachievable. 
   The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art. 
   SUMMARY OF THE INVENTION 
   Accordingly, the objective is achieved by providing an adjustment means for an office chair that includes a seat brace, a back brace installed to the seat brace and an adjustment unit disposed between the seat and back braces. The seat brace includes lower and upper support plates. The back brace includes a second end tightly disposed between the lower and upper support plates of the seat brace to prevent free movement of the second end between the lower and upper support plates. Users operate the adjustment unit to drive the back brace to move with respect to the seat brace. 
   The primary advantage of the adjustment means according to the present invention is that users can operate the adjustment means with a single hand and without utilizing further outside force to pull or push the back of chair for adjusting the back of chair frontward or rearward with respect to the seat of chair. 
   Other objectives, advantages, and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure and the technical means adopted by the present invention to achieve the above and other objectives can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein 
       FIG. 1  is a perspective view of an adjustment means for a backrest according to the present invention. 
       FIG. 2  is an exploded view of the adjustment means shown in  FIG. 1 . 
       FIG. 3  is a cross-sectional view taken along line  3 - 3  in  FIG. 1 . 
       FIG. 4  is another cross-sectional view of the adjustment means shown in  FIG. 1 , illustrating operating the adjustment means to move the back brace along the limited slot of the seat brace. 
       FIG. 5  is a perspective view of the adjustment means that is shown in  FIG. 1  installed to the seat and the back of an office chair. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, an adjustment means for a backrest in accordance with the preferred embodiment in the present invention includes a seat brace  10 , a back brace  20  installed to the seat brace  10  and an adjustment unit  30  disposed between the seat and back braces  10  and  20 . The back brace  20  can be driven via operation of the adjustment unit  30 , and then, moves with respect to the seat brace  10 . 
   Particularly referring to  FIG. 5 , the seat brace  10 , which is provided on the bottom of a seat  91  of an office chair (not numbered) and adjoins a back  92  of the office chair, includes two lateral walls  11 , a lower support plate  12  and an upper support plate  13 . The lateral walls  11  are parallel to each other, and a space (not numbered) is defined therebetween. The lower support plate  12  is connected to the bottom of the lateral walls  11  respectively and below the space. The upper support plate  13  is connected to the inner side of the lateral walls  11  respectively and provided in the space. An upper surface  121  and a lower surface  131  are defined on the lower and upper support plates  12  and  13 , respectively, and parallel to and spaced from each other. At least one cushion blocks  14  are disposed between the lower and upper support plates  12  and  13  and allow maintaining the distance from the lower support plate  12  to the upper support plate  13 . 
   A top plate  101  is provided on the top edge of the lateral walls  11  respectively and above the space. In this embodiment, the top plate  101  is parallel to the bottom of the seat  91 . The upper surface  121  of the lower support plate  12  is angled at 25-35 degrees to the top plate  101 , and equally the lower surface  131  of the upper support plate  13  is angled at 25-35 degrees to the top plate  101 . A limited slot  122  is defined on the lower support plate  12  longitudinally. 
   The upper support plate  13  is preferably in a form of a U-shaped plate and includes a yawn  132 . Two projections  133  are formed on two sides of the upper support plate  13  and extend toward the inside of the yawn  132 , respectively. 
   The back brace  20  is approximately L-shaped and includes a first end  21  and a second end  22  bent to the first end  21 . The first end  21  is adapted for assembly with the seat  92  (as shown in  FIG. 5 ). The second end  22  is installed between the lower and upper support plates  12  and  13  of the seat brace  10  for tight assembly of the seat and back braces  10  and  20 . A top side  221  and a bottom side  222  are defined on the second end  22  and are parallel to each other. A thickness of the second end  22  is equal to the distance between the top and bottom sides  221  and  222  and also equal to the distance between the upper and lower surfaces  121  and  131 . Accordingly, it will increase face friction between the lower and upper support plates  12 ,  13  and the second end  22 , respectively, and prevent unexpected movement of the second end  22  between the lower and upper support plates  12 ,  13 . Therefore, the back  92  and the back brace  20  will not freely slide on the seat brace  10  without operation of the adjustment unit  30 . 
   A coupled hole  223  is formed on the second end  22  and adapted to couple with a coupled element  224 . The coupled element  224  extends through the limited slot  122  of the lower support plate  12  and, then, is coupled to the coupled hole  223  for restricting movement of the back brace  20 . In this embodiment, the coupled element  224  has threads. A locating portion  225  is formed on the top side  221  of the second end  22  and longitudinally extends from the edge of the second end  22  toward the first end  21 . 
   The adjustment unit  30  is pivotally installed to the lateral walls  11  of the seat brace  10 . Two through holes  111  are defined on the lateral walls  11  respectively. An end of the adjustment unit  30  inserts through the through holes  111  respectively, and another end of the adjustment unit  30  is exposed outside for users to operate. 
   An actuated element  31  includes an engaged end  311  formed on an end thereof and a connected end  312  opposite to the engaged end  311 . A first through-hole  313  longitudinally penetrates the actuated element  31 , and two openings of the first through-hole  313  are respectively formed on the engaged and connected ends  311 ,  312 . The first through-hole  313  is adapted for inserting the end of adjustment unit  30  therethrough. A second through-hole  314  axially penetrates the connected end  312  and is perpendicular to the first through-hole  313 . A pin  315  is inserted through the second through-hole  314  and a hole  301  that is defined on the end of the adjustment unit  30  for fixing the actuated element  31  to the adjustment unit  30 . Furthermore, the actuated element  31  is disposed in the space of the seat brace  10  and inserted through the yawn  132  of the upper support plate  13  so that the engaged end  311  can cooperate with the locating portion  225  of the second end  22 . When a user turns the adjustment unit  30 , the second end  22  of the back brace  20  is driven to move between the lower and upper support plates  12  and  13  with respect to the seat brace  10  so that the position of the back  92  of the office chair will be adjusted to a desired position. Additionally, when the back brace  20  is driven to move by operation of the adjustment unit  30 , movement of the back brace  20  can be upward and rearward simultaneously or downward and frontward simultaneously. The cause of the above-mentioned is the inclined angle between the second end  22  of the back brace  20  and the top plate  101  of the seat brace  10 . 
   The engaged end  311  of the actuated element  31  is preferably in a form of a gear, and the locating portion  225  of the second end  22  is preferably in a form of a row of teeth and engaged with the engaged end  311  of the actuated element  31  so that the second end  22  of the back brace  20  is driven to move with respect to the seat brace  10 . A turning handgrip  32  is installed to another end of the adjustment unit  30  opposite to the actuated element  31  for an easy grip by users. The turning handgrip  32  has an outer diameter which is larger than that of the actuated element  31  as to save effect in operation. 
   Referring to  FIGS. 3 and 4 , when users turn the turning handgrip  32  to overcome friction between the lower and upper support plates  12 ,  13  and the second end  22 , respectively, the engaged end  311  of the actuated element  31  is operated to drive the locating portion  225  of the second end  22  for movement of the second end  22  between the lower and upper support plates  12 ,  13 . Therefore, users can adjust the back brace  20  frontward or rearward with respect to the seat brace  10  with a single hand. 
   Furthermore, when the adjustment unit  30  is turned in operation, the back brace  20  is driven to move simultaneously. Accordingly, when the adjustment unit  30  is stopped turning, the back brace  20  will be stopped to a desired position. Therefore, users do not need to further push or pull the back  92  of the office chair using the back or another hand of the user or the like.