Abstract:
A chair elbow capable of rotating with double shaft is disclosed. Two bearings are disposed on a mount board fixed on a chair. Each of the bearings connects one end of each of two rotating plates, while the other ends thereof are pivotally connected in a linear slot of a seat plate used for securing an armrest. The length of the slot is longer than the distance between the two bearings, and the latter is longer than the length of the rotating plates. Thus, the armrest on the seat plate can rotate against the mount board with 360 degrees and move forward and backward.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The invention generally relates to chairs, particularly to elbows of chairs. 
         [0003]    2. Related Art 
         [0004]    General chairs are usually equipped with fixed elbows whose height and position can not be adjusted for matching various users. Latterly, chairs with rotary elbows appear in the market. The rotary elbows allow horizontal rotation for satisfying various requirements of users. Such an elbow can provide better support to users to avoid aches and pains of hands and ill posture of bodies. However, because conventional rotary elbows adopt a single rotating shaft, the elongated elbows rotating around a single bearing can not maintain a stably planar rotation, and the bearing is easily damaged by unbalanced pressure. 
       SUMMARY OF THE INVENTION 
       [0005]    An object of the invention is to provide a rotary elbow with double shaft, which can stably support an armrest to rotate and enhance fixation strength of the armrest to avoid damage resulting from unbalanced pressure. 
         [0006]    To accomplish the above object, the invention disposes two bearings on a mount board fixed on a chair. Each of the bearings connects one end of each of two rotating plates, while the other ends thereof are pivotally connected in a linear slot of a seat plate used for securing an armrest. The length of the slot is longer than the distance between the two bearings, and the latter is longer than the length of the rotating plates. Thus, the armrest on the seat plate can rotate against the mount board with 360 degree and move forward and backward. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective exploded view of the invention; 
           [0008]      FIG. 2  is a perspective assembled view of the invention; 
           [0009]      FIG. 3  shows the rotation of the armrest; 
           [0010]      FIG. 4  shows the forward and backward move of the armrest; 
           [0011]      FIG. 5  shows the deflective move of the armrest; 
           [0012]      FIG. 6  is an exploded view of the positionable bearing; 
           [0013]      FIG. 7  is a sectional view of the positionable bearing in a positioned status; and 
           [0014]      FIG. 8  is a sectional view of the positionable bearing in a rotating status. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  is an exploded perspective view of the invention. Two bearings  2  are disposed on an elongated mount board  1 . The two bearings  2  are provided with two pivot seats  231 ,  213  axially aligning with each other (please further refer to  FIG. 6 ). The mount board  1  is fixed on a chair for supporting an armrest  5 . Each of the bearings  2  is embedded in a mounting hole  11  of the mount board  1  with one pivot seat  213  thereof, while the other pivot seat  231  is embedded in a connecting hole  31  in one end of an elongated rotating plate  3 . A fastening rod  24  penetrates the mounting hole  11 , bearing  2  and connecting hole  31  for pivotally connecting the rotating plate  3  with the mount board  1 . Thus the rotating plates  3  can separately rotate on the mount board  1  by means of the bearings  2 . And the length of the rotating plate  3  is shorter than the distance of the two bearings  2  thereby the rotating plates  3  can freely rotate not to be blocked by the bearings  2 . 
         [0016]    The other end of the rotating plate is provided with a pivot hole  32 . A seat board  4  having a linear slot  41  is used for fixing an armrest. Two pivot shafts  42  separately penetrate the slot  41  and pivot holes  32  to form a pivotal connection. The length of the slot  41  is longer than the distance of the two bearings  2 , thereby the seat board  4  can linearly move forward and backward under orientation of the pivot shafts  42  and slot  41 . 
         [0017]      FIG. 2  shows an assembled status of the invention. As can be seen in this figure, the mount board  1  is mounted on an elbow  6  and an armrest  5  is mounted on the seat board  4 . Thus, the armrest  5  can rotate by means of the bearings  2  and move forward and backward by means of the slot  41  and pivot shafts  42  as shown in  FIGS. 3 and 4 . When the two rotating plates  3  are parallel, the armrest  5  also can maintain a direction parallel to the mount board  1 . However, the armrest  5  can be deflected by asymmetrically rotating the two rotating plates  3 , i.e., the rotating plates  3  are not parallel as shown in  FIG. 5 . Thus, the armrest  5  can be both radially 360-degree rotated and linearly move forward and backward. And the double shaft structure further provides firm support. 
         [0018]    Preferredly, the bearings  2  are positionable ball bearings with a multiple positioning function. As can be seen in  FIG. 6 , the positionable ball bearing  2  is composed of a round seat  21 , a flexible depressor  22  and a cap  23 . The round seat  21  is provided with a plurality of rolling balls  211 . The rolling balls  211  are disposed in an annular arrangement with an identical pitch. The rolling balls  211  are rotarily disposed on the round seat  21  with exposure of about one second of volume. A first shaft base  213  is protrudent from a center of the round seat  21 . The first shaft base  213 , whose outline may be a cuboid or many-sided body, has a first shaft hole  212  therein. The flexible depressor  22  is a round disk. And a through hole  222  is provided at its center. The flexible depressor  22  is provided with circular holes  221  corresponding to the rolling balls  211 . The circular holes are the same as or an integer multiple of the rolling balls  211  in number. As can be seen in  FIG. 6 , the quantity of the circular holes  221  is two times of the rolling balls  211  for forming more compact positioning points. That is to say, the pitch of any two adjacent positioning points is one second of that of the rolling balls  211 . The pitch of any two adjacent positioning points is just the same as that of the rolling balls  211  if the circular holes  221  are the same as the rolling balls  211  in number. Besides, the inner diameter of the circular hole  221  is slightly smaller than the outer diameter of the rolling ball  211  so that the rolling balls can be embedded in the circular holes  221  to make positioned. 
         [0019]    The flexible depressor  22  is disposed on the rolling balls  211  to press them. The cap  23  covers the round seat  21  to accommodate the flexible depressor  22  therein. A second shaft base  231 , whose outline may be a cuboid or many-sided body, is disposed at the center of the cap  23  and extends inwards and outwards. The inward part of the second shaft base  231  penetrates into the through hole  222  of the flexible depressor  22  to secure the flexible depressor  22 . The cap  23  and flexible  22  can be integrated because of the non-round shape of the second shaft base  231 . The second shaft base  231  is provided with a second shaft hole  232  therein. The first shaft hole  212 , through hole  222  and second shaft hole  232  directly communicate with each other to be penetrated by a fastening rod  24 . Bending edges  223  extend from margins of the through hole  222  of the flexible depressor  22  to lean against the cap  23  for supporting the deformed flexible depressor  22 . 
         [0020]      FIG. 7  is a cross-sectional view of the ball bearing  2  in the positioned status. The flexible depressor  22  presses the round seat  21 . A positioned status is made once the rolling balls are embedded into the circular holes  221 . When the cap  23  is forced to rotate with the flexible depressor  22  against the round seat  21 , as shown in  FIG. 8 , the rolling balls  211  diverge from the circular holes to rotate. And the flexible depressor  22  is deformed by being leaned by the rolling balls  211  (the central portion of the flexible depressor  22  is leaned by the bending edges  223  so it is not deformed). At this time, though the rolling balls  211  are pressed by the flexible depressor  22 , they still can rotate. This makes the flexible depressor  22  also can rotate smoothly. When the rolling balls  211  move to the position of the circular holes  221  again, they will be automatically embedded into the circular holes  221  to make another positioned status by means of pressure from the flexible depressor  22 . Meanwhile the flexible depressor  22  restores its original shape. 
         [0021]    By employing the above positionable ball bearing, the armrest  5  can be automatically positioned at several positions. Thus the armrest  5  can maintain a specific position without arbitrarily rotation. It is much more convenient than before. 
         [0022]    It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.