Abstract:
An exhibiting rack for loading a billboard or bulletin board is disclosed. The rack includes a fixed frame and a movable frame. The movable frame is mounted by a board to be exhibited and linearly slidable against the fixed frame. The movable frame is disposed on the fixed frame and an extension stem is disposed therebetween. A fixed end and action end of the extension stem are connected to the fixed frame and movable frame, respectively. The extension stem exerts a force on the movable frame to support the movable frame with a board to a desired height.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to racks for loading billboards or bulletin boards, particular to racks capable of adjusting height of such boards. 
     2. Related Art 
     Usually, those large boards such as black boards or white boards used in classroom or exhibition are fastened on a wall because of cumbersomeness. If those boards placed in a classroom or exhibition cannot be adjusted in height, the information on the boards will not be clearly seen by the audience. Further, the weight of those large boards may exceed 100 kg, the supports of them must be difficult in structure. 
     SUMMARY OF THE INVENTION 
     A primary object of the invention is to provide an exhibiting rack which can support large boards and can be adjusted in height. 
     Another object of the invention is to provide an exhibiting rack which can stably and slowly move the loaded board to avoid accident. 
     Still another object of the invention is to provide an exhibiting rack which has a puller spring for stabilizing the moving action. And the elasticity of the puller spring can be adjusted for matching various boards with different weight. 
     To accomplish the above object, the exhibiting rack of the invention includes a fixed frame and a movable frame. The movable frame is mounted by a board to be exhibited and linearly slidable against the fixed frame. The movable frame is disposed on the fixed frame and an extension stem is disposed therebetween. A fixed end and action end of the extension stem are connected to the fixed frame and movable frame, respectively. The extension stem exerts a force on the movable frame to support the movable frame with a board to a desired height. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the invention; 
         FIG. 2  is an exploded view of the invention; 
         FIG. 3  is an assembled view of the invention in which the movable frame is in a low position; 
         FIG. 4  is an assembled view of the invention in which the movable frame is in a high position; 
         FIGS. 5 and 6  show the adjustment of the puller spring; 
         FIG. 7  is a schematic view showing the invention mounted on a wheeled stand; 
         FIG. 8  is a schematic view of the invention with an auxiliary arm; and 
         FIG. 9  is an explode view of the auxiliary arm. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIGS. 1-4 . The exhibiting rack includes a fixed frame  1  and a movable frame  2 . The fixed frame  1  is used to fix at a predetermined position, and the movable frame  2  is used to load an exhibiting board  3  and is slidable against the fixed frame  1 . 
     The fixed frame  1  includes a frame body  10  and a pair of rails  11  mounted thereon. 
     The movable frame  2  is assembled on the fixed frame  1  and includes a main frame  20  and a framework  21  for loading the exhibiting board  3 . The main frame  20  is provided with a plurality of sliders  22  penetrating into the rails  11 . The movable frame  2  can be moved by the sliders  22  sliding on the rails  11 . The framework  21  is provided with two holding members  23  for holding the exhibiting board  3 . Besides, a handle  24  is disposed on the movable frame  2  for assisting operation of the movable frame  2 . 
     The holding member  23  includes a mount plate  230 , a clamper  231  on the mount plate  230  and a nut  232  for fastening the clamper  231 . The mount plate  230  is provided with a sliding hole  233 . The bottom of the clamper  231  is formed with a positioning rod  234  penetrating the sliding hole  233 . The positioning rod  234  can linearly move in the sliding hole  233  so as to adjust the position of the clamper  231 . And the positioning rod  234  can be screwed by the nut  232  to fasten the clamper  231 . By adjusting the position of the clamper  231 , various exhibiting boards  3  with different thickness can be clamped. Preferably, a clamper  231  may be provided with two positioning rods  234 ,  234   a  penetrating the sliding hole  233 . The clamper  231  can be unrotatably fixed by the two fastening points. 
     An extension stem  4  with braking ability is disposed between the movable frame  2  and the fixed frame  1 . The extension stem  4  may be a gas spring composed of a cylinder  40  and an action rod  41 . The action rod  41  can be axially moved by the air pressure in the cylinder  40 . The extension stem  4  has a fixed end  410  fastened on the frame body  10  of the fixed frame  1  and an action end  400  connecting the movable frame  2 . The extension stem  4  may exert a force on the movable frame  2  to shift the movable frame  2  along the rails  11 . 
     A switch  411  for triggering the extension stem  4  is disposed near the fixed end  410  of the extension stem  4 . The switch  411  is controlled by a cord  412 . A distal end of the cord  412  connects to a driver  413  on the movable frame  2 . When the driver  413  is stirred, the cord  412  will be pulled to trigger the switch  411  and the extension stem  4  will be activated by the switch  411 . As abovementioned, the extension stem  4  may be a gas spring, if the action rod  41  serves as the fixed end  410 , then the cylinder  40  serves as the action end  400 . When the gas spring is activated, the action end  400  will protrude outwards to drive the movable frame  2 . 
     Preferably, the action end  400  of the extension stem  4  connects a guiding rod  42  whose distal end is a free end and provided with a sliding member  43 . The sliding member  43  may be a wheel and associates with the movable frame  2 . The guiding rod  42  is formed with a bend  421 . The bend  421  is pivotally connected to the frame body  10  by a shaft  44 . The length between the action end  400  of the extension stem  4  and the bend  421  is smaller than the length between the bend  421  and the sliding member  43 . Thus the guiding rod  42  functions as a lever and the shaft  44  serves as a fulcrum. Further, an end of a spring  45  is fixed at a section of the guiding rod  42  between the bend  421  and sliding member  421 , and the other end is fixed at the frame body  10  for providing a buffer force when the guiding rod  42  is acting. 
     The main frame  20  of the movable frame  2  is provided with a slideway  25  for accommodating the sliding member  43  so as to have the sliding member only move in the slideway  25 . 
     Please refer to  FIGS. 3 and 4 .  FIG. 3  illustrates the movable frame  2  at a lower position. When the extension stem  4  is activated, its action end  400  pushes the guiding rod  42  to turn about the shaft  44 . The free end of the guiding rod  42  is limited and slid in the slideway  25 , so that the guiding rod  42  generates a force pushing up the movable frame  2  as shown in  FIG. 4 . When the movable frame  2  reaches a desired position, a user may release the driver  413  to stop the extension stem  4  and thus the movable frame  2  is fixed instantly. That is, the extension stem  4  associating with the guiding rod  42  pushes the movable frame  2  to form a height variation. It should be noted that the guiding rod  42  pushes up the movable frame  2  by a horizontal motion. Thus the shift of the moveable frame  2  is slow and stable. It can avoid accidents resulting from quick shift if the loaded board is very heavy. When a user wants to lower the movable frame  2 , all he or she needs to do is to stir the driver  413  to release the extension stem  4  and to slightly exert a downward force on the handle  24 , then the board  3  will lower by its weight. Once the movable frame  2  is lowered to the desired position, the user re-stirs the driver  413  to brake the extension stem  4 , then the movable frame  2  is fixed instantly. At this time, the sliding member  43  goes back to the initial position as shown in  FIG. 3 . Additionally, the spring  45  is stretched to form a buffer resistance. This can slow down the lowering of the movable frame  2  for safety. 
     Besides, two puller springs  5  are disposed between the fixed frame  1  and the movable frame  2  for dragging each other. In detail, one end of each the puller spring  5  is fastened on the fixed frame  1  and the other end thereof is fastened on the movable frame  2 . The puller springs  5  can stabilize the connection between the movable frame  2  and fixed frame  1 . The puller springs  5  provides an auxiliary force to the movable frame  2  when rising and a buffer resistance to it when lowering. 
     Please refer to  FIGS. 5 and 6 . In order to accurately control the puller springs  5 , a screw rod  26  is disposed on the movable frame  2 . One end of the puller spring  5  is preferably fastened to a bracket  260  which is screwed on the screw rod  26  and may be axially moved by rotating the screw rod  26 . By the axial movement of the bracket  260 , the elasticity of the puller springs  5  can be adjusted for matching various boards  3  with different weight. More preferably, a scale  27  may be arranged on the movable frame  2  near the screw rod  26  for a reference of adjusting the puller springs  5 . 
     Please refer to  FIG. 7 . In order to have the exhibiting rack moved easily, the fixed frame  1  is mounted on a wheeled stand  6 . The wheeled stand  6  has a stand body  61  and a support frame  60  on which the fixed frame  1  is mounted. A plurality of wheels  62  are disposed on the bottom of the stand body  61 . The support frame  60  is further provided with a cover board  63  for cloaking and protecting the dynamic components of the movable frame  2 . 
     Please refer to  FIG. 8 . The movable frame  2  may be preferably provided with an auxiliary arm  7  including a support body  70  mounted on the movable frame  2  and a rotatable rod  71  pivotally connected on the support body  70 . As shown in  FIG. 9 , the support body  70  has a fixed portion  701 , an extensible portion  702  and a thumbscrew  703 . The fixed portion  701  is mounted on the movable frame  2 . The extensible portion  702  slidably penetrates into the fixed portion  702 . The fixed portion  701  is provided with a through hole  704  and the extensible portion  702  is provided with a series of tapped holes  705 . The extensible portion  702  can be adjustably fastened to the fixed portion  701  by inserting the thumbscrew  703  into the through hole to screw in one of the tapped holes  705 . The extensible portion  702  is further provided with a sleeve seat  706  for being penetrated by the rotatable rod  71 . 
     The rotatable rod  71  includes a spindle  710 , a sleeve  711  perpendicularly connecting the spindle  711 , a bar  712  put in the sleeve  711  and a screw  713 . The spindle  710  pivotally penetrates into the sleeve seat  706 . A distal end of the bar  712  is provided with a universal connector  714  for connecting an external device such as a projector. The bar  712  can be adjustably stretched from the sleeve  711  and fixed by the screw  713 . Thus the auxiliary arm  7  can be used to connect a projector for making presentation.