Abstract:
A conveyor belt tensioner is provided for a conveyor system in which a belt is trained about first and second end rollers that are suspended for rotation between opposed side frames. A motor is provided for moving the belt with respect to the side frames. A third roller that engages the belt is provided that is mounted between the side frames for incremental movement for tensioning the belt.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/642,204, filed Jan. 7, 2005. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a belt conveyor and, more particularly, to a belt tensioning or take up assembly for use in a belt conveyor. 
   In belt conveyors, in order to maintain consistent and accurate speed for the conveyor belt, it is necessary to properly tension the belt to insure that there is no slippage of the belts with respect to its drive rollers. The normal way of tensioning a belt is to wrap the belt around a moveable pulley, the pulley being moved to tension the belt by counter weights, air cylinder pressure, or a threaded shaft that is turned to move the pulley along a track. A problem with the conventional threaded shaft design is that measurements must taken both prior to and after moving the pulley to make sure that the pulley is moved the same amount with respect to both side frame members so that belt tracking is maintained. Thus, it is an object of the present invention to provide a tensioning mechanism for a belt conveyor that is easy to adjust and maintains proper tracking of the conveyor belt. 
   SUMMARY OF THE INVENTION 
   A conveyor belt tensioner that meets this object, as well as other objects which will become apparent upon reference to the following detailed description and accompanying drawings, is provided by a conveyor system in which a belt is trained about first and second end rollers that are suspended for rotation between opposed side frames. A motor is provided for moving the belt with respect to the side frames. A third roller that engages the belt is provided that is mounted between the side frames for incremental movement for tensioning the belt. 
   In keeping with one aspect of the invention, each side frame includes an elongated longitudinal slot having a plurality of seats spaced apart in discrete increments. The third roller comprises an axle with opposed ends with a spacer associated with each end of the axle and secured thereto so as to be interior of the side frames. A pair of spaced-apart shafts are secured to each spacer, the shafts extending through the side frames so as to be received in the seats. 
   In keeping with another aspect of the invention, the conveyor system further comprises a stop for limiting the vertical movement of the third roller when the shafts on the spacers are received in the U-shaped seats of the side frame. In the disclosed embodiment, the stop comprises a bumper especially co-extensive in length with the seats in the slots on the side frames. The bumper is disposed on the frame vertically above the slot so that an eccentrically-shaped plate that is received on the shafts of each spacer has an outer surface that is in close proximity with the bumper when the shafts are received in the seats. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a conveyor belt tensioner according to the present invention. 
       FIG. 2  is a top view of the conveyor belt tensioner of  FIG. 1 , with the belt and conveyor rollers removed to show detail. 
       FIG. 3  is an end view of the conveyor belt tensioner of  FIG. 1 . 
       FIG. 4  is enlarged fragmentary end view taken from  FIG. 3 . 
       FIG. 5  is a cross sectional view taken along lines  5 - 5  of  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to the accompanying drawings, a preferred embodiment of a tensioning mechanism is shown that insures substantially uniform movement of the tensioning roller so that tracking of the conveyor belt is maintained. To this end, a tensioning roller  10  is mounted for rotation between opposed side frame members  12  for tensioning conveyor belt  13 . As best seen in  FIGS. 2 and 5 , the side frames  12  each have matching cutouts  14  therein that define a track having a plurality of teeth  16 , with seats  18  defined between adjacent teeth  16 . The tensioning roller  10  includes a stationary axle  20  the opposite ends of which are mounted to a spacer  22  interior of the opposed side frame members  12 , best seen in  FIG. 4 . The spacer  22 , in turn, includes a pair of spaced-apart stub axles  24  secured thereto by, e.g., welding. The stub axles  24  extend from the spacer  22  through the cutouts  14  in the side frame members  12  and are spaced-apart so that they rest in adjacent seats  18  in the track. The stub axles  24  carry bushings (not shown) that facilitate the locating of the stub axles  24  in the seats  18  in the track. Movement of the tensioning roller  10  along the track to adjust the tension on the belt is effected by simultaneously pivoting the spacers  22  about one of the stub axles  24  so that the other of the stub axles  24  is moved into the next adjacent seat  18  in the track. 
   To effect the pivoting of the spacer  22  about one or the other of the stub axles  24 , a plate  26  is mounted on the stub axles  24  by, e.g., hex nuts  27 , so as to be on the exterior of the side frame  12 , as best seen in  FIGS. 4 and 5 . The plate  26  includes an aperture  28  between the stub axles  24  for receipt of a tool that serves as a lever for pivoting the spacer  22 . Preferably, the aperture comprises a ⅜ in. square hole so that a standard ⅜ in. ratchet handle can be used for the lever. However, other structures for receipt of a pivoting lever may be employed without departing from the scope of the invention. For example, the plate  26  may include a stud extending therefrom, rather then an aperture, the stud being engageable by a socket wrench. 
   In another aspect of the present invention, the plate  26  has an eccentric shape (as shown, a generally oblong shape) and the side frame has a stop member  30  that extends along substantially the length of the track  14  that lies in close proximity to the edge of the plate  26  when the stub axles  24  are located in the seats of the track. The stop  30  is preferably made of a UHMW plastic and is bolted to the side frame member  12 . The stop  30  limits the vertical movement of the tensioning roller  10  when the stub axles  24  are seated, while still allowing pivoting the tensioning roller  10  about one or other of the stub axles  24  to adjust the tension. The oblong shape of the plate  26  insures that with each 180° of rotation of the plate  26 , the edge of the plate  26  is in close proximity to the stop  30 . 
   In another aspect of the invention, a pin  32  is provided for locking the plate  26  relative to the side frame members  12 . To this end, the plate  26  has an aperture  34  adjacent each end for receipt of the pin  32  adjacent the edge of the plate  26  and along the major axis of the oblong. This aperture  34  in the plate  26  aligns with a corresponding aperture  36  in the side frame  12  when the stub axles  24  are received in the seats  18  in the track. The pin is received in the aligned holes  34 ,  36 , thus preventing any unintended movement of the tensioning roller  10 . 
   As best seen in  FIG. 4 , the spacer  22  is typically spaced away from the side frame  12  and includes an extension member  38  mounted on its face of a low friction material. The extension  38  limits the axial movement of the spacer with respect to the side frame  12  and, because it is of low friction material, does not impede pivoting of the stub axles  24  with respect to one another when adjusting the tension. 
   Thus, a conveyor belt tensioner has been provided that meets the objects of the present invention. While the invention has been described in terms of a preferred embodiment, there is not intent to limit it to the same. Instead, the invention is to be defined by the scope of the following claims.