Patent Publication Number: US-2011065540-A1

Title: Belt drive mechanism with belt tensioner

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive mechanism, and particularly to a belt drive mechanism with belt tensioner. 
     2. The Related Art 
     Belt tensioners are generally well known devices that have been used previously in many belt-drive systems. It is conventional practice to use a tensioner to apply a constant belt-tensioning force, which compensates for increases in belt length due to wear and other factors. U.S. Pat. No. 4,473,362, for example, teaches a belt tensioner that has a fixed structure and a pivoted structure eccentrically mounted on the fixed structure by means of a pivot assembly. The pivoted structure has a belt-engaging pulley rotationally mounted thereon. A coil spring surrounds the pivot assembly and has its ends connected between the fixed and pivoted structures so as to bias the pivoted structure in a belt take-up direction. As the pivoted structure moves from a position of minimum belt take-up to a position of maximum belt take-up, the biasing force of the spring decreases gradually. If this varying spring force is over the range of tensioner movement, then the constant belt tension will be maintained by the tensioner. However, such structure of the tensioner in described above is complicated and difficult to manufacture and assemble. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a belt drive mechanism with belt tensioner. The belt drive mechanism with belt tensioner has a driving pulley pivoted to a fixing frame, a driven pulley pivoted to the fixing frame and driven to rotate by the driving pulley with a belt wrapping thereon, and a tensioner. The tensioner has a wheel pivoted to a mounting block of the fixing frame and resting against the running belt, and a cap rotatably covered to a top of the wheel. The cap has a through hole engaged with the mounting block and is capable of moving along a direction substantially perpendicular to a running direction of the belt at a contact position with the wheel. An elastic element is mounted between the mounting block and an inner side of the through hole and compressed by the moved cap to store an elastic force which can be released to bring the wheel to press the running belt away from the mounting block for compensating a tensile force of the running belt. 
     As described above, the wheel is pivoted to the fixing frame. The cap is coupled with the wheel and moves along the direction substantially perpendicular to a running direction of the belt at a contact position with the wheel. The elastic element received in the through hole can release the stored elastic force to bring the wheel to press the belt for compensating the decreasing tensile force of the running belt, which guarantees the steady transmission of the belt drive system. Furthermore, the structure of the tensioner simplifies the manufacture and assembly, and reduces the occupied space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following description thereof, with reference to the attached drawings, in which: 
         FIG. 1  is an exploded, perspective view of a belt drive mechanism with belt tensioner of an embodiment in accordance with the present invention; 
         FIG. 2  is a perspective view of a cap of the belt drive mechanism with belt tensioner shown in  FIG. 1 ; and 
         FIG. 3  is an assembled, perspective view of the belt drive mechanism with belt tensioner shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in greater detail, and first to  FIGS. 1-3 , the embodiment of the invention is embodied in a belt drive mechanism with belt tensioner. The belt drive mechanism with belt tensioner may be applied on a scanning apparatus (not shown) and comprises a driving element  20  mounted to a fixing frame  10  of the scanning apparatus, a convey element  30 , and a tensioner  40 . 
     The fixing frame  10  may be manufactured by a plate and has a pivot  13 , a mounting opening  14  spaced away from the pivot  13  with a predetermined distance, and a circular protruding platform  11 . The platform  11 , the pivot  13  and the mounting opening  14  are located to form a substantially acute triangle shape. A center of a top of the platform  11  has a rectangular mounting block  12 . The mounting block  12  has a cross-section length of an upper portion  122  thereof along a transverse direction which is substantially parallel to a line formed by the pivot  13  and the mounting opening  14 , less than that of a lower portion  121  thereof. The upper portion  122  of the mounting block  12  has a fixing hole  15  for fixing the tensioner  40 . 
     The driving element  20  has a motor  21 , and a rotating shaft  22  projecting outside the motor  21 . The motor  21  is fixed to a bottom side of the fixing frame  10  opposite to the platform  11 . The rotating shaft  22  passes through the mounting opening  14  and projects outside a top side of the fixing frame  10 . 
     The conveying element  30  has a driven pulley  31 , a driving pulley  33  and a belt  32  wrapped around the driven pulley  31  and the driving pulley  33 . The driven pulley  31  is pivoted to the pivot  13 . The driving pulley  33  is fixed to the rotating shaft  22  of the driving element  20  and forced to rotate with the rotating shaft  22 . 
     The tensioner  40  has a wheel  41 , and a cap  42  mounted to a top of the wheel  41 . The wheel  41  has a cylindrical body  411  and a flange  412  extended outwards from a bottom edge of the body  411 . In this embodiment, the bottom edge of the body  411  is extended inwards a distance for increasing contact area between the wheel  41  and the platform  11  when the wheel  41  is mounted to the fixing frame  10 . The cap  42  has cylinder  421  for rotatably inserting into the body  411 , and a stopping plate  424  extended perpendicularly and outwardly from an upper edge of the cylinder  421  to show a ring shape. The stopping plate  424  has an outer border dimension thereof substantially same as that of the flange  412 , for blocking the running belt  32  which rotates the wheel  41 . The cylinder  421  has a rectangular through hole  422  at a middle thereof and passing through a top surface and a bottom surface thereof. The through hole  422  has a cross-section width substantially same as the transverse length of the upper portion  122  of the mounting block  12 . A middle portion of a short inner side  425  of the through hole  422  is extended inwards to form a positioning pillar  423 , spaced away from an opposite short inner side of the through hole  422 . 
     Please refer to  FIG. 3 , in assembly, the cylinder  421  is inserted into the body  411 , and the wheel  41  is rotated with respect to the cap  42 . An elastic element  43 , such as a spring, is provided to mount to the positioning pillar  423 . After the mounting block  12  inserted into the through hole  422  from a bottom direction and fixed with the cap  42  together by a fixing element  44 , such as a screw, engaged with the fixing hole  15 , the spring  43  is restrained between the mounting block  12  and the short inner side  425  of the through hole  422 . The belt  32  is against the body  411  of the wheel  41  in use and stopped between the flange  412  and the stopping plate  424  for preventing from falling off. When the drive mechanism with belt tensioner is in work, the belt  32  is running and pushes the wheel  41  moves along a lengthwise direction substantially perpendicular to the line formed by the pivot  13  and the mounting opening  14 , with respect to the fixing frame  10 . Correspondingly, the cap  42  is moved to compress the spring  43 . When a tensile force of the belt  32  decreases due to the belt  32  stretched in long-term usage or other factors, the elastic force stored in the spring  43  will release to drive the wheel  41  to press the belt  32  so as to compensate the tensile force of the belt  32 . 
     As described above, the cylindrical wheel  41  is pivoted to the mounting block  12  of the fixing frame  10 . The cap  42  coupled with the wheel  41  is fixed to the mounting block  12  and capable of moving lengthwise with respect to the running belt  30 . The spring  43  received in the through hole  422  can release the stored elastic force to bring the wheel  41  to press the running belt  32  for compensating the decreasing tensile force of the running belt  32 , which guarantees the steady transmission of the belt drive system. Furthermore, the structure of the tensioner  40  is simple and compact, which is easy to manufacture and assemble, and occupies a relatively small space. 
     The foregoing description of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. Such modifications and variations that may be apparent to those skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.