Abstract:
A band saw apparatus including a blade under tension and has a frame that includes a pivotably connected drive mount and a rotatable wheel supported by the drive mount. The blade extends about the rotatable wheel. A tensioner is used to set the blade tension so as to minimize objectionable noise and vibration. The tensioner also facilitates raising the drive mount and support wheel for blade removal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to tensioning mechanisms and more particularly to a tensioner assembly installable in a food product band saw apparatus for tensioning of a band saw blade. 
     BACKGROUND OF THE INVENTION 
     In the food processing industry large upright band saws such as band saw  10  of FIG. 1 are commonly used for cutting meat products of a variety of sizes. Such band saws typically include a frame  12  upon which is mounted a support surface  14  for positioning meat products to be cut. A housing portion  16  extends above support surface  14  and a housing portion  18  extends below support surface  14 . A band saw blade  20  passes though a plane defined by support surface  14  and extends around wheel members (not shown) located with housing portions  16  and  18  for being drivingly rotated by such wheel members. In particular, a drive motor  22  may be connected for rotating a drive wheel in housing portion  18 . 
     In the food processing industry the band saw, including the blade, has to be cleaned each day and each time the food product being cut is changed. Therefore, such band saws preferably include a system which allows easy removal of the saw blade and simple reinstallation and retensioning the saw blade. Further, food product band saws preferably run as quiet as possible since they may operate in supermarket settings. As the noise produced by the band saw can vary according to the tension of the saw blade, it is desirable to enable a user to establish the appropriate saw blade tension in a simple manner. A properly configured tensioner and tensioning system may achieve the above goals. 
     A tension of the band saw blade may be adjusted by adjusting the position of a drive mount which supports the drive motor  22  and accordingly the drive wheel in housing portion  18 . Referring to FIG. 2, and exemplary drive mount  24  is illustrated and is pivotably connectable to a frame  26  of the band saw by pivot pin  28 . The drive motor  22  is connected to the drive mount and a drive shaft extends to the lower drive wheel  30  for rotation and support thereof. Thus, the lower drive wheel  30  is also supported by the drive mount  24 . A tensioner  32  may be connected between the drive mount  24  at connection point  34  and the frame at a connection point  36 , enabling adjustment of the pivotable position of the drive mount  24  and thus the position of the lower drive wheel  30  and/or the tension force of a saw blade  20  extending thereabout. 
     Tensioner  32  represents a known prior art tensioner which is illustrated schematically in FIG.  3  and includes a mounting bushing  38  with a shaft  40  extending therethrough. A mounting nut  42  is threaded onto the shaft  40  and a spring  44  extends from the mounting bushing  38  to the mounting nut  42 . A handle  46  enables rotation of the shaft  40 . In operation the mounting bushing  38  is connected to connection point  36  of the frame and the mounting nut  42  is connected to connection point  34  of the drive mount  24 . Spring  44  provides a shock and vibration absorbing feature for the lower drive wheel  30  and associated drive motor  22 . Tension on the blade (represented schematically at  48 ) is increased by rotating handle  46  to increase the distance between the mounting bushing  38  and the mounting nut  42 . The spring  44  is pre-compressed to assure the blade  48  is properly tensioned when the mounting nut  42  is positioned at the far end of the threaded shaft  40 . The pre-compressed force on spring  44  is typically very large since the blade  48  needs a large tension force. To maintain the condition where the handle  46  abuts against the mounting bushing  38  at all times, the spring  44  must be compressed at all times. Unfortunately the compressive force of the spring  44  is largest when the blade  48  is placed in the slack, non-tensioned condition resulting in high spring forces which must be overcome in order to remove the blade  48 . 
     In order to remove a saw blade from a band saw the lower drive wheel  30  must be raised by rotating handle  46  to decrease the distance between the mounting bushing  38  and the mounting nut  42 . With the above tensioner  32  arrangement in order to decrease the distance between the mounting bushing  38  and the mounting nut  42  the compression force of the spring  44  must be overcome. Further, the downward weight of the drive motor  22  and lower drive wheel must also be overcome. Accordingly, rotation of the handle  46  can be difficult. 
     Accordingly, in one embodiment, the present invention is directed to an improved tensioner assembly. 
     SUMMARY OF THE INVENTION 
     A tensioner assembly includes a mounting bushing having an opening therethrough and a shaft having at least one threaded region along its axial length, the shaft extending through the opening. A mounting nut is threaded onto the shaft. A seating surface extends from the shaft at a position intermediate the mounting bushing and the mounting nut. A spring is disposed around the shaft between the mounting bushing and the seating surface. A first end of the spring is positioned against the seating surface so as to be fixed at the intermediate position along the shaft regardless of a distance between the mounting bushing and the mounting nut, a second end of the spring is positioned toward the mounting bushing. 
     In another embodiment a method of tensioning a blade of a band saw apparatus including a frame, a drive mount including a first portion pivotably connected to the frame, a rotatable wheel supported by the drive mount and movable therewith, the blade extending about said rotatable wheel, involves: (a) providing a tension bolt assembly including a mounting bushing having an opening therethrough, a shaft extending through the opening and having at least one threaded region along its axial length, a mounting nut threaded onto the threaded region of the shaft and spaced from the mounting bushing, a spring disposed around the shaft and positioned between the mounting bushing and the mounting nut, a first end of the spring positioned against a seating surface located intermediate the mounting bushing and the mounting nut such that said first end of said spring is spaced from the mounting nut, a second end of the spring positioned against a first side of the mounting bushing; (b) connecting the mounting bushing to the frame; (c) connecting the mounting nut to a second portion of the drive mount; and (d) rotating the shaft until the shaft moves through the mounting bushing opening and the spring is compressed, such that a tension force of the blade is balanced with a compression force of the spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an exemplary food product band saw; 
     FIG. 2 is a partial perspective view of a drive mount arrangement; 
     FIG. 3 is a schematic view of a prior art tensioner; 
     FIG. 4 is a cross-sectional view of one embodiment of a tension assembly of the present invention, in a non-tensioning configuration; and 
     FIG. 5 is a cross-sectional view of the tensioner assembly of FIG. 4 in a tensioning configuration. 
    
    
     DETAILED DESCRIPTION 
     Referring to drawing FIGS. 4 and 5, numeral  100  depicts one embodiment of a tensioner assembly of the present invention. The tensioner assembly  100  includes a shaft  102  having first and second ends  104  and  106 . A mounting bushing  108  includes an opening  110  therethrough. The shaft  102  extends through opening  110 . Mounting bushing  108  also includes a laterally extending bore  112  for facilitating attachment of the mounting bushing  108  to a connection point such as connection point  36  shown in FIG.  2 . Towards the end  106  of shaft  102  a threaded region  114  is provided and a mounting nut  116  is threaded onto the threaded region  114  to be spaced from mounting bushing  108 . Relative rotation between shaft  102  and mounting nut  116  increases or decreases the distance between mounting bushing  108  and mounting nut  116  depending upon the direction of relative rotation. Laterally extending pin  118  and washer  119  may be provided for preventing mounting nut  116  from being threaded off of the shaft  102 . Mounting nut  116  includes a laterally extending bore  117  for facilitating attachment to a drive mount connection point such as point  34  of FIG.  2 . 
     A seating surface  120  is provided at a position intermediate the mounting bushing  108  and the mounting nut  116 . The seating surface  120  may be provided by a laterally extending pin  111  with two washers  113  with a thrust needle bearing  115  positioned therebetween for facilitating relative rotation of the washers  113 , but it is also anticipated that the seating surface  120  could be provided by other means including an additional nut located on threaded region  114 , or even an integral extension of shaft  102 . A spring  122  is disposed around shaft  102  and extends from mounting bushing  108  to seating surface  120 . A first end  124  of the spring being positioned against seating surface  120  and a second end  126  of the spring  122  being positioned against a side of the mounting bushing  108 . A housing  128  formed by telescoping portions  130  and  132  is also provided. A handle  134  is positioned toward end  104  of shaft  102  for rotating the shaft  102  and may be connected to the shaft by any known means such as a pinned connection. A thrust bearing  136  may be provided between handle  134  and mounting bushing  108  to facilitate rotation of the handle when in the FIG. 4 position. Thrust bearing  136  could be a plastic washer which provides a smooth surface against which the handle  134  abuts. 
     FIG. 4 illustrates the tensioner assembly  100  in a first configuration when a non-tensioned state while FIG. 5 illustrates the tensioner assembly  100  in a second configuration when in a tensioning state. In the non-tensioned configuration of FIG. 4 spring  122  is preferably in a normal, non-compressed state to facilitate easy rotation of handle  134 . However, it is recognized that spring  122  may be precompressed when in the non-tensioned configuration. 
     When the tensioner assembly  100  is used in a band saw apparatus or other system in which tensioning is desired, the mounting bushing  108  is connected to a first connection point which is preferably a fixed connection point such as connection point  36  shown in FIG.  2 . Mounting nut  116  is connected to a second connection point which is preferably a movable connection point such as connection point  34  of the drive mount  24  shown in FIG.  2 . Once attached to their respective connection points neither mounting bushing  108  nor mounting nut  116  are rotatable. When first attached, the tensioner assembly  100  will be in the non-tensioned configuration of FIG.  4 . In order to apply tension to a blade of a band saw, handle  134  is rotated to cause mounting nut  116  to move toward first end  106  of shaft  102  thereby increasing the distance between mounting bushing  108  and mounting nut  116 . When the mounting nut  116 , and accordingly the drive mount  24 , drive motor  22  and lower drive wheel  30  of a band saw are moved sufficient to reach the length limit of the band saw blade, tensioning of the blade will begin and further rotation of the handle  134  causes a proportional amount of compressive force to be exerted on the spring  122 . As the tension in the band saw blade is increased the compressive force against the spring  122  likewise increases and the spring  122  is compressed causing the shaft  102  to move axially upward through the mounting bushing  108 . Once the handle  134  is moved away from the mounting bushing  108  (as shown in FIG. 5) the tension force on the band saw blade balances with the compression force on the spring  122 . In this tensioned state, spring  122  provides a shock and vibration absorbing feature. The vibration comes from the motor and the blade, and the shock is caused by the blade cutting the food product. 
     Notably, when it is desired to release the tension on the band saw blade to permit removal of the blade for cleaning, replacement or repair, the handle  134  is rotated in an opposite direction and the shaft  102  will move downward through the opening  110  in mounting bushing  108  until the handle  134  is again positioned adjacent the mounting bushing  108  (as shown in FIG.  4 ). During the downward movement of the handle  134  since the compressed spring  122  is being released the rotation of the handle  134  is very easy. From that point, further rotation of the handle  134  causes the mounting nut  116  to move upward along the shaft  102  towards end  104  and thus correspondingly pulls up the drive mount  24  and the attached drive wheel  30 . As the drive mount  24  is pulled upward due to its attachment to mounting nut  116 , spring  122  applies no forces which must be overcome and thus rotation of handle  134  is significantly easier as compared to the prior art tensioner  32  described above with reference to FIG.  3 . This result is achieved by providing the seating surface  120  against which the end  124  of spring  122  is positioned so as to be fixed relative to the shaft  102  regardless of the distance between mounting nut  116  and mounting bushing  108 . 
     When tensioner assembly  100  is in the tensioning configuration of FIG. 5 a distance between the seating surface  120  and the mounting bushing  108  is less than the distance between the seating surface  120  and the mounting bushing  108  when the tensioner assembly  100  is in the non-tensioning configuration of FIG.  4 . When the tensioner assembly  100  is in the tensioning configuration of FIG. 5 a distance between the handle  134  and mounting bushing  108  is greater than the distance between the handle  134  and mounting bushing  108  when in the tensioning configuration of FIG.  4 . 
     Another feature provided in the illustrated embodiment is that the blade tension does not need to be adjusted when the blade is retensioned using tensioner assembly  100 . When the nut  116  reaches the far end  106  of shaft  102  as shown in FIG. 5, the compression force of the spring  122  is fixed, and so is the blade tension. Thus, the user/installer turns the handle  134  to its stopping point (when mounting nut  116  contacts the stop surface at end  106  of shaft  102 ) and at that time the blade tension will be set appropriately. To release the tension and raise the lower drive wheel for blade removal, the user/installer rotates the handle  134  in the opposite direction to its stopping point (when the mounting nut  116  contacts the pin  111 ). O-ring  137  provides a seal between the shaft  102  and the mounting bushing  108  to prevent entry of food product contaminants and any other liquids. 
     Although the invention has been described and illustrated in detail it is to be clearly understood that the same is intended by way of illustration and example only and is not intended to be taken by way of limitation. For example, the configuration of the mounting bushing, mounting nut, handle and shaft could vary considerably.