Wide belt sander

Abstract

A wide belt sander has a base, a driving axle, a driven axle bracket, a driven axle, a belt and an automatic adjustment device. The driving axle has a central axis. The driven axle bracket is pivotally mounted on the base along a longitudinal axis perpendicular to the central axis of the driving axle. The driven axle is rotatably mounted on the driven axle bracket along a rotating axis parallel with the central axis of the driving axle. The automatic adjustment device drives the driven axle bracket to swing relative to the base along the longitudinal axis in a simple harmonic motion and has two pushed elements and a cam. The pushed elements are mounted separately on the driven axle bracket. The cam is mounted between and alternatively pushing the pushed elements to swing the driven axle bracket relative to the base.

What is claimed is: 
     
         1 . A wide belt sander comprising:
 a base;   a driving axle rotatably mounted on the base and having a central axis;   a driven axle bracket pivotally mounted on the base along a longitudinal axis perpendicular to the central axis of the driving axle;   a driven axle rotatably mounted on the driven axle bracket along a rotating axis parallel with the central axis of the driving axle;   a belt endlessly mounted around the driving and driven axles; and   an automatic adjustment device mounted between the base and the driven axle bracket to drive the driven axle bracket to swing relative to the base along the longitudinal axis in a simple harmonic motion and comprising
 two pushed elements mounted separately on the driven axle bracket; and 
 a cam rotatably mounted on the base and mounted between and alternatively pushing the pushed elements to swing the driven axle bracket relative to the base. 
   
     
     
         2 . The wide belt sander as claimed in  claim 1  further comprising an electrical adjustment device mounted on the base to pivot the driven axle bracket relative to the base to adjust a period of the simple harmonic motion of the automatic adjustment device. 
     
     
         3 . The wide belt sander as claimed in  claim 2 , wherein the automatic adjustment device comprises
 a gear box adjustably mounted on the base  10 ;   a driving shaft rotatably mounted on and extending into the gear box;   a driven shaft rotatably mounted on and extending out from the gear box and on which the cam is mounted; and   a gear device mounted in the gear box, mounted between the driving shaft and the driven shaft and comprising
 a worm rod co-axially mounted on the driving shaft; and 
 a worm gear securely mounted on the driven shaft and engaging the worm rod. 
   
     
     
         4 . The wide belt sander as claimed in  claim 3 , wherein the pushed elements are rotatably mounted on a bottom of the driven axle bracket at an interval and have a center line defined between centers of the pushed elements; and
 the cam has a rotating center where is mounted around the driven shaft and located at the center line between the pushed elements.   
     
     
         5 . The wide belt sander as claimed in  claim 4 , wherein each pushed element is a bearing having a central hole defined through the pushed element; and
 two securing bolts mounted respectively through the central holes of the pushed elements and mounted securely on the bottom of the driven axle bracket.   
     
     
         6 . The wide belt sander as claimed in  claim 5 , wherein
 the base has
 a channel defined along a direction perpendicular to the central axis of the driving axle; and 
 two threaded holes defined in the base adjacent to the channel; and 
   the gear box is mounted adjustably in the channel in the base and has
 a bottom; 
 two ribs formed on the bottom and slidably held in the channel in the base; 
 a wing mounted on and laterally protruding from the bottom of the gear box and having two elongated holes defined through the wing and aligning respectively with the threaded holes in the base; and 
 two bolts mounted respectively through the elongated holes and screwed respectively into the threaded holes in the base. 
   
     
     
         7 . The wide belt sander as claimed in  claim 6 , wherein
 the base further comprises a holding bracket to which the driven axle bracket is pivotally connected and the gear box is adjustably mounted and having an axle hole defined in a top of the holding bracket;   the driven axle bracket has a central shaft formed on and protruding downward from the driven axle bracket and rotatably and slidably extending into the axle hole in the holding bracket; and   a pneumatic cylinder is mounted between the holding bracket and the driven axle bracket and has
 a first end provided with a universal jointer and connected to the holding bracket with the universal jointer; and 
 a second end connected co-axially to the central shaft on the driven axle bracket to provide a supporting effect to the driven axle bracket. 
   
     
     
         8 . The wide belt sander as claimed in  claim 7 , wherein the electrical adjustment device comprises
 two contacting switches mounted on the base respectively at two sides of the belt;   two electromagnetic switches electrically connected respectively to the contacting switches and mounted on the base respectively at two sides of the driven axle bracket; and   two springs each having two ends connected respectively one of the electromagnetic switches and the driven axle bracket, wherein the springs are connected respectively to the two sides of the driven axle bracket to provide pulling forces in opposite directions to the driven axle bracket.   
     
     
         9 . The wide belt sander as claimed in  claim 8 , wherein each contacting switch has a contacting arm protruding from the contacting switch selectively abutting with the belt and having a ceramic sleeve mounted around the contacting arm. 
     
     
         10 . The wide belt sander as claimed in  claim 9  further comprising a limiting device mounted between the driven axle bracket and the holding bracket to limit the swinging range of the driven axle bracket and comprising
 a limiting bracket mounted on the bottom of the driven axel bracket, being inversed U-shaped and having two ears respectively formed on and protruding from two ends of the limiting bracket; 
 two limiting bolts mounted respectively on the ears of the limiting bracket and protruding toward each other; and 
 a base bracket mounted securely on the top of the bolding bracket and having a top extending into the limiting bracket to a position between the limiting bolts. 
 
     
     
         11 . The wide belt sander as claimed in  claim 2 , wherein the electrical adjustment device comprises
 two contacting switches mounted on the base respectively at two sides of the belt;   two electromagnetic switches electrically connected respectively to the contacting switches and mounted on the base respectively at two sides of the driven axle bracket; and   two springs each having two ends connected respectively one of the electromagnetic switches and the driven axle bracket, wherein the springs are connected respectively to the two sides of the driven axle bracket to provide pulling forces in opposite directions to the driven axle bracket.   
     
     
         12 . The wide belt sander as claimed in  claim 11 , wherein each contacting switch has a contacting arm protruding from the contacting switch, selectively abutting with the belt and having a ceramic sleeve mounted around the contacting arm. 
     
     
         13 . The wide belt sander as claimed in  claim 1 , wherein the automatic adjustment device comprises
 a gear box adjustably mounted on the base;   a driving shaft rotatably mounted on and extending into the gear box;   a driven shaft rotatably mounted on and extending out from the gear box and to which the cam is attached; and   a gear device mounted in the gear box, mounted between the driving shaft and the driven shaft and comprising
 a worm rod co-axially mounted on the driving shaft; and 
 a worm gear securely mounted on the driven shaft and engaging the worm rod. 
   
     
     
         14 . The wide belt sander as claimed in  claim 13 , wherein the pushed elements are rotatably mounted on a bottom of the driven axle bracket at an interval and have a center line defined between centers of the pushed elements; and
 the cam has a rotating center where is mounted around the driven shaft and located at the center line between the pushed elements.   
     
     
         15 . The wide belt sander as claimed in  claim 14 , wherein each pushed element is a bearing having a central hole defined through the pushed element; and
 two securing bolts mounted respectively through the central holes of the pushed elements and mounted securely to the bottom of the driven axle bracket.   
     
     
         16 . The wide belt sander as claimed in  claim 13 , wherein
 the base has
 a channel defined along a direction perpendicular to the central axis of the driving axle; and 
 two threaded holes defined in the base adjacent to the channel; and 
   the gear box is mounted adjustably in the channel of the base and has
 a bottom; 
 two ribs formed on the bottom and slidably held in the channel in the base; 
 a wing mounted on and laterally protruding from the bottom of the gear box and having two elongated holes defined through the wing and aligning respectively with the threaded holes in the base; and 
 two bolts mounted respectively through the elongated holes and screwed respectively into the threaded holes in the base. 
   
     
     
         17 . The wide belt sander as claimed in  claim 1 , wherein
 the base further comprises a holding bracket to which the driven axle bracket is pivotally connected and the gear box is adjustably mounted and having an axle hole defined in a top of the holding bracket;   the driven axle bracket has a central shaft formed on and protruding downward from the driven axle bracket and rotatably and slidably extending into the axle hole in the holding bracket; and   a pneumatic cylinder is mounted between the holding bracket and the driven axle bracket and has
 a first end provided with a universal jointer and connected to the holding bracket with the universal jointer; and 
 a second end connected co-axially to the central shaft on the driven axle bracket to provide a supporting effect to the driven axle bracket. 
   
     
     
         18 . The wide belt sander as claimed in  claim 17  further comprising a limiting device mounted between the driven axle bracket and the holding bracket to limit the swinging range of the driven axle bracket and comprising
 a limiting bracket mounted on the bottom of the driven axel bracket, being inversed U-shaped and having two ears respectively formed on and protruding from two ends of the limiting bracket; 
 two limiting bolts mounted respectively on the ears of the limiting bracket and protruding toward each other; and 
 a base bracket mounted securely on the top of the bolding bracket and having a top extending into the limiting bracket to a position between the limiting bolts.