Gripper bar for die cutting machine

Abstract

A hollow gripper bar having a hexagonal profile which reduces the bending and torsional stresses applied thereto by the acceleration and deceleration of the bar in a die cutting machine. The gripper bar includes an upper wall, a spaced lower wall, a leading wall and a trailing wall extending between the upper and lower walls. The leading wall includes a front top portion extending transversely from the upper wall and a front bottom portion disposed at an acute angle with respect to the front top wall portion. The trailing wall is similar in design to the leading wall and includes a rear top portion extending transversely from the upper wall and a rear bottom portion disposed at an acute angle with respect to the rear top portion. Both the front top portion and rear top portion have a thickness that is greater than the thickness of the upper wall. In addition, the front bottom portion as well as the rear bottom portion have a tapered thickness that gradually decreases from the front top portion and rear top portion, respectively, to the lower wall.

I claim:  
     
         1 . A gripper bar for gripping a sheet of paper material in a die cutting machine that processes said sheet into a box blank, comprising: 
 a longitudinally extending hollow bar which includes an upper wall having a leading end and a trailing end which define a width for said bar, a lower wall spaced from said upper wall to define a height for said bar, said lower wall having a leading end and a trailing end which define a width for said lower wall which is less than the width of said bar, a leading wall extending between and integral with the leading ends of said upper and lower walls, said leading wall including a front top wall portion extending transversely from the leading end of said upper wall to a front lower end which defines a height for said front top wall portion which is less than the height of said bar, and a front bottom wall portion extending between the front lower end of said front top wall portion and the leading end of said lower wall, said front bottom wall portion disposed at a first acute angle with respect to said front top wall portion, and a trailing wall extending between and integral with the trailing ends of said upper and lower walls, said trailing wall including a rear top wall portion extending transversely from the trailing end of said upper wall to a rear lower end which defines a height for said rear top wall portion which is less than the height of said bar, and a rear bottom wall portion extending between the rear lower end of said rear top wall portion and the trailing end of said lower wall, said rear bottom wall portion disposed at a second acute angle with respect to said rear top wall portion; and    a plurality of grippers disposed on said bar and spaced at regular intervals along its longitudinal length.    
     
     
         2 . The gripper bar of  claim 1  wherein said upper and lower walls are parallel.  
     
     
         3 . The gripper bar of  claim 1  wherein said upper and lower walls are planar.  
     
     
         4 . The gripper bar of  claim 1  wherein said upper and lower walls are of equal thickness.  
     
     
         5 . The gripper bar of  claim 1  wherein said front and rear top wall portions are parallel.  
     
     
         6 . The gripper bar of  claim 1  wherein said front and rear top wall portions are planar.  
     
     
         7 . The gripper bar of  claim 1  wherein said front and rear top wall portions are of equal thickness.  
     
     
         8 . The gripper bar of  claim 1  wherein the height of said front top wall portion is equal to the height of said rear top wall portion.  
     
     
         9 . The gripper bar of  claim 1  wherein said first and second acute angles range from about 30° to about 80°.  
     
     
         10 . The gripper bar of  claim 1  wherein said first and second acute angles are equal.  
     
     
         11 . The gripper bar of  claim 1  wherein said first and second acute angles are both about 74°.  
     
     
         12 . The gripper bar of  claim 1  wherein said upper wall has a thickness, and said front top wall portion has a thickness greater than the thickness of said upper wall.  
     
     
         13 . The gripper bar of  claim 1  wherein said upper wall has a thickness, and said rear top wall portion has a thickness greater than the thickness of said upper wall.  
     
     
         14 . The gripper bar of  claim 1  wherein said upper wall has a thickness, and said front and rear top wall portions each has a thickness greater than the thickness of said upper wall.  
     
     
         15 . The gripper bar of  claim 14  wherein a ratio of the thicknesses of said front and rear top wall portions to the thickness of said upper wall ranges from about 1.01 to 1 to about 2 to 1.  
     
     
         16 . The gripper bar of  claim 15  wherein said ratio is from about 1.1 to 1 to about 1.5 to 1.  
     
     
         17 . The gripper bar of  claim 15  wherein said ratio is about 1.2 to 1.  
     
     
         18 . The gripper bar of  claim 1  wherein said front bottom wall portion has a tapered thickness that gradually decreases from the front lower end of said front top wall portion to the leading end of said lower wall.  
     
     
         19 . The gripper bar of  claim 1  wherein said rear bottom wall portion has a tapered thickness that gradually decreases from the rear lower end of said rear top wall portion to the trailing end of said lower wall.  
     
     
         20 . The gripper bar of  claim 1  wherein said front bottom wall portion has a tapered thickness that gradually decreases from the front lower end of said front top wall portion to the leading end of said lower wall and said rear bottom wall portion has a tapered thickness that gradually decreases from the rear lower end of said rear top wall portion to the trailing end of said lower wall.  
     
     
         21 . The gripper bar of  claim 20  wherein the tapered thickness of said front and rear bottom wall portions is at an angle of from about 1° to about 10°.  
     
     
         22 . The gripper bar of  claim 21  wherein the angle is about 5° for both said front and said rear bottom wall portions.  
     
     
         23 . The gripper bar of  claim 1  wherein the hollow bar is composed of aluminum.  
     
     
         24 . A gripper bar for gripping a sheet of paper material in a die cutting machine that processes said sheet into a box blank, comprising: 
 a hollow bar defining a longitudinal axis;    a plurality of grippers disposed on said bar and spaced at regular intervals along said longitudinal axis and movable between open and closed positions;    a longitudinally extending axle rotatably mounted within said hollow bar for movement between a first position wherein said grippers are closed and a second position wherein said grippers are open;    a plurality of actuators mounted on said axle and spaced at regular intervals to correspond with said grippers, said actuators rotatable with said axle to open and close said grippers;    a lever disposed at one end of said axle operable to rotate said axle between said first and second positions; and    mounting means for mounting said lever on said axle, said mounting means comprising a key formed on said axle, a key-receiving opening formed in said lever, and a clamp for clamping said lever on said axle.    
     
     
         25 . The gripper bar of  claim 24  wherein said key comprises a flat area formed in said axle and said key-receiving opening includes a matching flat section corresponding thereto.  
     
     
         26 . The gripper bar of  claim 24  wherein said clamp comprises a pair of opposing jaws surrounding said axle.  
     
     
         27 . The gripper bar of  claim 26  wherein said clamp further includes a retainer for pinching said jaws together about said axle.