Paper stacking unit and image forming system

Abstract

The paper stacking unit includes a paper stacking section on which the paper is stacked, a paper stacking mechanism which carries the paper to the paper stacking section on which the paper is stacked, and an abutment surface on which an end of the paper is abutted. The paper stacking mechanism includes a gripper member for holding the paper and a gripper moving mechanism. The gripper member holds the paper under the first holding force in a moving range from a holding position to a stacking position, and holds the paper under the second holding force upon the abutment of the end of the paper on the abutment surface from the stacking position.

What is claimed is: 
     
         1 . A paper stacking unit comprising:
 a paper stacking section on which a paper is stacked;   a paper stacking mechanism which carries the paper to the paper stacking section on which the paper is stacked; and   an abutment surface on which an end of the paper carried by the paper stacking mechanism is brought into abutment, wherein:   the paper stacking mechanism includes a gripper member for holding the paper, and a gripper moving mechanism which moves the gripper member in a moving range at least from a holding position at which the paper is held to a stacking position at which the paper is stacked on the paper stacking section where the end of the paper held by the gripper member is brought into abutment on the abutment surface;   the gripper member makes a force for holding the paper switchable between a first holding force and a second holding force that is less than the first holding force; and   the gripper member holds the paper under the first holding force in the moving range from the holding position to the stacking position, and holds the paper under the second holding force upon the abutment of the end of the paper on the abutment surface from the stacking position.   
     
     
         2 . The paper stacking unit according to  claim 1 , wherein:
 the gripper member includes a lower gripper connected to the gripper moving mechanism via a joint member, and an upper gripper rotatably supported with the lower gripper via a first turning shaft;   the upper gripper includes a first upper gripper piece rotatably supported with the lower gripper via the first turning shaft, a second upper gripper piece rotatably supported with the first upper gripper piece via a second turning shaft, a first urging member for urging an end of the first upper gripper piece at a side of the second upper gripper piece toward the lower gripper, and a second urging member for urging the second upper gripper piece toward the lower gripper; and   an urging force of the second urging member is set to be less than an urging force of the first urging member.   
     
     
         3 . The paper stacking unit according to  claim 2 , wherein:
 a roller is attached to an end of the first upper gripper piece, opposite the end at the side of the second upper gripper piece, the first turning shaft being interposed between both ends of the first upper gripper piece;   the paper stacking mechanism includes a cam member to be abutted on the roller; and   the first upper gripper piece turns in a direction in which the end at the side of the second upper gripper piece is separated from the lower gripper against the urging force of the first urging member upon abutment of the roller on the cam member.   
     
     
         4 . The paper stacking unit according to  claim 1 , comprising a control unit for controlling an operation to drive the gripper moving mechanism so that a moving speed of the gripper member is controlled. 
     
     
         5 . The paper stacking unit according to  claim 4 , wherein the control unit controls the gripper moving mechanism to set a moving speed of the gripper member upon the abutment of the end of the paper on the abutment surface from the stacking position to be lower than the moving speed of the gripper member in the moving range from the holding position to the slacking position. 
     
     
         6 . The paper stacking unit according to  claim 5 , wherein the control unit controls the gripper moving mechanism to set the moving speed of the gripper member upon returning back to the holding position from the abutment of the end of the paper on the abutment surface to be higher than the moving speed of the gripper member upon the abutment of the end of the paper on the abutment surface from the stacking position. 
     
     
         7 . The paper stacking unit according to  claim 4 , wherein the control unit controls a movement of the gripper member in accordance with a type of the paper to be carried. 
     
     
         8 . An image forming system comprising:
 an image forming apparatus for forming an image on a paper; and   the paper stacking unit according to  claim 1 , to which the paper is carried from the image forming apparatus.