Sheet stacking apparatus, sheet finishing apparatus, image forming apparatus and sheet stacking method

Abstract

A sheet stacking apparatus according to an embodiment of the invention includes a movable tray having a sheet stack part whose center part is dented downward as the number of discharged and stacked sheets increases, and a movement control mechanism part to move and control the movable tray up and down.

1 . A sheet stacking apparatus comprising:
 a movable tray having a sheet stack part whose center part is dented downward as the number of discharged and stacked sheets increases; and   a movement control mechanism part to move and control the movable tray up and down.   
     
     
         2 . The apparatus of  claim 1 , wherein a dent of the sheet stack part is formed to be V-shaped in a direction vertical to a direction in which the sheets are discharged. 
     
     
         3 . The apparatus of  claim 2 , wherein the sheet stack part includes pressure springs, and when the sheets are stacked, the V shape is formed by elastic forces of the pressure springs and by the sheets own weight. 
     
     
         4 . The apparatus of  claim 3 , wherein
 the sheet stack part includes:   two plates provided right and left in the discharge direction of the discharged sheets;   a holding body provided under the two plates and to the two plates;   a first pressure spring that is provided on the holding body and supports the two plates; and   a second pressure spring that is provided on the holding body, supports the two plates, is provided at a position farther from a boundary of the right and left plates than the first pressure spring, and has an elastic force higher than that of the first pressure spring.   
     
     
         5 . The apparatus of  claim 2 , wherein the sheet stack part detects an amount of the stacked sheets, and forms the V shape by electrical control according to the amount. 
     
     
         6 . The apparatus of  claim 5 , wherein
 the sheet stack part includes:   a sheet amount detection part to detect a thickness or a weight of the stacked sheets;   two plates provided right and left in the discharge direction of the sheets;   a holding body provided under the two plates and to the two plates; and   an electromagnetic solenoid that is provided between the holding body and the two plates, and pulls a portion close to a boundary of the two plates downward as the thickness or the weight of the sheets detected by the sheet amount detection part increases.   
     
     
         7 . The apparatus of  claim 2 , wherein the sheet stack part forms the V shape by a cam mechanism. 
     
     
         8 . The apparatus of  claim 7 , wherein when the amount of the stacked sheets increases, the movable tray is lowered, and the sheet stack part detects the lowering of the movable tray and forms the V shape by the cam mechanism according to a detected position. 
     
     
         9 . The apparatus of  claim 8 , wherein
 the sheet stack part includes:   a position detection part to detect the position of the movable tray;   two plates provided right and left in the discharge direction of the sheets;   a holding body provided under the two plates and to the two plates;   a rotation shaft that is provided to the holding body to be rotatable in a direction vertical to a line of a boundary of the two plates, and is rotated as the position of the movable tray detected by the position detection part becomes low; and   a pair of eccentric cams that are provided on the rotation shaft, and contact lower surfaces of the two plates to raise ends of the two plates farther from the boundary as the position of the movable tray becomes low.   
     
     
         10 . A sheet stacking apparatus comprising:
 a movable tray including a sheet stack part that detects an amount of discharged and stacked sheets, and forms a V shape in a direction vertical to a discharge direction of the sheets by electrical control according to the amount; and   a movement control mechanism part to move and control the movable tray up and down.   
     
     
         11 . The apparatus of  claim 10 , wherein the sheet stack part includes:
 a sheet thickness detection part to detect a thickness of the stacked sheets;   two plates provided right and left in the discharge direction of the sheets;   a holding body provided under the two plates and to the two plates; and   an electromagnetic solenoid that is provided between the holding body and the two plates, and pulls a portion close to a boundary of the two plates downward as the thickness of the sheets detected by the sheet thickness detection part increases.   
     
     
         12 . The apparatus of  claim 11 , further comprising a weight detection part to obtain a weight of the sheets from the thickness of the sheets detected by the sheet thickness detection part, wherein the electromagnetic solenoid pulls the portion close to the boundary of the two plates downward as the weight detected by the weight detection part increases. 
     
     
         13 . The apparatus of  claim 10 , wherein
 the sheet stack part includes:   a sheet weight detection part to detect a weight of the stacked sheets;   two plates provided right and left in the discharge direction of the sheets;   a holding body provided under the two plates and to the two plates; and   an electromagnetic solenoid that is provided between the holding body and the two plates, and pulls a portion close to a boundary of the two plates downward as the weight of the sheets detected by the sheet weight detection part increases.   
     
     
         14 . A sheet finishing apparatus for finishing a sheet, comprising a sheet stacking apparatus including:
 a movable tray having a sheet stack part that detects an amount of discharged and stacked sheets and forms a V shape in a direction vertical to a discharge direction of the sheets according to the amount; and a movement control mechanism part to move and control the movable tray up and down.   
     
     
         15 . The apparatus of  claim 14 , wherein the sheet stack part includes pressure springs, and when the sheets are stacked, the V shape is formed by elastic forces of the pressure springs and by the sheets own weight. 
     
     
         16 . The apparatus of  claim 14 , wherein the sheet stack part detects the amount of the stacked sheets, and forms the V shape by the electrical control according to the amount. 
     
     
         17 . The apparatus of  claim 14 , wherein the sheet stack part forms the V shape by a cam mechanism. 
     
     
         18 . The apparatus of  claim 17 , wherein when the amount of the stacked sheets increases, the movable tray is lowered, and the sheet stack part detects the lowering of the movable tray and forms the V shape by the cam mechanism according to a detected position. 
     
     
         19 . An image forming apparatus comprising:
 an image forming part to form an image to be printed on a sheet;   a sheet print part to print the image formed by the image forming part onto the sheet;   a movable tray including a sheet stack part that stacks the sheet printed by the sheet print part, and has a center part which is dented downward as the number of the sheets increases; and   a movement control mechanism part to move and control the movable tray up and down.   
     
     
         20 . A sheet stacking method comprising:
 forming a V shape vertically to a sheet discharge direction according to an amount of sheets stacked on a sheet stack part that stacks discharged sheets and is included in a movable tray; and   moving and controlling the movable tray up and down.