Sheet stacking apparatus and image forming system

Abstract

A sheet stacking apparatus includes a stacking tray, a lowering unit, a conveyance unit, a first action unit and a second action unit, and a permitting portion. The stacking tray stacks sheets. The lowering unit lowers the stacking tray as the sheets are stacked. The conveyance unit conveys a sheet toward the stacking tray. The first action unit and the second action unit act on both edge ends in a width direction of a sheet bundle stacked on the stacking tray to align the sheet bundle. The permitting portion permits a next sheet to be temporarily received above the stacking tray when the first action unit and the second action unit are aligning the sheet bundle.

What is claimed is: 
     
         1 . A sheet stacking apparatus comprising:
 a stacking tray configured to stack sheets;   a lowering unit configured to lower the stacking tray as the sheets are stacked;   a conveyance unit configured to convey a sheet toward the stacking tray;   a first action unit and a second action unit configured to act on both edge ends in a width direction of a sheet bundle stacked on the stacking tray to align the sheet bundle; and   a permitting portion configured to permit a next sheet to be temporarily received above the stacking tray when the first action unit and the second action unit are aligning the sheet bundle.   
     
     
         2 . The sheet stacking apparatus according to  claim 1 , wherein the first action unit and the second action unit configured to act so as to align the next sheet temporarily received by the permitting portion together with the sheet bundle that has been aligned when the next sheet is temporarily received. 
     
     
         3 . The sheet stacking apparatus according to  claim 1 , wherein the first action unit and the second action unit include alignment portions configured to abut on both edge ends of the sheet bundle in the width direction when aligning the sheet bundle, and
 the permitting portion is formed on an upper surface of at least one of the alignment portions.   
     
     
         4 . The sheet stacking apparatus according to  claim 3 , wherein each of the alignment portions includes a first portion and a second portion located upstream of the first portion in a direction in which the sheet is conveyed by the conveyance unit, and
 a length of the first portion is longer than a length of the second portion in a vertical direction.   
     
     
         5 . The sheet stacking apparatus according to  claim 3 , wherein at least one of the first action unit and the second action unit configured to be movable between an alignment position where the alignment of the sheet bundle in the width direction is performed and a position farther away from an edge end of the sheet bundle in the width direction than the alignment position,
 the conveyance unit is a pair of conveyance rollers that nip and convey the sheet, and   an upstream edge portion of the permitting portion in the direction in which the sheet is conveyed by the conveyance unit is positioned below a line obtained by extending a nip surface formed between the pair of conveyance rollers downstream in the conveyance direction in a state where the first action unit and the second action unit are at the alignment position.   
     
     
         6 . The sheet stacking apparatus according to  claim 3 , wherein at least one of the first action unit and the second action unit configured to be movable between an alignment position where the alignment of the sheet bundle in the width direction is performed and a position farther away from an edge end of the sheet bundle in the width direction than the alignment position, and
 the sheet stacking apparatus further comprises an inclination portion provided at an upstream edge portion of the permitting portion in a direction in which the sheet is conveyed by the conveyance unit and inclined to be directed downward toward an inside, in the width direction, where the sheet bundle is positioned in a state where the first action unit and the second action unit are at the alignment position.   
     
     
         7 . The sheet stacking apparatus according to  claim 1 , wherein the permitting portion configured to be movable between a permitting position where it is permitted to temporarily receive the next sheet and a retraction position retracted from the permitting position. 
     
     
         8 . The sheet stacking apparatus according to  claim 7 , wherein the conveyance unit is a pair of conveyance rollers configured to nip and convey the sheet,
 at least one of the first action unit and the second action unit configured to be movable between an alignment position where the alignment of the sheet bundle in the width direction is performed and a position farther away from an edge end of the sheet bundle in the width direction than the alignment position,   the permitting position is a position above upstream edge portions of the first action unit and the second action unit in a direction in which the sheet is conveyed by the conveyance unit in a state where the first action unit and the second action unit are at the alignment position, and   the retraction position is a position further below a rotation shaft of a lower conveyance roller of the pair of conveyance rollers.   
     
     
         9 . An image forming system comprising:
 an image forming portion configured to form an image on a sheet;   a stacking tray configured to stack sheets on which images are formed by the image forming portion;   a lowering unit configured to lower the stacking tray as the sheets are stacked;   a conveyance unit configured to convey sheets toward the stacking tray;   a first action unit and a second action unit configured to act on both ends in a width direction of a sheet bundle stacked on the stacking tray to align the sheet bundle; and   a permitting portion configured to permit a next sheet to be temporarily received above the stacking tray when the first action unit and the second action unit is aligning the sheet bundle.