Sheet stacking device, sheet post-processing device, and image forming system

Abstract

A sheet stacking device includes a stacking tray, an aligning mechanism, a pair of alignment members, and a pair of height detectors. The pair of alignment members can move independently in a sheet width direction and in an up and down direction, and contact side edges in the sheet width direction of sheets stacked on the stacking tray, from both sides in the sheet width direction, so as to align the sheets in the sheet width direction. The pair of height detectors allow the pair of alignment members to contact an upper surface of the sheets near side edges of the sheets, so that sheet heights on both sides in the sheet width direction are detected. The sheet stacking device can individually correct heights of the pair of alignment members when aligning the sheets, based on the sheet heights detected by the pair of height detectors.

What is claimed is: 
     
         1 . A sheet stacking device comprising:
 a sheet discharge outlet from which a sheet is discharged;   a pair of discharge rollers for discharging the sheet from the sheet discharge outlet;   a stacking tray disposed below a downstream side of the sheet discharge outlet in a sheet discharge direction to stack the sheet discharged from the sheet discharge outlet; and   an aligning mechanism for aligning the sheet stacked on the stacking tray in a sheet width direction perpendicular to the sheet discharge direction, wherein   the aligning mechanism includes a pair of alignment members capable of moving independently of each other in the sheet width direction and in an up and down direction, the pair of alignment members contacting side edges in the sheet width direction of the sheet stacked on the stacking tray from both sides in the sheet width direction, so as to align the sheet in the sheet width direction, and a pair of height detectors for detecting heights of the sheet on both sides in the sheet width direction by allowing the pair of alignment members to contact an upper surface of the sheet at vicinities of the side edges of the sheet, and   the pair of alignment members can individually adjust the heights of the pair of alignment members so that the pair of alignment members face the side edges of the sheet when aligning the sheet, on the basis of the heights of the sheet detected by the pair of height detectors.   
     
     
         2 . The sheet stacking device according to  claim 1 , wherein
 the pair of alignment members are capable of rotating independently of each other about a rotation shaft extending in the sheet width direction, and   the pair of height detectors detect the heights of the sheet on the basis of rotation angles of the pair of alignment members.   
     
     
         3 . The sheet stacking device according to  claim 1 , wherein if a difference between the height of the sheet detected by one of the pair of height detectors and the height of the sheet detected by the other of the pair of height detectors is a predetermined value or larger, the discharging of the sheet from the sheet discharge outlet is stopped. 
     
     
         4 . The sheet stacking device according to  claim 1 , further comprising a controller for controlling an operation of the aligning mechanism, wherein
 the aligning mechanism includes a slide mechanism for moving each of the pair of alignment members in the sheet width direction, and a lifting mechanism for rotating each of the pair of alignment members about a rotation shaft in the up and down direction,   the pair of alignment members are attached to one end and the other end of the rotation shaft respectively in a rotatable manner with a predetermined play in the rotation direction,   each of the pair of height detectors includes an angle detection sensor capable of detecting a rotation angle of the alignment member, and   the controller controls the lifting mechanism to move each of the pair of alignment members independently from a first position facing side edge in the sheet width direction of the sheet stacked on the stacking tray to a second position above the sheet, then controls the slide mechanism to move each of the pair of alignment members to inside in the sheet width direction so as to be positioned at a third position facing the upper surface of the sheet, then controls the lifting mechanism to move each of the pair of alignment members downward from the third position to a contact position in contact with the upper surface of the sheet, while controlling the angle detection sensor to detect a rotation angle from the third position to the contact position, then derives an alignment position of each of the pair of alignment members after correcting height based on the rotation angle, and then performs an aligning operation for aligning the sheet in the sheet width direction at the alignment position.   
     
     
         5 . A sheet post-processing device comprising:
 a processing tray on which a sheet is loaded;   a post-processor for performing a predetermined post-processing on the sheet loaded on the processing tray; and   the sheet stacking device according to  claim 1 , including the pair of discharge rollers disposed on the downstream side of the processing tray in the sheet discharge direction, so that the sheet after the post-processing by the post-processor is stacked on the stacking tray by the pair of discharge rollers.   
     
     
         6 . An image forming system comprising:
 an image forming apparatus for forming an image on a sheet; and   the sheet post-processing device according to  claim 5 , configured to be connected to the image forming apparatus so as to perform a predetermined post-processing on the sheet after image formation.