Post-processing apparatus and image forming system

1 . A post-processing apparatus comprising:

a conveyance portion conveying a sheet;

a processing tray on which the sheet having passed through the conveyance portion can be stacked;

a post-processing portion that performs post-processing on the sheet on the processing tray;

a discharge tray to which the sheet is discharged;

a discharge portion disposed downstream of the conveyance portion in a sheet conveyance direction, the discharge portion discharging the sheet to the discharge tray; and

a control portion controlling the discharge portion,

wherein

the discharge portion includes:

an arm pivotable such that, about a one end part thereof, another end part thereof being movable up and down;

a driving roller that is supported on the other end part of the arm so as to be rotatable, the driving roller making contact with the sheet from above and rotating forward so as to discharge the sheet to the discharge tray; and

a driven roller disposed below the driving roller across a sheet conveyance passage, the driven roller nipping the sheet with the driving roller as the driving roller moves downward,

when stacking the sheet on the processing tray, the control portion moves the driving roller downward to bring, from above, the driving roller into contact with the sheet having passed through the conveyance portion and rotates the driving roller backward so as to retract the sheet from a trailing edge thereof onto the processing tray,

except when the sheet as a target of the post-processing is retracted onto the processing tray, the control portion sets a downward movement speed of the driving roller to a predetermined normal speed, and

when the sheet as the target of the post-processing is retracted onto the processing tray, the control portion sets the downward movement speed of the driving roller to a speed lower than the normal speed.

2 . The post-processing apparatus according to claim 1 , wherein

the post-processing portion is a stapler, and

the stapler performs, as the post-processing, a stapling process on a bundle of the sheets on the processing tray.

3 . The post-processing apparatus according to claim 1 , wherein

when the sheet as the target of the post-processing is retracted onto the processing tray, the control portion changes, depending on a number of the sheets stacked on the processing tray, the downward movement speed of the driving roller.

4 . The post-processing apparatus according to claim 3 , wherein

the fewer the sheets stacked, the lower the control portion makes the downward movement speed of the driving roller.

5 . The post-processing apparatus according to claim 1 , wherein

when the bundle of the sheets on the processing tray is discharged to the discharge tray, the control portion changes, depending on the number of the sheets stacked on the processing tray, a contact pressure of the driving roller on the bundle of the sheets on the processing tray.

6 . The post-processing apparatus according to claim 5 , wherein

the more the sheets stacked, the higher the control portion makes the contact pressure of the driving roller on the bundle of sheets on the processing tray.

7 . An image forming system comprising:

the post-processing apparatus according to claim 1 ; and

an image forming apparatus forming an image on the sheet,

wherein

the post-processing apparatus performs the post-processing on the sheet conveyed therein from the image forming apparatus.

8 . The image forming system according to claim 7 , wherein

the image forming apparatus is an inkjet recording apparatus and ejects ink onto the sheet to form the image on the sheet.