US Patent 10941013 Sheet post-processing device and image forming system including same

A paper sheet post-processing device includes a processing tray, an aligning member that aligns paper sheets on the processing tray, a swingable holder that supports the aligning member, a swinging mechanism that causes the holder to swing, and a control unit that controls the swinging mechanism. The swinging mechanism includes a rotation shaft inserted into a shaft insertion portion of the holder with play in a rotation direction. The control unit controls the rotation shaft to rotate and stop at a predetermined rotation angle position corresponding to a stack height of the sheets stacked on the processing tray, so that the holder is disposed at a contact position. At the contact position, the holder is allowed to swing in a retracting direction with respect to the rotation shaft within a predetermined play range. The play range is set to be larger in proportion to the stack height of the sheets.