Sheet post-processing device and image forming system including same

A sheet post-processing device comprising:

• a conveying member configured to convey a sheet;
• a processing tray configured to stack a plurality of the sheets carried in by the conveying member in a predetermined carry-in direction;
• a processing section configured to perform predetermined post-processing on the sheets placed on the processing tray;
• a reference plate configured to abut an end edge of the sheet carried in onto the processing tray, on a downstream side in an alignment direction opposite to the carry-in direction, so as to align the sheet in the carry-in direction;
• an alignment member including a paddle holder disposed above the processing tray so as to be supported in a swingable manner in the carry-in direction, and an alignment paddle having a paddle main body supported in a rotatable manner at a swinging end of the paddle holder and at least one paddle part protruding from the paddle main body in a radial direction, so as to move the sheet carried in onto the processing tray in the alignment direction for aiding alignment of the sheets;
• a holder drive unit configured to swing the paddle holder, so as to move the alignment paddle in a reciprocating manner between a reference position to separate the paddle part above a top sheet placed on the processing tray and an acting position to allow the paddle part to contact with the top surface of the sheet;
• and
• a control unit configured to control the holder drive unit, wherein
• the alignment paddle rotates so that the paddle part contacts with the sheet n1times, n1 being an integer of two or more, during a period after one sheet is carried in onto the processing tray until the alignment in the carry-in direction is completed by the reference plate, and
• the control unit sets a second acting position, which is the acting position when the paddle part contacts with the sheet at n1-th time, to be higher than a first acting position, which is the acting position when the paddle part contacts with the sheet at m1-th time, where 1≤m1<n1 holds.