Side position stapler for post-processing device

A sheet post-processing device that receives a sheet from an image forming apparatus and, directly discharges the sheet to outside when no post-processing is to be performed on the sheet, performs post-processing on the sheet and discharges post-processed sheet to outside when post-processing is to be performed on the sheet, the sheet post-processing unit comprising:

• a tray member configured to accumulate a plurality of the sheet as a sheet pile, the tray member having a first side that is parallel to a sheet width direction;
• an end aligning member having an end alignment surface configured to align trailing ends of the sheets in the sheet pile;
• a stapler unit is configured to staple together the sheet pile at a second side thereof at a staple position, the stapler unit having an opening in which the second side of the sheet pile is inserted, the stapler unit being arranged near the first side of the tray member such that a central portion of the second side of the sheet pile is situated inside the opening of the stapler unit, and the staple position is located downstream of the alignment surface of the aligning member in a sheet conveying direction;
• a pair of staple-tray entrance rollers that convey the sheet to the tray member;
• a moving mechanism that moves the staple-tray entrance rollers in the sheet width direction;
• a control unit that controls the moving mechanism, wherein
• the stapler unit is arranged under the staple-tray entrance rollers at a position where a central portion of a second side of a sheet pile of largest of receivable sheets is located inside the opening, and
• when a sheet is conveyed with a second side being outside of the opening, the control unit moves the staple-tray entrance rollers toward a third side of the tray member that is parallel to the sheet width direction before the sheet is delivered on the tray member so that the sheet can be delivered on the tray member with the second side thereof being inside of the opening;
• and
• a pair of conveyer rollers that convey the sheet from the image forming apparatus to the sheet post-processing device, the conveyer rollers being arranged upstream of the staple-tray entrance rollers and are movable between a sheet conveying position at which the conveyer rollers are in contact with the sheet and a release position that is away from the sheet conveying position.