Image forming apparatus having sheet finisher

An apparatus for finishing sheets having a sheet size of a plurality of different sheet sizes, comprising:

• a sheet conveyor to convey a sheet in a predetermined sheet conveyance direction on a sheet conveyance path;
• and
• a stapling device to conduct an edge stapling processing to put staple pins into an edge portion of sheets, and a center stapling processing to put staple pins into a central portion of sheets;
• and the stapling device constructed in a divided structure including a driving mechanism provided at one side of the sheet conveyance path and a receiving mechanism provided at the other side of the sheet conveyance path, so that the divided structure is constructed to allow the sheet to pass along the sheet conveyance path between the driving mechanism and the receiving mechanism;
• wherein the driving mechanism has a pin-putting section from which a staple pin is put into the sheets and the receiving mechanism has a clinching section located opposite to the pin-putting section so that the staple pin put from the pin-putting section is clinched by the clinching section;
• wherein the driving mechanism and the receiving mechanism shift simultaneously in a direction perpendicular to the sheet conveyance direction between an edge stapling position to conduct the edge stapling processing and a corner stapling position to conduct the corner stapling processing,
• wherein a plurality of different corner stapling positions are predetermined for the plurality of different sheet sizes, and when the stapling device conducts the corner stapling processing, the driving mechanism and the receiving mechanism shift simultaneously in accordance with the sheet size of the sheet so that the pin-putting section and the clinching section locate at a corner stapling position of the plurality of different corner stapling positions,
• wherein the pin-putting section rotates to a predetermined angle around the axis of rotation coinciding with the center of the staple pin at the corner stapling position at the one side of the sheet conveyance path and the clinching section rotate to the same angle as the predetermined angle around the axis of rotation coinciding with the center of the staple pin at the corner stapling position at the other side of the sheet conveyance path so that the driving mechanism and the receiving mechanism staple a pin diagonally at the corner position of the sheets.