Sheet processing apparatus and image forming system

A sheet processing apparatus comprising:

• an inlet portion configured to receive a sheet discharged from an image forming apparatus;
• an accumulation portion configured to accumulate sheets;
• a conveyance unit configured to convey the sheet received from the inlet portion to the accumulation portion;
• a saddle binding unit configured to perform a saddle binding process on a sheet bundle including a plurality of sheets accumulated in the accumulation portion;
• a half-folding processing unit including a folding roller pair and a pressing portion and configured to perform a half-folding process on the sheet bundle, the folding roller pair being configured to perform half-folding on the sheet bundle by conveying the sheet bundle while nipping the sheet bundle such that a spine of the sheet bundle is positioned downstream of a fore edge of the sheet bundle, the pressing portion being configured to press the sheet bundle, subjected to the saddle binding process by the saddle binding unit, toward a nip portion of the folding roller pair;
• a conveyance roller pair configured to nip and convey the sheet bundle subjected to the half-folding process by the half-folding processing unit;
• and
• a square back processing unit including a pair of clamp portions configured to relatively move with respect to the sheet bundle conveyed by the conveyance roller pair and thus nip the sheet bundle or release nipping of the sheet bundle and a pressing roller provided downstream of the pair of clamp portions in a conveyance direction of the conveyance roller pair and configured to press the spine of the sheet bundle nipped by the pair of clamp portions toward the pair of clamp portions,
• wherein the square back processing unit is configured to perform a square back process in which a corner is formed on the spine of the sheet bundle by pressing, by the pressing roller, the spine of the sheet bundle nipped by the pair of clamp portions such that the spine of the sheet bundle protrudes downstream in the conveyance direction with respect to the pair of clamp portions,
• wherein a length of a conveyance path from the folding roller pair to the pair of clamp portions is larger than a half of a length of a long side of a sheet of a maximum size capable of being subjected to the square back process by the square back processing unit, and
• wherein in a state in which conveyance by the conveyance roller pair of a first sheet bundle to be subjected to the square back process is stopped, the conveyance unit is configured to convey at least one sheet included in a second sheet bundle subsequent to the first sheet bundle toward the accumulation portion.