Sheet processing apparatus, sheet processing method, and image forming system

A sheet processing method comprising:

• performing a center-folding process, on a sheet bundle including multiple sheet materials, to form a fold portion in the sheet bundle,
• wherein the center-folding process comprises:
• guiding the sheet bundle with a folding plate in a first direction;
• nipping the sheet bundle at a nip position;
• advancing the sheet bundle in the first direction;
• and
• pressurizing a folding-roller pair toward the nip position in a second direction intersecting the first direction;
• forming a back portion on the sheet bundle subjected to the center-folding process;
• and
• responsive to completion of the center-folding process, performing a crimp-binding process on the back portion while forming the back portion on the fold portion of the sheet bundle,
• wherein the crimp-binding process comprises:
• engaging a folding-plate engagement member with the folding plate via the sheet bundle, and
• moving the folding-plate engagement member between:
• a retracted position at which the folding-plate engagement member is separated from the folding plate and an engagement position at which the sheet bundle is nipped between the folding plate and the folding-plate engagement member.

A sheet processing apparatus comprising:

• a center-folder to perform a center-folding process on a sheet bundle including multiple sheet materials, wherein the center-folder includes:
• a folding plate to guide a part of the sheet bundle in a first direction;
• a folding-roller pair to:
• nip the sheet bundle guided by the folding plate at a nip position;
• and
• advance the sheet bundle in the first direction;
• and
• a pressure mechanism to pressurize the folding-roller pair toward the nip position in a second direction intersecting the first direction;
• a back-crimp binder to:
• form a back portion on the sheet bundle subjected to the center-folding process;
• and
• perform a crimp-binding process on the back portion;
• and
• a controller configured to:
• cause the center-folder to perform the center-folding process;
• and
• responsive to completion of the center-folding process, cause the back-crimp binder to perform the crimp-binding process on the back portion while forming the back portion on the sheet bundle in the crimp-binding process,
• wherein the back-crimp binder includes a folding-plate engagement member to engage with the folding plate via the sheet bundle,
• the controller moves the folding-plate engagement member between:
• a retracted position at which the folding-plate engagement member is separated from the folding plate and an engagement position at which the sheet bundle is nipped between the folding plate and the folding-plate engagement member,
• wherein the back-crimp binder includes:
• a folding-plate-engagement heater including a heater to heat the sheet bundle and press the sheet bundle against the folding plate, and
• the folding-plate-engagement heater heats an adhesive medium in an adhesive portion of the sheet bundle.