Sheet folding method, image forming system, and sheet folding device with motor employing being controlled to perform a feedback control with an integral gain

A sheet folding method, comprising:

• conveying the sheet by a first sheet conveyor, driven by a first motor, toward a downstream side of a sheet conveying direction;
• receiving the sheet conveyed from the first sheet conveyor;
• conveying the sheet by a second sheet conveyor, driven by a second motor, toward the downstream side of the sheet conveying direction;
• setting a folding length of the sheet according to an amount of conveyance of the sheet conveyed by the second sheet conveyor while holding the sheet by the first sheet conveyor and the second sheet conveyor;
• performing a feedback control with an integral gain to control the second motor to rotate the second sheet conveyor in a reverse direction;
• and
• folding the sheet to the folding length set.

A sheet folding device comprising:

• a first drive motor;
• a first sheet conveyor drivable by the first drive motor, the first sheet conveyor configured to receive a sheet and configured to convey the sheet toward a downstream side of a sheet conveying direction;
• a second drive motor;
• a second sheet conveyor drivable by the second drive motor, the second sheet conveyor configured to receive the sheet conveyed from the first sheet conveyor and configured to convey the sheet further to the downstream side of the sheet conveying direction;
• a third drive motor;
• a third sheet conveyor drivable by the third drive motor;
• and
• a controller configured to stop the second drive motor and configured to rotate the third sheet conveyor and fold the sheet to a folding length set according to an amount of conveyance of the sheet by the second sheet conveyor while the sheet is being held between the first sheet conveyor and the second sheet conveyor, the controller being configured to perform a feedback control with an integral gain to control the third drive motor.