Sheet processing device, image forming system, and method of additionally folding sheet bundle

An image forming system including a sheet processing device, the sheet processing device comprising:

• a pressing device that presses a fold line part of a folded sheet bundle,
• a moving device that moves a pressing position of the pressing device in a fold direction of the folded sheet bundle, and
• the pressing device includes a first pressing roller arranged on one side of a thickness direction of the folded sheet bundle, and a second pressing roller and a third pressing roller arranged on another side across the fold line part of the folded sheet bundle, and the pressing device is arranged in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting a rotational center of the first pressing roller and a rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and a rotational center of the third pressing roller, wherein
• the second pressing roller and the third pressing roller are movable such that a distance between the rotational center of the second pressing roller and the rotational center of the third pressing roller changes only in the fold direction, and
• the fold direction is orthogonal to the thickness direction.

A method of additionally folding a folded sheet bundle, comprising:

• arranging a first pressing roller on one side of a thickness direction of the folded sheet bundle, and arranging a second pressing roller and a third pressing roller on another side of the thickness direction of the folded sheet bundle;
• holding a fold line part of the folded sheet bundle between the first pressing roller and the second and the third pressing rollers;
• moving the first, the second, and the third pressing rollers in a fold direction of the folded sheet bundle to additionally fold the fold line part of the folded sheet bundle in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting a rotational center of the first pressing roller and a rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and a rotational center of the third pressing roller;
• and
• moving the second pressing roller and the third pressing roller such that a distance between the rotational center of the second pressing roller and the rotational center of the third pressing roller changes only in the fold direction, wherein
• the fold direction is orthogonal to the thickness direction.