Sheet folding device, image forming system, and sheet folding method

An image forming system comprising:

• an image forming device that forms a visible image on a sheet member;
• and
• a sheet folding device
• that performs a folding process on one of a sheet member and a bundle of sheet members and
• that includes:
• a folding unit that folds the one of the sheet member and the bundle of the sheet members;
• a pushing unit
• that is formed like a plate and
• that abuts on a surface of the one of the sheet member and the bundle of the sheet members so as to push the one of the sheet member and the bundle of the sheet members into the folding unit;
• pressing plates
• that are provided to form a pair,
• that have convexly curved surfaces to face each other, and
• that form a crease at a center portion of the one of the sheet member and the bundle of the sheet members by interposing and pressing the one of the sheet member and the bundle of the sheet members having been pushed into the folding unit therebetween;
• a driving unit that performs a pressing operation and a press-releasing operation of the pair of the pressing plates;
• a moving unit that moves a pressing position of the pair of the pressing plates interposing the one of the sheet member and the bundle of the sheet members;
• and
• a control unit that controls the driving unit and the moving unit, wherein
• the control unit controls a moving speed of the pressing position moved by the moving unit.

A sheet folding method comprising:

• pushing performed by a plate-like pushing unit that pushes one of a sheet member and a bundle of sheet members into a folding unit by abutting on a surface thereof;
• interposing the one of the sheet member and the bundle of the sheet members having been pushed into the folding unit by the pushing between a pair of pressing plates whose mutually facing surfaces are convexly curved to each other, pressing a pressed position interposed between the pair of the pressing plates while the pressed position is being moved, and forming a crease at a center portion of the one of the sheet member and the bundle of the sheet members;
• and
• changing a moving speed of the pressed position based on sheet information that includes at least one of number of the sheet members, thickness of the sheet members, and a size of the sheet members when the crease is formed by the forming.