Patent ID: 7336921

Claim:
A sheet folding device for folding a sheet or a sheet stack conveyed thereto, said folding device comprising: a path along which the sheet or the sheet stack to be folded is conveyed; a fold plate movable in a direction substantially perpendicular to said path for forming a fold in the sheet or the sheet stack; tie bars; a movable shaft; a pair of first rotatable fold rollers facing said fold plate, positioned one above the other, and connected by the tie bars to the movable shaft; pressing means for exerting, when the fold is to be formed, a pair of equal pressing forces on said pair of first fold rollers to thereby maintain a nip between said pair of first fold rollers on a line including a locus of movement of said fold plate; pressure varying means for varying the pressing force in accordance with a condition in which the sheet stack is conveyed; and first support means supporting said pair of first fold rollers, wherein said pair of first fold rollers have the nip positioned on the locus of movement of said fold plate or an extension of said locus when not folding the sheet or the sheet stack and wherein the pair of first fold rollers are movable substantially symmetrically to each other with respect to said locus or said extension when folding said sheet or said sheet stack.