Sheet finisher with sheet folding capability and image forming system using the same

A sheet finisher for finishing a sheet or a sheet stack conveyed thereto and each carrying an image thereon, said sheet finisher comprising:

• a path along which the sheet or the sheet to be finished is conveyed;
• a sheet folding device configured to fold the sheet or the sheet stack conveyed along said path;
• and
• sheet discharging means for discharging the sheet or the sheet stack folded by said folding device;
• said sheet 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 perpendicular to said path for forming a fold in the sheet or the sheet stack;
• a pair of first rotatable fold rollers facing said fold plate and positioned one above the other;
• and
• 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.

An image forming apparatus comprising:

• toner image forming means for forming a toner image on a sheet;
• and
• a sheet folding device for folding the sheet or a sheet stack driven out of said toner image forming means and each carrying a toner image thereon;
• said sheet 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 perpendicular to said path for forming a fold in the sheet or the sheet stack;
• a pair of first rotatable fold rollers facing said fold plate and positioned one above the other;
• and
• 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.

A sheet folding device for folding a sheet or a sheet stack, said sheet folding device comprising:

• a pair of first fold rollers configured to form a fold in the sheet or the sheet stack;
• a fold plate configured to contact the sheet or the sheet stack substantially perpendicularly to a surface of said sheet or said sheet stack for thereby pushing said sheet or said sheet stack into a nip between said pair of first fold rollers;
• and
• first support means supporting said pair of first fold rollers such that said pair of first fold rollers have, when not folding the sheet or the sheet stack, the nip positioned on a locus of movement of said fold plate or an extension of said locus or are movable, when folding said sheet or said sheet stack, substantially symmetrically to each other with respect to said locus or said extension.

A sheet finisher comprising:

• stapling means for stapling a sheet stack;
• and
• a sheet folding device configured to fold the sheet stack stapled by said stapling means;
• said sheet folding device comprising:
• a pair of first fold rollers configured to form a fold in the sheet or the sheet stack;
• a fold plate configured to contact the sheet or the sheet stack substantially perpendicularly to a surface of said sheet or said sheet stack for thereby pushing said sheet or said sheet stack into a nip between said pair of first fold rollers;
• and
• first support means supporting said pair of first fold rollers such that said pair of first fold rollers have, when not folding the sheet or the sheet stack, the nip positioned on a locus of movement of said fold plate or an extension of said locus or are movable, when folding said sheet or said sheet stack, substantially symmetrically to each other with respect to said locus or said extension.

An image forming system comprising:

• an image forming apparatus configured to form a toner image on a sheet;
• and
• a sheet finisher constructed integrally with or operatively connected to said image forming apparatus for finishing the sheet carrying the toner image formed by said image forming apparatus;
• said sheet finisher comprising:
• stapling means for stapling a sheet stack;
• and
• a sheet folding device configured to fold the sheet stack stapled by said stapling means;
• said folding device comprising:
• a pair of first fold rollers configured to form a fold in the sheet or the sheet stack;
• a fold plate configured to contact the sheet or the sheet stack substantially perpendicularly to a surface of said sheet or said sheet stack for thereby pushing said sheet or said sheet stack into a nip between said pair of first fold rollers;
• and
• first support means supporting said pair of first fold rollers such that said pair of first fold rollers have, when not folding the sheet or the sheet stack, the nip positioned on a locus of movement of said fold plate or an extension of said locus or are movable, when folding said sheet or said sheet stack, substantially symmetrically to each other with respect to said locus or said extension.

A sheet folding device for folding a sheet or a sheet stack by causing a fold plate to contact a surface of said sheet or said sheet stack substantially perpendicularly to said surface and press said sheet or said sheet stack into a nip between a pair of fold rollers, said sheet folding device comprising:

• a pair of first members respectively supporting the pair of fold rollers independently of each other;
• support portions respectively supporting said pair of first members such that said pair of first members are angularly movable;
• a pair of first elastic members respectively constantly biasing said pair of first members to thereby exert relatively weak pressing forces on the pair of fold rollers;
• a pair of second members respectively angularly movably supported by said support portions and respectively pressing said pair of first members at intermediate portions thereof to thereby exert pressing forces on the pair of fold rollers;
• a second elastic member constantly biasing said pair of second members toward each other to thereby exert relatively strong pressing forces on the pair of fold rollers;
• a third member connecting said pair of second members to each other and controlling operations of said pair of second members for pressing said pair of first members;
• and
• a pressing force control member configured to cause said third member to operate in accordance with a condition in which the sheet or the sheet stack is conveyed;
• wherein said pair first members, said support portions, said pair of first elastic members, said pair of second members, said third elastic member and said third member are positioned substantially symmetrically with respect to a center of a path corresponding to a locus of movement of the fold plate.

A sheet finisher comprising:

• stapling means for stapling a center of a sheet stack;
• and
• a sheet folding device for folding the sheet stack stapled by said stapling means with a pair of rollers by conveying said sheet stack via a nip between said pair of rollers;
• said sheet folding device comprising:
• pressing means for pressing said pair of fold rollers to thereby apply a pressing force for folding the sheet stack;
• and
• pressure varying means for varying the pressing force in accordance with a condition in which the sheet stack is conveyed.

A sheet finisher comprising:

• stapling means for stapling a center of a sheet stack;
• and
• a sheet folding device for folding the sheet stack stapled by said stapling means by causing a fold plate to contact a surface of said sheet stack substantially perpendicularly to said surface and press said sheet stack into a nip between a pair of fold rollers;
• said folding device comprising:
• a pair of first members respectively supporting the pair of fold rollers independently of each other;
• support portions respectively supporting said pair of first members such that said pair of first members are angularly movable;
• a pair of first elastic members respectively constantly biasing said pair of first members to thereby exert relatively weak pressing forces on the pair of fold rollers;
• a pair of second members respectively angularly movably supported by said support portions and respectively pressing said pair of first members at intermediate portions thereof to thereby exert pressing forces on the pair of fold rollers;
• a second elastic member constantly biasing said pair of second members toward each other to thereby exert relatively strong pressing forces on the pair of fold rollers;
• a third member connecting said pair of second members to each other and controlling operations of said pair of second members for pressing said pair of first members;
• and
• a pressing force control member configured to cause said third member to operate in accordance with a condition in which the sheet stack is conveyed;
• wherein said pair first members, said support portions, said pair of first elastic members, said pair of second members, said third elastic member and said third member are positioned substantially symmetrically with respect to a center of a path corresponding to a locus of movement of the fold plate.

An image forming system comprising:

• an image forming apparatus for forming a toner image on a sheet;
• and
• a sheet finisher constructed integrally with or operatively connected to said image forming apparatus;
• said sheet finisher comprising:
• stapling means for stapling a center of a sheet stack;
• and
• a sheet folding device for folding the sheet stack stapled by said stapling means with a pair of rollers by conveying said sheet stack via a nip between said pair of rollers;
• said folding device comprising:
• pressing means for pressing said pair of fold rollers to thereby apply a pressing force for folding the sheet stack;
• and
• pressure varying means for varying the pressing force in accordance with a condition in which the sheet stack is conveyed.

An image forming system comprising:

• an image forming apparatus for forming a toner image on a sheet;
• and
• a sheet finisher constructed integrally with or operatively connected to said image forming apparatus;
• said sheet finisher comprising:
• stapling means for stapling a center of a sheet stack;
• and
• a sheet folding device for folding the sheet stack stapled by said stapling means by causing a fold plate to contact a surface of said sheet stack substantially perpendicularly to said surface and press said sheet stack into a nip between a pair of fold rollers;
• said folding device comprising:
• a pair of first members respectively supporting the pair of fold rollers independently of each other;
• support portions respectively supporting said pair of first members such that said pair of first members are angularly movable;
• a pair of first elastic members respectively constantly biasing said pair of first members to thereby exert relatively weak pressing forces on the pair of fold rollers;
• a pair of second members respectively angularly movably supported by said support portions and respectively pressing said pair of first members at intermediate portions thereof to thereby exert pressing forces on the pair of fold rollers;
• a second elastic member constantly biasing said pair of second members toward each other to thereby exert relatively strong pressing forces on the pair of fold rollers;
• a third member connecting said pair of second members to each other and controlling operations of said pair of second members for pressing said pair of first members;
• and
• a pressing force control member configured to cause said third member to operate in accordance with a condition in which the sheet stack is conveyed;
• wherein said pair first members, said support portions, said pair of first elastic members, said pair of second members, said third elastic member and said third member are positioned substantially symmetrically with respect to a center of a path corresponding to a locus of movement of the fold plate.