Sheet finishing method, sheet finisher and image forming apparatus for use therewith

A sheet finisher comprising:

• (a) a sheet placement table on which sheets delivered and conveyed from an image forming apparatus main body, are stacked;
• (b) a folding device for folding the stacked sheets which have been positioned and aligned, a folding device comprising paired folding rollers and a folding plate;
• (c) a detector for detecting the number of sheets stacked;
• (d) a first driving device for rotating the paired folding rollers;
• (e) a second driving device for making the folding plate to advance or retreat;
• and
• (f) a controller for controlling the first driving device and the second driving device,
• wherein the controller controls the first driving device and the second driving device such that a rotation motion of the paired folding rollers is switched between a first state wherein the paired folding rollers are rotated and the folding plate is advancing and a second state wherein the paired folding rollers are stopped and the folding plate is advancing, the switching between the first state and the second state, in accordance with the number of sheets stacked on the sheet placement table.

An image forming apparatus comprising:

• an image forming apparatus main body composed of an image writing station, and sheet conveying station;
• and
• a sheet finisher comprising:
• (a) a sheet placement table on which sheets delivered and conveyed from an image forming apparatus main body, are stacked;
• (b) a folding device for folding the stacked sheets which have been positioned and aligned, a folding device comprising paired folding rollers and a folding plate;
• (c) a detector for detecting the number of sheets stacked;
• (d) a first driving device for rotating the paired folding rollers;
• (e) a second driving device for making the folding plate to advance or retreat;
• and
• (f) a controller for controlling the first driving device and the second driving device,
• wherein the controller controls the first driving device and the second driving device such that a rotation motion of the paired folding rollers is switched between a first state wherein the paired folding rollers are rotated and the folding plate is advancing and a second state wherein the paired folding rollers are stopped and the folding plate is advancing, the switching between the first state and the second state, in accordance with the number of sheets stacked on the sheet placement table.