Postprocessing device that matches moving speed of tip portion of folding blade with moving speed of circumferential surface of pair of folding rollers, at predetermined timing

A postprocessing device comprising:

• a pair of folding rollers that form a nip region by being pressed against each other, and pinch and fold a sheaf of the sheets, by rotating in opposite directions to each other;
• a folding blade supported so as to move toward and away from the nip region at predetermined moving speed, and configured to squeeze the sheaf of the sheets into the nip region;
• a transport device that transports the sheets to a position between the nip region and the folding blade;
• a drive portion that moves the folding blade toward and away from the nip region;
• and
• a drive controller configured to control an operation of the drive portion,
• the drive controller being configured to control the operation of the drive portion to match the moving speed of a tip portion of the folding blade with moving speed of a circumferential surface of the pair of folding rollers, at a time point that the sheaf of the sheets makes contact with the circumferential surface of the pair of folding rollers,
• wherein the drive portion includes:
• a contact roller located at an end portion of the folding blade;
• a rotary cam formed in such a shape that a radius between a rotation center and a cam surface is different, depending on a position on the cam surface, and configured to move the folding blade toward and away from the nip region, by rotating to move the contact roller along the cam surface;
• and
• a motor that drives the rotary cam so as to rotate, and
• the drive controller is configured to:
• identify in advance a position on the cam surface of the rotary cam to be contacted by the contact roller, at a time point that the sheaf of the sheets makes contact with the circumferential surface of the pair of folding rollers;
• calculate rotation speed of the rotary cam that matches the moving speed of the tip portion of the folding blade with the moving speed of the circumferential surface of the pair of folding rollers, at the time point that the sheaf of the sheets makes contact with the circumferential surface of the pair of folding rollers, on a basis of the radius of the rotary cam between the rotation center and the identified position on the cam surface and a rate of change of the radius;
• and
• control operation of the drive portion, on a basis of the rotation speed calculated.