Patent ID: 7835040

Claim:
An optical scanning apparatus which performs main scanning on a surface of an image bearing member with light beams, and moves light beams in a sub-scanning direction by rotating the image bearing member, comprising: an optical unit adapted to collimate optical axes of light beams emitted from a plurality of semiconductor lasers; a driving unit adapted to drive said optical unit to change directions of emerging light beams; a detection unit adapted to detect a beam interval between a plurality of light beams collimated by said optical unit; a first control unit adapted to drive/control said driving unit to make a beam interval detected by said detection unit become a predetermined value; a period detection unit adapted to detect a rotation period of the image bearing member; an error calculation unit adapted to calculate an error between a period detected by said period detection unit and a reference period; and a second control unit adapted to change the directions of the light beams by driving said driving unit in a direction to cancel out a variation in sub-scanning pitch by the light beams which corresponds to an error calculated by said error calculation unit.