US Patent 7742189 Optical scanning apparatus

Data concerning misalignment of beams is measured and held in an optical scanning apparatus before the optical scanning apparatus is incorporated in an image forming apparatus. The optical scanning apparatus includes a light source for emitting multiple beams, an optical lens for converting the multiple beams to parallel lights and a rotating polygon mirror for rotary-deflecting the multiple beams. Furthermore, the measurement apparatus measures main scanning direction misalignment among the multiple beams on a photosensitive member provided for the image forming apparatus, which has been determined by detecting the multiple beams from the rotating polygon mirror (and an fθ lens). The optical scanning apparatus includes a holding unit for holding the data concerning misalignment. The image forming apparatus in which the optical scanning apparatus is incorporated corrects the misalignment with the use of the data concerning misalignment inputted directly or indirectly from the holding unit.