US Patent 7697184 Optical scanning device and image forming apparatus

An optical scanning device includes a polygon mirror, a beam detector, a correcting unit, and a controller. The polygon mirror deflects and scans a light beam in a main scanning direction on a surface of an image carrier. The beam detector detects a beam position of the deflected light beam in a sub-scanning direction. The correcting unit calculates a correction amount of out-of-color registration based on the beam position, and corrects out-of-color registration in the sub-scanning direction based on the correction amount. The controller controls, during correction of out-of-color registration, a deflection speed of the deflector to be less than a deflection speed for writing a latent image on the surface of the image carrier.