Patent ID: 7528363

Claim:
An image forming apparatus comprising: a plurality of optical scanners, each including a rotating polygon mirror, the mirror having weight imbalance and weight imbalance direction that scans and exposes a surface of an image bearing medium to create an electrostatic latent image on the surface in accordance with image data; a plurality of phase detectors, each assigned to a respective optical scanner to detect rotated phases of the rotating polygon mirrors; and a rotated phase controller that controls the rotated phases of the rotating polygon mirrors, wherein the rotated phase controller controls the rotated phases of the rotating polygon mirrors in accordance with results of detection by the plurality of rotated phase detectors so that a relationship of the weight imbalance direction of each of the polygon mirrors is set in a predetermined pattern to reduce vibration of the optical scanners which is caused by weight imbalance of the polygon mirrors, wherein the rotated phase controller controls the rotated phases of the rotating polygon mirrors in accordance with the result of detection in a unit of one surface of the rotating polygon mirror so that the relationship of the weight imbalance direction of each of the polygon mirrors is set in the predetermined pattern and wherein, after controlling the rotated phases of the rotating polygon mirrors in the unit of one surface, the rotated phase controller controls the rotated phases of the rotating polygon mirrors in accordance with color misregistration data in a unit of not greater than one surface of the rotating polygon mirror.