Light beam scanning apparatus employing beam modulation in accordance with the start of scan and end of scan signals

摘要

A light beam scanning apparatus is constituted for scanning a light beam deflected by a rotating polygon mirror on a scanning surface in a main scanning direction, moving the scanning surface with respect to the light beam in a subscanning direction, and generating a picture element clock signal. The light beam scanning apparatus comprises photodetectors for respectively detecting passage of the light beam over a main scanning start point and passage thereof over a main scanning end point, and a clock signal generating circuit for receiving outputs of the photodetectors, calculating the time required for the main scanning for each of the mirror surfaces of the rotating polygon mirror, and changing a period of the picture element clock signal in the course of each main scanning so that the period is proportional to the required time with respect to the mirror surface utilized for the main scanning.