Patent ID: 6989851

Claim:
A light beam scanning apparatus comprising: light beam emitting means for outputting a plurality of light beams; a beam scanner for reflecting the light beams output from said light beam emitting means towards a to-be-scanned surface to scan the to-be-scanned surface by use of the light beams in a main scanning direction; a beam position detector including a first beam sensing section for detecting all of the light beams scanned on the to-be-scanned surface by said beam scanner, said beam position detector generating an output signal whose level is continuously changed with a variation in the passage position in a sub-scanning direction perpendicular to the main scanning direction of the light beams; passage detecting means including a second beam sensing section arranged on the upstream side in the main scanning direction of the light beams with respect to the first beam sensing section of said beam position detector, said passage detecting means detecting the passage of the light beams scanned by said beam scanner and generating a timing signal, and the size of the passage detecting means in the sub-scanning direction being larger than that of the first beam sensing section; level shift means for shifting a level of an output signal of said beam position detector; integration means for starting integration of the output signal of said beam position detector shifted by said level shift means, the integration being started in response to the timing signal supplied by said passage detecting means; and a controller for controlling each position of the light beams scanned by said beam scanner on the to-be-scanned surface to be in a preset position based on an output signal of said integration means.