| 摘要 |
PURPOSE:To prevent position shift of an exposure beam even if the speed of an image forming body is irregular by detecting the irregularity in the speed of said body and moving a write device based on a signal generated in said detection. CONSTITUTION:A rotation speed detector 11 detects the rotation speed of the photosensitive body 7, transmitting an obtained frequency signal to an arithmetic operation part 20 to rotate a motor 22 so that a light emitting unit 24 is carried in parallel moving. At the time when the unit 24 in a position A, a laser beam is scanning just the position of (a) on the photosensitive body 7, however, if the unit 24 is moved to a position B, the laser beam moves on the body 7 for the same length as that the unit 24 moves and scans a position (b). The length of said moving is determined from an irregular-speed frequency at which a streak tends to appear and its magnitude. In such a way, the positional shift of an exposure beam even if the speed of an image forming body is irregular, and the occurrence of a periodic streaks on a halftone image can be prevented.
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