| 摘要 |
PROBLEM TO BE SOLVED: To prevent a color smear caused by that distances between a laser scanner unit and a photosensitive body are dispersed in each color due to fitting errors and temp. fluctuation and scanning speeds on the photosensitive body are dispersed. SOLUTION: A photosensitive body top aperture detection detector 11, a photosensitive body central aperture detection detector 12 and a photosensitive body rear aperture detection detector 13 detects respectively the apertures provided in the vicinity of a laser beam scan start end part of a photosensitive body belt, on the vicinity of the central part and on the vicinity of the terminal end. A horizontal synchronizing signal detection detector 20 exists in the laser scanner unit, and detects a laser beam scan start. A counter circuit 16 counts the time to pulses outputted from the photosensitive body top aperture detection detector 11, the photosensitive body central aperture detection detector 12 and the photosensitive body rear aperture detection detector 13 based on the pulse outputted from the horizontal synchronizing signal detection detector 20. A CPU 14 compares these values with a prescribed value to calculate a clock frequency to be outputted from a clock generator 15.
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