| 摘要 |
PURPOSE:To enable satisfactory writing for all times by detecting independently two light beams related to the main scan of the respective line. CONSTITUTION:First of all, with regard to a deflection of a light beam, when a rotary polygon mirror 16 is rotated in the direction as indicated with an arrow by turning off a semiconductor laser 10B for giving the succeeding light beam, and turning on only a semiconductor laser 10A, the preceding light beam is made incident on a photodetector 22 and detected. In this way, when the preceding light beat is detected, the semiconductor laser 10A is turned off, and simultaneously, the semiconductor laser 10B is turned on. As a result, detection of the preceding light beam is delayed a little, and a light beam from the succeeding light beam is detected. In such a way, the light beams from the semiconductor lasers 10A, 10B are detected independently, respectively, by the same photodetector 22, prior to the main scan. Accordingly,by setting the timing of the main scan at every light beam, each light beam can make the origin of its main scan uniform correctly.
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