| 摘要 |
PURPOSE:To exactly arrange a start position for writing a picture to a photosensitive body, by providing a means for guiding so that a laser beam always passes through a regular position of a photodetecting element placed in the proximity of the start position for writing a picture, between a deflecting device and the photodetecting element. CONSTITUTION:A cylindrical lens 30 is placed between a rotary polyhedral mirror 6 and a photodetecting element 11, and is constituted so that a laser beam always passes through a regular position of the photodetecting element 11. Accordingly, even if a deflection angle of each mirror 7-7e of the rotary polyhedral mirror 6 is different respectively, a locus Lx of a laser beam passing through the photodetecting element 11 becomes always constant at every scanning. In this way, the waveform of a synchronization detecting signal generated when the photodetecting element 11 has detected a laser beam becomes constant at all times, and the generation time of a picture signal becomes constant at every scanning, therefore, the start position for writing a picture to a photosensitive body 12 becomes constant, and the quality of a copying picture is elevated. |
