| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of interval unevenness in a subscanning direction caused by the rotational unevenness of a photosensitive drum at the time of the scanning the photosensitive drum by a laser beam by detecting the rotational speed of the photosensitive drum and controlling the rotational speed of a rotary polygon mirror according to the detected rotational speed. SOLUTION: The photosensitive drum 1 is provided with barcode shaped marks 21 for detecting the rotational speed at the scanning position of a laser beam on the circumference of the photosensitive drum 1 out of an image area. A photosensor 20 outputs a periodic signal corresponding to the barcode-shaped marks 21 by emitting a light beam on the marks 21 and by receiving the reflected light. The output of the optical sensor 20 is converted into a speed signal V1 in a frequency to speed converter 22 to be outputted to a rotation control circuit 23. In the rotation control circuit 23, a pulse signal PLS corresponding to the speed signal V1 is outputted to a motor driving circuit 17, which rotates a polygon motor 11 in synchronization with the pulse signal PLS and rotates a polygon mirror 12 with the speed corresponding to the rotational speed of the photosensitive drum 1. |
