| 摘要 |
PURPOSE:To form a rotational speed detector highly accurately and comparatively easily by forming a detector for detecting a projected part from the inscribed cylinder formed on the mirror surface of a rotary polygon mirror to the outside to detect the rotational speed of the rotary polygon mirror on the basis of the number of oscillated detecting signals per fixed period. CONSTITUTION:A transmission type detecting means 2 consisting of a light source 2-1 and a photodetector 2-2 is arranged on a position where its optical axis 2-3 is arranged on a surface rectangular to the rotary shaft 3 of the rotary polygon mirror 1 and a distance from the rotary shaft 3 is set up to the length between the radius of a virtual inscribing circle and a ridge line. When the rotary polygon mirror 1 is rotated, a state interrupting the optical axis 2-3 of the detecting means 2 by a projection part P and a state photodetecting the optical axis 2-3 by a photodetector 2-2 without interruption by the projection part P are periodically repeated and a signal is generated in each period. Thus, the rotational speed of the rotary polygon mirror can be accurately detected on the basis of the number of oscillated signals per unit period. |
