| 摘要 |
PURPOSE:To improve the precision of speed control, by arranging a fixed mask, which has the same pitch as patterns or a pitch similar to that of patterns, on the optical axis connecting a light emitting element, patterns on a rotary disc, and a photodetector. CONSTITUTION:Reflective patterns 7 are provided at a prescribed pitch throughout the circumferential edge part of one light-absorptive face of a rotary disc 6 fixed to a revolving shaft 5. A fixed mask 8 is fixed on the front face near a part of patterns 7 independently of the rotation of the rotary disk 6 by a proper method, and light-absorptive patterns 9 which have the same shape and the same pitch as patterns 7 are provided on the fixed mask 8. These patterns 7 and 9 are irradiated by a light emitting element 10, and the interrupted light reflected by patterns 7 on the rotary disc 6 is received by a photodetector 11. |
