| 摘要 |
PURPOSE:To prevent an error due to deviation, by forming two slits to the first plate fixed to a housing and displacing the same by a scheduled displacement amount detected by the other encoder to irradiate a cord wheel to etch the same. CONSTITUTION:A phase plate 3 having two slits 2 at predetermined positions thereof is fixed to the recessed part 1a of a housing 1 and the slits 2 are irradiated with a laser beam irradiation means 13. A cord wheel 7 is provided to the under side of the plate 3 in the recessed part 1a in a freely rotatably manner and rotated by a servo motor 9 through a shaft 5. A control means 12 reads the displacement amount preset to an encoder 10 and the cord wheel 7 is stepped by the servo motor 9. The laser beam irradiation means 13 is energized in synchronous relation to stepping and the cord wheel 7 is exposed to the slit images of the phase plate 3 to a light passing region. By this method, the encoder free from a detection error due to the deviation or the irregularity in phase difference is obtained. |
