| 摘要 |
PURPOSE:To take a precise measurement without using any long-sized ladder pattern having high precision and high density by providing a moving body with surfaces which have patterns differing in light reflection factor, and measuring the period of variation in the light intensity of reflected light passed through a grating-shaped filter. CONSTITUTION:A platen 10 and a photosensitive body 11 are provided with random patterns 14 and 15. Light beams from light sources 16 and 17 are reflected by the random patterns 14 and 15 to form images on grating-shaped filters 20 and 21 through image-forming lenses 18 and 19. The intensities of the light beams passed through the grating-shaped filters 20 and 21 vary periodically at a frequency f(Hg) shown by an equation, where the lateral magnification of the optical system consisting of the image-forming lenses 18 and 19 is (m), the moving speed of the platen 10 and photosensitive body 11 is nu, and the pitch of gratings is (p). The frequency (f) is outputted as speed signals 24 and 25 from photodetectors 22 and 23 to measure the speed of the platen 10 and photosensitive body 11. |
