| 摘要 |
PURPOSE:To measure an accurate moving distance by detecting the diffracted light caused by laser light projected on the scale through a lens, a plurality of light receiving elements, and the optical scale which are arranged so as to satisfy a specified relationship. CONSTITUTION:The luminous flux from a laser diode 1 is converged by a lens L1 and further converged by a lens L2 and projected on the scale 2 having a scale grid with an equal interval. The zero and linear diffracted lights are reflected by the half mirror M via a stop and the like and inputted to a light detector 3 comprising four light receiving elements A-D. Its outputs are inputted to a control circuit 4. A moving distance signal PA and a moving direction signal PB are sent to a display 5. With the center of the lens L2 as an original point, the equation H=fYd/(f-Yd) is satisfied, where (f) is the focal length of the lens L2, Yd is the Y coordinate of a light receiving surface, H is the image position of the projected light, and (h) is the Y coordinate of the reflecting surface of the scale 2. Since the pitch of interference fringes is not related to an operating distance (h), the accurate moving distance is measured. |
