| 摘要 |
PURPOSE:To set easily, speedily, and automatically an absolute origin by operating a resetting means which normally resets an isolating means which isolates an origin mark and an origin detecting means in a viewing state. CONSTITUTION:The resetting means 26 is fitted threadably at a position corresponding to the origin mark 20 as the absolute origin. Then, a slider 14 moves according to the movement of a detecting mechanism 38 for a head 40 and when it reaches the means 26, its base 24c abuts on the tip of the spherical shape of the means 26, so that the bent plate type isolating means 24 is displaced upward elastically. Therefore, the tip part of a means 24 which covers a light emitting body 30 moves up and an adjacent cut comes to the position of the light emitting body 30. Output light from the light emitting body 30, therefore, reaches a photodetector 32 through a mark 20 on a main scale 12 and an optical grating scale 28 for detection on an index scale 16, so that the overlap of the mark 20 and scale 28 is detected by an electric circuit 34. Then, the detection of the absolute origin, i.e. the setting of a zero point is performed on the basis of the detection signal. |
