| 摘要 |
PURPOSE:To reduce the loss of the quantity of light and stray light due to reflection, and to facilitate manufacture by composing a main scale of a light transmitting member which has V-shaped grooves at equal intervals perpendicularly to a measurement direction. CONSTITUTION:An index scale 3 is provided in opposition to the main scale 1; luminous flux from a light source 4 is collimated by a collimator lens 5 and reaches the main scale 1, and transmitted luminous flux reaches photodetecting elements 6a and 6b, which generate output signals. The main scale 1 has the V- shaped grooves at equal intervals perpendicularly to the lengthwise directions, and two slanting surfaces 1a and 1b slant at a specific angle theta to constitute a prism made of a transparent material with a vertical angle theta. When luminous flux is made incident at right angles, pieces of projected parallel luminous flux from the slanting surfaces of each groove are diffracted to the opposite directions at an equal angle to obtain light parts (11a, 11b, 11c-) of width P/2 and dark parts of width P/2 alternately at specific intervals P, forming a corresponding light/dark grading on the main scale. |
