| 摘要 |
PURPOSE:To enable the measuring of a moving speed at a high accuracy, by making a parallel diffraction light irradiate the surface of an object to be measured with the action of a first convex lens, a light shielding plate and a second convex lens. CONSTITUTION:When a parallel laser light is generated from a laser light source 22, a direct light (0-order light) passing intact through a slit of a diffraction grating 23 and primary, secondary lights... diffracted with the slit are emitted to a first convex lens 24. As these 0-order, primary lights and the like are parallel laser lights, they are diffracted with the lens 24 to be focusing at a position equivalent to a focal length of the lens 24. A light shielding plate 25 is arranged at the position and provided with a pair of transmitting holes to let the primary light alone pass. So, a pair of primary lights alone are made incident into a secondary convex lens 26 and diffracted to be emitted as a pair of parallel laser lights LB1 and LB2. The laser lights LB1 and LB2 interfere with each other to form a interference fringe on the surface of an object M to be measured. The scattered light with the interference fringe is processed 50 through a light receiver 40 to be detected as moving speed of the object M.
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