| 摘要 |
PURPOSE:To obtain a small-sized and highly accurate tachometer reducing influence due to the eccentricity of a radiation grating by making the diffracted light obtained from light flux made incident upon the radiation grating formed on the periphery of a disc again incident upon the radiation grating to diffract the incident light and reducing the load of a rotary substance to be tested. CONSTITUTION:Light flux is made incident from a light source 1 upon the radiation grating 5 obtained by forming a grating pattern consisting of light transmission parts and reflection parts on the periphery of the disc at equal angles. Two diffracted light rays having specific degrees out of the diffracted light reflected and diffracted by the radiation grating 5 are reflected by reflectors 41, 42, 41', 42' and the reflected light rays are again made incident upon a position of the radiation grating 5 which is approximately point-symmetrical with the incident position of the initial light flux about the rotation center of the rotary substance. The two diffracted light rays diffracted again and having specific degrees are superposed, divided into two light flux components by a polarized beam splitter 8 and then detected by two photodetecting elements 9, 9'. The outputs of the elements 9, 9' are differentially amplified and the amplified output is converted into a binary value through a comparator or the like. The binary signal is analyzed at its frequency to find out the frequency, so that the displacement of the rotation speed of the rotary body can be obtained on the basis of the frequency. |
