| 摘要 |
PURPOSE:To accurately detect a rotary speed, by a method wherein luminous flux is allowed to irradiate the light reflective member of an inside rotor to be reflected therefrom and the reflected luminous flux is received to generate a light receiving signal while a high frequency component is removed from the light receiving signal to generate a rotary signal. CONSTITUTION:A rotary speed measuring apparatus has light reflective plates 35A, 35B, 35C... constituted so that luminous flux 32 from a light source 30 is turned ON/OFF at a cycle slower than a blocking cycle by twisters 22 according to the rotation of an over-twister 26. Luminous fluxes reflected by the light reflective plates 35A, 35B, 35... are received to generate a light receiving signal and the high frequency component of the output of an amplifier 38 is removed from said receiving signal at cut-off frequency fC by a low pass filter 40. The ratio of the rotary speed No of the over-twister 26 and the rotary speed Nt of the twister 22 of the output of a twister tachometer 46 is calculated by a divider 48 to calculate a rotary ratio and a rotary speed can be detected accurately by relatively simple constitution.
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