| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the need for the maintenance of a light source and to secure a long detection distance by providing a laser fight emitting element at the focal location of a lens for condensation along its optical axis and a light receiving element to receive reflected light on the side of the lens along the optical axis of the lens. SOLUTION: In the case of detecting the number of revolutions of a motor, laser light which widens to some degree to the lower side of a lens part 11 is shined as a spot from a laser light emitting element 9 in such a way as to avoid a laser light receiving element 10 provided in the front to irradiate a reflecting tape adhered to a rotating coupling through the lens part 11. The light reflected by the reflecting tape is condensed onto the light receiving surface of the light receiving element 10 on the optical axis through the lens part 11 and is received as a pulse-shaped waveform at the light receiving element 10. The pulse waveform is shaped and guided to a part for computing the amount of displacement to count rising periods of pulses. Then the period is computed form a count period and a count value, and the number of revolutions is obtained from back calculation.
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