| 摘要 |
<p>The front end portion of a rotational blade (54) is accurately located in a non-contact manner although the quantity of wear of the blade (54) has been changed. The structure (10) is so arranged that a pair of prisms (36, 38) are disposed to oppose each other at a predetermined interval, either (36) of the two prisms (36, 38) converges light beam emitted from a light emitting diode (16) within a predetermined interval, and the residual prism (38) again converges the light beams which have been diffused after they have been converged. A photodiode (23) receives beams converged by the other prism (38). The disturbance light and noise are eliminated by an amplifier (22) so as to fetch only light emitted from the light emitting diode (16). A blade (54) shields light beams converged at the central portion located at a predetermined interval, while reading devices (45A, 45B) read the quantity of light received by the photodiode (23) and as well as read the displacement of the blade. A comparator (74) transmits a signal when the quantity of light received by said photodiode (23) agrees with a predetermined value which has been previously stored, so that the front position of the blade (54) is located to correspond to the wear and the like. <IMAGE></p> |
