| 摘要 |
PROBLEM TO BE SOLVED: To smoothly perform the automatic operation of a crane by setting a threshold for swing judgment according to the degree of contamination of a reflecting plate in the judgment of swing of a hoisting accessory by a swing detecting means for judging the shaking of the hoisting accessory on the basis of the received light intensity of a light receiving means for detecting a reflected light beam. SOLUTION: A photoelectric switch 21 provided on a crane body 10 has an optical beam emitting means, a reflecting plate 22 is provided on the upper surface of a hoisting accessory 13 suspended from the crane body 10, and the optical beam reflected thereby is received by a light receiving device. When the light receiving device cannot catch the reflected optical beam, the hoisting is stopped. A threshold is provided on the basis of the reflected light intensity in the resting state of the crane. The ratio of the reflected optical beam intensity to the emitted optical beam intensity is calculated, and the threshold is set according to the intensity ratio. According to this, a trouble in that the reflected light is weakened by the accumulation of dust on the upper surface of the hoisting accessory 13 to cause the wrong operation of the photoelectric switch 21 can be solved.
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