| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a highly reliable detector with wide sensitive range by providing, between a projector and a light receiver, an obstruction detecting optical path filled with a transparent liquid having a refractive index higher than a synthetic resin-made flexible tube therein. SOLUTION: The optical axes of a projector 1 and a light receiver 2 are conformed to the central axis of the winding drum D of a shutter curtain C. A transparent liquid having a low refractive index is filled in a synthetic resin- made flexible tube 3 having a high refractive index, and an obstruction detecting optical path is constituted by the tube 3 and the transparent liquid. Sealing plugs 4 made of transparent resin are provided on both ends of the tube 3, one end of an optical fiber 5 is opposed to a free disc F concentric to the drum D, and the other end 6 is fixed onto the upper surface of a seat plate through the side end part of the curtain C. One end of the tube 3 is opposed to the other end 6, and the other end is opposed to the disc F through the bent obstruction detecting optical path. The bent part of the tube 3 is crushed by an obstruction, the optical path is closed, and when the obstruction is removed, it is returned to the original from by the action of the piston 8 of a cylinder 7.</p> |
