| 摘要 |
<p>PURPOSE: To surely detect a beam by utilizing the displacement of the beam caused by a retroreflection mirror having three mirrors. CONSTITUTION: A light source 20 is positioned in a light emitting and receiving device 14 and irradiates a lens 18 having the pupil 15 of the light emitting device and, as a result, a parallel light beam 21 is produced. A light receiving lens 19 is positioned near the lens 18 in the device 14 and a photodetector 22 is positioned to the focal surface of the lens 19 on the rear side of the lens 19. A retroreflection reflector 13 using a large number of reflecting mirrors 11 having three mirrors is constituted so that each reflecting mirror 11 can have a large bottom face B. Accordingly, the displacement V of the beam 21 caused by the mirrors 11 increases and a sufficient quantity of light enters the lens 19 and is received by the photodetector 22 even when the reflector 13 is positioned near the device 14. Therefore, the lgiht receiving signal of photodetector the 22 when the reflector 13 is positioned at a near distance does not change substantially from the light receiving signal when the reflector 13 is positioned at a far distance. Thus the beam 21 can be detected surely.</p> |
