| 摘要 |
PURPOSE:To enable the detection of the presence of a light transmitting material by a method wherein reflection of light is done several times between light reflecting materials facing each other to apply the resulting actions of reflection to a light transmitting material interposed therebetween so that the quantity of transmission light is varied and detected. CONSTITUTION:An object 2 to be detected is positioned between a pair of light reflection plates 1 and 1' parallel facing each other and a projector 3 is used to admit light at the incident angle of 30 deg.. The light thus admitted hits a reflection plate 1 transmitting the object 2 being detected and reflected again at 30 deg. hitting the reflection plate 1' transmitting the object 2 being detected. Thereafter, this operation is repeated twice. The quantity of the transmission light is detected with a photodetector 4 and the presence of the object being detected depending on the difference in the detection value or the quantity of incident light. With such a method, the incident light transmits the object being detected six times. But a gradual decrease in the quantity of light makes the difference from the quantity of incident light more conspicuous thereby improving the detection accuracy. |
