METHOD AND APPARATUS FOR SEARCHING FOR OBJECT WITH SPECKLE PATTERN LIGHT

摘要

A speckle pattern light reflected from the surface of an object is received and the approach or presence of the object is detected without regulating the sensitivity volume regardless of the distance to the object, the surface inclination, reflectance or size of the object. A beam coherent light (2) modulated intermittently with low frequency is projected into a space to be monitored and a returned speckle pattern light (4) is transduced photoelectrically. A resulting signal current is amplified by a logarithmic amplifier and only the modulated frequency component is extracted by a DC reproducer. The voltage of the component is compared with a comparison voltage, and a detection signal (7) is outputted when the relation of magnitude is between both voltages reverved.