Flexible tube optical intrusion detector

Claim 1

An optical detector for sensing physical intrusion of an object into a curved path comprising, a curved flexible hollow tube positioned in the curved path, the tube having reflective inner walls for transmitting radiation by reflection from one end of the tube to the other, the tube being subject to indentation by an intruding object, a radiation emitter and a radiation sensor at opposite ends of the tube so that the tube transmits radiation by internal reflection from the emitter to the sensor to yield a sensor signal, a drive circuit for periodically energizing said emitter to produce a series of spaced radiation pulses, said radiation pulses being applied to said sensor by means of said tube when radiation pulses are produced, and a logic circuit coupled to said drive circuit and to the sensor output for producing a signal when radiation pulses are produced and the tube is indented by said object to attenuate the transmission of radiation pulses between the emitter and sensor, said logic circuit including means for producing said signal when ambient light is admitted into the interior of said tube and causes said sensor to produce an output.