Patent ID: 6377167
Filing Date: 2002-04-23
Classification: G01S

Abstract:
An electro-optical detection system for detecting objects within the boundaries of a monitored zone, comprising an emitter and photodetector pair, wherein the emitter emits a beam of pulses of light energy into the monitored zone, and the photodetector detects light energy including light energy from the beam that is reflected from an object within the monitored zone and generates light detection signals, and a controller for operating the emitter and photodetector pair and for generating an object detection signal when it determines that an object is in the monitored zone, characterized bythe emitter emitting a beam of pulses of light energy at multiple frequencies into the monitored zone, and the controller generating a phase-delayed reference signal at each frequency, mixing the light detection signals and the reference signals to produce a phase difference signal for each frequency that varies in polarity sinusoidally with the distance to the object, and comparing the polarity of these phase difference signals to determine the presence of an object in the monitored zone.