Abstract: An detection system emits a light beam and has a photodetector that senses when light is reflected by objects to be detected. Because reflectivity of the objects varies greatly, the intensity of the reflected light varies over a large range. To prevent false object detection, an automatic sensitivity control mechanism is provided which controls the intensity of the emitted light beam and attenuation of the signal from the photodetector. That control is in response to the level of the photodetector signal.

Abstract: An object detection system has an emitter that produces a light beam for reflection by objects to be detected. At least three photodetectors are aimed to receive reflected light from an object and produce separate signals indicating the amount of light received. The photodetectors are aimed so that the signal from one of the photodetectors will be greater than the combined signals from the other two photodetectors when an object is within a given distance from the emitter. The combined signals from those other two photodetectors exceed the signal from the one photodetector when light is reflected by an object that is beyond the given distance from the emitter. By combining all the photodetector signals, an indication can be produced when a object is within the given distance. This has application to detect objects moving along an assembly line, without detecting objects moving in the factory on the remote side of the assembly line from the object detection system.