Abstract: A system for sensing the presence of nearby objects includes an emitter-detector assembly and retroreflector. The emitter-detector assembly has a light emission area from which light is transmitted toward the retroreflector. The retroreflector returns that light to a light detection area of the emitter-detector assembly which produces a signal indicating an unbroken light path. Objects passing near the assembly interrupt the light path thereby providing an indication of their presence. The light emission area and the light detection area are concentric to each other which enables the light detection area to have close proximity to the light emission area. That parameter optimizes response to light from the retroreflector, while minimizing response to light reflected by other objects.

Abstract: A system for sensing the presence of nearby objects includes an emitter-detector assembly and retroreflector. The emitter-detector assembly has a light emission area from which light is transmitted toward the retroreflector. The retroreflector returns that light to a light detection area of the emitter-detector assembly which produces a signal indicating an unbroken light path. Objects passing near the assembly interrupt the light path thereby providing an indication of their presence. The light emission area and the light detection area are concentric to each other which enables the light detection area to have close proximity to the light emission area. That parameter optimizes response to light from the retroreflector, while minimizing response to light reflected by other objects.

Abstract: The positions of objects in a holder, such as a cassette containing semiconductor wafers, are determined by a system that projects a pair of coplanar light beams through the cassette from one side. A reflector on the opposite side reflects both light beams back though the cassette and onto separate photodetectors on the one side. A computer analyzes signals from the photodetectors as the cassette is moved through the light beams. As the cassette moves the light beams are interrupted by the wafers. The relative widths and timing of pulses in the signals indicate the location of wafers in the cassette and whether a wafer is misaligned.

Abstract: An improved optical sensor includes a light source from which light is projected onto an object. A photodetector detects the light reflected from the object. A refraction element is movable relative to the photodetector to vary the range of the optical sensor. The position of the light source relative to the photodetector can be varied.