Importance

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Abstract

An optical position indicating apparatus having a light source, a detector for detecting the presence of light and producing an electrical output in response thereto, a reflecting structure for reflecting light from the light source across a target zone, and, a retroreflecting structure for reflecting the light incident thereupon along a path substantially coincident with the path of incidence of the light. The retroreflecting structure comprises a plurality of retroreflective assemblies, the reflecting structure and the plurality of retroreflective assemblies are substantially disposed about the target zone and a limiting structure limits the detector to a finite viewing range so that rotation of the detector effects scanning of the target zone. The detector is capable of measuring angular displacement from a reference so that presence of an opaque object within the target zone will register upon the detector as a plurality of shadows thereby resulting in absence of electrical output from the detector for each of the plurality of shadows, whereby the location of the opaque object within the target zone can be determined in two dimensions by geometric calculations involving angular displacements of the plurality of shadows.

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First Claim