Absolute and incremental optical encoder

Abstract

An apparatus optically detects the position of a movable element through the use of six discrete tracks. Each of the tracks is formed on a glass substrate and has a preselected pattern of optically transmissive and opaque sections arranged thereon. A light source and optical sensors are associated with each of the tracks such that the light is either blocked or passed to the optical sensors respectively responsive to the opaque and transmissive sections. Five of the tracks correspond to form a five bit absolute gray code pattern indicative of the position of the movable element. The sixth remaining track has alternately opaque and transmissive sections arranged to form an incremental track where the count of the number of opaque and transmissive sections travelling past an initial set point is maintained in memory and corresponds to an incremental position within each of the absolute positions. The microprocessor base controller limits the number of incremental transitions within an absolute position to thirty-two or two to the fifth power. The thirty-two possible positions, when used as the lower five bits of a ten bit binary word, where the upper five bits come from the five absolute tracks, forms a ten bit pseudo-gray code indicative of the position of the movable element and is highly accurate without the necessity of ten absolute tracks and the cumbersome packaging associated therewith.