Apparatus for producing a phase insensitive index pulse for motion

Abstract

A motion encoder includes a code member that extends along the route of the object whose movement is to be encoded, an energy emitter, and a modulated energy detector assembly. An incremental movement modulation track and two index modulation tracks are positioned on the code member for modulating the emitted energy in response to movement of the object along its route. The energy detector assembly includes an incremental movement energy detector and two index energy detectors. The two index modulation tracks are positioned on opposite sides of, and are each spaced a substantially equal distance from the incremental movement track. Similarly, the two index energy detectors are positioned on opposite sides of, and are each spaced a substantially equal distance from the incremental movement energy detector. The two index energy detectors are adapted for receiving energy modulated by the two index modulation tracks and for generating two index signals that each reach their extreme amplitude at least once as the object travels along its route, and from which an index pulse can be derived with a comparator. Where the code member and the detector assembly are misaligned by certain amounts in the object's direction of motion, such misalignment does not affect the phase of the index pulse derived from the two index signals with the comparator.