Optical EngineeringLinear and rotary encoders using eletronic speckle correlation
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Speckle patterns can be used as natural surface markings that are printed by the high coherence of laser light. Speckle displacement caused by linear or rotary motion of a surface is detected with a linear image sensor whose output is analyzed by a real-time correlator. By using an image sensor of 15-μm pitch and 1024 elements, resolution of a micrometer and 1/1000 deg have been attained. The main advantages of the encoders are extreme simplicity in optical configurations and wide ranges of measurement.