Linear and rotary encoders using eletronic speckle correlation

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.