Laser speckle rotary encoder

A new rotary encoder is proposed which detects displacement of speckle arising in the diffraction field of a cylinder illuminated by a narrow laser beam. The displacement is detected from the peak position of the cross-correlation between the outputs of a linear image sensor. The speckle displacement due to small rotation of the cylinder is derived first. In experiments correlation is computed on a microcomputer for investigating the sensitivity and repeatability. A He-Ne laser and a laser diode are used for metal and paper surfaces. Acceleration and extension of the measurement range has also been possible by developing a real-time correlator.