This paper describes a vernier-type optical encoder for absolute angular measurement. The vernier encoder has only two tracks, so it is much smaller and simpler than conven-tional Gray code encoders. Two "spatial filter" detectors are used with the vernier to provide interpolation between encoder slit positions. Each detector consists of a LED light source on one side of the disk, and two photodiode arrays (PDA) -- one for each track of the vernier -- on the other. The two detectors are placed at diametrically-opposed positions, and the intensities of the LED light sources are modulated in quad-rature by a sinusoidal signal. The signals from the detector arrays are combined to generate two vernier signals, and the difference between these vernier signals is a high-precision "absolute vernier" signal. The accuracy of angular measurement for a prototype encoder was as high as 1/10,000 (2.2 arc-min).

Date Published: 17 February 1987
PDF: 5 pages
Proc. SPIE 0814, Photomechanics and Speckle Metrology, (17 February 1987); doi: 10.1117/12.941698

Published in SPIE Proceedings Vol. 0814:
Photomechanics and Speckle Metrology
Fu-Pen Chiang, Editor(s)