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Proceedings Paper

Laser galvo-angle-encoder with zero added inertia
Author(s): Michael Hercher; Geert J. Wijntjes
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Paper Abstract

The authors describe an interferometric angle encoder for a high-speed galvanometer having the following characteristics: (1) zero added mechanical moment of inertia, (2) microradian resolution, (3) laser diode light source, and (4) small package. The design uses the rear face of the existing galvanometer scan mirror to scan a laser diode beam across a cylindrical scale (a grating width on the order of 1000 lines/inch) whose axis coincides with the galvo axis of rotation. The +/- 1 diffracted orders are collected after being again reflected by the galvo mirror and are made to interfere. The phase of the resulting interference fringe pattern is measured with a resolution of approximately equals 1/400-fringe (or 1/800-line spacing on the grating) to achieve an angular resolution of 1.3 microradian (0.2 arcsec). The measurement update frequency is nominally 4 MHz, corresponding to a maximum angular velocity for full on-the- fly resolution of 5 rad/sec (fringes can be accurately tracked at angular velocities of greater than 1000 rad/sec). The design concept is described in detail and test data are presented.

Paper Details

Date Published: 1 February 1991
PDF: 5 pages
Proc. SPIE 1454, Beam Deflection and Scanning Technologies, (1 February 1991); doi: 10.1117/12.28034
Show Author Affiliations
Michael Hercher, OPTRA, Inc. (United States)
Geert J. Wijntjes, OPTRA, Inc. (United States)

Published in SPIE Proceedings Vol. 1454:
Beam Deflection and Scanning Technologies
Leo Beiser; Gerald F. Marshall, Editor(s)

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