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Proceedings Paper

Ultrahigh-resolution Cartesian absolute optical encoder
Author(s): Douglas B. Leviton; Jeff Kirk; Luke Lobsinger
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Paper Abstract

A new optical encoder which measures absolute, true-Cartesian displacement with ultra-high sensitivity and linearity has been developed at NASA's Goddard Space Flight Center. The device is the two-dimensional analog of recently developed linear and rotary encoders based on optical pattern recognition. In this encoder, a glass scale carrying absolute Cartesian position information travels with the payload in an X-Y motion system. Because the scale comprises the entire measurement coordinate system in a monolithic form, motion control axes can be skew to one another to an arbitrary degree and can exhibit substantial lateral drift with no effect on the correctness of X-Y readout, thus eliminating challenges of orthogonal mounting for motion axes and challenges of mounting independent encoders parallel to the directions of travel for each constituent X and Y axis. Prototype devices with ranges of 30 x 30 mm and 150 x 150 mm with 5 nm and 50 nm resolutions, respectively, have been built in the laboratory. Performance data from the Cartesian encoder in the Point Target Assembly for the optical calibration stimulus for Hubble Space Telescope's Wide Field Camera 3 are presented.

Paper Details

Date Published: 20 November 2003
PDF: 11 pages
Proc. SPIE 5190, Recent Developments in Traceable Dimensional Measurements II, (20 November 2003); doi: 10.1117/12.518376
Show Author Affiliations
Douglas B. Leviton, NASA Goddard Space Flight Ctr. (United States)
Jeff Kirk, Orbital Sciences Corp. (United States)
Luke Lobsinger, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 5190:
Recent Developments in Traceable Dimensional Measurements II
Jennifer E. Decker; Nicholas Brown, Editor(s)

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