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Proceedings Paper

Sin/cosine encoder interpolation methods: encoder to digital tracking converters for rate and position loop controllers
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Paper Abstract

Pointing and tracking applications usually require relative gimbal angles to be measured for reporting and controlling the line-of-sight angular position. Depending on the application, angular resolution and/or accuracy might jointly or independently determine the angle transducer requirements. In the past decade, encoders have been increasingly taking the place of inductive devices where the measurement of angles over a wide range is required. This is primarily due to the fact that encoders are now achieving very high resolution in smaller sizes than was previously possible. These advances in resolution are primarily due to improved encoder disk and detector technology along with developments in interpolation techniques. Measurement accuracy, on the other hand, is primarily determined by mounting and bearing eccentricity as it is with all angular measurement devices. For very demanding accuracy requirements, some type of calibration of the assembled system may be the only solution, in which case transducer repeatability is paramount. This paper describes a unique encoder-to-digital tracking converter concept for improving interpolation of optical encoders. The new method relies on Fraunhofer diffraction models to correct the non-ideal sin/cos outputs of the encoder detectors. Diffraction model concepts are used in the interpolation filters to predict the phase of non-ideal sin and cosine encoder outputs. The new method also minimizes many of the open loop pre-processing requirements and assumptions that limit interpolation accuracy and rate loop noise performance in ratiometric tracking converter designs.

Paper Details

Date Published: 24 March 2008
PDF: 15 pages
Proc. SPIE 6971, Acquisition, Tracking, Pointing, and Laser Systems Technologies XXII, 69710F (24 March 2008); doi: 10.1117/12.777741
Show Author Affiliations
Steven T. Jenkins, Texas Instruments (United States)
J. M. Hilkert, Alpha Theta Technologies (United States)

Published in SPIE Proceedings Vol. 6971:
Acquisition, Tracking, Pointing, and Laser Systems Technologies XXII
Steven L. Chodos; William E. Thompson, Editor(s)

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