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Proceedings Paper

Error reduction and modeling for hexapod positioners of secondary mirrors for large ground-based telescopes
Author(s): Ryan C. Sneed; Paul J. Keas
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Paper Abstract

The positioning requirements for secondary mirrors and instruments for large ground-based telescopes are becoming increasingly challenging. Modern telescope designs, such as LSST and TMT, are specifying repeatability and/or absolute accuracy limits below 10 μm and 10 μrad for the hexapod positioning systems generally used for these applications. Hexapod error sources, including lead screw pitch variations, windup, backlash, friction, thermal expansion, compliance, sensing, and joint node location uncertainties, are examined along with methods for reducing or eliminating these errors by mechanical means or through calibration. Alternative sensing approaches are discussed and their relative benefits are evaluated. Finally, a model-based design approach is presented for conducting initial design trade studies, assessing technical risk, predicting achievable performance, establishing subsystem and component requirements, and tracking positioning error budgets through the entire development process. A parametric actuator model and its initial results are described, and testing approaches are outlined to identify key model parameters and verify subsystem and component performance.

Paper Details

Date Published: 4 August 2014
PDF: 14 pages
Proc. SPIE 9150, Modeling, Systems Engineering, and Project Management for Astronomy VI, 915020 (4 August 2014); doi: 10.1117/12.2056644
Show Author Affiliations
Ryan C. Sneed, Moog CSA Engineering (United States)
Paul J. Keas, Moog CSA Engineering (United States)

Published in SPIE Proceedings Vol. 9150:
Modeling, Systems Engineering, and Project Management for Astronomy VI
George Z. Angeli; Philippe Dierickx, Editor(s)

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