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Proceedings Paper

Adaptive secondary mirror for LBT and its capacitive sensors: how can we calibrate them?
Author(s): Marco Xompero; Armando Riccardi; Daniela Zanotti
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Paper Abstract

The Adaptive Secondary Mirror (ASM) for LBT arrived in its final characterization phase. In order to use its large stroke performances and high order correction capability, we needed to develop a fast and accurate calibration procedure which use optical measurements and correlates them with signals of capacitive sensors co-located with the actuators. Each capacitive sensor gives a signal related to the local gap between the Reference Body and the Thin Shell of the ASM. The main issue in this implementation is the inverse relationship between mirror position (quantity to be measured) and capacitance (sensed quantity), and the evaluation of the effective reference and stray capacitance for each actuators that affects the calibration parameters. We developed a new method to correlate interferograms optically describing the mirror shape and the shell pistoning: moreover, with a non-linear data fit, we solved the unknown calibration parameters to find the linearization formula to be implemented in the system, giving a optimal solution to the capacitive sensor calibration problem.

Paper Details

Date Published: 14 July 2008
PDF: 9 pages
Proc. SPIE 7015, Adaptive Optics Systems, 70153Q (14 July 2008); doi: 10.1117/12.789572
Show Author Affiliations
Marco Xompero, INAF, Osservatorio Astrofisico di Arcetri (Italy)
Armando Riccardi, INAF, Osservatorio Astrofisico di Arcetri (Italy)
Daniela Zanotti, INAF, Osservatorio Astrofisico di Arcetri (Italy)

Published in SPIE Proceedings Vol. 7015:
Adaptive Optics Systems
Norbert Hubin; Claire E. Max; Peter L. Wizinowich, Editor(s)

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