Adaptive secondary mirror for LBT and its capacitive sensors: how can we calibrate them?

Marco Xompero; Armando Riccardi; Daniela Zanotti

doi:10.1117/12.789572

14 July 2008 Adaptive secondary mirror for LBT and its capacitive sensors: how can we calibrate them?

Marco Xompero, Armando Riccardi, Daniela Zanotti

Proceedings Volume 7015, Adaptive Optics Systems; 70153Q (2008) https://doi.org/10.1117/12.789572
Event: SPIE Astronomical Telescopes + Instrumentation, 2008, Marseille, France

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.

Citation Download Citation

Marco Xompero, Armando Riccardi, and Daniela Zanotti "Adaptive secondary mirror for LBT and its capacitive sensors: how can we calibrate them?", Proc. SPIE 7015, Adaptive Optics Systems, 70153Q (14 July 2008); https://doi.org/10.1117/12.789572

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