22 July 2014 Real-time estimation of differential piston at the LBT
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In this paper, we present and compare different strategies to minimize the effects of telescope vibrations to the differential piston (OPD) for LINC/NIRVANA at the LBT using an accelerometer feedforward compensation approach. We summarize why this technology is of importance for LINC/NIRVANA, but also for future telescopes and instruments. We outline the estimation problem in general and its specifics at the LBT. Model based estimation and broadband filtering techniques can be used to solve the estimation task, each having its own advantages and disadvantages, which will be discussed. Simulation results and measurements at the LBT are shown to motivate and support our choice of the estimation algorithm for the instrument LINC/NIRVANA. We explain our laboratory setup aimed at imitating the vibration behaviour at the LBT in general, and the M2 as main contributor in particular, and we demonstrate the controller's ability to suppress vibrations in the frequency range of 8 Hz to 60 Hz. In this range, telescope vibrations are the most dominant disturbance to the optical path. For our measurements, we introduce a disturbance time series which has a frequency spectrum comparable to what can be measured at the LBT on a typical night. We show promising experimental results, indicating the ability to suppress differential piston induced by telescope vibrations by a factor of about 5 (RMS), which is significantly better than any currently commissioned system.
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Michael Böhm, Michael Böhm, Jörg-Uwe Pott, Jörg-Uwe Pott, Oliver Sawodny, Oliver Sawodny, Tom Herbst, Tom Herbst, Martin Kürster, Martin Kürster, } "Real-time estimation of differential piston at the LBT", Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91451B (22 July 2014); doi: 10.1117/12.2055833; https://doi.org/10.1117/12.2055833


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