The adaptive secondary mirror for the Large Binocular Telescope: results of acceptance laboratory test

Riccardi, Armando; Xompero, Marco; Zanotti, D.; Busoni, Lorenzo; Vecchio, Ciro Del; Salinari, Piero; Ranfagni, Piero; Zappellini, Guido Brusa; Biasi, Roberto; Andrighettoni, Mario; Gallieni, Daniele; Anaclerio, Enzo; Martin, Hubert M.; Miller, Stephen Matteo

doi:10.1117/12.790527

Cited by 36 publications

(35 citation statements)

References 5 publications

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“…As first, we tested the stability of the mirror itself and measured the step responses when a faster pre-shaping command is sent [7]. We have been able to test frequency up to 1.8kHz and the mirror showed to be stable and the modal step responses had a maximum overshoot of about 15% in the worst cases.…”

Section: Adaptive Secondary and Real Time Computermentioning

confidence: 99%

SOUL: the Single conjugated adaptive Optics Upgrade for LBT

et al. 2016

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We present here SOUL: the Single conjugated adaptive Optics Upgrade for LBT. Soul will upgrade the wavefront sensors replacing the existing CCD detector with an EMCCD camera and the rest of the system in order to enable the closed loop operations at a faster cycle rate and with higher number of slopes. Thanks to reduced noise, higher number of pixel and framerate, we expect a gain (for a given SR) around 1.5-2 magnitudes at all wavelengths in the range 7.5 70% in I-band and 0.6asec seeing) and the sky coverage will be multiplied by a factor 5 at all galactic latitudes. Upgrading the SCAO systems at all the 4 focal stations, SOUL will provide these benefits in 2017 to the LBTI interferometer and in 2018 to the 2 LUCI NIR spectro-imagers. In the same year the SOUL correction will be exploited also by the new generation of LBT instruments: V-SHARK, SHARK-NIR and iLocater.

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Section: Adaptive Secondary and Real Time Computermentioning

confidence: 99%

SOUL: the Single conjugated adaptive Optics Upgrade for LBT

et al. 2016

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“…For example, a concept including piezo-electrical actuators has been proposed for the E-ELT [2] and the 911 mm-diameter deformable secondary mirrors for the large binocular telescope AO system using a concept encompassing force actuators, applied by an Italian group based at the Arcetri Astrophysical Observatory. The project team first demonstrated correct function of the DM in a laboratory environment [3], and first light on the telescope was made in 2010 [4].…”

Section: Introductionmentioning

confidence: 99%

“…The actuators encompass a moving rod, which is driven by a voice coil and has a linear variable differential transformer (LVDT) measuring the relative position of the rod. Use of commercially available voice coils, which limit the actuator bandwidth compared to the force actuators used in [3,4], can reduce the costs. The rod is connected to the DM through a suction cup, avoiding direct physical contact between the mirror and the actuators.…”

Section: Introductionmentioning

confidence: 99%

“…A system with such actuators can be inexpensive because tight tolerances are not needed. As a comparison, the existing force actuators used for large DMs [3,4] use permanent magnets glued to the back of the mirror, which give a large uniform (flat) frequency response. In contrast, the actuator concept proposed here has a flat response of only a few kHz, and there is no need for extra components at the back of the mirror.…”

Section: Introductionmentioning

confidence: 99%

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Concept, modeling, and performance prediction of a low-cost, large deformable mirror

et al. 2012

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While it is attractive to integrate a deformable mirror (DM) for adaptive optics (AO) into the telescope itself rather than using relay optics within an instrument, the resulting large DM can be expensive, particularly for extremely large telescopes. A low-cost approach for building a large DM is to use voice-coil actuators connected to the back of the DM through suction cups. Use of such inexpensive voice-coil actuators leads to a poorly damped system with many structural modes within the desired bandwidth. Control of the mirror dynamics using electro-mechanical sensors is thus required for integration within an AO system. We introduce a distributed control approach, and we show that the "inner" back sensor control loop does not need to function at low frequencies, leading to significant cost reduction for the sensors. Incorporating realistic models of low-cost actuators and sensors together with an atmospheric seeing model, we demonstrate that the low-cost mirror strategy is feasible within a closed-loop AO system.

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“…It is useful to include large deformable mirrors (DMs) in a telescope to avoid lossy relay optics; these typically have either piezo-electric (displacement) actuators (as in M4 for E-ELT [1]) or voice-coil (force) actuators (as in the LBT M2 [2,3]). …”

Section: Introduction and Conceptmentioning

confidence: 99%

Distributed control of large deformable mirrors

et al. 2012

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While it is attractive to integrate a deformable mirror (DM) for adaptive optics (AO) into the telescope itself rather than using relay optics within an instrument, the resulting large DM can be expensive, particularly for extremely large telescopes. A low-cost approach for building a large DM is to use voice-coil actuators, and rely on feedback from mechanical sensors to improve the dynamic response of the mirror sufficiently so that it can be used in a standard AO control system. The use of inexpensive voice-coil actuators results in many lightlydamped structural resonances within the desired control bandwidth. We present a robust control approach for this problem, and demonstrate performance in a closed-loop AO simulation, incorporating realistic models of low-cost actuators and sensors. The first contribution is to demonstrate that high-bandwidth active damping can be robustly implemented even with non-collocated sensors, by relying on the "acoustic limit" of the structure where the modal bandwidth exceeds the modal spacing. Next we introduce a novel local control approach, which significantly improves the high spatial frequency performance relative to collocated position control, but without the robustness challenges associated with a global control approach. The combination of these "inner" control loops results in DM command response that is demonstrated to be sufficient for integration within an AO system.

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The adaptive secondary mirror for the Large Binocular Telescope: results of acceptance laboratory test

Cited by 36 publications

References 5 publications

SOUL: the Single conjugated adaptive Optics Upgrade for LBT

SOUL: the Single conjugated adaptive Optics Upgrade for LBT

Concept, modeling, and performance prediction of a low-cost, large deformable mirror

Distributed control of large deformable mirrors

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