Vibrations in AO control: a short analysis of on-sky data around the world

Kulcsár, Caroline; Sivo, Gaetano; Raynaud, Henri François; Neichel, Benoît; Rigaut, François; Christou, Julian C.; Guesalaga, Andrés; Correia, Carlos; Véran, Jean-Pierre; Gendron, É.; Vidal, Fabrice; Rousset, G.; Morris, Tim; Esposito, Simone; Quirós-Pacheco, Fernando; Agapito, Guido; Fedrigo, Enrico; Pettazzi, Lorenzo; Clare, Richard; Muradore, Riccardo; Guyon, Olivier; Martinache, Frantz; Meimon, Serge; Conan, Jean Marc

doi:10.1117/12.925984

Cited by 34 publications

(18 citation statements)

References 16 publications

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“…Theoretical studies [10,11] have also shown that an advantage of LQG controllers over integrator was the possible relaxation of system constraints (actuator saturation, sampling frequency, noise requirements) which may be of particular interest for ELT systems. A major issue in AO is also the correction of non-turbulent perturbations such as windshake or vibrations [12][13][14][15]. LQG control, thanks to its flexibility, can provide a very efficient compensation of these effects, as shown for vibrations through laboratory tests [16], and through numerical simulations for windshake [17].…”

Section: Introductionmentioning

confidence: 99%

First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

Sivo¹,

Kulcsár²,

Conan³

et al. 2014

Opt. Express

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Adaptive optics provides real time correction of wavefront disturbances on ground based telescopes. Optimizing control and performance is a key issue for ever more demanding instruments on ever larger telescopes affected not only by atmospheric turbulence, but also by vibrations, windshake and tracking errors. Linear Quadratic Gaussian control achieves optimal correction when provided with a temporal model of the disturbance. We present in this paper the first on-sky results of a Kalman filter based LQG control with vibration mitigation on the CANARY instrument at the Nasmyth platform of the 4.2-m William Herschel Telescope. The results demonstrate a clear improvement of performance for full LQG compared with standard integrator control, and assess the additional improvement brought by vibration filtering with a tip-tilt model identified from on-sky data, thus validating the strategy retained on the instrument SPHERE at the VLT.

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Section: Introductionmentioning

confidence: 99%

First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

Sivo¹,

Kulcsár²,

Conan³

et al. 2014

Opt. Express

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“…[1][2][3][4] The requirement in pre-coronagraphic tip/tilt correction is usually about a few milliarcseconds for instruments on 8-m class telescopes. It will be even less with the next generation of extremely large telescopes.…”

Section: Introductionmentioning

confidence: 99%

Characterizing and mitigating vibrations for SCExAO

Lozi

Guyon

Jovanović

et al. 2016

Adaptive Optics Systems V

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The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, under development for the Subaru Telescope, has currently the fastest on-sky wavefront control loop, with a pyramid wavefront sensor running at 3.5 kHz. But even at that speed, we are still limited by low-frequency vibrations. The current main limitation was found to be vibrations attributed mainly to the rotation of the telescope. Using the fast wavefront sensors, cameras and accelerometers, we managed to identify the origin of most of the vibrations degrading our performance. Low-frequency vibrations are coming from the telescope drive in azimuth and elevation, as well as the elevation encoders when the target is at transit. Other vibrations were found at higher frequency coming from the image rotator inside Subaru's adaptive optics facility AO188. Different approaches are being implemented to take care of these issues. The PID control of the image rotator has been tuned to reduce their high-frequency contribution. We are working with the telescope team to tune the motor drives and reduce the impact of the elevation encoder. A Linear Quadratic Gaussian controller (LQG, or Kalman filter) is also being implemented inside SCExAO to control these vibrations. These solutions will not only improve significantly SCExAOs performance, but will also help all the other instruments on the Subaru Telescope, especially the ones behind AO188. Ultimately, this study will also help the development of the TMT, as these two telescopes share very similar drives.

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“…Furthermore, they mainly affect low-order aberration components such as tip and tilt modes. Recently, vibration cancelation has obtained a lot of attention in context of AOS design [3].…”

Section: Introductionmentioning

confidence: 99%

Optical axis jitter rejection for double overlapped adaptive optics systems

Qinghong

Luo

2016

Opt Rev

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Optical axis jitters, or vibrations, which arise from wind shaking and structural oscillations of optical platforms, etc., cause a deleterious impact on the performance of adaptive optics systems. When conventional integrators are utilized to reject such high frequency and narrow-band disturbance, the benefits are quite small despite their acceptable capabilities to reject atmospheric turbulence. In our case, two suits of complete adaptive optics systems called double overlapped adaptive optics systems (DOAOS) are used to counteract both optical jitters and atmospheric turbulence. A novel algorithm aiming to remove vibrations is proposed by resorting to combine the Smith predictor and notch filer. With the help of loop shaping method, the algorithm will lead to an effective and stable controller, which makes the characteristics of error transfer function close to notch filters. On the basis of the spectral analysis of observed data, the peak frequency and bandwidth of vibrations can be identified in advance. Afterwards, the number of notch filters and their parameters will be determined using coordination descending method. The relationship between controller parameters and filtering features is discussed, and the robustness of the controller against varying parameters of the control object is investigated. Preliminary experiments are carried out to validate the proposed algorithms. The overall control performance of DOAOS is simulated. Results show that time delays are a limit of the performance, but the algorithm can be successfully implemented on our systems, which indicate that it has a great potential to reject jitters.

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Vibrations in AO control: a short analysis of on-sky data around the world

Cited by 34 publications

References 16 publications

First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

First on-sky SCAO validation of full LQG control with vibration mitigation on the CANARY pathfinder

Characterizing and mitigating vibrations for SCExAO

Optical axis jitter rejection for double overlapped adaptive optics systems

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