Single Conjugated Adaptive Optics is a proven technique used in order to correct the effect of at... more Single Conjugated Adaptive Optics is a proven technique used in order to correct the effect of atmospheric turbulence and telescope vibrations. The corrected field of view (FoV) is however limited by the anisoplanatism effect. Many concepts of Wide Field AO (WFAO) systems are under study, especially for the design of Extremely Large Telescopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts that is particularly suited for high redshifts galaxies observations in very wide FoV. The E-ELT instrument EAGLE will use this approach. CANARY, the on-sky pathfinder for MOAO, obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010. The control and performance optimization of such complex system are a key issue. Linear Quadratic Gaussian (LQG) control is an appealing strategy that provides optimal control for an explicit minimum variance performance criterion. It also provides a unified formali...
ABSTRACT This paper is devoted to model reduction of linear time invariant (LTI) systems with ran... more ABSTRACT This paper is devoted to model reduction of linear time invariant (LTI) systems with random parameters. A novel framework is proposed to deal with this challenging problem. It consists in the combination of the generalized polynomial chaos (GPC) formalism and the truncated balanced realization (TBR) based method. The GPC formalism is known to be a powerful tool for the random uncertainty propagation and quantification while the TBR is efficient in model reduction of LTI systems. So, to couple these two methods helps to generate an efficient methodology to reduce linear models with random parameters. Two techniques exploiting this combination are proposed and tested on the model reduction of a mechanical system with random parameters. High efficiency is shown for both methods.
... C. Petit, J.-M. Conan, C. Kulcsár, H.-F. Raynaud, T. Fusco, J. Montri, D. Rabaud. Abstract. .... more ... C. Petit, J.-M. Conan, C. Kulcsár, H.-F. Raynaud, T. Fusco, J. Montri, D. Rabaud. Abstract. ... We use a classic AO bench available at Onera with a deformable mirror (DM) in the pupil and a Shack-Hartmann Wave Front Sensor (WFS) pointing at an on-axis guide-star. ...
ABSTRACT Adaptive Optics (AO) is a technique that allows the compensation of the atmospheric turb... more ABSTRACT Adaptive Optics (AO) is a technique that allows the compensation of the atmospheric turbulence effects on ground-based telescopes by means of an actively controlled deformable mirror (DMs), fed back based on the measurements obtained with one or more wavefront sensors (WFSs). For extremely large telescope (more than 20 m in diameter) the number of input and output channels can be in the range of the thousands or tens of thousands, making it problematic to apply optimal control solutions due to the heavy computational load. In this paper we show how it is possible to obtain a quick approximation of the solution of the Discrete Algebraic Riccati Equation (DARE) associated to a certain class of AO optimal control problems, and how the performance are affected by the use of such approximations.
Astronomical Adaptive Optics Systems and Applications II, 2005
We present a laboratory demonstration of open loop Off-Axis Adaptive Optics with optimal control.... more We present a laboratory demonstration of open loop Off-Axis Adaptive Optics with optimal control. The control based on a Minimum Mean Square Error Estimator brings a noticeable performance improvement. The next step will be to close the Off-Axis Adaptive Optics loop with a Kalman based optimal control. While this last experiment is currently under progress, a classic Adaptive Optics loop
We address the problem of proper handling of deformable mirror (DM) dynamics in Adaptive Optical ... more We address the problem of proper handling of deformable mirror (DM) dynamics in Adaptive Optical (AO) systems. We develop a state-space approach based on a continuous stochastic model of the atmospheric turbulence, which yields a fully optimal minimum mean-square ...
Entering the ELT era implies reconsidering adaptive optics concepts at all levels, including cont... more Entering the ELT era implies reconsidering adaptive optics concepts at all levels, including controller design. Concentrating mainly on temporal aspects, one may wonder if integral controllers remain an adequate solution.We recall for instance the impressive correction brought by Linear Quadratic Gaussian (LQG) controllers for the rejection of windshake and vibration components. Based on this experience, we present here a careful evaluation of the respective performance of integrator versus LQG control on turbulent modes both in a VLT and ELT configuration. The main questions addressed are: 1/ How do integral and LQG controllers compare in terms of performance for a given sampling frequency and noise level?; 2/ Could we relax sampling frequency and noise level specifications with LQG control?; 3/ How are these considerations affected by the choice of open-loop rather than closed-loop strategies? What about LQG in the context of large degrees of freedom?
The corrected Field of View (FoV) in Adaptive Optics (AO) is limited by the anisoplanatism effect... more The corrected Field of View (FoV) in Adaptive Optics (AO) is limited by the anisoplanatism effect. Multi-Conjugate AO (MCAO) aims at providing a wide FoV correction through the use of several Deformable Mirrors (DMs) and of multi-guide-star WaveFront Sensor (WFS). However the performance optimization of such complex systems raises new questions in terms of calibration and control. We present our current developments on performance optimization of MCAO systems. We show that performance can be significantly improved with tomographic control based on LQG control, compared with standard methods. An experimental demonstration of this new approach is now implemented on HOMER, the recent bench developed at ONERA, and devoted to MCAO laboratory research. We present here simulation results of the LQG control in HOMER case, compared with results obtained with an integrator control. We also present very preliminary results of the implementation of LQG control in AO and tomographic AO.
2010 IEEE International Conference on Control Applications, 2010
The SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument is an ESO project ai... more The SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument is an ESO project aiming at the direct detection of extra-solar planets. It will equip one of the four VLT 8-m telescopes in 2011. The heart of the SPHERE instrument is its eXtrem Adaptive Optics (XAO) SAXO (SPHERE AO for eXoplanet Observation) subsystem which aims at correcting any atmospheric and system defect. It should deal with a tight error budget, particularly concerning the optical axis stability. To fulfill SAXO challenging requirements a mixed control law has been designed. While a classic optimized modal gain integrator ensures the control of the deformable mirror, a linear quadratic Gaussian control has been designed to manage the tip-tilt mirror. It thus provides correction of turbulence induced optical axis fluctuations but also filtering of vibrations. A specific scheme has been developed to identify on-line the prior models for the turbulent and vibration components. We describe this original control architecture and present expectable performance of SAXO.
Single Conjugated Adaptive Optics is a proven technique used in order to correct the effect of at... more Single Conjugated Adaptive Optics is a proven technique used in order to correct the effect of atmospheric turbulence and telescope vibrations. The corrected field of view (FoV) is however limited by the anisoplanatism effect. Many concepts of Wide Field AO (WFAO) systems are under study, especially for the design of Extremely Large Telescopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts that is particularly suited for high redshifts galaxies observations in very wide FoV. The E-ELT instrument EAGLE will use this approach. CANARY, the on-sky pathfinder for MOAO, obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010. The control and performance optimization of such complex system are a key issue. Linear Quadratic Gaussian (LQG) control is an appealing strategy that provides optimal control for an explicit minimum variance performance criterion. It also provides a unified formali...
ABSTRACT This paper is devoted to model reduction of linear time invariant (LTI) systems with ran... more ABSTRACT This paper is devoted to model reduction of linear time invariant (LTI) systems with random parameters. A novel framework is proposed to deal with this challenging problem. It consists in the combination of the generalized polynomial chaos (GPC) formalism and the truncated balanced realization (TBR) based method. The GPC formalism is known to be a powerful tool for the random uncertainty propagation and quantification while the TBR is efficient in model reduction of LTI systems. So, to couple these two methods helps to generate an efficient methodology to reduce linear models with random parameters. Two techniques exploiting this combination are proposed and tested on the model reduction of a mechanical system with random parameters. High efficiency is shown for both methods.
... C. Petit, J.-M. Conan, C. Kulcsár, H.-F. Raynaud, T. Fusco, J. Montri, D. Rabaud. Abstract. .... more ... C. Petit, J.-M. Conan, C. Kulcsár, H.-F. Raynaud, T. Fusco, J. Montri, D. Rabaud. Abstract. ... We use a classic AO bench available at Onera with a deformable mirror (DM) in the pupil and a Shack-Hartmann Wave Front Sensor (WFS) pointing at an on-axis guide-star. ...
ABSTRACT Adaptive Optics (AO) is a technique that allows the compensation of the atmospheric turb... more ABSTRACT Adaptive Optics (AO) is a technique that allows the compensation of the atmospheric turbulence effects on ground-based telescopes by means of an actively controlled deformable mirror (DMs), fed back based on the measurements obtained with one or more wavefront sensors (WFSs). For extremely large telescope (more than 20 m in diameter) the number of input and output channels can be in the range of the thousands or tens of thousands, making it problematic to apply optimal control solutions due to the heavy computational load. In this paper we show how it is possible to obtain a quick approximation of the solution of the Discrete Algebraic Riccati Equation (DARE) associated to a certain class of AO optimal control problems, and how the performance are affected by the use of such approximations.
Astronomical Adaptive Optics Systems and Applications II, 2005
We present a laboratory demonstration of open loop Off-Axis Adaptive Optics with optimal control.... more We present a laboratory demonstration of open loop Off-Axis Adaptive Optics with optimal control. The control based on a Minimum Mean Square Error Estimator brings a noticeable performance improvement. The next step will be to close the Off-Axis Adaptive Optics loop with a Kalman based optimal control. While this last experiment is currently under progress, a classic Adaptive Optics loop
We address the problem of proper handling of deformable mirror (DM) dynamics in Adaptive Optical ... more We address the problem of proper handling of deformable mirror (DM) dynamics in Adaptive Optical (AO) systems. We develop a state-space approach based on a continuous stochastic model of the atmospheric turbulence, which yields a fully optimal minimum mean-square ...
Entering the ELT era implies reconsidering adaptive optics concepts at all levels, including cont... more Entering the ELT era implies reconsidering adaptive optics concepts at all levels, including controller design. Concentrating mainly on temporal aspects, one may wonder if integral controllers remain an adequate solution.We recall for instance the impressive correction brought by Linear Quadratic Gaussian (LQG) controllers for the rejection of windshake and vibration components. Based on this experience, we present here a careful evaluation of the respective performance of integrator versus LQG control on turbulent modes both in a VLT and ELT configuration. The main questions addressed are: 1/ How do integral and LQG controllers compare in terms of performance for a given sampling frequency and noise level?; 2/ Could we relax sampling frequency and noise level specifications with LQG control?; 3/ How are these considerations affected by the choice of open-loop rather than closed-loop strategies? What about LQG in the context of large degrees of freedom?
The corrected Field of View (FoV) in Adaptive Optics (AO) is limited by the anisoplanatism effect... more The corrected Field of View (FoV) in Adaptive Optics (AO) is limited by the anisoplanatism effect. Multi-Conjugate AO (MCAO) aims at providing a wide FoV correction through the use of several Deformable Mirrors (DMs) and of multi-guide-star WaveFront Sensor (WFS). However the performance optimization of such complex systems raises new questions in terms of calibration and control. We present our current developments on performance optimization of MCAO systems. We show that performance can be significantly improved with tomographic control based on LQG control, compared with standard methods. An experimental demonstration of this new approach is now implemented on HOMER, the recent bench developed at ONERA, and devoted to MCAO laboratory research. We present here simulation results of the LQG control in HOMER case, compared with results obtained with an integrator control. We also present very preliminary results of the implementation of LQG control in AO and tomographic AO.
2010 IEEE International Conference on Control Applications, 2010
The SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument is an ESO project ai... more The SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument is an ESO project aiming at the direct detection of extra-solar planets. It will equip one of the four VLT 8-m telescopes in 2011. The heart of the SPHERE instrument is its eXtrem Adaptive Optics (XAO) SAXO (SPHERE AO for eXoplanet Observation) subsystem which aims at correcting any atmospheric and system defect. It should deal with a tight error budget, particularly concerning the optical axis stability. To fulfill SAXO challenging requirements a mixed control law has been designed. While a classic optimized modal gain integrator ensures the control of the deformable mirror, a linear quadratic Gaussian control has been designed to manage the tip-tilt mirror. It thus provides correction of turbulence induced optical axis fluctuations but also filtering of vibrations. A specific scheme has been developed to identify on-line the prior models for the turbulent and vibration components. We describe this original control architecture and present expectable performance of SAXO.
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