Investigations of an Accelerometer-based Disturbance Feedforward Control for Vibration Suppression in Adaptive Optics of Large Telescopes

Adaptive Optics (AO) systems in large telescopes do not only correct atmospheric phase disturbances, but they also telescope structure vibrations induced by wind or telescope motions. Often the additional wavefront error due to mirror vibrations can dominate the disturbance power and contribute significantly to the total tip-tilt Zernike mode error budget. Presently, these vibrations are compensated for by common feedback control laws. However, when observing faint natural guide stars (NGS) at reduced control bandwidth, high-frequency vibrations (>5 Hz) cannot be fully compensated for by feedback control. In this paper, we present an additional accelerometer-based disturbance feedforward control (DFF), which is independent of the NGS wavefront sensor exposure time to enlarge the "effective servo bandwidth". The DFF is studied in a realistic AO end-to-end simulation and compared with commonly used suppression concepts. For the observation in the faint (>13 mag) NGS regime, we obtain a Strehl ratio by a factor of two to four larger in comparison with a classical feedback control. The simulation realism is verified with real measurement data from the Large Binocular Telescope (LBT); the application for on-sky testing at the LBT and an implementation at the E-ELT in the MICADO instrument is discussed.

[1]  Armando Riccardi,et al.  First light AO (FLAO) system for LBT: final integration, acceptance test in Europe, and preliminary on-sky commissioning results , 2010, Astronomical Telescopes + Instrumentation.

[2]  Oliver Sawodny,et al.  Accelerometer-based online reconstruction of vibrations from delayed measurements , 2015, 2015 IEEE Conference on Control Applications (CCA).

[3]  Armando Riccardi,et al.  Observer-Based Control Techniques for the LBT Adaptive Optics under Telescope Vibrations , 2011, Eur. J. Control.

[4]  T. Bertram,et al.  Vibration measurements at the Large Binocular Telescope (LBT) , 2008, Astronomical Telescopes + Instrumentation.

[5]  J. Conan,et al.  Wave-front temporal spectra in high-resolution imaging through turbulence , 1995 .

[6]  Jörg-Uwe Pott,et al.  Simulation of an accelerometer-based feedforward vibration suppression in an adaptive optics system for MICADO , 2016, Astronomical Telescopes + Instrumentation.

[7]  Oliver Sawodny,et al.  Accelerometer-Based Online Reconstruction of Vibrations in Extremely Large Telescopes , 2014 .

[8]  G. Oriolo,et al.  Robotics: Modelling, Planning and Control , 2008 .

[9]  Caroline Kulcsar,et al.  Tip-tilt disturbance model identification for Kalman-based control scheme: application to XAO and ELT systems. , 2010, Journal of the Optical Society of America. A, Optics, image science, and vision.

[10]  David Mouillet,et al.  NACO performance: status after 2 years of operation , 2004, SPIE Astronomical Telescopes + Instrumentation.

[11]  Oliver Sawodny,et al.  Real-time vibration compensation for large telescopes , 2014 .

[12]  Christophe Verinaud,et al.  On the nature of the measurements provided by a pyramid wave-front sensor , 2004 .

[13]  Malcolm Smith,et al.  Evaluation of the on-sky performance of Altair , 2004, SPIE Astronomical Telescopes + Instrumentation.

[14]  J.-U. Pott,et al.  Simultaneous water vapor and dry air optical path length measurements and compensation with the large binocular telescope interferometer , 2016, Astronomical Telescopes + Instrumentation.

[15]  C. Kulcsár,et al.  Optimal control law for classical and multiconjugate adaptive optics. , 2004, Journal of the Optical Society of America. A, Optics, image science, and vision.

[16]  Oliver Sawodny,et al.  OVMS-plus at the LBT: disturbance compensation simplified , 2016, Astronomical Telescopes + Instrumentation.

[17]  G. Agapito,et al.  Optimal control techniques for the adaptive optics system of the LBT , 2008, Astronomical Telescopes + Instrumentation.

[18]  M. Shinozuka,et al.  Simulation of Stochastic Processes by Spectral Representation , 1991 .

[19]  Thierry Fusco,et al.  First laboratory validation of vibration filtering with LQG control law for adaptive optics. , 2008, Optics express.

[20]  Rolf Isermann,et al.  Identification of Dynamic Systems , 2011 .

[21]  S. Esposito,et al.  Pyramid Wavefront Sensor behavior in partial correction Adaptive Optic systems , 2001 .

[22]  T. Fusco,et al.  SPHERE eXtreme AO control scheme: final performance assessment and on sky validation of the first auto-tuned LQG based operational system , 2014, Astronomical Telescopes and Instrumentation.

[23]  David G. Sandler,et al.  Adaptive optics for diffraction-limited infrared imaging with 8-m telescopes , 1994 .