Comparison of vibration mitigation controllers for adaptive optics systems

Abstract

Vibrations are detrimental to the performance of modern adaptive optics (AO) systems. In this paper, we describe new methods tested to mitigate the vibrations encountered in some of the instruments of the Gemini South telescope. By implementing a spectral analysis of the slope measurements from several wavefront sensors and an imager, we can determine the frequencies and magnitude of these vibrations. We found a persistent vibration at 55 Hz with others occurring occasionally at 14 and 100 Hz. Two types of AO controllers were designed and implemented, Kalman and H∞, in the multiconjugate AO tip-tilt loop. The first results show a similar performance for these advanced controllers and a clear improvement in vibration rejection and overall performance over the classical integrator scheme. It is shown that the reduction in the standard deviation of the residual slopes (as measured by wavefront sensors) is highly dependent on turbulence, wind speed, and vibration conditions, ranging--in terms of slopes RMS value--from an almost negligible reduction for high speed wind to a factor of 5 for a combination of low wind and strong vibrations.

Vibrations in MagAO: resonance sources identification and first approaches for modeling and control

“…The standard structure for an AO closed loop, 6 consisting of a wavefront sensor (WFS), a deformable mirror (DM) and a controller, is presented in Figure 11. A modal control approach will be used.…”

“…For this process, a standard AO loop scheme is used, 6 taking into account the presence of disturbances due to turbulence and vibration components, to obtain a space-state model for the AO loop. Autoregressive models 7 are used to describe the temporal correlation of the turbulence and vibration phases.…”

“…Previous work has been made studying the design of LQG control or frequency-based control for specific AO systems. 6 With a state-space model, LQG control can be implemented on simulation and compared to the integrator-based controller alternative, and a predictive control approach (MPC) is analysed for the system. Table 1 presents the system element's status during six of the tests conducted during the observing run.…”

Vibration budget for observatory equipment

“…Efforts are being made to reduce the impact of vibration on the delivered AO performance by changing the AO control algorithm [3][4][5] without changing the vibration environment; similar approaches are being explored for interferometer optical-pathdifference control. 6 Passive or active damping can also be used to change the structural response to vibration; 7 this changes the vibration environment without changing the sources of vibration.…”

Robust Control of a Deformable Mirror for Adaptive Optics Systems

“…For instance, A. Guesalaga et al added a notch on the weight function of sensitivity function to mitigate vibration at specific frequency [17][18][19][20].…”