Design of frequency-based controllers for vibration mitigation at the Gemini-South telescope

Abstract

Reduction of tip and tilt vibrations at the Gemini South MCAO System (GeMS) is addressed in this paper. A frequency framework for the synthesis of controllers is described, with particular emphasis on the search for better closed-loop performances by minimizing a H 2 norm of the tilt residuals. Previous results have shown that modeling the turbulence via identification tools using standard AR or Laplace representations can lead to non-optimal solutions, resulting in excessive rejection of certain frequencies or an unbalanced residual spectrum due to poor modeling of vibrations. In this novel approach we reconstruct the open loop slopes (pseudo-open-loop) from on-sky data and then perform a fine tuning of the controller by finding the parameters that minimize the variance of residuals during a sequence of closed-loop runs with increasing controller complexity. Although the method is not optimal, it effectively rejects the main vibrations in the loop and it also improves the overall performance of the system. The method is compared to two standard integrators: one with fixed gain and the other with optimized integral gain. Results show substantial improvements of this new method when compared to the classical integrator.

Mirrors' dynamics: A plague for adaptive optics systems performance?

“…Thus, tip-tilt controllers can ultimately be implemented in fully decentralized from, i.e. as two independent SISO control loops (see, e.g., [12], [11], [13]). …”

Science readiness of the Gemini MCAO system: GeMS

“…The vibration seen around 14Hz is also eectively suppresed with the new method. The new controller has proven to be stable on-sky, and we are implementing an on-line adjustment of its parameters, 30 which should keep the vibrations to a minimal level. Figure 13.…”

Optical axis jitter rejection for double overlapped adaptive optics systems

“…Otherwise, significantly increased computation burden originated from identification process will be of slight advantages. Some advanced algorithms incorporating with online identification on the basis of observed data have been proposed to counter varying work circumstances and system models [9][10][11]. The biggest difference between these methods above and ours is that vibrations, in our applications, are removed by utilizing an independent AOS, which is incorporated into a double overlapped AOS architecture [15].…”

“…However, benefits are extremely small because of bandwidth limit due to stability [4]. At present, most control algorithms are based on a linear quadratic Gaussian controller frame [5][6][7][8][9][10][11][12][13][14]. These techniques have been tested on laboratory level [5,6] and applied on some realistic systems in recent years [7,8].…”