Error-based plug-in controller of tip–tilt mirror to reject telescope’s structural vibrations

Abstract. Structural vibrations usually feature tip–tilt modes and affect the closed-loop performance of the tip–tilt mirror control system in astronomical telescopes. Long integration time of the image sensor always restricts the closed-loop control bandwidth, resulting in difficulties in rejecting structural vibrations. An error-based plug-in controller to mitigate multimodal structural vibrations is proposed. Only position error is used in this proposed controller, which can be plugged into existing feedback loops to create high gain at the frequencies of multimodal disturbances, and thereby the closed-loop performance can be optimized by designing an appropriate Q-filter. When the centered frequencies of energetic disturbances are determined, a band-pass filter is suggested to mitigate multimodal vibrations. This improved band-pass filter can avoid big amplifications at other frequencies. Due to not being restricted by an accurate model, the plug-in controller does not lead to a compromise between vibration rejection and control stability. Both simulation and experiment validate the effectiveness of the proposed method in the tip–tilt mirror control system under the condition of vibrations.