The 8m ring segmented telescope is an important candidate solution for the Chinese Giant Solar Telescope project in the future. Being different from these full aperture segmented telescope, the ring segmented telescope need an additional tip sensing for closing the active control loop. Optical measurement method is a good choose for tip sensing, as its inherent sensitivity for angle measurement. This thesis focus on the discussion about the application of high accuracy optical measurement method to the segmented telescope active control, and the primary problem for the application, and the solution for the problem. The goal of these discussions is to propose a real-time optical measurement method for active control of the ring segmented solar telescope. The basic concept, principle, process, and requirement of the active control are presented in the chapter 1. While, the characteristic of the ring segmented telescope active control is emphasized in this chapter. The optical measurement method and optical sensor for active control is reviewed, and three candidate solutions of tip sensing for the ring telescope are proposed in the chapter 2. Based on the consideration of accuracy, bandwidth, thermal sensitivity, an internal optical metro-logy developing from Shack-Hartmann wavefront sensor is chose for further discussion. The tip measurement error from detector noise, thermal distortion of segments, turbulence noise, and the temperature gradient of environment is analyzed in the chapter 3. To compare these errors, it's found that the phase fluctuation caused by the turbulence is the most serious error source in these three. The turbulence error of differential tip measurement among these segments is derived in the case of local turbulence environment. Then, a temporal integral measurement method is proposed for suppressing the turbulence noise. Based on the Taylor's atmosphere frozen hypothesis, the curve of the error falling with the increasing of integral time is calculated with different pair of segments, and different case of ventilation. The result show that the high frequency surface error on the ring primary mirror can be corrected more quick than the low frequency error in the case of ventilation, when the control accuracy of different error mode is same. The relationship between the local atmosphere environment and optical measurement of active control is discussed in the chapter 5. Then an idea of constructing a synthetic system composed of environment control and active control is proposed. Then, a semi-empirical theoretical model of local seeing is introduced for environment control. And a result of temperature gradient measurement in field is shown in the end. The conclusion is that a high accuracy active control with optical metrology can be achieved, by proper environment control and thermal control. The point is a good cooperation between active control system and environment control system.
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