科研之友
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摘要
The 8-meter ring segmented primary mirror is one of the important alternatives for China Giant Solar Telescope plan. The active control technology of the segmented mirror is the key to realizing the high spatial resolution of the segmented solar telescope. In the active control of the ring segmented mirror，high precision edge detection and tip/tilt detection are important factors in determining the co-phase maintenance of the primary mirror. In the current CGST active segmented scheme，the piston error of the segmented primary mirror is detected and corrected by the electromechanical edge sensors. However，in solar observations，the daytime temperature fluctuates greatly，and the primary mirror surface is affected by solar thermal radiation to generate temperature gradients. The primary mirror temperature control is required to improve mirror seeing. The temperature of the telescope truss system will also change due to the influence of thermal radiation. Therefore，the complex observation environment of the solar telescope will cause the zero-point drift of the electromechanical edge sensor，which will gradually increase the figure error of the primary mirror and will not be able to maintain the co-phase for a long time. To solve the problem of the unstable zero-point of the electromechanical edge sensor in the solar telescope，it is necessary to find a short-period calibration method for the electromechanical edge sensor，and the calibration period is about tens of seconds to several minutes. The accuracy of edge detection is better than 5 nm，and CGST can achieve the co-phase maintenance of the primary mirror in visible or near infrared. Therefore，the calibration accuracy of the edge sensor needs to be better than 5 nm. The optical co-phase detection technology detects the figure error of the primary mirror and the phasing error，and measures the absolute position of the segments. The short-period calibration of edge sensors of segmented solar telescopes using the optical detection technology is an optional solution. In this paper，in order to verify the feasibility of short-period calibration of edge sensors with the optical detection technology，edge detection research based on point spread function is carried out. Cross-calibration experiments are carried out using actuators，edge sensors and point spread function cross-correlation detection. The detection error level of this method is evaluated，and an active control experiment based on point spread function edge detection is carried out on a two-mirror system. In the 5-hour active control experiment，the RMS of the tilt/tip change of the segmented mirror is maintained at 0.01″，the RMS of the edge height change of the segmented mirror is maintained at 6.33 nm，and the RMS of the figure error of the segmented mirror is maintained at 18.73 nm. The experimental results show that the optical edge detection can accurately reflect the change of the position state of the segments in the active control，and the edge detection accuracy is better than 5 nm. The edge detection accuracy and detection frequency based on the point spread function satisfy the short-period calibration of edge sensors. The research results provide a reference for the active maintenance of the ring segmented solar telescope in the near infrared or visible light.
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