Research On Primary Mirror Control System Of Segmented Ring Solar Telescope

Chinese Giant Solar Telescope(CGST)is the next generation of large groundbased solar telescopes of China.CGST is required to observe the high resolution imaging of solar surface at near infrared bands(~ 1 ?m),and to detect the fine structure of solar magnetic field and dynamic field.Due to the advantages of ring structure in polarization detection and thermal control,the current design of CGST is an 8 meter Ring Solar Telescope(8m-RST).The primary mirror of 8m-RST is a ring parabolic formed by isosceles trapezoid segments.The primary mirror control system(M1CS)keeps the shape by restricting the in-plane displacement of segments and adjusting the out-of-plane displacement of segments.Different from the active control of the full aperture segmented mirror,the segmented ring mirror requires added tip sensor for active maintaining.However,there is no research on the influence of the key parameters such as the in-plane displacement of segments and the sampling frequency of the control system on M1 CS of 8m-RST.This dissertation attends to on modeling,simulation,improving control strategy and building experimental platform.Firstly.The in-plane displacement of segments will affect the reading of edge sensors and tip sensors.This study establishes a 6-dof simulating platform for primary mirror system of 8m-RST.Simulation shows that the M1 CS can not maintain the right surface for 8m-RST imaging quality on 50 nm in-plane displacement of segments.For this,the improvement of primary mirror control strategy of 8m-RST is proposed.The gap and shear sensor are added for estimating the in-plane displacement,and then,modifying edge sensor and tilt sensor readings.The measurement accuracy of these two kinds of added sensors should be better than 26 nm.Secondly.The sampling frequency affects the stability and bandwidth of M1 CS.In this study,the discrete time simulation model of 8m-RST main mirror system was established,and the relationship between the relative stability of the system,the control bandwidth and the sampling period was obtained.A simulation method for asynchronous sampling of tip sensor and edge sensor is designed.Wind load model is imported to analyze the influence of wind disturbance on 8m-RST primary mirror system.It is obtained that the sampling frequency of tip sensor should be faster than 10 Hertz.Finally.Lots of research results for M1 CS of 8m-RST are based on the simulation analysis,which is still to be carried out to advance the feasibility verification.The author participated in the construction of the experimental platform of yunnan observatories segmented mirror(YNOSM),and carried out some active optical experiment based on this platform.The first unit of this dissertation(the first three chapters)is the background introduction.The second unit of it(chapters 4 through 6)is the main studies of three problems above.The last of it(chapter 7)is summary and outlook.