Study On The Active Control Technology Of A Thin Primary Mirror

Active optics is one of the key technologies for building modern large telescopes,active optics uses the wavefront sensor to measure the optical aberration in the telescope system,and corrects them by changing the primary mirror’s surface with the actuators on the back of the mirror,in order to improve the telescope’s image quality.This dissertation works on a 1.2m thin primary mirror active optics system and devotes to the control technology of the thin primary mirror.This dessertation starts from the designing of the 1.2m mirror’s support method,conducts theoretical and experimentaldesigning,analyses and researches on the 1.2m active optics system’s support method,active correction algorithm,control system and detection method,meanwhile,a 1.2m thin mirror active optics experiment platform is established and used to verify the thin mirror’s active correction.The 1.2m thin mirror’s active supports system is designed and optimized according to the thin plate theory and the finite element method,including both the axial and lateral supports’ spatial configurations and forces,the mirror’s gravitational deformation is significantly reduced;a new pure-shear lateral support method is proposed,it simplified the lateral support’s structure without degrading the mirror’s gravitational deformation.The 1.2m mirror’s active correction algorithm is studied,the mirror’s deformations caused by gravity,temperature,and so on,as well as its correction capability on these deformations are analyzed,at last,the requirements on the actuators are analyzed.A control system is designed for the 1.2m thin mirror’s surface correction,it can works in closed loop control or open loop control.The control system models and transfer functions of the 1.2m mirror active optics system under closed/open loop control are established.The effect of the axial actuators’ error on the 1.2m mirror’s surface is studied,furthermore,the mirror surface deviations induced by the control system when observing the natural/artificial targets are analyzed.A surface detection module is designed for the 1.2m mirror,it detects the mirror’s surface with an auto-collimation optical path and a Shack-Hartmann sensor.The position error between the detection module and the primary mirror is studied,as well as the surface detection error caused by it.In-depth study is conducted on one of the position errors-the misalignment between the Shack-Hartmann sensor and the primary/deformable mirror-as well as its detection method,two new high precision detection algorithms are proposed and studies both theoretically and experimentally.At last,the correction methods and effects of the 1.2m mirror experiment platform on the position errors are analyzed.A 1.2m thin primary mirror active optics experiment platform is designed and established,the mirror’s active correction experiment is conducted on the platform and verified the studies in the previous chapters.The platform and the experiment provide certain technical references for the large telescope being built by the Institute of Optics and Electronics,Chinese Academy of Sciences,meanwhile,they also provides certain theoretical and practical experiences for the development of China’s future large telescopes.