Research On Six Degrees Of Freedom Adjustment Of Secondary Mirror In Space Telescopes

With the gradual development of micro and nano satellite technology and the extension of application field of earth observation technology in recent years, researchers show more concern and attention on how to obtain high-resolution images with micro and nano satellite platform equipped with deployable space telescope. As the precision of the position between primary mirror and secondary mirror cannot be guaranteed after deployment of telescope, The secondary mirror adjustment mechanism is one of the key techniques of deployable space telescope, and this paper focuses on the study of a six degrees of freedom adjustment of secondary mirror.Firstly, a secondary mirror adjustment platform with six degrees of freedom adjustment is designed, Stewart platform is used as the foundation structure of this adjustment platform, the characteristics of this platform structure is introduced, the degrees of this platform is also verified, and an algorithm to solve the forward and reverse motion problem of this platform is presented.Secondly,according to the structure characteristics of the adjustment platform and the difficulty of achievement, joint type computer distributed control strategy is determined to be the overall control strategy for the secondary mirror adjustment Stewart platform.Thirdly, according to the results of telescope optical system error distribution, the control index of the secondary mirror adjustment Stewart platform is achieved. Through the study of the work principle of voice coil motors, the mathematical model of this VCM is described, And after the unit order step response characteristics of this model are analyzed, a double closed loop position control system with a current loop and a position loop is designed, results of the simulation shows that this double closed loop control system has superior unit order step response characteristics and dynamic tracking characteristics. Using ASD driver to complete the position control system, and a VCM position control experiment is done, the experiment results show that the precision of the position control system is ±0.5um, the design requirements are met.Finally, structure model of the secondary mirror adjustment Stewart platform is established in SimMechanics, and the accuracy of inverse kinematic problem solving algorithm is verified through combined with Simulink. A secondary mirror six degree of freedom control program is designed with the help of C++ function library in DMC2610, with this program, the VCM’s motion is according to the planning trajectory, and the adjustment procedure is simplified.At the end of this paper, the research work is summarized, the problems need to be solved and the future work is discussed.