Research On Adjustment Mechanism For Secondary Mirror Of Large-Aperture Telescope

The secondary mirror is one of the most important part of large-aperture telescope system. It is necessary to research and analyze the theory thoroughly to satisfy the requirement of the system. Based on a 315mm diameter secondary mirror in Cassegrain telescope msystem,mutil-degree of freedom adjustment mechanism of the secondary mirror was planed after lightweighting the secondary mirror and optimizing its support systemeight design, which could provide reference for large-aperture telescope project.The development of the secondary mirror structure was introduced comprehensively both at home and abroad, and the key structural techniques were compared. Finally a structure scheme for secondary mirror was put forward which would fit the requirements of the system.Based on theoretical analysis and traditional experience, the lightweight design and optimal support for secondary mirror was carried out, and the corresponding finite element model was built. The surface precision of the mirror was analyzed. To meet alignment accuracy between primary and secondary mirror, a combined five-degree of freedom adjustment mechanism for secondary mirror was introduced, including a XY displacement platform and a Tip/Tilt/Focus stage. The XY platform, consisted of two one-way translation platform driving by hand wheel, transmitted by precision leadscrew and supported by cross roller guider, is to correct the eccentric error of X and Y direction. The Tip/Tilt/Focus stage, composed of three actuators, base and moving platform, is to adjust defocus and tip/tilt error. The moving platform and actuators were connected by flexure hinges, and the motion of the platform was performed by the extension of three actuators and the rotation of flexure hinges.The kinematic principle of three-dimension platform was presented in detail and the theory of flexure hinges was discussed detailedly.At last,the finite element simulation analysis of structural system of secondary mirror was done, verified the feasibility of the designed mechanism,furthermore some expectations were proposed for the future work.