Hardpoints Defining Technologies For Large Mirror Based On Active Optics

Hardpoints define the position and orientation of the mirrors relative to their mirror cells, are key elements of the active optics system and play a significant role in improving the imaging quality and safety performance of the telescopes. With the development of the telescope in the direction of large aperture, lightweighted and high resolution, the sensitivity of the imaging system is sharply increasing to the position and orientation of the mirrors and theirs surface accuracy. That is, the requirement of positioning accuracy, load monitoring and safety protection of the large mirror presents a great challenge to the hardpoint positioning system.This paper, after summarizing comprehensively the principles and structures and typical representatives of all kinds of hardpoints, concludes the develop tendency of the hardpoints and discusses in detail the key structures and technologies of the hardpoints which are arranged in a hexapod configuration in view of its superiorities in comparison with other types of hardpoints. At the same time, gives out a sets of solutions for improving the positioning accuracy, axial stiffness and safe reliability of the hexapod.In this paper, a set of the most promising of the hexapod positioning system(consisting of six same hardpoint) which will be used in 8m level active optical system is designed. Among them, each hard point includes five major components: base, displacement type Actuator(by stepping motor, precision planetary reducer, antibacklash gear pair, angular contact thrust bearings, circulating planetary roller screw, LVDT, tangential support assemblies, a rotary encoder, etc.), the axial breakaway mechanism / upper biaxial flexure hinge / load cell / torsion limiter assembly, plus the extension arm / counterweight mounting flange / lower biaxial flexure hinge and counterweight.On the basis of in-depth study of hexapod hardpoint system, firstly, the structure of the hard point of the six bar is designed.Then the finite element analysis and optimization are carried out.At last, the most important and most closely related two technical indexes(structural rigidity and positioning accuracy) of the key technology of the six bar hard point device are studied, so that it can improve the performance of the maximum.The research results of this paper include: Based on the requirements of fuctions stiffness and precision of the hexapod positioning system, a cage-circulating planetary roller screw, a biaxial flexure hinge and the torsion limiter is designed. In addition, a high axial stiffness of the pneumatic axial breakaway mechanism is devised which compared to the traditional mechanical Overload protection device is simpler, and can achieve better results.