Research On Component Technology Of The TMT Tertiary Mirror System Tilt Mechanism

The tertiary mirror system (M3S) of thirty meter telescope (TMT) is the largesttertiary mirror in the world. It is a huge structure with high precision and wonderful lowspeed performance under many working cases, which makes it a challenge. Even more,we are inexperienced with the innovative methods to do the measurement. M3S issimilar to an azimuth-altitude (az-alt) telescope. But its working conditions are quiteeven worse, which prompts us to apply the new method to complete a perfect product.This paper mainly focuses on the design for Tilt mechanism of M3S. Many scientificcomputing and simulations are applied to study every feasible solution. And the finaldesign seems to be good according to the analysis.Above all, a stiffness allocation has been developed to guide the designer. Then,there are two plans proposed on the basis of M3S functional requirement. One is aparallel manipulator, while the other one is a classic solution. Plenty of research andsimulations are accomplished to guarantee a correct design. According to the load path,some analyses were done to determine which bearing layout is the best choice. We alsofocus on the driver design. A linear actuator is employed to supply the support force.The stroke and mounting dimensions are determined. It also attracts many attentions tostudy the key components design. It’s particularly useful that a parameterized finitemodel is constructed to investigate the mainly deflection of M3S in all the conditions.The analysis results show that the maximum deflection can be up to1.28mm and the deflection angle is about62", while the first modal frequency is15.1Hz. Finally, MonteCarlo simulation method is applied to study the pointing presion by the various errorsfrom a statistical point of view, and there are a lot of interesting conclusions, of whichthe maximum measurement error of the tilt axis is about4.1"RMS.From allocating the stiffness and working for the preliminary design to final systemaccuracy analysis, the procedure follows a reasonable design methodology. The supportprinciple of the tilt axis system and the structure characteristics even with the errorsimulation were analyzed.The design decisions were made by lots of theoretical analysis and finite elementsimulation. All analysis showed that the final design could meet the requirements.Meanwhile, it deals well with balancing the cost and the performance for eachcomponent, which makes the subsystem in keeping with the overall system.This paper completes a plenty of work for M3S, and will promote the TMTconstruction process. Meanwhile, many experiences can be learned by this paper.