Research On TMT Tertiary Mirror System Rotator Assembly Structure Technique

Thirty Meter Telescope (TMT) Tertiary Mirror System (M3S) is different fromother telescopes in requiring tracking and pointing capability. The M3S featurescomplex and nonlinear load conditions compared to the alt-azimuth telescope. Themajor challenge is to ensure the high-precision of the axes. According to therequirements of TMT, this article majors on investigating the Rotator Assemblydesign and the key technologies involved in the system. Furthermore, large numbersof simulation analysis are applied to predict and ensure the system performances.In order to meet the requirements of high-precision, the investigation in thispaper is developed from four aspects, namely scheme selection, static performance,dynamic performance and interface accuracy. The work can be described as follows:(1) Supporting way, driving scheme and angle measurement method of the axesare studied, respectively. Different kinds of slewing bearings are evaluated byestablishing the bearing mathematical models under complex load conditions, whichmakes an evaluation of bearing performance. The gear driving scheme is applied inRotator and the dual-motor driving principle is analyzed. Moreover, the fast andsteady tracking performance is simulated, which shows the system can meet therequirements of tracking accuracy. Since the round encoder cannot meet thedemands, the tape encoder is selected. The precision and using method areresearched. The result verifies the effectiveness of improving the angle measurement accuracy of the turntable by applying the multiple reading heads combing withFourier harmonic analysis. With reasonable choices of the schemes, the axesperformance has been optimized greatly.(2) In order to evaluate the performance of Rotator, the finite element model(FEM) of the system is established, some static and dynamic performance isanalyzed by simulation. Meanwhile, in order to evaluate the performance of M3S,the FEM of the whole system is established as well, and the performance undergravity is analyzed to ensure the system’s safety. The finite element analysis resultshows that the first order natural frequency of the system is15.93Hz, which canmeet the requirements of the system modal characteristics.(3) As the supporting tower’s deformation would affect the M3S performance,it is necessary to investigate the connection methods between M3S and the tower.Two methods are proposed, one is kinematic connection method, and the other isnon-kinematic. The impacts on the accuracy of the bearing mounting surface arecalculated, respectively. The results indicate that the latter can get a higher precision,and meet the requirement of0.02mm of the bearing mounting surface flatness.In addition, environmental adaptability of the M3S is another important index.For seismic analysis, the spectral analysis method is applied to analyze the systemresponse under different levels of seismic loads. For wind loads analysis, thefluid-structure interaction and random vibration methods are used for structureresponse under static and dynamic wind loads, respectively.This paper has researched some key technologies of Rotator. A mount ofsimulation analysis of Rotator and M3S are carried out to predict the performance ofthe system in different working states, which effectively guides the design of M3S.Some of the methods and conclusions involved in this paper have a certain referencevalue on the large telescope design.