Research In Pointing Error And Shafting Technologies For Large Telescope

Large Telescope as the main equipment of astronomical observation, the positioning accuracy of telescope is the basic guarantee to achieve high-precision orbit determination observing. Telescope pointing accuracy is the basic indicators of the observation target position accuracy.Shafting precision has played a decisive role in the telescope pointing process. Studies shafting technology ia an important wrok during research telescope pointing accuracy. The telescope pointing error analysis and correction, as a means to improve positioning accuracy of the telescope, is an important direction of current research, and development path of large telescopes.Based on the theory of multi-body system kinematics, combined with the structure and motion characteristics of the telescope, the relationship between the topology of the mechanical structure of the telescope system was established. Through the transferring theory of motion and position error error topology between the body and the body, the fundamental coordinate systems of telescope was established. All the errors from the telescope system are analyzed in detail. Then, the key technology of pointing error compensation were proposed, they are pointing errors modeling, parameter fitting, model updating and data acquisition. Based on the geometric error tranfer during the movement of telescope, to various sources of error for impacting telescope pointing, the pointing error correction model with clear physical meaning was established. On the basis of a detailed analysis of the model’s stability and parameters’ correlation, the model was proposed amendments. The model conforms to the actual requirements, and verified by actual observation.Hydrostatic bearings are a key component for many large telescopes. This paper analyzes the working principle of hydrostatic bearing, and establishs mechanics calculation model of the hydrostatic bearings. For hydrostatic thrust bearings, the fluid dynamics theory was used to analysis the influence in detail, that it was the static and dynamic performance of oil film. The effect of different ways of supply oil to shaft stiffness was presented. The finite element model of oil film was established by finite element analysis method and computational fluid dynamics. The simulation analysis was carried out on the flow field of oil film, it is concluded that oil pressure and temperature distribution in the oil film. The static equilibrium equation of pads is used to establish static pressure oil film homogenizing effects on geometric error model. The measurement of geometric error and shaft motion error was verified. The result verifies the advantages of hydrostatic bearing shafting.According to the characteristics of large telescope shafting structure size, the scale tape encoder is proposed to measure angle of telescope shaft. From the point of geometry, the measurement angle error of encoder is analyzed in detail. The multi reading head and principle of eliminate difference are studied. Harmonic compensation method was used to improve the accuracy of angle measuring system. The experiment of mearsuring angle scheme was verified by turntable. At the same time, the the scheme is feasibility, and the harmonic compensation method is effectivenss.Through the precision analysis of telescope azimuth axis and elevation axis, we study the principle and mathematical model of wobble of azimuth axis, which proved that the precision of shafting on the importance of the telescope pointing accuracy. Based on the effect shafting error to pointing accuracy, the principle and calculation method of the accuracy index of the shafting was determined.