| Compared with ground-based optical telescopes,space optical telescopes are free from atmospheric turbulence and have obvious advantages in capturing cosmic space images.As the resolution requirements for space telescopes continue to increase,the aperture of telescopes becomes larger and larger.However,the traditional large-caliber mirrors are subject to very severe transportation requirements and manufacture challenges due to the occurrence of excessive specular deformation caused by gravity rebound and the occurrence of defocus aberration caused by the space thermal environment.In response to the above problems,active optics technology can be used to correct the shape of the mirror surface in real time.And this technology has been successfully applied in ground-based large-caliber telescopes and their scaled active optical experimental systems.Thus,based on this,the surface correction technology of the space optical telescope primary can be studied.In order to deal with the working conditions such as microgravity or temperature change,and improve the shape of the primary of the space telescope,the mirror surface correction technology of the active support system of the voice coil actuator was studied.Through theoretical analysis,discussion of mechanical properties of different structures and numerical simulation analysis,the surface fitting and active correction algorithm,active support structure and working condition analysis results were given.The research content is mainly divided into the following three parts:a)Based on the comparison and analysis of the modal calibration method and the Zernike polynomial fitting method,the advantages and disadvantages of these two common fitting methods and their applicable occasions were discussed.It was determined that the Zernike coefficient is used to fit the surface shape and the least squares method is used to solve the problem.The process of surface fitting and active correction was deduced in detail.Finally,the Zernike coefficients and the mirror stiffness matrix were calculated by programming using Matlab.b)The mirror material and structural dimensions in the mirror support system were determined based on the spatial conditions and processing techniques.The four positioning support schemes were elaborated.Besides,axial support and lateral support were designed.The mirror shape and system natural frequency of the two supports were compared,thus the three-point support scheme of the axial of the mirror was proposed.Based on the optimized number and arrangement of active support points,combined with the structural forms and driving methods of common force actuators at home and abroad,the design index of voice coil force actuators,key component selection and flexible structure were introduced.The overall structure of the mirror support system was designed.c)A mirror model was build using HyperMesh,and the mirror deformation under different gravity and 2°C temperature rise conditions were analyzed.The improvement of the shape after active correction were also given.The results showed that the voice coil actuator active support system can correct the mirror profile to the RMS value ?/18.The correction effect after introducing actuator failure and assembly error was analyzed.The results showed that the mirror surface accuracy can still be corrected after a single voice coil force actuator fails.However,after two or more force actuators fail,the system no longer has the ability to correct.After introducing the assembly error,the corrected surface accuracy is ?/20.As a non-contact corrector,voice coil actuator has the advantages of no inherent stiffness,high resolution and fast response.After correction by voice coil force actuator group,the surface quality of mirror under gravity and temperature conditions was significantly improved.Therefore,this paper verified the feasibility of mirror shape correction technology based on voice coil actuator and the effectiveness of improving the accuracy of mirror shape. |
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