Study on moment correction method of primary mirror semi-active support
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摘要: 主镜支撑技术一直是大口径望远镜技术的关键技术，以2 m SiC轻量化主镜为研究对象，探究了通过力矩校正的半主动支撑方法，用于校正一些由于加工误差、装配误差等因素引起的一些不可预知的因素所导致的低阶波前像差。首先建立有限元仿真模型，进行仿真分析，分别在6处Tripod柔铰处施加两个方向正交的，大小为1 Nmm的单位校正力Mx和My，共分析12种工况下的主镜变形情况；然后利用微小变形的线性叠加原理，分析计算该力矩校正方法对低阶波前像差的校正能力，由分析计算可知，该力矩校正方法对于加工、装配及装调过程中最常出现的倾斜和像散具有很好的校正能力，可以将初始镜面RMS值归一化为1/10（=632.8 nm）的像差，分别校正到0.687 nm和2.97 nm，校正能力分别为98.9%和95.3%，所需的最大校正力矩分别为6.3 Nmm和19.9 Nmm；然后根据主镜的whiffletree支撑结构，设计了力矩校正结构方案；最后通过试验验证柔性薄片力矩校正结构形式的可行性，进而验证半主动支撑力矩校正方案的可行性，为半主动支撑的工程应用积累了一定的宝贵经验，具有一定的指导意义。Abstract: In the development of large ground-based telescope technology, the primary mirror support technology is always a key technology. In this paper, a semi-active support method was researched based on a 2 m SiC lightweight primary mirror, which was used to correct some unpredictable low-order wavefront aberration caused by machining error, assembly error and other factors. Firstly, the finite element simulation model was established, and the finite element simulation was carried out. An unit correction moment (1 Nmm) of Mx or My, which were two orthogonal moments, was separately applied to the 6 Tripod soft hinge, so the primary mirror deformations under a total of 12 cases of the situation were respectively analyzed. And then with the linear superposition principle of small deformation, the correction ability of the moment correction method for low order wavefront aberration was analyzed and calculated. It could be seen from the analysis that the moment correction method could correct the tilt and astigmatism very well. The initial mirror RMS value of the tilt and initial astigmatism which were normalized to 1/10(=632.8 nm), could be respectively corrected to 0.687 nm and 2.97 nm, the correction abilities were respectively 98.9% and 95.3%, and the required maximum correction moments were respectively 6.3 Nmm and 19.9 Nmm. Then, according to the whiffletree support structure of the primary mirror, a structure of the moment correction was designed with the leaf spring at the Tripod soft hinge. Finally, the feasibility of the leaf spring correction structure was verified through experiments, and the feasibility of the semi-active support scheme of moment correction was verified further. And a certain degree of engineering experience for the implementation of the moment correction method has been accumulated with high guiding significance.
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Key words:
- SiC /
- primary mirror support /
- moment correction /
- semi-active
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