中国科学院云南天文台机构知识库

重力和温度作用会导致结构变形从而引起副镜姿态失调、像质变差等问题，如何获取副镜相对主镜的失调量是进行副镜姿态校正的关键环节。以2 m环形太阳望远镜副镜姿态校正系统为例，研究了基于小视场波前像差测量的副镜姿态校正方法。针对偏心和倾斜存在耦合，而在小视场中无法通过多视场的波前像差探测实现解耦的问题，分析了采用正则因子约束低灵敏度失调量和直接约束低灵敏度失调量两种方法的校正效果。提出了正则因子对失调量约束的两种实施方案：基于稳定0点位置的失调量调整和相对位置的失调量调整。根据失调量校正的灵敏度矩阵模型、波前探测系统的测量精度以及六杆机构的执行误差，分别从像质补偿效果、失调量求解精度和累积误差三个方面对不同的校正方法进行了仿真研究。仿真结果表明，以一定的正则因子对失调量基于稳定0点位置进行整体约束的校正方案，失调量的求解和系统的像质改善均能取得较好效果，该方法能够将波面均方根误差从0.495 9λ改善到0.006 2λ，且不会在连续的调整过程中引入较大的累积误差，该方案更适用于基于小视场像差测量的副镜姿态校正系统。

Ground-based solar telescopes take high-resolution observations as their main goal, and have stricter image quality requirements. Due to the direct observation of the sun, solar telescopes are more susceptible to heat and other factors during operation. Gravity and temperature will cause changes in the positional relationship between the primary and secondary mirrors, resulting in time-varying aberrations. If not improved, it will affect the effect of high-resolution observation. In order to better realize highresolution imaging observation, it is necessary to strictly control the image quality of the telescope during operation. How obtain the misalignment of the secondary mirror relative to the primary mirror is a key link in the attitude alignment of the secondary mirror. In the attitude alignment problem of the secondary mirror based on aberration detection, due to the coupling relationship between the translation and the tilt of the optical axis of the telescope, they will both lead to the coma aberration of the system. Therefore, the aberration measurement cannot completely distinguish decenter and tilt, which will have a certain impact on the attitude adjustment accuracy of the secondary mirror. For telescopes with a large field of view, aberration detection can be performed in different fields of view, and decenter and tilt can be decoupled through aberrations in different fields of view. Small field telescopes cannot achieve decoupling through multi-field wavefront aberration detection. Taking the attitude alignment system of the secondary mirror of the 2 m Ring Solar Telescope as an example, the attitude alignment method of the secondary mirror based on the measurement of the wavefront aberration of the small field of view is studied. To reduce the influence of coupling on the accuracy of misalignment solution, there are usually two schemes. The first scheme is to directly constrain the low-sensitivity misalignment, that is, not to adjust the low-sensitivity misalignment; the second scheme is to use a regular factor to constrain the low-sensitivity misalignment. In the correction scheme of using the regular factor to constrain low-sensitivity misalignment, two implementations are proposed on this basis："alignment based on stable 0-point position" and "alignment based on relative position". Due to the real-time nature of the attitude alignment of the secondary mirror, multiple corrections are required during the observation time. Based on the misalignment calculation accuracy and image quality compensation effect, the concept of "accumulated error" in the control system is proposed. According to the sensitivity matrix model of the misalignment correction, the measurement accuracy of the wavefront detection system and the execution error of Hexapod, different correction methods are simulated from three aspects：image quality compensation effect, misalignment solution accuracy and cumulative error. The simulation results show that although the scheme of directly constraining the low-sensitivity misalignment has a certain compensation ability, the root mean square error of the corrected wavefront is greater than λ/14, which cannot meet the target accuracy requirement of 2mRST. The solution accuracy of the misalignment is not as good as that of using a regular factor to constrain the low-sensitivity misalignment, and since the decenter does not participate in the control, the accumulated error on the decenter will also exacerbate the deviation of the misalignment from the adjustment range of Hexapod. In the scheme in which the low-sensitivity misalignment is constrained by the regular factor, the misalignment adjustment scheme of the relative position is adopted. With the increase of the adjustment times, there is a problem of accumulation of errors, and the coupling between the decenter and the tilt leads to a low solution accuracy of the decenter and the tilt, the cumulative error range is larger. And as the accuracy of the detection and execution links decreases and the correction frequency increases, the speed of error accumulation will increase, and the execution of the misalignment will exceed the travel range of the Hexapod, which may cause damage to the mechanism. A correction scheme that uses a certain regular factor to make an overall constraint on the misalignment based on the stable 0-point position, can achieve better results in solving the misalignment and improving the image quality of the system. This method can improve the wavefront root mean square error from 0.495 9λ to 0.006 2λ, and will not introduce a large cumulative error in the continuous adjustment process. This scheme is more suitable for the attitude alignment system of the secondary mirror based on the measurement of small field of view aberrations.