Recently, the Astronomy and Space Mirror Technology Laboratory of the Chinese Academy of Sciences Nanjing Institute of Astronomical Optics Technology completed the grinding of the 1.93-meter aspheric primary mirror of the Mutian Telescope. The Mutian Telescope was jointly launched by Su Dingqiang, Cui Xiangqun, academicians of the CAS Member, and He Xiangtao, professor of Beijing Normal University. It was jointly built by Beijing Normal University, Chinese Academy of Sciences Xinjiang Observatory, Nanjing Tianguang Institute and Xinjiang University, and was developed by Nanjing Tianguang Institute. The fine grinding and polishing of the mirror surface are completed using an active polishing disc. The technology was successfully developed by a team led by Cui Xiangqun in China. The active polishing disc undergoes real-time deformation through computer control to match the required mirror surface shape, and optimizes various process parameters to achieve high-speed, high smoothness, and high surface accuracy in large mirror processing. In just two months, the mean square accuracy of the mirror surface reached 0.8 micrometers, indicating that Nanjing Tianguang Institute has made new improvements in the processing efficiency and accuracy of large mirror grinding through the development of active polishing disc technology in recent years.
The project team combined a six joint industrial robot with a swing arm profilometer to solve the problem of accuracy affected by the jumping error of the turntable, providing sub micron level measurement data for the fine grinding and rough polishing stages of the mirror, and achieving seamless connection with optical interference inspection. This method reduces the risk and time of reciprocating transportation of large-diameter mirrors in processing and inspection positions, and improves inspection efficiency.
Precision polishing is achieved by a parallel planetary grinding tool driven by a robot, which achieves stable grinding characteristics through precise control of revolution, rotation, and grinding pressure. The independently developed process analysis software integrates detection data processing, residence time calculation, and machining path generation, achieving digital automatic grinding, good certainty, and fast error convergence. The root mean square value of the 1.93-meter mirror full aperture surface shape error is better than 1/50 wavelength, which is better than the design specifications.
The successful grinding of the 1.93-meter main mirror of the Mutian telescope marks the routine application of advanced technology processing and inspection methods represented by Nanjing Tianguang, such as active disc polishing, robot swing arm profilometer, and parallel flat rotation grinding tools. It is expected to play a role in the development of large and extremely large astronomical optical telescopes in China.
Actively polishing the disc to grind the 1.93-meter main mirror
Robot swing arm profilometer for mirror inspection (left), parallel planetary grinding tool for precision polishing (center), mirror interference fringes (right)
