Polishing large aperture mirrors by manipulator

Abstract

To meet the requirement of Multi-mode Combined Manufacturing (MCM) in a large aperture mirror polishing process, a JP-01 NC polishing manipulator was developed. The manipulator adapted cylindrical coordinates with axes of ρ-θ, and the motions of axis ρ and axis θ were linked to realize all trajectories demanded by MCM. Based on the Preston hypothesis, a mathematical model of material removal was established by analysis on the relative velocity, pressure and dwell time at any point of the optical surface. Meanwhile, the position transform matrix of the manipulator was deduced. Furthermore, the model was used to simulate the usual motion modes of a single lap for zonal errors and local errors in the process of MCM and to achieve deterministic processes. A spherical surface with a diameter of 240 mm, and F number of 1.5 was polished by the manipulator and obtained results show that it can offer a surface accuracy of 14.6 nm (RMS). The experiments indicate that the theoretical analysis is coincident with observed experiment results. Moreover, the mathematical model can correctly reflect the practical material removal and can conduct deterministic processes. The polishing manipulator provides better motion modes for the MCM in the polishing process.