The suppression of edge error in time-controlled grinding for optical components

The demand for production capacity and manufacturing precision of large aperture mirrors is increasing. Almost all the existing deterministic machining methods produce edge error, which will take a long time to eliminate otherwise part of the available aperture will be lost, thus affecting the performance of the optical system. Time-controlled grinding (TCG) is proposed as a novel and efficient optical deterministic machining method, but the control of edge error has not been studied. Based on the motion structure of TCG device and numerical calculation, an optimization method of contact wheel suitable for a concave surface is given, and the generation model of the corresponding removal function is established. The fluctuation of removal efficiency in overhanging situation is evaluated by finite element analyses and experiments. TCG experiment is carried out on a concave spherical mirror with 196 mm aperture and a radius of 500 mm which takes 168 min to converge the surface error to 1.02 μm PV and 0.07 μm RMS. Measurements indicate that the entire aperture loss is <1 mm with almost no warpage/collapse edge. The results show that the surface shape error can be improved to <0.1 μm RMS with a removal efficiency of mm 3 /min-level after wheel grinding without significant edge error, which greatly reduces the difficulty and time of subsequent processes, indicating the great advantage of TCG in efficient optical machining.