Ultra-precision machining of a large amplitude umbrella surface based on slow tool servo

Due to its excellent optical performance and system integration property, micro-nano structure function surface has been widely used in optical apparatus and energy collection equipment. But using traditional processing method can't obtain a mirror-like surface with high form accuracy and low roughness for sake of its complex micro-nano structure. In this paper, a large amplitude umbrella surface is special designed and single point diamond turning (SPDT) technology based on slow tool servo (STS) is used for umbrella surface machining. The tool path generation, tool radius compensation and tool geometry optimization are detailed for fabricating the desired surface. A new method combined with constant angle and analytical mathematical optimization is proposed for tool path optimization. A large amplitude umbrella surface with the maximum amplitude 0.2 mm and period 8 per cycle is designed, and the machining experiment is carried out on Nanoform 250 ultra-precision machine tool. From the form accuracy 1 mu m in surface residual error and 279.12 nm in RMS and the surface roughness 230.10 nm in Ra for the machined surface, it can be seen that a large amplitude umbrella surface is easily fabricated by SPDT under STS controlling.