High-precision machining of optics by ultraprecision milling with compensated feeding mechanisms

摘要

In general,waviness tends to be generated on cut surfaces even when an ultraprecision milling machine with a single-crystal diamond tool is used. The present study deals with the prevention of waviness by controlling the feeding mechanisms of the milling machine. A machining experiment on spherical surfaces shows that machined surfaces exhibit periodic waviness with an amplitude of 30 nm and a wavelength of 300 um. Such waviness is found to result from interpolation errors between the pulses of encoders used in feeding mechanisms of the machine. To reduce such interpolation errors, the positioning accuracy of the machine stages is measured using a laser interferometer. On the basis of the measured results, the feeding mechanisms are compensated such that the positioning errors, even in the short distance moved between pulses of the encoder, are corrected. Using the machine with the compensated feeding system, mirror arrays with spherical surfaces are shaped. Consequently, waviness is reduced so that the surface smoothness is less than 10 run, demonstrating that such compensation produces superior optical surfaces.