Implementation of capacitive probes for ultra-high precision machine for cylindricity measurement with nanometre level of accuracy

摘要

Capacitive probes are widely used on new ultra-high precision machines to perform measurements with an uncertainty of few nanometres, especially for cylindricity measuring machines. For this reason, their insitu calibration has to be carried out by using a specific structure. Therefore, a preliminary high precision set-up has been designed and manufactured to investigate the behaviour and the implementation of the capacitive probes. Both the number and the locations of the capacitive probes in the set-up are presented and detailed, to justify how they minimize the homogenous thermal expansion effects. The experimental set-up allows validating the insitu calibration principle of the capacitive probes with regard to the laser interferometers. The recorded residual errors are about 2 nm over the 80 A mu m-travel range. The effect of a transverse offset of the capacitive probe from the cylinder's generatrix has been investigated both experimentally and theoretically, as well as they present a good agreement.