Geometric error measurement of an ultra-precision machine tool using integrated confocal sensor

The geometric error of an ultra-precision machine tool will degrade the form accuracy of machined surfaces. This paper proposes a error measurement method for a three-axis (XZC) ultra-precision machine tool based on an integrated confocal probe (1 kHz sampling rate and 9 nm repeatability). A variance-based global sensitivity analysis method was used to identify major error sources. To avoid potential alignment runout, a Φ30 mm brass bar was SPDT turned (Sa < 5 nm) and used as the artefact for the error measurement. The reveral method and improved multi-probe method were used to measure the straightness errors of linear slides and the radial/axial errors of the aerostatic spindle respectively. The results indicate that the straightness error of linear slide (EZX EYX EXZ EYZ) and axial/radial errors of the spindle (EXC EYC EZC) are major geometric error sources. The spindle axis offsets are within 20 nm and radial errors are less than 80 nm under tested spindle speeds (60/120/180/240 RPM).