Research on spatial error calibration method of CNC machine tool based on laser tracker

Abstract

Laser tracker is widely used in the performance detection of high-grade CNC machine tool, as a portable and largescale spatial coordinate measurement benchmark. The coordinate measurement accuracy of commercial laser trackers is about 10 microns, which makes it difficult to correctly evaluate the performance of high-grade manufacturing equipment. Therefore, taking laser ranging as pure input and abandoning the accuracy of the angle measurement of the tracker, has gradually become a common key technology in the field of large-scale spatial coordinate measurement. However, this method usually requires the self-calibration of the base station to realize the coordinate measurement of the spatial point, which greatly reduces the measurement accuracy. Therefore, a method is proposed to directly determine the spatial error in the machine tool coordinate system. A spatial point measurement model using the principle of three-dimensional trilateration network adjustment is established. Equations for solving the spatial error are derived and established. Experiment results were verified by comparing with geometric error obtained by traditional measurement methods. Finally, the experiments were performed to calibrate spatial error of a three-axis CNC machine tool, and the measurement uncertainty evaluation was performed based on Monte Carlo method. Results show that this method can realize the micron-level coordinate measurement uncertainty, and can satisfy the spatial precision detection requirements of high-grade machine tool. The maximum difference of measured spatial error in single axis of machine tool between this method and laser interferometer is 6.0 μm. The maximum of the spatial error of the CNC machine tool is 31.6 μm, and the standard uncertainty is 10.2 μm.