Geometric error identification for machine tools using a novel 1D probe system

Measuring and evaluating the geometric error of a linear axis periodically, is an essential operation in the day-to-day usage of a machine tool. In this paper, a system consisting of a novel one-dimension probe and a ball array is developed to fast estimate the geometric error a linear axis from the ball center deviations in three dimensions. The proposed 1D probe is assembled by an inductance micrometer and a simple fixture. Five measuring positions on the ball surface are selected to recognize the ball center offset caused by the geometric error. Then, an identification model is established to recognize the error at the ball center in the array. Moreover, a correction method is proposed to eliminate the installation error. It applies the least square method to form the virtual baseline by the measured ball centers, in order to eliminate the effect that resulted from the inaccuracy and the misalignment of the ball array during the manufacturing and setting, respectively. Then, the remaining part of the measured results is applied to evaluate the geometric error of the measured linear axis, including one positioning error and two straightness errors. Finally, a prototype system is developed to verify the correctness of the proposed 1D probe, while a measurement experiment is conducted on a machining center to verify the validity of the proposed method. The results indicate that the maximum absolute error among one positioning error and two straightness errors reach to 2.1 mu m, 2.3 mu m, and 1.6 mu m, respectively, while the root mean square error, and the average absolute error are no more than 2.0 mu m, when comparing with the results from the laser interferometer.