Abstract
Error compensation has become an important means of improving the manufacturing and processing accuracy of computer numerical control (CNC) machine tools. Quick and precise measurement of the various geometric motion errors (GMEs) of CNC machine tools is crucial. We propose a novel laser method for the efficient and direct high-precision measurement of the 21 GMEs of a three-axis CNC machine tool, or three linear axes of a five-axis tool. A corresponding system was developed, comprising a fiber-coupled laser unit, sensor head, target unit, and beam-steering unit. The beam-steering unit was designed to perform high-accuracy 90° rotation of the measuring beam, and the target unit was designed to be sensitive to 18 GMEs of the three linear axes. Stability, repeatability, and comparison experiments were conducted to verify the performance of the proposed system. The results showed that the stability of the position error measurement is ± 6.3 nm. For straightness error measurement, the stability, repeatability error, and residual are within ± 60.3 nm, ± 0.5 μm, and ± 0.7 μm, respectively. These are within ± 0.12 arcsec, ± 0.5 arcsec, and ± 0.5 arcsec for the pitch and yaw measurements, and within ± 0.37 arcsec, ± 1.5 arcsec, and ± 1.0 arcsec for the roll measurements, respectively. For squareness error measurement, the repeatability error and residual are within ± 0.6 arcsec and ± 1.6 arcsec, respectively. Compared with a laser interferometer, the proposed system can measure the 21 GMEs of a three-axis machine tool with one-step installation. Without accuracy loss, the measurement efficiency is approximately 45 times higher than that of a laser interferometer, thus providing a new quick and accurate measurement method of GMEs and error compensation of CNC machine tools.
Highlights
Improving the accuracy of computer numerical control (CNC) machine tools has been a long-standing issue in the field of mechanical manufacturing and precision engineering
We proposed a series of direct methods for simultaneously measuring six geometric motion errors (GMEs) of a single linear axis and developed the corresponding systems [41,42,43,44]
A commercial heterodyne interferometer (LH2000, Leice Technology, accuracy 0.4 ppm), which can measure at a speed up to 2 m/s, was integrated into the system, and the two orthogonal linearly polarized lasers generated by the LH2000 were coupled into a polarization-maintaining fiber (PMF) (PMJ-633, OZ Optics) to provide the laser source of the measurement system
Summary
Improving the accuracy of computer numerical control (CNC) machine tools has been a long-standing issue in the field of mechanical manufacturing and precision engineering. Two key challenges exist in the error compensation of CNC machine tools: measuring all the GMEs accurately and establishing an accurate error compensation model [4, 5]. For a three-axis CNC machine tool, 21 GMEs need to be measured [6]. A five-axis CNC machine tool has 42 GMEs [7, 8], 21 of which come from its three linear axes. As the error compensation models for the three linear axes of machine tools have been well established [6, 9, 10], it is vital to be able to quickly and accurately measure all the 21 GMEs in the error compensation of CNC machine tools
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