Aiming at the influence of beam divergence angle on the distance measuring system such as Michelson interferometer, the Michelson interference system model of point light source is established. The influence of beam divergence on the interference signal is calculated by numerical simulation. The theoretical calculation results show that when the incident light source has a divergence angle, the optical path difference between the reference path and the measurement path will cause the size of the measurement spot and the reference spot to be inconsistent, and the interference spot will show circular interference fringes, resulting in energy loss and interference efficiency reduction. Meanwhile, the interference signal intensity will decrease with the increase of the measurement path distance and beam divergence angle. By reducing the divergence angle, the interference signal can maintain high intensity. Finally, an equivalent Michelson interference optical system is built based on a He-Ne laser with a divergence angle of 1.7 mrad. The experiment results show that the interference signal intensity is significantly improved after the addition of the collimator. The results of this paper show that for the measurement system such as Michelson interferometer, reducing the beam divergence angle to 0.5 mrad can obtain relatively high interference signal intensity during the measurement.
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.
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