Research On The Measurement Detection Method Of Geometric Errorfor Heavy Duty Vertical Machining Center

Nowadays heavy-duty NC machine tools have been widely applied in defense, manned spaceflight, lunar exploration engineering, shipbuilding, metallurgy, military industry and other key fields. The accuracy of heavy-duty NC machine tools directly reflects the level of manufacturing industry. Heavy-duty vertical machining center is suitable for large parts machining, due to its open-processing structure. Because of the large size and scale of structure, it generally takes a long time to measure the geometric errors by large numbers of measure points under the influence of great temperature variation, which results in a great measurement error. There is no method with high efficiency and high precision to measure the geometric errors of heavy-duty vertical machining center. It has important practical significance to measure the geometric errors of these NC machine tools.Because of the large structure of heavy-duty CNC machine tools, it is necessary to verify the rationality of puny angle assumption that is the precondition in geometric error model. In this paper, the work of the rationality of puny angle assumption has been done. The influence of angle errors and movement ranges the machine tools on the accuracy of geometric error model is analyzed by changing these two factors. Geometric error models of linear axes and revolving axes based on the assumption of puny angle are established. The model of geometric errors for heavy-duty vertical machining center is established by multi-body theory and low order body array.The measurement uncertainty of single station method, multilateral method, sequentially multilateral method based laser tracker in heavy-duty vertical machining center is analyzed by Monte Carlo method. At the same time, the measurement uncertainty of various number of stations is analyzed. The method of coordinates measurement for heavy-duty vertical machining center is determined by combining the actual demand of the project. A mathematical model based on the laser tracker sequentially multilateral method is established. The layout of stations of sequentially multilateral method is optimized in theory. The layout of stations of sequentially multilateral method is verified by computer simulation technology.The principle of errors measurement based on the laser tracker sequentially multilateral method of linear axes and rotary axes are respectively studied. According to the geometric error modeling, the measuring principle of the geometric error for linear axes and rotary axes is conducted as well as the principle of squareness errors.To verify the validity of the geometric errors measurement method of heavy-duty vertical machining center based on sequentially multilateral method, some experiments are designed and carried out. The geometrical errors of the linear axis of the heavy-duty vertical machining center are detected by using proposed method. At the same time, all the geometric errors are detected directly by laser interferometer to compare with the ones detected by the proposed method. The results show that laser tracker accomplishes the precision detection of heavy-duty vertical machining center within 4 hours and the errors are close to the ones detected by laser interferometer. The high efficiency and high precision of this method is verified.