Research On Error Modeling And Measurement For Fast Tool Servo Based Turning System

The freeform optical surface element can improve the optical utilization due to its superior optical performance and small size. This type lenses have a widely applications requirement in new energy, engineering optics and other fields. However, due to the complex geometric characteristics of the surface, the freeform surface cannot be described by a unified mathematical equation, and the processing accuracy and surface quality are also increased in applications which are the difficult in machining. Therefore, improving the machine accuracy and surface quality of freeform surface parts has become the research direction under the ensuring of the processing efficiency.Because of the advantage of high efficiency and high precision and low cost, the fast tool servo(FTS) turning is widely regarded as a more promised processing method. This method can not only used in processing of optical freeform surface, but also in compensating the processing errors of the system. This method has received widespread attention. Based on domestic and international research, the processing errors of the FTS turning machine system are studied in this dissertation.The existing research on the error of the FTS turning process is often only for the FTS device or the CNC machine tools respectively, and the combination of the two are very few. In this paper, processing errors are analyzed by the combination of the FTS and the CNC machine tools. The kinematic chain of the FTS turning system is established, and the error sources are analyzed. Translational axis and rotation shaft of the geometric error and spindle and the FTS dynamics response caused by the dynamic error are analyzed, and the processing system of the key components of machine tool spindle and FTS mechanism dynamics model is built.Based on the multi-body system theory, the adjacent body array of the multi body topology system is combined with the traditional homogeneous coordinate transformation theory. A comprehensive error model is set up for the FTS turning system. Based on the multi-body system theory, the adjacent array in topology structure is described. Combined with the homogeneous coordinate transformation theory, the ideal motions and the characteristics of the adjacent bodies in multi-body system are described by mathematics. The actual motions and the characteristics of the adjacent bodies are described through the transform of the error motions between adjacent bodies. The error sources in the FTS turning process system are considered as the parameters, the ideal and the actual static and kinematic error characteristics are considered, and the integrated error model of the FTS turning system is established. With the aid of the measurement data of the X-axis and the spindle error, the influence of the guideway and the spindle error on the relative error of the tool is analyzed.In the processing system, the translation axis is one of the most critical moving parts. Error elements of the movement axis are the extremely important error sources, which influenced the machining precision of the processing system directly. On the analysis of the principle of the interferometer measurement of the translation axis motion errors, the positioning errors of the guideway and the motion errors of the FTS mechanism are measured using Renishaw XL-80 laser interferometer, and the measurement results of the positioning errors are compensated by the XC80 environmental compensation unit. In order to solve the coupling problem between the straightness error and the yaw error in the measurement data of the translational axis, enhance the efficiency of the laser interferometer measurement and eliminate motion errors of the reflect mirror that induced in the measuring process, the shift measuring method is proposed. Based on the laser interferometer measured through the multi-shifting set of initial sampling point, measurement gives a differential output measurement results. The multiple sets of measurement data are combined and transformed by the discrete Fourier. Thereby, the straightness errors of the translation axis and the angle deviation are separated. Furthermore, the yaw error of the slide is measured by a laser interferometer in laboratory environment and compared with the evaluated values. Experimental results confirmed the feasibility of the proposed method.In the processing system, the error motion of the spindle is a key factor that affected the processing precision in the FTS turning system. According to the characteristics of the error motion of the spindle, the precision of the indirect measurement is significant impacted by the contour error of the standard part inevitably. In order to get the accurate motion errors of the spindle, the measurement results should be separated. In this paper, three typical error separation method of the spindle rotary motion are summarized, and the choice of the three methods is determinate in different measurement requirements and conditions by comparison. On this basis, according to the existing problems of the spindle rotation error measurement, a method of the improved measurement of the rotational motion error is proposed. The round section and the cylindrical helix of the standard part are measured using two displacement sensors. The contour error of the standard part and the motion error of the spindle can be separated from the measurement results. The radial error and yaw angle error of the spindle motion can be obtained. By using the proposed method, the motion errors of the spindle of the Spinner machine tools are measured. The radial error and yaw error of the spindle are obtained, and the measurement results are analyzed.In this paper, the comprehensive error model and the motion errors of the FTS turning machining system is established and analyzed. The parameter error elements of the key moving parts in the system are measured and analyzed, which provides a theoretical guidance for the realization of high efficiency and high accuracy of the freeform surface machining.