Research On Trajectory Error Prediction Method Of Five-axis NC Machining

The machining accuracy of NC machine tools is an important index to measure the performance of the numerical control machine tools, and the factors that affect the machining accuracy of NC machine tools are mainly divided into static error and dynamic error. At present, the domestic and foreign research on the static error is perfect and mature,so that the machining accuracy of the traditional machine tools is greatly improved; In high speed machining environment, the dynamic characteristics of servo feed system are becoming more and more prominent with the increase of feed speed of machine tools, and the dynamic error is the main reason of the high speed machining accuracy.In this paper,according to the dynamic model and the kinematic model of the machine tool feed system,and a prediction method of the trajectory error of five axis NC machining is proposed. This method can be used to guide the selection and optimization of the tool path, and reasonable adjustment of feed rate, and improve the dynamic characteristics of mechanical transmission system,and adjustment and compensation processing track,and reducing the influence of the trajectory error on the machining precision.The dynamic characteristics of feed system of NC machine tool is the important reason for the tracing error and the machining path error of the five axis linkage machine tool. In this paper, the five-axis linkage CNC machine tool is used as the research object,based on the principle of double inertia system, the three inertia dynamic model is established for the mechanical drive system of the linear shaft, and tuning the parameters of current loop, speed loop and position loop.The effect of stiffness and damping on the dynamic characteristics of the system is analyzed. Based on the principle of double inertia system, the dynamic model of the mechanical drive system of the rotating shaft is established. And through Simulink simulation analysis, and lay the foundation for the simulation of the cutter center position and the cutter axis vector of the discrete control point in the machining trajectory of the actual machine tool.The kinematic model of the machine tool is the basis for the realization of the solution and control of the motion of the machine tool,and it is an important transition link in the study of trajectory errors. In this paper, through the analysis of the specific structure of five axis CNC machine tools, and the whole homogeneous coordinate transformation matrix from the workpiece coordinate system to the tool coordinate system is derived in the five-axis machine tools. The dynamic forward solution model and inverse solution modelof five axis machine tool are established. Combined the feed system dynamics model with kinematics model, the simulation of the actual machining trajectory in discrete control point cutter position and cutter axis vector is calculated, for trajectory error prediction method provide the basis and foundation.The prediction method of the trajectory error is based on the machine tool dynamic model and the kinematic model.In this paper, according to the interpolation method of the numerical control system, the linear interpolation method and the three-spline interpolation method are used to obtain the theoretical fitting trajectory.In the theoretical fitting trajectory, the search algorithm is used to determine the coordinates of the cutter center position points with the shortest distance between discrete points.The prediction error of the cutter center position is deduced. The cutter axis vector is converted to the unit vector,and the cutter center position of the discrete point is the starting point, and the end of the cutter axis vector will form a spherical surface. Take a moment of the cutter location points before and after the two discrete points of the geometric relationship is applied to the derivation of the tool axis vector, based on machining simulation trajectory in discrete points of the tool axis vector and deduced the cutter shaft vector trajectory error of the prediction algorithm.In Matlab software, using the linear interpolation trajectory error prediction algorithm,the three spline interpolation trajectory error prediction algorithm processing spiral line,determine the three spline interpolation trajectory error prediction algorithm is more effective. Three spline interpolation trajectory error prediction algorithm is used to simulate the circular trajectory, and the effectiveness of the algorithm is verified by comparing the trajectory error of the circular arc curve. Combined with other researchers to study the trajectory error prediction method, this paper describes the advanced nature of the trajectory error prediction method.