Kinematics Modeling And Contour Error Controling For Five-Axis NC Machine Tool With Two Rotations On The Table

Five-axis NC machine tool with three translational axes and two rotational axes can adjust both tool tip position and tool orientation. So it can process free surface that has more complex geometry and needs high precision. Five-axis NC machine tool is widely used to process mold, aerospace parts, sophisticated medical equipment, etc. It reflects a country or region’s level of development of the manufacturing industry.There are many kinds of errors in five-axis NC machining, such as the machine tool‘s geometric errors in it’s machining and assembly, deformation errors caused by the temperature change, errors caused by the nonuniformity of cutting force, errors caused by mismatching of each axis’ dynamic characteristics and control parameters, etc. All of these errors will eventually result in the deviation between the machined contour and the theoretical contour, that is, contour error. So controling contour error can effectively improve the machining accuracy of parts. Compared with the three-axis machine tool, the five-axis machine tool has two axes of rotation, so it can adjust tool pose to process free surface. But just because of this, the contour error compensation becomes more complicated.In order to decrease contour error in the five-axis machining and improve the machining accuracy, this paper proposes a contour error compensation control method based on the kinematics model. The main research contents are as follows:(1) Kinematics model is established using D-H method for a five-axis CNC machine tool with with two rotations on the table, including forwrad kinematics model and backward kinematics model. They demonstrate the mapping relationship between the position of five axes and tool position and orientation in the workpiece coordinate system. According to the forwrad Kinematics model, the rules that how five axes’ errors affect the tool tip error and tool orientation error are obtained. This provides a theoretical basis for the contour error compensation.(2) In five-axis NC machine tools, the shape and size of the contour surface are determined by both tool tip position and tool orientation. So in this paper, the contour error is divided into two parts: tool tip contour error and tool orientation contour error. Then the calculation models of the two kinds of contour errors are established for arbitrary space curve.(3) Because the two axes of rotation will lead to the change of the tool orientation and nonlinear motion of the tool tip, the traditional cross coupled controller can not be applied to five-axis machine tools. In this paper a contour error compensation method is designed for the proposed two kinds of contour errors. By using the contour error model and kinematics model, the contour error compensation are distributed to three translational axes and two rotational axes, and the particle swarm optimization algorithm is used to optimize PID controller parameters.(4) According to the designed contour error compensation method and dynamics model of the servo drive system, a simulation program is written and run in Matlab to verify the validity of the method. By comparing the results of two simulation experiments before and after using the contour error compensation method, it is proved that the method can effectively reduce the contour error.