Research On The Five-Axis CNC Interpolation Technology Based On PH Spline

More and more manufactured products with sculptured surfaces are expected higher accuracy at the present time. However, those products cannot be machined on the 3-axis machine in only one fixing. The processing speed and processing accuracy cannot be well ensured. So, manufacturing these complicated products in the manner of high speed and high accuracy, machines with five simultaneous motion axes are applied most widely. When machining the model created by free-formed surfaces, many tiny line segments are used to approach these surfaces. This manufacturing method has a large NC file, so it results in great amount data transmission, disconnected speed in joint of motion segments and poor manufacturing quality. Because of the processing speed is uniform in the spline interpolation, it can improve the manufacturing quality.PH curve is a kind of polynomial curves which has a good characteristic and posses many positive properties. It can solve the problem of computing the arc length, retains full compatibility with standard Bézier represtation and tends to produce fairer loci than ordinary polynomial curves and so on. So the interpolation technology of PH curve in 5-axis CNC system is studied in this paper.When the tool-axis vector crossing quadrant in five-axis machining the tool needs to be raised that the processing speed and accuracy of products are hard to be sure. In order to solve this problem, cross-quadrant method has been proposed in this paper. Then the structure form of 5-axis machine tool, space-movement and post-processing based on RPCP of 5-axis machine tool is analyzed.Prediction-correction method is proposed instead of Taylor expression to improve the accuracy of interpolation. For the nature and characteristics of PH curve, four kinds of real-time interpolation arithmetic for spatial PH curve are designed and developed, and also the curvature interpolation is improved.To solve the smooth transition in interpolation of PH curve, the method of realizing C1 and C~2 continuous interpolation of quintic spatial PH curves is proposed. To deal with the large NC codes that CAD/CAM system generated and velocity discontinuity, NC codes are handled according to the lengths and the angels of lines. Knot removal is used to approximate the discrete points with PH curve. Converting these codes to PH interpolation codes is realized. The NC code format of five-coordinate PH curve is designed. The arithmetic of five-coordinate PH curve interpolation and surface machining are verified by simulation. Simulation and experiment prove that the cross-quadrant method and RPCP algorithm are feasible.