A High-Speed And High-Precision Interpolation Mathod For Free-Form Curve

The application of NURBS methods in the CAD/CAM fields advance the development of mould manufacturing in the world. When these complex-shape workpieces are machined, the tool paths are random-space-curves. With the development of computer technology, the requirements of machining random-space-curves in the machine-tool CNC system becomes more important.In order to meet the requirements of high-speed and high-accuracy machining of random-space-curves, two methods are presented on the basis of investigating carefully the above technology at home and abroad. At first, an interpolation method based on NURBS model is presented in this thesis. It bases on the reverse-calculation of NURBS. It is simplified by approximating the radius of curvature, which provides the NURBS curves interpolators with good real-time performance. At the same time it can ensure the coherence of machining precision and meet various requirements of machining precision. It adapts feed-rate with the curve's curvature to satisfy the demand for high-speed and high precision of modern CNC machine tools.Another multi-axis interpolation method with a random-space-curve restricted on free-formed surface is proposed on the basis of the former interpolation method. Its basic principle is that the free-formed curve is interpolated on the projection plane. Then according to the parameter equation of NURBS surface, the parameters of the curve points on the NURBS surface are calculated. Finally, a series of cutter contact points from the free-formed curve restricted on NURBS surface should be generated by the step of calculating cutter contact points according to the stipulated tool step error.