Research On Integrated Design Method Of NURBS For RE/NC

RE (Reverse Engineering) and NC (Numerical Control) are the key technologies of AMT (Advanced Manufacturing Technology), and they play an important role in product reproducing and innovatively designing. The integration of RE/NC can shorten the period of product with measuring, modeling, machining (3 MS), and improve the quality of designing and efficiency of manufacturing. Therefore, this paper systemically studies the surface reconstruction from measured points and the tool-path planning of surface based on Non-uniform Rational B-Splines (NURBS), so as to realize the integration of RE/NC, and to boost the ability of RPD.According to the two styles (cross-sections, scatter points) of measured points, the methods of modeling are discussed respectively. Firstly, for the cross-sections, given the uniform knot vectors a fitted NURBS surface can be produced by skinning, and the algorithm avoids the problem of knot compatibility by knot insertion. Secondly, for the scattered points with no obvious rectangular topology, it is difficult for them to be parameterized, and a NURBS surface fitting method with tight tolerance for wrap-around models is presented. By means of sectional design technique and skinning method, these points can be parameterized by constructed base surface. Plus with ICP, the precise NURBS model is constructed, which boost the quality of mode!. In addition, the problem of surface extension is often neglected in the engineering, this paper presents the expatiation on the problem, and how to choose these methods is also to be given.Using differential geometry and vector analysis, a new tool-path generation method for freeform surface machining is presented. Given the tool-path direction of the parameter domain of machined surface, a tool-path director vector field model based on NURBS can be constructed by fitting discrete sample vector value according to the relation of scalar quality field and gradient field. And the generated tool-paths not only are side-by-side and smooth, but also are in favor of repairing and controlling. Furthermore, some other tool-path planning methods can be represented with the above method, especially which can cope with the problem of intersectant operation form iso-planar method. Based on the feature of anisotropy of machining width on the local of the free-form surface, a tool-path planning method of optimal cutting direction field is given.Above all, the technologies , surface modeling and tool-path planning by means of NURBS based on the same parameter domain, offer a way for integration of RE/NC. Related samples show the feasibility and precision of the methods.