Research On Key Technologies Of NC Tool Path Generation Based On Catmull-Clark Subdivision Surface

Subdivision surfaces have strong ability and potential in free-form surface modeling. However, subdivision surfaces are not extensively applied in the field of CAD/CAM yet because there are not complete matching techniques for subdivision surfaces. To generate NC tool paths on subdivision surfaces is a fundamental work to apply subdivision surfaces in the CAD/CAM field. According to properties of subdivision surfaces and methods to offset curves and surfaces, this paper researches on methods to generate NC tool paths, then presents two algorithms to generate NC tool paths for subdivision surfaces. The main researches are as follows:Firstly, study properties of subdivision surfaces and present a method of estimating subdivision depth according to the relation between control points and limit points. On the premise of given precision, it can quickly approach to limit surface during the process of subdivisions.Secondly, study the relation between CCP and CLP, and then present an approach to generate tool path with the section method. The main process of the approach includes : generate CCP on the surface satisfying error with section method, calculate normal vector of CCP, offset CCP along normal vector ,and generate CLPs. NC tool paths can be generated by linking these CLPs. This paper also gives methods to eliminate self-intersections and noise.Thirdly, study theories and methods of surface offsetting. Raise an accurate method of surface offsetting based on forepassed researches and estimate offsetting error. Generate CLP using section method on offset sutface and then form tool path by linking these CLPs in certain order. The method of eliminate self-intersections is applied not on offset surface but on tool path.