Research On Searching Local Machining Interference Area For Subdivision Surface Based On Multi-resolution Mesh Segmentation

The process of local machining interference is one of key problems in NC machining.And it directly determines the machining quality and efficiency of the workpiece.Efficient searching method for local machining interference of machining model provides the necessary theoretical basis for local machining cut and compensation machining undercut.Therefore,this study integrated use the related theoretical knowledge of CAD/CAM,computational geometry and computer graphics etc.And combine topological characteristics of subdivision surface and multi-resolution mesh segmentation.In order to achieving efficient search of local machining interference area in machining model.The problem of searching local self-intersection interference area in tool offset model are solved by analysis of the correspondence between local self-intersection interference area and local machining interference area in machining model.The primary items in this work are as follow:Subdivision surface processing model construction.Based on the topological characteristics of Catmull-Clark subdivision surface,the CELL structure is proposed.Based on CELL structure,piecewise representation of subdivision surface is realized.By using The topological characteristics of the limit mesh of Catmull-Clark subdivision surface,the method of machining model construction is proposed.Computational formulas for position and normal of limit vertex are deduced by feature analysis of local subdivision matrix.Two methods of calculating the curvature of limit vertex are deduced based on Parametric Surfaces and discrete grid.Rapid estimation of the probability of occurrence of local machining interference in NC machining model.First of all,Based on Catmull-Clark subdivision surface piecewise representation and the morphological analysis of subdivision surface control grid,a method of efficient searching concave area patches.On the basis,combining multi-resolution sampling technology and topological structure of subdivision surface patch,a method for searching the interference areas which are most likely to occur in NC machining model is proposed.Taking the interference areas which are most likely to occur in NC machining model on as the object,a method of estimating the probability of occurrence of local machining interference in NC machining model rapidly is proposed.Based on edge detection,local machining interference areas search in NC machining model.The relationship between local interference of the machining model and local self-interference of cutter location surface is analyzed.Based on the piecewise representation of subdivision surface and the characteristic of curvature continuity,taking the tool offset model patches as search unit,combining segmentation of patches and multi-segmentation of subpatches,a method of searching local self-Intersection Interference Region Boundary Grid Sets in a Single Patch is proposed.Combining searching in a single patch with searching between patches,a method of efficiently searching local self-Intersection Interference Region Boundary Grid Sets in tool offset model is proposed.On the basis,using the topological structure of Subdivision surface grid,a method of efficiently searching local self-Intersection Interference areas in tool offset model is proposed.Thereby,obtaining the corresponding local machining interference area in NC machining model.These key methods about local machining interference area in NC machining model presented in this dissertation are validated through algorithm implementations.