Research On Processing Trajectory Optimization And Pre-machining System Based On Denture STL File

With the development of society and the improvement of living standards,an aging population trend has emerged worldwide.The proportion of elderly population in China’s total population has also increased year by year,resulting in an increasing demand for dentures and higher precision requirements for dentures.This has put higher demands on the denture CNC(Computer Numerical Control)machining technology.However,there is no CAM(Computer-Aided Manufacturing)system with independent intellectual property rights in our country,and the core technology is controlled by foreign enterprises.To break through the technical limitations imposed by foreign countries,independently developing denture machining systems has become an urgent problem to solve.Therefore,thesis focuses on the preprocessing issues of denture machining systems,and researches the visualization of denture STL file models,interaction between denture models and connecting rods,bias processing of models,determination of cutting planes,and tool path trajectory planning.The related software system design and development of these functions have been completed.To achieve the visualization of denture models,this is based on the characteristics and rules of STL files and uses functions in the VTK three-dimensional visualization library to first identify and read the vertices of the denture’s three-dimensional model,then render the read triangular faces,and finally use the average normal vector of adjacent triangular faces to read the critical points.Secondly,in order to keep the denture stable during the processing,the software implementation problem of adding connecting rods to the denture model is researched.Through continuous exploration and attempts,the denture and connecting rod STL files are simultaneously imported into the denture preprocessing system,and interactive operations are completed by rotation and translation,and the interactive model is finally saved to solve the problem of connecting the denture model and connecting rod.To achieve bias processing of denture models,after analyzing the advantages and disadvantages of vertex bias algorithms and face bias algorithms,the vertex bias algorithm is chosen,and the coordinates and normal vectors after vertex bias are calculated using the angle weighting method.Furthermore,considering the problem of defects in tool position points,the layered incremental method is used to optimize the tool position points of each cutting plane of the denture model,so that the tool position points are corrected and ordered,laying the foundation for subsequent tool path trajectory planning.For the problem of tool path trajectory planning,in order to ensure the smoothness of the tool path trajectory,the third-order non-uniform B-spline curve is chosen to plan the tool position points.To solve the problem of difficult solution of the equation of the control points,a particle swarm algorithm based on the third-order non-uniform B-spline curve is proposed,and the curve is iteratively optimized until the conditions are met,and the smooth tool path trajectory is obtained.Based on the above research,this thesis develops a denture preprocessing and machining system using the VTK visualization library in C++ language and QT framework,and realizes a series of functions from model visualization to tool path trajectory planning.The system is easy to operate and the interface is clear.Just import the STL file of the model once and enter the bias distance and layer number,and the tool path trajectory can be automatically generated,laying a good foundation for the subsequent CAM post-processing system to generate NC(Numerical Control)machining G-code.