Research And System Development Of Denture Machining Trajectory Planning Based On STL Model

Dentures,as restorations made for missing teeth,are important roles in the treatment and restoration of oral problems.At present,dentures are mainly processed by CNC machine tools and CAD/CAM technology.However,the core technologies such as tool path planning in denture CNC machining system have been monopolized by foreign countries.In order to break the foreign technical barriers,it is necessary to design and independently develop a computer-aided machining system for dentures.Therefore,the preprocessing of denture processing problem is studied in this thesis from the aspects of preprocessing of STL file,generation of tool position points of STL model,generation of trajectory of tool position points,and etc.,and the design and implementation of the preprocessing system of denture processing are completed.The STL file expressing denture model is a three-dimensional format file composed of vertices and triangular facets.Aiming at the problem of redundant data and hole-breaking of missing triangular facets in STL files,the denture STL file is preprocessed firstly in this thesis.According to the STL file format,the data structure of the triangular facet and vertex topological list is established,and the topological relationship of the STL file is reconstructed.The repeated vertex coordinates are stored once by the nodes in the vertex list,which simplifies the repeated vertices in STL files.By analyzing the relationship between the number of adjacent points and surfaces,an improved algorithm for finding the hole boundary in STL model is designed,which can accurately find the hole boundary points of the STL model,and the triangulation repair of the hole is completed by using the point-by-point insertion method.Aiming at the problem of slow and redundant generation of tool location points,the generation and optimization algorithm of tool location points is studied.In order to further obtain the tool position data,the weight value method of angle shape factor is used to solve the vertex normal vector of triangular facet in the denture STL model,so that the calculation error of the vertex normal vector is reduced,then,the equidistant model of the denture is established according to the vertex normal vector,and the initial tool position set is calculated by the equidistant section method.For effectively reducing the time complexity of tool location calculation,by analyzing the positional relationship between the cross section and the model,a tool location data optimization algorithm based on the division of the intersection area is proposed in this thesis.In order to remove redundant tool location points,an optimization algorithm for redundant tool location points is established.Through the above two algorithms,the tool location points without redundancy can be quickly obtained.For the purpose of generating a smooth tool path trajectory,which is suitable for the execution of CNC machine tools,the tool position data fitting algorithm is studied in this thesis.The algorithm is used by cubic NURBS interpolation fitting curve to fit the trajectory of tool position points.By analyzing the complex problem of solving the control points of the tool path trajectory fitting curve,the least squares progressive and iterative approximation fitting algorithm based on NURBS curve is given,and the square of the difference between the tool position point and the fitting point is used as the least squares optimization objective.Through the continuous iteration of the initial tool path,the high-order matrix calculation is effectively avoided,and the ideal tool path is obtained.In order to develop a pre-processing system for denture processing,this thesis combines the actual needs of a denture processing enterprise.With VTK 3D visual library in Qt environment,the software was developed by C++ language.The functions of the hole-breaking repair and visualization of denture model,connecting rod addition and interaction,model offset and tool path generation were completed,and the goal of tool path planning for denture processing was realized.The system has a simple interface and easy to operate.The tool path trajectory can be generated by inputting STL files and corresponding data to be processed,which is suitable for denture processing enterprises and dentists.