Research On Robot Cutting Path Planning Of Orthodontic Appliance

With the development of people’s living standard,people are paying more and more attention to their dental health.Dental deformities not only affect the external image,but also affect the oral function,cranial and maxillofacial development,mental outlook,etc.,causing great distress to the physical and mental health of patients.The pathology of dental deformities is complex and related to genetics,so it is difficult to remove the causes of treatment,so orthodontic treatment is often used.Compared with the traditional bow appliance,the emerging invisible appliance in recent years has the advantages of transparency,beautiful appearance,and easy to take off and put on.Invisible appliance manufacturing process including impression,die,cutting,grinding.In this paper,robot machining is taken as the research field,improving the cutting accuracy and speed of invisible appliance is taken as the research problem,trying to explore the non-interference and smooth cutting path,and build the appliance cutting simulation software platform to test and verify the proposed algorithm.The main research contents of this paper are as follows:(1)Generation of initial tool path.The topological structure of the triangular surface was established according to the gingival STL model,and the coordinate system was rebuilt.The gingival margin lines were extracted according to the adjacency relationship of triangular surfaces,and the connected gingival margin lines were separated by expansion and contraction.For adjacent gingival margins,a series of algorithms are proposed to carry out arc connection.For gingival margins far apart,geodesics are directly connected according to the minimum distance D,and the cutting path can be obtained by merging the gingival margins and connecting arcs.The cutting path was biased and combined with the local features of the model,the smoothing curve was discretized into the initial cutter site and the initial cutter axis vector.(2)interference detection algorithm.Due to the large number of triangular surfaces,the efficiency of directly intersecting triangular surfaces is low.In order to improve the speed of model interference detection,a method of model interference detection based on slice is studied.Aiming at the input STL model,slice the model and the cutter first,and then judge whether the cutter point interferes by Boolean operation on the slice contour,and mark the interference position.(3)Tool feasible domain solving algorithm.The tool axis vector was represented by a discrete grid in two-dimensional C space.Aiming at the tool point on the tool path,the problem of solving the interference range between the tool and the model was transformed into solving the interference range between the tool and the slice of each layer by using the slice of the model.The feasible domain of the tool pose Angle was solved by eliminating the interference range of the tool in the grid.(4)interference-free tool axis vector programming algorithm.The adjacent feasible domains were connected with directed graphs,the distance function was set according to the feasible domain of the cutter point and the initial tool axis vector,and the interference free path planning was carried out by the Dijkstra algorithm for local or global planning.If necessary,the cutter point should be adjusted and the feasible domain was solved again until the path reached the goal of interference free and smooth.(5)Software development and processing experiment of cutting path planning for orthodontic appliance.The cutting path planning software of orthodontic appliance was developed based on Visual Studio2019 with C++ and C# programming.According to the parameters set,the software can obtain the interference-free smoothing path which can be directly used for machining by reading the relevant model.And according to the path derived by the software,the cutting experiment is carried out.