| With development of3D measurement, discrete modeling and NC machining technologies,CAD/CAM technologies are widely applied to dental medical treatment. The NC machiningtechnology of dental restoration is one of the most important parts of Dental CAD/CAM technologies.Aiming at dental restoration high efficiency machining, the relevant theories, methods andtechnologies are researched in this dissertation. The main contents and contributions are as follows:1. Technologies for section-based tool path generation of dental restoration are researched. Thesection lines are calculated rapidly by the method of model segmentation, then self-intersections andredundant CL points are eliminated. An improved section plane algorithm for constant scallop heighttool path generation is proposed. Cutter contact projected traces are calculated and adjusted accordingto scallop height, and constraint surfaces are constructed by the adjusted projected traces, thenconstant scallop height tool paths are calculated iteratively by intersecting the constraint surfaces withmesh surface. Experimental result indicates that machining efficiency of constant scallop height toolpath is improved by about28%without reducing machining quality, compared with CL section planetool path.2. Technologies for parameter-based tool path generation of dental restoration are researched.Algorithm for iso-parametric tool path generation is proposed for dental restoration machining. Fourtypes of iso-parametric tool paths are generated according to harmonic map theory and parametricplanning styles. Algorithm for parametric spiral tool path generation is proposed for dental restorationmachining. The parametric loops of dental restoration model are calculated in parametric mesh, thenpoints of adjacent parametric loops are matched group by group, and initial, exact diagonal parametricspiral lines are calculated in sequence. Based on these, free-interference parametric spiral tool pathsare generated. Experimental result indicates that machining efficiency of parametric spiral tool pathsis improved by about30%with better machining quality, compared with CL section plane tool path.3. Technologies for tool path optimization of dental restoration are researched. Algorithm forarc spline tool path generation based on segment fitting is proposed for dental restoration machining.CL points of line tool paths are fitted into line-arc tool path by segment fitting, and fitting precision ofCL points is revised by method of deviation mapping.Algorithm for NURBS tool path generationbased on IDOM method is proposed for dental restoration machining. DOM fitting is improved byIDOM fitting in aspects of selection of initial dominant points, determination of new dominant points and parameters revision of the dominant points. Based on these, NURBS tool paths, whichposses higher fitting precision and fewer control points, are generated, then transition tool paths areimplemented by NURBS curves, and adjustments of knot vectors and control points are used tokeep the connections of cutting and transition tool paths continuity. Experimental result indicates thatmachining efficiency is improved by about19%after CL section plane tool path is optimized, andmachining quality is also improved.4. Technologies for5-axis tool path generation based on MMR(Maximal Material Removal rate)of dental restoration are researched. The method of MMR-based cutter orientation anglesdetermination without curvature interference is researched. Algorithm for5-axis tool path generationof MMR with flat-end cutter is proposed. Cutter contact points are calculated by section method, thencutter orientation angles are determined with constraint of MMR and free-interference. According tothese, MMR tool paths with flat-end cutter are generated. Experimental result indicates thatmachining efficiency of MMR tool paths is improved by about17%compared with Sturz tool paths,and machining quality is also improved.5. Technologies for feed-rates generation based on acceleration and deceleration control ofpiecewise tool paths are proposed for dental restoration machining. Algorithm for feed-rate transitionsof CL points, which is based on curve ADC (Acceleration and Deceleration Control) and adjustingahead, is proposed. Algorithm for adaptive feed-rate generation based on feed-rate transition ofsegment tool paths is proposed. With constraints of kinematic characters and actual cutting speeds,tool path segments of micro segment tool path are obtained, and feed-rates are planned in thesesegments, then feed-rates transition of the segments are processed by the method of S shape curveADC, and adaptive feed-rates generation for dental restoration machining is implemented.Experimental result indicates that machining efficiency of adaptive feed-rates method is improved by6%~10%with smooth movement of machine tool, compared with constant feed-rates method. |
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