Research Of Curvature Contiuous And Interpolation Algorithm For High Speed Machining Of Continuous Small Segments

High-speed and high-precision numerical control(NC)machining is mainly applied to machining a series of continuous small line segments that are discretely formed by complex curves and surfaces.Five-axis tool path is composed by linear path which is tangency discontinuities,so that the velocity fluctuations and acceleration mutation around the corner of the adjacent segments will affect the stability motion of the machine.This paper studies the global and local tool path smoothing transition in three-axis maching and the smooth transition of speed,then proposes the scheme of fair transition,which can be applied in five-axis machining complex surface.Tool path fairing and feed schedule for five-axis interpolation are studied in this dissertation,including:the local fairing for the linear tool path in MCS(Machine Coordinate System)and smooth feed scheduling,dual-NURBS(Non-Uniform Rational B-Spline)tool path fairing for the linear tool path in WCS(Work Coordinate System)and real-time adaptive feed scheduling considering comprehensive constraints for dual-NURBS interpolation.The main contents of this paper and the innovatory results are listed as follows:Firstly,the theory of the B-spline curve,NURBS curve,parametric curve interpolation algorithm and real-time adaptive feed scheduling are researched,and these theories lay the solid theoretical foundation for the next sections that use B-spline and NURBS curve to smooth the linear tool path and propose the real-time adaptive feed algorithm.Secondly,a real-time global fairing algorithm for continuous small segments based on cubic B-spline interpolation,which ensures that small continuous line segments that satisfy the constraint of corner and bow height error are interpolated,is proposed to solve the problem of the machine vibration and shocks caused by abrupt change of velocity and acceleration.This algorithm ensures that the tool path is fitted with G~2 continuity to achieve smooth tool path.In order to meet the requirements of the acceleration and deceleration of the machine and the geometrical characteristics of tool path,the path speed schedule and interpolation algorithm of the B-spline tool path is proposed,and the look-ahead control S-curve acceleration and deceleration strategy is used to smooth the speed.Then,the interpolation of the new smoothing tool path is accomplished by linear interpolation and spline interpolation.Through experiments and simulation,the algorithm can effectively improve the feedrate,reduce the feedrate and acceleration fluctuations and reduce the vibration of the processing technology system.Thirdly,For the five-axis linear tool path in the workpiece coordinate system,cubic NURBS curves are inserted into the tool axis point and the tool center point respectively.Then corner smoothing in tool axis point and the center point respectively,and the dual NURBS corner tool path can meet the constraints and reach G~2 continuous,which can effectively improve the quality of the workpiece processing and processing feedrate.On the basis of above,the error constraints of velocity,acceleration and jerk are used to optimize the feedrate,and the constraints of the servo axis of the machine tool are taking into account,which achieves real-time interpolation in smooth tool path.Finally,this paper studies the adaptive speed schedule in five-axis coordinated isometric dual NURBS curves interpolation,and uses window-based bi-directional scanning speed schedule,wchich meets the real-time requirements of CNC hardware platform,make full use of the ability of the machine according to the given constraints for adaptive acceleration and deceleration,access to higher processing efficiency,better processing quality.In summary,this is based on the three-axis tool smooth transfer model,the real-time global fairing algorithm with cubic B-spline interpolation method is proposed to fit the continuous small segment path,and the tool path satisfies interpolation precision and reaches G~2 continuous.Under the comprehensive constraints of the feasible range of maximum feedrate and acceleration,adaptive speed planning method of bi-directional scanning is proposed to establish an adaptive speed schedule model for 5-axis coordinated dual NURBS interpolation.