Research On Adaptive NURBS Curve Fitting And Its Feedrate Scheduling Algorithm

Along with the proposal and implementation of the strategy of manufacturing power,the development momentum of the manufacturing industry is flourishing and the demand for high-speed and high-accuracy machining of complex curves represented by NURBS curves is increasing.The traditional method of discretizing the curve into a large number of small line segments for transmission to CNC equipment not only has the defects of discontinuous processing path,but also leads to frequent acceleration and deceleration of the equipment,which affects the quality of processing.Therefore,the development of NURBS curve fitting and feedrate scheduling is of great significance for improving the efficiency and accuracy of complex curve processing.Aiming at the key problems in NURBS curve fitting and feedrate scheduling,this paper proposes an adaptive algorithms of NURBS curve fitting and its feedrate scheduling.Firstly,the acquisition of data points and its preprocessing method are discussed.Based on the discrete code specification of CAM software,a GM code interpreter is developed to obtain the initial data points.Combined with the nature and characteristics of the NURBS curve,the initial data point is designed.Based on the characteristics of NURBS curve fitting and feedrate scheduling,the preprocessing algorithm of initial data points is designed to facilitate the subsequent calculation,and its reliability is verified by simulation.Aiming at the defects of existing curve fitting algorithms which are not suitable for dense spatial points and slow iterative approximation speed,an adaptive NURBS curve fitting algorithm-FKTP algorithm is proposed.The algorithm adaptively selects the initial interpolation point through the spatial feature points recognition module and the local knot placement module.After generating the first fitting curve,the node insertion module with full interval error control performs rapid iteration,and the fitting curve satisfying the accuracy requirement can be efficiently obtained even in the face of dense points.In the federate scheduling of NURBS curve,this paper focuses on the continuity of motion parameters and various constraints,and proposes an adaptive NURBS curve feedrate scheduling algorithm.The algorithm uses the recognition result of FKTP algorithm to segment the NURBS curve and complete the feedrate look-ahead.In the bidirectional feedrate scheduling process,based on the interpolation progress,it can be judged whether the interpolation of the two directions can meet smoothly and adaptively adjust the feedrate according to the meeting situation.Compared with traditional algorithms,the proposed algorithm has better dynamic performance and can always meet the continuous limitation of equipment and curve on motion parameters.Finally,the software implementation of the whole algorithm is carried out.Based on the experimental platform,the performance of the proposed algorithms is compared with the traditional algorithms from the aspects of curve fitting and velocity planning.The feasibility and efficiency of the proposed algorithm are verified.