Research On The Look-ahead Interpolation Algorithm Based On NUBRS

With the implementation of the “Made in China 2025” strategy,China will gradually transform from a manufacturing nation to a manufacturing powerhouse,and the CNC will play a decisive role in the manufacturing industry,especially the smart manufacturing industry.In order to meet the ever-increasing demands for accuracy and efficiency in modern manufacturing,NURBS direct interpolation algorithms have been developed.The interpolation technology based on NURBS curve not only can adapt to the processing of various complex curves and surfaces,but also can effectively improve the surface quality and processing efficiency of the parts.Therefore,it is very important to study the NURBS interpolation algorithm deeply.Based on the theories of NURBS curve interpolation and feedrate planning,this dissertation focuses on the following aspects of high-speed,high-precision machining of complex workpieces:(1)NURBS curve interpolation parameter calculation.Due to the nonlinear relationship between the arc length of the NURBS curve and the parameters,the orderly execution of the NURBS interpolation must depend on the real-time calculation of the parameters.To solve the problems such as low precision or high computational complexity in current interpolation algorithms,this dissertation proposes two methods to calculate interpolation parameters.One is the prediction-correction method based on the Runge-Kutta,the other is bisection method.The simulation results show that the proposed algorithm has good real-time performance and high precision,and can control the feedrate fluctuation rate strictly within the allowable range of processing.(2)Feedrate planning algorithm.Traditional linear and exponential acceleration /deceleration control algorithm has abrupt changes in acceleration,which makes machine tools easy to generate vibration and affect machining quality.The commonly used seven-stage Stype acceleration/deceleration control algorithm is very complex,especially for some NURBS curves with varying curvature,the feedrate planning process is more tedious.This dissertation proposes a cubic polynomial feedrate planning algorithm that adjusts the velocity equation based on the curve length,which simplifies the feedrate planning process.The simulation results show that the proposed feedrate planning algorithm has good flexibility and high efficiency.(3)NURBS interpolation look-ahead control algorithm.In the processing of NURBS curves,some sudden feedrate changes are often encountered.If the machining accuracy is to be guaranteed,the feedrate must be strictly limited.Look-ahead control is to allow the machine tool to decelerate ahead of time,safely pass through the sudden change point with a smooth feedrate curve,and avoid the impact of acceleration overrun on the machine tool to achieve high-quality machining.This dissertation presents a new look-ahead control algorithm for NURBS curve interpolation.Firstly,according to the machining accuracy requirements,the adaptive feedrate curve is obtained,then the feedrate extreme point in the feedrate curve is identified,the feedrate interference between feedrate extreme points is analyzed,the extreme feedrate points are optimized,and finally,the feedrate for each interpolation intervals are planned.The simulation results show that the proposed algorithm can guarantee the smooth transition of the feedrate during the machining process.The acceleration and jerk are within the allowable range of the machine tool.