Abstract: During the traditional NURBS machining,the calculation precision of the interpolation parameters of the interpolation algorithm is low,the real-time performance is poor,and too high acceleration causes a dramatic im- pact on machine tools.In order to solve these problems,a real-time look-ahead interpolation algorithm for NURBS curves based on Runge-Kutta is proposed.In the algorithm,first,the interpolation parameters are calculated by using the four-order Runge-Kutta method,and the feedrate is adjusted automatically according to the constraints of the chord error and the normal acceleration.Next,the parameters are revised according to the deviation between the theoretical feed step and the actual one.Then,based on the offline data from a rough interpolation,the extreme points of the feedrate are calculated and the parametric curves are divided into several look-ahead sections,thus finding the first and last sensitive feedrate points in each look-ahead section.Finally,the feedrate is re-planned ac- cording to the relationship between the sensitive feedrate and the interpolation distance,so as to avoid the dramatic variation of the feedrate.Thus,the demand of the machine tool in the acceleration and deceleration performance is satisfied.The proposed algorithm is proved to be effective by a Matlab simulation.

Key words: numerical control system, NURBS curves, Runge-Kutta, look-ahead interpolation algorithm