| The CNC(computer numerical control) system is called the "brain" of the machine tool, it is the kernel of the numerical control equipments, it relates to our country economy, industry safety and national security. So it plays a very important role in natioanl industry. Further, in the CNC, the motion controler is very important in which its kernel is interpolation. Interpolation function can determines the grade of CNC.Present, most CNC provide liner and circle interpolation, so CAD/CAM have to disperse the curve into minuteness liners then pass them to CNC to finish machining. The process will lead too many programes and less accuracy. High speed, high accuray, complex motion trajectory motion control method is the researching hot, NURBS interpolation is typical representative, it resovles the probem which the liner interplotion comes with, and the NURBS interpolation have many advantages, for example, high reliability, short maching time and high accuracy.This dissertation compares the common accelerate/decelerate methods, analyzes the factors that affect the real machining. Using the present S-shape accelerate/decelerate to combine with the NURBS interplation, design a real-time looking-forward NURBS interpolation algorithm which can forecast the decelerating points based on curvatures changing rate with smooth accelerate, solving the problem of the traditional way which calculates decelerating points accompanied with error. This algorithm has a looking-ahead interpolation and a real-time interpolation. First, the curve is dividing into some segments according to the different curvature changing rate after looking-ahead. Second, the real-time interpolation is working within the segments with a looking-forward process which can forcast the starting point of the third stage to the S-shape A/D. By the results of simulations, it demonstrats that this interpolator can get a smooth feedrate and accelerate profile with high machining accuracy.
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