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Research on Adaptive Feedrate Planning of NURBS Curves for CNC System

In CNC machining, non-uniform rational B-spline (NURBS) curve is commonly used to describe the tool path for machining complex curves and surfaces. In order to improve the machining accuracy of NURBS curve, it is necessary to control the feedrate under geometric and kinematic constraints throughout the machining process. This paper proposes a segmental adaptive feedrate planning algorithm with low allowable feedrate at critical sub-curves and high allowable feedrate at regular sub-curves, which makes a balance between interpolation precision and efficiency. To solve the remaining distance problem caused by the contradiction between continuous feedrate planning and periodic interpolation as well as the nonlinear relationship between arc length and parameters, this paper calculates step-length using displacement-time function on every interpolation period and proposes a step-length correcting algorithm at the intersection of two adjacent sub-curves. The simulation results show that smooth motion under the chord-error and kinematic constraints can be obtained within curves with sharp curvature variation throughout the interpolation process, which validate the advantages of the proposed algorithm.