Design of a NURBS interpolator with minimal feed fluctuation and continuous feed modulation capability

With the growing demands to machine complex dies, moulds, aerospace, automotive, and biomedical parts in shorter cycle time, the utilization of Non-Uniform Rational B-Spline (NURBS) toolpaths has become more important than ever before. There are two challenges associated with realizing a successful NURBS trajectory generator—minimizing feedrate fluctuations and being able to modulate the feed continuously. This paper presents a robust and numerically efficient NURBS interpolation strategy. Unwanted feed fluctuations and sensitivity to round-off errors are avoided by applying the feed correction polynomial concept to NURBS toolpaths in an adaptive manner. A numerically efficient feedrate modulation strategy is developed, based on the trapezoidal acceleration profile, which guarantees that the final trajectory is jerk limited in all axes and kinematic continuity is achieved between connecting segments throughout the long toolpaths. The feed modulation strategy can be integrated with various feed optimization techniques as well. Effectiveness of the overall NURBS interpolation scheme is demonstrated in 3-axis machining of a complex sculptured surface.