Smoothing interpolation of five-axis tool path with less feedrate fluctuation and higher computation efficiency

Abstract

Five-axis machine tools are widely used in aerospace, die and mold industries. Most of the time, the tool path is described by connecting a series of short linear segments. The tangency discontinuity of the linear segments leads to the discontinuity of the kinematic profiles, hence generating discontinuous interpolation points, and resulting in fluctuation of machine motion, which reduces the machining efficiency and causes excessive tracking and contouring errors. This paper aims to generate smooth interpolation points at servo sample intervals with the proposed G2 continuous five-axis corner rounding algorithm suitable for reducing feedrate fluctuation along the smoothed toolpath and improving machining efficiency, and the modified jerk-limited feedrate planning algorithm suitable for eliminating feedrate fluctuation within the feedrate planning units and improving interpolation computation efficiency. In this paper, the five-axis linear segments are first smoothed by curvature-optimized cubic Bezier splines, which reduces the number of the feedrate planning units along the smoothed toolpath and improves machining efficiency. Then, the jerk-limited feedrate planning algorithm is modified to ensure that the time interval of each different scheduled feedrate phase is an integer multiple of the axis position control loop closure time (i.e. servo sample interval), which eliminates the feedrate fluctuation within each feedrate planning unit and reduces the interpolation computation load of position command in each interpolation period (i.e. servo sample interval). At last, the effectiveness of the proposed algorithm is demonstrated with simulations and experiments following a five-axis, curved tool path on a CNC (Computer Numerical Control) machine tool.