An optimized feedrate scheduling method for CNC machining with round-off error compensation

Abstract

Feedrate scheduling is one of the most important factors of computer numerical control (CNC) machining and has become a crucial research problem. In order to improve the machining accuracy and motion smoothness, an optimized feedrate scheduling method considering round-off error compensation based on S-shaped acceleration/deceleration (ACC/DEC) algorithm is proposed in this paper. There are two main stages, namely initial feedrate scheduling and parameters calculation of round-off error compensation. In the stage of initial feedrate scheduling, a novel time rounding principle is introduced to reduce the round-off error. Meanwhile, the motion parameters of each section can be calculated based on the proposed feedrate scheduling method. The constant feedrate section used for round-off error compensation is always guaranteed to exist although the actual maximum feedrate might be smaller than the command feedrate. Then, in the stage of compensation parameters calculation, the round-off error can be obtained based on the proposed time rounding principle and the scheduled parameters should be updated. In order to maintain the continuity of the acceleration profile, the improved trapezoidal ACC/DEC algorithm is introduced to conduct the error compensation and the crucial parameters can be calculated based on its special properties. In addition, the feedrate look-ahead strategy is also tweaked to enhance the reliability of feedrate scheduling. Finally, a series of simulations and practical experiments with two non-uniform rational B-spline (NURBS) curves are conducted to verify the good performance and applicability of the proposed method.