A look-ahead and adaptive speed control algorithm for parametric interpolation

Abstract

A novel interpolation algorithm for parametric curves is proposed. The algorithm improves the machining efficiency and precision greatly with full consideration of the geometrical characteristic of the machining curves and the kinematical characteristic of the machine tools. Firstly, a look-ahead process, including a pre-interpolation and a speed adjustment, is sought to achieve an optimal machining speed profile for the whole parametric curve. The pre-interpolation stage with a constant feedrate is performed on the parametric curve. Critical zones are selected according to the chord errors and the changing values of the speed. The criterion for selection is that the chord error or the changing value of the speed exceeds the given threshold values. Then, a speed adjustment is applied to the sampling points of the critical zones. Meanwhile, the speed profile between two adjacent critical zones is developed with an acceleration/deceleration strategy to satisfy the dynamical requirements. After that, some relevant information about critical zones is stored into a dynamic memory buffer for the following fine interpolation process. Secondly, the fine interpolation is adaptively fulfilled with the data stored in the dynamic memory buffer based on the lengths of adjacent critical zones. Finally, a non-uniform rational basis spline curve is selected for simulation and experiment to demonstrate the feasibility of the proposing algorithm. The experimental results show that the algorithm can achieve not only smooth and high-speed transitions but also high accuracy with the minimization of chord errors in critical zones.