Method for tuning feedforward in electric feed drive control systems

Abstract

The electric feed drive used in metal-cutting machines like any high-precision electric drive requires high accuracy of reference processing and robustness against perturbations. For this purpose, feedforwards are added to the position controller to improve set point processing time and to compensate for disturbances. Feedforwards are usually tuned manually when the machine is setup, either by applying a series of tests on the motor or by calculation. The calculation requires some information about the magnitudes of disturbances that can be compensated by appropriate feedforwards, but this information is not always available a priori. In this paper, we propose tuning the feedforward coefficients based on the results of the parametric identification of the values of the torques acting on the electric drive, as well as the apparent moment of inertia. For parametric identification the methods of electric drive theory, method of least squares, and digital signal processing method are used; mathematical modeling method is applied to assess the compensation quality. The authors propose the method of tuning the parameters of the control system of electric feed drive based on parametric identification of the values of torques acting on the motor and/or the operating device. The results of control system simulation show both high identification accuracy and significant reduction of dynamic control error when feedforwards are activated. The considered structure of the control system and the proposed algorithm of identification and adjustment of its parameters can be used in electric drives of metal-cutting machine tools. The simulation results have shown that the use of feedforwards, tuned in accordance with the algorithm, enable to reduce the dynamic position tracking error by more than 50 times, which can be critical in contour machining.