Robust tracking controller design for high-speed machining

For robust high-speed tracking, a combination of a feedforward controller and a feedback controller is used. A disturbance estimation problem for a closed-loop servo system is formulated and a modified disturbance observer is developed to accommodate the presence of an existing closed-loop servo system. The robust feedback controller based on a disturbance observer compensates external disturbances, unmodeled dynamics, parameter variations, and mechanical nonlinearities. It provides robustness and ideal feedback characteristics for feedforward tracking controllers based on the zero phase error tracking controller (ZPETC). Performance enhancement was achieved by adding feedforward friction compensation. Through experiments, it has been demonstrated that the robust tracking controller compensated well for the adverse effect due to nonlinear friction, and achieved an excellent tracking performance