Fuzzy logic controller for accurate positioning of direct-drive mechanism using force pulses

The paper describes a novel approach to accurate positioning control of mechanical devices with nonlinear (stick-slip) friction. The controller applies narrow torque pulses to achieve the desired displacement of the mechanism. The pulse shapes are computed through fuzzy logic approximation of the dependence between the desired displacement and the pulse shape. The stability conditions of the proposed controller are derived taking into account an influence of random variation of the friction properties. A detailed experimental study of the system response to the torque pulses of different shapes and a detailed controller design are presented for a direct-drive manipulator setup. It is experimentally demonstrated that the developed controller achieves positioning precision up to the limits of the position encoder resolution.