Nonlinear phase shift control of semi-active friction devices for optimal energy dissipation

Semi-active friction devices are usually designed to dissipate the vibratory energy in a mechanical system by controlling a dry friction interface. When the normal force applied on the friction interface is controlled by a feedback loop, the design of an optimized compensator is challenging due to the complexity of the nonlinear behavior of the dry friction. Usually, with some simplifications, a nonlinear feedback controller can be designed either by the Lyapunov method or by the feedback linearization approach. This paper investigates the interest of narrow-band filtering and phase shift compensation in such nonlinear feedback controllers when the system is excited by an external harmonic force. The complex envelope approach is used to implement the narrow-band filtering with an adjustable phase shift compensation within the nonlinear controllers. Experiments are conducted to validate the control approaches using a friction device composed of two piezoelectric stack actuators, each one applying a normal force on a friction pad in order to stop the movement of a mobile mass excited by a sinusoidal force. The experimental results show that for a proper choice of the phase shift compensation, the sticking period per cycle is reduced, and consequently the power dissipation is increased.