Control Concepts of Semi-Active Friction Dampers

Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines and increasing structure durability. Besides design optimization and passive damping treatments, active structural vibration control can be applied to reduce unwanted vibrations. In this contribution, two semi-active control laws for control of friction dampers are derived and investigated in simulations and experiments. Thereby, semi-active control concepts have the advantage over active control to yield intrinsically stable closed-loop systems and low energy consumption. In the experimental implementation, the control makes use of piezoelectric stack actuators to apply adjustable normal forces between structure and attached friction dampers. The control uses an observer based on reduced finite-element models to estimate the unknown relative displacement beneath the normal force actuator from acceleration measurements. Experimental results of the control algorithms for a structure with attached friction damper show the effectiveness of the proposed control algorithms.