Vibration control using semi-active friction damping

Large space structures often consist of truss elements which are connected by bolted joints. The dry friction energy dissipation in these junctions turns out to be a major source of damping. For vibration suppression, the joints are designed such that the normal force to a frictional interface is controlled which improves damping performance. The use of active control to vary the normal contact force in a joint by using a piezoelectric element is explored. A system consisting of two elastic beams connected by a single active joint is considered. A friction model with velocity dependent dynamics is used to describe the friction phenomena. A control law for friction dampers which maximizes energy dissipation in an instantaneous sense by controlling the normal force at the friction interface is proposed. While the control law requires the knowledge of the internal friction state which cannot be measured, an extended Luenberger observer is designed.