Vibration control of machines by use of semi-active dry friction damping

A semi-active device for the vibration control of machinery foundations or for ride control of vehicles is proposed. A semi-active damper utilising dry friction is employed, with balance logic, a class of sequential damping, being used to minimise the force transmitted. The friction force applied to the mass is controlled so as to cancel the spring force, which is only possible when these forces act in opposite directions. Otherwise, the friction force must be set to zero, which is quite achievable, unlike the case of a viscous damper. The friction damper can be controlled so as to mimic the addition of a viscous damper. Both the ideal case of instantaneous switching and a more realistic model with finite switching time are studied. The results of numerical simulations show that a successful implementation of this strategy could produce a significant reduction of the forces transmitted to the foundation by a machine subject to a rotating imbalance force or of the mean square acceleration in a car riding on a randomly profiled road. (C) 1998 Academic Press Limited.