Shock isolation using an isolator with switchable stiffness

A semi-active control strategy is presented for the shock isolation of resiliently mounted equipment where the isolator has light damping. This is achieved by switching the stiffness of the isolator between a high-state and a low-state. The control strategy involves two stages: the first stage involves the displacement control of the equipment during the shock, and the second stage involves suppression of the subsequent residual vibrations. The performance of the switchable isolation system is illustrated using a base-excited single degree-of-freedom system. It is characterized in terms of the maximum absolute acceleration and displacement of the isolated mass, the relative displacement between the base and the mass, and the effective damping ratio of the system. Provided that the damping in the isolator is light, it is found that the semi-active system can outperform a linear passive system during both stages of control.