Semi-active systems with variable stiffness and damping have demonstrated excellent performance. However,
conventional devices for controlling variable stiffness are complicated and difficult to implement in most applications.
To address this issue, a new configuration using two controllable dampers and two constant springs is proposed. This
paper presents theoretical and experimental analyses of the proposed system. A Voigt element and a spring in series are
used to control the system stiffness. The Voigt element is comprised of a controllable damper and a constant spring. The
equivalent stiffness of the whole system is changed by controlling the damper in the Voigt element, and the second damper
which is parallel with the other elements provides variable damping for the system. The proposed system is experimentally
implemented using two magnetorheological fluid dampers for the controllable dampers. Eight different control schemes
involving soft suspension, stiff suspensions with low and high damping, damping on–off (soft and stiff), stiffness on–off
(low and high), and damping and stiffness on–off control are explored. The time and frequency responses of the system to
sinusoidal, impulse and random excitations show that variable stiffness and damping control can be realized by the
proposed system. The system with damping and stiffness on–off control provides excellent vibration isolation for a broad
range of excitations.