Liu Y., Matsuhisa H., Utsuno H.

Semi-active vibration systems expend a small amount of energy to change the system parameters, such as damping and stiffness. The semi-active systems with variable damping and stiffness have demonstrated excellent performances. However, conventional devices for controlling variable stiffness are typically complicated and difficult to implement in most applications. To address this issue, a new configuration that requires two controllable dampers is proposed. A controllable damper and a constant spring comprise a Voigt element. The Voigt element and a spring are in series. The stiffness of the whole system is changed by the controllable damper in the Voigt element, and the other damper provided variable damping for the system. The proposed configuration is experimentally implemented using two magnetorheological (MR) fluid dampers for the controllable dampers in one degree-of-freedom (DOF) vibration isolation system. This paper presents theoretical and experimental analyses of the proposed system. The experimental results agree well with the theoretical analyses. Five different control schemes involving low damping, high damping, damping on-off, stiffness on-off, and damping and stiffness on-off control are explored. The responses of the system to sinusoidal and random excitations show that the variable damping and stiffness control can be realized by the proposed system, and the system with damping and stiffness on-off control provides the best vibration isolation over the whole frequency region. To expand this work, it is useful to apply this semi-active vibration isolation method to 2 DOF structures, such as two floors of a building or the body and the wheel of an automobile. Therefore, a 2 DOF vibration isolation system with variable damping and stiffness is also studied. The time and frequency responses of the system to impulse and sinusoidal base excitations show that the damping and stiffness on-off control system has the best performance.