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This paper focuses on suppression of free vibration of single degree-of-freedom systems that possess time delay. The switchable stiffness (SS) control strategy is reviewed. The implication of time delay is examined. It shows that the system delay can cause malfunction of the direct SS control. To overcome this problem, the two time-delay control strategies are proposed. The first strategy named as half period delay SS control introduces an intentional delay such that the switch action takes place in a half of oscillation period later. The second strategy named as quarter period delay SS control is to add an intentional delay such that the switch action occurs in a quarter of oscillation period later. In this case, the SS control law is inverted. An apparatus consisting of an electromagnetic (EM) spring is developed to validate the proposed strategies. The stiffness models of the system are established. In computer simulation, three cases have been examined. In case A, the system is simplified as linear and the dynamics of the EMs is neglected. In case B, the stiffness models are used and the dynamics of the EMs is neglected. In case C, the stiffness models are used and the dynamics of the EMs is considered. An experimental study is conducted in real time. The results have validated the observations obtained from the computer simulations. [ABSTRACT FROM AUTHOR]

This study focuses on the control of a novel active vibration isolator using an adaptive backstepping approach. The developed active isolator is introduced and its dynamic model is presented. It is shown that the unknown nonlinear restoring force and damping parameter pose control challenges. The nonlinear restoring force is approximated as a polynomial with unknown coefficients. Adaptive control is chosen as a suitable approach to tackle the control challenges. An existing lower-order adaptive backstepping controller is modified in order to include the actuator dynamics and avoid the zero convergence of the estimated parameter vector. An extensive experimental study is conducted to test the effectiveness of the modified controller. The performance of the controller is compared with that of the lower-order controller. The results from several testing scenarios are presented and interpreted, and the issues related to parameter estimation and control performance are addressed. [ABSTRACT FROM PUBLISHER]

In this paper, a vibration isolation system based on a parallel mechanism is proposed to isolate the multi-dimensional (MD) vibrations. The parallel mechanism, which is composed of three uniform P∧UU (Prismatic pair with spring and damper elements–Universal joint–Universal joint) limbs and two platforms, has three translational degrees of freedom. First, the isolator is introduced and the dynamic model is achieved by a Newton–Euler method. Further, a sliding mode controller is designed to obtain the optimal damping forces as the control strategy is very essential to a vibration isolation system. At the same time, the time-domain hard constraints are considered in the controller design as the damping force can only be produced along the direction contrary to the relative velocities of the MR damper’s two ends. Simulations results demonstrate that the semi-active isolator using MR dampers has fine performance in reducing MD vibrations. [ABSTRACT FROM PUBLISHER]