A novel semi-active tuned mass damper with a continuously tunable stiffness

A passive tuned mass damper can only be designed to have a good damping effect near the resonance frequency of the primary structure. To overcome this limitation, a novel semi-active tuned mass damper with continuously tunable stiffness is proposed in this paper. The proposed design features a compact mechanism that can vary its stiffness by changing the number of active coils in parallel and series configurations of helical springs. The real-time control of the stiffness is achieved by designing and implementing a driving system for this mechanism. The motion characteristics and required driving torque for the designed prototype are also examined during the stiffness tuning process. It is demonstrated that the novel semi-active tuned mass damper can tune its stiffness over a wide range, and consequently tune its working frequency band to a desirable region with a proper control law. The effectiveness of the proposed prototype was investigated numerically and experimentally with respect to one-degree-of-freedom harmonic excitations in the frequency ratio range of 0.8-1.2. The results indicate that the prototype preserves optimal vibration suppression performance across a broad frequency range. Thus, the proposed semi-active tuned mass damper can provide a simple and effective in-situ tunable tool for suppressing primary structure vibration in the presence of non-stationary vibratory excitations.