A semi-active quasi-zero-stiffness vibration isolation system through controllable lateral spring stiffness

In this work, a semi-active quasi-zero-stiffness (QZS) vibration isolation system with controllable lateral springs was proposed and its practical vibration isolation effectiveness was demonstrated through theoretical and experimental studies. A semi-active control strategy was developed to allow for the regulation of the lateral spring length to address the large resonant responses in the low-frequency range of the QZS system, while maintaining QZS benefits of increasing the control bandwidth with sufficiently low transmissibility and satisfactory static stiffness. The effect of the length of the lateral springs on the negative stiffness of the system under static conditions was investigated, and the stability of the system was analyzed to ensure the system’s stability during its operation. Moreover, by employing the semi-active control strategy with the resonance-detuning approach, the dynamic characteristics of the QZS system could be altered from linear to nonlinear through the highly-responsive adjustment of the lateral spring stiffness. As a result, the excitation of low-frequency resonance could be avoided while simultaneously obtaining an increase of control bandwidth with low transmissibility. Specifically, experimental results showed that the developed QZS vibration isolation system could achieve a reduction of transmissibility peaks by 9.68 dB and 15.59 dB, compared to the linear isolation system and the QZS vibration isolation system without control, respectively. The QZS vibration isolation system also achieved an overall reduction in vibration transmissibility with its low-frequency 0-dB bandwidth reduced by 11.8% (from 3.64 to 3.21 Hz) when compared to the linear system, demonstrating an improved vibration isolation effectiveness.