A nonlinear ultra-low-frequency vibration isolator with dual quasi-zero-stiffness mechanism

A quasi-zero-stiffness (QZS) vibration isolator is an ideal device for low-frequency vibration isolation. However, its stiffness increases steeply against the displacement, which renders a QZS isolator to be less effective in an ultra-low-frequency range. Aiming at solving this issue, a new nonlinear ultra-low-frequency vibration isolator with a dual quasi-zero-stiffness (DQZS) mechanism is put forward by combining two subordinate QZS mechanisms with a vertical linear spring in parallel. The subordinate mechanism itself has a QZS feature, which provides negative stiffness along the vertical direction through an oblique link rod. The parameter design of the isolator is carried out to fulfil quasi-zero stiffness, which shows that the stiffness-displacement curve is much lower and more flat than the traditional QZS (TQZS) isolator in a wide displacement range. The dynamic behaviours of the DQZS vibration isolation system (VIS) are determined by employing the harmonic balance method, and the vibration isolation performance is evaluated by using theoretical, numerical and experimental transmissibility. It shows that both the beginning frequency of the vibration isolation and the peak transmissibility of the DQZS VIS are lower than the TQZS isolator, which indicates better vibration isolation performance of this ultra-low-stiffness DQZS VIS.