Quasi-zero stiffness vibration isolator with variable stiffness and variable damping for ultralow-frequency vibration under variable mass load

A quasi-zero-stiffness (QZS) vibration isolation system presents the characteristics of high-static-low-dynamic, which can effectively isolate ultralow-frequency vibrations. However, most QZS vibration isolation systems are highly susceptible to external loads, causing deviations from the equilibrium position, which degrades their vibration isolation performance and severely restricts the range of QZS. To overcome these limitations, a novel vibration isolator was proposed by integrating a QZS structure with a variable stiffness and variable damping (VSVD) structure. The stiffness and damping of the vibration isolation system can be regulated to resist variable mass loads, and the QZS vibration isolation band can be broadened using the nonlinear positive stiffness of the conical rubber spring to effectively suppress ultralow-frequency vibrations. The dynamic characteristics of the QZS-VSVD vibration isolator were analyzed using the harmonic balance method. The effects of damping coefficients, excitation amplitude, and mass load on the amplitude–frequency characteristics and displacement transmissibility of the vibration isolation system were investigated. A virtual prototype of the QZS-VSVD vibration isolator was established using the ADAMS software, and vibration simulations were conducted. The results indicate that the QZS-VSVD vibration isolator can achieve ultralow-frequency vibration isolation at approximately 1 Hz under variable mass loads ranging from 3300 N to 3700 N. When the mass load was 3500 N, the amplitudes of the isolated object were attenuated by 70.6% and 86.2% under displacement excitation at 3 Hz and 5 Hz, respectively. Compared to linear isolators and a typical QZS structure, the proposed QZS-VSVD vibration isolator exhibited a greater load-bearing capacity, stronger anti-interference capability, and broader vibration isolation bandwidth.