Enhanced Design of X-Shaped Structure for Ultra-Low-Frequency Nonlinear Vibration Isolation

An improved X-shaped quasi-zero stiffness (QZS) isolator, consisting of several pivoted bars and springs, is proposed to explore its advantages in isolating ultra-low frequency vibrations. The proposed compact structure can maintain enhanced QZS properties with large strokes through convenient connections between pivoted bars and springs. The static stiffness behaviors are examined theoretically using the virtual work principle. To validate the theoretical results, nonlinear restoring forces are simulated using ADAMS, revealing that the static stiffness exhibits enhanced QZS properties. A comprehensive investigation is conducted into how the design parameters influence the load capacity and QZS range. By adjusting the oblique springs, the negative stiffness can be entirely counterbalanced, ensuring the stability of the system. By employing the Lagrange principle, the dynamic equation is obtained and solved by the harmonic balance method. The vibration transmissibility for the improved X-shaped isolator under various parameters is calculated. The improved QZS isolator can achieve excellent ultra-low frequency and full-band vibration isolation performance while maintaining a stable equilibrium, according to the numerical results, which also show advantageous nonlinear stiffness properties. The findings from this research present innovative perspectives on the design of ultra-low frequency passive isolation systems, offering valuable implications for various engineering fields and applications.