X-shaped mechanism based enhanced tunable QZS property for passive vibration isolation

A novel spring arrangement based on the X-shaped anti-vibration structure with tunable contact mechanism (NXSC) is proposed to explore much better low-frequency vibration isolation performance. An enhanced quasi-zero-stiffness (QZS) with large stroke is obtained by tuning contact position between the horizontal springs and vertical fixed rods. The loading capacity and working range of the NXSC structure can be extended by 2, 3 times compared with classical X-shaped structures. The proposed NXSC structure is adjustable to different loading requirements and resonant frequencies, and excellent vibration isolation performance can be achieved readily by tuning the contact parameter. Three types of the NXSC structure with different contact modes are designed. The effects of structural parameters on the loading capacity and QZS zone are analyzed. By tuning the contact parameter via special tuning mechanisms, the negative stiffness can be compensated completely to ensure the stability of isolation systems. Comparisons with a typical spring-mass-damper (SMD) isolator and an existing QZS isolator exhibit that the stiffness-displacement curve of the NXSC structure is much more adjustable with significantly extended QZS in a wider displacement range, and does not sacrifice loading capacity. Moreover, the NXSC structure is less sensitive to excitation amplitude than the traditional QZS isolator, and it does not produce frequency jump phenomenon and softening and hardening stiffness effects. Experiments are implemented to verify the theoretical result and demonstrate that the proposed NXSC structure possesses superior vibration isolation performance and can effectively attenuate vibration at low-frequency range. This NXSC structure presents a new and efficient way for manipulating beneficial nonlinearity based on the X-shaped structure for better engineering performance.