Modeling and analysis of a novel multi-directional micro-vibration isolator with spring suspension struts

In this work, a novel spring suspension strut with quasi-zero-stiffness (QZS) and zero-stiffness (ZS) properties is proposed to improve the performance of the multi-directional micro-vibration isolator. The QZS and ZS properties are achieved by developing a hexagon structure with negative stiffness mechanism to counteract the positive stiffness of a vertical suspension spring. The strut also has high loading capacity and excellent equilibrium stability. Based on the Stewart platform, the spring suspension strut can largely lower the isolation frequency in all 6-degrees-of-freedom (6DOFs), while the effectiveness of micro-vibration isolator is notably improved. The effects of nonlinearity on the stability, equivalent cross-coupling force and vibration response are discussed in detail. The design concept of the spring suspension strut is first proposed, and the static modeling is conducted. Then, by using such struts as supporting mounts, a 6DOFs micro-vibration isolator is achieved, and the equivalent cross-coupling force and stiffness of the isolator are analyzed. Furthermore, the equations of motion of the isolator are established by the Hamilton principle. The frequency response characteristics particularly for force transmissibility of the platform are obtained to achieve the parameter optimization for maximum frequency band of isolation. Finally, compared with the linear counterpart, the 6DOFs QZS and ZS micro-vibration isolator has broader bandwidth of isolation starting from lower frequency and possesses higher effectiveness in ultra-low-frequency range. The results presented herein provide an insight of dynamics into the QZS and ZS mechanisms for their application in multi-directional vibration engineering.