The vibration isolation proprieties of an X-shaped structure with enhanced high-static and low-dynamic stiffness via torsional magnetic negative stiffness mechanism

Bionic X-shaped structure is widely studied for low-frequency vibration isolation. In this paper, an X-shaped structure with torsional magnet negative stiffness (TMNS) mechanisms and torsion springs is proposed to enhance the high-static and low-dynamic stiffness characteristics. The TMNS contains multiple pairs of inner and outer tile permanent magnets, and can generate periodic torsional negative stiffness. With the compensation of torsion springs, the QZS point can be realized flexibly within the whole stroke, and one or multiple QZS regions can be obtained. Considering the nonlinear inertia caused by TMNS mass, the system motion equation is established and the displacement transmissibility is solved by harmonic balance method (HBM). The results show that the nonlinear inertia causes the system to experience anti-resonance phenomenon, meanwhile, the resonance frequency slightly shifts to the left. Compared to the typical QZS isolator or the classic X-shaped structure with vertical spring, the proposed model possesses higher equivalent static stiffness, and can achieve better low-frequency vibration isolation performance. An experimental prototype is fabricated, and its static nonlinear property as well as absolute displacement transmissibility are tested. The validity of proposed model is verified by comparing the experimental results with theoretical values.