An innovative quasi-zero stiffness isolator for excitation adaptability via dual nonlinear stiffness regulation

Conventional quasi-zero stiffness (QZS) vibration isolators suffer from low-frequency resonance, severely compromising their isolation performance and limiting their usable frequency range. This work proposes a novel adaptive-excitation QZS isolator (AQZSI) based on dual nonlinear stiffness regulation, which achieves excellent resonance suppression, broadband vibration isolation, and varying-load capacity. The experimental prototype consists of a negative stiffness mechanism made of spring steel buckling beams and a positive stiffness mechanism made of neodymium-iron-boron (NdFeB) magnets, which have the advantages of low energy consumption and low damping characteristics. The vibration isolation system is designed based on a smart and rapid switch between dual nonlinear systems of QZS and high stiffness (HS) isolators by tuning the positive stiffness. By timely identifying the excitation frequency, a semi-active control system is employed to adaptively switch the working state to the HS mode at the low frequency and to the QZS mode at the high frequency. Thus, the resonance at low frequencies is alleviated while maintaining excellent isolation performance at high frequencies. In addition, the varying-load adaptability is achieved by simultaneously tuning both positive and negative stiffness to realize the rated load adjustment. Static analyses are conducted, and the dynamic characteristics are analyzed by using the harmonic balance method. Experimental results show that the resonance peak of AQZSI in the low-frequency region is reduced by up to 82.3% compared to a standalone QZS system and that the rated load can be readily changed according to the payload, verifying its superior broadband vibration isolation performance as well as varying-load capacity.