Pneumatic Quasi-Zero-Stiffness Isolator for Low-Frequency Vibration Isolation: A Theoretical Study

The concept of quasi-zero-stiffness (QZS) vibration isolator was proposed in recent decades to improve the low-frequency vibration isolation performance while maintaining the load-bearing capacity. This paper presents a novel QZS vibration isolator by employing pneumatic springs (PS-QZS isolator). The QZS feature is achieved by proper design of the initial state of the pneumatic springs to produce negative stiffness that exactly counteracts the positive stiffness at the static equilibrium position. This paper is primarily a theoretical study with numerical validation. First the stiffness characteristics of the PS-QZS isolator is derived and the equation of motion is formulated. Then the frequency response is analytically calculated and verified by numerical simulations, and the stability is analyzed. Finally the vibration isolation performance is compared with the equivalent linear isolator and the effects of damping and excitation amplitude are investigated. It is shown that the PS-QZS isolator can achieve much better isolation performance than the equivalent linear isolator for its wider frequency range of isolation and lower peak transmissibility.