Analysis And Experimental Assessment Of An Adjustable Pneumatic Vibration Isolator With Quasi-zero-stiffness Characteristic

In design of a high-static-low-dynamic stiffness vibration isolation system, thechange of the loading weight may significantly affect the performance of vibrationisolation. A weight adaptable nonlinear pneumatic vibration isolator with thecharacteristic of quasi-zero stiffness (QZS) was developed on the basis of designtheory of the nonlinear vibration isolation system. The QZS isolator is devised byconnecting a vertical double-chamber air cylinder with two symmetrical horizontalsingle-chamber air cylinders. This new type isolator has the characteristic ofhigh-static-low-dynamic stiffness near the equilibrium, which makes the systempossess high load capacity and good vibration isolation performance. Analytical resultreveals a unique relationship between the design parameters of air cylinder for theQZS systems. The adjustable QZS isolator can maintain the characteristic ofquasi-zero stiffness by tunning air pressure when the mass loading changes.The dynamic characteristics of the QZS system are analyzed with harmonicexcitations. The dynamic model is established to obtain the governing equation of thesystem. Analytical solutions of the equation are derived with the harmonic balancemethod for the characteristic analysis of jumping phenomena and the forcetransmission. The influence factors of jumping frequency are analyzed. Comparedwith the linear system, it is found that the QZS system has smaller forcetransmissibility and larger frequency interval for vibration isolation under appropriateexcitation conditions, which makes it more suitable for low-frequency vibrationisolation.The force transmissibility of the QZS system and the corresponding linearisolator is experimentally tested. By comparing the experimental results, it is foundthat the QZS isolator outperforms significantly the corresponding linear systemespecially in the low-frequency bandwidth near the resonance. In addition, theexperimental results reveal that the vibration isolation performance of the QZS systemis also dependent on the amplitude of vibration. The QZS system can only exhibit itsexcellent vibration isolation capability in the condition where relatively largeoscillations are involved. By comparing the force transmissibility of different massloadings, it proves that the adjustable QZS isolator can maintain good vibration isolation performance by tunning air pressure.