Theoretical And Experimental Study On A Class Of Geometrically Nonlinear Quasi-zero Stifness Vibration Isolation System

With the development of science and technology in recent years, much research has been done on the developments of high-precision instruments and the improvements of major infrastructure. The performance of existing isolator cannot meet the needs gradually, due to the harsh mechanical environment such as impacts, random vibrations, seismic waves, and so on. Traditional linear vibration isolation system is only available in the frequency signals above 10 Hz. Although the active vibration isolation technology achieves the goal of low frequency vibration isolation, it’s still facing the problem of control algorithm complexity, large auxiliary equipment weight, high cost, maintenance and operation. Therefore, expanding research on the mechanical nonlinear low-frequency passive isolators is of great significance to the project through the application of the advantages of simple design, without complex auxiliary equipment, light weight, simply maintenance and easy operation.Through a new angle of view, a geometric nonlinear structure evolved from dipteran flight mechanism are considered. Passive vibration isolator design and plan are proposed to improve the low-frequency vibration isolation performance by using its stable-quasi-zero stiffness characteristics. The main contents can be summarized as follows:Based on a geometric nonlinear structure, a kind of quasi zero gravity load stiffness vibration isolator mechanics model has been set up, and its vibration control equation was deduced. The model consists of a pair of spring connecting rod mechanism and vertical bearing spring, and the existence of the positive and negative stiffness parallel to stable quasi zero stiffness characteristics. The nonlinear force-displacement characteristics and the stiffness characteristics are mainly studied, meanwhile The bifurcation phenomenon of the system equilibrium point are analyzed with different parameters, and the attraction domain of a damping system are also considered. Numerical method are used to study the dynamic response, bifurcation and chaos characteristics of the system under the condition of simple harmonic vibration.For the irrational and bounded characteristics of vibration equation, the average method solution are given by using Jacoby incomplete elliptic integral formula to describe the amplitude-frequency characteristic and phase-frequency characteristics of the Wings vibration isolation system in global motion. Bounded boundary conditions of the system determines its maximum vibration amplitude, meanwhile sufficient stiffness is provided to ensure the loading capacity and the low dynamic stiffness to a low natural frequency of vibration corresponding to a wider isolation frequency band. The isolation transfer rate given by average method illustrates this phenomenon, at the same time the influence of different parameters on the peak isolation transfer rate and jumping points, are studied.Considering the mechanical model under gravity load, the mechanical design of quasi-zero-stiffness passive isolators are completed and the experiment expanded. Experimental results show the influence of different parameters on the preceding transfer rate and jumping points. The conclusion shows that, through appropriate damping configuration, the frequency band and formant suppression of quasi-zero-stiffness passive isolator is significantly better than the corresponding linear isolation system, and by using quasi-zero-stiffness passive isolator the system can enter the isolation area faster than linear systems(T_max＜25%).