On Nonlinear Vibration Isolation Characteristics And Experimental Research Of A Quasi-Zero-Stiffness Isolator With CRSM

Firstly, piecewise nonlinear static and dynamic models of a quasi-zero stiffness(QZS) vibration isolation system(VIS) with cam-roller-spring mechanisms(CRSM) that had negative stiffness were developed. The dynamic characteristics of the system under the harmonic motion of the base and harmonic exciting force were analyzed theoretically by using the averaging method, and the primary resonance responses were obtained. The analytical solutions were verified by the numerical solutions of the equation of motion, which confirms the efficiency of the averaging method to solve the piecewise nonlinear problem. Further, the effects of excitation amplitude and damping on responses were discussed. Displacement transmissibility and force transmissibility were used to evaluate the performance of vibration isolation. The results show that excitation amplitude and damping notably influence the response of the system. When the excitation amplitude is small, the system outperforms the corresponding linear system obviously. The vibration isolation performance becomes worse as the exciting amplitude increases, but it is at least equal to the linear system. This feature of the system is superior to that of the traditional quasi-zero stiffness vibration isolation system.Then, a piecewise nonlinear dynamic model of a two-stage quasi-zero stiffness vibration isolation system with cam-roller-spring mechanisms(CRSM) was developed. The solution of the nonlinear dynamical equations of the vibration isolation system and the force transmissibility were obtained by using the averaging method. The analytical force transmissibility of the two-stage QZS system was used to evaluate the performance of vibration isolation. The results show that the two-stage quasi-zero stiffness vibration isolation system has good performance on vibration isolation in low frequency range and a better effect of isolating vibration is achieved in a wide band. The effects on the vibration isolation performance caused by mass ratio of the first stage to the second stage, stiffness ratio, and damping were discussed. Results indicate that it is preferable to have relatively high damping in the upper stage to restrain resonance, widen the effective vibration isolation frequency band and ensure higher vibration isolation efficiency at the same time.Finally, the experimental prototype of the single-stage QZS system was designed and made. The experiment was carried out to study the dynamic characteristics and vibration isolation performance. The force transmissibility under excitations with various frequencies achieved in the experiment was compared with that of the corresponding linear vibration isolation system. The results show that the cam-roller mechanism with negative stiffness lowers the starting isolation frequency and enhances the isolation efficiency, and suppresses the resonant response. Also shown is that, under the condition of keeping touch between the cam and the roller, the larger the excitation amplitude is, the more likely to reduce the system's stiffness the negative-stiffness mechanism is, to achieve more notable vibration isolation performance. Therefore, the QZS vibration isolation system with CRSM has an excellent low-frequency vibration isolation performance.