Isolation performances and optimization of triple quasi-zero stiffness isolators

In this paper, triple quasi-zero stiffness (QZS) passive vibration isolators whose restoring force curve has a three-stage softening effect are proposed. Multi-coupled SD oscillators with three independent geometrical parameters are used as negative stiffness mechanisms to achieve QZS characteristics at the origin and symmetrical positions on both sides of the origin. Isolation performances of different triple QZS isolators are analyzed to show influences of the selection of QZS regions away from the origin on the range of isolation regions. Pareto optimizations of system parameters are carried out to get a larger range of small restoring force regions and small stiffness regions. Isolation performances of two triple QZS isolators are discussed to show the influence of different Pareto optimization solutions through the comparisons with single and double QZS isolators. Results showed that triple QZS isolators have both the advantages of single and double QZS isolators which results in better isolation performances under both small and large excitation amplitudes. An improvement in isolation performances for triple QZS isolators is found with the decrease in average stiffness due to the appearance of two symmetrical QZS regions away from the origin. Larger displacements of QZS regions away from the origin result in better isolation performances when excitation amplitude is large, and triple QZS characteristics are similar to double QZS isolators at this time. Smaller restoring forces of QZS regions away from the origin lead to better isolation performances when excitation amplitude is small, and triple QZS characteristics are similar to single QZS isolators at this moment. Compared with the decrease in average stiffness, the improvement of isolation performances shows a hysteresis phenomenon due to the difference between static and dynamic characteristics.