Harnessing the compressed-spring mechanism for a six-degrees-of-freedom quasi-zero-stiffness vibration isolation platform

The compressed-spring structure is a simple and reliable mechanism to achieve negative stiffness, which has been vastly investigated for achieving quasi-zero-stiffness isolation. However, six-degrees-of-freedom quasi-zero-stiffness isolators based on this kind of negative-stiffness mechanism still have not been touched. In this study, we propose a six-degrees-of-freedom quasi-zero-stiffness isolation platform constructed by six modules that use compressed-spring structures. Its underlying quasi-zero-stiffness principles in the translational and torsional directions are explained. By establishing the static model of the platform and linearizing it at the static equilibrium position, we find that the linear cross-coupling effects appear if the static load exists. Linearized dynamic analysis of the isolation platform is then performed and the results demonstrate that by applying spring compression, the isolation frequency band can be expanded to lower frequency range in six directions. Because of cross-coupling effects resulted from the static load, the platform cannot achieve whole-frequency-range isolation in the coupling directions even if the spring compressions satisfy quasi-zero-stiffness conditions.