A novel quasi-zero-stiffness strut and its applications in six-degree-of-freedom vibration isolation platform

Generally, existing isolators with quasi-zero stiffness (QZS) are designed for mitigating transmission of vertical translational excitations, but vibration isolation in multiple directions is much more desirable and useful. The major contribution of this paper is extending the QZS vibration isolation method from one degree of freedom (DOF) to all six DOFs, by using a novel QZS strut to construct a 6-DOF QZS vibration isolation platform. Firstly, the design concept of the QZS strut is proposed, and then a pyramidal 3-QZS-strut isolator is assembled. Finally, a 6-DOF QZS platform is achieved by using such isolators as supporting mounts. The equations of motion of this platform are established, and solved by the Harmonic Balance method to obtain amplitude-frequency relationships. Moreover, the performance of vibration isolation is evaluated in terms of force/moment transmissibility. Compared with the linear counterpart, the 6-DOF QZS platform has broader bandwidth of vibration isolation starting from lower frequency, and possesses higher effectiveness in low-frequency range, most importantly, in all six DOFs.