Analytical study of the low frequency multi-direction isolator with high-static-low-dynamic stiffness struts and spatial pendulum

By now, existing isolators with quasi-zero stiffness (QZS) or high-static-low-dynamic stiffness (HSLDS) have been designed to migrate the vibration in single direction, but the vibration isolation in multiple directions is more expected. Hence a passive low frequency multi-direction isolator based on the HSLDS struts and spatial pendulum is developed in this study. The remarkable feature of the proposed mount is that the dynamic coupling is so weak that the responses in different directions do not interact with each other, which is desirable for low frequency vibration isolation in multiple directions. Firstly, the design of the low frequency multi-direction isolator is presented. With the Lagrange principle, the equations of motion of the isolator are established, and then solved via harmonic balance method to obtain the amplitude-frequency relationships. The vibration isolation performance is evaluated in terms of the displacement transmissibility, and the parameter studies are carried out as well. The results show that: (a) the isolator can realize the high-static-low-dynamic stiffness in the vertical direction and quasi-zero stiffness in the other two horizontal directions; (b) with the spatial ball hinges, the displacement-velocity-dependent nonlinear damping is introduced in two horizontal directions, which is the function of the displacement and velocity; (c) compared with the linear counterpart, the combination of the HSLDS struts and spatial pendulum enables the proposed passive isolator to achieve much better low frequency vibration isolation performance in multiple directions, especially in the vertical direction.