On the Characteristics and Practical Parameters Selection of a Quasi-Zero-Stiffness Isolator

Quasi-zero-stiffness (QZS) isolators, characterized by high-static-low-dynamic stiffness (HSLDS), have attracted interest in the field of low-frequency vibration isolation. An existing QZS isolator, using horizontal springs in series with rigid oblique rods as a negative stiffness mechanism, has been proposed to obtain desirable low-frequency isolation performance. However, it is unknown if the rigid oblique rods will obtain the optimal isolation performance for the existing QZS isolation system. In this research, considering that the oblique rods are flexible rather than rigid, the effects of the stiffness of the springs and the rods on mechanical characteristics and isolation performance of this QZS isolator are investigated to answer the above question and to guide design of the QZS isolator. The QZS conditions ensuring the QZS characteristics of the proposed QZS isolator are derived, and the parametric analysis on QZS characteristics is conducted. Further, amplitude-frequency response of the QZS isolation system is obtained by the average method and the numerical methods; the following parametric analysis indicates that the optimal stiffness ratio of horizontal spring to vertical spring should be slightly greater than 0.5 to obtain a reasonable compromise between the peak amplitude control and peak force transmissibility reduction. Meanwhile, when the stiffness ratio of the oblique rod to the vertical spring is greater than 2, the QZS isolator with finite-stiffness oblique rods has similar isolation performance as that of the existing QZS isolator with rigid oblique rods. Therefore, designers could select oblique rods with finite stiffness to avoid excessive size or non-negligible weights of the rods.