An absolute-zero-stiffness vibration isolator for continuously varying mass: Theoretical design and numerical simulation

Nonlinear quasi-zero-stiffness (QZS) vibration isolators can provide low dynamic but high static stiffness, and thus attract much attention in the fields of vibration isolation and reduction. However, it seems difficult for QZS isolators to protect continuously varying mass from the surrounding vibratory disturbance of relatively large amplitude. In this article, an adjustable absolute-zero-stiffness vibration isolator is designed by updating the classical QZS isolator in two steps. First, each hinged constraint in the QZS isolator that connects the oblique spring with the outer rigid framework, is released and replaced by a sliding constraint supported on an additional vertical linear side-spring. Second, the two oblique springs in the QZS isolator are further replaced by two identical oblique cam-roller-spring units, which can synthetically provide a constant negative-stiffness at will in the vertical direction. Once the stiffness ratios among the main-spring (as in the QZS isolator), side-springs and oblique-units of the new isolator are rationally determined, for a target object with any weight to be protected, absolute zero stiffness and transmittance can always be achieved by appropriately exerting an additional time-independent vertical force on each sliding constraint. The validity and efficiency of the theoretical design are fully verified by numerical simulations for both fictitious loads and real seismic spectra. This work provides a possible means for nonlinear vibration isolations of continuously varying mass.