Study on a quasi-zero-stiffness isolator for variable mass load.

• The mechanism including the adjustable positive stiffness configuration is adopted. • The dynamic property with deviation of mass load is analyzed. • The influence of the asymmetric stiffness is studied at small displacement. • The isolation performance with various mass load is evaluated. Generally, the performance of the quasi-zero-stiffness (QZS) isolator is very sensitive to the deviation of mass load. Due to the ultra-low stiffness, even a slight deviation could lead to a large offset from the designed equilibrium. The performance degradation for low frequency vibration would be caused by the increase of the stiffness around the actual equilibrium. In this paper, a QZS isolator with the deviation of mass load is studied. The isolator comprises a nonlinear positive stiffness configuration with a pair of torsion springs, oblique bars and linear bearings, and a negative stiffness configuration with a pair of oblique bars connected to horizontal springs. The dynamic equation of the isolator with the deviation of mass load is derived. The amplitude-frequency property and force transmissibility are investigated. It is found that the deviation of mass load could significantly change the dynamic properties of the QZS isolator. To improve the isolation performance, the parameters of the positive stiffness configuration are considered to be adjustable. The results show that the adjustability can help remain the initial equilibrium, and reduce the response amplitude and force transmissibility in low frequency. The negative effect of the deviation of mass load on the QZS isolator can be decreased to a great extent. [ABSTRACT FROM AUTHOR]