QZS isolators with multi-pairs of oblique bars for isolating ultralow frequency vibrations

Quasi-zero stiffness (QZS) vibration isolators have been intensively studied due to their importance in isolating low-frequency vibration, but isolating the ultralow frequency vibration and supporting variable mass are still challenging and open research issues. This paper proposes novel QZS isolators with two or three pairs of oblique bars. The distinctive feature of the proposed isolators is the constant QZS and thus it can achieve the isolation of ultralow frequency vibration and the capacity of supporting variable mass. Static and dynamic analyses of the proposed isolators are carried out to obtain the stiffness and displacement transmissibility. The QZS features of the proposed isolators are compared with the QZS isolators with two or three pairs of oblique springs. Prototypes of the proposed isolators with two or three pairs of oblique bars are fabricated and tested to verify the theoretical formulations and the constant QZS feature. The experiment results show that the proposed QZS isolators with constant QZS features have lower transmissibility and can isolate vibration in the frequency of 1–1.5 Hz. The isolators with constant QZS are expected to be used for practical applications in the situations of large amplitude and ultralow frequency vibration, and variable mass loading.