A quasi-zero-stiffness vibration isolator using a cam mechanism with user-defined profile

This paper presents a passive quasi-zero-stiffness (QZS) vibration isolator via a cam mechanism (CM), where the cam has a user-defined profile to generate the desired force-displacement relation that yields the QZS characteristic. Without using the common configurations connecting positive and negative stiffness in parallel, this CM based QZS isolator is much simpler in structure due to utilizing fewer key components. Unlike previous studies where the high calculation complexity must be simplified by Taylor expansion for the convenience of dynamic analyses, this QZS isolator has the superiority that the ideal simplest restoring force with QZS property can be directly realized through the well-designed CM, which can eliminate the approximation error between the theoretical design and actual implementation. The nonlinear differential motion equations based on pure-cubic restoring force and both viscous and friction damping are derived and solved with the harmonic balance method, followed by the discussion of the relevant dynamic characteristics. Experiments on the fabricated physical prototype of the QZS isolator are carried out. The static results verify the proposed design principle due to the agreement between the tested and designed force-displacement curves. The vibration tests show the advantages of QZS isolator in most cases, since it can exhibit the wider isolation frequency bandwidth and much weaker resonance effect than the corresponding linear counterpart. The actual transmissibility characteristics of the QZS and linear isolators under different force and base motion excitation levels are obtained and comprehensively compared to reveal the specific isolation efficiency and how excitation amplitudes affect the vibration attenuation performance.