Analytical study of a pneumatic vibration isolation platform featuring adjustable stiffness

Abstract This paper proposed a pneumatic vibration isolation platform (named VIP) with adjustable stiffness characteristics in which two opposite stiffness mechanisms are introduced. One with positive stiffness is formed by the wedge-roller mechanism used to support the load, which is named the load bearing mechanism (LBM), the other (called stiffness correction mechanism-SCM) generating negative stiffness in vertical direction, constructed by the cam-roller mechanism, is used for correction of the total stiffness of the VIP. Instead of using coil spring, the rubber air spring is employed, hence the stiffness of the VIP can be easily adjusted to adapt to the change of the isolated load as well as improve the isolation effectiveness in low frequency region. The force model of the rubber air spring generated by the compressed air, friction and viscoelastic is then built and identified via the experiment. Next, the dynamic stiffness model of the VIP will be established and analyzed. The primary resonant response of the proposed model subjected to harmonically excited base will be analyzed by employing the normal form technique. The effects of the configurative parameters on the amplitude-frequency curve are investigated. Furthermore, due to the nonlinear dynamical system, the complex dynamical analysis including coexistence solution, bifurcation and so on is necessary to explore in this work by using the numerical integration and Poincare map. Finally, the isolation response of the VIP subjected to the random excitation is also evaluated and compared with that of the equivalent linear isolator (named ELI in which the SCM is removed). The result shows clearly the advantages of the VIP against the ELI. This work will furnish a useful insight into the design and manufacture of the low frequency vibration isolation systems.