On the coupled dynamics of near-field acoustic levitation bearing

Abstract

Near field acoustic levitation (NFAL) bearings, as an alternative non-contact bearing solution, has been proposed and advanced in variable aspects in recent years. To further investigate the property of NFAL and fulfill its theoretical frame, a model based on the stiffness model to analysis the coupled dynamics of the NFAL bearing system, which takes the impact of dynamic stiffness on the levitated object into consideration is proposed. In this model, due to the impact of the driving surface vibration and the dynamic stiffness on the levitated object, a real-time movement of the levitated object is superimposed on the time-averaged movement. By inducing the real-time vibration of the levitated object into the model, it is found that the levitation force and the driving frequency will no longer follow an approximate hyperbolic tangent relationship. The model indicates that, when approaching a certain frequency, the stiffness-mass system of the bearing resonates, and then the phase of the two surfaces begins to increase rapidly, thereby increasing the amplitude of the actual air gap. It is verified with experiments that the object can only be levitated above the resonant frequency.