Magnetic damping and stiffness effects on rod translation by active magnetic bearing

Abstract

The purpose of this article is to apply the wavelet transform algorithm to identify the magnetic damping and magnetic stiffness coefficients of the drive rod with which a set of 4-pole active magnetic bearing (AMB) is equipped. By taking advantage of time–frequency analysis feature, the ridge curve of rod free response after wavelet transformation can be extracted to find the natural frequency of the rod/AMB system. In other words, due to the influence of magnetized field by AMB, the stiffness of the rod dynamics is not linear any more and can be estimated from the curve of the amplitude versus frequency by wavelet transformation. On the other hand, the non-linear damping coefficients can be estimated from the derivative of amplitude versus amplitude by wavelet transformation of rod free vibration. It is found that the non-linear magnetic damping coefficients are up to second order in polynomial and the stiffness coefficient is mainly of third order, respectively. In addition, the identified second-order damping coefficient is negative and hence implies that under specific rod displacement and speed, the dynamic of rod/AMB system in axial direction is unstable.