TRANSIENT-RESPONSE TECHNIQUE APPLIED TO ACTIVE MAGNETIC BEARING MACHINERY DURING ROTOR DROP

The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system, the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and starer, and other stationary se als along the rotor shaft. In this paper a theoretical formulation is proposed and solved numerically to examine the transient response of t he flexible rotor, from the time just previous to when the AMB shuts d own and including the rotor drop onto the back-up bearing. The backwar d whirl of the rotor, which may lead to the destructive damage of the machinery, has been analytically predicted at very light support dampi ng and very high support damping. Also, the vibration due to the nonli nearity of the contact point geometry has been included in the analysi s. The influence of the support damping on the displacement of the dis k and also the contact force between the journal and the inner-race of the back-up bearing have been compared for various rotor system param eters. By comparing these results with the optimum support damping for the simple flexible rotor model, it is shown that this support dampin g optimization can be applicable for specifying the required optimum r ange of support damping for the back-up bearings of AMB systems.