Rotor/Auxiliary Bearing Contact Issues In Magnetic Bearing Systems

This paper assesses the characteristics of displacements in a rotor/magnetic bearing system when contact with an auxiliary bearing occurs. The dynamic rotor response is examined in fixed and rotating frames of reference with initial conditions to induce contact. In the rotating frame, it is demonstrated that the phase lag in the synchronous response vector relative to the unbalance vector may change by more than 90 deg due to contact. This is of particular relevance to controllers that utilise the synchronous harmonic components of measured signals. The analytical study in the paper considers contact forces derived from Hertzian theory. This allows the frictional heat source to be specified over the contact zone. A simple method of estimating surface temperature around the contact zone is also presented.