On the Design of an Active Auxiliary Bearing for Rotor/Magnetic Bearing Systems

This paper considers the design of an actively controlled auxiliary bearing system for use with magnetic bearings. During rotor/auxiliary bearing contact large frictional contact forces can lead to significant thermal stresses. Furthermore, the nonlinear nature of the contact can induce unfavourable rotor dynamic behaviour. An active auxiliary bearing capable of reducing the contact forces and influencing the rotor dynamics during contact is proposed. Active auxiliary bearing design objectives include reducing the rotor / bearing contact forces during impact and influencing the rotor dynamics to prevent a trapped contact mode from becoming established. A piezo actuated system, using a closed hydraulic coupling, is presented. The dynamic performance of the actuators and hydraulic line are identified. In particular, the transfer function from actuator control signal to auxiliary bearing displacement is identified. Closed loop control of the active auxiliary bearing using local proportional integral differential control is also considered.