Design and Application of a Magnetic Bearing for Vibration Control and Stabilization of a Flexible Rotor

This paper describes the design of a magnetic actuator designed to control the synchronous vibration of a 2.3m long 100mm diameter rotor supported on oil-film bearings. An algorithm is described which allows the control force to be computed to minimise the synchronous rotor vibration without prior knowledge of oil-film or rotor characteristics nor of the inherent out-of-balance distribution along the rotor. In this approach the magnetic actuator is first used to apply sequential test signals along two orthogonal axes whilst the shaft is rotating. The corresponding displacements are measured and the algorithm used to determine the control forces to be applied by the actuator. The process is applied sequentially as the rotor is run-up from rest to the required operating speed. Some experimental results are presented to demonstrate the ability of this technique to significantly reduce the synchronous vibration. It is also discussed how the electromagnetic actuator can be used to avoid the instability associated with oil-whirl.