503 Vibration Characteristics of a Rotor System Supported by a Magnetic Bearing : Influence of Rotational Speed on Major Critical Speed

Abstract

Vibration characteristic of a rotor supported by a PID controlled magnetic bearing is investigated. The differential equation of motion is derived with nonlinearities of the magnetic force for the gap, the current, the characteristics of a current amplifier and also the weakening of force due to surface eddy current caused rotation of the rotor. The influence of the rotational speed on the magnetic force is approximated by a fractional function and the coeffcients are determined by experimental results. By this approximation, the resonance curves for a major critical speed by the shooting method have good agreements with the experimental results.