Development of magnetic bearing device for analysing external forces in arbitrary trajectory to rotor system

Abstract

In design of rotating machines, analysis of external force is important for stable rotating operation. The various external forces such as unbalance force, seal contact force and rotor dynamic fluid force effect on the rotor system, dynamic characteristics of rotating system is changed by the external forces. The external force can vary depending on a rotor trajectory. In previous studies, a mathematical model of the dynamic characteristics had been formulated for small amplitude orbit around the equilibrium point for the rotor trajectory. However, the formulation hasn't been yet established in the rotor trajectory with large amplitude or eccentricity caused by the external forces. In this study, an experimental system using active magnetic bearing (AMB) is developed to achieve the formulation. The system can generate any arbitrary trajectory assuming various external forces and the rotor system follow the generated trajectory. The system can estimate the external force at the same time. Current flowing through coil of the AMB is controlled by a controller designed based on the frequency response to follow the arbitrary orbit. Then, the external forces are estimated from the control signal by the disturbance observer. Experiments were performed by assuming unbalance forces generated in the elastic rotor. From the results it was confirmed experimentally that high precision tracking control and estimation of external force are possible. The various rotor trajectory under the action of the external forces can be repeated by using the system, and the external force can be analyzed by the experimental data.