Seismic Test on Turbo-Molecular Pumps Levitated by Active Magnetic Bearing

To evaluate the behavior of a rotating shaft undergoing seismic vibration, two types of turbo-molecular pumps were installed on a vibration table. One of the tested pumps has unique 4-axis control magnetic bearings that utilize both electromagnets and permanent magnets and features excellent zero power control, while the order has 5-axis control magnetic bearings that control all five degrees of freedom except for the rotating component around the shaft. Three types of seismic waves, El-centro, Taft, and Hachinohe and their time responses on a building floor were produced on the vibration table. The displacement of the shaft under vibrating conditions was less than 60 ~mp-p in each test, thus it was confirmed that active magnetic bearings do actually possess sufficient bearing stiffness.