Control of resonance for a rotating shaft levitated by the high temperature super conductor by using a rotating magnetic damper

The levitation system which has a combination of a small superconductor and a set of permanent magnets was used in our previous report. In this system , a small superconductor is connected to the bottom of the vertical shaft. The superconductor supports the gravity force and axial vibration force. A circular permanent magnet is attached to the top of the shaft, and the othe r circular permanent magnet lies at the frame. The N-pole of one of the mag nets faces the S-pole of the other magnet, so a drag force acts between the magnets. The drag force is unstable in the axial direction, but the pinnin g force in the axial direction of the superconductor makes it stable. This implies that the levitated shaft is stable without control. Although the sy stem is stable in both directions in our system, the restoring force in the horizontal direction is small when the conductor is small. Hence it is dif ficult to pass through the critical speeds. In order to pass through the cr itical speed, this article presents a method of resonance control by using a magnetic damper. In the system, a conductor plate is inserted between two permanent magnets, which lie at the top of the levitation shaft. Theoretic al analyses have been developed for the electromagnetic force and the respo nse of the shaft during rotation. In order to validate the system, experime ntal tests have also been performed. (C) 2001 Elsevier Science B.V. All rig hts reserved.