Abstract
Turbo molecular pump, an accurate mechanism, is characterized by the small volume and high rotary speed (3,000~60,000rpm). To achieve contact-free rotor spinning in the confined space, passive magnetic bearing system inside the pump must be designed accurately to avoid the unstableness of the rotor, which requires the design of the bearing to attain the preciseness in the micrometer’s level. Thus, the study aims to analyze the dynamic stiffness of passive magnetic bearing and to design the stiffness of the bearing for the system. Two parts are covered in this paper. In the first part, we measured the magnetic flux of passive magnetic bearing and analyzed the magnetic field by the standpoint of magnetic circuits. Besides, we compared the results of multiplayer magnets with different materials. In the second part, I used computer program Ansoft, which is based on finite element method, to analyze magnetic field and force. Furthermore, we analyzed the effect of displacement to magnetic bearing stiffness. Implementing 3D simulation with different parameters, we then discussed what the best design is. Finally, the result of simulation and the experimental data were compared and suggestions were further provided.