Dynamic Characteristics of a Millimeter-Sized Magnetic Bearing with a Cylindrical Rotor

In order to study contact-free levitation systems for micromachines, our group has developed a bearing system with a millimeter-sized cylindrical rotor. The system consists of a rotor (2.0mm Ø X 8mm, 95mg), a pair of electromagnets for levitation, two pairs of photo diodes for sensing, and an analog PD controller. The photo diodes detect axial displacements and rotation speeds of the rotor. This paper describes the dynamic characteristics of the millimeter-sized rotor. From the results, it is found that the levitating rotor makes a very quick response and the magnetic friction is dominant for the rotation decays. Furthermore, our group has succeeded in applying the small cylindrical rotor to the PM type motor.