Magnetic bearings are relatively new machine elements that present same functionality of traditional bearings such as sliding and rolling bearings, enabling only the rotation of a rotor and retaining other motions. In magnetic bearings, this retention is made by magnetic forces. Although magnetic bearings do not present load capacity comparable to mentioned traditional bearings, present the unique advantages such as the absence of solid contact between moving and stationary parts, that is, the absence of friction forces. Besides, they can operate even in vacuum ambient.
Such characteristics, makes de magnetic bearing suitable for special applications such as energy storing flywheel, ultra-centrifuges, gyroscopes, MagLev high speed trains, artificial hearts and others.
Each year, new applications for magnetic bearings are presented. There are many possible ways for achieving a magnetic bearing, through the use of various physical effects such as the superconductivity, the use of magnetic fields of permanent magnets or electromagnets or the electrodynamic induction. This work describes efforts in the development of hybrid magnetic bearings that combine permanent magnets and electromagnets. Using these elements, a rotor is levitated in the radial directions by a pair of magnets in attraction mode and, only in the axial direction, the active control is executed. These are bearings known as single axis controlled bearing which have the advantage of constructive simplicity, especially concerning the control system.
Starting with the first version presented in year of 2000, this work shows the evolution in the topology of such bearing, showing at the same time, a practical application of the bearing on sustaining the rotor of a blood pump, that is, an artificial heart. This application showed to be particularly interesting since the immersion of the levitated rotor in a liquid, minimized the major limitation of this type of magnetic bearing: the absence of vibration damping capability in the radial direction. Next, this work presents a single axis controlled bearing in which the damping in the radial direction is achieved by using an electrodynamic bearing. The electrodynamic effect attenuates vibration when rotor is at relatively high speeds, enabling the rotor to overcome critical speeds. Finally, aiming still simple magnetic bearings, this work presents possibilities of achieving rotor retention in the radial directions through permanent magnets and, replacing active control in the axial direction by sliding type thrust bearings.
Oswaldo Horikawa was born in São Paulo, Brazil, on October 22, 1960. He received the B.S. in Mechanical Engineering from Escola Politécnica of the São Paulo University (EPUSP, Brazil) in 1984 and received the PhD degree in Precision Machinery Systems from Tokyo Institute of Technology (TITech), Japan, in 1991. From 1991 to 1992, he was Assistant Professor at TITech.
Since 1992, he has been Professor at the Department of Mechatronics Engineering at EPUSP. His research interests include motion control, mechatronic systems and metrology.