**1. Introduction**

192 Performance Evaluation of Bearings

966-7, (*in Polish*).

[14] Kozanecka D., (2010), *Diagnostics of Rotating Machinery Mechatronic System,*  Monographic Series of Publications: Maintenance Problems Library, Scientific Publishing House of Institute for Sustainable Technologies in Radom, ISBN 978-83-7204

> A bearing fixes a rotating spindle to a specific location and is a mechanical component that supports the load applied to the axis and its dead load. Therefore, it is inevitable for mechanical contact between the axis and the bearing to occur, causing friction, abrasion, heat, noise, and user environment contamination from lubrication. Magnetic bearings are mechanical components that use the attractive or repulsive force of electromagnets to support the mechanical axis is a non-contact state. The use of such components significantly reduced the disadvantages that accompany the use of general mechanical bearings such as friction, abrasion, heat, noise, and user environment contamination from lubrication. Moreover, magnetic bearings can support the mechanical axis in special environments(vacuum, high temperature, low temperature, zero gravity) and have the advantage of being able to adjust the damping coefficient and spring constant of the system that supports the axis according to the control objective.

> Magnetic levitation can be categorized into the following systems depending on the form of force that supports the levitated object: the system that uses magnetic attraction, magnetic repulsion, induction levitation, and superconducting Meissner Effect. Magnetic levitation that utilizes attractive force has a closed magnetic circuit so efficiency is high and 1-axis control is possible due to the stability in the attraction and perpendicular directions. However, it has been reported that the uncontrolled directions have poor stability due to the nonlinearity of the attraction. Magnetic levitation that uses the repulsive power has stable characteristics with respect to the longitudinal direction that the repulsive force is applied to, but the transverse direction has unstable characteristics. However the electromagnet is arranged, all the axes cannot be stabilized. Magnetic levitation that uses induction levitation is able to perform stable levitation without special control as Fleming force caused by the relative velocities between the electromagnet and the conductor supports the levitation. However, without a velocity over a certain level, levitation cannot be supported where overall efficiency is low due to Eddy current loss

© 2012 Jeong, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Jeong, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and brake loss. Magnetic levitation that uses superconducting Meissner Effect takes advantage of the repulsion with permanent magnets caused by the strong diamagnetism from the superconductor. Like that of the induction levitation, stable levitation is possible without any control. However, the operational temperature of the levitation system using superconductor is very low: 4.2K(liquid Helium), 77K(liquid Nitrogen). Generally, the magnetic levitation applied to the magnetic bearing is the method using attraction and repulsion. Magnetic bearing systems discussed here refers to a system that utilizes the attraction.

Control of Magnetic Bearing System 195

Fig. 3 is the assembly of the magnetic bearing system to make. In the assembly, the levitated object will be supported by magnetic bearing at X and Y axis direction. But thrust direction has only the mechanical backup bearing. And Fig. 4 is the levitated object that is 1.4kg.

**Figure 2.** Schematic of the magnetic bearing system

**Figure 3.** Assembly of the magnetic bearing system

**Figure 4.** Levitated object

**Figure 1.** Levitation system according to the magnetic levitation method

In this chapter, the method to designing a magnetic bearing system, to obtaining a mathematical model, and understanding the preparations necessary for control will be discussed. For this, the calculation of attraction using the Probable Flux Paths Method, selection of circuitry about the amplifier to operate the electromagnet, and method to identify the magnetic bearing system that includes a PID controller are discussed.
