Magnetic Bearings Technische Universit228;t （科技大学228;磁轴承 t）.pdf

Magnetic Bearings Joint Advanced Student School April 2006 – St. Petersburg, Russia Jeffrey Hillyard Department of Mechanical Engineering Technical University of Munich Introduction The use of bearings is essential to all types of machines, in that they provide the function of supporting another piece or component in a desired position. Two major types include radial and axial bearings. Furthermore, bearings are usually implied to be supporting a rotating object or shaft, which is addressed in this paper, but that is not always the case. The other situation would be one of translational sliding, which is merely a linear case of supporting a rotating object. A further classification can be made into active and passive bearings. Active bearings are electrically controlled with some type of controller, whereas passive bearings are not electrically powered and thus have no control mechanism. There are numerous advantages to using magnetic bearings, the most notable being contact-free, in that the magnetic force is used to support the object as opposed to contact between two surfaces. This enables very high rotational speeds to be realized. A magnetic bearing is free of lubricant, which avoids servicing and also enables use in clean room environments. Maintenance is also decreased due to the absence of surface wear, so that as long as the control system functions as intended, there could even be no maintenance. Lastly, the magnetic properties of the materials used are highly resistive or immune to changes in temperature, pressure, and the presence of chemicals, further reasons for use in extreme conditions and highly sensitive applications. One major disadvantage to using magnetic bearings is their complexity. A very knowledgeable person in t