Magnetic Bearing Literature Review. Team 2: The Floaters. Ivett Ortega, Wole Oyelola, Claudia Vargas

Transcription

1 Magnetic Bearing Literature Review Team 2: The Floaters Ivett Ortega, Wole Oyelola, Claudia Vargas Our project is to create a semi-frictionless bearing that is controlled by a feedback control system. Based on our literature search there are many methods of implementing a control system, as well as many ways to arrange the internal magnets. Because this project has been extensively researched over the years, we were able to find many sources with details specific to our intended setup. Internet Keyword Search A basic Internet keyword search of magnetic bearing on Google helped us understand the basic principles of magnetic bearings as well as define the differences between passive and active magnetic bearings. Based on the results, passive magnetic bearings are much more costeffective but are required to be used in conjunction with ball and/or air bearings, and also require the use of a permanent magnets. An active magnetic bearing uses a control system to continually levitate an object through the use of power amplifiers and gap sensors as well as a feedback controller to control the desired levitation height, and has the benefits of being a much more stable system. A simple design overview can be Figure 1: Control System Diagram

2 seen in Figure 1. The gap sensors measure the displacement of the rotor from the reference position, a microprocessor derives a control signal for the measurement, a power amplifier transforms this signal into a control current, and the control current generates the magnetic forces within the actuating magnet in order to maintain the rotor in a hovering position. Based on this basic search we chose to continue research on an active magnetic bearing. In addition, our basic keyword search yielded references from a paper printed by the International Centre for Magnetic Bearings. This paper depicts calculations for some of the basic physical characteristics of magnetic bearing systems, including: load, force, and angular velocity. The most important item our basic keyword search yielded was several references to a doctoral thesis by Dr. Torjbjorn A. Lambke titled Design and Analysis of a Novel Low Loss Homopolar Electrodynamic Bearing. This 200 page paper goes into detail about types of bearings, and more importantly has a chapter dedicated entirely to bearing analysis which covers the effects of eddy currents, damping, stability and losses. Technical Journal Review The technical journal review began with a basic search of magnetic bearings. An article by Samanta et al. explains the basics behind magnetic bearings. It describes an experimental setup to investigate the performance of bearing configurations under different operating conditions. From On the Theory and Application of Magnetic Bearings (Budig), we learn the principles and theories behind magnetic bearings and look at a flywheel-vacuum set-up as a case study. It explains how to achieve stability in a magnetic bearing by controlling the height of the gap between the shaft and the bearing. Equations are given for the attractive forces and the

3 amount of current needed to maintain the gap at an optimal height. The journal article also goes into different designs for radial magnetic bearings and the advantages of each. The paper Nonlinear Control of Active Bearings: A Backstepping approach (Queiroz), gave us insight on the inherent nonlinearities involved with electromechanical dynamics. This paper also mentions the integrator backstepping (IB) control technique as a possible method to solve active magnetic bearing problems. Quieroz also goes into detail on the mathematics behind the electromechanical system. This paper raises the question on how the differential equations for magnetic levitation and stability are derived and references some sources that discuss this topic. Magnetic Bearing Control Systems and Adaptive Forced Balancing, (B. Shafai), discusses the idea of adaptive force balancing as a type of control system used in solving active magnetic bearing problems. This paper lays out an in depth control system block diagram, in addition to control circuitry that would be needed to implement the adaptive force balancing techniques. In order to further refine the search, we modified our search to include the keywords magnetic bearing and theory. From this refined search we were able to find an article addressing the problem of compensation of combined unbalance and sensor runout disturbances. The journal article, by Setiawan et al., discusses how to fix the sensor runout problem on magnetic bearings. This will help us with the design of a more stable system. Patent Category Search Using the patent search engine available to the United States Patent and Trademark Office website, we were able to find the patent US , by searching the

4 keywords, Active Magnetic Bearing Flywheel. This patent is entitled Flywheel Device with Active Magnetic Bearings. Upon reviewing the patent, we learned more about using flywheels as a practical application of magnetic bearings. This patent argues the use of permanent magnets rather than electromagnets to decrease power consumption, reduce cost, and increase reliability. This patent also provides an inclusive control system block diagram. From this patent we were able to obtain the following parameter to be used for a category search in the USPTO databases. 310/90.5 o This subclass is indented under subclass 90. Subject matter wherein the bearing has an induction field. Because this category is so specific, we were able to find several patents that addressed our exact project. The first most relevant patent is titled Magnetic bearing control device having a threephase converter, and use of a three-phase converter for controlling a magnetic bearing (US ) and provides an in-depth discussion on the control system used for the magnetic bearings. More specifically, it addresses the hardware components needed to complete the task. Magnetic axial bearing and a spindle motor having this kind of magnetic axial bearing (US ) also provides a substantial amount of information related to our project. Although it is important to note that this patent focuses on a rotating axial bearing, the methods of employing permanent magnets and flux guide elements are still applicable to our project. Method and systems for operating magnetic bearings and bearingless drives (US ) focuses on the circuitry used to generate a signal for energizing the windings of the magnetic bearing element. This addresses the issues of detecting the radial position of the

5 element within the bearing. According to this patent, this is a low-cost and efficient means for dynamically suspending the rotor of the rotary device. Large gap horizontal field magnetic levitator (US ) this last patent addresses magnetic levitation conducted over large gaps. It is important to note that this patent discusses cases with two types of magnets, permanent magnets and electromagnets. In order to control the levitating object the employment of a servomechanism is discussed. All the patent searches provided very in-depth information on the details of magnetic bearings, such as part arrangements, control system options, and control system components.

6 Bibliography: B. Shafai, S. Beale, P. LaRocca, and E Cusson, "Magnetic bearing control systems and adaptive forced balancing," IEEE Contr. Syst. Mug., vol. 14, no. 2, pp. 4-13, Apr B. V. Jayawant, Electromagnetic Levitation and Suspension Techniques. UK: Edward Arnold, Budig, P.-K.;, "On the theory and application of magnetic bearings," Systems, Signals and Devices (SSD), th International Multi-Conference on, vol., no., pp.1-9, March 2012 doi: /SSD < Denk, Kopken, Stoiber, Wedel (2007) US Magnetic bearing control device having a three-phase converter, and use of a three-phase converter for controlling a magnetic bearing F. Matsumura et al., Fundamental equation of horizontal shaft magnetic bearing and its control system, Trans. JIEE, vol. 101-C, pp. Gabrys (2001) US Flywheel Device with Active Magnetic Bearings M. S. de Queiroz and D. M. Dawson. Nonlinear control of active magnetic bearings: A backstepping approach. IEEE Transactions on Control System Technology, 4(5): , 1996.

7 Popov, Bauer, Schmid, Schwamberger (2008) US Magnetic axial bearing and a spindle motor having this kind of magnetic axial bearing Rakov (2009) US Method and systems for operating magnetic bearings and bearingless drives Samanta, P.; Hirani, H.;, "Magnetic Bearing Configurations: Theoretical and Experimental Studies," Magnetics, IEEE Transactions on, vol.44, no.2, pp , Feb doi: /TMAG URL: Schweitzer, G. "Active Magnetic Bearings - Chances and Limitations." International Centre for Magnetic Bearings, n.d. Web. 11 Nov < Setiawan, Joga D., Ranjan Mukherjee, and Eric H. Maslen. "Adaptive Compensation of Sensor Runout for Magnetic Bearings With Uncertain Parameters: Theory and Experiments." Journal of Dynamic Systems, Measurement, and Control (2001): 211. Print. Simon (2010) US Large gap horizontal field magnetic levitator

8 T. Lembke (2005). PhD Thesis "Design and Analysis of a Novel Low Loss Homopolar Electrodynamic Bearing". Stockholm: Universitetsservice US AB. ISBN