Active vibration control of flexible rotors supported by magnetic bearings is discussed. Using a finite-element method for a mathematical model of the flexible rotor, the eigenvalue problem is formulated taking into account the interaction between a mechanical system of the flexible rotor and an electrical system of the magnetic bearings and the controller. However, for the sake of simplicity, gyroscopic effects are disregarded. It is possible to adapt this formulation to a general flexible rotor-magnetic bearing system. Controllability with and without collocation sensors and actuators located at the same distance along the rotor axis is discussed for the higher order flexible modes of the test rig. In conclusion, it is proposed that it is necessary to add new active control loops for the higher flexible modes even in the case of collocation. Then it is possible to stabilize for the case of uncollocation by means of this method. Nonami, Kenzou Glenn Research Center RTOP 505-63-1B...

The focus of this thesis is the development and demonstration of adaptive control algorithms for Active Magnetic Bearings AMBs) that account for uncertainties associated with structural vibration modes. A flexible rotor AMB test rig is designed and modeled using Finite Element Analysis (FEA). The flexible modes and equations of motion are obtained using modal analysis techniques. Typically, such analyses accurately predict the low frequency modes, but accuracy at higher frequencies is greatly reduced. Adaptive control algorithms that account for parametric uncertainties and unmodeled dynamics are developed to levitate and control the flexible rotor. Model parameters for the system are identified using recursive least squares, and used to update a self-tuning pole-placement controller. This self-tuning approach dramatically improves the performance and robustness of the magnetic levitation system, as demonstrated through simulations and experimental demonstrations. The flexible rotor AMB test rig is fabricated to experimentally validate the identification and control algorithms. Results clearly demonstrate the performance and limitations of the adaptive control design.

Compiling the expertise of nine pioneers of the field, Magnetic Bearings - Theory, Design, and Application to Rotating Machinery offers an encyclopedic study of this rapidly emerging field with a balanced blend of commercial and academic perspectives. Every element of the technology is examined in detail, beginning at the component level and proceeding through a thorough exposition of the design and performance of these systems. The book is organized in a logical fashion, starting with an overview of the technology and a survey of the range of applications. A background chapter then explains the central concepts of active magnetic bearings while avoiding a morass of technical details. From here, the reader continues to a meticulous, state-of-the-art exposition of the component technologies and the manner in which they are assembled to form the AMB/rotor system. These system models and performance objectives are then tied together through extensive discussions of control methods for both rigid and flexible rotors, including consideration of the problem of system dynamics identification. Supporting this, the issues of system reliability and fault management are discussed from several useful and complementary perspectives. At the end of the book, numerous special concepts and systems, including micro-scale bearings, self-bearing motors, and self-sensing bearings, are put forth as promising directions for new research and development. Newcomers to the field will find the material highly accessible while veteran practitioners will be impressed by the level of technical detail that emerges from a combination of sophisticated analysis and insights gleaned from many collective years of practical experience. An exhaustive, self-contained text on active magnetic bearing technology, this book should be a core reference for anyone seeking to understand or develop systems using magnetic bearings.

Magnetic Bearings are bearings where the suspension forces are generated magnetically without any contact. The advantages to modern machinery are obvious: no mechanical wear, no lubrication, potential for high rotor speed, accuracy, and high dynamic performance, new constructional solutions to a classical problem in machine dynamics. The realization of such bearings is in rapid progress. Examples for application areas are turbomachinery, centrifuges, vacuum techniques, machine tool spindles, chemical industry, medical devices, robotics, high speed drives, spacecraft equipment, con tactless actuators, vibration isolation. The Symposium is demonstrating the current state of the art in this developing field of mechatronics, showing actual research efforts, reporting on applications in the various areas, and discussing open questions. The main purpose of the Symposium has been to establish a common information basis for people working on magnetic bearings. It will point to promising areas, and it will help to facilitate decisions on research and development projects, and on investments for applications.

The effective use of active magnetic bearings for vibration control in turbomachinery depends on an understanding of the forces available from a magnetic bearing actuator. The purpose of this project was to characterize the forces as functions shaft position. Both numerical and experimental studies were done to determine the characteristics of the forces exerted on a stationary shaft by a magnetic bearing actuator. The numerical studies were based on finite element computations and included both linear and nonlinear magnetization functions. Measurements of the force versus position of a nonrotating shaft were made using two separate measurement rigs, one based on strain gage measurement of forces, the other based on deflections of a calibrated beam. The general trends of the measured principal forces agree with the predictions of the theory while the magnitudes of forces are somewhat smaller than those predicted. Other aspects of theory are not confirmed by the measurements. The measured forces in the normal direction are larger than those predicted by theory when the rotor has a normal eccentricity. Over the ranges of position examined, the data indicate an approximately linear relationship between the normal eccentricity of the shaft and the ratio of normal to principal force. The constant of proportionality seems to be larger at lower currents, but for all cases examined its value is between 0.14 and 0.17. The nonlinear theory predicts the existence of normal forces, but has not predicted such a large constant of proportionality for the ratio. The type of coupling illustrated by these measurements would not tend to cause whirl, because the coupling coefficients have the same sign, unlike the case of a fluid film bearing, where the normal stiffness coefficients often have opposite signs. They might, however, tend to cause other self-excited behavior. This possibility must be considered when designing magnetic bearings for flexible rotor applications, such as gas t...