Data processing: generic control systems or specific application – Specific application – apparatus or process – Mechanical control system
Reexamination Certificate
2001-08-21
2004-07-13
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Mechanical control system
C310S090500, C310S095000, C310S323020, C310S323210, C073S001140, C073S066000
Reexamination Certificate
active
06763285
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
Reference to a “Computer Listing Appendix Submitted on a Compact Disc”
A Computer Program Listing Appendix of the programming language, which can be used to practice the method of the present invention, is submitted with this application on two identical compact discs (CD). The compact discs are labeled Copy 1 and Copy 2. Copy 1 is entitled “010811
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1041” and copy 2 is entitled “010811
—
1038.” Each CD is hereby incorporated herein by reference.
The CDs are write-only and are IBM-PC compatible. Each compact disc contains ASCII text files “data_feb25.m” and “adapt.m” disclosing a computer program and parameter values, respectively, which can be used to demonstrate the method and system of the present invention. The file “data_feb25.m” was created Jul. 17, 2000, and the file contains 2,202 bytes. The file “adpat.m” was created Feb. 27, 2000, and the file contains 137 bytes.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and system for stabilizing a rotor about its geometric center in a magnetic bearing system at a constant rotor speed. In the method, the controller for controlling the magnetic bearing uses an adaptive control algorithm which simultaneously identifies and compensates for synchronous sensor runout and rotor mass unbalance while determining a control action that drives the rotor rotating at a constant speed to its geometric center. Sensor runout and mass unbalance is determined by varying the magnetic stiffness of the magnetic bearing which is achieved by perturbation of the bias currents in opposing electromagnet coils using an algorithm that does not alter the equilibrium of the rotor while the rotor is rotating at a constant speed.
2. Description of Related Art
Periodic disturbances are common in rotating machinery. Compensating for such disturbances is critical to the performance of systems using active magnetic bearings. The two dominant sources of periodic disturbances in magnetic bearings are synchronous sensor runout and mass unbalance. Mass unbalance, which results from a lack of alignment between the principal axis of inertia and the geometric axis of the rotor, generates a force disturbance synchronous with rotor angular speed. Runout originates from non-uniform electrical and magnetic properties around the sensing surface and lack of concentricity of the sensing surface. It generates a disturbance in rotor position at multiple harmonics of the frequency of rotation. Both synchronous sensor runout and mass unbalance are unavoidable since they result from manufacturing imperfections and cause rotor vibration, degrade performance, and can lead to instability if they are not adequately compensated.
Although the problem of simultaneous compensation of mass unbalance and synchronous sensor runout has appeared in the literature only recently (Kanemitsu, et al., Identification and Control of Unbalance and Sensor Runout on Rigid Active Magnetic Bearing Systems, 5
th
Int. Symp. on Magnetic Suspension Technol., Santa Barbara, Calif. (1999); Setiawan, et al., Adaptive Compensation of Sensor Runout and Mass Unbalance in Magnetic bearing Systems, IEEE/ASME Int. Conf. on Advanced Intelligent Mechatronics, Atlanta, Ga. (1999); Setiawan, et al., ASME J. Dyn. Sys. Meas. and Cont. 123: 211 (2001); Sortore, Observer Based Critical Response in Rotating Machinery, PhD Dissertation, University of Virginia, Charlottesville, Va. (1999)), a large volume of research exists on compensation of the individual disturbances. Some of the early work on mass unbalance compensation is based on insertion of a notch filter in the control loop (Beatty, Notch Filter Control of Magnetic Bearings, MS Thesis, Mass. Institute of Technology, Cambridge, Mass. (1988)). The drawback of this approach stems from negative phase of the notch transfer function which can reduce the stability margin of the closed-loop system and lead to instability (Bleuler, et al., IEEE Trans. on Control Sys. Tech. 2: 280-289 (1994); Na and Park, J. Sound Vibration 201: 427-435 (1997)). Another popular approach is adaptive feedforward control (Hu and Tomizuka, ASME J. Dyn. Sys. Meas., and Cont. 115: 543-546 (1993); Shafai, et al., IEEE Control Sys. 14: 4-13 (1994)), where Fourier coefficients of the disturbance are estimated and cancelled on-line. Operationally, these controllers resemble notch filters (Na and Park, ibid.) and can result in instability if designed without considering the underlying structure of the closed-loop system. To preserve stability, Herzog, et al. (IEEE Trans. on Control Sys. Technol. 4: 580-586 (1996)) developed the generalized notch filter and Na and Park (ibid.) proposed variation of the least mean square algorithm. Other approaches that compensate for mass unbalance while ensuring stability include adaptive auto-centering (Lum, et al., IEEE Trans. on Control Sys. Technol. 4: 587-597 (1996)) and output regulation with internal stability (Matsumura, et al., Modeling and Control of Magnetic Bearing Systems Achieving a Rotation Around the Axis of Inertia, 2
nd
Int. Symp. on Magnetic Bearings, Tokyo, Japan. pp 273-280 (1990)). Both of these approaches stabilize the rotor about its mass center.
Though mass unbalance compensation has been widely studied with the objective of stabilization about the mass center, most commercial applications require geometric centering to avoid seal wear. The problem of geometric center stabilization has been addressed by a few researchers (Hisatani and Koizumi, Adaptive Filtering for Unbalance Vibration Suppression, 4
th
Int. Symp. on Magnetic Bearings, ETH Zurich, Switzerland (1994); Song and Mukherjee, Integrated Adaptive Robust Control of Magnetic bearings, IEEE Int. Conf. on System, Man, and Cybernetics, Beijing, China (1996)), but more general results (Reinig and Desrochers, ASME J. Dyn. Sys. Meas. Cont. 108: 24-31 (1986); Mizuno, An Unified Approach to Controls for Unbalance Compensation in Active Magnetic Bearings, IEEE Int. Conf. on Control Applications, Italy (1998)) establish that mass or geometric center stabilization can be achieved through cancellation of the disturbance in current or displacement signal, respectively. In a general approach for disturbance attenuation, Knospe, et al., J. Vibration and Control 2: 33-52 (1996); Knospe, et al., ASME J. Dyn. Sys. Meas. Cont. 119: 243-250 (1997)) claimed that any form of vibration, which can be measured, can be attenuated using a pseudo-inverse of the pre-computed influence coefficient matrix. The performance of the algorithm amidst uncertainties was investigated and experiments used to demonstrate effectiveness. The method decouples the problem into two independent tasks, and while it has been demonstrated to work successfully, there is no theoretical basis for stability of the two interacting processes. Other approaches employed for disturbance compensation include robust control designs (Fujita, et al., Experiment on the Loop Shaping Based H-Infinity Control of Magnetic Bearing, Proc. Am. Control Conf. (1993); Rutland, et al., Comparison of Controller Designs for attenuation of Vibration in a Rotor Bearing System under Synchronous and Transient Conditions, 4
th
Int. Symp. on Magnetic Bearings, ETH Zurich, Switzerland, pp 107-112 (1994); Setiawan, et al., ibid. (1999)), Q-parameterization control (Mohamed et al., Q-parameterization Control of Vibrations in a Variable Speed Magnetic Bearing, IEEE Int. Conf. on Control Applications, Hartford, Conn. (1997)), and off-line adaptation (Kim and Lee, IEEE/ASME Trans. on Mechatronics 2:51-57 (1997)). Among them, the work by Kim and Lee (ibid.) and Setiawan et al., ibid. (2001) address the problem of sensor runout compensation.
Unfortunately, none of the above approaches lend themselves to mass unbalance compensation in the presence of significant synchronous sensor runout. This problem, widely acknowledged in the literature but essentially unsolved, stems from lack of observability of disturbances with the same frequency content. A cre
Mukherjee Ranjan
Setiawan Joga Dharma
Board of Trustees of Michigan State University
Kasenge Charles
McLeod Ian C.
Picard Leo
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