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  • 1
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    Modeling and Identification of a Large Gap Magnetic Suspension System (1996)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This paper presents the results of modeling and system identification efforts on the NASA Large-Angle Magnetic Suspension Test Fixture (LAMSTF). The LAMSTF consists of a cylindrical permanent magnet which is levitated above a planar array of five electromagnets mounted in a circular configuration. The analytical model is first developed and open-loop characteristics are described. The system is shown to be highly unstable and requires feedback control in order to apply system identification. Limitations on modeling accuracy due to the effect of eddy-currents on the system are discussed. An algorithm is derived to identify a state-space model for the system from input/output data acquired during closed-loop operation. The algorithm is tested on both the baseline system and a perturbed system which has an increased presence of eddy currents. It is found that for the baseline system the analytic model adequately captures the dynamics, although the identified model improves the simulation accuracy. For the system perturbed by additional unmodeled eddy-currents the analytic model is no longer adequate and a higher-order model, determined through system identification, is required to accurately predict the system's time response.
    Keywords: Mechanical Engineering
    Type: Third International Symposium on Magnetic Suspension Technology; Part 2; 403-419; NASA-CP-3336-Pt-2
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Experimental Robust Control Studies on an Unstable Magnetic Suspension System (1993)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: This study is an experimental investigation of the robustness of various controllers designed for the Large Angle Magnetic Suspension Test Fixture (LAMSTF). Both analytical and identified nominal models are used for designing controllers along with two different types of uncertainty models. Robustness refers to maintain- ing tracking performance under analytical model errors and dynamically induced eddy currents, while external disturbances are not considered. Results show that incorporating robustness into analytical models gives significantly better results. However, incorporating incorrect uncertainty models may lead to poorer performance than not designing for robustness at all. Designing controllers based on accurate identified models gave the best performance. In fact, incorporating a significant level of robustness into an accurate nominal model resulted in reduced performance. This paper discusses an assortment of experimental results in a consistent manner using robust control theory.
    Keywords: Mechanical Engineering
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Identification and control of a flexible beam using modal domain sensor (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The use of a distributed-effect, modal domain optical fiber sensor (MD sensor) as a component in an active control system to suppress vibrations in a flexible beam is discussed. The sensor model is integrated into the model for a flexible structure. Based on this system model, a control system with a dynamic compensator is designed to add damping to the low order modes of the flexible structure. To verify the modeling procedure, a cantilevered beam was instrumental with a piezoelectric actuator and an MD sensor. It is shown that experimental responses closely match simulated responses for both open loop and closed loop tests.
    Keywords: CYBERNETICS
    Type: Fiber Optic Smart Structures and Skins III; Sept. 19-21, 1990; San Jose, CA; United States
    Format: text
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  • 4
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    Robust tracking control of a magnetically suspended rigid body (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This study is an application of H-infinity and microsynthesis for designing robust tracking controllers for the Large Angle Magnetic Suspension Test Facility. The modeling, design, analysis, simulation, and testing of a control law that guarantees tracking performance under external disturbances and model uncertainties is investigated. The type of uncertainties considered and the tracking performance metric used is discussed. This study demonstrates the tradeoff between tracking performance at low frequencies and robustness at high frequencies. Two sets of controllers were designed and tested. The first set emphasized performance over robustness, while the second set traded off performance for robustness. Comparisons of simulation and test results are also included. Current simulation and experimental results indicate that reasonably good robust tracking performance can be attained for this system, using multivariable robust control approach.
    Keywords: CYBERNETICS
    Type: International Symposium on Magnetic Suspension Technology; Aug 11, 1993 - Aug 13, 1993; Seattle, WA; United States|; 22 p.
    Format: text
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  • 5
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    State-Dependent Riccati Equation Regulation of Systems with State and Control Nonlinearities (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The state-dependent Riccati equations (SDRE) is the basis of a technique for suboptimal feedback control of a nonlinear quadratic regulator (NQR) problem. It is an extension of the Riccati equation used for feedback control of linear problems, with the addition of nonlinearities in the state dynamics of the system resulting in a state-dependent gain matrix as the solution of the equation. In this paper several variations on the SDRE-based method will be considered for the feedback control problem with control nonlinearities. The control nonlinearities may result in complications in the numerical implementation of the control, which the different versions of the SDRE method must try to overcome. The control methods will be applied to three test problems and their resulting performance analyzed.
    Keywords: Numerical Analysis
    Type: NASA/CR-2004-213245 , NIA-2004-08
    Format: application/pdf
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