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Identification and Cancellation of Harmonic Disturbances in Radio Telescopes

Franke, Timothy Joseph
http://rave.ohiolink.edu/etdc/view?acc_num=case1427897871

Abstract Details

2015, Doctor of Philosophy, Case Western Reserve University, EECS - System and Control Engineering.
A new class of algorithms for the identification and cancellation of harmonic disturbances on rotary dynamic systems is proposed and demonstrated with applications on the Green Bank Telescope (GBT). The approach is a model-based iterative algorithm that exploits the structure of the problem to significantly reduce the number of tests needed to perform identification. During each such test, the system is in steady-state periodic operation. The crucial trick involves constructing a correspondence between the coefficients of disturbance terms and their time-periodic harmonics. This transformation enables the modeling and calibration of the system in a compact, harmonic representation. This approach has numerous advantages. The harmonic model fully captures the behavior of arbitrarily complex linear systems. It is not a feedback approach and therefore will not destabilize existing controllers. The algorithm displays rapid convergence and requires a minimal number of tests to construct a model. Finally, a previously identified model may be reused to quickly update a calibration. All of these properties make it ideal for the calibration of feedforward compensators on a wide range of systems. The nature of cogging on the GBT motors is rigorously studied. Various system identification tests are performed to characterize the behavior of the cogging with respect to operating conditions. A single motor calibration routine is developed and deployed on telescope hardware. The performance of the GBT with individually calibrated motors is tested. Additionally, the algorithm is extended to handle multiple interacting motors. A solution method is presented that yields reliable, physically reasonable solutions to the multiple motor problem. The calibration method is updated to compensate for the GBT encoder measurement error. The behavior of interpolation error was studied on two different encoders. Global variation of encoder calibrations is studied over the range of the telescope's elevation axis. Finally, generalization of the algorithm to non-constant rate, but still periodic trajectories, is explored. These tests probe the limits of the algorithm's underlying ideas.
Mario Garcia-Sanz, Dr. (Advisor)
M. Cenk Cavusoglu, Dr. (Committee Member)
Vira Chankong, Dr. (Committee Member)
Roger Quinn, Dr. (Committee Member)
112 p.
Engineering
control theory; feedforward compensation; parameter identification; motor cogging; encoder interpolation; telescope control

Recommended Citations

Citations

  • Franke, T. J. (2015). Identification and Cancellation of Harmonic Disturbances in Radio Telescopes [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1427897871

    APA Style (7th edition)

  • Franke, Timothy. Identification and Cancellation of Harmonic Disturbances in Radio Telescopes . 2015. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1427897871.

    MLA Style (8th edition)

  • Franke, Timothy. "Identification and Cancellation of Harmonic Disturbances in Radio Telescopes ." Doctoral dissertation, Case Western Reserve University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1427897871

    Chicago Manual of Style (17th edition)

case1427897871
457
© 2015, some rights reserved.Creative Commons License Identification and Cancellation of Harmonic Disturbances in Radio Telescopes by Timothy Joseph Franke is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.