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Thesis Title: Magnetic Coupling in DC Motor and Tachometer assembly and its Effect on Motion Control Advisor: Prof. Kevin C. Craig Submitted: May 2000
Abstract Tachometer feedback is commonly used in DC motor servo system design. This servo system may suffer from performance degradation and closed-loop instability in the presence of compliant components in the drive system. An accurate model of the entire system, including the tachometer, is necessary to predict and attenuate these undesirable phenomena. This paper presents an enhanced tachometer model that takes into account the effect of inductive coupling between the actuator and sensor, both of which are electromagnetic devices, in an integrated DC motor-tachometer assembly. The inadequacy of the conventional zero-order model for DC tachometers in such applications is explained. The tachometer dynamics identified in this paper is experimentally verified, and incorporated in the modeling and parameter identification of a motion system that has multiple flexible elements. It is shown that the tachometer dynamics contributes to additional non-minimum phase zeros that degrade the servo system performance in terms of closed-loop bandwidth, and sensitivity to disturbances and modeling uncertainty. The zeros of the open-loop system are found to vary with the geometric parameters of the motor-tachometer assembly. This fact is used in generating a zero locus plot for the openloop system. Based on the insight gained by modeling the electromagnetic coupling, methods for eliminating it and its resulting ill effects are also suggested. Keywords:
DC motor servo control, tachometer feedback, flexible drive elements, DC
tachometer model, sensor dynamics, electromagnetic coupling between motor
tachometer, sensor actuator cross-talk, non-minimum phase zero, collocated
and non-collocated controls, zero locus
The resulting journal and conference papers may be found on the publications page.
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