Electromagnetic Coupling in a dc Motor and Tachometer Assembly

Abstract

This paper presents an enhanced tachometer model that takes into account the effect of electromagnetic coupling that can exist between the actuator and sensor in an integrated dc motor-tachometer assembly, where the conventional model is found to be inadequate. 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 additional nonminimum phase zeros that degrade the servo system performance in terms of closed-loop bandwidth, disturbance rejection and sensitivity to modeling uncertainty. The zeros of the open loop system are found to vary with the geometric parameters of the motor-tachometer assembly. Based on the insight gained by modeling the electromagnetic coupling, methods for eliminating it and its resulting detrimental effects are also suggested.