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Introducing Discrete Event Systems into an Undergraduate Controls Course: Development, Pilot Study and Assessment

Abstract

Discrete event systems are characterized by discrete states with event-driven state transitions. The modeling and control of such systems is often handled in a rather ad-hoc manner. Emerging research in developing analytical results for ‘discrete event control’ is leading to the formation of graduate level courses in the United States, and more commonly in Europe and Canada. This paper outlines a small instructional module introducing this material into a typical undergraduate controls course. Results of the implementation of such a module during the Fall 2005 semester are discussed.

Introduction

Courses on systems and control have become standard elements of most any undergraduate curriculum in mechanical engineering. These courses are very useful to their students and typically cover material ranging from the modeling of physical systems, to system analysis and controller design. In general, techniques for analysis and design are taught in both the time and frequency domains, and in the undergraduate curriculum are applied to continuous linear time invariant single input single output systems. While it is true that the techniques learned are very powerful and cover a large portion of the techniques the students will find being employed in industry, the students generally complete these undergraduate courses with little understanding of the limitations of the techniques they have learned. The students often fail to recognize that most systems they will encounter in the real world are inherently nonlinear, time varying, have multiple inputs and multiple outputs, and that controllers are often implemented digitally. Although the typical undergraduate curriculum is crowded enough as it is, and students have the ability to learn how to deal with these difficulties through elective courses and graduate study, it is important that the students come away knowing that these subtleties exist and that there are techniques out there for dealing with them. Much of the advancement taking place in controls education seeks to address these deficiencies through laboratory work and project-based learning.1 2

A specific area of control system design and analysis that even many advanced graduate students are unaware of is that of discrete event system (DES) control. Discrete event control is often confused with digital control. Whereas digital control systems involve the sampling of an inherently continuous system at discrete time intervals, a DES is a system whose states are inherently discrete. For example, a milling machine is in an initialization state or a fault state, or the controller for an inverted pendulum is in the swing-up mode or the balancing mode. Another distinguishing characteristic of DES is that their evolution is event driven, not time driven. The transition between states occurs because of an event (such as a part arrives, or a continuous

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Hill, R., & Tilbury, D. (2006, June), Introducing Discrete Event Systems Into An Undergraduate Controls Course Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--382