Complex Discrete Event Systems Research Articles

A Event Occurrence Rules based Compact Modeling Formalism for a Class of Discrete Event Systems

The analysis, failure diagnosis and control of discrete event systems (DESs) requires an accurate model of the system. In this paper we present a methodology which makes the task of modeling DESs considerably less cumbersome, less error prone, and more user-friendly than it usually is. In doing so we simplify the modeling formalism of [4, 5], proposed for obtaining valid models of complex discrete event systems, by eliminating ‘precedence relations’, and capturing them as part of the ‘event occurrence rules’. Under the new modeling formalism the size of the system model is polynomial in the number of signals; whereas the number of states in the commonly used automata models is exponential in the number of signals. We present automated techniques for deriving an automaton model from the model in the proposed formalism. We illustrate the modeling formalism using examples drawn from manufacturing and process control systems.

Supervisory Monitoring and Control of Complex Discrete Event Systems

This paper presents an approach oriented to the handling of failure situations in production systems. Based on monitoring activities concepts, this approach provides an exhaustive set of monitoring procedures to apply among several situation during a manufacturing cycle. These procedures are proposed in a monitoring and control reference model, whose elaboration is presented. This model leads to design a monitoring strategy adaptable to each industrial requirement

Petri nets in semiconductor manufacturing automation: A review

This paper presents an overview of Petri net (PN) approaches to modeling, analysis, simulation, scheduling, and control of semiconductor manufacturing systems. These systems can be characterized as discrete event systems that exhibit sequential, concurrent, and conflicting relations among the events and operations. Their evolution is dynamic over time. The system complexity is tremendous owing to the complex semiconductor manufacturing processes and test procedures. A formal approach such as Petri nets enables one to describe such complex discrete event systems precisely and thus allows one to perform qualitative and quantitative analyses, scheduling and discrete-event control of them. The paper concludes with several research issues critical to enable PNs to be a truly useful industrial technology in semiconductor manufacturing automation.

Modeling, analysis, simulation, scheduling, and control of semiconductor manufacturing systems: A Petri net approach

This paper presents a Petri net approach to modeling, analysis, simulation, scheduling, and control of semiconductor manufacturing systems. These systems can be characterized as discrete event systems that exhibit sequential, concurrent, and conflicting relations among the events and operations. Their evolution is dynamic over time. The system complexity is tremendous owing to the complex semiconductor manufacturing processes and test procedures. A formal approach such as Petri nets enables one to describe such complex discrete event systems precisely and thus allows one to perform both qualitative and quantitative analysis, scheduling and discrete-event control of them. This paper also serves as a tutorial paper. It briefly reviews applications of Petri nets in semiconductor manufacturing automation. It then introduces definitions and concepts of Petri nets. It proceeds with a discussion of basic Petri net modules in system modeling, a modeling method and a practical system's modeling example. Next, the paper presents their properties and their implications in manufacturing systems, as well as their analysis methods. Timed Petri nets are introduced for system simulation, performance evaluation, and scheduling purposes. An application-oriented case study is presented. Finally, the paper concludes with the active research areas in applying Petri nets to design of semiconductor manufacturing systems.

A QUEUEING MODELLING APPROACH TO CLUSTERED HETEROGENEOUS DISCRETE EVENT DYNAMIC SYSTEMS

In this paper we propose a new, more realistic queueing modelling of Discrete Event Dynamic Systems. Being based on the analysis of the real-world complex discrete event systems, the model allows hot only the exploitation of their inherent parallelism, but also the implementation and the efficiency analysis of deadlock detection/recovery and shared resource conflict solving algorithms. Unlike in most approaches developed so far, we consider the case in which the completion of a task is achieved by sequentially running its subtasks on a heterogeneous system composed of homogenous clusters. Moreover, our model makes distinction between processing clusters and system resources. Each cluster is composed of an infinite length queue and of many identical processing units, and is individualised by the type of processing units it contains and by its position in the subtask processing sequence. A parallel simulator based on this model was implemented on a Sequent Balance shared-memory parallel computer. As the sim...

Hierarchical Modeling and Control for Complex Discrete-Event Systems

In this paper we present a way of modeling and control complex discrete event systems. The model is modular and is described hierarchically . The desired behavior is given in terms of specifications which are distributed within the modular structure of the process and this gives rise to a distributive control design technique. The paper addresses the issues of the distributive control design associated with complex discrete-event systems.

SIGMA—A graphical approach to teaching simulation

SIGMA (Simulation Graphical Modeling and Analysis) is a graphics environment for building, testing, and experimenting with discrete event simulation models on personal computers. SIGMA is based on “event graphs,” a concept that utilizes symbolic representations to concisely depict large, complex discrete event systems (like airports, hospitals, and factories) so that they can be understood more easily. SIGMA, the computer animation of event graphs, captures the logic of the computational processes underpinning a simulation.

Hierarchical Models for the Time Delays of Command and Control (C2) Systems

A hierarchical aggregation approach for the time delay analysis of a class of complex discrete event systems whose activity durations are generally distributed is presented via stochastic Petri net models. The basic idea is to turn the time delay research of a complex stochastic Petri net model into that of several simple subnets. The Petri net model of a generic naval C2 system is given, and its time delay characteristics are analyzed by using the algorithm developed in this paper.

Statecharts: a visual formalism for complex systems

We present a broad extension of the conventional formalism of state machines and state diagrams, that is relevant to the specification and design of complex discrete-event systems, such as multi-computer real-time systems, communication protocols and digital control units. Our diagrams, which we call statecharts, extend conventional state-transition diagrams with essentially three elements, dealing, respectively, with the notions of hierarchy, concurrency and communication. These transform the language of state diagrams into a highly structured and economical description language. Statecharts are thus compact and expressive—small diagrams can express complex behavior—as well as compositional and modular. When coupled with the capabilities of computerized graphics, statecharts enable viewing the description at different levels of detail, and make even very large specifications manageable and comprehensible. In fact, we intend to demonstrate here that statecharts counter many of the objections raised against conventional state diagrams, and thus appear to render specification by diagrams an attractive and plausible approach. Statecharts can be used either as a stand-alone behavioral description or as part of a more general design methodology that deals also with the system's other aspects, such as functional decomposition and data-flow specification. We also discuss some practical experience that was gained over the last three years in applying the statechart formalism to the specification of a particularly complex system.