Petri net-based modelling of workflow systems: An overview

Risk assessment and management for supply chain networks: A case study

Deadlocks are a rather undesirable situation in a highly automated flexible manufacturing system. Their occurrences often deteriorate the utilization of resources and may lead to catastrophic results in safety-critical systems. Graph theory, automata, and Petri nets are three important mathematical tools to handle deadlock problems in resource allocation systems. Particularly, Petri nets are considered as a popular formalism because of their inherent characteristics. They received much attention over the past decades to deal with deadlock problems, leading to a variety of deadlock-control policies. This study surveys the state-of-the-art deadlock-control strategies for automated manufacturing systems by reviewing the principles and techniques that are involved in preventing, avoiding, and detecting deadlocks. The focus is deadlock prevention due to its large and continuing stream of efforts. A control strategy is evaluated in terms of computational complexity, behavioral permissiveness, and structural complexity of its deadlock-free supervisor. This study provides readers with a conglomeration of the updated results in this area and facilitates engineers in finding a suitable approach for their industrial scenarios. Future research directions are finally discussed.

Deadlock Control of Automated Manufacturing Systems Based on Petri Nets—A Literature Review

This paper presents a novel method to derive a Petri net from any specification model that can be mapped into a state-based representation with arcs labeled with symbols from an alphabet of events (a Transition System, TS). The method is based on the theory of regions for Elementary Transition Systems (ETS). Previous work has shown that, for any ETS, there exists a Petri Net with minimum transition count (one transition for each label) with a reachability graph isomorphic to the original Transition System. Our method extends and implements that theory by using the following three mechanisms that provide a framework for synthesis of safe Petri nets from arbitrary TSs. First, the requirement of isomorphism is relaxed to bisimulation of TSs, thus extending the class of synthesizable TSs to a new class called Excitation-Closed Transition Systems (ECTS). Second, for the first time, we propose a method of PN synthesis for an arbitrary TS based on mapping a TS event into a set of transition labels in a PN. Third, the notion of irredundant region set is exploited, to minimize the number of places in the net without affecting its behavior. The synthesis method can derive different classes of place-irredundant Petri Nets (e.g., pure, free choice, unique choice) from the same TS, depending on the constraints imposed on the synthesis algorithm. This method has been implemented and applied in different frameworks. The results obtained from the experiments have demonstrated the wide applicability of the method.

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Deriving Petri nets from finite transition systems

The use of structure theory of Petri nets to develop efficient deadlock prevention and deadlock avoidance methods for flexible manufacturing systems (FMSs) modelled by S4R nets is demonstrated Major synchronisation patterns, such as generalised parallel and sequential mutual exclusion, frequently observed in FMS contexts can be represented by this class The liveness property of a given S4R net (deadlock-freeness in the context of FMSs) is characterised in terms of structural Petri net elements called siphons An efficient method for controlling minimal siphons of a given S4R net is developed where local control places are added to the net A sufficient condition for liveness of the augmented net is provided This constitutes a deadlock prevention approach When the net liveness condition is not satisfied, an on-line controller, using a dynamic resource allocation policy, is developed for the augmented net The performance of the proposed approaches is illustrated using several examples

Deadlock prevention and avoidance in FMS : A Petri net based approach

Introduction. 1: Introducing Petri nets M. Silva. Nets and net systems. On modelling features. On net systems interpretations. Approaching concurrency qualitative problems. Qualitative analysis of net system models. Some net subclasses and their analysis. Concluding remarks. 3: Principles of system modelling J.M. Proth. Manufacturing system modelling: basic concepts. Transportation system between two points on a shop-floor. Storage facilities. Operation modelling. Tool systems. Material-handling systems. Conclusion. 3: Synthesis for manufacturing systems integration F. DiCesare, Mu Der Jeng. Introduction to Synthesis. Bottom-up synthesis. Top-down methods. Hybrid synthesis: combining top-down and bottom-up. Summary. 4: Performance evaluation of manufacturing systems J.M. Proth. Introduction. Event graphs: definition and properties. Manufacturing systems working on a cyclic basis. The general case. 5: Petri nets for manufacturing information systems G. Harhalakis, F.B. Vernadat. Introduction. Basics of manufacturing information systems. High-level Petri nets. Organization analysis and conceptual database design. Modeling, analysis and implementation of company policies. Conclusions. Index.

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Simon Peck

Papers

Practice of Petri Nets in Manufacturing