Modeling Of Discrete Event Systems Research Articles

Structural Decomposition and Decentralized Control of Petri Nets

Control of a large-scale automated manufacturing system is an important and challenging issue. Its discrete event system model represented by Petri nets tends to become highly complicated in structure, especially when there exist uncontrollable or unobservable events. The existing approaches are nontrivial to design both efficient and maximally permissive supervisors to impose constraints on an overall system. In this paper, instead of considering the control problem from an overall system perspective, we intend to transform an overall control problem into the one designing multiple controllers in parallel, each of which is much simpler in structure. A Petri net structure is decomposed via integer linear programming or a polynomial decomposition method to obtain multiple state-machine subnets that constitute a decentralized system. A necessary and sufficient condition for preserving the equivalence in terms of states and behaviors between the overall system and its decentralized version is reported. Constraints representing control requirements are further converted and enforced in the respective subnets. Then, supervisors are generated via a generalized mutual exclusion constraint method. By considering the deviations between the subnet control and overall control, this paper formulates a communication mechanism to guarantee that the decentralized system runs in an appropriate manner. Finally, two examples are presented to demonstrate the proposed approach.

Modeling, Simulation and Verification of Probabilistic Reconfigurable Discrete-Event Systems Under Energy and Memory Constraints

Adaptive probabilistic systems have ability to modify their behaviors to cope with unpredictable significant changes at run-time such as component failures or resources depletion. Reconfiguration is often a major task for systems, i.e., it may violate the memory usage, the required energy and the concerned real-time constraints. It might also make the system’s functions unavailable for some time and make potential harm to human life or large financial investments. Thus, updating a system with any new configuration requires that the post-reconfigurable system fully satisfies the related constraints. Formal modeling and verification could avoid the resources and constraints violation. Thus, the paper proposes a new formalism to specify such systems. We also develop a new visual environment named ZIZO which helps in modeling, constructive simulation and CTL-based verification of adaptive probabilistic systems. The contributions are used to guarantee the resources and correctness of an IPv4 ZeroConf protocol.

Design of light weight exact discrete event system diagnosers using measurement limitation: case study of electronic fuel injection system

ABSTRACTEmploying a state-based Discrete Event System (DES) modelling framework, this paper proposes a new fault diagnosis approach called measurement limitation-based abstract DES diagnosis (MLAD), which attempts to reduce state space complexity of the diagnosis process while simultaneously preserving full diagnosability. The MLAD approach carefully applies a set of distinct measurement limitation operations on the state variables of the original DES model based on fault compartmentalisation to obtain separate behaviourally abstracted DES models and corresponding abstract diagnosers with far lower state spaces. The set of measurement limitation operations are so designed that although, any single abstract diagnoser may compromise diagnosability in seclusion, the additive combination of all diagnosers running in parallel always ensures complete diagnosability. Effective measurement limitation also ensures that the combined state space of the abstract diagnosers is much lower than that of the single full diagnoser that may be derived from the original DES model. As a case study, we have employed MLAD to incorporate failure diagnosability in a practical electronic fuel injection system. Evaluations on standard practical benchmarks show that MLAD achieves significant reduction in state space as compared to conventional monolithic full diagnosis approaches.

Algorithms of reduced complexity to design control sequences for untimed Petri nets in varying and uncertain environments

Petri nets have been widely used for the modelling, analysis, control and optimization of discrete event systems with shared resources in the domains of engineering. This article concerns the design of control sequences for such systems modelled with untimed Petri nets. The aim of the controller is to incrementally compute sequences of transition firings with minimal size. Such sequences aim to move the marking from an initial value to a reference value. The resulting trajectory must avoid some forbidden markings and limit as possible the exploration of non-promising branches. For this purpose, the approach explores a small part of the reachability graph in the neighbourhood of the current marking. Then from the explored markings, it estimates a distance to the reference. The main contributions are (a) to reduce the explored part of the reachability graph according to a double limitation in breadth and in depth in order to provide solutions with a low computational effort; (b) to provide conditions to ensure the converge and optimality of the proposed algorithms and derive necessary and sufficient conditions for reachability; and (c) to include the firing sequence design in a global control schema suitable for reactive scheduling problems in uncertain and perturbed environments. The main application concerns deadlock-free scheduling problems in the domain of flexible manufacturing systems, but the approach is also applicable for systems in computer science and transportation.

Special Issue on Modeling, Simulation, Operation and Control of Discrete Event Systems

Information and computer technologies provide the spur to burgeoning man-made, highly automated systems.[...]

Priority-free conditionally-preemptive scheduling of modular sporadic real-time systems

For a real-time system (RTS) processing both sporadic and (multiple-period) periodic tasks, this study presents a novel modular modeling framework to describe the parameters of tasks, conforming to the pertinent concepts and techniques of discrete-event systems (DES). A task is represented by an automaton synchronized by the modular models corresponding to its parameters. As a consequence, a DES model depicting the RTS is synchronized by the DES representing these tasks. Based on supervisory control theory, priority-free conditionally-preemptive (PFCP) real-time scheduling is solved by finding all the safe execution sequences. Finally, the PFCP scheduling is illustrated by real-world examples.

Performance Evaluation of Discrete Event Systems with GPenSIM

Petri nets are a useful tool for the modeling and performance evaluation of discrete event systems. Literature reveals that the Petri Net models of real-world discrete event systems are most frequently event graphs (a subclass of Petri nets). Literature also reveals that there are some simple methods for the performance evaluation of event graphs. The general-purpose Petri Net simulator (GPenSIM) is a new simulator that runs on the MATLAB platform. GPenSIM provides a Petri net language, with which Petri net classes and extensions can be developed. GPenSIM also provides functions for performance analysis. Since real-world discrete event systems usually possess a large number of resources, the Petri net models of these systems tend to become huge. Activity-Oriented Petri Nets (AOPN) is an approach that reduces the size of the Petri nets. In addition to the simulator functions, GPenSIM also realizes the AOPN approach on the MATLAB platform. Thus, AOPN is an integral part of GPenSIM. As a running example, a flexible manufacturing system is firstly modeled as an event graph, and then the size of the model is reduced with the AOPN approach. The advantages of GPenSIM and AOPN are discussed in this paper.

Integrated power supply system for station equipment of rail traffic control

Railway Traffic Control Systems (RTCS) provide a safe, reliable and efficient movement of rolling stock on railway networks. RTCSs are classified as critical process systems. The power supply system is required to provide a high level of power reliability so that a station equipment of an RTCS safely executes the rail traffic process. The article describes typical solutions of power supply of station equipment of RTCSs. Analysis of these solutions led to the development of assumptions and structures for the integrated power supply system of station equipment. Useful tools for the formal modeling of such systems can be Petri Nets. These nets are a graphical and formal tool for modeling, formal analysis, and design of discrete event systems. The basic element of the integrated power system which is described in the article is the Automatic Reserve Switching system (ARS system). The ARS controller Marked Petri Net (ARS controller MPN) that has been developed by the authors is presented here. The net was subject to reduction resulting in an ARS controller hierarchical simplified MPN. The article also presents the practical application of the ARS controller built using the hardware platform and graphical programming environment LabView National Instruments (NI).

Model Decomposition of Timed Event Graphs under Partial Synchronization in Dioids

Timed Event Graphs (TEGs) are a graphical model for decision free and time-invariant Discrete Event Systems (DESs). To express systems with time-variant behaviors, a new form of synchronization, called partial synchronization (PS), has been introduced for TEGs. Unlike exact synchronization, where two transitions t1, t2 can only fire if both transitions are simultaneously enabled, PS of transition t1 by transition t2 means that t1 can fire only when transition t2 fires, but t1 does not influence the firing of t2. Under some assumptions, we can show that the dynamic behavior of a TEG under PS can be decomposed into a time-variant and a time-invariant part. The time-invariant part can be interpreted as a standard TEG. Moreover, it is shown that the tools introduced for standard TEGs can be used to analyze the overall system.

Влияние частичности и адаптивности на сложность задачи идентификации состояний автомата

State identification is a long standing problem in the area of Finite State Machine (FSM) based modeling and testing of discrete event systems. For the identification of the current state of the system, so-called homing and synchronizing experiments with FSMs are used whereas for the initial state identification one can perform a distinguishing experiment. The homing, synchronizing, and distinguishing experiments are known as “gedanken” experiments, and the sequences for these experiments can be derived for deterministic and nondeterministic, partial and complete specification FSMs that are used to formally represent the required behavior of systems under investigation. The problems of checking the existence and derivation of homing, synchronizing, and distinguishing sequences are known to become harder as a specification FSM turns to be nondeterministic and partial. It is also known that in some cases the complexity can be reduced through a ‘switch’ from preset to adaptive experiment derivation. In this paper, we study how the partiality and adaptivity affect the complexity of checking the existence of homing/synchronizing/distinguishing sequences for deterministic and nondeterministic FSMs and visualize the complexity issues via appropriate figures. We also mention that the existing solutions to state identification problems are widely used for verification and testing of finite state transition systems.

Discrete-event demonstrator HANS

This paper presents a model manufacturing cell for the testing of modelling and control design methods of discrete-event systems. It is a handling system for the transport and the processing of workpieces. The hardware and automation structure is introduced and its possible applications as a demonstrator of advanced control methods are discussed. It is also shown how this manufacturing cell can be used for education.

Petri Nets at Modelling and Control of Discrete-Event Systems Containing Nondeterminism -- Part 1

Discrete-Event Systems are discrete in nature, driven by discrete events. Petri Nets are one of the mostly used tools for their modelling and control synthesis. Place/Transitions Petri Nets, Timed Petri Nets, Controlled Petri Nets are suitable when a modelled object is deterministic. When the system model contains uncontrollable/unobservable transitions and unobservable/unmeasurable places or other failures, such kinds of Petri Nets are insufficient for the purpose. In such a case Labelled Petri Nets and/or Interpreted Petri Nets have to be used. Particularities and mutual differences of individual kinds of Petri Nets are pointed out and their applicability to modelling and control of Discrete-Event Systems are described and tested.

Robust production scheduling under machine failures - A DES based evaluation approach

Discrete Event Systems (DES) have already proved their efficiency to model and solve scheduling production problems in the field of manufacturing systems. Their main asset is the capacity to represent the dynamic behavior of workshops.The stochastic extensions of DES models offers, actually, interesting characteristics to take into consideration the perturbations in scheduling. In this paper, we propose to use a stochastic DES approach (using stochastic timed automata) to evaluate the robustness of schedules under perturbations. The perturbations that are considered are the machine failures with uncertain reparation duration.

A class of extended time Petri nets for modeling and simulation of discrete event systems

Time Petri nets (TPNs) have been widely used for modeling discrete event systems such as manufacturing, supply chain, and military systems. However, TPNs still have many drawbacks in some scenarios where an operation or process is associated with probability, and also lack appropriate simulation algorithms for analyzing different types of systems. In this paper, we address these two issues by proposing a class of extended time Petri nets (ETPNs) and presenting an appropriate simulation algorithm. We illustrate and validate our approach using a hypothetic command and control system, which shows that this approach could be a powerful tool for modeling and analyzing discrete event systems.

Ururau: a free and open-source discrete event simulation software

This paper has the purpose of describing the architecture and operation of Ururau, a software used to create discrete event simulation models based on the Java Simulation Library. Ururau is a free and open-source multiplatform software, which allows the user to develop models in the graphical interface or implement them directly in the source code. This characteristic allows the user to employ it as a tool for modeling and simulation of discrete event systems and also as a learning tool. Thus, an experienced modeler can add specific algorithms to simulation models or new features to the simulator. Also, with access to the source code, a beginner modeler can understand the internal structure of a discrete event simulation software. Initial results have demonstrated this new software’s ability in building small and simple models efficiently.

Modelado de compras verdes mediante redes de Petri coloreadas

Los países desarrollados han implementado políticas de desarrollo sostenible específicamente en Consumo y Producción Sustentable. El proceso de compras verdes suele ser considerado crítico para el adecuado rendimiento de la cadena de suministro porque gestiona y garantiza la adquisición de los productos/servicios para que la empresa cumpla con sus actividades misionales, generando beneficios económicos, mitigando los efectos de sus actividades en el medio ambiente y en la sociedad. Este artículo presenta un modelo para el proceso de compras verdes, basada en una herramienta para la modelación de sistemas de eventos discretos complejos llamada Redes de Petri Coloreadas (RdPC).

State-Based Decentralized Diagnosis of Bi-Fuzzy Discrete Event Systems

Recently, we have introduced bi-fuzzy discrete event systems (BFDESs) and established their supervisory control theory under full observations and partial observations, respectively. Compared with the models of discrete event systems and fuzzy discrete event systems, BFDESs are more satisfactory models to characterize some high-uncertainty systems. In this paper, we study the fault diagnosis problems of BFDESs. First, the framework of state-based decentralized diagnosis is introduced. Then, the notion of state-based codiagnosability is defined and a necessary and sufficient condition for state-based codiagnosability is provided. In particular, a polynomial-time algorithm for state-based codiagnosability verification and an online decentralized diagnosis method are presented. In addition, a compact state-based decentralized diagnosis framework is introduced, and the notion of state-based jointly diagnosability and its verification algorithm are proposed. Finally, the implication relationships between the two diagnosabilities are investigated.

Impact of Driving Behavior on Traffic Delay at a Congested Signalized Intersection

This paper proposes a methodology to categorize drivers’ behaviors at a congested signalized intersection. As a discrete event system model, timed Petri nets (TPNs) are used in this paper to formally define two kinds of behaviors: non-jam-induced driving behavior and jam-induced one. In order to systematically assess the performances of both behaviors, a new urban traffic network model is built: a cell transmission model is used to depict the road link traffic that is consistent with the kinematic property of traffic flow, and TPNs are used to model the behaviors and the conflicting traffic flow at the intersection. Some simulation results are given to evaluate the impact of driving behavior on the traffic delay.

Modeling, analysis and control of Discrete Event Systems: a Petri net perspective

The goal of this contribution is to briefly overview the historical development of the field of Petri nets under a System Theory and Automatic Control perspective. It is by far not meant to be comprehensive or inclusive, but to review through several representative areas a few of the conceptual issues studied in the literature. It was not possible to consider here the many domains of application were the Petri Nets modeling paradigm was used, among many others: manufacturing, logistic, hardware and software, protocols engineering, health management, transportation, etc.

UltraDES - A Library for Modeling, Analysis and Control of Discrete Event Systems

In this paper a library of functions and data structures for analysis and control of Discrete Event Systems based in the. NET Framework is proposed. The main objective is to create an environment for the implementation of algorithms for Discrete Event Systems, as well as the integration of these algorithms and codes in the fields of IT (Information Technology) and AT (Automation Technology). The data structure, and the functions implemented so far are presented. The performance of the current version of the library is evaluated.