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This paper addresses the problem of optimal sensor selection for ensuring diagnosability of discrete event systems. Given a nondiagnosable discrete event system modeled with labeled Petri nets, a new labeling function can be designed to enforce the system to be diagnosable. An ad‐hoc parallel composition of non‐deterministic finite automata (derived from the original labeled Petri net model) that are observed at multiple observation sites is employed. In order to optimize a given labeling function as well as a sensor selection, an integer linear programming problem is formulated to associate numerical sensor costs with transition relabelings. In a multi‐fault system, this method can determine the type of faults that occur and the fault sequences pertaining to this fault type if multiple faults occur. Examples are presented to demonstrate the proposed method. [ABSTRACT FROM AUTHOR]

Abstract This paper addresses the problem of optimal sensor selection for ensuring diagnosability of discrete event systems. Given a nondiagnosable discrete event system modeled with labeled Petri nets, a new labeling function can be designed to enforce the system to be diagnosable. An ad‐hoc parallel composition of non‐deterministic finite automata (derived from the original labeled Petri net model) that are observed at multiple observation sites is employed. In order to optimize a given labeling function as well as a sensor selection, an integer linear programming problem is formulated to associate numerical sensor costs with transition relabelings. In a multi‐fault system, this method can determine the type of faults that occur and the fault sequences pertaining to this fault type if multiple faults occur. Examples are presented to demonstrate the proposed method.

This paper discusses the problem of marking constraints in a class of partially controllable timed Petri nets. Specifically, these are Timed Event Graphs (TEGs) which include disturbed input transitions and which are subject to token capacity constraints in some paths. Using the Min-Plus algebra formalism, formal approaches are proposed to design causal control laws to guarantee compliance with marking constraints in TEGs. Sufficient conditions are defined to show the existence and synthesis of these controllers. The developed methodologies are illustrated in a case study of a disassembly system with a limited stock of components. [ABSTRACT FROM AUTHOR]

Abstract This work investigates quantitative supervisory control of discrete event systems modeled with Petri nets under the fixed‐initial‐credit energy objective. A weight function referred to as an energy function is defined on a Petri net to characterize the energy level of a transition. The proposed fixed‐initial‐credit energy problem aims to design a supervisor such that the energy level of a transition sequence in a supervised system is higher than 0 under a given initial energy level. The problem is eventually transformed into a two‐player game between a system and a supervisor; supervisor synthesis is reduced to finding a winning strategy in the two‐player game. Instead of enumerating the complete state space of the underlying Petri net, two information structures are utilized, namely the conventional basis reachability graph and the newly proposed essential marking graph, to construct two‐player games based on each of them. It is shown that a winning strategy for a supervisor decoded from the game based on the basis reachability graph of the Petri net is a solution to the problem but is in general restrictive. Further, it is shown that the set of strategies for a supervisor in the game based on the essential marking graph is consistent with that from the game based on the reachability graph of a Petri net. The two developed approaches do not require an exhaustive exploration of the state space of a plant, thus achieving higher efficiency.

This work investigates quantitative supervisory control of discrete event systems modeled with Petri nets under the fixed‐initial‐credit energy objective. A weight function referred to as an energy function is defined on a Petri net to characterize the energy level of a transition. The proposed fixed‐initial‐credit energy problem aims to design a supervisor such that the energy level of a transition sequence in a supervised system is higher than 0 under a given initial energy level. The problem is eventually transformed into a two‐player game between a system and a supervisor; supervisor synthesis is reduced to finding a winning strategy in the two‐player game. Instead of enumerating the complete state space of the underlying Petri net, two information structures are utilized, namely the conventional basis reachability graph and the newly proposed essential marking graph, to construct two‐player games based on each of them. It is shown that a winning strategy for a supervisor decoded from the game based on the basis reachability graph of the Petri net is a solution to the problem but is in general restrictive. Further, it is shown that the set of strategies for a supervisor in the game based on the essential marking graph is consistent with that from the game based on the reachability graph of a Petri net. The two developed approaches do not require an exhaustive exploration of the state space of a plant, thus achieving higher efficiency. [ABSTRACT FROM AUTHOR]

The public health sector, considered to be vital, especially in this pandemic crisis of COVID‐19, requires automation and control of drug distribution in pharmacies commonly called: "Dispensing." In this paper, we address the medication assignment problem for automated dispensing cabinets (ADCs). First, we use a network of conflicting timed event graphs (CTEGs), a class of timed Petri nets with shared resources, to model pharmaceutical cabinets. Second, we develop a new method for controlling CTEGs under mutual exclusion constraints (MECs) to solve the problem of drug assignment, using a control approach based on Min‐Plus algebra. Finally, a case study of assigning drugs is given to illustrate the proposed methodology and show the efficiency of the developed control laws. [ABSTRACT FROM AUTHOR]

This study proposes an analytical control method for the meeting of capacity constraints in discrete event systems with disturbances. More precisely, it consists of computing control laws for partially controllable and observable timed event graphs that are subject to marking constraints. To resolve the issue, linear Min‐Plus models are used to describe the behavior of these graphs, and the constraints are expressed by inequalities in Min‐Plus algebra. Sufficient conditions for the existence of causal control laws to guarantee marking specifications are established. Finally, to illustrate the efficiency of the proposed approaches in this paper, an application for a disassembly process with some disturbance inputs and limited component capacities is carried out. [ABSTRACT FROM AUTHOR]

To ensure opacity, it is optimal to retain as many as possible occurring event sequences. Contrary to this problem, the other optimal goal is to preserve the minimal occurring event sequences. Based on the choosing cost, an optimal opacity-enforcing problem with minimal discount choosing cost is presented under two constraints in this paper. The first constraint is the opacity of the controlled system. The second is the retention of the secret to the maximum. To solve the model, two scenarios on opacity are considered. For the two scenarios, some algorithms are presented to achieve the optimal solution for the model by using the method of dynamic programming. Then, the solutions produced by the algorithms are proved to be correct by theoretical proof. Finally, some illustrations and an application example on location privacy protection for the algorithms are given. [ABSTRACT FROM AUTHOR]

Opacity is an essential security indicator in archive systems. There exists a set of secret states and an external intruder who can observe the behavior of the system in the archive system. The intruder can steal private information by observing the behavior of the system. The system is said to be ${K}$ -step opaque when the intruder cannot confirm whether the system has been in a secret state at any time, within the observation of ${K}$ events. In the case where an intruder can never be sure whether the system has ever been in a secret state, the system is referred to be infinite-step opaque. To be realistic, we consider an archive system modeled as a bounded labeled Petri net, and propose an algorithm for constructing a modified state estimator to increase the security of the archive system. Our aim is to verify the two types of opacity of the system by the observer and the modified state estimator. Our new algorithm improves the security of the system so that an intruder cannot easily know whether the system is in a secret state or not, which also improves the previously-known results.

Abstract This work proposes a symbolic method to verify and enforce the current‐state opacity of labelled Petri nets (LPNs). The notion of basis markings of partially observed Petri nets currently dominates the development of opacity verification and enforcement for discrete event systems. However, the related computational efficiency, to a great extent, depends on the number of basis markings in a system, which increases exponentially with respect to the size of its corresponding LPN model. Binary decision diagrams (BDDs) are capable of computing a set of basis markings in a compact shared structure. To mitigate the computational overheads, a BDD‐based method to efficiently model the structure and behaviour of an LPN is proposed. Then, the current‐state opacity of LPNs is verified and enforced in a symbolic manner. Finally, a number of examples are provided to demonstrate the effectiveness and efficiency of the proposed method.

This work proposes a symbolic method to verify and enforce the current‐state opacity of labelled Petri nets (LPNs). The notion of basis markings of partially observed Petri nets currently dominates the development of opacity verification and enforcement for discrete event systems. However, the related computational efficiency, to a great extent, depends on the number of basis markings in a system, which increases exponentially with respect to the size of its corresponding LPN model. Binary decision diagrams (BDDs) are capable of computing a set of basis markings in a compact shared structure. To mitigate the computational overheads, a BDD‐based method to efficiently model the structure and behaviour of an LPN is proposed. Then, the current‐state opacity of LPNs is verified and enforced in a symbolic manner. Finally, a number of examples are provided to demonstrate the effectiveness and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Petri net (PN) based prevention and control methods are widely studied in the literature to solve deadlock problems in flexible manufacturing systems (FMS). In PN models of FMS suffering from deadlocks, the reachability graph (RG) of the PN model can provide all reachable system states from the initial state, including all legal states, bad states, and deadlock states. A maximally permissive deadlock controller allows the system to reach all legal states exist within the live zone (LZ) that determines the optimal live behavior, while prohibits reaching bad and deadlock states exist within the dead zone. It is necessary to know the exact number of legal states that must be provided by a deadlock controller to determine the behavioral permissiveness of a control policy. Therefore, the number of legal states has been considered as a quality measure for deadlock prevention methods available in the literature. Unfortunately, to date for a given RG of a PN model of an FMS suffering from deadlocks, no study has been reported to provide the number of reachable legal states exist within the LZ of the given RG. In this paper, a method is proposed for the computation of the number of legal states that must be provided by an optimal deadlock prevention policy. The proposed method makes use of the reachability analysis of a given PN model of a deadlock-prone FMS together with the first strongly connected component (SCC) by using INA (Integrated Net Analyzer). The number of legal states computed from the first SCC that includes the initial marking represents the LZ of a RG. The proposed algorithm is implemented as an executable program. The number of legal states of a deadlock controller can easily and correctly be computed by using the proposed method and tool. Several well-known examples of FMS are considered to illustrate the applicability and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this work, we introduce a modelling and simulation process based on Matlab/Simulink for Petri nets that considers inhibitor arcs and priorities of transitions, herein named eXtended Petri nets, for modelling deterministic complex systems. The presented process comprises the method for modelling the system, the functions for the import to Matlab of all the data structures that define a Petri net with inhibitory arcs and priorities in transitions, and the functions to perform the simulation of the Petri net behaviour as a Simulink block. We present an exploratory case study about Rate Monotonic Scheduling for tasks with harmonic periods to show the complete modelling and simulation process. First, the scheduling system is modelled with Renew editor and saved as a PNML file. Then, this file is read and transformed into a Matlab data type. The produced data structures are the inputs to the proposed Simulink block, which performs the dynamic of the eXtended Petri net. Finally, the outputs of the simulation help validate the logical and temporal correctness of the scheduler model used as a case study. The concluding remarks section provides a link for downloading and testing the simulation process. [ABSTRACT FROM AUTHOR]

The feedback control system with network-connected components is vulnerable to cyberattacks. We study a problem of attack detection in supervisory control of discrete-event systems. The scenario of a system subjected to actuator enablement attacks is considered in this article. We also consider that some unsafe places that should be protected from an attacker exist in the system, and some controllable events that are disabled by a supervisor might be re-enabled by an attacker. This article proposes a defense strategy to detect actuator enablement attacks and disable all controllable events after detecting an attack. We design algorithmic procedures to determine whether the system can be protected against damage caused by actuator enablement attacks, where the damage is predefined as a set of "unsafe" places. In this way, the system property is called "AE-safe controllability". The safe controllability can be verified by using a basis diagnoser or a basis verifier. Finally, we explain the approach with a cargo system example. [ABSTRACT FROM AUTHOR]

In this paper, incremental computation of schedules for complex discrete event systems in an uncertain environment is studied. Uncertainties are assumed to occur due to uncontrollable events. A particular class of flexible manufacturing systems (FMSs) with partial precedence constraints is proposed where some operations are performed with total precedence constraints and others with full routing flexibility (namely partial routing FMSs). Interruptions may occur due to unavailability of resources and interruption of operations. Such interruptions may deviate the trajectory from the planed schedule. For the modeling of the partial routing FMS, a systematic multi-level formalism based on the hierarchical structuration of the operations is introduced. Then, the risk of deviation is integrated and a new cost function is defined accordingly. Finally, a modified beam search algorithm referred to as generation double filtered beam search algorithm that accelerates the convergence of the method is proposed. The new algorithm is based on a new filtering mechanism that uses the cost function to selectively explore the state space of Petri net model in order to find a control sequence from an initial state to a reference one with a trade-off between performance and robustness. Examples are used to illustrate the efficiency of the proposed scheduling approach. [ABSTRACT FROM AUTHOR]

An approach to the Colored Petri Nets (CPN)-based control is proposed in this paper. CPN are used for modeling the dynamics of both the controller and the controlled process in the control system structure. The mathematical model of the controlled process is discretized in order to use CPN in modeling the controlled process and the control system as well. The proposed controller implements a Moore automaton. The theoretical aspects of the controller design are presented in the paper, as well as aspects of the system controllability. The level control of three-tank systems is considered to validate the proposed controller. Extensive simulations are performed using the CPN Tools tool and experimental results on laboratory equipment are included. [ABSTRACT FROM AUTHOR]

The complexity of industrial processes imposes a lot of challenges in building accurate and representative causal models for abnormal events diagnosis, control and maintenance of equipment and process units. This paper presents an innovative data-driven causality modeling approach using interpretable machine learning and process mining techniques, in addition to human expertise, to efficiently and automatically capture the complex dynamics of industrial systems. The approach tackles a significant challenge in the causality analysis community, which is the discovery of high-level causal models from low-level continuous observations. It is based on the exploitation of event data logs by analyzing the dependency relationships between events to generate accurate multi-level models that can take the form of various state-event diagrams. Highly accurate and trustworthy patterns are extracted from the original data using interpretable machine learning integrated with a model enhancement technique to construct event data logs. Afterward, the causal model is generated from the event log using the inductive miner technique, which is one of the most powerful process mining techniques. The causal model generated is a Petri net model, which is used to infer causality between important events as well as a visualization tool for real-time tracking of the system's dynamics. The proposed causality modeling approach has been successfully tested based on a real industrial dataset acquired from complex equipment in a Kraft pulp mill located in eastern Canada. The generated causality model was validated by ensuring high model fitness scores, in addition to the process expert's validation of the results. [ABSTRACT FROM AUTHOR]

Petri nets (PNs) can model various event-driven systems well and detect a fault via reachability analysis. Some state-equation-based approaches are designed for only subclasses of PNs with specific structures. A key issue for PNs’ reachability analysis approach based on state equation is that a non-negative integer solution (NIS) to a state equation is necessary but not sufficient for a marking’s reachability. In this paper, we propose a circuit-based subnet. For ordinary Petri nets with token-free circuit-based subnets, we present an algorithm to determine that the state equation has NISs but the marking is non-reachable. We adopt a divide-and-conquer strategy to consider each circuit-based subnet. The proposed method is tested on a PN-based flexible manufacturing system with unreliable resources. When unreliable resources are lost, the non-reachable markings can be determined effectively. Besides, simulations are done, and the results verify the efficiency of the proposed algorithm compared with the reachability-tree-based method.

This paper presents the descriptive compositional approach for uncertainty modelling and performance evaluation of dynamic reconfigurable discrete event systems (ReDES) using rewriting stochastic reward nets (ReSRN) with Z-fuzzy parameters (FReSRN) that can modify in run-time their own structure by the rewriting of the rules. The expected Z-fuzzy values of the transition and rewriting rule firing rates are calculated based on credibility theory, the FReSRN model is degenerated to a conventional ReSRN model. A case study for performance modelling and analysis of particular ReDES is given in order to show the effectiveness of the proposed method.

'Topological reverse mirroring' (TRM) is a new knowledge-based methodology for more efficiently analysing reachability to derive the closed-form formulas (CFF) of the number of Control-Related states for PNs. According to variant k-th order systems, TRM is constructed by proving that both Gen-Right(k, gen) and Gen_Left(k, k−gen) are the topological reverse nets of Gen-Left(k, gen) such that there is a reversible one-to-one mapping (Mirroring) between these two systems. Thus Gen-Right(k, gen) and Gen-Left(k, k−gen) have same CFF which can be immediately derived by replacing the parameter 'gen' by 'k−gen' in validated CFF for Gen-Left(k, gen). The shown applications of TRM include the reachability analysing for systems with non-sharing sub-net; Deficient tokens; multi-non-sharing/multi-tokens resources; and multi-processes. This paper reports the core methodology to accelerate furthering emerging system-control applications for more complicated PNs based on the real-time information derived by their CFF. [ABSTRACT FROM AUTHOR]

In this work, we propose a new algorithm for the verification of codiagnosability of a discrete event system with dynamic observations, which is an extension of a recently proposed algorithm for the verification of codiagnosability of discrete event systems with static observations. The proposed verifier, called E-VERIFIER, is compared with two different verifiers presented in the literature: (i) the T-VERIFIER, which is proposed for the verification of transition-based codiagnosability; and (ii) the C-VERIFIER, which employs cluster automata as the basic element for computation instead of the original states of the automaton system model. We show that although the E-VERIFIER has the same computational complexity as the C-VERIFIER and the T-VERIFIER, it has the following advantages over the other methods: (i) since the E-VERIFIER represents all faulty and fault-free traces of the system that have the same dynamic projection, then, unlike the C-VERIFIER, the traces that lead the system to violating the codiagnosability condition can be straightforwardly obtained from the E-VERIFIER, and the delay for decentralized diagnosis can be computed using only the E-VERIFIER; and (ii) the E-VERIFIER can be computed more efficiently than the T-VERIFIER when its number of states grows. As a consequence of the proposed approach, we present a method for the computation of the delay for decentralized diagnosis of discrete event systems with dynamic observations, adapting an algorithm based on the verifier for the case of static observations. [ABSTRACT FROM AUTHOR]

Fault diagnosis problem is discussed for discrete events systems described by partially observed Petri nets. Our goal is to detect and identify faults that may have occurred in both transitions and places assuming that we can measure some of them. The proposed approach is based on two mains steps (i) designing an algebraic observer for estimating the markings and the transitions of a partially observed Petri nets and (ii) presenting algorithms to detect and identify faults based on comparing the estimation of both the transitions and markings of the faulty system provided by an algebraic observer with those of the normal system. The effectiveness of the proposed approach is illustrated through a simple and a manufacturing example. • Fault diagnosis model-based approach for discrete events systems modeled by Petri nets is proposed. • An algebraic observer for partially observed Petri nets is designed. • Algorithms capable to detect and identify faults for partially observed Petri nets are presented. • Application to a manufacturing systems. [ABSTRACT FROM AUTHOR]

Mobile computing systems, service-based systems, and some other systems with mobile interacting components have recently received much attention. However, because of their characteristics, such as mobility and disconnection, it is difficult to model and analyze them by using a structure-fixed model. This work proposes a new Petri net model called variable Petri net (VPN) for modeling and analyzing these systems. The definition, firing rule, and related analysis technology of VPN are introduced in detail. In a VPN, the possible interaction interfaces are abstracted as a new kind of places called virtual places, and the occurrences of (dis)connections are described by new functions, which makes it appropriate to describe the component collaboration in systems and realize the scalability and pluggability of systems. Moreover, to overcome the shortcoming that markings cannot reflect the link capability of a system, VPNs add a constraint function along with a marking to represent a complete system configuration. Several examples are used to demonstrate the newly proposed model and method. [ABSTRACT FROM AUTHOR]

The radio block center (RBC) is one of the most essential ground systems in a high-speed train control system both in Europe and in China. The RBC handover procedure is an important function of RBC, which affects the transport efficiency, reliability and safety of railways. Analysis of crucial states in the RBC handover procedure is helpful to determine whether there are potential risks in the procedure, and to locate the fault in time when a fault occurs. In this paper, we study a property, called C-detectability, of the RBC handover. This property has been defined in discrete event systems and requires that the crucial states can be determined uniquely by observing the system output. Taking the RBC handover procedure in the Chinese train control system level 3 (CTCS-3) as an example, we first model the RBC handover procedure using Petri nets, which are a graphical and mathematical modeling tool to formalize the behavior of discrete event systems. Then, based on the notion of basis reachability graph, an efficient approach is used to check C-detectability of the Petri net modeling the handover procedure. Note to Practitioners—The railway system is a safety-critical system. System safety is essential to the railway system. It is necessary to provide formal methods to model the system and analyze its properties. The motivation of this work is to present a general modeling framework of railway systems for the crucial states estimation. The crucial states estimation of the railway system has not been discussed yet in the literature despite its importance due to its relationship with the safety of the railway. In particular, estimating the crucial states in the railway system helps to determine whether there are potential risks in the system. In this paper, we investigate a new state estimation property (C-detectability), which is related to fault diagnosis, marking estimation and fault identification. Future research will consider the use of timed Petri nets to increase the modeling power and to allow the performance analysis of the railway system. [ABSTRACT FROM AUTHOR]

The notion of the “ $h$ -ordered” traffic state provides an efficient approach for maintaining liveness in an open, irreversible, dynamically routed zone-controlled guidepath-based transport system. The restriction of these transport systems in their class of $h$ -ordered states can be performed with polynomial complexity with respect to the size of these systems, while the resulting supervisory control policy retains high levels of operational latitude. The work presented in this article provides novel efficient algorithms for the following two problems: 1) assessing whether a given traffic state is $h$ -ordered; and 2) bringing the underlying transport system from some general traffic state to the class of its $h$ -ordered states in a way that minimizes a certain measure of “operational disruption.” The developed algorithms are motivated by, and find immediate applicability, in the model predictive control (MPC) scheme for the considered transport systems that was developed in. Note to Practitioners—Open and irreversible, zone-controlled, guidepath-based transport systems is a natural abstraction of the traffic dynamics taking place in many unit-load material handling systems (MHSs), like the automated guided vehicle (AGV) systems and the overhead monorail systems that are used in many industrial facilities. In these environments, vehicles are circulating in a “guidepath network” that is defined either by the physical structure of the corresponding MHS (as in the case of the overhead monorail systems) or more artificially, in an effort to isolate the traffic of these vehicles from the surrounding environment (as in the case of the AGV systems). Furthermore, in order to ensure collision-free motion for the traveling vehicles, the edges of this guidepath network are divided into zones, and it is stipulated that each zone is allocated to at most one vehicle at any time. This restriction renders the considered transport systems susceptible to deadlock, and therefore, their traffic controller must control the generated traffic for ensuring high productivity, but also for ensuring “traffic liveness,” i.e., the ability of every vehicle to complete successfully its current assignment and engage in similar assignments in the future. An effective and computationally efficient manner to maintain traffic liveness is by restricting the considered transport systems within a particular subclass of traffic states that is known as $h$ -ordered. The considered article provides streamlined, customized algorithms for effecting this restriction. [ABSTRACT FROM AUTHOR]

Regulation control for Petri nets is a control framework that allows the design of sequence controllers for automation systems in a systematic and efficient way. In order to implement this control framework, the MATLAB® app RCPetri has been developed. In this work, the RCPetri tool functionalities are described, including model generation, automatic specification generation, automatic control design, model and control simulation, automatic translation to PLC code, and communication by Modbus TCP/IP and OPC UA. Furthermore, three examples are presented to illustrate the application of the tool and the regulation framework: an electro-pneumatic device, a process control system, and a robotic manufacturing cell under a decentralized control scheme. [ABSTRACT FROM AUTHOR]

The feedback control system with network-connected components is vulnerable to cyberattacks. We study a problem of attack detection in supervisory control of discrete-event systems. The scenario of a system subjected to actuator enablement attacks is considered in this article. We also consider that some unsafe places that should be protected from an attacker exist in the system, and some controllable events that are disabled by a supervisor might be re-enabled by an attacker. This article proposes a defense strategy to detect actuator enablement attacks and disable all controllable events after detecting an attack. We design algorithmic procedures to determine whether the system can be protected against damage caused by actuator enablement attacks, where the damage is predefined as a set of “unsafe” places. In this way, the system property is called “AE-safe controllability”. The safe controllability can be verified by using a basis diagnoser or a basis verifier. Finally, we explain the approach with a cargo system example.

A generic well-defined methodology for the construction and operation of dynamic process models of discrete industrial systems following a number of well-defined steps is introduced. The sequence of steps for the application of the method as well as the necessary inputs, conditions, constraints and the results obtained are defined. The proposed methodology covers the classical offline modelling and simulation applications as well as their online counterpart, which use the physical system in the context of digital twins, with extensive data exchange and interaction with sensors, actuators and tools from other scientific fields as analytics and optimisation. The implemented process models can be used for what-if analysis, comparative evaluation of alternative scenarios and for the calculation of key performance indicators describing the behaviour of the physical systems under given conditions as well as for online monitoring, management and adjustment of the physical industrial system operations with respect to given rules and targets. An application of the proposed methodology in a discrete industrial system is presented, and interesting conclusions arise and are discussed. Finally, the open issues, limitations and future extensions of the research are considered. [ABSTRACT FROM AUTHOR]

The right control of systems, especially when different constraints exist, can avoid many problems of cost and time loss. This paper relates to the resolution of the mutual exclusion problem for discrete event systems modeled with a Network of Timed Event Graphs (NTEGs). It aims to propose formal approaches based on Min-Plus algebra formalisms for the synthesis of control laws to guarantee mutual exclusion constraints in NTEGs. In these studies, the behavior of the network is described by a set of linear Min-Plus equations and mutual exclusion specifications are represented by inequalities that are also linear in Min-Plus algebra. Computed laws are modeled by control places which are connected to the initial NTEGs in order to prevent the violation of mutual exclusion constraints. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach for fault tolerant control of large-scale manufacturing systems is presented. A specification governor is introduced, which is inspired by the concept of "reference governor" in feedback control systems. The goal is to modify an infeasible sequence of specifications, which can be used to generate a distributed logic controller, in such a way that the desired product requirements are satisfied in case of faults. The procedure considers redundancies in the manufacturing system and has the capability of keeping the modification of the infeasible specification sequence as less as possible. A modeling process is proposed that automatically adapts fault-free models in form of signal interpreted Petri nets (SIPNs) according to the occurring faults. Based on these faulty models, it is possible to find out which of the natural language specifications in the specification sequence cannot be executed. [ABSTRACT FROM AUTHOR]

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This work investigates a scheduling problem of deadlock-prone flexible manufacturing systems modeled by place-timed Petri nets. It proposes an anytime branch and bound (AB&B) algorithm for it to minimize system makespan based on the branch tree of a net model and a highly permissive deadlock controller. The proposed algorithm searches a sequence of transitions in the branch tree that evolves the model from the initial marking to the final one. In order to prune the branch tree and increase search speed, this work develops two pruning rules, a lower bound of makespan, and a novel branching strategy. Their usage ensures AB&B’s high search efficiency. Experimental results demonstrate that the proposed algorithm surpasses the state-of-the-art ones. Note to Practitioners—In practice, scheduling is one of the most important issues for production managers to address. Existing approaches to deadlock-prone flexible manufacturing system (FMS) scheduling have multiparameters. Their settings can impact the scheduling results greatly. Since their turning is a challenging task, it is difficult to find the best parameter settings. This article proposes an anytime branch and bound (AB&B) algorithm for minimizing the makespan of deadlock-prone FMSs. It has only one parameter, i.e., maximal CPU time, which needs no turning. When it is highly tight, AB&B can output a feasible and decent schedule. If it is larger and larger, AB&B can output a better and better schedule. Comparison studies show that AB&B outclasses existing ones significantly. It is suitable for real-time scheduling cases in which satisfied schedules must be offered in a very short time. [ABSTRACT FROM AUTHOR]

This paper presents the descriptive compositional approach for uncertainty modelling and performance evaluation of dynamic reconfigurable discrete event systems (ReDES) using rewriting stochastic reward nets (ReSRN) with Z-fuzzy parameters (FReSRN) that can modify in run-time their own structure by the rewriting of the rules. The expected Z-fuzzy values of the transition and rewriting rule firing rates are calculated based on credibility theory, the FReSRN model is degenerated to a conventional ReSRN model. A case study for performance modelling and analysis of particular ReDES is given in order to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the problem of optimal supervisory control for cyclic tasks in the context of discrete-event systems (DES). We consider the completion of each single task as the visit of a marked state, and overall control objective is to complete tasks cyclically in the sense that marked states are visited infinitely often. Following the standard optimal supervisory control framework, two types of costs, disable cost and occurrence cost, are considered. However, instead of considering the standard accumulated total cost or the average cost per event, we consider the measure for the control performance using the average cost per task. We show that such an optimality measure is more suitable for tasks that need to be completed cyclically. Our goal is to design a live and non-blocking supervisor such that the average cost per task in the worst-case is minimized. To solve the problem, we propose a game-theoretical approach by converting the optimal control problem as a two-player graph game. Structural properties of the converted game are discussed. In particular, we show that this game can be solved by a set of mean payoff decision problems, for which effective algorithms exist. Our problem can be considered as a special instance of the general ratio-game in the literature. However, by exploring new structural property for this problem, we achieve superior computational efficiency when compared to the conventional solution designed for more general problem formulations. Illustrative examples are provided to demonstrate the proposed algorithm. [ABSTRACT FROM AUTHOR]

Workflow management technology has become a key means to improve enterprise productivity. More and more workflow systems are crossing organizational boundaries and may involve multiple interacting organizations. This article focuses on a type of loosely coupled workflow architecture with collaborative tasks, i.e., each business partner owns its private business process and is able to operate independently, and all involved organizations need to be synchronized at a certain point to complete certain public tasks. Because of each organization’s privacy consideration, they are unwilling to share the business details with others. In this way, traditional correctness verification approaches via reachability analysis are not practical as a global business process model is unavailable for privacy preservation. To ensure its globally correct execution, this work establishes a correctness verification approach for the cross-organizational workflow with task synchronization patterns. Its core idea is to use local correctness of each suborganizational workflow process to guarantee its global correctness. We prove that the proposed approach can be used to investigate the behavioral property preservation when synthesizing suborganizational workflows via collaborative tasks. A medical diagnosis running case is used to illustrate the applicability of the proposed approaches. Note to Practitioners—Cross-organizational workflow verification techniques play an increasingly important role in ensuring the correct execution of collaborative enterprise businesses. This work addresses the issue of correctness verification for loosely coupled interactive workflows with collaborative tasks. To ensure the globally correct execution, a behavioral correctness verification approach is established. All proposed concepts and techniques are supported by open-source tools, and evaluation over a medical diagnosis process case has shown their applicability. The proposed methodology is readily applicable to industrial-size workflow correctness verification problems. [ABSTRACT FROM AUTHOR]

We address in this paper the design of robust supervisors that are able to cope with intermittent loss of observations and also make the controlled system achieve the specification language under nominal operation. In order to do so, we introduce a definition of robust observability that leverages possible observations of the events that are subject to intermittent loss of observations and address language permissiveness by extending the recently introduced definition of relative observability to robust relative observability. We present necessary and sufficient conditions for the existence of robust supervisors that make the controlled system achieve robustly controllable and observable or relatively observable languages and present a characterisation of all achievable languages. A running example illustrates all the results presented in the paper, and an example taken from the open literature is used to illustrate the efficiency of the robust design strategy proposed in the paper. [ABSTRACT FROM AUTHOR]

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In this paper, we present a diagnoser‐based approach to deal with fault diagnosis of bounded labeled Petri nets. The approach consists in building a semi‐symbolic diagnoser to analyze diagnosability and perform online diagnosis. The contribution of this paper is twofold: (i) from the theoretical point of view, we provide new conditions for checking diagnosability based on a novel diagnoser variant that explicitly separates the normal reachable markings from the faulty ones, in each diagnoser node. This allows us to independently keep tracking the normal and the faulty diagnoser paths more efficiently. (ii) From the practical point of view and in order to reduce the memory required to build the diagnoser efficiently, we establish a semi‐symbolic encoding of the diagnoser state‐space. Such a representation deploys a symbolic encoding of the diagnoser nodes content, using Binary Decision Diagrams, while it keeps an explicit encoding of the observable transitions between the nodes. In addition, we provide an on‐the‐fly algorithm to simultaneously construct the diagnoser and analyze diagnosability. The effectiveness of the approach is illustrated through some experimentation performed on a Petri net benchmark. [ABSTRACT FROM AUTHOR]

Iterative deadlock prevention strategies based on siphons have drawn increasing attention. For iterative strategies, selecting which siphon to control at each iteration has an influence on the final supervisor in structural complexity, computational complexity, and behavioral permissiveness. In this paper, we define two kinds of emptiable siphons and provide two modified mixed-integer programming (MIP) formulations to compute such siphons. On the basis of them, a three-stage iterative deadlock prevention policy that specifies the siphon control order is proposed. The experimental results show that a supervisor with a simpler structure, higher behavioral permissiveness, and lower computational complexity can be obtained by the proposed strategy since neither the exhaustive siphon enumeration nor the reachability analysis is required.