Showing papers on "Petri net published in 2015"

Coloured Petri Nets Basic Concepts, Analysis Methods and Practical Use

Abstract: Control of Discrete-event Systems provides a survey of the most important topics in the discrete-event systems theory with particular focus on finite-state automata, Petri nets and max-plus algebra. Coverage ranges from introductory material on the basic notions and definitions of discrete-event systems to more recent results. Special attention is given to results on supervisory control, state estimation and fault diagnosis of both centralized and distributed/decentralized systems developed in the framework of the Distributed Supervisory Control of Large Plants (DISC) project. Later parts of the text are devoted to the study of congested systems though fluidization, an over approximation allowing a much more efficient study of observation and control problems of timed Petri nets. Finally, the max-plus algebraic approach to the analysis and control of choice-free systems is also considered. Control of Discrete-event Systems provides an introduction to discrete-event systems for readers that are not familiar with this class of systems, but also provides an introduction to research problems and open issues of current interest to readers already familiar with them. Most of the material in this book has been presented during a Ph.D. school held in Cagliari, Italy, in June 2011. This book constitutes the refereed proceedings of the Third International Workshop on Tools and Algorithms for the Construction and Analysis of Systems, TACAS '97, held in Enschede, The Netherlands, in April 1997. The book presents 20 revised full papers and 5 tool demonstrations carefully selected out of 54 submissions; also included are two extended abstracts and a full paper corresponding to invited talks. The papers are organized in topical sections on space reduction techniques, tool demonstrations, logical techniques, verification support, specification and analysis, and theorem proving, model checking and applications. The refereed proceedings of the 24th International Conference on Applications and Theory of Petri Nets, ICATPN 2003, held in Eindhoven, The Netherlands, in June 2003. The 25 revised full papers presented together with 6 invited contributions were carefully reviewed and selected from 77 submissions. All current issues on research and development in the area of Petri nets are addressed, in particular concurrent systems design and analysis, model checking, networking, business process modeling, formal methods in software engineering, agent systems, systems specification, systems validation, discrete event systems, protocols, and prototyping. The contents of this volume are application oriented. The volume contains a de tailed presentation of 19 applications of CP-nets, covering a broad range of ap plication areas. Most of the projects have been carried out in an industrial set ting.

Design of Optimal Petri Net Controllers for Disjunctive Generalized Mutual Exclusion Constraints

Abstract: In this paper, a type of specifications called OR-AND Generalized Mutual Exclusion Constraints (GMEC) for place/transition nets is defined. Such a specification consists of a disjunction of conjunction of several single GMECs, i.e., the requirement is that, at any given time, the controlled system should satisfy at least one set of conjunctive GMECs. We show that a bounded OR-AND GMEC can be enforced by a special control structure composed by a set of AND-GMEC monitor places plus a switcher that determines the current active ones. We also show that such a simple control structure can be modified to ensure maximal permissiveness. This approach can be used in the framework of supervisory control in Petri nets.

A Petri Net-Based Discrete-Event Control of Automated Manufacturing Systems With Assembly Operations

Abstract: In the context of automated manufacturing systems (AMSs), Petri nets are widely adopted to solve the modeling, analysis, and control problems. So far, nearly all known approaches to liveness-enforcing supervisory control study AMSs with flexible routes, whereas little work investigates the ones with synchronization operations. Compared with flexibility, synchronization allows the disassembly and assembly operations that correspond to splitting to and merging from different subprocesses, respectively. Such structures bring difficulties to establish a liveness condition of the Petri net model of AMSs. In this paper, we propose a novel class of systems, which can well deal with these features so as to facilitate the investigation of such complex systems. Using structural analysis, we show that their liveness can be attributed to deadlock freeness, which is much easier to analyze, detect, and control by synthesizing a proper supervisory controller. Furthermore, a set of mathematical formulations is proposed to describe and extract the corresponding deadlocks. This facilitates the synthesis of liveness enforcing supervisors as it avoids the consideration of deadlock-free but nonlive scenarios. The effectiveness and efficiency of this new method is shown by AMS examples.

State Estimation and Fault Diagnosis of Labeled Time Petri Net Systems With Unobservable Transitions

Abstract: In this paper, we present a procedure for the state estimation and fault diagnosis of a labeled Time Petri net system. Starting from the State Class Graph defined by Berthomieu and Diaz, we introduce a new graph called Modified State Class Graph (MSCG) that allows an exhaustive representation of the evolution of the timed system. Then, we present a procedure that, given a timed observation, i.e., a sequence of labels with their firing time instants, and a time instant $\tau$ , allows one to determine in which states the system can be at time $\tau$ by using the MSCG and solving a certain number of linear programming problems. Finally, we present a procedure to perform fault diagnosis using the MSCG.

Petri Net Synthesis

Abstract: This book is a comprehensive, systematic survey of the synthesis problem, and of region theory which underlies its solution, covering the related theory, algorithms, and applications. The authors focus on safe Petri nets and place/transition nets (P/T-nets), treating synthesis as an automated process which, given behavioural specifications or partial specifications of a system to be realized, decides whether the specifications are feasible, and then produces a Petri net realizing them exactly, or if this is not possible produces a Petri net realizing an optimal approximation of the specifications. In Part I the authors introduce elementary net synthesis. In Part II they explain variations of elementary net synthesis and the unified theory of net synthesis. The first three chapters of Part III address the linear algebraic structure of regions, synthesis of P/T-nets from finite initialized transition systems, and the synthesis of unbounded P/T-nets. Finally, the last chapter in Part III and the chapters in Part IV cover more advanced topics and applications: P/T-net with the step firing rule, extracting concurrency from transition systems, process discovery, supervisory control, and the design of speed-independent circuits. Most chapters conclude with exercises, and the book is a valuable reference for both graduate students of computer science and electrical engineering and researchers and engineers in this domain.

Decentralized Supervision of Petri Nets With a Coordinator

Abstract: This paper develops a decentralized supervision policy for a Petri net through collaboration between a coordinator and subnet controllers. The coordinator is chosen from the subnet controllers by solving an integer linear programming problem. An optimal objective function is used to minimize the communication cost between the subnet controllers and the coordinator. Furthermore, a protocol to reach an agreement on the firing conditions of common transitions among the subnet controllers is proposed. Observation agreement and control agreement can be achieved by the “AND” operator in logic algebra. Control agreement is used to decide the firing conditions of common transitions in the next step. The firing of common transitions, which will lead to a new marking that violates the given constraints, will be forbidden by the control agreement. A feasibility analysis of the proposed decentralized control framework is discussed. Finally, four examples are presented to illustrate the proposed approach.

Automatic Composition of Semantic Web Services Based on Fuzzy Predicate Petri Nets

Abstract: Web service composition is a challenging research issue. This paper presents an automatic Web service composition method that deals with both input/output compatibility and behavioral constraint compatibility of fuzzy semantic services. First, user input and output requirements are modeled as a set of facts and a goal statement in the Horn clauses, respectively. A service composition problem is transformed into a Horn clause logic reasoning problem. Next, a Fuzzy Predicate Petri Net (FPPN) is applied to model the Horn clause set, and T-invariant technique is used to determine the existence of composite services fulfilling the user input/output requirements. Then, two algorithms are presented to obtain the composite service satisfying behavioral constraints, as well as to construct an FPPN model that shows the calling order of the selected services.

Design of Traffic Safety Control Systems for Emergency Vehicle Preemption Using Timed Petri Nets

Abstract: Timed Petri nets (TPNs) are useful for performance evaluation of discrete event systems due to their mathematical formalism. This paper focuses on their use to model the preemption of emergency vehicle systems. The advantage of the proposed approach is the clear presentation of traffic light behaviors in terms of conditions and events that cause the preemption of phases being changed. The resulting models allow one to identify and thus avoid urgent spectacles in such systems by conditions and events of the model that control the phase of traffic light alternations. Moreover, this work proposes a new emergency vehicle preemption policy to ensure that emergency vehicles can pass through intersections with no or less delay. The analysis is performed to demonstrate how the models enforce the phase of traffic transitions by a reachability graph with time information. The liveness and reversibility of the proposed model are verified. To our knowledge, this is the first work that employs TPNs to model an emergency vehicle preemption system and identify its urgent spectacles for the purpose of their complete avoidance. This helps advance the state-of-the-art in traffic safety related to the intersection of roadways.

Deadlock-Free Scheduling of Automated Manufacturing Systems Using Petri Nets and Hybrid Heuristic Search

Abstract: This paper focuses on the deadlock-free scheduling problem of automated manufacturing systems with shared resources and route flexibility, and develops novel scheduling methods by combining deadlock control policies and hybrid heuristic search. Place-timed Petri nets are used to model the systems and find a feasible sequence of firing transitions in the built model such that the firing time of its last transition is as small as possible. Based on the reachability graph of the net and a minimum processing time matrix, new heuristic and selection functions are designed to guide search processes. The proposed hybrid heuristic search is based on state space exploration and hence suffers from the state space explosion problem. In order to reduce the explored space, the search is restrained within a limited local search window. By embedding the deadlock-avoidance policies into the search processes, a novel deadlock-free hybrid heuristic search algorithm is developed. Experimental results indicate the effectiveness and superiority of the proposed algorithm over the state-of-the-art method.

E-Net Modeling and Analysis of Emergency Response Processes Constrained by Resources and Uncertain Durations

Abstract: Time and resource management and optimization are two important challenges for an emergency response process, by which all individuals and groups manage hazards in an effort to avoid or ameliorate the impact of disasters. Compared with a traditional business process, an emergency response process has its own features. To our best knowledge, there is no formal method to model and analyze emergency response processes by taking uncertain activity execution duration, resource quantity, and resource preparation duration into account. This paper presents such a method based on an E-Net that is a Petri net-based formal model for an emergency response process constrained by resources and uncertain durations. According to the number of available resources, execution of an E-Net is classified into the worst, delayed, and best cases. Based on a priority-activity-first strategy and corresponding algorithms, this paper finds the duration to execute each activity for the delayed case. By experiments, we prove that the proposed strategy can ensure shorter execution duration of the whole process than a conventional one. A running case of a chlorine tank explosion is given to validate the proposed method.

Control Program Design for Automated Guided Vehicle Systems via Petri Nets

Abstract: An ordinary Petri-net (PN) based approach is proposed to design a programmable logical controller (PLC) that prevents collisions among vehicles in an automated guided vehicle (AGV) system. First, a procedure is proposed to model an AGV system as a control-hardware PN. Second, a method is formulated to design a PN supervisor (the closed-loop PN) for collision prevention. This paper defines the line, merge, divide and intersection alignments, and then adds the transitions and arcs for these four alignments into the control-hardware PN, respectively. As a result, a closed-loop PN is obtained as the supervisor for preventing collisions among vehicles in an AGV system. Finally, a method is introduced to automatically translate a closed-loop PN into a ladder diagram by Boolean expressions. Consequently, the closed-loop PN can be implemented by a PLC. An example is used to illustrate this methodology.

Stochastic Petri Net Modeling, Simulation and Analysis of Public Bicycle Sharing Systems

Abstract: Public Bicycle-Sharing Systems (PBSS) have been appearing in more and more cities around the world in the last few years. Although their apparent success as an alternative form of public transportation mode, there are major challenges confronting the operators while few scientific works are available to support such complex dynamical systems to influence their economic viability and operational efficiency. One of the most crucial factors for the success of a PBS system is its ability to ensure that bicycles are available for pick up and vacant berths available for bicycle drop off at every station. In this paper, we develop an original discrete event approach for modelling and performance evaluation of public bicycle-sharing systems by using Petri nets with time, inhibitor arcs and variable arc weights.

Dynamic Petri Fuzzy Cerebellar Model Articulation Controller Design for a Magnetic Levitation System and a Two-Axis Linear Piezoelectric Ceramic Motor Drive System

Abstract: This brief aims to propose a more efficient control algorithm for a magnetic levitation system (MLS) and a two-axis linear piezoelectric ceramic motor (LPCM) drive system. A dynamic Petri fuzzy cerebellar (DPFC) model articulation controller is developed to allow control of the position of the metallic sphere of an MLS and the trajectory tracking of a two-axis LPCM drive system. In the DPFC, the concept of a Petri net and a fuzzy frame are incorporated into a cerebellar model articulation controller (CMAC), which alleviates the computational burden that accompanies the learning of parameters and enhances the fuzzy reasoning inference of CMACs. The supervised gradient-descent method is used to develop the online-training algorithm for the DPFC. To guarantee the convergence of trajectory tracking errors, analytical methods that use a discrete-type Lyapunov function are proposed for the DPFC. The experimental results demonstrate the effectiveness of the proposed DPFC for different experimental systems.

Deadlock Prevention for Flexible Manufacturing Systems via Controllable Siphon Basis of Petri Nets

Abstract: Siphons are a kind of special structural objects in a Petri net, and plays a key role in synthesizing a live Petri net controller for flexible manufacturing systems. In order to obtain a small size Petri net controller, this paper introduces the concept of a controllable siphon basis. It then proves that a live Petri net controller can be established by adding a control place and related arcs to each strict minimal siphon (SMS) in a controllable siphon basis. The initial markings of control places are determined by an integer linear program. The number of control places in the obtained controllers is the same as the number of SMSs in the controllable siphon basis, while the latter is no more than that of the activity places in a Petri net model. An algorithm for constructing a controllable siphon basis is proposed, and a new deadlock prevention policy based on it is established. A few examples are provided to demonstrate the proposed concepts and policy and used to compare them with the state-of-the-art methods.

Scheduling of Single-Arm Multi-cluster Tools With Wafer Residency Time Constraints in Semiconductor Manufacturing

Abstract: This paper studies the challenging problem of scheduling single-arm multi-cluster tools with wafer residency time constraints. They have a linear topology and their bottleneck tool is process-bound. This work aims to find an optimal one-wafer cyclic schedule. With the Petri net model developed in our previous work and the minimal cycle time for a multicluster tool without wafer residency time constraints, it derives the necessary and sufficient schedulability conditions for multicluster tools with wafer residency time constraints for the first time. Then, it gives an algorithm to find an optimal one-wafer cyclic schedule if schedulable. This is done by simply setting the robots’ waiting time for each tool. Thus, it is very computationally efficient and applicable to practical problems. An example is presented to illustrate the proposed method.

Modeling and Verification for Cross-Department Collaborative Business Processes Using Extended Petri Nets

Abstract: Recently, cross-department business processes are becoming more and more complex. Different kinds of coordination patterns exist among different departments, which make modeling and analysis work more difficult. To our best knowledge, there is no formal method to give systematic modeling and verification for the cross-department processes when considering different kinds of coordination patterns among different departments. This paper proposes such a method based on Petri nets. The WF-net model extended with resource and message factors, RM_WF_Net for short, is first introduced. Then, the formal model of tasks is proposed and its coordination relations are given. Next, RM_WF_Net modeling for intradepartment processes is investigated and cross-department coordination patterns, including message interaction pattern, resource interaction pattern, task collaboration pattern, procedure abstract, service outsourcing pattern, and process activation pattern, are formally defined. The soundness of the RM_WF_Net is verified based on the reachability graph. A running case of the cross-department medical diagnosis business process is given to validate our proposed method.

Petri nets in systems biology

Abstract: Petri nets are used in many areas. This article discusses the application of Petri nets in systems biology. Using an example from biochemistry, concepts for the automatic decomposition of biochemical systems are introduced. The article focuses on those concepts that fulfill steady-state conditions. Interestingly, all the concepts are based on minimal, semi-positive transition invariants. The article describes, which new definitions for network decomposition can be derived and how they can be interpreted in the context of biology. This is illustrated with the example of the citric acid cycle, for which a new metabolic pathway could be predicted with the help of such an analysis.

A Petri Net Diagnoser for Discrete Event Systems Modeled by Finite State Automata

Abstract: We propose in this paper a Petri net approach to online diagnosis of discrete event systems (DESs) modeled by finite state automata. The diagnosis method is based on the construction of a Petri net diagnoser (PND) which is constructed in polynomial time and requires less memory than other methods proposed in the literature. We also present methods for the conversion of the PND to both sequential function chart and ladder diagram for implementation on a programmable logic controller (PLC). Implementation issues are also addressed in the paper.

A Survey of Petri Net Tools

Abstract: Petri net is a mathematical modeling language used to describe a system graphically. It is a strong language that can be used to represent parallel or concurrent activities in a system. With a Petri net tool, users can view the overall system graphically and edit it with the editor. A Petri net tool can also be used to analyze the performance of the system, generate code, simulate the system and perform model checking on it. A review on twenty Petri net tools in this paper will give the readers an idea on what is a Petri net tool and the main functions of a Petri net tool. This paper can serve as an introduction of twenty Petri net tools to the reader. However, to date, there are many Petri net tools available to be downloaded online. This survey paper aims to compare twenty Petri net tools in different aspect. This is important as users will not have to read the reviews of Petri net tools online one by one. Just be having a look at the discussion provided, readers can determined the best recommended Petri net tools to be used based on their operating systems and the types of Petri net tool to be analyzed. The main purpose of this survey paper is to recommend Petri net tools based on the operating system and the types of Petri net to be analyzed.

Maximally Permissive Distributed Control of Large Scale Automated Manufacturing Systems Modeled With Petri Nets

Abstract: Ensuring nonblockingness remains challenging for automated manufacturing systems (AMSs) owing to their discrete event dynamics Both scalability and maximal permissiveness are essential for the synthesis and implementation of their centralized supervisors Inspired by the divide and conquer philosophy, this brief proposes a partition methodology and distributed control technique for large-scale AMSs They are represented as interconnected and overlapping subsystems sharing some common components in terms of buffers For each subsystem, a local supervisor is designed based on its local behavior and neighboring information only Generalizing the existing results, we develop a condition under which the control law via decomposition promises the maximal permissiveness Buffer capacities are well designed for the sake of their decomposition into multiple overlapping subsystems Theoretical results are developed to characterize the behavior compatibility among local controllers An experimental study illustrates the effectiveness of the proposed method

Charlie – An Extensible Petri Net Analysis Tool

Abstract: Charlie is an extensible thread-based Java tool for analysing Petri nets. Its built-in functionalities apply standard analysis techniques of Petri net theory (e.g. invariants, siphon/trap property) to determine structural and behavioural properties of place/transition Petri nets, complemented by explicit CTL and LTL model checking. Charlie comes with a plugin mechanism, which permits to easily extend its basic functionality as it has been demonstrated for, e.g., structural reduction and time-dependent Petri nets. Charlie’s primary focus is teaching. For thispurpose, it has a rule system comprising standard theorems of Petri net theory to possibly decide further properties based on the already determined ones. All applied rules are reported by default, so the user may keep track of all analysis steps. The tool is in use for model verification of technical systems, especially software-based systems, as well as for model validation of natural systems, i.e. biochemical networks, such as metabolic, signal transduction, and gene regulatory networks. It is publicly available at http://www-dssz.informatik.tu-cottbus.de/DSSZ/Software/Charlie.

A Branch and Bound Algorithm for Cyclic Scheduling of Timed Petri Nets

Abstract: A timed Petri net (TPN) has been widely used for modeling, scheduling, and analyzing discrete event dynamic systems. This study examines cyclic scheduling problems of a TPN to minimize the cycle time especially for automated manufacturing systems. Appropriate token routing at each conflict place can make a TPN repeat an identical firing sequence. We propose a systematic procedure to transform a TPN with such cyclic token routing into an equivalent timed event graph (TEG) for which the cycle time and firing schedules can be evaluated by a linear programming (LP). Based on the transformation procedure, we develop an efficient branch and bound algorithm to solve the scheduling problem. A partial solution is defined as a partial token route that has only a subset of token routes for determining the complete schedule. The lower bound of a partial solution is determined by the cycle time of a TEG that has the partial token route. The cycle time of a TEG with an additional token route for a new partial solution is computed by a dual-simplex algorithm which avoids solving the LP completely again. A dynamic branching strategy that prevents unnecessary branching for the scheduling decision is also proposed. We demonstrate the computational efficiency through intensive experiments of cluster tools and robotic flow shops.

Simultaneous Reduction of Petri Nets and Linear Constraints for Efficient Supervisor Synthesis

Abstract: Due to state-space explosion and uncontrollable events in discrete-event systems, it is very difficult to design supervisors to enforce user-defined linear-constraints and ensure the liveness of their Petri-net (PN) models with complex structures. Different from all the existing methods, which are to transform original constraints into admissible or weakly admissible ones, the method proposed in this work aims to reduce linear-constraints and PN models simultaneously. As a result, an original PN control problem is equivalently reduced to a simpler one, i.e., the optimal supervisors for them make the same restriction on the behavior of a discrete-event system. Moreover, it can be guaranteed that the original PN system is live if and only if the reduced one is so. Since the state space of a PN may grow exponentially with its size, and the sizes of real discrete-event systems are often too large to handle, the proposed method is useful to greatly reduce the computational complexity of both property-analysis and supervisor-synthesis of discrete-event systems.