Showing papers on "Process architecture published in 2014"

Optimal Supervisory Control of Flexible Manufacturing Systems by Petri Nets: A Set Classification Approach

Abstract: Supervisory control is usually considered as an external control mechanism to a system by controlling the occurrences of its controllable events. There exist Petri net models whose legal reachability spaces are nonconvex. In this case, they cannot be optimally controlled by the conjunctions of linear constraints. For Petri net models of flexible manufacturing systems, this work proposes a method to classify the legal markings into several subsets. Each subset is associated with a linear constraint that can forbid all first-met bad markings. Then, the disjunctions of the obtained constraints can make all legal markings reachable and forbid all first-met bad markings, i.e., the controlled net is live and maximally permissive. An integer linear programming model is formulated to minimize the number of the constraints. A supervisory structure is also proposed to implement the disjunctions of the constraints. Finally, examples are provided to illustrate the proposed method.

Supervisor Simplification for AMS Based on Petri Nets and Inequality Analysis

Abstract: In the framework of automated manufacturing systems (AMS), Petri nets are widely used to model, analyze, and control them. Resolving deadlocks is of paramount significance because their emergence may likely zero a systems throughput, if not necessarily. Supervisory control technique is the most widely adopted method to resolve them. A control policy can be converted into satisfying a set of inequalities, each of which corresponds to a siphon in a Petri net structure. The number of siphons can be exponential in the worst case, so does the number of inequalities. Taking into account the independent and dependent inequalities, this paper proposes a method to remove all the dependent inequalities, while preserving only the independent ones. This method can significantly reduce the size of a supervisory controller. Examples are presented to illustrate the effectiveness and efficiency of this method.

Modeling and Validating E-Commerce Business Process Based on Petri Nets

Abstract: E-commerce and online shopping with a third-party payment platform have rapidly developed recently, and encountered many fault tolerance and security problems concerned by users. The causes of these problems include malicious behavior and imperfect business processes. The latter lead to the emergence of security vulnerabilities and loss of user funds which become more and more serious these years. We focus on the business process of e-commerce, and propose a formal model for constructing an e-commerce business process called an E-commerce Business Process Net. It integrates both data and control flows based on Petri nets. Rationality and transaction consistency are defined and validated to guarantee the transaction properties of an e-commerce business process. This paper offers a complete methodology for modeling and validating an e-commerce system with a third-party payment platform from the view point of a business process. Its use enables a designer to identify errors early in the design process and correct them before the deployment phase. In order to demonstrate the applicability and feasibility of the methodology, we have modeled and validated a real-world e-commerce business process and discovered the problems that cause the violation of transaction properties.

Petri Net-Based Polynomially Complex Approach to Optimal One-Wafer Cyclic Scheduling of Hybrid Multi-Cluster Tools in Semiconductor Manufacturing

Abstract: Due to the different behavior of single-arm and dual-arm cluster tools, it is challenging to schedule a hybrid multi-cluster tool containing both of them. This paper aims to find an optimal one-wafer cyclic schedule for such a multi-cluster tool. It is assumed that the bottleneck individual cluster tool in it is process-bound, thereby making it process-dominant. To do so, this paper models a hybrid multi-cluster tool with Petri nets. With this model, it derives the conditions under which individual cluster tools can operate in a paced way. Based on these conditions, this paper shows that for any process-dominant hybrid multi-cluster tool there is always a one-wafer cyclic schedule. Then, it develops the algorithms to find the minimal cycle time and the optimal one-wafer cyclic schedule. It is computationally efficient and easy-to-implement in practice. Examples are given to show the application and effectiveness of the proposed method.

A Modeling and Simulation Framework for Health Care Systems

Abstract: In this paper, we propose a new modeling methodology named MedPRO for addressing organization problems of health care systems. It is based on a metamodel with three different views: process view (care pathways of patients), resource view (activities of relevant resources), and organization view (dependence and organization of resources). The resulting metamodel can be instantiated for a specific health care system and be converted into an executable model for simulation by means of a special class of Petri nets (PNs), called Health Care Petri Nets (HCPNs). HCPN models also serve as a basis for short-term planning and scheduling of health care activities. As a result, the MedPRO methodology leads to a fast-prototyping tool for easy and rigorous modeling and simulation of health care systems. A case study is presented to show the benefits of the MedPRO methodology.

Modeling self-adaptive software systems with learning petri nets

Abstract: Traditional models have limitation to model adaptive software systems since they build only for fixed requirements, and cannot model the behaviors that change at run-time in response to environmental changes. In this paper, an adaptive Petri net is proposed to model a self-adaptive software system. It is an extension of hybrid Petri nets by embedding a neural network algorithm into them at some special transitions. The proposed net has the following advantages: 1) It can model a runtime environment; 2) The components in the model can collaborate to make adaption decisions; and 3) The computing is done at the local, while the adaption is for the whole system. We illustrate the proposed adaptive Petri net by modeling a manufacturing system.

IOPT-tools — Towards cloud design automation of digital controllers with Petri nets

Abstract: This paper describes the IOPT-Tools cloud-based tool-chain, offering a complete set of Petri net tools with a Web interface supporting digital controllers development. The tools include an interactive graphical Petri net editor, a model-checking subsystem composed of a state-space generator, state-space visualization and a query system, and automatic code generation tools that produce software “C” code or VHDL hardware descriptions ready to be deployed into implementation platforms. All interactive tools are executed directly in the user's Web Browser using AJAX principles, but file-storage and intensive processing operations are processed in the cloud. For example, state-space computation and the storage of the resulting data is performed in dedicated fast servers, minimizing network traffic and enabling the use of lightweight terminal equipment to access the tools, as simple as smart-phones or tablet computers. The tools are available on-line at http://gres.uninova.pt.

How to respond to process module failure in residency time-constrained single-arm cluster tools

Abstract: Cyclic scheduling and operation of a residency time- constrained single-arm cluster tool with failure-prone process modules are highly challenging. In some cases, when a fail- ure occurs, there still exists a feasible cyclic schedule for the performance-degraded tool. In other cases, such a schedule no longer exists. For the latter, it is highly desired to respond to a process module failure properly such that the tool can continue working and the wafers in the tool can be completed in a feasi- ble way. This work is the first one to study this important issue. The idea is to apply Petri nets to describe the dynamic behav- ior of a single-arm cluster tool. With the developed Petri net model, this paper formulates failure response policies to control the cluster tool such that it can keep working without violat- ing any residency time constraint. The failure response policies are implemented via efficient real-time control laws. Illustrative examples are presented to show their usage. Index Terms—Wafer fabrication, Cluster tools, Petri net, Scheduling, Failure response.

Toward the Minimal Universal Petri Net

Abstract: A universal Petri net with 14 places, 42 transitions, and 218 arcs was built in the class of deterministic inhibitor Petri nets (DIPNs); it is based on the minimal Turing machine (TM) of Woods and Neary with 6 states, 4 symbols, and 23 instructions, directly simulated by a Petri net. Several techniques were developed, including bi-tag system (BTS) construction on a DIPN, special encoding of TM tape by two stacks, and concise subnets that implement arithmetic encoding operations. The simulation using the BTS has cubic time and linear space complexity, while the resulting universal net runs in exponential time and quadratic space with respect to the target net transitions' firing sequence length. The technique is applicable for simulating any TM by the Petri net.

A Configurable State Class Method for Temporal Analysis of Time Petri Nets

Abstract: A task' s end-to-end delay in its execution is a key requirement to real-time systems. This paper presents a configurable state class method based on time Petri nets for their quantitative analysis. The proposed method has a flexible state class structure. A firing domain is separated into a kernel domain that supports the basic evolution of state classes, and a configurable domain that is used to evaluate end-to-end delays. Since both domains adopt a uniform representation for time constraints, end-to-end delays can be computed synchronously with the evolution of state classes via the same firing rules. Firing rules are decomposed into basic timing operations. This treatment not only makes the calculation of end-to-end delays more flexible, but also provides a scalable way to add new timing operations into a time Petri net model. The proposed method computes arbitrary end-to-end delays along a trace with time O(ml2) and space O(l2), where m is the number of firing transitions along the trace and l is the maximum number of transitions in configurable and kernel domains. Compared with the existing state class methods, it has better performance and flexibility in on-the-fly computation of end-to-end delays.

Verifying soundness of business processes: A decision process Petri nets approach

Abstract: This paper presents a trajectory-tracking approach for verifying soundness of workflow/Petri nets represented by a decision-process Petri net. Well-formed business processes correspond to sound workflow nets. The advantage of this approach is its ability to represent the dynamic behavior of the business process. We show that the problem of finding an optimum trajectory for validation of well-formed business processes is solvable. To prove our statement we use the Lyapunov stability theory to tackle the soundness verification problem for decision-process Petri nets. As a result, applying Lyapunov theory, the well-formed verification (soundness) property is solved showing that the workflow net representation using decision process Petri nets is uniformly practically stable. It is important to note that in a complexity-theoretic sense checking the soundness property is computationally tractable, we calculate the computational complexity for solving the problem. We show the connection between workflow nets and partially ordered decision-process Petri net used for business process representation and analysis. Our computational experiment of supply chains demonstrate the viability of the modeling and solution approaches for solving computer science problems.

Bridging the Gap Between Design and Implementation of Discrete-Event Controllers

Abstract: Extended labeled Petri nets (ELPNs), i.e., labeled Petri nets with inhibitor arcs, are usually used to model the desired closed-loop behavior of a controlled discrete-event system, and, as such, their states are formed with both the controller and the plant states. However, the control logic is based on the controller states only and the interaction between controller and plant is carried out through sensor readings from the plant and control actions (forced events) from the controller. This makes ELPN not suitable for modeling the controller. Control interpreted Petri nets (CIPNs), on the other hand, include control actions in the places and sensor readings in the transitions as part of their formal structure, and so provide a better formalism for controller modeling. In this paper, we propose a two-step approach to discrete-event controller implementation, as follows: (i) we first propose a set of transformation rules to convert the initial ELPN to an equivalent CIPN, therefore extracting the control logic from the desired closed-loop behavior and (ii) we present a straightforward systematic way to translate the CIPN into a ladder diagram. We apply the results presented here to the implementation of the automation system of a plastic molding machine.

Extending input-output place-transition Petri nets for distributed controller systems development

Abstract: Petri nets have been widely used in the design of embedded controllers, namely in electronic hardware and computing platforms design, as well as within automation application areas This paper presents updated characteristics of one class of Petri nets, named Input-Output Place-Transition Petri nets (IOPT nets), extended to support networked embedded controllers design and globally-asynchronous locally-synchronous (GALS) systems modeling, together with its associated metamodel and execution semantics The proposed meta-model is compliant with the Petri Net Markup Language (PNML) metamodel, augmented with the descriptions for inputs and outputs, as well as for time domains and communication channels The meta-model is described using UML class diagrams and has an equivalent Ecore meta-model that positioning IOPT nets within the Eclipse Modeling Framework (EMF)

Compositional Reachability in Petri Nets

Abstract: We introduce a divide-and-conquer algorithm for a modified version of the reachability/coverability problem in 1-bounded Petri nets that relies on the compositional algebra of nets with boundaries: we consider the algebraic decomposition of the net of interest as part of the input. We formally prove the correctness of the technique and contrast the performance of our implementation with state-of-the-art tools that exploit partial order reduction techniques on the global net.

Data Center Network Throughput Analysis Using Queueing Petri Nets

Abstract: In this paper, we contribute performance modeling and analysis approach in computer networks. We present a meta-model designed for the performance modeling of network infrastructures in modern data centers. Instances of our meta-model can be automatically transformed into stochastic simulation models for performance prediction. In this paper, we present a transformation to Queueing Petri Nets (QPNs). We show that despite the high level of abstraction of the QPN models, we are able to predict the utilization of resources with good accuracy within a short time.

Decomposition, validation and documentation of control process specification in form of a Petri net

Abstract: The article focuses on some aspects regarding logic controller design. Control process is formally specified using interpreted Petri nets. It is then formally verified against behavioral properties using model checking technique and temporal logic. Formal specification can also be documented as UML activity diagram. One can then benefit from advantages of both specification techniques - Petri nets with a wide range of mathematical support and user-friendly UML activity diagrams. An interpreted Petri net can also be decomposed into state machine components (SMCs), each of them to be implemented in a separate module of FPGA device.

Distributed Agent-Based Computing in Material-Embedded Sensor Network Systems With the Agent-on-Chip Architecture

Abstract: Distributed material-embedded systems like sensor networks integrated in sensorial materials require new data processing and communication architectures. Reliability and robustness of the entire heterogeneous environment in the presence of node, sensor, link, data processing, and communication failures must be offered, especially concerning limited service of material-embedded systems after manufacturing. In this paper, multiagent systems with state-based mobile agents are used for computing in unreliable mesh-like networks of nodes, usually consisting of a single microchip, introducing a novel design approach for reliable distributed and parallel data processing on embedded systems with static resources. An advanced high-level synthesis approach is used to map the agent behavior to multiagent systems implementable entirely on microchip-level supporting agent-on-chip (AoC) processing architectures. The agent behavior, interaction, and mobility are fully integrated on the microchip using a reconfigurable pipelined communicating process architecture implemented with finite-state machines and register-transfer logic. The agent processing architecture is related to Petri Net token processing. A reconfiguration mechanism of the agent processing system achieves some degree of agent adaptation and algorithmic selection. The agent behavior, interaction, and mobility features are modeled and specified with an activity-based agent behavior programming language. Agent interaction and communication is provided by a simple tuple-space database implemented on node level and signals providing remote inter-node level communication and interaction.

Hierarchy Modeling and Formal Verification of Emergency Treatment Processes

Abstract: Petri nets are suitable for modeling and analysis of business processes. However, the lack of data concepts often makes Petri-net-based models excessively large and difficult to analyze especially when process logic is sensitive to changes of process attribute values. Emergency treatment processes are a typical example of this situation. To solve the aforementioned problems, this paper proposes a new hierarchical Petri net model for modeling and verification of emergency treatment processes. The hierarchical Petri net model includes three separate but closely related models, i.e., a business process logic net, a business process semantic net, and a set of case models. Business process logic nets are used to model the task dependencies disregarding semantic information. Business process semantic nets introduce data concepts to business process logic nets to model semantic information such as process attributes or conditions of sequence flows. Case models are used to model the practical routes of specific business instances. Based on the three models, a formal verification algorithm of an emergency treatment process is presented. Finally, the hierarchical modeling and verification methods are validated by an emergency treatment process of highways under snow/ice weather conditions.

Distributed supervisor synthesis for automated manufacturing systems using Petri nets

Abstract: Due to the competition for limited resources by many concurrent processes in large scale automated manufacturing systems (AMS), one has to resolve a deadlock issue in order to reach their production goal without disruption and downtime. Monolithic resolution is a conventional approach for optimal or acceptable solutions, but suffers from computational difficulty. On the other hand, some decentralized methods are more powerful in finding approximate solutions, but most are application-dependent. By modeling AMS as Petri nets, we develop an innovative distributed control approach, which can create a trajectory leading to a desired destination and are adaptable to different kinds of constraints. Control strategies are applied to processes locally such that they can concurrently proceed efficiently. Global destinations are always reachable through the local observation upon processes without knowing external and extra information. Efficient algorithms are proposed to find such distributed controllers.

Propositional dynamic logic for Petri Nets

Abstract: Propositional Dynamic Logic (PDL) is a multi-modal logic used for specifying and reasoning on sequential programs. Petri Net is a widely used formalism to specify and to analyse concurrent programs with a very nice graphical representation. In this work, we propose a PDL to reasoning about Petri Nets. First we define a compositional encoding of Petri Nets from basic nets as terms. Second, we use these terms as PDL programs and provide a compositional semantics to PDL Formulas. Finally, we present an axiomatization and prove completeness w.r.t. our semantics. The advantage of our approach is that we can do reasoning about Petri Nets using our dynamic logic and we do not need to to translate it to other formalisms. Moreover our approach is compositional allowing for construction of complex nets using basic ones.

Application and Theory of Petri Nets and Concurrency

Abstract: In this lecture we first introduce supervisory control theory for discrete-event systems (DES) in a framework of finite automata and regular languages, with emphasis on the criteria of nonblocking and maximal permissiveness. Also stressed is the importance of control modularity and transparency. Turning to Petri Nets (PN), we indicate how the counterpart control design problem can be posed and (in many but not all cases) solved using integer linear programming. Finally we discuss the feasibility of a “DES transform” approach by which the PN problem is first converted to a DES problem, and the DES solution converted back to a PN implementation. Here we point out several interesting issues for further research.

Event‐driven model predictive control of timed hybrid Petri nets

Abstract: SUMMARY Hybrid Petri nets represent a powerful modeling formalism that offers the possibility of integrating, in a natural way, continuous and discrete dynamics in a single net model. Usual control approaches for hybrid nets can be divided into discrete-time and continuous-time approaches. Continuous-time approaches are usually more precise, but can be computationally prohibitive. Discrete-time approaches are less complex, but can entail mode-mismatch errors due to fixed time discretization. This work proposes an optimization-based event-driven control approach that applies on continuous time models and where the control actions change when discrete events occur. Such an approach is computationally feasible for systems of interest in practice and avoids mode-mismatch errors. In order to handle modelling errors and exogenous disturbances, the proposed approach is implemented in a closed-loop strategy based on event-driven model predictive control. Copyright © 2013 John Wiley & Sons, Ltd.

Petri net discovery of discrete event processes by computing t-invariants

Abstract: In this paper the problem of discovering a Petri net (PN) from sampled events sequences representing the execution of industrial or business processes is addressed A method for building a 1-bounded PN from a single event sequence S composed of numerous execution traces is presented; it is based on determining causal and concurrency relations between tasks. A technique for computing the t-invariants of the PN from S is proposed; the obtained invariants allow determining the structure of a PN that executes S. The algorithms derived from the method have been implemented and tested on numerous examples of diverse complexity.

Petri Nets to B-Language Transformation in Software Development

Abstract: Petri nets and B-Method represent a pair of formal methods, for computer systems engineering, with interesting complementary features. Petri nets have nice graphical representation, valuable analytical properties and can express concurrency. B- Method supports verified software development. To gain from these complements, a mapping from Petri nets to the language of B-Method has been defined and its correctness proved. This paper presents, by means of a case study, the usefulness of incorporation of Petri net designs in a software application developed by B-Method. Modifications of this mapping intended for the Event-B method and treatment of concurrency are also discussed.

Coloured stochastic Petri nets modelling for the reliability and maintenance analysis of multi-state multi-unit systems

Abstract: Purpose – The purpose of this paper is to introduce a method for modelling the multi-state repairable systems subject to stochastic degradation processes by using the coloured stochastic Petri nets (CSPN). The method is a compact and flexible Petri nets model for multi-state repairable systems and offers an alternative to the combinatory of Markov graphs. Design/methodology/approach – The method is grounded on specific theorems used to design an algorithm for systematic construction of multi-state repairable systems models, whatever is their size. Findings – Stop and constraint functions were derived from these theorems and allow to considering k-out-of-n structure systems and to identifying the minimal cut sets, useful to monitoring the states evolution of the system. Research limitations/implications – The properties of this model will be studied, and new investigations will help to demonstrate the feasibility of the approach in real world, and more complex structure will be considered. Practical implic...