时间Petri网在即时检验流程建模中的应用

针对即时检验系统的设计与开发建模问题,提出一种基于时间Petri网的并发系统建模分析方法,为即时检验流程设计建立较为准确的信息化模型。通过将活动持续时间概念引入Petri网模型中,提出了适用于即时检验系统建模的时间Petri网建模方法,并设计了嵌入Petri网模型中的调度仿真器协助分析、优化即时检验控制过程。仿真实验结果表明所提出的时间Petri网建模方法在可达节点和运行时间等方面能够满足并行多类别即时检验调度与控制系统的流程建模实际需要,为流程仿真和分析提供有力工具,从而辅助系统设计者对即时检验系统进行优化。     

微流程的建模与分析

业务流程管理技术是组织实施信息系统的重要使能技术.为确保微流程能正常运行,提出了一种建模与分析微流程的方法.首先,该方法以Petri网为形式化基础,对微流程以及微流程间的同步组合和异步组合进行建模.其次,基于Petri网的分析技术,该方法对组合微流程进行了合理性分析.实验结果表明,该方法能建模微流程,并检测出组合微流程...     

基于Petri网的海关业务流程工作流模型设计

现在人们大多都用Petri网进行工作流建模,但是传统Petri网的柔性和结构性不好,它会使图形变得庞大复杂难以理解.在时间Petri网的基础上引入了资源/变迁Petri网.这里通过对基于Petri网的海关业务流程工作流模型的实例分析可知,通过调整工作流程,最终可以得出优秀的工作流模型来优化工作流程、提高企业运行效率、增强企业竞争力,而且该建模方式也为设计与开发高可靠性、柔性和适用性的工作流模型提供很好的依据.     

基于Petri网的流程间元素映射方法

对流程进行比较,在业务流程管理中有着重要的应用价值,可用于流程版本控制、流程相似度计算、流程合并等应用场景当中.流程间的元素映射是流程比较的首要步骤.现有的流程比较方法仅考察了流程任务活动的映射,忽略了流程中其他元素的对应关系,进而无法保障流程比较结果的可靠性.为此,提出一种基于Petri网的流程间元素映射模型,侧重描述了库所映射时所需要满足的上下文环境;随后,在此基础上提出了基于上下文环境的流程间库所映射算法.对于任意给定的两个Petri网建模的流程模型,该算法通过双边和单边映射的策略,优先选择上下文环境相似程度最高的库所作为对应库所返回.大量基于真实数据集的实验展示了该方法在库所映射方面的有效性,也展示了其用于流程相似度计算方面的高效性.     

基于Petri网的非集中式电子商务平台建模与仿真

随着Internet的普及和网络安全性的提高,电子商务得到了迅速的发展.为了更好地满足网络环境下电子交易发展的需求,详细分析了电子商务的业务流程,设计了一个具有交易约束机制的电子商务系统框架.首先,基于Petri网这一建模分析工具,建立了电子商务系统业务流程的Petri模型,并设计了有界Petri网可达树生成算法,用于分析所设计的电子商务系统Petri网模型的性质;然后,运用Petri网系统动态仿真工具--CPNTools,对所设计的电子商务系统模型进行了仿真运行,并分析了实验结果.从静态和动态两个方面检验了所设计的电子商务平台框架的可行性,该框架可以用来指导下一步的系统开发工作.     

基于有限容量库所的离散事件系统的Petri网控制器综合——第1部分

针对由Petri网建模的离散事件系统, 提出了一种新的控制器设计方法. 控制器是基于有限容量库所的概念构造而成的, 并使被控对象在给定的一组线性不等式约束下运行, 而给定的线性不等式约束是定义在库所标识上的. 控制器的综合利用了有限容量库所Petri网转换为 (普通 )无限容量库所Petri网的技术. 针对约束的不同情况, 给出了相应的Petri网的控制器的设计方法.     

基于Petri网的办公自动化系统设计

在明确办公自动化系统重要性的基础上,分析办公自动化系统的体系结构、公文处理流程以及模块设计,提出基于Petri网的工作流过程建模、基于工作流技术的办公自动化系统结构模型.     

一类活性Petri网控制器的冗余检测及结构简化

S4R(systems of sequential systems with shared resources)网是分析和解决柔性制造系统死锁现象常用的一种重要的Petri网子类模型,现有的基于S4R网的死锁预防方法通常采用对部分或者全部严格极小信标添加控制库所来实现.此类方法的不足在于得到的活性S4R控制器中往往存在冗余控制库所.针对已为网中每一个严格极小信标都逐一添加了控制库所和相关连接弧的活性S4R控制器,本文提出并设计了一种基于整数规划技术的冗余检测及结构简化方法,由此得到结构更简单、行为允许度更高的活性S4R控制器.该方法的核心思想是:如果网中已经存在一个p-不变式使得某个严格极小信标满足最大受控条件,那么为该严格极小信标添加的控制库所就是冗余的.由于该方法无需进行Petri网的可达性分析,避免了状态组合爆炸问题,因此具有较高的可行性和计算效率.最后用实验验证了本文方法的正确性和有效性.     

一类Petri网及其在离散事件系统的仿真与控制中的应用

设计和实现了一类Petri网--控制Petri网,基于控制Petri网,给出了离散事件系统的仿真与控制的算法和离散事件系统控制的实现方案,最后以柔性机床为例,演示了基于控制Petri网的离散事件系统的仿真与控制过程.结果表明,使用控制Petri网可以有效地模拟和控制离散事件系统.     

改进的面向对象Petri网及其应用研究

在面向对象Petri网建模的基础上,在对象内部引入了一个特殊的变迁--控制变迁,在各对象之间引入了控制器,提出了一种基于控制结构的面向对象Petri网(CS-OOPN)模型,并阐述了CS-OOPN建模的步骤.该模型克服了传统的面向对象Petri网建模缺乏流程柔性和系统灵活性的缺点,能更加直观、灵活地描述工作流程.最后通过利用该模型为某集团公司设备采购管理系统建模,以审批部门的CS-OOPN模型为例,求其关联矩阵、可覆盖性树和P不变量,并进行相关性分析,结果表明了CS-OOPN的有效性和强大的建模能力.     

Knowledge intensive Petri net framework for concurrent intelligent design of automatic assembly systems

The integration of design and planning of flexible assembly system has been recognized as a tool for achieving efficient assembly in a production environment that demands assembly with a high degree of flexibility. This paper proposes a concurrent intelligent approach and framework for the design of robotic flexible assembly systems. The principle of the proposed approach is based on the knowledge Petri net formalisms, incorporating Petri nets with more general problem-solving strategies in AI using knowledge-based system techniques. The complex assembly systems are modeled and analyzed by adopting a formal representation of the system dynamic behaviors through knowledge Petri net modeling from the specifications and the analysis of those models. A template is first defined for a knowledge Petri net model, and then the models for assembly system individuals are established in the form of instances of the template. The design of assembly systems is implemented through a knowledge Petri net-based function–behavior–structure model. The research results show that the proposed knowledge Petri net approach is applicable for design, simulation, analysis and evaluation, and even layout optimization of the flexible assembly system in an integrated intelligent environment. The integration of assembly design and planning process can help reduce the development time of assembly systems.     

Petri net modules in the transformation-based component framework

Component-based software engineering needs to be backed by thorough formal concepts and modeling techniques. This paper combines two concepts introduced independently by the two authors in previous papers. On one hand, the concept of Petri net modules introduced at IDPT 2002 in Padberg [J. Padberg, Petri net modules, Journal on Integrated Design and Process Technology 6 (4) (2002) 105–120], and on the other hand a generic component framework for system modeling introduced at FASE 2002 in Ehrig et al. [H. Ehrig, F. Orejas, B. Braatz, M. Klein, M. Piirainen, A generic component concept for system modeling, in: Proceedings of FASE ’02, Lecture Notes in Computer Science, vol. 2306, Springer, 2002]. First we develop a categorical formalization of the transformation based approach to components that is based on pushouts. This is the frame in which we show that Petri net modules can be considered as an instantiation of the generic component framework. This allows applying the transformation based semantics and compositionality result of the generic framework to Petri net modules. In addition to general Petri net modules we introduce Petri net modules preserving safety properties which can be considered as another instantiation of pushout based formalization of the generic framework.     

An interactive tool for design,simulation, verification,and synthesis of protocols

We have developed a user-friendly CAD graphical tool for the design, verification, simulation, and synthesis of protocols based on an interactive tool for Petri net and state diagram designs. Special features of this tool are: the capability of modeling both control and data flows, reduction and analysis, simulation of network behavior and performance, coding (parametrized protocols and automatic implementation), synthesis (two party protocol and ordinary Petri nets), animation and flexible design. Since it is Petri-net based, it allows simulation during all design phases and has extensive applications such as parallel debugging and simulation, expert systems, etc. Future enhancements of this tool are also discussed.     

A knowledge intensive multi-agent framework for cooperative/collaborative design modeling and decision support of assemblies

Multi-agent modeling has emerged as a promising discipline for dealing with decision making process in distributed information system applications. One of such applications is the modeling of distributed design or manufacturing processes which can link up various designs or manufacturing processes to form a virtual consortium on a global basis. This paper proposes a novel knowledge intensive multi-agent cooperative/collaborative framework for concurrent intelligent design and assembly planning, which integrates product design, design for assembly, assembly planning, assembly system design, and assembly simulation subjected to econo-technical evaluations. An AI protocol based method is proposed to facilitate the integration of intelligent agents for assembly design, planning, evaluation and simulation process. A unified class of knowledge intensive Petri nets is defined using the O-O knowledge-based Petri net approach and used as an AI protocol for handling both the integration and the negotiation problems among multi-agents. The detailed cooperative/collaborative mechanism and algorithms are given based on the knowledge objects cooperation formalisms. As such, the assembly-oriented design system can easily be implemented under the multi-agent-based knowledge-intensive Petri net framework with concurrent integration of multiple cooperative knowledge sources and software. Thus, product design and assembly planning can be carried out simultaneously and intelligently in an entirely computer-aided concurrent design and assembly planning system.     

基于变迁覆盖的制造系统死锁控制策略

基于系统Petri网模型,研究柔性制造系统的死锁控制问题.论文利用变迁覆盖为系统设计活性控制器.变迁覆盖是由一组极大完备资源变迁回路组成的集合,其变迁集覆盖了Petri网中所有极大完备资源变迁回路的变迁集.验证变迁覆盖的有效性,然后仅对有效变迁覆盖中的极大完备资源变迁回路添加控制位置,就得到系统的活性受控Petri网.这种受控Petri网包含的控制位置个数少,从而结构相对简单.最后通过一个例子说明了所提出的死锁控制策略的构成与特点.     

Synthesis a Petri net based control model for a FMS cell

Petri nets have been recognised as a high level formal and graphical specification language for modelling, analysis, and control of concurrent asynchronous distributed systems. This paper presents a PN model, synthesised by an extended version of the knitting synthesis technique. This method, as an incremental design approach, establishes the conditions under which the fundamental behavioural properties of the synthesised systems are fulfilled and preserved. That is, the synthesised models are live, bounded, and reversible (cyclic). A Petri net with the aforementioned properties is called a well-behaved Petri net system which is guaranteed to operate in a deadlock-free, stable, and cyclic fashion. Well-behaved Petri net models, synthesised using the proposed method can be compiled into control codes and implemented as real-time controllers for flexible manufacturing systems. The significance of this paper is due to the application of an extended version of knitting synthesis technique to a real life example of a flexible manufacturing system.     

On systematic methods to remove redundant monitors from liveness-enforcing net supervisors

Petri nets based deadlock prevention for flexible manufacturing systems has received much attention over the past decade, primarily due to the seminal work of Ezpeleta et al. in 1995. A Petri net based deadlock prevention mechanism is usually implemented by adding monitors or control places to a plant Petri net model such that liveness can be enforced. The significance of this methodology lies in that both a plant model and its supervisor are in a same formalism-Petri nets. Due to the inherent complexity of Petri nets, in theory, the number of additional monitors that have to been added to achieve liveness-enforcement purpose for an uncontrolled plant model is exponential with respect to the size of the model. This paper first proposes a systematic method to minimize the number of additional monitors in a liveness-enforcing Petri net supervisor such that the resultant net system has the same permissive behavior while liveness can still be preserved. Furthermore, for the liveness-enforcing Petri net supervisors of flexible manufacturing systems, which have some particular property, an algorithm is developed such that more permissive liveness-enforcing Petri net supervisors can be obtained after liveness-restrictive monitor removal. Compared with the existing techniques of eliminating redundant monitors in the literature, the complete state enumeration of a supervisor is avoided, which implies the high computational efficiency of the methods in this paper. Flexible manufacturing examples are used to demonstrate the proposed approaches.     

含过程和控制库所的层次化Petri网模型及应用

引入一种含过程和控制库所的Petri网模型,增强了Petri网的表述能力,扩展了Petri网的应用范围,并以铁路车站信号联锁逻辑中的进路控制为背景,较详细地给出了该类Petri网模型的实际应用。     

Modeling and control of workstation level information flow in FMS using modified Petri nets

A flexible manufacturing system (FMS) has a traditional structure of three levels: cell, workstation, and equipment. The workstation level plays an important role in the overall performance of the FMS. This paper focuses on modeling and control of the FMS workstation level information flow. In order to have a unified workstation level system structure, front-end interfaces are introduced as a standard communication medium between the workstation level and the equipment level. A detailed information flow analysis is then carried out on the workstation level. For modeling purposes, a modified Petri net is proposed with its increased modeling capability over an ordinary Petri net. It associates data structures with places and programs with transitions. Finally, the modified Petri net is used to model and control the FMS workstation level information flow. The designed control system has been implemented in a real manufacturing factory with satisfactory performance.     

Suboptimal time management of discrete event systems with uncontrollable events modeled by Petri nets

Preventing systems from entering to forbidden states is a crucial issue in discrete event systems control. Adding supervisors to the system is a common method to avoid entering to forbidden states. In discrete event systems modeled by Petri net adding a supervisor could be done by means of control places. Since, the time is not considered in designing this supervisor, in presence of uncontrollable transitions adding control places can lead to increase the operation time of the system modeled by timed Petri net. Because, the firing of some transitions is prevented when it is not necessary. So, to design a more efficient controller, we will be required to use time information of the system component. Therefore, in this paper, a method for optimizing the time behavior of a supervised timed Petri net will be proposed. To obtain an efficient operation, some timed places as timer will be added to the net. The time of this timer places is calculated to permit firing of some controllable transitions in order to enter into some weakly forbidden states while entering to forbidden states is prevented. This concept leads to increase the speed of system as well as obtain an acceptable operation. This method can be applied for all systems modeled by Petri nets. The efficiency of proposed approach will be discussed and validated with a case study.