A re-configurable multi-agent system architecture for error recovery in production systems

Multi-agent systems for manufacturing systems appear to provide adequate response to abrupt disturbances on the shop floor. To date, most of the work has been focused on planning and scheduling but very little work has been done on issues pertaining to monitoring, diagnostics and error recovery. Our approach addresses the issue of combining the discipline of hierarchical systems with the agility of multi-agent systems. Within the context of a hierarchy, the focus is on the workstation level and, in particular, the construction of a re-configurable system having production agents, error recovery agents, and a mediator agent structure connecting production and recovery agent hierarchies. In addition, the relationship to a multi-level, multi-layer hierarchy control is established. This latter hierarchy, based on Petri Net constructs, serves, in one sense, as a retrieval based resource for process planning and generation of recovery plans for production and recovery agents within the proposed multi-agent system. An objective of this effort is to provide a test-bed for comparison of hierarchical systems, heterarchical, and a hybrid combination which is the focus of the investigation presented here.     

Modular Petri Net based modeling,analysis, synthesis and performance evaluation of random topology dedicated production systems

Ordinary t-timed modular Petri Nets are used for modeling, analysis, synthesis and performance evaluation of random topology dedicated production systems. Each system is first decomposed into production line, assembly, disassembly and parallel machine modules followed by derivation of their modular Petri Net models. Two sets of modules, generic and generalized respectively, are derived corresponding to the simplest and most general cases. Overall system Petri Net model is obtained via synthesis of the individual modules satisfying system features (production rates, buffer capacities, machine expected up, down or idle times). Detailed mathematical expressions are derived for modules P-invariants (and T-invariants when exist); they are further generalized for a random topology and complexity dedicated production system. Total number of the individual Petri Net module nodes as well as of the combined system Petri Net model is also calculated. Results show the applicability of the proposed methodology and justify its modeling power and generality.     

Petri net control of an automated manufacturing cell

This paper discusses the Petri Net approach to real time production control. Petri nets were developed to model concurrent and asynchronous systems. Having modeled a machining cell or a production system as a Petri net, one can analyze the effects of controller behavior on the system before implementing the controller.

Petri net principles are illustrated for a machining cell being implemented in the Manufacturing Automation Laboratory at Rutgers University. Observations are made concerning the difference between a Petri Net Controller and a Programmable Logic Controller for the same application.     

基于ExSpect的维修保障联邦成员开发

分析了ExSpect的建模方法和软件接口,建立了基于ExSpect的维修保障仿真模型。开发了仿真对象模型（SOM）,并对其信息接口进行了改造,从而实现了Petri网仿真模型与RTI运行支撑环境的无缝连接,为后续开发高层体系结构（HLA）环境下的Petri网仿真模型集成环境进行了初步的探索工作。     

Fault-tolerant deadlock avoidance algorithm for assembly processes

Unreliable resources pose challenges in design of deadlock avoidance algorithms as resources failures have negative impacts on scheduled production activities and may bring the system to dead states or deadlocks. This paper focuses on the development of a suboptimal polynomial complexity deadlock avoidance algorithm that can operate in the presence of unreliable resources for assembly processes. We formulate a fault-tolerant deadlock avoidance controller synthesis problem for assembly processes based on controlled assembly Petri net (CAPN), a class of Petri nets (PNs) that can model such characteristics as multiple resources and subassembly parts requirement in assembly production processes. The proposed fault-tolerant deadlock avoidance algorithm consists of a nominal algorithm to avoid deadlocks for nominal system state and an exception handling algorithm to deal with resources failures. We analyze the fault-tolerant property of the nominal deadlock avoidance algorithm based on resource unavailability models. Resource unavailability is modeled as loss of tokens in nominal Petri Net models to model unavailability of resources in the course of time-consuming recovery procedures. We define three types of token loss to model 1) resource failures in a single operation, 2) resource failures in multiple operations of a production process and 3) resource failures in multiple operations of multiple production processes. For each type of token loss, we establish sufficient conditions that guarantee the liveness of a CAPN after some tokens are removed. An algorithm is proposed to conduct feasibility analysis by searching for recovery control sequences and to keep as many types of production processes as possible continue production so that the impacts on existing production activities can be reduced.     

基于Petri网的Stateflow建模方法的研究与应用

以输送机器人生产线控制系统设计为例,提出将基于Petri网的Stateflow建模仿真方法应用于PLC控制软件的开发过程中。首先利用Petri网对系统控制功能进行分析,结果表明系统在运行时序上存在并行冲突,采用Petri网的数学建模功能协调冲突后,通过可达图验证了此Petri网模型是安全无死锁的;其次在上述基础上将Petri网与Stateflow组成元素相对应并进行转换;最后利用Simulink构建模型进行系统仿真分析,证明输送机器人生产线控制逻辑正确,状态转移有效。     

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.     

资源配置混杂Petri网的混杂系统生产过程动态调度

为了增强混杂生产过程应对突发事件的能力,以一种新的混杂Petri网(资源配置混杂Petri网)为研究模型,给出了相应的使能和激发规则.并在资源配置混杂Petri网建立的仿真模型的基础上,融入事件逻辑网和逻辑规划,提出一种适用于混杂系统动态生产调度建模和优化的方法.以典型的混杂生产过程为例,研究混杂系统生产过程建模及优化.研究结果表明,资源配置混杂Petri网模型描述能力强,能够有效描述混杂系统生产过程,所提出的动态调度方案切实有效.     

一种基于代数语义的软件体系结构求精方法

软件体系结构是引导需求到实现的桥梁,目前在软件体系结构建模方法中主要分为形式化和非形式化两种。针对大型分布式系统的体系结构采用Petri网进行建模,兼顾了可视化操作和形式化的准确性,同时利用细化求精操作建立体系结构的层次模型,有效解决了状态空间爆炸问题。此外,在求精过程中为了保证用于下层求精的子网能准确表达上层行为规约,引入了进程代数来刻画Petri网的行为语义。最后,给出了进程项构造子网的算法及案例研究,并通过开源工具验证上述内容的正确性。     

Petri网到VHDL的翻译器设计与实现

研究了如何用CONPAR语言对Petri网图形进行描述,来获得Petri网模型对应的等效文本文件;然后设计了由Petri网文本文件到VHDL转换的文法规则及对应的语义动作源文件,并由编译工具YACC自动生成Petri网到VHDL转换的语法分析器;语法分析生成的中间代码是一棵抽象语法树,可以自顶向下遍历此抽象语法树,并按照相应的语义规则,通过比较Petri网文本描述和VHDL代码的差别生成VHDL目标代码;由此实现了Petri网到VHDL的翻译器,为基于Petri网的并行控制器的自动硬件实现提供了一种快速有效的方法。     

基于Petri网的ASIP体系结构形式化建模方法研究

根据SOC（System on chip）的软硬件协同设计的需求．针对ASIP体系结构空间搜索（DSE，Design Space Exploration）问题，考虑复杂的流水线结构，提出了一种扩展的时序Petri网模型——PNP模型，该模型可以以简洁直观的形式精确有效地描述目标体系结构．文中给出了PNP模型的确切定义，并通过对一个流水化的体系结构进行形式化建模的实例展示了该模型的有效性．     

面向对象的Petri网方法及其在软件工程中的应用

本文介绍了面向对象Ｐｅｔｒｉ网方法，给出了ＯＯＰＮ的基本定义和图形表示，讨论了ＯＯＰＮ的特性和子网细化方法。     

一种基于执行力模型的服务平台自主控制方法

开放的分布式服务平台倾向于涵盖更丰富的管理功能,支持更强的分散交互性,从而导致软件管理和维护的难度和成本问题日益突出.为此,引入一种自管理的服务平台体系结构参考模型,以构件作为功能实现载体,服务作为功能组织手段,交互作为功能扩展方式.提出了一种基于分层反馈的自主控制架构,以服务构件及相互之间的交互关系为控制对象,执行力模型为决策基础.在管理服务的可用性和性能建模中运用了马尔可夫过程、随机Petri网和排队网模型理论,并考虑了链路和节点的失效修复机制.仿真结果表明,基于排队Petri网的执行力模型能够反映失效率和修复时间对服务平台性能和可用性的影响,并验证了自主控制方法对提高服务平台有效性的积极作用.     

Development of context-aware workflow systems based on Petri Net Markup Language

The Petri Net Markup Language (PNML) is originally an XML-based interchange format for Petri nets. Individual companies may specify their process models in Petri nets and exchange the Petri nets with other companies in PNML. This paper aims to demonstrate the capabilities of PNML in the development of applications instead of an industrial interchange format only. In this paper, we apply PNML to develop context-aware workflow systems. In existing literature, different methodologies for the design of context-aware systems have been proposed. However, workflow models have not been considered in these methodologies. Our interests in this paper are to propose a methodology to automatically generate context-aware action lists for users and effectively control resource allocation based on the state of the workflow systems. To achieve these objectives, we first propose Petri net models to describe the workflows. Next, we propose models to capture resource activities. Finally, the interactions between workflows and resources are combined to obtain a model for the whole processes. Based on the combined model, we propose architecture to automatically generate context-aware graphical user interface to guide the users and control resource allocation in workflow systems. We demonstrate our design methodology using a health care example.     

一类受控Petri网的反馈控制

受控Petri网是离散事件动态系统(DEDS)的一种控制理论模型.通过模型来研究实现 禁止状态避免的最大允许反馈控制是DEDS控制理论中的一个重要课题.文中对受控Petri网 的一个子类(非受控变迁子集的外延子网为TC网)讨论控制综合问题,给出求这类受控网中实 现禁止状态避免的最大允许反馈控制的一个算法.     

基于Petri网的飞行数据智能处理

现有的飞行数据处理专家系统多以产生式规则而构建,随之带来的问题是当规则之间存在多层嵌套的复杂逻辑关系时,知识表达不易完备并极易导致推理错误.为此,以识别飞机起飞状态为例,深入研究了基于Petri网的飞行数据智能处理的知识表示和推理方法,并采用Visual C 语言编制了一种实用的飞行数据快速处理专家系统.对多架次实际飞行数据的处理结果表明,基于Petri网的飞行数据智能处理方法能很好地满足飞行数据处理准确性和快速性的要求.该文对研究飞行数据的并行智能处理方法有一定的参考价值.     

Petri网共享T型子网合成结构性质分析及其应用

为了解决系统设计中的子系统共享问题,提出了经由Petri网共享T-型子网构成共享T-型子网合成网的解决方案;研究了共享T-型子网合成网的结构性质,提出了共享T-型子网合成网保持结构有界性、守恒性、可重复性、相容性、P-不变量、T-不变量、公平性和结构活性的充分条件或充要条件;特别在证明结构活性保持性的过程中,体现了Petri网层次化的描述方法。本文的结果可为Petri网系统合成性质的考察提供有效途径,为复杂大系统的分析提供重要手段,并特别适合于一类系统的设计和分析,具有一定的实用价值。     

Petri网用于煤矿绞车调压调速系统的故障诊断

应用Petri网对系统逻辑关系进行建模,并利用其可达性概念和状态方程来解决煤矿绞车调压调速系统的故障检测与诊断问题,方法简单易于。     

Petri网在煤矿绞车调压调速系统故障诊断中的应用

应用Petri网对系统逻辑关系进行建模 ,并利用其可达性概念和状态方程来解决煤矿绞车调压调速系统的故障检测与诊断问题 ,方法简单易行。     

Self-adapting recovery nets for policy-driven exception handling in business processes

In this paper, we propose Self-Adapting Recovery Net (SARN), an extended Petri net model, for specifying exceptional behavior in business processes. SARN adapts the structure of the underlying Petri net at run time to handle exceptions while keeping the Petri net design easy. The proposed framework caters for the specification of high-level recovery policies that are incorporated either with a single task or a set of tasks, called a Recovery Region. These recovery policies are generic directives that model exceptions at design time together with a set of primitive operations used at run time to handle the occurrence of exceptions. We identified a set of recovery policies that are useful and commonly needed in many practical situations. A tool has been developed to illustrate the viability of the proposed exception handling technique. B. Medjahed’s work is supported by a grant from the University of Michigan’s OVPR.