基于自控网系统的混杂控制

混杂控制系统通常是复杂的非线性控制系统,难以用统一的模型进行建模. David和Alla提出的混杂Petri网,虽然可以解决一般混杂系统的建模问题,并得到了广泛的应用,但对于传统的如PID这类控制器,缺乏统一建模的能力.探讨了基于广义自控网系统的混杂控制方法,实现了对混杂控制器中监控器和数字控制器进行统一的Petri网建模.仿真实例设计了基于广义同步自控网系统的电加热炉控制系统,给出了可根据不同温度状态实施多种控制策略的变结构数字控制器模型,并详细分析了控制器的性能,证明了广义自控网系统具有十分强大的建模能力和广泛的应用前景.     

Decentralized supervisory controller design to avoid deadlock in Petri nets

A decentralized supervisory controller design approach, using overlapping decompositions, is proposed for discrete-event systems modelled by Petri nets to avoid deadlock. In this approach, the given original Petri net is first decomposed into overlapping Petri subnets. A controller for each disjoint Petri subnet is then designed. A controller for the expanded Petri net is next obtained by combining these controllers in a certain way. In the final phase, the controller obtained for the expanded Petri net is contracted in a certain way to obtain a controller for the original Petri net. It is proved that this final controller avoids deadlock in the original Petri net.     

A divide-and-conquer-method for the synthesis of liveness enforcing supervisors for flexible manufacturing systems

In this paper a divide-and-conquer-method for the synthesis of liveness enforcing supervisors (LES) for flexible manufacturing systems (FMS) is proposed. Given the Petri net model (PNM) of an FMS prone to deadlocks, it aims to synthesize a live controlled Petri net system. For complex systems, the use of reachability graph (RG) based deadlock prevention methods is a challenging problem, as the RG of a PNM easily becomes unmanageable. To obtain the LESs from a large PNM is usually intractable. In this paper, to ease this problem the PNM of a system is divided into small connected subnets. Each connected subnet prone to deadlocks is then used to compute the LES for the original PNM. Starting from the simplest subnet prone to deadlocks to make the subnet live, monitors (control places) are computed. The RG of each subnet is considered and split into a dead-zone (DZ) and a live-zone. All states in the DZ are prevented from being reached by means of a well-established invariant-based control method. Next, the computation of monitors is followed for bigger subnets. Previously computed monitors are included within the bigger subnets based on a criterion. This process keeps the DZ of the bigger subnets smaller compared with the original uncontrolled subnets. When all subnets are live we obtain a set of monitors that are included within the PNM to obtain a partially controlled PNM (pCPNM). A new set of monitors is also computed for the pCPNM. Finally, a live controlled Petri net system is obtained. The proposed method is generally applicable, easy to use, effective and straightforward although its off-line computation is of exponential complexity in theory. Its use for FMS control guarantees deadlock-free operation and high performance in terms of resource utilization and system throughput. Two FMS deadlock problems from the literature are used to illustrate the applicability and the effectiveness of the proposed method.     

基于Time Petri Nets的实时系统资源冲突检测

Time Petri Nets在实时系统的建模和性能分析中得到广泛应用,而冲突是Petri网及其扩展模型的重要行为,解决冲突是正确分析模型动态行为的关键.目前随机Petri网、混合Petri网和区间速率连续Petri网的冲突检测方法由于没有考虑到时间约束因此无法在TPN网中使用.时间约束的引入使得Time Petri Nets模型的使能和触发语义比Petri网模型的语义复杂,冲突检测变得更加困难.为了计算冲突发生的时间和概率,首先根据时间约束,给出了变迁持续使能时延迟区间的计算方法,并证明了该方法的合理性和完备性;然后在此基础上定义并证明了Time Petri Nets模型中不冲突的检测方法;并提出了Time Petri Nets模型的冲突检测方法,给出了冲突时间区间和变迁实施概率的计算方法;最后通过实例验证说明了该方法的正确性和有效性.     

Implementation of real-time distributed control for discrete event robotic systems using Petri nets

This article presents a systematic method of modeling and implementing real-time control for discrete-event robotic systems using Petri nets. Because, in complex robotic systems such as flexible manufacturing systems, the controllers are distributed according to their physical structure, it is desirable to realize real-time distributed control. In this article, the task specification of robotic processes is represented as a system control-level net. Then, based on the hierarchical approach, it is transformed into detailed subnets, which are decomposed and distributed into the local machine controllers. The implementation of real-time distributed control through communication between the system controller and the machine controllers on a microcomputer network is described for a sample robotic system. The proposed implementation method is sufficiently general, and can be used as an effective prototyping tool for consistent modeling, simulation, and real-time control of large and complex robotic systems.     

Hybrid Petri net based modeling for biological pathway simulation

Hybrid Petri net (HPN) is an extension of the Petri net formalism, which enables us to handle continuous information in addition to discrete information. Firstly, this paper demonstrates how biological pathways can be modeled by the integration of discrete and continuous elements, with an example of the λ phage genetic switch system including induction and retroregulation mechanisms. Although HPN allows intuitive modeling of biological pathways, some fundamental biological processes such as complex formation cannot be represented with HPN. Thus, this paper next provides the formal definition of hybrid functional Petri net with extension (HFPNe), which has high potential for modeling various kinds of biological processes. Cell Illustrator is a software tool developed on the basis of the definition of HFPNe. Hypothesis creation by Cell Illustrator is demonstrated with the example of the cyanobacterial circadian gene clock system. Finally, our ongoing tasks, which include the development of a computational platform for systems biology, are presented.     

基于变迁指标分解的Petri网性质分析

Petri网的分解技术是复杂网系统分析的一种重要手段,基于变迁指标的分解方法将系统分解为一组T-网。通过获得分解子网的结构性质以及子网与原网间的性质保持关系,得到了判定原网结构性质的一些方法和结论;同时给出了判定原网系统活性的一个条件。所得结果为结构复杂Petri网的性质分析提供了有效的方法。     

基于分层Petri网的半导体生产线建模

论文提出了一种分层Petri网模型用于半导体生产线建模。首先,总结了Petri网在半导体生产线建模中的应用,继而给出了分层Petri网的定义及其建模过程。最后以一个典型的半导体生产线为例,进行该方法的应用研究。     

COMPLEXITY REDUCTION FOR OPTIMIZATION OF DETERMINISTIC TIMED PETRI-NET SCHEDULING BY TRUNCATION

Methods of applying Petri nets to model and analyze scheduling problems, with constraints such as precedence relationships and multiple resource allocation, have been available in the literature. Searching for an optimum schedule can be implemented by combining the branch-and-bound technique with the execution of the timed Petri net. The resulting complexity problem in a large Petri net is handled by a truncation technique such that the original large Petri net is divided into several smaller subnets. The complexity involved in the analysis of each subnet individually is greatly reduced. However, as illustrated in this paper, the schedules for the subnets obtained by treating them separately may not lead to an optimal overall schedule for the original Petri net. To circumvent this problem, algorithms are developed that can be used to search for a proper schedule for each subnet such that the combination of these schedules yields an overall optimum schedule for the original timed Petri net. These algorithms are based on the idea of Petri net execution and branch-and-bound with modification. Finally, the practical application of the timed Petri net truncation technique to scheduling problems in manufacturing systems is illustrated by an example of multirobot task scheduling.     

混合Petri 网及其在混合系统中的应用探讨

针对混合系统的建模，提出一种混合Petri网(HPN)模型，并用数学语言严格地定义和描述与此Petri网有关的基本概念和一些性质。以一个生产系统为例，用Petri网来描述并分析此生产系统，并用VisObjNet软件包仿真此生产系统。     

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。     

Timed Petri Nets in Hybrid Systems: Stability and Supervisory Control

In this paper, timed Petri nets are used to model and control hybrid systems. Petri nets are used instead of finite automata primarily because of the advantages they offer in dealing with concurrency and complexity issues. A brief overview of existing results on hybrid systems that are based on Petri nets is first presented. A class of timed Petri nets named programmable timed Petri nets (PTPN) is then used to model hybrid systems. Using the PTPN, the stability and supervisory control of hybrid systems are addressed and efficient algorithms are introduced. In particular, we present sufficient conditions for the uniform ultimate boundness of hybrid systems composed of multiple linear time invariant plants which are switched between using a logical rule described by a Petri net. This paper also examines the supervisory control of a hybrid system in which the continuous state is transfered to a region of the state space in a way that respects safety specifications on the plant's discrete and continuous dynamics.     

面向原油库存管理过程的Petri网建模

石油化工工业属于典型的连续型生产工业,但在连续生产过程中又包含有离散变量, 具有明显的混杂动态系统特征.对于这样的混杂动态系统,混合Petri网是一种有效的建模方法.文章在已有的混合Petri网结构基础上,在离散变迁激发规则中加入了逻辑控制条件,并对原油库存管理过程这一兼有连续时间特性和离散事件特性的混合动态系统进行建模,并通过建模实例验证了其有效性和灵活性,从而为解决原油库存问题提供了具有参考价值的方法.     

基于时序Petri网的火电厂管控信息系统模型研究

为了优化火电厂管控信息系统,提出了基于时序Petri网的火电厂管控信息系统模型研究.首先提出了时序Petri网的分层建模方法,并给出了时序Petri网对复杂系统的建模步骤;其次,建立了整个火电厂管控信息系统的时序Petri网模型;再次,为了更好地分析和优化Petri网模型,对其进行了简化;最后,证明了简化后的时序Petri网大大减少了库所和变迁的数量并保持了原网的功能性.     

基于Petri网的超媒体模型HPN

本文提出了一个基于Ｐｅｔｒｉ网的超媒体形式化模型ＨＰＮ。它采用层次组织,各层由一个扩展Ｐｅｔｒｉ网、若干对象以及Ｐｅｔｒｉ网与对象之间的映射表示,通过Ｐｅｔｒｉ网结构和执行语义说明超媒体的连接机制、浏览和媒体表现,具有刻画超媒体主要性质的能力。文中给出了ＨＰＮ模型的模式化定义并举说明其用途。     

基于等级PRES+的嵌入式系统的建模与实现

为了有效的描绘规模较大的系统,需要一个分层机制,使模型可以有条理地构建.它由简单的单元组件构成,使得设计师在每个描述级上都可以很容易理解.提出并定义了用于形式化描述嵌入式系统建模的petri网的分层概念,显示了一个规模较大系统中的小部件如何使用层次的概念进行转换.该方法使得复杂的嵌入式系统描述更加模块化,具有可重用性,提高了嵌入式系统建模和分析的效率.通过一个实例表明了该方法的可行性.     

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.     

层次建模分析方法在C4ISR系统中的应用

C4ISR系统是一个规模庞大、层次分明的离散动态系统。文章提出了一种面向C4ISR系统的UML和Petri网结合的建模分析方法。该方法采用从上到下的层次分析方法。用扩展的UML模型对系统组织结构和系统的静态特征进行描述，用扩展的Petri网模型描述和分析系统动态特性，通过相应的规则将Petri网模型转化成状态图和序列图。新方法可以对系统要求进行验证，同时还可以编程实现。最后通过该方法，对一个C4ISR系统进行了建模分析。