Discrete event control system design using automation Petri nets and their ladder diagram implementation

As automated manufacturing systems become more complex, the need for an effective design tool to produce both high-level discrete event control systems (DECS) and low-level implementations becomes more important. Petri nets represent the most effective method for both the design and implementation of DECSs. In this paper, automation Petri nets (APN) are introduced to provide a new method for the design and implementation of DECSs. The APN is particularly well suited to multiproduct systems and provides a more effective solution than Grafcet in this context. Since ordinary Petri nets do not deal with sensors and actuators of DECSs, the Petri net concepts are extended, by including actions and sensor readings as formal structures within the APN. Moreover, enabling and inhibitor arcs, which can enable or disable transitions through the use of leading-edge, falling-edge and level of markings, are also introduced. In this paper, the methodology is explained by considering a fundamental APN structure. The conversion of APNs into the IEC1131-3 ladder diagrams (LD) for implementation on a PLC is also explained by using the token passing logic (TPL) concept. Finally, an illustrative example of how APNs can be applied to a discrete manufacturing problem is described in detail.     

业务过程模型的Petri网形式化检查方法

为解决企业间业务协同模型形式化检查的问题,将采用标准业务过程建模符号的业务模型转换为Petri网,构造出一种可建模企业问复杂业务协同的业务过程流网.采用过程定义可扩展标记语言2.1版本,开发了一种具有通用性的业务过程模型转换和检查工具.采用业务过程流网对供应链中企业间采购订单过程进行了建模.实验结果表明,业务过程流网能将符合过程定义町扩展标记语占规范的业务模型完整地转换为Petri网,得到的Petri网易于化简和分析.     

An improved evaluation of ladder logic diagrams and Petri nets for the sequence controller design in manufacturing systems

Substrate design is one of the major tasks involved in packaging design. In current business practice, the circuits of a substrate design are mostly designed by professional designers and produced by suppliers. Due to manufacturing limitations, some features of the circuit need to be modified before manufacturing. The original design and the modified design must be compared in order to ensure the desired functions. However, the circuits of a substrate design are highly complex and embedded in several physical layers. This makes the comparison task difficult, even for experienced individuals.The aim of this research is to develop an effective computer-aided inspection approach to decrease the design cost and lead time for substrate design. Three procedures and a knowledge base are developed to identify, categorise, and compare the information extracted from a substrate design drawing. First a feature extraction procedure was developed to search the related information in the data exchange format (DXF) file. Important features such as width and position of traces and vias are extracted from the original and modified designs of a substrate and are classified into three categories. The proposed feature comparison procedure is then used to compare the classified features with the assistance of a pre-defined knowledge base. Finally, the difference between the original and modified designs is marked with diverse colours and restored in a new DXF file.     

梯形图设计软件的重构技术

为解决梯形图（LD）设计过程中大量复用片段引起的设计繁琐等问题,提出了将重构技术应用于梯形图设计软件中的相关理论研究和实现。该理论包含梯形图构件模型和构件重构模型,着重探讨了构件组装方式和构件间结构关系,最终实现了梯形图程序设计的动态可重构。实验结果表明,该设计软件可有效地提高梯形图设计效率,优化内存利用率,并且具有广泛的通用性和适应性。     

Petri网在制造系统建模与仿真中的应用

介绍制造系统的概念以及制造系统建模与仿真的目的和意义,阐述Petri网的内涵,同时引出面向对象的Petri网的定义.依据面向对象的Petri网的理论,给出制造系统的建模过程,最后将统一建模语言(UML)融入到制造系统的建模与仿真中,通过实例进一步阐明了Petri网在制造系统建模与仿真中的应用.     

基于过程控制网的协同设计建模与分析

为解决协同设计中多任务实例并发执行,以及设计过程动态控制的可视化与形式化问题,提出了协同设计全过程的概念及其形式化方法——过程控制网。协同设计全过程由设计对象、设计阶段和过程转移机制组成。过程控制网是在面向对象Petri网的基础上,通过扩展其变迁的语义得到。设计对象建模为托肯,过程转移建模为过程网,各设计阶段建模为单元网,过程网和单元网通过特定的变迁进行交互。最后,给出了协同设计全过程的过程控制网模型的运行实例。多实例并行执行所产生的变迁序列表明,该模型不仅胜任动态设计过程的控制,而且允许多个任务按照不同的过程定义同时执行。     

微粒群算法在模糊Petri网参数优化中的应用

模糊产生式规则的置信度的获得大多依赖专家的经验,使得基于模糊产生式规则的模糊Petri网参数难以获得.将微粒群算法引入到模糊Petri网的置信度寻优过程,提出一种基于改进的微粒群算法的参数优化策略,该算法对初始输入无严格要求,求解速度快、精度较高,提高了模糊Petri网的泛化能力,降低了对专家经验的依赖程度.     

Petri nets based coordination component for CSCW environment

In view of the lack of efficient coordination of interdependent task in the collaborative design system, the mechanisms for temporal and resource coordination problems are established based on Petri Nets, respectively. Both of the mechanisms are encapsulated and implemented in the coordination component so as to increase the flexibility and acceptability of the system. We model the CSCW system based on Petri Nets for simulation, analysis and optimization. A case study on the overhead traveling crane is given to demonstrate and validate our theory.     

PLC控制系统的Petri网模型研究

运用Petri网方法,给出了PLC控制系统的建模准则,在此基础上,对PLC控制系统进行了性能分析和仿真研究。     

面向企业能源消耗过程的模糊Petri网模型研究

针对企业能源消耗系统模型的需求性,在分析企业能源消耗过程的特点和模糊Petri网基本原理的基础上,从实用、可行的角度探索基于模糊Petri网的企业能耗过程模型,详细阐述了面向企业能源消耗过程的模糊Petri网模型的定义和运行规则,并依据特定的建模原则,进行举例说明.模型的建立独立于特定的能源类型和用能设备,全面反映企业能耗过程及其影响因素,为进一步仿真分析企业能耗状况提供了依据.     

基于 Petri网的柔性制造系统动态优化模型

为解决柔性制造系统的动态优化调度问题,在基于扩展高级全局决策Petri网的柔性制造系统优化模型的基础上,提出了实时一优化切换控制Petri网模型。该模型在柔性制造系统发生加工设备故障、急件插入等异常情况时,自动切换并运行全局优化调度算法,并在系统允许的时间范围内,再切换返回到原有系统状态,按照新的优化结果运行。最后,以实时一优化切换控制Petri网模型与基于遗传的最小平衡算法结合为例,证实了该模型是有效的。     

Modular synthesis of Petri nets for modeling flexible manufacturing systems

This paper proposes a modular Petri net synthesis method for modeling flexible manufacturing systems based on synchronization among control processes of the manufacturing resources (such as robots and machines). In the method, the target system is modeled in a bottom-up and uniform manner by first describing the system's control processes using strongly connected state machines (SCSMs) as the basic modules. Each SCSM may contain multiple tokens to represent resources from the same type such as spaces in a buffer. Next, the common transitions and common transition subnets of the modules are merged to represent their synchronization. The system model constructed is proven to be conservative and thus bounded. Moreover, a restricted class of merged nets is proven to be live and reversible. For general classes of merged nets, this paper shows theorems that easily calculateP-invariants of the final net without solving the linear system equations. TheseP-invariants can be used to help in verifying the model's qualitative properties such as liveness.     

基于广义随机Petri网的装配可靠性建模

为了在装配环节保障产品的可靠性,提出可靠性驱动的装配技术的概念,并用广义随机Petri网对该技术进行了建模,通过同构的Markov链对模型进行定量分析。在可靠性驱动的装配技术建模分析中,采用结构分析和设计技术对产品进行功能分析并建立起完整的功能分析模型;将功能分析的结构分析和设计技术模型转化为相应的具有动态分析和定量研究能力的广义随机Petri网模型;为获得可信准确的分析模型,利用三角模糊数中的r截集对同构的Markov链进行优化;针对装配产品的可靠性特征,用装配可靠度指标对产品进行评价。以某加工中心的分度工作台为例,验证了该建模与分析方法的有效性。     

An architecture for a shop-floor controller using colored Petri nets

In a dynamic and flexible manufacturing environment, a shop-floor controller must be designed so that it automatically (or with minimum human intervention) and quickly responds to the changes (e.g., in part type or part routing) in the system. Such a performance may be achieved provided that the controller is simple and sufficiently general in its scope of application. In this article, we present an architecture for such a shop-floor controller. The architecture is based on colored Petri nets with ordered colored sets and structured input and output functions.     

Object-oriented Petri nets for modelling and analysis of automated manufacturing systems

This paper presents an Object-oriented Petri Net (OPN) approach to model and analyse the dynamic behaviours of an Automated Manufacturing System (AMS). Both the basic and the complete OPN models are introduced to represent the generic and specific dynamic behaviours of an AMS, respectively. Based on the basic OPN model, we need to construct the Object Communication Net (OCNet) for each physical object, and then employ the theory of invariants to perform the deadlock analysis. For an analysed non-deadlock basic OPN model, the complete OPN model for a specific AMS may be effectively derived from it by only including those related system constraints (e.g. part routing, resource capacity), since the basic OPN class library is reusable. A conflict analysis approach is then introduced to identify all the conflicting events involved in the complete OPN model, so that the most suitable control/decision strategy for resolving each conflict event may be suggested. Consequently, a rule-based control software may be implemented directly from the specification of the validated complete OPN model by following a number of transformation rules.     

Modeling and scheduling for manufacturing grid workflows using timed Petri nets

A manufacturing grid workflow can be viewed as the composition of activities that execute on heterogeneous, distributed, and job-dependent resources in a virtual organization to accomplish a specific manufacturing goal. Scheduling emerges as a key issue in manufacturing grid workflows since it assigns manufacturing resources to perform the required activities such that the optimal service is obtained. However, scheduling problems prove to be NP-hard due to the inherent combination explosion vices adhered to discrete event systems, such as the grid manufacturing. To crack such a hard nut, we focus on the formulation of a heuristic search algorithm based on timed Petri nets. When the activities involved in the manufacturing grid workflow can be executed by more than one resource, this scheduling algorithm selects the optimal one so as to minimize the makespan. Furthermore, the proposed scheduling policy in this paper aims to be dynamic rather than static such that the whole algorithm can be applied in a dynamic manufacturing grid environment. Both the theoretical and experimental results validate the legitimacy of the proposed approach.     

数控系统中梯形图编辑软件研究及实现

针对目前PLC梯形图编辑软件的缺陷和不足,选用Borland C Builder作为开发语言,采用面向对象的设计方法,开发一种基于Windows 2000面向数控PLC的使用梯形图语言编写PLC程序的通用开发平台。该系统实现了对多种PLC的图形编辑和仿真,使用方便,提高了工作效率。     

基于面向对象Petri网的多Agent系统交互协议建模

为了描述、分析和验证多Agent系统交互协议,提出了一种面向对象Petri网。与现有的形式化方法相比,面向对象Petri网能形象、直观地刻画多Agent系统复杂、并行的交互协议,可以描述其静态和动态语义,并可利用Petri网的数学分析方法对交互协议进行动态分析。面向对象Petri网还具有较好的模块性和柔性,能单独地分析参与交互的每一个Agent,而不会影响其他Agent和环境的状态。最后,利用面向对象Petri网描述了智能物理代理基金会请求协议和合同网协议,并对一个买卖Agent交互实例进行了建模和动态分析,验证了面向对象Petri网具有较好的建模能力。     

基于Petri网的柔性制造系统建模的调度算法

针对柔性制造系统(FMS)建模中存在的问题,通过分析FMS的组成和特点,提出了基于赋时对象Petri网的建模方法.该方法集中了Petri网和面向对象技术的优点,利用赋时对象Petri网,建立了FMS的资源对象模型和动态行为模型.同时分析了传统调度算法的优缺点,在传统调度算法的基础上提出了时间-A搜索算法,该算法能有效地解决了FMS仿真时的调度问题,使得加工路径代价较低,同时避免了A搜索算法搜索节点多、搜索效率低的弊端.     

Modeling extended Petri nets compatible with GHENeSys IEC61131 for industrial automation

Petri net (PN) modeling is one of the most used formal methods in the automation applications field, together with programmable logic controllers (PLCs). Therefore, the creation of a modeling methodology for PNs compatible with the IEC61131 standard is a necessity of automation specialists. Different works dealing with this subject have been carried out; they are presented in the first part of this paper [Frey (2000a, 2000b); Peng and Zhou (IEEE Trans Syst Man Cybern, Part C Appl Rev 34(4):523–531, 2004); Uzam and Jones (Int J Adv Manuf Technol 14(10):716–728, 1998)], but they do not present a completely compatible methodology with this standard. At the same time, they do not maintain the simplicity required for such applications, nor the use of all-graphical and all-mathematical ordinary Petri net (OPN) tools to facilitate model verification and validation. The proposal presented here completes these requirements. Educational applications at the USP and UEA (Brazil) and the UO (Cuba), as well as industrial applications in Brazil and Cuba, have already been carried out with good results.