Performance Modelling and Evaluation of Dynamic Tool Allocation in Flexible Manufacturing Systems using Coloured Petri Nets: An Object-Oriented Approach

Manufacturing systems are faced with ever-increasing customisation and unstable demand. The traditional hierarchical control structures for shop floor (pre-release planning, scheduling, dispatching and activity control) are often inflexible in responding to unexpected scenario changes and are thus not robust to system disturbances. In this paper, an object-oriented approach to modelling of FMS dynamic tool allocation and control under a non-hierarchical shop floor control scheme using coloured Petri nets is presented. A client–server paradigm is used in the proposed modelling method. The complete FMS model is partitioned into individual classes (machines, magazines, tool transport system, SGVs, tool storage, etc.) thereby significantly reducing the complexity of the model to a tractable size. The system performance under different tool request selection rules is also evaluated using coloured Petri net simulation. The proposed method can provide the designer of a tool management system with a high-level and structured representation of the tool-sharing control. It also provides an effective method for prototyping and evaluating performance of object-oriented shop floor control software.     

基于Petri网的非串行制造系统的可靠性分析

对带有中间缓冲区的非串行系统深入研究其可靠性问题,建立基于广义随机Petri网的可靠性模型,着重考虑出现的装配、拆分以及按不同比例进行装配或拆分的加工工序,其中间缓冲区可用度对机器可用度的影响,在此模型基础上,采用缓冲区可用度定理,对中间缓冲区和机器本身的状态转移概率分别分类求解,计算出相应的缓冲区可用度和等效机器可用度;同时通过功能可靠度指标,对整个加工任务车间的可靠性进行总体评价,从时间量和产品量因子出发,来衡量由于生产率的不平衡以及中间缓冲区的库存太小,引起生产流程中传输道的阻塞和缺料,进而造成的相关工件的加工时间延迟等问题。以三台机床和两个待加工工件的加工装配单元为例,验证该模型与分析方法的有效性。     

Modelling,simulation and scheduling of flexible assembly systems with coloured Petri nets

Scheduling in flexible assembly systems is a complicated phenomenon owing to the large variability in the operating parameters. In this paper, coloured Petri nets are shown to be useful in modelling, simulating and scheduling flexible assembly systems. Case studies from published literature are chosen to show its superiority over some of the heuristic and analytical tools. In addition, the tool is also shown to model and analyse systems with some realistic constraints.     

一种基于Petri网的顺序共享资源AMS＊s

Ｐｅｔｒｉ网控制器自动设计及控制程序自动生成方法的研究是自动制造系统ＡＭＳｓ和柔性制造系统ＦＭＳｓ领域研究的热点问题之一〔２～６〕。本文以ＡＭＳｓ计划和调度产生的生产序列ＰＳ和资源需求序列ＲＲＳ为基础，为顺序共资源ＡＭＳｓ设计了一种规格说明语言，以自动生成ＡＭＳｓＰｅｔｒｉ网模型的矩阵形式，并给出了转换步骤。由于引入了资源状态反馈，故生成的Ｐｅｔｒｉ网模型是无死锁的。最后，用一个实例说明了设计过程。     

Performance Modelling of Complex Dynamic Production Systems Using Temporised Object-Oriented Petri Nets with Changeable Structure (TOPNs-CS)

An object-oriented Petri net with changeable structure (OPN-CS) is capable of modelling complex dynamic production systems subject to changes. However, an OPN-CS is limted to functionality modelling of the system. For performance modelling of a complex dynamic production system, OPNs-CS are extended to temporised OPNc-CS (TOPNs-CS). The extension is carried out by temporising OPNs of production resources and the message passing relationships among production resources. The methods of capturing some performance proprieties based on a TOPN-CS model of a system are presented. A case study is provided to show how TCPN-CS is used for modelling complex dynamic production systems. TOPNs-CS can be applied in control, scheduling, and optimisation of the processes of a dynamic production system subject to changes.     

复杂Petri网模型的仿真

针对复杂Petri网模型难于仿真的问题 ,本文提出一种仿真思路 ,该思路包括模型元素实现和仿真算法两部分。在模型元素实现部分通过采用面向对象编程的思想抽象出与Petri网模型各元素相对应的类 ,然后利用各类生成模型中各元素的实例对象以实现从Petri网结构到程序结构的转换。仿真算法部分给出了利用所建模型进行仿真的详细步骤。作为案例 ,在文章的最后给出了应用所述方法开发的某管材轧制企业生产过程仿真程序的程序结构及其仿真结果     

A Case Study in Design and Verification of Manufacturing System Control Software with Hierarchical Petri Nets

The application of Petrinets is one of the well-known approaches for developing provably error-free control software for manufacturing systems. To evaluate the practicability of available methods and tools for at least medium-sized systems, a case study has been performed to develop modularised control software of a production cell with hierarchical Petri nets, supporting reuse as well as stepwise validation.     

一种面向对象的Petri网及其应用研究

提出了一种面向对象的Petri网(OPN),较好地避免了一般Petri网建模时经常产生状态爆炸的问题,并具有较好的模块性、重用性及可维护性。通过利用OPN建立一个FMS模型的实例,说明了OPN的有效性和强大的建模能力。OPN为离散事件系统的建模提供了一种强有力的工具,具有良好的应用前景。     

基于混杂Petri网的混杂系统建模方法

给出了混杂Petri网的定义并综述了基于混杂Petri网对混杂系统的建模方法。以一简单的反应器为例详细阐述了这几种方法。对这几种方法进行了比较并指出各自的适用性     

Object-Oriented Petri Nets with Changeable Structure (OPNs-CS) for Production System Modelling

We propose object-oriented Petri nets with changeable structure (OPNs-CS) in this paper for effective modelling of production systems with changing structures. Two mechanisms for carrying out the structural changes in OPNs-CS are defined. One is for the modification of message passing relationships between distinct OPNs and the other is for adding of OPNs to, and the removing of OPNs from, a model. A case study is provided to show that OPNs-CS can cope with both the uncertainties which may exist during the model-building phase of a one-of-a-kind production (OKP) system and the structural changes of the system which often occur while the production system is in operation.     

Material flow and control sequence specification of flexible production systems using coloured Petri nets

Starting with the specification of each resource and the whole structure of a flexible production system, in this approach a special kind of coloured Petri nets is used for performing the modelling and the validation of the coordination control structure of the systems. In a second phase, it is proposed to modify the first models to synchronised Petri net schemas to facilitate the supervision and the interaction of the coordination model with the physical components of the system as well as the development and maintainability of the discrete-event control structures. The final result is a formal specification of coloured Petri net based coordination control of resources of the system, and logic control structures for control sequencing based on the use of synchronised subPetri net structures derived from the first one by refining transitions, i.e., their occurrence. Based on the proposed approach, the coordination control model of resources and a first skeleton of the logic control structures of a flexible assembly cell located at the Institute of Manufacturing Automation and Production Systems at the University of Erlangen-Nuremberg, Germany is elaborated and then the correctness of the obtained models with regard to material flow and control sequence specifications is validated by means of the structural analysis of the coloured Petri net-based models.     

Maintenance Integration in Manufacturing Systems: From the Modeling Tool to Evaluation

In manufacturing systems, wear-out and eventual failure are unavoidable. However, to reduce the rate of their occurrence and to prolong the life of equipment or the capacity for extended productive use of the equipment under the necessary technological functioning and servicing, maintenance can be performed. For large manufacturing systems, maintenance integration involves a particular development concerned with both complexity models and computing time. This paper presents an effective way of modeling complex manufacturing systems through hierarchical and modular analysis by using stochastic Petri nets and Markov chains. In the proposed approach, the integration of maintenance policies in a manufacturing system is facilitated by the development of a generic model. With this generic modeling, the user doesn't need to code the strategies but only to instantiate the generic model with the structure of the manufacturing system. This method allows various maintenance strategies to be coded in the generic model with the aim of studying their influence on system dependability and performance.     

基于扩展一阶混合Petri网的机械制造系统碳流动态建模方法

机械制造系统是生产与能源的强耦合系统.针对其耦合特性,提出一种基于扩展一阶混合Petri网的碳流动态建模方法.对机械制造系统碳流动态特性进行分析,建立相应的系统边界,由系统边界分析制造系统的生产构成、运行模式,并导出能量、物料平衡方程以及碳排放量计算公式,为模型的建立奠定数量分析基础.针对机械制造系统能耗的连续性及离散状态对连续过程的影响等,在原一阶混合Petri网的基础上,引入控制弧、抑制弧相关元素以增强建模语义,并给出模型的形式化定义及规则说明.以某制造系统自动生产线为例,建立相应的多目标函数及约束条件,仿真优化其能量流、物料流的时域特性,并计算碳排放量,对所建模型进行验证,为企业实施低碳制造奠定一定的理论基础.     

A Heuristic Search Approach Using Approximate Solutions to Petri Net State Equations for Scheduling Flexible Manufacturing Systems

This paper proposes a new heuristic search approach based on an analytic theory of the Petri net state equations for scheduling flexible manufacturing systems (FMSs) with the goal of minimizing makespan. The proposed method models an FMS using a timed Petri net and exploits approximate solutions of the net's state equation to predict the total cost (makespan) from the initial state through the current state to the goal. That is, the heuristic function considers global information provided by the state equation. This makes the method possible to obtain solutions better than those obtained using prior works (Lee and DiCesare, 1994a, 1994b) that consider only the current status or limited global information. In addition, to reduce memory requirement and thus to increase the efficiency of handling larger systems, the proposed scheduling algorithm contains a procedure to reduce the searched state space.     

基于随机Petri网的复杂机械设备可用度分析方法研究

设备的可用度是衡量设备运行过程中随机故障的主要指标,提高其可用度是设备优化运行过程中极为重要的一环。通过分析不同维修策略下设备状态的演变规律,研究不同状态之间的时间依赖关系,建立基于随机Petri网的复杂设备可用度模型。模型着重描述设备运行过程中的劣化状态以及不同维修策略对运行过程的影响。在此模型的基础上,根据设备不同维修策略分析模型的可达图,构造同构的马尔可夫链模型,求解模型不同状态下的各个稳态概率,计算不同维修策略下的设备可用度。通过可用度的求解可得到较优的设备维修策略,从设备预防性维修效率和故障维修效率因子出发,定量分析这两个因子对设备可用度以及设备维修费用的影响,并给出趋势图。以一个实例说明该模型及分析方法的有效性。     

Petri Nets for Project Management and Resource Levelling

Conventional management tools are restricted in their application. This paper details the use of Petri nets (PNs) in project management. In this context, the benefits of PNs are indicated. Extensions to PNs are proposed to suit this area of application. The use of a P-matrix for token movements is proposed. A resource levelling algorithm is described and applied to a case study.     

Synthesis of feedback control elements for discrete event systems using Petri net models and theory of regions

This paper describes a method for constructing a Petri-net-based controller for a discrete event system (DES) modelled by a Petri net. Assuming that an uncontrolled Petri net model of the DES and a set of forbidden state specifications are given, feedback control elements, i.e. a set of places and related transitions, with initial marking, are computed using the theory of regions, which is a formal synthesis technique for deriving Petri nets from automaton-based models. When feedback control elements are added to the uncontrolled Petri net model, the controlled (closed-loop) Petri net model of the system is obtained. The controlled Petri net model obtained is maximally permissive while guaranteeing that forbidden states do not occur. The proposed method is computationally efficient and does not suffer from the state explosion problem. Two examples are provided to show the applicability of the proposed method.     

A review of petri-net applications in manufacturing

Petri-nets (PNs) can model concurrent and synchronous activities in a manufacturing system at various levels of abstraction. They have been used for modelling manufacturing systems, knowledge representation on the shop floor, process-planning applications, decisionsupport tasks, etc. PNs are being used in a growing variety of application areas. This paper focuses on PN applications in manufacturing. A comprehensive review of research is provided. The paper also describes the design and application of PNs in the modelling of a manufacturing cell, the representation of the working of the cell at various levels of abstraction, and the inferences that can be drawn through PN use. Ideas for future research are presented.     

基于广义随机Petri网的工作流性能分析

通过引入广义随机Petri网，将工作流管理联盟定义的工作流模型映射为广义随机工作流网络。利用广义随机Petri网与马尔可夫链的等价关系，得到一种Petri网与马尔可夫链理论相结合的工作流性能分析的新方法，为工作流性能的有效评估提供了理论依据，并通过实例验证，该方法可用于分析工作流模型的时间性能和资源利用率。