共查询到19条相似文献,搜索用时 78 毫秒
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死锁是柔性制造系统中容易发生的异常现象,如不加以消除,将会导致整个系统的瘫痪.文中通过Petri网模型对FMS的结构分析,揭示出导致FMS死锁的结构元素和活性特征,在此基础上,提出了FMS的无死锁Petri网控制器算法,并举例说明这种控制器算法在FMS中的应用. 相似文献
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信标的受控性是检测柔性制造系统(flexible manufacturing system,FMS)Petri网模型是否存在死锁的关键因素.对于普通Petri网,在任何可达标识下所有信标不被清空是检测网系统非死锁的充分条件.然而,该条件对于建模能力更强的一般Petri网并不适用,max可控性条件由此产生.研究证明,该条件对于一般Petri网的死锁检测过于严格了.虽然其后有很多研究者通过改进max可控性条件以求给出条件更宽松的一般Petri网非死锁的充分条件,但大部分的研究成果都仅仅局限于一种顺序资源共享分配系统Petri网模型S4PR(systems of sequential systems with shared resources)网.因此,本文在max可控性条件的基础上提出了新的名为max#可控的信标可控性条件,并在此条件的基础上实现了基于混合整数规划(mixed integer programming,MIP)的死锁检测方法.与现有研究成果相比,max#可控性条件更宽松,可适用于更多类型的一般网,为解决大规模柔性制造系统中死锁监督控制器的结构复杂性问题提供了有力的理论支撑. 相似文献
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首次研究离散制造装配系统的活性控制问题.建立了系统的工件加工过程Petri网模型.通过对系统Petri网模型的结构分析,提出了导致系统死锁的两类元素结构及活性特征.对一类离散制造装配系统提出了避免死锁的Petri网控制器,这类控制器容易实现,对系统的限制小,而且使得受控系统仍具Petri网模型.对一般离散制造装配系统提出了保证系统活性的控制策略. 相似文献
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Petri网死锁的分析与检测 总被引:5,自引:0,他引:5
本文在讨论Petri网静态结构和动态运行特性的基础上,给出了死锁的定义,描述了死锁的物理意义,并且给出了死锁的分析方法和检测算法.本文的研究对Petri网的工程应用具有基础性的重要作用. 相似文献
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基于Petri网的柔性制造系统一种预防死锁方法 总被引:3,自引:0,他引:3
基于Petri网的结构特性分析,研究了FMS(柔性制造系统)一种预防死锁方法.提出了
Petri网的一种特殊拓扑结构--基本信标的概念.在Petri网中基本信标的集合是SMS(严格极
小信标)集合的一个真子集.尤其在大型Petri网系统中,基本信标的集合比SMS的集合要小得
多.对于Petri网的一个子类S3PR,只对每一个基本信标添加一个库所使其不被清空,就可实现
预防死锁,也就是说无须控制S3PR的所有SMS而达到无信标被清空的目的.此外,对于S3PR,
还提出了一种求取SMS和基本信标的方法.相对于现在普遍采用的控制所有SMS来预防死锁
的策略,其具三方面优势.1)只需控制少量的SMS即所谓的基本信标.相应地,添加少量的控制
库所和连接弧,就可得到无死锁或活的Petri网.2)不需要先行计算出极小信标的集合.3)明显
地,这种方法更适合大型Petri网系统.我们通过穿插在文中的一个例子来说明这些方法. 相似文献
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通过对自动制造系统的Pctri网模型的分析.可以揭示出被模拟系统的死锁跟其初始标识和其结构有关。要想消除自动制造系统的死锁异常,可以通过修改Petri网的初始标识或Pctri网的结构来解决。该文结合具体示例,给出了具体的可操作算法并设计出了控制自动制造系统死锁的Petri网模型,从而为自动制造系统的异常处理提供了一条有效途径。 相似文献
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自动制造系统异常情况Petri网控制器的形式化设计方法 总被引:1,自引:0,他引:1
CIMS,FMS等自动制造系统的控制器一般由有序控制器和异常情况处理控制器两个部
分组成.两者都可以用Petri网来实现.这里讨论用于异常情况处理的Petri网控制器的形
式化设计方法,其基本思想是利用状态表作为异常情况处理的规格说明语言,然后将状态表形
式化描述为MOORE自动机,最后给出构造与MOORE自动机行为等价的Petri网控制器
的形式化设计方法.并且用一个实例说明其设计过程.该方法也适用于Petri网的自动建
模. 相似文献
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针对赋时有界Petri网模型下柔性制造系统的生产调度问题,给出了有界Petri网的零压缩二叉决策图表示方法,进而建立了此类生产调度问题求解的符号零压缩二叉决策图算法.该算法在求解过程中对状态空间及其搜索过程中的相关数据,采用零压缩二叉决策图表示,避免了状态和搜索的显式枚举,实现了隐式高效操作,有效地改善了算法的计算性能.实验结果表明了算法的有效性. 相似文献
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To scheduling flexible manufacturing system (FMS) efficiently, we propose and evaluate an improved search strategy and its application to FMS scheduling in the P-timed Petri net framework. On the execution of Petri net, the proposed method can simultaneously use admissible heuristic functions and nonadmissible heuristic functions for A* algorithm. We also prove that the resulting combinational heuristic function is still admissible and more informed than any of its constituents. The experimental results of an example FMS and several sets of random generated problems show that the proposed search method performs better as we expected. 相似文献
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Robust design of flexible manufacturing systems using, colored Petri net and genetic algorithm 总被引:3,自引:0,他引:3
A method is presented for the robust design of flexible manufacturing systems (FMS) that undergo the forecasted product plan variations. The resource allocation and the operation schedule of a FMS are modeled as a colored Petri net and an associated transition firing sequence. The robust design of the colored Petri net model is formulated as a multi-objective optimization problem that simultaneously minimizes the production costs under multiple production plans (batch sizes for all jobs), and the reconfiguration cost due to production plan changes. A genetic algorithm, coupled with the shortest imminent operation time (SIO) dispatching rule, is used to simultaneously find the near-optimal resource allocation and the event-driven schedule of a colored Petri net. The resulting Petri net is then compared with the Petri nets optimized for a particular production plan in order to address the effectiveness of the robustness optimization. The simulation results suggest that the proposed robustness optimization scheme should be considered when the products are moderately different in their job specifications so that optimizing for a particular production plan creates inevitably bottlenecks in product flow and/or deadlock under other production plans. 相似文献
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The reaction time of a controller is a fundamental matter in discrete event control systems. Petri nets are extensively used
in this field. The controller reads the inputs, executes the control Petri net and writes the output in a cyclic manner. The
reaction time of this controller depends on the Petri net structure, on the events sequence and on the algorithm that executes
the net. In this paper we present a performance evaluation of interpreted and centralized implementation techniques for ordinary
Petri nets. Four techniques have been analyzed: brute force, enabled transitions, static representing places and dynamic representing
places. The analysis has been carried out over a Petri net library composed of well know models which can be scaled using
a parameter. The analysis of the results shows that the performance of the algorithms depends on the Petri net behavior (concurrency
vs. effective conflicts).With the objective of minimizing the reaction time, we decided to design a Supervisor controller,
which we have called execution time controller (ETC). The aim of the ETC is to determine in real time which algorithm executes
the Petri net fastest and to change the execution algorithm when necessary. One possible application of the technique is the
minimization of execution time of the programmable logic controllers programs developed in sequential function chart (SFC). 相似文献