冗余信标及其在Petri网结构控制中的应用

提出了冗余严格极小信标的概念 ,冗余信标是网拓扑的一种特殊结构。在保证网系统的所有信标不被清空时 ,只需要考虑那些非冗余的严格极小信标即可。这样便降低无死锁Petri控制器设计的复杂性 ,大大增强了Petri网处理复杂系统的能力。同时提出了一种死锁控制的迭代算法 ,使用冗余信标的概念可以大大简化Petri网的设计。以自动制造系统为例 ,说明了这种概念的应用。     

S3PMR网的一种死锁预防优化策略

针对Petri网的S3PMR中的死锁预防问题,提出一种优化的控制器设计方法.当控制器的优化性不能保证时,要对所添加的控制器进行结构分析,提出了一个输出弧位置最优化的死锁预防控制算法.将S3PMR中的严格极小信标分为基本信标和从属信标,对每一个基本信标添加一个控制库所,使其P-不变式可控,且不会产生新的可被清空信标,对从属信标的控制则通过调整基本信标的控制深度变量来实现.从而用少量的控制库所得到结构更简单、许可行为更多的活性Petri网控制器.     

自动制造系统的一种死锁避免策略

基于Petri网的结构分析理论，提出了自动制造系统Petri网模型的一种死锁控制方法，在这种策略的控制下，避免了系统中死锁的产生，从而许多制造系统的Petri网模型具有活性，提出了一种保证所有严格极小信标至少含有一个托肯的方法，对冗余严格极小信标的研究，提高了Petri网复杂自动制造系统的建模能力。结果表明，在设计无死锁的Petri网格型时，不是所有的严格极小信标都要考虑，从而简化了设计结果和控制算法。     

S3PR网的一种最大许可活性监督控制器设计方法

针对S3PR网的死锁预防问题,提出一种基于信标的最大许可死锁控制策略.采用迭代方法对网系统中存在的所有可清空严格极小信标添加一组广义互斥约束,使信标的标志数不超过某个上限值,将基于信标的死锁预防控制转化为禁止状态监控问题,使得受控网系统的所有禁止状态不可达,从而保证受控网具有最大许可行为.通过柔性制造系统实例验证了该策略的有效性,该算法尤其适用于结构相对简单的可达状态性能要求比较高的网模型.     

用混合Petri网对微开关加工系统建模和仿真

半导体加工系统是一个非常复杂的、离散事件和连续时间相结合的混合动态系统,离散Petri网不能很好地对这样的系统进行建模和分析,混合Petri网可以很好地描述半导体加工系统的静态属性及动态行为.实际上,运用离散Petri网将面临状态爆炸以及仿真的高消耗的问题.混合Petri网用来对半导体加工系统进行建模和仿真,这类模型用于微开关加工流程的建模和仿真,证明结果很精确并且仿真速度很快.     

基于含不可观变迁Petri网的码垛机器人零件加工系统故障检测方法

研究了基于含不可观变迁Petri网的码垛机器人零件加工系统故障检测问题。结合机器系统运行过程中的故障特征,对Petri网在机器系统故障诊断中的应用进行了研究,提出了包含不可观变迁Petri网的基本可达树和诊断分析函数的概念及基本可达树故障检测算法。以码垛机器人零件加工系统为例,建立了Petri网系统模型,应用基本可达树故障检测算法进行检测,故障检测结果符合码垛机器人零件加工系统实际运行情况,验证了该方法的有效性。     

基于质量特征产品装配顺序规划的逆向推理算法探究

在Petri网柔性装配系统装配顺序规划中引入装配质量要素,并以装配零件的装配自由度,装配作业后稳定性,装配零件配合精度对装配质量的影响作为基本因子,提出装配质量置信度概念,解决柔性装配系统装配规划中装配质量及其定量化问题。根据装配形成的产品在Petri网装配状态图中表示为一个最终库所的特点,应用改进B树模型,提出仅以变迁信息的产品装配顺序规划Petri网逆向推理算法,简化装配顺序规划推理过程,对于多个变迁均可生成最终成品的情况,亦给出装配顺序规划的解决方案,并以摩托车发动机的装配为例,证明该算法是可行的。     

分布式控制系统的混合Petri网建模和分析

分布式控制系统是一个离散和连续相结合的混合动态系统,具有动态、并发及同步等特征,Petri网已经被证明是离散事件或异步系统很好的建模和分析工具,而混合Petri网是用于混合系统建模和分析的一个主要工具.基于混合Petri网描述了分布式控制系统的混合Petri网模型,并且能够进行故障检测.并运用VisObjNet对模型实例进行了仿真分析.     

柔性制造系统一种次优化的死锁控制设计

为解决柔性制造系统中的死锁问题,以受控系统的许可行为作为指标,根据Petri网基本信标理论,提出了一种次优化的活性控制器设计方法.根据基本信标和从属信标的可控性关系,通过调整控制库所的初始标志,获得了具有较多许可行为的活性Petri网控制器.与文献中其他方法相比,所提的控制策略具有更好的许可性.     

一种基于Petri网和AGA算法的测试系统死锁预防策略

在自动测试系统中,很多任务需要并行测试.测试过程比串行测试复杂,较容易出现死锁现象,因此提出一种基于Petri网和自适应遗传算法(adaptive genetic algorithm)的死锁预防策略.在该策略中,首先为自动测试系统建立一个Petri网模型,然后将Petri网的状态方程作为约束条件,最后求出模型的发射序列即系统中无死锁的任务调度路径.Petri网的发射序列求解一直是NP问题,针对这种情况,引入自适应遗传算法对可行解空间进行全面的搜索,可得到所有无死锁的路径.最后,通过雷达接收机的并行测试例子,和启发式算法搜索进行对比,进一步体现了该死锁预防策略的优越性.     

Deadlock control of flexible manufacturing systems via invariant–controlled elementary siphons of petri nets

Effective resolution for deadlock problems plays an important role in the operation of automated flexible manufacturing systems (FMS). Based on P-invariants and elementary siphons of Petri nets, a deadlock prevention policy is developed for a special class of Petri nets that can well model many FMS. Siphons in a plant net model are divided into elementary and dependent ones. For each elementary siphon, a monitor is added to the plant model such that the siphon is invariant-controlled. Our method guarantees that no emptiable control-induced siphon is generated due to the addition of the monitors. When all elementary siphons are controlled, the controllability of a dependent siphon is ensured by properly setting the control depth variables of its related elementary siphons. An FMS example is utilized to illustrate the proposed methods.     

Design of deadlock prevention supervisors using Petri nets

This paper proposes a methodology to synthesize supervisors for a class of sequential resource allocation system for flexible manufacturing systems. The type of Petri nets are called S3PR, where deadlocks are related to emptied siphons. In a former paper (Huang et al., IEEE Trans Syst Man Cybern, 2007), a deadlock prevention policy was proposed based on Petri nets siphons for the type of Petri nets. Since all minimal siphons should be controlled, the deadlock prevention policy is very time-consuming when the system is large. In this research, a concept of the elementary siphon is used to reduce the number of control places. A new siphon-based policy of deadlock prevention for the type of Petri nets is presented. This policy consists of two main stages: The first stage, called elementary siphons control, adds control places to the original net model to prevent elementary siphons from being emptied. The second stage, called generalized siphons control, adds control places that adopt a conservative policy of controlling only the release of parts into the system are used. Compared to the existing approaches, the new deadlock prevention policy can obtain a structurally compact deadlock prevention supervisor by adding only a few control places. Finally, numerical experiments under reachable states illustrate that the proposed algorithm appears to be more permissive than the closely related approaches.     

Enhancement of an efficient control policy for FMSs using the theory of regions and selective siphon method

Deadlocks are an important problem in resource allocation systems such as flexible manufacturing systems. The theory of regions and the siphon-based method are usually used in the most deadlock prevention policies. The theory of regions that can obtain a maximally permissive controller is usually considered to be a natural solution with seasonable computational cost for flexible manufacturing systems. The selective siphon method allows one to use fewer control places than the conventional one. This paper employs both methods above. The former can identify the set of curial marking/transition–separation instance; the latter can reduce the computational cost. We can infer that the novel policy is the most efficient policy than the traditional methods, and also, the maximal permissive behavior of Petri net models can still be obtained.     

A resource decoupling approach for deadlock prevention in FMS

Many deadlock prevention approaches have been suggested in the literature for Petri net models of flexible manufacturing systems, based on siphon enumeration and control. With medium and large problem dimensions, such methods often require both an excessive computational load and extremely large control sub-nets, making them unfeasible or impractical. In this work, a simple approach is proposed for the design of sub-optimal but compact controllers. The approach is based on the anticipated allocation of a sub-set of resources that decouples the deadlock prevention problem in two much smaller and simpler problems, each devoted to the deadlock prevention for a sub-set of resources only. The application of the two designed control sub-nets to the original Petri net together with resource anticipation ensures deadlock prevention. A heuristic algorithm is also provided for the selection of a suitable resource partition, in order to maximize the control quality and performance. Several illustrative benchmark examples are provided.     

An optimal-elementary-siphons-based iterative deadlock prevention policy for flexible manufacturing systems

Petri nets have been proved to be a tool with prominent capabilities to describe discrete event systems, such as flexible manufacturing systems (FMS), thanks to their excellent properties over other models. Characterization in terms of special structural elements in a Petri net called siphons has been a major approach for the investigation of deadlock-freeness in context of FMS. Utilizing the optimal elementary siphons and the modified mixed integer programming (MIP) algorithm proposed in this paper, one can detect and solve deadlock problems arising in FMS in an iterative mode with tractable computational complexity. Moreover, the MIP approach can be exploited to implement the flexibility enhancement in the resultant net system so that the obtained system is less restricted. In contrast to the conventional typical policies, this approach evolves without explicitly enumerating all the strict minimal siphons. Its legitimacy and feasibility are proved and validated through an experimental study.     

A live subclass of petri nets and their application in modeling flexible manufacturing systems

In this paper a novel policy is proposed to solve the deadlock problem in a class of flexible manufacturing systems based on the notion that each shared buffer is partitioned into parts to store different types of products, respectively. A subclass of Petri nets called resource-shared net with buffers (RSNB) is defined. An RSNB is constructed by synthesizing some marked graphs, and each marked graph can model the process of manufacturing one type of product. RSNB cannot only model the concurrent execution of manufacturing processes, but also ensure that the modeled system is live. The process of constructing RSNB is described in detail, and a minimal siphon based necessary and sufficient condition is provided to characterize the liveness of RSNB.     

Deadlock avoidance control for manufacturing systems with multiple capacity resources

This paper addresses the problem of designing a control scheme capable of avoiding deadlock conditions for a class of manufacturing systems. The considered model for the system under control is based on Petri nets, and is formulated according to well-known modelling rules. A deadlock avoidance policy is proposed which is an extension of a previously presented one. The proofs of its main properties are briefly sketched. Finally, an example of an automated manufacturing system for which such a deadlock avoidance policy has been applied is discussed.     

多资源服务处理系统的活性控制策略

为解决一类具有多资源服务处理制造系统中的死锁问题,提出了利用Petri网描述系统结构和动态特征的方法,以及循环结构的新概念,证明了循环结构是导致系统死锁的惟一结构特征。利用辅助系统Petri网模型,提出了计算系统的所有基本极大循环结构的方法。对每个基本极大循环结构增加一个控制位置及其相关弧以限制其资源的利用,从而有效地避免系统死锁的发生。