共查询到20条相似文献,搜索用时 15 毫秒
1.
Control Synthesis of Petri Nets Based on S-Decreases 总被引:8,自引:0,他引:8
Chen Haoxun 《Discrete Event Dynamic Systems》2000,10(3):233-249
A method for constructing a controller for a discrete event system modeled by a Petri net is presented in this paper. The control specification of the system is given by a set of linear inequality constraints defined on the marking of the net. The controller that forces the net to obey the constraints is an extended Petri net, which is synthesized based on minimal support S-decreases. The method can deal with general Petri nets with uncontrollable transitions, and then provides a systematic way for synthesizing net-based controllers for discrete event systems. 相似文献
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Rongming Zhu 《Asian journal of control》2012,14(1):217-229
Deadlocks are a highly undesired situation in a fully automated flexible manufacturing system, whose occurrences are tied to the existence of shared resources that are competed by different production processes. In the last two decades, a fair amount of research has been done on deadlock analysis and control for flexible manufacturing systems, leading to a variety of strategies in the literature. Petri nets are a promising mathematical tool to handle deadlock problems in flexible manufacturing systems. However, most deadlock control policies based on a Petri net formalism assume that all the transitions in a plant model are controllable. However, uncontrollability of events are a natural feature in a real‐world production system. This paper proposes a deadlock prevention policy for a class of Petri nets by considering the existence of uncontrollable transitions. Deadlocks are prevented by adding monitors to a plant Petri net model, whose addition does not inhibit the firings of uncontrollable transitions. Linear programming techniques are employed to find transitions to which a monitor points in order that a more permissive liveness‐enforcing Petri net supervisor can be found. A number of manufacturing examples are used to demonstrate the proposed methods. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society 相似文献
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T-组合Petri网的活性和公平性分析 总被引:1,自引:0,他引:1
同步合成是研究复杂Petri网系统性质的有效途径.文中通过引入可引发变迁序偶的概念,研究了T-组合(同步合成)Petri网对子网的活性和公平性继承关系,给出了一组T-组合Petri网活或公平的充要条件和充分条件.这些结果对网组合同步设计具有重要的指导意义 相似文献
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Krzysztof M. Sacha 《Real-Time Systems》1994,6(2):153-172
The paper presents the executable specification method for real-time (embedded) systems Transnet. The method is based on an extension to Petri nets. A specification is developed by a problem decomposition into a set of parallel processes. Each process is defined by an extended Petri net with functions assigned to transitions, and conditions and time constants assigned to arcs. It is shown that Transnet matches with the characteristics of the intended class of applications. The available specification languages and the internal representation of data which describe the functional as well as nonfunctional requirements are outlined. The advantages of the Petri net-based representation and the possibilities of automatic net analysis and early validation are discussed. 相似文献
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Compositional Petri Net Approach to the Development of Concurrent and Distributed Systems 总被引:1,自引:0,他引:1
Anisimov N. A. Golenkov E. A. Kharitonov D. I. 《Programming and Computer Software》2001,27(6):309-319
In the paper, a formal model based on Petri nets is proposed in the context of a compositional approach to the development and analysis of complex concurrent and distributed systems. Mutlilabels of Petri nets are introduced allowing labeling a transition not only with a single symbol, but also with a multiset of symbols. Operations on multilabeled Petri nets—parallel composition and restriction—are defined. A definition of a Petri net entity is given based on the notion of multilabels. A Petri net entity is a Petri net with a set of multilabels, where each multilabel is regarded as an access point of the entity. The operation of entity composition is introduced. Equivalence of entities is defined based on bisimulation equivalence of Petri nets. It is shown that the equivalence relation is congruent with respect to entity composition. It is also demonstrated that the composition operation is commutative and associative. 相似文献
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Maximally Permissive Petri Net Supervisors for Flexible Manufacturing Systems with Uncontrollable and Unobservable Transitions 下载免费PDF全文
Kamel Barkaoui 《Asian journal of control》2014,16(6):1646-1658
This paper presents a deadlock prevention policy to obtain behaviorally optimal supervisors for flexible manufacturing systems with uncontrollable and unobservable transitions. The conditions of uncontrollability and unobservability of transitions are revealed in the sense of the implementation of a Petri net supervisor. Then, integer linear programming models are designed to obtain a Petri net supervisor such that all legal markings are reachable and the number of control places is reduced. We also show that a controllable transition can be unobservable and self‐loops can be used to disable the transition but do not observe its firing. Finally, examples are provided to illustrate the proposed approach. 相似文献
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在基于Petri网建模的离散事件系统中, 提出利用局部关联信息进行约束转换, 并实现Petri网结构监控器综合的方法. 对以Parikh矢量约束形式给出的控制规范, 不可控不可观变迁会导致约束成为非法约束, 分析了不可控变迁的前向关联结构和不可观变迁的后向关联结构, 利用局部关联变迁实现对不可控和不可观变迁的间接控制, 从而将非法矢量约束转换为合法约束, 并保证初始控制规范的实现. 与基于矩阵的监控器综合方法相比, 本文的方法只需利用局部信息, 最后通过实例对该方法进行了说明. 相似文献
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Preventing systems from entering to forbidden states is a crucial issue in discrete event systems control. Adding supervisors to the system is a common method to avoid entering to forbidden states. In discrete event systems modeled by Petri net adding a supervisor could be done by means of control places. Since, the time is not considered in designing this supervisor, in presence of uncontrollable transitions adding control places can lead to increase the operation time of the system modeled by timed Petri net. Because, the firing of some transitions is prevented when it is not necessary. So, to design a more efficient controller, we will be required to use time information of the system component. Therefore, in this paper, a method for optimizing the time behavior of a supervised timed Petri net will be proposed. To obtain an efficient operation, some timed places as timer will be added to the net. The time of this timer places is calculated to permit firing of some controllable transitions in order to enter into some weakly forbidden states while entering to forbidden states is prevented. This concept leads to increase the speed of system as well as obtain an acceptable operation. This method can be applied for all systems modeled by Petri nets. The efficiency of proposed approach will be discussed and validated with a case study. 相似文献
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Necessary and sufficient conditions for reachability exist only for special classes of Petri nets, acyclic Petri nets being one among them. We present a net transformation procedure that converts a general Petri net into an acyclic Petri net to utilize the available sufficient condition. We show the relationship between the reachable markings of the original Petri net and the associated acyclic Petri net. Given a firing count vector, we discuss how the sufficient condition for reachability in an acyclic Petri net could be utilized for a general Petri net. We also discuss the utility of the acyclic transformed net in determining the transition firing sequences of the reachable markings with known firing count vectors. 相似文献
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This paper presents an adaptation of a supervisory control theory and a supervisor synthesis problem to a class of colored Petri nets. More specifically, the forbidden state control problem with full observation, in which a discrete-event system is modeled as a colored Petri net with a symmetry specification, is investigated. This problem is decidable if the colored Petri net has finite color sets and bounded places. A new algorithm for deriving a controller is presented in detail with a proof of correctness. Unlike conventional algorithms that explore the entire reachable set of states, our algorithm avoids an exhaustive search of the state space by exploiting a symmetry specification. It performs particularly well when applied to large but structured processes with similar components. Furthermore, this approach leads to a representation of controllers which are smaller than those obtained with automaton-based approaches. 相似文献
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首先分析了一类结构简单的Petri网--S-网的语言性质,得到了它们的行为描述方法.拓展了Petri网同步合成的概念,证明了给定一个结构复杂的Petri网都可通过一组S-网的同步合成运算而得到,并给出了相应的求解算法.引入语言的同步交运算,分析了结构复杂的Petri网与其同步合成子网之间的行为关系,给出了结构复杂Petri网的行为描述算法,为利用网语言分析实际系统的行为特征提供了可靠的理论依据和方法. 相似文献
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Deadlock-free Supervisor Design for Robotic Manufacturing Cells With Uncontrollable and Unobservable Events 下载免费PDF全文
Bo Huang MengChu Zhou Cong Wang Abdullah Abusorrah Yusuf Al-Turki 《IEEE/CAA Journal of Automatica Sinica》2021,8(3):597-605
In this paper, a deadlock prevention policy for robotic manufacturing cells with uncontrollable and unobservable events is proposed based on a Petri net formalism. First, a Petri net for the deadlock control of such systems is defined. Its admissible markings and first-met inadmissible markings (FIMs) are introduced. Next, place invariants are designed via an integer linear program (ILP) to survive all admissible markings and prohibit all FIMs, keeping the underlying system from reaching deadlocks, livelocks, bad markings, and the markings that may evolve into them by firing uncontrollable transitions. ILP also ensures that the obtained deadlock-free supervisor does not observe any unobservable transition. In addition, the supervisor is guaranteed to be admissible and structurally minimal in terms of both control places and added arcs. The condition under which the supervisor is maximally permissive in behavior is given. Finally, experimental results with the proposed method and existing ones are given to show its effectiveness. 相似文献
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The method is proposed to design the maximally permissive and efficient supervisor for enforcing linear constraints, in which the weights of places are not negative, on ordinary Petri nets with uncontrollable transitions. First, the weakly admissible linear constraint is introduced. Second, a method is proposed to design the monitor place for enforcing a weakly admissible linear constraint on Petri nets. Third, a theorem proving that a linear constraint can be equivalently transformed at an uncontrollable transition into a disjunction of new constraints is proposed. Fourth, using this theorem, an algorithm is presented to equivalently transform a linear constraint, each place weight of which is not negative, into a disjunction of weakly admissible ones. Lastly, the supervisor, which consists of the plant net and a set of monitor places, is designed for the weakly admissible linear constraints calculated by the above algorithm. 相似文献
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Extended Elementary Siphons and Their Application to Liveness‐Enforcement of Generalized Petri Nets 下载免费PDF全文
Emad Abouel Nasr 《Asian journal of control》2014,16(6):1789-1810
As a significant structural object, siphons are extensively employed to implement a large number of deadlock prevention and liveness‐enforcing methods for flexible manufacturing systems modeled by Petri nets. By linear combinations, a set of elementary siphons is chosen from all strict minimal ones to be controlled and thus the structural complexity of a supervisor is greatly reduced. The concept of elementary siphons is originally proposed for ordinary Petri nets. When applied to generalized Petri nets, their selection and controllability require an additional study. In this work, the concept of augmented siphons is proposed to extend the application of the elementary ones to a class of generalized Petri nets, GLS3PR. Based on graph theory, a siphon extraction algorithm is developed to obtain all strict minimal siphons, from which augmented elementary ones are computed. In addition, the controllability conditions of dependent siphons are developed. Through fully investigating the net structure, especially weight information, the set of augmented elementary siphons is more compact and well suits for generalized Petri net models under consideration. Some examples are used to illustrate the proposed method. 相似文献
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Configuring production processes based on process platforms has been well recognized as an effective means for companies to
provide product variety while maintaining mass production efficiency. The production processes of product families involve
diverse variations in manufacturing and assembly processes resulted from a large variety of component parts and assemblies.
This paper develops a multilevel system of nested colored object-oriented Petri nets with changeable structures to model the
configuration of production processes. To capture the semantics associated with production configuration decisions, some unique
modeling mechanisms are employed, including colored Petri nets, object-oriented Petri nets, changeable Petri net structures,
and net nesting. The modeling formalism comprises resource nets, manufacturing nets, assembly nets and process nets. The paper
demonstrates how these net definitions are applied to the specification of production process variants at different levels
of abstraction. Also reported is a case study in an electronics company. The system model is further analyzed with focus on
conflict prevention and deadlock detection. 相似文献