具有不可控变迁离散事件系统的Petri网控制器

考虑可用具有不可控变迁的受控Petri网建模的离散事件动态系统.提出了在这类 系统中实现一组不等式约束的控制器的综合方法.所提出的控制器可通过给系统Petri网模 型增加一些Petri网元素来实现,其计算是建立在本文提出的Petrl网的路增益概念基础上 的.方法是系统、简单、计算量小.     

针对一般线性约束的Petri网控制器设计方法

针对基于Petri网离散事件系统关于标识向量和Parikh向量的不等式约束反馈控制器设计问题,提出一种新的控制器设计方法.该方法首先利用Petri网的状态方程把关于标识向量和Parikh向量的不等式约束转变成关于Parikh向量的不等式约束,然后基于Petri网库所是关于Parikh向量的不等式约束的观点构造控制器.最后将该方法与Iordache和Moody提出的方法作比较,实验结果显示该方法更简单、有效.     

Suboptimal time management of discrete event systems with uncontrollable events modeled by Petri nets

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.     

基于有限容量库所的离散事件系统的Petri网控制器综合——第1部分

针对由Petri网建模的离散事件系统, 提出了一种新的控制器设计方法. 控制器是基于有限容量库所的概念构造而成的, 并使被控对象在给定的一组线性不等式约束下运行, 而给定的线性不等式约束是定义在库所标识上的. 控制器的综合利用了有限容量库所Petri网转换为 (普通 )无限容量库所Petri网的技术. 针对约束的不同情况, 给出了相应的Petri网的控制器的设计方法.     

Petri net supervisors for DES with uncontrollable and unobservabletransitions

A supervisor synthesis technique for Petri net plants with uncontrollable and unobservable transitions, that enforces the conjunction of a set of linear inequalities on the reachable markings of the plant, is presented. The approach is based on the concept of Petri net place invariants. Each step of the procedure is illustrated through a running example involving the supervision of a robotic assembly cell. The controller is described by an auxiliary Petri net connected to the plant's transitions, providing a unified Petri net model of the closed-loop system. The synthesis technique is based on the concept of admissible constraints. Procedures are given for identifying all admissible linear constraints for a plant with uncontrollable and unobservable transitions, as well as methods for transforming inadmissible constraints into admissible ones. A technique is described for creating a modified Petri net controller that enforces the union of all of these control laws. The method is practical and computationally inexpensive in terms of size, design time, and implementation complexity     

Control synthesis of timed discrete event systems based onpredicate invariance

In this paper, arc-timed Petri nets are used to model controlled real-time discrete event systems, and the control synthesis problem that designs a controller for a system to satisfy its given closed-loop behavior specification is addressed. For the problem with the closed-loop behavior specified by a state predicate, real-time control-invariant predicates are introduced, and a fixpoint algorithm to compute the unique extremal control-invariant subpredicate of a given predicate, key to the control synthesis, is presented. For the problem with the behavior specified by a labeled arc-timed Petri net, it is shown that the control synthesis problem can be transformed into one that synthesizes a controller for an induced arc-timed Petri net with a state predicate specification. The problem can then be solved by using the fixpoint algorithm as well. The algorithm involves conjunction and disjunction operations of polyhedral sets and can be algorithmically implemented, making automatic synthesis of controllers for real-time discrete event systems possible.     

Deadlock p revention f or flexible manufacturing system

Deadlock must be prevented via the shop controller during the flexible manufacturing system (FMS) performing. Various models have been tried for the analysis and design of shop controller. Petri net is suitable to describe the dynamic behavior of the discrete event system , such as concurrency , conflict and deadlock , however , the verification of the system behavior needs ructure analysis with complex theoretical proof method. Temporal logic model checking has important advantages over traditional theorem prover. It is fully automatic and can produce possible unter- example which is particularly important in finding subtle error in complex transition systems. In this paper ,a new method for the deadlock prevention based on Petri net and Temporal Logic model checking is presented. The specification in the Temporal Logic is expressed according to some result of structure analysis of the Petri net . The model checking is employed to execute the formal verification ,which will conduct an exhaustive exploration of all possible behaviors. Finally ,an example is presented to demonstrate how the method works.     

Deadlock prevention for flexible manufacturing system

Deadlock must be prevented via the shop controller during the flexible manufacturing system （FMS） performing. Various models have been tried for the analysis and design of shop controller. Petri net is suitable to describe the dynamic behavior of the discrete event system, such as concurrency, conflict and deadlock, however, the verification of the .system behavior needs structure analysis with complex theoretical proof method. Temporal logic model checking has important advantages over traditional theorem prover. It is flatly automatic and can produce possible counter-example which is particularly important in finding subtle error in complex transition systems. In this paper, a new method for the deadlock prevention based on Petri net and Temporal Logic model checking is presented. The specification in the Temporal Logic is expressed according to some result of structure analysis of the Petri net. The model checking is employed to execute the formal verification, which will conduct an exhaustive exploration of all possible behaviors. Finally, an example is presented to demonstrate how the method works.     

A Survey of Petri Net Methods for Controlled Discrete Event Systems

This paper surveys recent research on the application of Petri net models to the analysis and synthesis of controllers for discrete event systems. Petri nets have been used extensively in applications such as automated manufacturing, and there exists a large body of tools for qualitative and quantitative analysis of Petri nets. The goal of Petri net research in discrete event systems is to exploit the structural properties of Petri net models in computationally efficient algorithms for computing controls. We present an overview of the various models and problems formulated in the literature focusing on two particular models, the controlled Petri nets and the labeled nets. We describe two basic approaches for controller synthesis, based on state feedback and event feedback. We also discuss two efficient techniques for the on-line computation of the control law, namely the linear integer programming approach which takes advantage of the linear structure of the Petri net state transition equation, and path-based algorithms which take advantage of the graphical structure of Petri net models. Extensions to timed models are briefly described. The paper concludes with a discussion of directions for future research.     

Design and Implementation of Discrete Event Control Systems: A Petri Net Based Hardware Approach

This paper presents a methodology for modeling and hardware implementation of discrete event control systems based on the formalism of Petri nets (PN). The control algorithm is initially specified as an executable PN specification which is subsequently compiled directly into a compact machine code and stored in commercially available programmable read only memory (PROM). As an implementation platform, a programmable Petri net based dedicated discrete event controller is proposed. The scalable architecture of the controller is optimized to process PN constructs of all possible classes. A remarkable feature of the proposed architecture is its ability to handle explicit concurrency. The controller exploits hardware-level parallelism to track multiple tokens (control threads) through the net. The performance of the architecture has been verified and benchmarked on the fabricated integrated circuit (IC) prototype of the controller.