基于Petri网的并行控制器的VHDL实现

Petri网是离散事件系统建模的重要工具,本文使用硬件描述语言VHDL实现了基于Petri网的并行控制器。文中通过一个液位控制系统实例具体介绍了这一方法,并通过仿真波形证明了该方法的正确性。这对于离散事件系统并行控制器的设计具有十分重要的意义。     

可重构制造系统监督控制器的自动重构

提出了基于改进的网重写系统(Improved net rewriting system, INRS)的可重构制造系统(Reconfigurable manufacturing systems, RMS) Petri网监督控制器的自动重构方法, 以快速适应由市场需求变化所引起的制造系统构形的频繁变化. INRS解决了网重写系统存在的问题, 可动态调整给定Petri网模型的结构而不改变其行为属性. 以集合和图的组合形式定义了RMS的构形, 并提出了基于INRS的一类模块化、可重构的Petri网控制器的设计方法. 针对这类Petri网控制器, 提出了基于INRS的自动重构方法. 方法可将RMS构形的变化转变为INRS的图重写规则, 并作用于当前Petri网控制器, 使其快速、自动地重构为所求的新控制器. 所提出的Petri网控制器的设计与重构方法, 均从理论上保证了结果的正确性, 免校验. 仿真研究验证了方法的有效性.     

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.     

混合动态系统中连续状态系统用离散事件系统描述的一致性

混合动态系统起因于离散事件系统用于监控连续状态系统的行。本文用抽象语言方法描述连续状态系统，研究状态离散事件系统描述的一致性。基于输入输出观点简要地 讨论了离散控制器综合。     

一类Petri网及其在离散事件系统的仿真与控制中的应用

设计和实现了一类Petri网--控制Petri网,基于控制Petri网,给出了离散事件系统的仿真与控制的算法和离散事件系统控制的实现方案,最后以柔性机床为例,演示了基于控制Petri网的离散事件系统的仿真与控制过程.结果表明,使用控制Petri网可以有效地模拟和控制离散事件系统.     

一类DEDS状态反馈控制器综合的新方法

对具有无穷状态空间的并发离散事件动态系统提出了一种基于Petri网图示的矩阵代数 综合方法.该方法借助于对Petri网的结构分解可以用于结构无竞争Petri网描述的一类离 散事件动态系统状态反馈控制器的离线综合.     

网简化技术在Petri网反馈控制器设计中的应用

针对基于Petri网离散事件系统库所标识不等式约束反馈控制器的设计问题,提出一项新型网简化技术--标识总量保持网简化技术,并利用此项技术把所有约束库所融合为一个与它们标识总量相等的库所,使控制器的设计更为简单,尤其是对规模较大的系统,其优势更加明显.借助一个应用实例,将该控制器设计方法与Moody等人提出的控制器设计方法作比较,表明所提出的控制器设计方法更简单、更有效.     

离散制造装配系统的活性控制

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.     

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.     

离散制造装配系统的活性控制1)

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.     

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.     

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.     

Automatic Reconfiguration of Petri Net Controllers for Reconfigurable Manufacturing Systems With an Improved Net Rewriting System-Based Approach

The advent of reconfigurable manufacturing systems (RMSs) has given rise to a challenging problem, i.e., how to reconfigure rapidly and validly a RMS supervisory controller in response to frequent changes in the manufacturing system configuration driven by fluctuating market. This paper presents an improved net rewriting system (INRS)-based method for automatic reconfiguration of Petri net (PN) supervisory controllers for RMS. We begin with presenting the INRS which overcomes the limitations of the net rewriting system and can dynamically change the structure of a PN without damaging its important behavioral properties. Based on INRS, a method for design reconfigurable PN controllers of RMS is introduced. Subsequently, we presented an INRS-based method for rapidly automatic reconfiguration of this class of PN controllers. In the reconfiguration method, changes in a RMS configuration can be formalized and act on an existing controller to make it reconfigure rapidly into a new one. Noticeably, no matter the design or reconfiguration, the expected behavioral properties of the resultant PN controllers are guaranteed. Thus, efforts for verification of the results can be avoided naturally. We also illustrate the reconfiguration of a PN controller for a reconfigurable manufacturing cell.     

Control Synthesis of Petri Nets Based on S-Decreases

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.     

Towards a synthesis method for distributed safety controllers based on net condition/event systems

An idea is presented for the synthesis of modular distributed controllers for forbidden state problems. The model of the uncontrolled plant behaviour is designed in a modular way by net condition/event systems. This modularity is the precondition for classification of forbidden markings with respect to design of local controllers. A modified backward search method is proposed for synthesis of the function of local controllers as well as for their communication. The method is illustrated using a manufacturing system example.     

Symbolic Supervisory Control of Infinite Transition Systems Under Partial Observation Using Abstract Interpretation

We propose algorithms for the synthesis of state-feedback controllers with partial observation of infinite state discrete event systems modelled by Symbolic Transition Systems. We provide models of safe memoryless controllers both for potentially deadlocking and deadlock free controlled systems. The termination of the algorithms solving these problems is ensured using abstract interpretation techniques which provide an overapproximation of the transitions to disable. We then extend our algorithms to controllers with memory and to online controllers. We also propose improvements in the synthesis of controllers in the finite case which, to our knowledge, provide more permissive solutions than what was previously proposed in the literature. Our tool SMACS gives an empirical validation of our methods by showing their feasibility, usability and efficiency.     

Optimal Nonblocking Directed Control of Discrete Event Systems

For the control of discrete event systems, the notion of directed control refines that of supervisory control. A directed controller is one that selects at most one controllable event to be enabled at any state (without disabling any uncontrollable event), which is in fact how a discrete event control is implemented. In contrast, a supervisory controller computes a maximal allowable set of controllable events at each state, leaving undecided exactly which controllable event should be enabled. In previous works, we developed a framework for the computation of optimal directed controllers and a polynomial synthesis algorithm for acyclic plants. In this paper, we present a novel synthesis approach for general plants, i.e., plants with or without cycles, thus providing a complete solution to the optimal directed control problem. The complexity of the approach remains polynomial in the size of plant.