Directed Control of Discrete Event Systems for Safety and Nonblocking

We introduce the notion of directed control, where a directed controller is one that selects at most one controllable event to be enabled at any instant. This is in contrast to supervisory control, where a supervisory controller enables a maximum allowable set of controllable events at any instant, i.e., no specific selection for executing an enabled event is made. While the design of a supervisory controller is meaningful for plants that are generator of controllable events, a directed controller design makes more sense for plants that are executor of controllable events. The control goal is the same as that in a supervisory control setting, namely, safety and nonblockingness. A safe and nonblocking directed controller exists if and only if a safe and nonblocking supervisory controller exists, thereby proving the polynomiality of verifying existence. We also develop a set of algorithms of polynomial complexity to compute a safe and nonblocking directed controller (whenever one exists).     

An Optimal Directed Control Framework for Discrete Event Systems

In an earlier paper, we introduced the notion of directed control, where a directed controller, which is simply referred to as a director, is one that selects at most one controllable event to be enabled at any instant. In this paper, we develop an optimization-based approach for the design of a director: starting from any state, the worst cost to the nearest reachable marked state is minimized. The motivation is that a pending task can be completed in the least possible cost. A necessary and sufficient condition for the existence of an optimal director is obtained. Furthermore, for systems that are cycle-free, we provide an algorithm of polynomial complexity to compute an optimal director.     

Supervisory control of fuzzy discrete event systems.

To cope with situations in which a plant's dynamics are not precisely known, we consider the problem of supervisory control for a class of discrete event systems modeled by fuzzy automata. The behavior of such discrete event systems is described by fuzzy languages; the supervisors are event feedback and can only disable controllable events with any degree. In this new sense, we present a necessary and sufficient condition for a fuzzy language to be controllable. We also study the supremal controllable fuzzy sublanguage and the infimal controllable fuzzy superlanguage.     

离散事件系统的一种N步在线监控策略

文中给出了离散事件系统的一种N步在线监控策略.其特点是控制策略取决于系 统当前运行的N步后继运行投影或预测,无需计算非能控语言的上限能控子语言,通过适当 选取N,仍可保证系统的最优运行.同时还给出了与之相关的一些理论结果.     

实时离散事件系统的动态反馈控制

本文研究了一类含确定性状态时间的实时离散事件系统的动态反馈控制问题.基于一定 语言的实时可控性的概念,证明了对给定实时离散事件系统G,存在完备监控器φ使L(φ/ Gr)=K的充分必要条件是K是闭及实时可控的,并得到了有关实时监控问题解存在的充要 条件.     

离散事件动态系统中的控制综合问题

本文将离散事件动态系统（ＤＥＤＳ）监控方法中的控制综合问题作了系统的分类，得到了六种控制综合问题，并将它们表示成泛函极值问题，讨论了它们的可行解，最优解的存在性，可生解集的结构以及相互之间的关系。     

Supervisory control and reactive synthesis: a comparative introduction

This paper presents an introduction to and a formal connection between synthesis problems for discrete event systems that have been considered, largely separately, in the two research communities of supervisory control in control engineering and reactive synthesis in computer science. By making this connection mathematically precise in a paper that attempts to be as self-contained as possible, we wish to introduce these two research areas to non-expert readers and at the same time to highlight how they can be bridged in the context of classical synthesis problems. After presenting general introductions to supervisory control theory and reactive synthesis, we provide a novel reduction of the basic supervisory control problem, non-blocking case, to a problem of reactive synthesis with plants and with a maximal permissiveness requirement. The reduction is for fully-observed systems that are controlled by a single supervisor/controller. It complements prior work that has explored problems at the interface of supervisory control and reactive synthesis. The formal bridge constructed in this paper should be a source of inspiration for new lines of investigation that will leverage the power of the synthesis techniques that have been developed in these two areas.     

An optimal effective controller for discrete event systems

An approach to the online synthesis of an optimal effective controller for discrete event systems is presented. The optimal effective controller can achieve the prescribed (cumulative) effectiveness measure while minimizing the total cost incurred for the execution of events. This approach is constructed over a generalized control framework for automata‐based discrete event systems, which allows event enforcement in addition to the (original) event disablement/enablement as the control mechanism. The optimal effective control policy generated by this approach is proved to be the least restrictive among all the possible optimal effective control policies for the given online expansion tree of the system behavior. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Current-state opacity enforcement in discrete event systems under incomparable observations

In this paper we tackle the opacity enforcement problem in discrete event systems using supervisory control theory. In particular, we consider the case where the intruder and the supervisor may observe different sets of events and neither of these sets needs to be contained in the other one. Moreover, there may be controllable events that cannot be observed by the supervisor. We propose a finite structure, called an augmented I-observer, to characterize the strings that will not leak the secret. Based on such a structure, a locally optimal supervisor enforcing current-state opacity is designed.     

组件多工作模式下的离散事件系统监督控制方法研究

针对组件多工作模式下的离散事件系统,提出一种监督控制方法.利用Ramadge-Wonham监督控制架构,计算出组件各工作模式下对应的监督控制器.然后,利用所提的merge算法将组件各工作模式下对应的监督控制器合并,以生成融合监督控制器.再利用所提的事件选择函数得到在融合监督控制器各状态允许发生的事件,从而保证系统在融合监督控制器作用下的可控且非阻塞运行.最后,通过一个带反馈功能的制造系统演示本文所提方法的有效性,该系统中的检测单元将根据工件未通过检测的次数选择工作模式.相比于运用扩展有限状态机进行变量抽象的方法,本文所提方法更加直观简便,并能适应多个工件同时处于系统中时的情形.     

Control of Non-Deterministic Systems With μ-Calculus Specifications Using Quotienting

The supervisory control problem for discrete event system(DES) under control involves identifying the supervisor, if one exists, which, when synchronously composed with the DES,results in a system that conforms to the control specification. In this context, we consider a non-deterministic DES under complete observation and control specification expressed in action-based propositional μ-calculus. The key to our solution is the process of quotienting the control specification against the plan resulting in a new μ-calculus formula such that a model for the formula is the supervisor. Thus the task of control synthesis is reduced a problem of μ-calculus satisfiability. In contrast to the existing μ-calculus quotienting-based techniques that are developed in deterministic setting, our quotienting rules can handle nondeterminism in the plant models. Another distinguishing feature of our technique is that while existing techniques use a separate μ-calculus formula to describe the controllability constraint(that uncontrollable events of plants are never disabled by a supervisor), we absorb this constraint as part of quotienting which allows us to directly capture more general state-dependent controllability constraints. Finally, we develop a tableau-based technique for verifying satisfiability of quotiented formula and model generation. The runtime for the technique is exponential in terms of the size of the plan and the control specification. A better complexity result that is polynomial to plant size and exponential to specification size is obtained when the controllability property is state-independent. A prototype implementation in a tabled logic programming language as well as some experimental results are presented.     

Optimal supervisory control of finite state automata

This paper presents optimal supervisory control of dynamical systems that can be represented by deterministic finite state automaton (DFSA) models. The performance index for the optimal policy is obtained by combining a measure of the supervised plant language with (possible) penalty on disabling of controllable events. The signed real measure quantifies the behaviour of controlled sublanguages based on a state transition cost matrix and a characteristic vector as reported in earlier publications. Synthesis of the optimal control policy requires at most n iterations, where n is the number of states of the DFSA model generated from the unsupervised plant language. The computational complexity of the optimal control synthesis is polynomial in n. Syntheses of the control algorithms are illustrated with two application examples.     

Robust optimal control of regular languages

This paper presents an algorithm for robust optimal control of regular languages under specified uncertainty bounds on the event cost parameters of the language measure that has been recently reported in literature. The performance index for the proposed robust optimal policy is obtained by combining the measure of the supervised plant language with uncertainty. The performance of a controller is represented by the language measure of the supervised plant and is minimized over the given range of event cost uncertainties. Synthesis of the robust optimal supervisory control policy requires at most n iterations, where n is the number of states of the deterministic finite-state automaton (DFSA) model, generated from the regular language of the unsupervised plant behavior. The computational complexity of the control synthesis method is polynomial in n.     

Modular nonblocking state feedback control of discrete event systems and its application to dynamic oligopolistic markets

This article addresses a modular state feedback supervisory control problem where two local controllers should achieve a common control objective against another local controller. Each local controller has its own control objective described as a predicate. This article also addresses a nonblocking modular control problem in which a discrete event system controlled by three local controllers tends to reach the common marked states of two local controllers that are, however, prohibited by the third local controller. For a case study, we apply the proposed theory to an oligopolistic market composed of two firms and one government. Two oligopolistic firms have a common objective to maximise their total profit through collusion. However, the government prevents them from engaging in collusion. We show that the modular supervisory control theory presented in this article can be used to solve the problem of ‘how can the firms maximise their total profit against the intervention of government’?     

A behavior-based intelligent control architecture with applicationto coordination of multiple underwater vehicles

Presents a behavior-based intelligent control architecture for designing controllers which, based on their observation of sensor signals, compute the discrete control actions. These control actions then serve as the “set-points” for the lower level controllers. The behavior-based approach yields an intelligent controller which is a cascade of a perceptor and a response controller. The perceptor extracts the relevant symbolic information from the incoming continuous sensor signals, which enables the execution of one of the behaviors. The response controller is a discrete event system that computes the discrete control actions by executing one of the enabled behaviors. The behavioral approach additionally yields a hierarchical two layered response controller, which provides better complexity management. The inputs from the perceptor are used to first compute the higher level activities, called behaviors, and next to compute the corresponding lower level activities, called actions. The paper focuses on the discrete event subsystem, namely, the response controller. We illustrate the intelligent control architecture by discussing its application to the design of intelligent controllers for autonomous underwater vehicles used for ocean sampling missions. A complete set of discrete event models of the response controller of the underwater vehicles for the above application has been given, and their formal verification discussed     

How to design a discrete supervisory controller for real-time fuzzycontrol systems

The task of the supervisory controller is to stabilize the systems states within a bounded region defined by designer. In this paper, a discrete approach to the solution of the stable fuzzy control system is presented. It is proved that the fuzzy control system equipped with the discrete supervisory controller is globally stable in the Lyapunov sense. Finally, a fuzzy controller with a discrete supervisory controller is applied to the balance control system, both in simulations and in the real-time implementation     

Signed real measure of regular languages for discrete event supervisory control

This paper reviews, expands, and clarifies the underlying concepts of a signed real measure of regular languages, which has been used as a novel tool for synthesis of discrete event supervisory control systems. The language measure is constructed upon the principles of automata theory and real analysis. It allows total ordering of a set of partially ordered sublanguages of a regular language for quantitative evaluation of the supervised behaviour of deterministic finite state automata (DFSA) under different supervisors. In the setting of the language measure, a supervisor's performance is superior if the supervised plant is more likely to terminate at a good marked state and/or less likely to terminate at a bad marked state. The computational complexity of the language measure algorithm is polynomial in the number of DFSA states.     

Grid automata and supervisory control of dense real-time discrete event systems

We present a generalization of the classical supervisory control theory for discrete event systems to a setting of dense real-time systems modeled by Alur and Dill timed automata. The main problem involved is that in general the state space of a timed automaton is (uncountably) infinite. The solution is to reduce the dense time transition system to an appropriate finite discrete subautomaton, the grid automaton, which contains enough information to deal with the timed supervisory control problem (TSCP). The plant and the specifications region graphs are sampled for a granularity defined in a way that each state has an outgoing transition labeled with the same time amount. We redefine the controllability concept in the context of grid automata, and we provide necessary and sufficient solvability conditions under which the optimal solution to centralized supervisory control problems in timed discrete event systems under full observation can be obtained. The enhanced setting admits subsystem composition and the concept of forcible event. A simple example illustrates how the new method can be used to solve the TSCP.     

Formulas for a class of controllable and observable sublanguages larger than the supremal controllable and normal sublanguage

In this paper, we give some new methods for synthesis of controllers of discrete event dynamical systems (DEDS) with partial event informations. Given a regular target language L, we construct some effective computable algorithms for computing the controllable and observable sublanguages of L. We show that any one of these controllable and observable sublanguages obtained by our algorithms is larger than the supremal controllable and normal sublanguage of L.     

Reliable decentralized supervisory control of discrete eventsystems

We consider a discrete event system controlled by a decentralized supervisor consisting of n local supervisors, and formulate a new decentralized supervisory control problem, called a reliable decentralized supervisory control problem. A decentralized supervisor is said to be k-reliable (1相似文献