Nonblocking supervisory control of state tree structures

It is well known that the nonblocking supervisory control problem is NP-hard, subject in particular to state space explosion that is exponential in the number of system components. In this paper we propose to manage complexity by organizing the system as a state tree structure (STS). STS are an adaptation of statecharts to supervisory control theory. Based on STS we present an efficient recursive symbolic algorithm that can perform nonblocking supervisory control design (in reasonable time and memory) for systems of state size 10/sup 24/ and higher. The resulting controllers are tractable and readily comprehensible.     

模糊离散事件系统监督控制理论

为了将经典离散事件系统 (Discrete event systems, DES) 中的监控理论扩展到模糊离散事件系统 (Fuzzy discrete event systems, FDES) 中, 总结了目前 FDES 建模和监控理论方面的成果, 进一步讨论了 FDES 的能控性, 给出了非阻塞监控的条件. 对 FDES 的能控子语言与优化监控进行了分析, 得到了能控子语言的性质. 以模糊自动机作为监控的一种形式, 给出了监督控制具体的实现方法, 这对于进一步开展 FDES 的研究工作是有益的.     

Robust and nonblocking supervisor for discrete-event systems withmodel uncertainty under partial observation

Addresses a robust and nonblocking supervisory control problem based on a framework of discrete-event systems with model uncertainty under partial observation. The uncertainty introduced in the paper is associated with internal and unobservable events occurring in systems. The paper presents a systematic method for modeling uncertainty described as a Δ-transition representing the internal and unobservable events. In particular, at a state with the assigned positive integer value p a system is assumed to experience at most a p-step state transition by the internal and unobservable event. Under the framework for model uncertainty, the paper presents necessary and sufficient conditions for the existence of a robust supervisor with the nonblocking property     

Improving evolvability of a patient communication control system using state-based supervisory control synthesis

Supervisory control theory enables control system designers to specify a model of the uncontrolled system in combination with control requirements, and subsequently use a synthesis algorithm for automatic controller generation. The use of supervisory control synthesis can significantly reduce development time of supervisory controllers as a result of unambiguous specification of control requirements, and synthesis of controllers that by definition are nonblocking and satisfy the control requirements. This is especially important for evolving systems, where requirements change frequently.For successful industrial application, the specification formalism should be expressive and intuitive enough to be used by domain experts, who define control requirements, and software experts, who implement control requirements and synthesize controllers. This paper defines such a supervisory control specification formalism that consists of automata, synchronizing actions, guards, updates, invariants, independent and dependent variables, where the values of the dependent variables can be defined in terms of functions on the independent variables.We also show how the language enables systematic, compositional specification of a control system for a patient communication system of an MRI scanner. We show that our specification formalism can deal with both event-based and state-based interfaces. To support systematic, modular specification of models for supervisory control synthesis, we introduce state trackers that record sequences of events in terms of states. The synthesized supervisor has been successfully validated by means of interactive user guided simulation.     

Robust and nonblocking supervisory control of nondeterministicdiscrete event systems using trajectory models

This note considers the robust supervisory control problems of uncertain nondeterministic discrete-event systems (DESs). The uncertain DES to be controlled is assumed to be modeled as a set of some possible nondeterministic automata. Then, the control objective is to achieve a given language specification and guarantee the nonblockingness of any nondeterministic automata of the set which are controlled by a robust nonblocking supervisor. Based on trajectory models, this note presents the necessary and sufficient conditions for the existence of a robust nonblocking supervisor for a given uncertain nondeterministic DES     

Decentralized supervisory control of nondeterministic discrete event systems: The existence condition of a robust and nonblocking supervisor

This paper addresses a decentralized supervisory control problem for an uncertain discrete event system (DES) modeled by a set of possible nondeterministic automata with unidentified internal events. For a given language specification, we present the existence condition of a robust and nonblocking decentralized supervisor that achieves this specification for any nondeterministic model in the set. In particular, we show that the given language specification can be achieved based on the properties of its controllability and coobservability with respect to the overall nominal behavior of the uncertain DES. It is further shown that the existence of a nonblocking decentralized supervisor can be examined with a trajectory model of the language specification.     

A modified normality condition for decentralized supervisory control of discrete event systems

In this paper, we study nonblocking decentralized supervisory control of discrete event systems. We introduce a modified normality condition defined in terms of a modified natural projection map. The modified normality condition is weaker than the original one and stronger than the co-observability condition. Moreover, it is preserved under union. Given a marked language specification, there exists a nonblocking decentralized supervisor for the supremal sublanguage which satisfies L_m(G)-closure, controllability, and modified normality. Such a decentralized supervisor is more permissive than the one which achieves the supremal L_m(G)-closed, controllable, and normal sublanguage.     

Solvability of Centralized Supervisory Control Under Partial Observation

The problem of synthesizing a nontrivial controllable and observable sublanguage of a given non-prefix-closed language is addressed. This problem arises in supervisory control of discrete-event systems, when the objective is to synthesize safe nonblocking supervisors for partially observed systems. The decentralized version of this problem is known to be unsolvable. We show that the centralized version of this problem is solvable by presenting a new algorithm that synthesizes a nontrivial controllable and observable sublanguage of the given non-prefix-closed language, if one exists. We also show that the union of all nonblocking solutions to the associated supervisory control problem can be expressed as the union of all regular nonblocking solutions. This work was done when the first author was at the University of Michigan as a Ph.D. student.     

Nonblocking supervisory control of nondeterministic systems viaprioritized synchronization

Shayman and Kumar (1995) showed that supervisory control of nondeterministic discrete-event systems, in the presence of driven events, can be achieved using prioritized synchronous composition as a mechanism of control, and trajectory models as a modeling formalism, first introduced by Heymann (1990). The specifications considered in this earlier work were given by prefix-closed languages. In this paper, we extend this work to include markings so that nonclosed specifications and issues such as blocking can be addressed. It is shown that the usual notion of nonblocking, called language model nonblocking, may not be adequate in the setting of nondeterministic systems, and a stronger notion, called trajectory model nonblocking, is introduced. Necessary and sufficient conditions for the existence of language model nonblocking as well as trajectory model nonblocking supervisors are obtained for nondeterministic systems in the presence of driven events in terms of extended controllability and relative-closure conditions and a new condition called the trajectory-closure condition     

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).     

Nonblocking and deterministic decentralized control for networked discrete event systems under communication delays

Discrete Event Dynamic Systems - Nonblocking is an important issue in supervisory control of discrete event systems. In this paper, we investigate nonblocking control for networked discrete event...     

面向对象远程监控系统框架研究

针对目前远程监控系统开发成本高、大量冗余局部解决方案的现状 ,提出了可复用远程监控系统框架的通用解决方案 .通过抽取远程监控系统的基本逻辑模型 ,建立了易于扩展、可复用的远程监控系统基本框架 ,从而在大大减少重复劳动、提高劳动生产率的同时 ,促进各方面性能都比较优越的远程监控系统的诞生 .并通过某小型变电站应用实例验证了本方案的可行性以及应用前景     

The real-time supervisory control of an experimental manufacturing system based on a hybrid method

In this paper, the real-time supervisory control of an experimental manufacturing system is reported based on a recently proposed hybrid (mixed PN/automaton) approach. Assuming that an uncontrolled bounded Petri net (PN) model of a (plant) discrete event system (DES) and a set of forbidden state specifications are given, the proposed approach computes a maximally permissive and nonblocking closed-loop hybrid model. The method is straightforward logically, graphically and technologically. This paper particularly shows the applicability of a hybrid (mixed PN/automaton) approach to low-level real-time DES control. To do this, programmable logic controller (PLC) based real-time control of an experimental manufacturing system is considered.     

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’?     

Supervisory control of fuzzy discrete event systems: a formal approach.

Fuzzy discrete event systems (DESs) were proposed recently by Lin and Ying [19], which may better cope with the real-world problems of fuzziness, impreciseness, and subjectivity such as those in biomedicine. As a continuation of [19], in this paper, we further develop fuzzy DESs by dealing with supervisory control of fuzzy DESs. More specifically: 1) we reformulate the parallel composition of crisp DESs, and then define the parallel composition of fuzzy DESs that is equivalent to that in [19]. Max-product and max-min automata for modeling fuzzy DESs are considered, 2) we deal with a number of fundamental problems regarding supervisory control of fuzzy DESs, particularly demonstrate controllability theorem and nonblocking controllability theorem of fuzzy DESs, and thus, present the conditions for the existence of supervisors in fuzzy DESs; 3) we analyze the complexity for presenting a uniform criterion to test the fuzzy controllability condition of fuzzy DESs modeled by max-product automata; in particular, we present in detail a general computing method for checking whether or not the fuzzy controllability condition holds, if max-min automata are used to model fuzzy DESs, and by means of this method we can search for all possible fuzzy states reachable from initial fuzzy state in max-min automata. Also, we introduce the fuzzy n-controllability condition for some practical problems, and 4) a number of examples serving to illustrate the applications of the derived results and methods are described; some basic properties related to supervisory control of fuzzy DESs are investigated. To conclude, some related issues are raised for further consideration.     

Nonblocking Hierarchical Control of Decentralized Discrete Event Systems

This contribution investigates the hierarchical control of decentralized discrete event systems (DES) that are synchronized by shared events. A hierarchical control architecture providing hierarchical consistency is introduced. Moreover, it allows for composition of decentralized subsystems on the high-level of the hierarchy and hence reduces the computational complexity of supervisory control synthesis for language inclusion specifications. In this context, a crucial issue is the nonblocking operation of the overall system. Our main theorem identifies sufficient conditions for this desirable property.      

Robust supervision using shared-buffers in automated manufacturing systems with unreliable resources

It has been an active area of research to solve the modeling, analysis, and deadlock control problems for automated manufacturing systems (AMSs). So far, all the system resources are assumed to be reliable in most of the existing approaches for deadlock-free and nonblocking supervisory control. However, many resources of AMSs are subject to failure in the real world. In order to develop a more practical and applicable supervisor, this work takes into consideration of multiple unreliable resources in a class of AMSs. On the basis of two variants of Banker’s Algorithm, this paper presents a robust supervisory control policy to avoid deadlock and blocking in these systems. The policy tries to make the best use of buffers of the shared resources to achieve the control objectives. Our controller is qualified to handle simultaneous multi-resource failures. By using formal language and automata theory, we establish its correctness. Moreover, our proposed method is verified via an AMS example, and we make comparison studies between our policy and some of the other similar type of policies in the literature.     

A new delay system approach to network-based control

This paper presents a new delay system approach to network-based control. This approach is based on a new time-delay model proposed recently, which contains multiple successive delay components in the state. Firstly, new results on stability and H_∞ performance are proposed for systems with two successive delay components, by exploiting a new Lyapunov-Krasovskii functional and by making use of novel techniques for time-delay systems. An illustrative example is provided to show the advantage of these results. The second part of this paper utilizes the new model to investigate the problem of network-based control, which has emerged as a topic of significant interest in the control community. A sampled-data networked control system with simultaneous consideration of network induced delays, data packet dropouts and measurement quantization is modeled as a nonlinear time-delay system with two successive delay components in the state and, the problem of network-based H_∞ control is solved accordingly. Illustrative examples are provided to show the advantage and applicability of the developed results for network-based controller design.     

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.     

Modular Supervisory Control with Equivalence-Based Abstraction and Covering-Based Conflict Resolution

A modular approach to control is one way to reduce the complexity of supervisory controller design for discrete-event systems (DES). A problem, however, is that modular supervisors can conflict with one another. This paper proposes requirements on coordinating filters that will resolve this conflict. Abstractions are employed to reduce the complexity of the filter construction. Our specific approach is unique in that it employs a conflict-equivalent abstraction that offers the potential for greater reduction in model size than those abstractions employed in previous works on conflict resolution. The resulting control implemented by the modular supervisors in conjunction with coordinating filters meeting the proposed requirements is shown to be safe and nonblocking. Approaches for constructing these filters are discussed and a methodology that implements deterministic coordinating filter control laws by nondeterministic automata is presented. The covering-based filter law construction methodology presented here is further demonstrated to provide less restrictive control than existing results on state-feedback supervisory control.