We identify a new observability concept, called relative observability, in supervisory control of discrete-event systems under partial observation. A fixed, ambient language is given, relative to which observability is tested. Relative observability is stronger than observability, but enjoys the important property that it is preserved under set union; hence there exists the supremal relatively observable sublanguage of a given language. Relative observability is weaker than normality, and thus yields, when combined with controllability, a generally larger controlled behavior; in particular, no constraint is imposed that only observable controllable events may be disabled. We design new algorithms which compute the supremal relatively observable (and controllable) sublanguage of a given language, which is generally larger than the normal counterparts. We demonstrate the new observability concept and algorithms with a Guideway and an AGV example. I. INTRODUCTIONIn supervisory control of discrete-event systems, partial observation arises when the supervisor does not observe all events generated by the plant [1], [2]. This situation is depicted in Fig. 1(a), where G is the plant with closed behavior L(G) and marked behavior L m (G), P is a natural projection that nulls unobservable events, and V o is the supervisor under partial observation. The fundamental observability concept is identified in [3], [4]: observability and controllability of a language K ⊆ L m (G) is necessary and sufficient for the existence of a nonblocking supervisor V o synthesizing K. The observability property is not, however, preserved under set union, and hence there generally does not exist the supremal observable and controllable sublanguage of a given language. K. Cai is with Urban Research Plaza,

We study supervisor localization for real-time discrete-event systems (DES) in the Brandin-Wonham framework of timed supervisory control. We view a real-time DES as comprised of asynchronous agents which are coupled through imposed logical and temporal specifications; the essence of supervisor localization is the decomposition of monolithic (global) control action into local control strategies for these individual agents. This study extends our previous work on supervisor localization for untimed DES, in that monolithic timed control action typically includes not only disabling action as in the untimed case, but also "clock preempting" action which enforces prescribed temporal behavior. The latter action is executed by a class of special events, called "forcible" events; accordingly, we localize monolithic preemptive action with respect to these events. We demonstrate the new features of timed supervisor localization with a manufacturing cell case study, and discuss a distributed control implementation.

ω−closure (together with ω−controllability) plays an important role in the supervisor synthesis for liveness specifications imposed on discrete-event systems (DESs) with infinite behavior. However, it is not closed under arbitrary unions, and thus there does not exist the supremal ω−closed (and ω−controllable) sublanguage. In this paper, we first develop an algorithm to compute a subautomaton of the automaton representing an arbitrarily given ω-language by deleting all bad loops (which lead to un-closedness of the given language) in the automaton, and show that the obtained subautomaton represents an ω−closed sublanguage and is maximal from the perspective of an automaton transition graph. With this algorithm, we propose a new approach to construct a supervisor synthesizing an ω−language even if it is not ω−closed. Furthermore, we prove that, compared with the supervisor computed by the Thistle's supervisor synthesis approach, the supervisor synthesized by our approach is often more permissive. Examples are presented for illustration. INDEX TERMS Discrete-event systems, infinite behavior, ω−closure, ω−automata.

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This paper aims at developing a compact-size and low-power active control system for harmonic vibration attenuation. A new switching control system is proposed for this purpose. In the new system, the power amplifier in charge of voltage amplification is replaced by a filterless switching circuit, which directly receives digital pulse control signal from the external adaptive controller and produces high voltage in pulse form across PZT. The compact circuit design combining with adaptive filter dramatically simplifies the control system by removing digital-toanalog converter and voltage (current) feedback originally used in most amplifiers for less distortion. In particular, the hybrid switching control mode of the new system is specially addressed. The theoretical and experimental analysis reveals that hybrid switching control brings a great power reduction at the price of small control performance loss. Finally, the validating experiments are carried out, and experimental results show remarkable effectiveness for vibration suppression.

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We study the new concept of relative coobservability in decentralized supervisory control of discrete-event systems under partial observation. This extends our previous work on relative observability from a centralized setup to a decentralized one. A fundamental concept in decentralized supervisory control is coobservability (and its several variations); this property is not, however, closed under set union, and hence there generally does not exist the supremal element. Our proposed relative coobservability, although stronger than coobservability, is algebraically well-behaved, and the supremal relatively coobservable sublanguage of a given language exists. We present an algorithm to compute this supremal sublanguage. Moreover, relative coobservability is weaker than conormality, which is also closed under set union; unlike conormality, relative coobservability imposes no constraint on disabling unobservable controllable events.