Supervisor Localization Research Articles

Transformational Supervisor Localization

Supervisor localization can be applied to distribute a monolithic supervisor into local supervisors. Performing supervisor localization can be computationally costly. In this work, we consider systems that evolve over time. We study how to reuse the results from a previous supervisor localization, to more efficiently compute local supervisors when the system is adapted. We call this approach transformational supervisor localization, and present algorithms for the procedure. The efficiency of the procedure is experimentally evaluated.

Distributed supervisory control for multiple robot autonomous navigation performing single-robot tasks

This paper proposes two new approaches based on the Supervisory Control Theory (SCT) of Discrete Event Systems (DES) for autonomous navigation of multiple robots with single-robot tasks being assigned by a centralized scheduler. The two planning strategies differ regarding their implementation, which can be centralized or distributed. Nevertheless, both approaches share the central objective of considering the scheduler and robots as DES, allowing the use of SCT to model and control the behavior of the whole multi-robotic system. Particularly, SCT is used to gather deliberative and reactive motion planning algorithms through a structured procedure, aiming to safely navigate in cluttered, dynamic, partially-known environments. The open-loop behavior of the autonomous navigation system is modeled for both approaches. Moreover, standard supervisors are obtained for the centralized planning approach. In addition, the supervisor localization method is considered to allow a distributed planning approach. Furthermore, as a case study, real experiments considering mobile robots are carried out to corroborate the proposed framework.

On coparanormality in distributed supervisory control of discrete‐event systems

AbstractDecomposition and localization of a supervisor are both reduction methods in distributed supervisory control of discrete‐event systems. Decomposition is employed to reduce the number of events and localization is used to reduce the number of states of local controllers. In decomposition of a supervisor both observation and control scopes are restricted, whereas in localization only control authority is restricted to the corresponding local controller. In this paper, we propose a decomposition method by defining a coparanormality property, and by using the relative observability property of a monolithic supervisor. Coparanormality is a coobservation property defined based on a paranormality property for a set of natural projections. It is shown that each supervisor can be coparanormal, provided a set of appropriate natural projections exist. Moreover, it is proved that relative observability is a sufficient condition to decompose a supervisor. Furthermore, the supervisor localization procedure is generalized to find a set of local controllers for any partition of the controllable events set. The implementation of such local controllers may become easier in industrial systems.

Supervisor Localization of Timed Discrete-Event Systems Under Partial Observation

We study supervisor localization for timed discrete-event systems under partial observation in the Brandin–Wonham framework. First, we employ timed relative observability to synthesize a partial-observation monolithic supervisor; the control actions of this supervisor include not only disabling action of prohibitible events (as that of controllable events in the untimed case) but also “clock-preempting” action of forcible events. Accordingly, we decompose the supervisor into a set of partial-observation local controllers one for each prohibitible event, as well as a set of partial-observation local preemptors one for each forcible event. We prove that these local controllers and preemptors collectively achieve the same controlled behavior as the partial-observation monolithic supervisor does. The above-mentioned results are illustrated by a timed workcell example.

What information really matters in supervisor reduction?

To make a supervisor comprehensible to a layman has been a long-lasting goal in the supervisory control community. One strategy is to reduce the size of a supervisor to generate a control equivalent version, whose size is hopefully much smaller than the original one so that a user or control designer can easily check whether a designed controller fulfils its objectives and requirements. After the first journal paper on this topic appeared in 1986 by Vaz and Wonham, which relied on the concept of control covers, in 2004 Su and Wonham proposed to use control congruences to ensure computational viability. This work is later adopted in the supervisor localization theory, which aims for a control equivalent distributed implementation of a given centralized supervisor. But after so many publications, some fundamental questions, which should have been addressed in the first place, have not been answered yet, namely what information is critical to ensure control equivalence, what information is responsible for size reduction, and whether the partial observation really makes things different. In this paper we will address these fundamental questions by showing that there does exist a unified supervisor reduction theory, which is applicable to all feasible supervisors regardless of whether they are under full observation or partial observation. Our theory provides a partial order over all control equivalent feasible supervisors based on their enabling, disabling and marking information, which can be used to categorize the corresponding reduction rates. Based on this result we can see that, given two control equivalent feasible supervisors, the one under full observation can always result in a reduced supervisor no bigger than that induced by a supervisor under partial observation.

Supervisor Localization of Discrete-Event Systems with Infinite Behavior

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems (DES) with finite behavior. Its essence is the allocation of monolithic (global) control action among individual (local) control strategies of component agents. In this paper, we extend supervisor localization to study distributed control of DES with infinite behavior, in order to address specifications of the ‘eventuality’ or ‘liveness’ type. Specifically, we first employ Thistle and Wonham’s supervisory control theory for DES with infinite behavior to compute a safety supervisor (enforcing desired finite behavior) and a liveness supervisor (enforcing desired infinite behavior), and then design a suitable localization procedure to decompose the obtained supervisors respectively into local safety and liveness controllers. We prove that the derived local safety/liveness controllers collectively achieve the same controlled behavior as the monolithic supervisors do.

Supervisor localization of discrete-event systems under partial observation

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems. Its essence is the allocation of monolithic (global) control action among the local control strategies of individual agents. In this paper, we extend supervisor localization by considering partial observation; namely not all events are observable. Specifically, we employ the recently proposed concept of relative observability to compute a partial-observation monolithic supervisor, and then design a suitable localization procedure to decompose the supervisor into a set of local controllers. In the resulting local controllers, only observable events can cause state change. We finally illustrate our result by a Transfer Line example.

New results on supervisor localization, with case studies

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems in the Ramadge-Wonham supervisory control framework. Its essence is the allocation of monolithic (global) control action among the local control strategies of individual agents. In this paper, we start by presenting several refinements of our localization theory. First, we drop the original assumption that the event sets of component agents are pairwise disjoint. Second, we show that consistent marking information can be enforced by just one agent, which can be selected arbitrarily. Third, the event sets of localized controllers are explicitly defined, in general as proper subsets of the entire event set. For these generalizations, we again prove that the collective local controlled behavior is identical to the global optimal and nonblocking controlled behavior. Moreover, we provide a language interpretation of localization by relating the key concept of control cover/congruence on the supervisor's state set to a special right congruence on the supervisor's language.W e go on to apply the extended supervisor localization to solve a multi-agent formation problem. We introduce a suitable formulation of formation invariance as well as shortest paths to formation. Local strategies are synthesized for a group of agents to arrive at a pre-specified formation in shortest paths; then issues of information exchange and control logic are examined. We further demonstrate the extended localization on a large-scale Cluster Tool example. By first synthesizing a set of decentralized supervisors and coordinators by an efficient heterarchical approach, our localization yields a distributed control architecture with comprehensible local control/coordination logic.

Supervisor Localization of Discrete-Event Systems Based on State Tree Structures

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems in the Ramadge-Wonham supervisory control framework. Its essence is the decomposition of monolithic (global) control action into local control strategies for individual agents. In this technical note, we establish a counterpart localization theory in the framework of State Tree Structures, known to be efficient for control design of very large systems. We prove that the collective localized control behavior is identical to the monolithic optimal (i.e. maximally permissive) and nonblocking controlled behavior. Further, we propose a new and more efficient localization algorithm which exploits BDD computation.

Supervision localization of timed discrete-event systems

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.

New Results on Supervisor Localization, with Application to Multi-Agent Formations

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems in the Ramadge-Wonham supervisory control framework. Its essence is the allocation of monolithic (global) control action among the local control strategies of individual agents. In this paper, we start by presenting several refinements of our localization theory. First, we drop the original assumption that the event sets of component agents are pairwise disjoint. Second, we show that consistent marking information can be enforced by just one agent, which can be selected arbitrarily. Third, the event sets of localized controllers are explicitly defined, in general as proper subsets of the entire event set. For these generalizations, we again prove that the collective local controlled behavior is identical to the global optimal and nonblocking controlled behavior. We go on to apply supervisor localization to solve a multi-agent formation problem. A suitable formulation of convergence to formations is first introduced; then local strategies are synthesized for a group of agents to arrive at an arbitrarily pre-specified formation, and issues of information exchange and control logic are examined.

Supervisor localization for large discrete-event systems

Supervisor localization for large discrete-event systems

Supervisor Localization: A Top-Down Approach to Distributed Control of Discrete-Event Systems

We study the design of distributed control for discrete-event systems (DES) in the framework of supervisory control theory. We view a DES as comprised of a group of agents, acting independently except for specifications on global (group) behavior. The central problem investigated is how to synthesize local controllers for individual agents such that the resultant controlled behavior is identical with that achieved by global supervision. In the case of small-scale DES, a supervisor localization algorithm is developed that solves the problem in a top-down fashion: first, compute a global supervisor, then decompose it to local controllers while preserving the global controlled behavior. In the case of large-scale DES where owing to state explosion a global supervisor might not be feasibly computable, a decomposition-aggregation solution procedure is developed that combines the supervisor localization algorithm with an efficient modular control theory.