272 research outputs found
Distributed Nonblocking Supervisory Control of Timed Discrete-Event Systems with Communication Delays and Losses
This paper investigates the problem of distributed nonblocking supervisory
control for timed discrete-event systems (DESs). The distributed supervisors
communicate with each other over networks subject to nondeterministic
communication delays and losses. Given that the delays are counted by time,
techniques have been developed to model the dynamics of the communication
channels. By incorporating the dynamics of the communication channels into the
system model, we construct a communication automaton to model the interaction
process between the supervisors. Based on the communication automaton, we
define the observation mappings for the supervisors, which consider delays and
losses occurring in the communication channels. Then, we derive the necessary
and sufficient conditions for the existence of a set of supervisors for
distributed nonblocking supervisory control. These conditions are expressed as
network controllability, network joint observability, and system language
closure. Finally, an example of intelligent manufacturing is provided to show
the application of the proposed framework
Distributed Supervisory Control of Discrete-Event Systems with Communication Delay
This paper identifies a property of delay-robustness in distributed
supervisory control of discrete-event systems (DES) with communication delays.
In previous work a distributed supervisory control problem has been
investigated on the assumption that inter-agent communications take place with
negligible delay. From an applications viewpoint it is desirable to relax this
constraint and identify communicating distributed controllers which are
delay-robust, namely logically equivalent to their delay-free counterparts. For
this we introduce inter-agent channels modeled as 2-state automata, compute the
overall system behavior, and present an effective computational test for
delay-robustness. From the test it typically results that the given delay-free
distributed control is delay-robust with respect to certain communicated
events, but not for all, thus distinguishing events which are not
delay-critical from those that are. The approach is illustrated by a workcell
model with three communicating agents
Symbolic Supervisory Control of Distributed Systems with Communications
We consider the control of distributed systems composed of subsystems communicating asynchronously; the aim is to build local controllers that restrict the behavior of a distributed system in order to satisfy a global state avoidance property. We model distributed systems as \emph{communicating finite state machines} with reliable unbounded FIFO queues between subsystems. Local controllers can only observe the behavior of their proper subsystem and do not see the queue contents. To refine their control policy, controllers can use the FIFO queues to communicate by piggy-backing extra information (some timestamps and their state estimates) to the messages sent by the subsystems. We provide an algorithm that computes, for each local subsystem (and thus for each controller), during the execution of the system, an estimate of the current global state of the distributed system. We then define a synthesis algorithm to compute local controllers. Our method relies on the computation of (co-)reachable states. Since the reachability problem is undecidable in our model, we use abstract interpretation techniques to obtain overapproximations of (co-)reachable states. An implementation of our algorithms provides an empirical evaluation of our method
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