Input/output discrete event processes and communication delays

This paper proposes an input/output interpretation for the control of discrete event systems. In supervisory control theory, the plant is usually considered to be a process which spontaneously generates outputs. Its behavior is controlled by disabling some of its output events. In this paper the plant accepts inputs (commands) and generates outputs (responses). For many real-life problems, e.g., manufacturing problems, this model semantics seems more applicable than the original generator perspective proposed by Ramadge and Wonham. In real-life systems the message exchange between the plant and the controller is affected by communication delays. The class of supervisors that must be used in a closed-loop system subject to communciation delays is a subset of the set of solutions to the original problem introduced by Ramadge and Wonham. After having characterized this class of supervisors, the present paper states conditions on the plant language that allow the supervisors solving the (delay-free) supervisory control problem of Ramadge and Wonham to be used also for the case of closedloop systems affected by delays.