Supervisory control of timed discrete-event systems subject to communication delays and non-FIFO observations

Conventional supervisory control synthesis techniques are not adequate anymore when a network between the plant and the supervisor introduces communication delays. This paper presents a method to synthesize a networked supervisor handling delays in both observation and control channels. To deal with the problem of delayed observations, we propose an automaton modeling the behaviour of the plant observed by a supervisor through a network, called observed plant. In this automaton, events observed by a supervisor are delayed from those occurring in the plant. Moreover, since observation channels are considered not to have the first in first out (FIFO) characteristic, events may not be necessarily observed in the same order as they occurred within the plant. A safe, observable, controllable and nonblocking supervisor is synthesized for the observed plant by means of an adapted synthesis algorithm for timed discrete-event systems (TDES). By enabling the achieved supervisor to predict the effects of control delays, it will be further transformed to a networked supervisor. The networked supervisor makes decisions ahead of time to ensure that the commands will be applied on the right (plant) state

Supervisory Control Synthesis of Timed Automata Using Forcible Events

Considering real-valued clocks in timed automata (TA) makes it a practical modeling framework for discrete-event systems. However, the infinite state space brings challenges to the control of TA. To synthesize a supervisor for TA using the conventional supervisory control theory, existing methods abstract TA to finite automata (FA). For many applications, the abstraction of real-time values results in an explosion in the state space of FA. This paper presents a supervisory control synthesis algorithm directly applicable to the TA without any abstraction. The plant is given as a TA with a set of uncontrollable events and a set of forcible events. Forcible events can preempt the passage of time when needed. The synthesis algorithm works by iteratively strengthening the guards of edges labeled by controllable events and invariants of locations where the progression of time can be preempted by forcible events. The synthesized supervisor, which is also a TA, is guaranteed to be controllable, maximally permissive, and results in a nonblocking and safe supervised plant

Networked Supervisory Control Synthesis of Timed Discrete-Event Systems

Conventional supervisory control theory assumes full synchronization between the supervisor and the plant. This assumption is violated in a networked-based communication setting due to the presence of delays, and this may result in incorrect behavior of a supervisor obtained from conventional supervisory control theory. This paper presents a technique to synthesize a networked supervisor handling communication delays. For this purpose, first, a networked supervisory control framework is provided, where the supervisor interacts with the plant through control and observation channels, both of which introduce delays. The control channel is FIFO, but the observation channel is assumed to be non-FIFO so that the observation of events may not necessarily be received by the supervisor in the same order as they occurred in the plant. It is assumed that a global clock exists in the networked control system, and so the communication delays are represented in terms of time. Based on the proposed framework, a networked plant automaton is achieved, which models the behavior of the plant under the effects of communication delays and disordered observations. Based on the networked plant, the networked supervisor is synthesized, which is guaranteed to be (timed networked) controllable, nonblocking, time-lock free, (timed networked) maximally permissive, and satisfies control requirements for the plant

Supervisory Control Synthesis of Timed Automata Using Forcible Events

Considering real-valued clocks in timed automata (TA) makes it a practical modeling framework for discrete-event systems. However, the infinite state space brings challenges to the control of TA. To synthesize a supervisor for TA using the conventional supervisory control theory, existing methods abstract TA to finite automata (FA). For many applications, the abstraction of real-time values results in an explosion in the state space of FA. This paper presents a supervisory control synthesis algorithm directly applicable to the TA without any abstraction. The plant is given as a TA with a set of uncontrollable events and a set of forcible events. Forcible events can preempt the passage of time when needed. The synthesis algorithm works by iteratively strengthening the guards of edges labeled by controllable events and invariants of locations where the progression of time can be preempted by forcible events. The synthesized supervisor, which is also a TA, is guaranteed to be controllable, maximally permissive, and results in a nonblocking and safe supervised plant

Supervisory Control Synthesis of Timed Automata Using Forcible Events

This paper presents an algorithm for synthesizing a supervisor for timed automata (TA) using the conventional supervisory control theory. The algorithm is directly applicable to TA without explicit transformation into finite automata, and iteratively strengthens the guards of edges labeled by controllable events and invariants of locations where the progression of time can be preempted by forcible events. The synthesized supervisor, also a TA, is controllable, maximally permissive, and guarantees a non-blocking and safe supervised plant. The use of real-valued clocks in TA makes it a practical modeling framework, however, the infinite state space brings challenges. The proposed algorithm addresses these by providing a synthesis method that avoids the state-space explosion of finite automata and the loss of information that can result from abstraction of real-time values

Networked Supervisory Control Synthesis of Timed Discrete-Event Systems

Conventional supervisory control theory assumes full synchronization between the supervisor and the plant. This assumption is violated in a networked-based communication setting due to the presence of delays, and this may result in incorrect behavior of a supervisor obtained from conventional supervisory control theory. This paper presents a technique to synthesize a networked supervisor handling communication delays. For this purpose, first, a networked supervisory control framework is provided, where the supervisor interacts with the plant through control and observation channels, both of which introduce delays. The control channel is FIFO, but the observation channel is assumed to be non-FIFO so that the observation of events may not necessarily be received by the supervisor in the same order as they occurred in the plant. It is assumed that a global clock exists in the networked control system, and so the communication delays are represented in terms of time. Based on the proposed framework, a networked plant automaton is achieved, which models the behavior of the plant under the effects of communication delays and disordered observations. Based on the networked plant, the networked supervisor is synthesized, which is guaranteed to be (timed networked) controllable, nonblocking, time-lock free, (timed networked) maximally permissive, and satisfies control requirements for the plant