Networked Supervisor Synthesis Against Lossy Channels with Bounded Network Delays as Non-Networked Synthesis

In this work, we study the problem of supervisory control of networked discrete event systems. We consider lossy communication channels with bounded network delays, for both the control channel and the observation channel. By a model transformation, we transform the networked supervisor synthesis problem into the classical (non-networked) supervisor synthesis problem (for non-deterministic plants), such that the existing supervisor synthesis tools can be used for synthesizing networked supervisors. In particular, we can use the (state-based) normality property for the synthesis of the supremal networked supervisors, whose existence is guaranteed by construction due to our consideration of command non-deterministic supervisors. The effectiveness of our approach is illustrated on a mini-guideway example that is adapted from the literature, for which the supremal networked supervisor has been synthesized in the synthesis tools SuSyNA and TCT.Comment: This paper is under review for Automatic

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

Detection and Prevention of Cyber-Attacks in Networked Control Systems

This paper addresses the problem of detection and prevention of cyber attacks in discrete event systems where the supervisor communicates with the plant via network channels. Random control delays may occur in such networked systems, hence the control of the supervisor could be affected. Furthermore, there is an attacker targeting the vulnerable actuators. The attacker can corrupt the control input generated by the supervisor, and aims at driving the plant to unsafe states. We propose a new approach to model the closed-loop system subject to control delays and attacks. The notion of AE-safe controllability in the networked control system is defined: it describes the ability to prevent the plant from reaching unsafe states after attacks are detected. A method for testing AE-safe controllability is also presented. Copyright (C) 2020 The Authors

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