It is well known that type-1 fuzzy sets (T1 FSs) have limited capabilities to handle some data uncertainties directly, and type-2 fuzzy sets (T2 FSs) can cover the shortcoming of T1 FSs to a certain extent. Fuzzy discrete event systems (FDESs) were proposed based on T1 FSs theory. Hence, FDES may not be a satisfactory model to characterize some high-uncertainty systems. In this paper, we propose a new model, called as bi-fuzzy discrete event systems (BFDESs), by combining classical DESs theory and T2 FSs theory. Then, we consider the supervisory control problem of BFDESs. The bi-fuzzy controllability theorem and nonblocking bi-fuzzy controllability theorem are demonstrated. Also, an algorithm for checking the bi-fuzzy controllability condition is presented. In addition, two controllable approximations to an uncontrollable language are investigated in detail. An illustrative example is provided to show the applicability and the advantages of BFDESs model.
This paper proposes a robust design of Hybrid Fuzzy Controller for speed and steering angle control in an Intelligent Autonomous Parking System (IAPS). The Hybrid Fuzzy Controller consists of a Base Fuzzy Controller (BFC) and a Supervisory Fuzzy Decision Tree Controller (SFDTC). The BFC evolves from previous work on fuzzy logic control for unmanned parking and it ensures that optimal parking trajectory is achieved with minimal computational cost. SFDTC further increases the system robustness when there is noise in the operating environment. The design of SFDTC combines Decision Tree theory and…
In the supervisory control framework of discrete-event systems (DES) with infinite behavior initiated by Thistle and Wonham, a supervisor satisfying the minimal acceptable specification and the maximal legal specification is synthesized. However, this supervisor may incur livelocks as it cannot ensure that the infinite behavior under supervision will always visit some marker states. To tackle this problem, we propose the definition of markability by requiring that all infinite cycles include at least one marker state. Then we formulate the problem of $ω-$nonblocking supervisory control of DES …
This paper presents an intelligent autonomous parking system with Hybrid Fuzzy Controllers (HFCs). The system enables intelligent vehicles to perform slot detection, parallel and vertical parking in a completely unmanned environment. The HFC, constituting of a Base Fuzzy Controller (BFC) and a Supervisory Fuzzy Controller (SFC), optimizes the control logic to counteract external disturbances in parking process by implementing additional fuzzy rule base. Customized HFCs are designed for critical steps in parking, namely turning control and posture stabilization. As a result, more accurate and e…
In this paper we investigate multi-agent discrete-event systems with partial observation. The agents can be divided into several groups in each of which the agents have similar (isomorphic) state transition structures, and thus can be relabeled into the same template. Based on the template a scalable supervisor whose state size and computational cost are independent of the number of agents is designed for the case of partial observation. The scalable supervisor under partial observation does not need to be recomputed regardless of how many agents are added to or removed from the system. We gen…
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 wh…
On Scalable Supervisory Control of Multi-Agent Discrete-Event Systems
School of Electro-Mechanical Engineering, Xidian University（西安电子科技大学机电工程学院）；Department of Electrical & Information Engineering, Osaka City University（大阪城市大学电气与信息工程系）；Institute of Systems Engineering, Macau University of Science and Technology（澳门科技大学系统工程研究所）
This paper investigates the problem of co-synthesis of edit function and supervisor for opacity enforcement in the supervisory control of discrete-event systems (DES), assuming the presence of an external (passive) intruder, where the following goals need to be achieved: 1) the external intruder should never infer the system secret, i.e., the system is opaque, and never be sure about the existence of the edit function, i.e., the edit function remains covert; 2) the controlled plant behaviors should satisfy some safety and nonblockingness requirements, in the presence of the edit function. We f…
We propose an on-line supervisory control scheme for discrete event systems (DESs), where a control specification is described by a fragment of linear temporal logic. On the product automaton of the DES and an acceptor for the specification, we define a ranking function that returns the minimum number of steps required to reach an accepting state from each state. In addition, we introduce a permissiveness function that indicates a time-varying permissive level. At each step during the on-line control scheme, the supervisor refers to the permissiveness function as well as the ranking function i…
This paper presents an overview of the networked supervisory control framework for discrete event systems with imperfect communication networks, which can be divided into the centralized supervisory control setup and the decentralized supervisory control setup. We review the state-of-art networked control frameworks with observation channel delays and control channel delays, for untimed and timed models. Data losses in communication channels are also considered. The review of the state-of-art networked control frameworks will be focused on the following parts: 1) the construction of the networ…
We study the security of Cyber-Physical Systems (CPS) in the context of the supervisory control layer. Specifically, we propose a general model of a CPS attacker in the framework of discrete event systems and investigate the problem of synthesizing an attack strategy for a given feedback control system. Our model captures a class of deception attacks, where the attacker has the ability to hijack a subset of sensor readings and mislead the supervisor, with the goal of inducing the system into an undesirable state. We utilize a game-like discrete transition structure, called Insertion-Deletion A…
Distributed Supervisory Control of Discrete-Event Systems with Communication Delay
School of Automation, Northwestern Polytechnical University（西北工业大学自动化学院）；Urban Research Plaza, Osaka City University（大阪市立大学城市研究广场）；School of Electrical Engineering, Xi¡¯an Jiaotong University（西安交通大学电气工程学院）；Systems Control Group, Department of Electrical and Computer Engineering, University of Toronto（多伦多大学电气与计算机工程系系统控制组）
This work deals with the production planning problem in Discrete Event Systems, using the Supervisory Control Theory to delimit the search universe and developing two heuristics based on the maximization of the parallelism to find sequences that minimize makespan. The role of the Supervisory Control Theory is to provide the set of all safe production sequences, given by the closed loop behavior. Although the use of heuristics does not provide necessarily the absolute optimal solution in general, we present a case study where it happens for all batch sizes. The efficiency in terms of computatio…
We consider feedback control systems where sensor readings may be compromised by a malicious attacker intending on causing damage to the system. We study this problem at the supervisory layer of the control system, using discrete event systems techniques. We assume that the attacker can edit the outputs from the sensors of the system before they reach the supervisory controller. In this context, we formulate the problem of synthesizing a supervisor that is robust against the class of edit attacks on the sensor readings and present a solution methodology for this problem. This methodology blend…
Supervisory Control of Discrete-event Systems under Attacks
Graduate School of System Informatics, Kobe University（神户大学系统信息学研究科）；Department of Electrical Engineering, University of California, Los Angeles（加州大学洛杉矶分校电气工程系）；Center for Control, Dynamical-systems, and Computation, University of California, Santa Barbara（加州大学圣塔芭芭拉分校控制、动力学与计算中心）
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 o…
Conditions preserving observability of specifications between the plant and its abstraction are essential for hierarchical supervisory control of discrete-event systems under partial observation. Observation consistency and local observation consistency were identified as such conditions. To preserve normality, only observation consistency is required. Although observation consistency preserves normality between the levels for normal specifications, for specifications that are not normal, observation consistency is insufficient to guarantee that the supremal normal sublanguage computed on the …
Manufacturing systems may be subject to external attacks and failures, so it is important to deal with the recovery of the system after these situations. This paper deals with the problem of recovering a manufacturing system, modeled as a Discrete Event System (DES) using the Supervisory Control Theory (SCT), when the control structure, called supervisor, desynchronizes from the physical plant. The desynchronization may be seen as plant and supervisor being in uncorresponding states. The recovery of the system may be attained if there is a word, the synchronizing word, that regardless the stat…
Abstract-In this manuscript, model predictive control for class of discrete fuzzy large-scale systems subjected to bounded time-varying delay and disturbances is studied. The considered method is Razumikhin for time-varying delay large-scale systems, in which it includes a Lyapunov function associated with the original non-augmented state space of system dynamics in comparison with the Krasovskii method. As a rule, the Razumikhin method has a perfect potential to avoid the inherent complexity of the Krasovskii method especially in the presence of large delays and disturbances. The considered l…
In this paper, we investigate joint sensor-actuator cyber attacks in discrete event systems. We assume that attackers can attack some sensors and actuators at the same time by altering observations and control commands. Because of the nondeterminism in observation and control caused by cyber attacks, the behavior of the supervised system becomes nondeterministic and may deviate from the safety specification. We define the upper-bound on all possible languages that can be generated by the supervised system to investigate the safety supervisory control problem under cyber attacks. After introduc…
This paper investigates the problem of synthesizing sensor deception attackers against privacy in the context of supervisory control of discrete-event systems (DES). We consider a DES plant controlled by a supervisor, which is subject to sensor deception attacks. Specifically, we consider an active attacker that can tamper with the observations received by the supervisor by, e.g., hacking on the communication channel between the sensors and the supervisor. The privacy requirement of the supervisory control system is to maintain initial-state opacity, i.e., it does not want to reveal the fact t…
In decentralized networked supervisory control of discrete-event systems (DESs), the local supervisors observe event occurrences subject to observation delays to make correct control decisions. Delay coobservability describes whether these local supervisors can make sufficient observations. In this paper, we provide an efficient way to verify delay coobservability. For each controllable event, we partition the specification language into a finite number of sets such that strings in different sets have different lengths. For each of the sets, we construct a verifier to check if delay coobservab…
In this paper, we investigate the enforcement of opacity via supervisory control in the context of discrete-event systems. A system is said to be opaque if the intruder, which is modeled as a passive observer, can never infer confidently that the system is at a secret state. The design objective is to synthesize a supervisor such that the closed-loop system is opaque even when the control policy is publicly known. In this paper, we propose a new approach for enforcing opacity using non-deterministic supervisors. A non-deterministic supervisor is a decision mechanism that provides a set of cont…
Maximally Permissive Coordination Supervisory Control -- Towards Necessary and Sufficient Conditions
Institute of Mathematics, Academy of Sciences of the Czech Republic（捷克科学院数学研究所）；Faculty of Computer Science, TU Dresden（德累斯顿工业大学计算机学院）；Van Schuppen Control Research（范舒彭控制研究）
Opacity Enforcing Supervisory Control with a Priori Unknown Supervisors
Shanghai Jiao Tong University（上海交通大学）；Key Laboratory of System Control and Information Processing, the Ministry of Education of China（教育部系统控制与信息处理重点实验室）；Xidian University（西安电子科技大学）；University of Cagliari（卡利亚里大学）
There is an increasing need to study the vulnerability of communication protocols in distributed systems to malicious attacks that attempt to violate properties such as safety or nonblockingness. In this paper, we propose a common methodology for formal synthesis of successful attacks against two well-known protocols, the Alternating Bit Protocol (ABP) and the Transmission Control Protocol (TCP), where the attacker can always eventually win, called For-all attacks. This generalizes previous work on the synthesis of There-exists attacks for TCP, where the attacker can sometimes win. We model th…
This paper introduces an add-on, supervisory scheme, referred to as Action Governor (AG), for discrete-time linear systems to enforce exclusion-zone avoidance requirements. It does so by monitoring, and minimally modifying when necessary, the nominal control signal to a constraint-admissible one. The AG operates based on set-theoretic techniques and online optimization. This paper establishes its theoretical foundation, discusses its computational realization, and uses two simulation examples to illustrate its effectiveness.
Some problems in discrete-event systems (DES) model large, time-varying state spaces with complex legal languages. To address these problems, Chung et al. introduced limited lookahead policies (LLP) to provide online supervisory control for discrete-event systems. This seminal paper, along with an addendum of technical results, provided the field with a series of very important and powerful results, but in a notationally- and conceptually-dense manner. In this tutorial, we present Chung et al.'s problem formulation for online control and unravel the formal definitions and proofs from their ori…
This work introduces a general formulation of the reconfiguration problem for untimed discrete-event systems (DES), which can be treated directly by supervisory control theory (SCT). To model the reconfiguration requirements we introduce the concept of reconfiguration specification (RS); here reconfiguration events (RE) are introduced to force a transition from one system configuration to another. Standard SCT synthesis is employed to obtain a reconfiguration supervisor (RSUP) in which designated states serve as the source states for RE. The reconfiguration problem itself is formulated as that…
