Limited Lookahead Policies for Robust Supervisory Control of Discrete Event Systems

In this thesis, Limited Lookahead Policies (LLP) have been developed for Robust Nonblocking Supervisory Control Problem (RNSCP) of discrete event systems. In the robust control problem considered here, the plant model is assumed to belong to a given finite set of DES models. The introduced supervisor computes the control action in online fashion and it is named Robust Limited Lookahead (RLL) supervisor. In comparison with offline supervisory control, RLL supervisor can reduce the complexity associated with the computation of control law as it looks at the behavior of system at the current state and of a limited depth in future. Since a conservative policy is adopted here, the behavior of the system under supervision of the RLL supervisor is generally more restrictive than the optimal offline supervisor. A sufficient condition is presented under which a limited lookahead window can guarantee the optimality (maximal permissiveness) of the RLL supervisor. In some problems, the required window length for maximally permissive RLL supervisor may become unbounded. To overcome this limitation RNSCP with State information (RNSCP-S) is studied and solved resulting in a state-based RLL (RLL-S) supervisor. The results of this thesis can be regarded as an extension of previous work in the literature on limited lookahead policies for (non-robust) supervisory control to the case of nonblocking robust supervisory control. The robust limited lookahead design procedures are implemented in MATLAB environment and applied to two examples involving spacecraft propulsion systems

Non-Blockingness Verification of Bounded Petri Nets Using Basis Reachability Graphs -- An Extended Version With Benchmarks

In this paper, we study the problem of non-blockingness verification by tapping into the basis reachability graph (BRG). Non-blockingness is a property that ensures that all pre-specified tasks can be completed, which is a mandatory requirement during the system design stage. In this paper we develop a condition of transition partition of a given net such that the corresponding conflict-increase BRG contains sufficient information on verifying non-blockingness of its corresponding Petri net. Thanks to the compactness of the BRG, our approach possesses practical efficiency since the exhaustive enumeration of the state space can be avoided. In particular, our method does not require that the net is deadlock-free.Comment: This article is an extended version of the paper "C. Gu, Z. Ma, Z. Li and A. Giua. Non-blockingness verification of bounded Petri nets using basis reachability graphs. IEEE Control Systems Letters, doi:10.1109/LCSYS.2021.3087937, 2021" with benchmark

A survey on compositional algorithms for verification and synthesis in supervisory control

This survey gives an overview of the current research on compositional algorithms for verification and synthesis of modular systems modelled as interacting finite-state machines. Compositional algorithms operate by repeatedly simplifying individual components of a large system, replacing them by smaller so-called abstractions, while preserving critical properties. In this way, the exponential growth of the state space can be limited, making it possible to analyse much bigger state spaces than possible by standard state space exploration. This paper gives an introduction to the principles underlying compositional methods, followed by a survey of algorithmic solutions from the recent literature that use compositional methods to analyse systems automatically. The focus is on applications in supervisory control of discrete event systems, particularly on methods that verify critical properties or synthesise controllable and nonblocking supervisors

Modular Verification and Supervisory Controller Design for Discrete-Event Systems Using Abstraction and Incremental Construction.

The subject of this dissertation is modular approaches to the verification and control of discrete-event systems (DES). DES are dynamic systems characterized by discrete states and event-driven evolution. In recent years, a substantial body of work has been built up to provide a theory and framework for the control and verification of DES. Despite all the advancements that have been made in this area, application to real-life systems has been somewhat slow. A significant hurdle to the adoption of these methods is the state-space explosion that occurs in modeling systems of the size most commonly found in industry. A common approach that has been applied to address this complexity problem is to construct a series of smaller modular supervisors, rather than a single monolithic supervisor. The problem with this approach is that the modular supervisors can often conflict with one another. This dissertation develops three new approaches to the supervisory control of DES that adopt a modular aspect to their control, while addressing the potential problem of conflict. The first approach addresses the problem of state-space explosion by offering a procedure for incrementally building modular supervisors that are guaranteed to not conflict with one another by construction. An observer type abstraction is employed to make the procedure more computationally feasible. The second approach of this dissertation constructs traditional modular supervisors, then adds another level of coordinating control to resolve conflict between the supervisors. This work employs a conflict-equivalence preserving abstraction to detect and resolve the conflict. The final approach of this dissertation employs interfaces between different components of the global system. The additional structure of these interfaces allows global properties to be verified through the achievement of local properties. Additionally, these interfaces allow for modular supervisors to be synthesized locally such that the necessary requirements are met by construction. In this work, the correctness of the three approaches is proven. Additionally, application to some manufacturing based examples are employed to illustrate the potential strengths and weaknesses of each of the approaches.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60669/1/rchill_1.pd

Supervisory control of discrete event systems for bisimulation or simulation equivalence

The supervisory control of discrete event systems provides a framework for control of event-driven systems. Applications of supervisory control theory include protocol design for communication processes, control logic synthesis in manufacturing systems, and collision avoidance in human-computer interaction systems.;When designing a system at a certain level of abstraction, lower level details of the system and its specification are normally omitted to obtain higher level models that may be (non-deterministic) event-driven systems. Nondeterministic systems exhibit both branching and sequential behaviors and are captured using bisimulation equivalence (the traditional language equivalence only captures sequential behaviors). Simulation equivalence is more expressive than language equivalence but captures only the universal fragment of branching behaviors.;This dissertation presents supervisory control of discrete event systems for enforcing bisimulation equivalence or simulation equivalence with respect to given specifications. We show that in the general setting of nondeterministic systems and specifications, the complexity for bisimilarity enforcing control is doubly exponential and for similarity enforcing control remains polynomial solvable. So the choice of behavioral equivalence used depends on the application at hand and there is a trade-off between the expressivity and the complexity. We further show that the bisimilarity enforcing control problem becomes polynomially solvable when the system model is deterministic and there is complete observability of events. When the complete observability requirement is relaxed, the control existence problem remains polynomially solvable and the control synthesis problem becomes singly exponential. These complexities are similar to the ones for control under partial observation in completely deterministic setting Tsitsiklis (1989).;We introduce various notions of state-controllability (SC), state-recognizability (SR), state-achievability (SA), state-controllable-similar (SCS), state-controllability-bisimilar (SCB), and state-achievability-bisimilar (SAB) for deterministic system model. SC is a property of a controlled system under complete observation. Under partial observation, an additional property of a controlled system due to the partial observation is SR. The combined property of SC and SR is called SA. We show that properties of SC, SR and SA are not preserved under bisimulation equivalence and therefore cannot be served as a necessary condition for the existence of a bisimilarity enforcing supervisor. We introduce the notions of SCB and SAB, which are preserved under bisimulation, as part of the necessary and sufficient condition for the existence of a supervisor under complete and partial observation, respectively. We show that SC is not preserved under simulation equivalence and introduce SCS as a necessary and sufficient condition for the existence of a similarity enforcing supervisor under complete observation.;The aforementioned results use strict synchronous composition (SSC) of the system and supervisor as a mechanism of control. In SSC, it is required that individual systems synchronously execute all events. Prioritized synchronous composition (PSC) relaxed such synchronization requirements and this has been shown to enrich the control capability when the plant is non-deterministic. (The presence of nondeterminism in a plant model may cause the current state to be known with ambiguity, and allowing the flexibility of not synchronizing an event at all the candidate states that plant may have reached provides for additional benefits.) This dissertation introduces a notion of prioritized synchronous composition under mask (PSCM) to account for partial observation. We study the supervisory control when PSCM is adopted as a mechanism of interaction for both language and bisimulation equivalences. We show that the control & observation-compatibility requirements are removed of a supervisor. For control to achieve a language equivalence, the existence condition is given by achievability that is weaker than controllability and observability combined. (The weaker condition is required since we allow supervisors to be nondeterministic.) This suggests that the notion of PSCM is an appropriate generalization of PSC to account for partial observation

From Security Enforcement to Supervisory Control in Discrete Event Systems: Qualitative and Quantitative Analyses

Cyber-physical systems are technological systems that involve physical components that are monitored and controlled by multiple computational units that exchange information through a communication network. Examples of cyber-physical systems arise in transportation, power, smart manufacturing, and other classes of systems that have a large degree of automation. Analysis and control of cyber-physical systems is an active area of research. The increasing demands for safety, security and performance improvement of cyber-physical systems put stringent constraints on their design and necessitate the use of formal model-based methods to synthesize control strategies that provably enforce required properties. This dissertation focuses on the higher level control logic in cyber-physical systems using the framework of discrete event systems. It tackles two classes of problems for discrete event systems. The first class of problems is related to system security. This problem is formulated in terms of the information flow property of opacity. In this part of the dissertation, an interface-based approach called insertion/edit function is developed to enforce opacity under the potential inference of malicious intruders that may or may not know the implementation of the insertion/edit function. The focus is the synthesis of insertion/edit functions that solve the opacity enforcement problem in the framework of qualitative and quantitative games on finite graphs. The second problem treated in the dissertation is that of performance optimization in the context of supervisory control under partial observation. This problem is transformed to a two-player quantitative game and an information structure where the game is played is constructed. A novel approach to synthesize supervisors by solving the game is developed. The main contributions of this dissertation are grouped into the following five categories. (i) The transformation of the formulated opacity enforcement and supervisory control problems to games on finite graphs provides a systematic way of performing worst case analysis in design of discrete event systems. (ii) These games have state spaces that are as compact as possible using the notion of information states in each corresponding problem. (iii) A formal model-based approach is employed in the entire dissertation, which results in provably correct solutions. (iv) The approaches developed in this dissertation reveal the interconnection between control theory and formal methods. (v) The results in this dissertation are applicable to many types of cyber-physical systems with security-critical and performance-aware requirements.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/150002/1/jiyiding_1.pd

Design and Management of Manufacturing Systems

Although the design and management of manufacturing systems have been explored in the literature for many years now, they still remain topical problems in the current scientific research. The changing market trends, globalization, the constant pressure to reduce production costs, and technical and technological progress make it necessary to search for new manufacturing methods and ways of organizing them, and to modify manufacturing system design paradigms. This book presents current research in different areas connected with the design and management of manufacturing systems and covers such subject areas as: methods supporting the design of manufacturing systems, methods of improving maintenance processes in companies, the design and improvement of manufacturing processes, the control of production processes in modern manufacturing systems production methods and techniques used in modern manufacturing systems and environmental aspects of production and their impact on the design and management of manufacturing systems. The wide range of research findings reported in this book confirms that the design of manufacturing systems is a complex problem and that the achievement of goals set for modern manufacturing systems requires interdisciplinary knowledge and the simultaneous design of the product, process and system, as well as the knowledge of modern manufacturing and organizational methods and techniques