By Topic

Discrete Event Systems, 2002. Proceedings. Sixth International Workshop on

Date 4-4 Oct. 2002

Filter Results

Displaying Results 1 - 25 of 59
  • Proceedings Sixth International Workshop on Discrete Event Systems

    Save to Project icon | Request Permissions | PDF file iconPDF (293 KB)  
    Freely Available from IEEE
  • Author index

    Page(s): 411 - 412
    Save to Project icon | Request Permissions | PDF file iconPDF (185 KB)  
    Freely Available from IEEE
  • A deadlock avoidance strategy for AGV systems modelled by coloured Petri nets

    Page(s): 61 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    Automated Guided Vehicle Systems (AGVSs) are material handling devices representing an efficient and flexible alternative for material handling. The vehicles follow a guidepath under computer control that assigns route, tasks, velocity, etc. However, the design of AGVSs has to take into account some management problems such as collisions and deadlock. This paper presents a control strategy to avoid deadlock and collisions in zone controlled AGVSs. In particular, the control scheme manages the assignments of new paths and next zone acquisition. Moreover, we propose coloured timed Petri nets to model the AGVS structure and dynamics. The model allows us an easy implementation of the control strategy working on the basis of the knowledge of the system state. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A discrete-event systems approach to communication induced checkpointing

    Page(s): 69 - 74
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    A particular communication protocol for distributed computations is examined in the context of supervisory control. A critical part of these protocols allows for the formation of special system states the system reliably returns to in the event of deadlock or failure. The proposed discrete-event system makes use of Z-path theory from distributed computing literature to provide decentralized controllers with information to identify these special states. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An extended event graph with negative places and negative tokens for time window constraints

    Page(s): 91 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (322 KB) |  | HTML iconHTML  

    We introduce negative places and negative tokens into timed event graphs in order to model and analyze time window constraints. A negative token moves backward at an associated transition firing. We develop a necessary and sufficient condition, based on the circuits, for the event graph to be live. A sequence of feasible infinite firing epochs exists for each transition. We present a linear programming model for finding a stable firing schedule. We also characterize the minimal cycle time as a revised critical circuit ratio and the range of the feasible cycle times. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Firing instant approach to control time critical systems in multi-product processing

    Page(s): 97 - 102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB) |  | HTML iconHTML  

    Time-critical systems are characterized by operation times between a minimum and a maximum value. Any transgression of these specifications acts against production quality. In this paper, we propose to use a firing instant approach to build temporal control when the systems process several kinds of parts. The formalism presented refers to lot switching when the cyclic scheduling is the same whatever the type of part. Under the same assumption, it can be applied to interlaced production leading to a steady state. The P-time Petri net is used as a modeling tool. The method is illustrated for an electroplating line with two types of products. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Diagnosis of asynchronous discrete event systems, a net unfolding approach

    Page(s): 182 - 187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    This paper studies the diagnosis of asynchronous discrete event systems. We follow a so-called true concurrency approach, in which neither the global state nor global time are available. Instead, we use only local states in combination with a partial order model of time; our basic mathematical tool is that of Petri net unfoldings. This study was motivated by the problem of event correlation in telecommunications network management. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • About disturbance decoupling of timed event graphs in dioids

    Page(s): 203 - 208
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (397 KB) |  | HTML iconHTML  

    This paper deals with control of timed event graphs (TEG) when a disturbance acts on transitions. We synthesize the greatest feedback controller which allows to match the disturbance action. Formally, this problem is very close of the classical problem of disturbance decoupling for linear systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Generalized multivariable control of discrete event systems in dioids

    Page(s): 197 - 202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    Dioids are algebraic structures suitable to represent a timed event graph by means of a linear state-space or transfer function model, where synchronization of events can be described. This paper proposes a model reference control strategy under partial observation and control of internal system transitions, where a controller is obtained by matching the closed-loop transfer function to a given transfer function (control specification). The problem formulation is quite general, allowing to deal studied cases in the literature as particular cases and to generalize some of them. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Liveness enforcing supervisors for railway networks using ES2PR Petri nets

    Page(s): 55 - 60
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (362 KB) |  | HTML iconHTML  

    In this paper we consider a high-level description of a railway network using a skeleton net that belongs to the class of ES2PR nets. The resource places of this model correspond to the action of a safeness enforcing supervisor. Liveness constraints may also be enforced for this class by adding appropriate monitor places designed using siphon analysis. We show how this can be done without an exhaustive computation of all siphons and characterize the cases in which this procedure can be recursively applied, giving a simple test for the closed loop net to remain an ES2PR net. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A method for estimating the holding times in timed event graphs

    Page(s): 209 - 216
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB) |  | HTML iconHTML  

    This contribution addresses the estimation problem of holding times in timed event graphs. Based on the known Petri net topology the holding times are determined such that an equation error is minimized. The paper investigates the important issue of convergence of the estimated parameters to the true parameter values and shows that this objective can be achieved by applying particularly chosen input signals. A new iterative estimation procedure is proposed using these suitably designed input signals. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An assume-guarantee reasoning for hierarchical coordination of discrete event systems

    Page(s): 75 - 80
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    The construction of a consistent abstraction plays a central role in the hierarchical control of discrete event systems. When constructing a consistent abstraction of a composed system it is first necessary to build the entire system, whose state space grows exponentially with the number of system components. Therefore it is desirable to build this consistent abstraction directly from the composition of consistent abstractions of the subsystems. But the composition of consistent abstractions of the subsystems is not necessarily a consistent abstraction of the composed system. This paper presents a method based on an assume-guarantee reasoning to build a consistent abstraction of the composed system by the composition of modified consistent abstractions of the subsystems. The method is then applied for a case of an Cooperative Adaptive Cruise Controller (CACC) system for an automobile. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Computing bounds for forbidden state reachability functions for controlled Petri nets

    Page(s): 225 - 230
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB) |  | HTML iconHTML  

    Characterizing uncontrollable reachability is a central issue in forbidden state control of discrete event systems. In this paper, we present methods for building expressions which estimate uncontrollable reachability in a general class of Petri nets and which characterize the control sets to ensure future markings will not be forbidden. These expressions are determined by constructing an abstract syntax tree from an analysis of the Petri net model of the system. We show that these expressions represent bounds that are useful for evaluating uncontrollable reachability and for evaluating control actions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • State feedback stabilizing controller for the failure recovery of timed discrete event systems

    Page(s): 113 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    While being placed resolutely within the reactive systems framework, this article approaches two techniques of failure recovery making it possible to characterize the essential properties of a safe controller but also to be able to generate its expression formally. The system, modeled as a timed discrete event system (TDES), will be characterized by two operating modes: nominal and degraded. When a failure occurs, the system continues its service on the basis of controllers that provide switching from the nominal to the degraded operating mode. In this spirit, concepts of controllability and stability may arise and we propose to investigate them within TDES. On the basis of these concepts, an algorithm is proposed for the synthesis of controllers able to carry out the system from its state of breakdown towards one of these operating modes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Equivalence of timed state machines and safe TPN

    Page(s): 119 - 124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB) |  | HTML iconHTML  

    We show that an important subclass of timed automata (Alur and Dill, 1994), called timed state machines, is weakly time equivalent to safe non-zero time Petri nets (TPNs) in the sense of Merlin and Farber (1976). We present an explicit construction for two-way translation between 1-safe TPNs and TSMs. The translation improves on the efficiency of other methods: the TSM obtained for a given net is polynomial in the size of the reachability graph, and a given TSM is translated into a net whose size grows linearly with that of the automaton model. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • IPA for loss volume and buffer workload in tandem SFM networks

    Page(s): 393 - 398
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (298 KB) |  | HTML iconHTML  

    This paper considers congestion-related performance metrics in tandem networks of Stochastic Fluid Models (SFMs), and derives their IPA gradient estimators with respect to buffer sizes. Specifically, the performance metrics in question are the total loss volume and the cumulative buffer workload (buffer contents), and the control parameter consists of buffer limits at both the node where the performance is measured and at an upstream node. The IPA estimators are unbiased and nonparametric, and hence can be computed on-line from field measurements as well as off-line from simulation experiments. The IPA derivatives are applied to packet-based networks, where simulation results support the theoretical developments. Possible applications to congestion management in telecommunications networks are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A compositional semantics for UML state machines aimed at performance evaluation

    Page(s): 295 - 302
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (406 KB) |  | HTML iconHTML  

    Unified Modeling Language (UML) is gaining acceptance to describe the behaviour of systems. It has attracted the attention of researchers that are interested in deriving, automatically, performance evaluation models from system's descriptions. A required step to automatically produce a performance model (as any executable model) is that the semantics of the description language is formally defined. Among the UML diagrams, we concentrate on state machines (SMs) and we build a semantics for a significant subset of them in terms of generalized stochastic Petri nets (GSPNs). The paper shows how to derive an executable GSPN model from a description of a system, expressed as a set of SMs. The semantics is compositional since the executable GSPN model is obtained by composing, using standard Petri net operators, the GSPN models of the single SMs, and each GSPN model is obtained by composition of submodels for SM basic features. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On minimal representations of Petri net languages

    Page(s): 237 - 242
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (287 KB) |  | HTML iconHTML  

    Given a metric over the class of labeled Petri nets, we consider the existence of a procedure that takes as input a description of an arbitrary, labeled Petri net, and returns a description of a (possibly different) labeled Petri net with the smallest metric that generates the same language as the input. We refer to such procedures as minimization procedures. In this paper we investigate the existence of minimization procedures for a variety of metrics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Undirected colored Petri net for modelling and supervisory control of AGV systems

    Page(s): 135 - 142
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    This paper presents closed AGV systems with bidirectional guide path networks, zone control for avoiding collisions, and dynamic route planning. An AGV system is represented as a colored Petri net with undirected arcs and directed tokens, which substantially reduces the number of net components and simplifies the insight into the model. We study the problem of marking liveness and associate this property with the permanent ability of the vehicles to attain any edge in the network. The requirement is a weak form of marking liveness, as it does not require that each transition be live with respect to each of its colors. For the analysis of the net dynamics, we introduce the notion of a partially directed graph, that is, a graph which can have both directed and undirected edges. The results allow us to determine uniquely the character (live or not-live) of states in the system, which can thus be applied in the design of the supervisory control for AGV systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Decentralized control of discrete event systems with bounded or unbounded delay communication

    Page(s): 18 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1030 KB) |  | HTML iconHTML  

    We introduce problems of decentralized control with delayed communication, where delays are either unbounded or bounded by a given constant k. In the k-bounded-delay model, between the transmission of a message and its reception, the plant can execute at most k events. In the unbounded-delay model, the plant can execute any number of events between transmission and reception. We show that our framework yields an infinite hierarchy of control problems, 𝒞𝒞 =𝒟𝒞𝒞0⊃𝒟𝒞𝒞1⊃𝒟𝒞𝒞2⊃···⊃𝒟𝒞𝒰𝒞⊃𝒟𝒞 , where CC is the set of control problems solvable with a single controller (centralized case) and 𝒟𝒞𝒞k (resp. 𝒟𝒞𝒰𝒞, 𝒟𝒞) is the set of problems solvable with two controllers in a k-bounded-delay network (resp. two controllers in an unbounded-delay network, two controllers without communication). The above containments are strict. We prove the undecidability of checking the existence of controllers in the unbounded-delay case, or in the case without any communication. Finally, we prove that a decentralized observation problem with bounded-delay communication is decidable. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Intelligent simulation for the estimation of the uplink outage probabilities in CDMA networks

    Page(s): 405 - 410
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB) |  | HTML iconHTML  

    In CDMA mobile networks, callers that are transmitting through a power station may cause interference at other power stations. When many users are already connected in the network, a new call may cause the signal to noise ratio to drop below a tolerance threshold. This phenomenon is called 'outage' and it provides an important measure of performance, useful in the design and control of the system. Evaluating this probability analytically has proven unsuccessful and only approximations exist today. Direct simulation of such networks is at present very slow because outage occurs infrequently - it may take hours to simulate directly a realistic model if a reasonable precision is desired. Thus this approach is not useful for design problems where one wishes to evaluate and compare performance of many different network models. In this work we implement a change of measure to estimate the outage probability using importance sampling. We present a functional estimator and a stochastic approximation method that are capable of learning the best parameters for the change of measure. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An algebraic approach for PLC programs verification

    Page(s): 303 - 308
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (299 KB) |  | HTML iconHTML  

    This article presents a verification based on a specific Boolean algebra, called II, and symbolic reasoning on equations defined in this algebra. The formal definition of this algebra enables to model binary signals that include variables states, events, as well as physical delays between events. The behavior of the generic function blocks of the IEC 61131 standard as well as of PLC programs using these function blocks can be described in this algebra. Properties proof on PLC programs is performed by demonstrating, from the program, the formulas that express in the II algebra the properties to be proved. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modelling and PLC-based implementation of modular supervisory control

    Page(s): 371 - 376
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (259 KB) |  | HTML iconHTML  

    Implementation of supervisory control in Programmable Logic Controllers (PLCs) typically requires that the underlying discrete event models of plant, specification and the supervisor itself fulfil a number of properties. These properties are discussed and methods for solving related problems are given. In particular, determinism and synchronisation issues are investigated. In a manufacturing system, for instance, there is typically a set of processes using a set of shared resources. Poor modelling may cause the system model to become nondeterministic. This can be circumvented by relabelling the relevant models. For industrial-sized models, though, this must be done automatically, something that we achieve by parameterising the models. Given a deterministic model, consisting of several interacting entities, we discuss its PLC-based implementation. In addition to the synchronisation of plant and supervisor, a modular supervisor must be internally synchronised. However, synchronisation of the submodules is not well defined in the PLC-world. This may be achieved by using event monitors and an immediate transit/immediate action execution model. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Variability expansion for performance characteristics of (max,plus)-linear systems

    Page(s): 245 - 250
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (506 KB) |  | HTML iconHTML  

    We propose a new approach to performance evaluation of transient performance characteristics of stochastic (max,+)-linear systems. Our motivating example is the transient waiting time in the G/G/1 queue. Numerical results are given to illustrate the performance of our method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Model checking embedded system designs

    Page(s): 151 - 158
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    We survey the basic principles behind the application of model checking to controller verification and synthesis. A promising development is the area of guided model checking, in which the state space search strategy of the model checking algorithm can be influenced to visit more interesting sets of states first. In particular, we discuss how model checking can be combined with heuristic cost functions to guide search strategies. Finally, we list a number of current research developments, especially in the area of reachability analysis for optimal control and related issues. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.