1,721,077 research outputs found
Safe diagnosability for fault-tolerant supervision of discrete-event systems
No full textThe problem of achieving fault-tolerant supervision of discrete-event systems is considered from the viewpoint of safe and timely diagnosis of unobservable faults. To this end, the new property of safe diagnosability is introduced and studied. Standard definitions of diagnosability of discrete-event systems deal with the problem of detecting the occurrence of unobservable fault events using model-based inferencing from observed sequences of events. In safe diagnosability, it is required in addition that fault detection occur prior to the execution of a given set of forbidden strings in the failed mode of operation of the system. For instance, this constraint could be required to prevent local faults from developing into failures that could cause safety hazards. If the system is safe diagnosable, reconfiguration actions could be forced upon the detection of faults prior to the execution of unsafe behaviour, thus achieving the objective of fault-tolerant supervision. Necessary and sufficient conditions for safe diagnosability are derived. In addition, the problem of explicitly considering safe diagnosability in controller design, termed active safe diagnosis problem, is formulated and solved. A brief discussion of safe diagnosability for timed models of discrete-event systems is also provided
Diagnosability Analysis of a Class of Hierarchical State Machines
No full textThis paper addresses the problem of fault detection and isolation for a particular class of discrete event dynamical systems called hierarchical finite state machines (HFSMs). A new version of the property of diagnosability for discrete event systems tailored to HFSMs is introduced. This notion, called L1-diagnosability, captures the possibility of detecting an unobservable fault event using only high level observations of the behavior of an HFSM. Algorithms for testing L1-diagnosability are presented. In addition, new methodologies are presented for studying the diagnosability properties of HFSMs that are not L1-diagnosable. These methodologies avoid the complete expansion of an HFSM into its corresponding flat automaton by focusing the expansion on problematic indeterminate cycles only in the associated extended diagnoser
Optimal sensor selection for ensuring diagnosability in labeled bounded Petri nets
No full textThis paper studies the problem of optimal static sensor selection for ensuring diagnosability in labeled
bounded and unbounded Petri nets. Starting from a non-diagnosable labeled Petri net system, we present
a systematic procedure to design a new labeling function that makes the system diagnosable and
optimizes a given objective function. This procedure employs a particular net, called Verifier Net, that
is built from the original Petri net and provides necessary and sufficient conditions for diagnosability.
We exploit the system structure captured in the verifier net to guide the search for the desired new
labeling function. The search is performed over an unfolding of the reachability/coverability tree of the
verifier net and follows a set of rules that capture the relabeling strategy. We allow for unobservable
transitions that cannot be labeled as well as for multiple fault classes. We formulate an integer linear
programming problem that finds an optimal labeling function when numerical costs are associated with
transition relabeling
On the diagnosability of a class of hierarchical state machines
No full textThis paper addresses the problem of Fault Detection and Isolation for a particular class of discrete event dynamic systems named Hierarchical Finite State Machines (HFSMs). A new version of the property of diagnosability for discrete event systems tailored to HFSMs is introduced. This notion, called L1-diagnosability, captures the possibility of detecting an unobservable fault event using only high level observations of HFSMs. Algorithms for testing L1- diagnosability are presented. In addition, guidelines are presented for studying the diagnosability of HFSMs that are not L1-diagnosable
A fault tolerant architecture for supervisory control of discrete event systems
No full textIn this paper the problem of Fault Tolerant Control (FTC) in the framework of Discrete Event Systems (DES) modeled as automata is considered. The approach we follow is the so-called active approach in which the supervisor actively reacts to the detection of a malfunctioning component in order to eventually meet degraded control specifications. Starting from an appropriate model of the system, we recall the notion of safe diagnosability as a necessary step in order to achieve fault tolerant supervision of DES. We then introduce two new notions: (i) "safe controllability", which represents the capability, after the occurrence of a fault, of steering the system away from forbidden zones and (ii) "active fault tolerant system", which is the property of safely continuing operation after faults. We show how it is possible to define a general control architecture to deal with the FTC problem by introducing a special
kind of automaton, called a "diagnosing-controller"
Point Symmetries of the Generalized Toda Field Theories: II, Symmetry reduction
Full text linkAbstract The Lie symmetries of a large class of generalized Toda field theories are studied and used to perform symmetry reduction. Reductions lead to generalized Toda lattices on one hand, to periodic systems on the other. Boundary conditions are introduced to reduce theories on an infinite lattice to those on semi-infinite, or finite ones. Résumé Les symétries de Lie d'une grande classe de théories de champs de Toda sontétudiées et utilisées pour faire des réductions par symétries. D'une part, ces réductions nous donnent des treillis de Toda généralisés et, d'autre part, des systèmes périodiques. Nous utilisons des conditions frontières pour réduire les théories définies sur un réseau infinià des cas finis ou semi-infinis
A methodology for modular model-building in discrete automation
No full textOur objective is to develop a general and versatile approach for building structured formal models of complex automated systems in order to facilitate their control and diagnosis. For this purpose, we present a methodology that builds the complete model of a system by composing models of the individual hardware components, their physical coupling, and the associated control logic. We choose to employ a hierarchical decomposition that separates the control logic into a high level that manages the sequence of control actions and a low level that implements the control actions. The low level is composed of control logic and physical components (sensors and actuators) grouped into a device. In order to capture the physical constraints between the components in a device, we propose the notion of a physical constraint automaton, which is composed with the generic component automata to generate the complete model of the device. We also show how the methodology allows the introduction of component faults into the overall model. The effectiveness of the proposed approach is demonstrated on a micro flexible manufacturing system
Active fault tolerant control of discrete event systems using online diagnostics
No full textThe aim of this paper is to deal with the problem of fault tolerant control in the framework of discrete event systems modeled as automata. A fault tolerant controller is a controller able to satisfy control specifications both in nominal operation and after the occurrence of a fault. This task is solved by means of a parameterized controller that is suitably updated on the basis of the information provided by online diagnostics: the supervisor actively reacts to the detection of a malfunctioning component in order to eventually meet degraded control specifications. Starting from an appropriate model of the system, we recall the notion of safe diagnosability as a necessary step in order to achieve fault tolerant control. We then introduce two new notions: (i) “safe controllability”, which represents the capability, after the occurrence of a fault, of steering the system away from forbidden zones and (ii) “active fault tolerant system”, which is the property of safely continuing operation after faults. Finally, we show how the problem can be solved using a general control architecture based on the use of special kind of diagnoser, called “diagnosing controller”, which is used to safely detect faults and to switch between the nominal control policy and a bank of reconfigured control policies. A simple example is used to illustrate the new notions and the control architecture introduced in the paper
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