Diagnosis using labeled Petri nets with silent or undistinguishable fault events

A commonplace assumption in the fault diagnosis of discrete event systems (DESs) is that of modeling faulty events with unobservable transitions, i.e., transitions whose occurrence does not produce any observable label. The diagnostic system must thus infer the occurrence of a fault from the observed behavior corresponding to the firing of nonfaulty transitions. The presence of nonfaulty unobservable transitions is a source of additional complexity in the diagnostic procedure. In this paper, we assume that fault events can also be modeled by observable transitions, i.e., transitions whose occurrence produces an observable label. This does not mean, however, that the occurrence of such a transition can be unambiguously detected: In fact, the same label may be shared with other fault transitions (e.g., belonging to different fault classes) or with other nonfaulty transitions. We generalize to this new setting our previous results on the diagnosis of DESs using Petri nets based on the notions of minimal explanations and basis markings. The presented procedure does not require the enumeration of the complete reachability set but only of the subset of basis markings, thus reducing the computational complexity of solving a diagnosis problem

Petri Nets at Modelling and Control of Discrete-Event Systems Containing Nondeterminism - Part 1

Discrete-Event Systems are discrete in nature, driven by discrete events. Petri Nets are one of the mostly used tools for their modelling and control synthesis. Place/Transitions Petri Nets, Timed Petri Nets, Controlled Petri Nets are suitable when a modelled object is deterministic. When the system model contains uncontrollable/unobservable transitions and unobservable/unmeasurable places or other failures, such kinds of Petri Nets are insufficient for the purpose. In such a case Labelled Petri Nets and/or Interpreted Petri Nets have to be used. Particularities and mutual differences of individual kinds of Petri Nets are pointed out and their applicability to modelling and control of Discrete-Event Systems are described and tested

On the Equivalence of Observation Structures for Petri Net Generators

Observation structures considered for Petri net generators usually assume that the firing of transitions may be observed through a static mask and that the marking of some places may be measurable. These observation structures, however, are rather limited, namely they do not cover all cases of practical interest where complex observations are possible. We consider in this paper more general ones, by correspondingly defining two new classes of Petri net generators: labeled Petri nets with outputs (LPNOs) and adaptive labeled Petri nets (ALPNs). To compare the modeling power of different Petri net generators, the notion of observation equivalence is proposed. ALPNs are shown to be the class of bounded generators possessing the highest modeling power. Looking for bridges between the different formalisms, we first present a general procedure to convert a bounded LPNO into an equivalent ALPN or even into an equivalent labeled Petri net (if any exists). Finally, we discuss the possibility of converting an unbounded LPNO into an equivalent ALPN

Uma rede de petri diagnosticadora para sistemas a eventos discretos modelados por autômatos finitos

Este trabalho consiste no desenvolvimento de uma rede de Petri diagnosticadora para sistemas a eventos discretos modelados por autômatos. O método de diagnose proposto requer, em geral, menos memória do que outros métodos existentes na literatura. Além disso, métodos para a conversão da rede de Petri diagnosticadora em SFC e em diagrama ladder para a implementação em um controlador ́logico programável (CLP) são apresentados. Os métodos de conversão geram códigos de programação quepreservam a estrutura e representam a evolução das fichas na rede de Petri diagnosticadora