Jean-Jacques Lesage

Towards the automatic verification of PLC programs written in Instruction List

We propose a framework for the automatic verification of PLC (programmable logic controller) programs written in Instruction List, one of the five languages defined in the IEC 61131-3 standard. We propose a formal semantics for a significant fragment of the IL language, and a direct coding of this semantics into a model checking tool. We then automatically verify rich behavioral properties written in linear temporal logic. Our approach is illustrated on the example of the tool-holder of a turning center.

Probabilistic Algebraic Analysis of Fault Trees With Priority Dynamic Gates and Repeated Events

This paper focuses on a sub-class of Dynamic Fault Trees (DFTs), called Priority Dynamic Fault Trees (PDFTs), containing only static gates, and Priority Dynamic Gates (Priority-AND, and Functional Dependency) for which a priority relation among the input nodes completely determines the output behavior. We define events as temporal variables, and we show that, by adding to the usual Boolean operators new temporal operators denoted BEFORE and SIMULTANEOUS, it is possible to derive the structure function of the Top Event with any cascade of Priority Dynamic Gates, and repetition of basic events. A set of theorems are provided to express the structure function in a sum-of-product canonical form, where each product represents a set of cut sequences for the system. We finally show through some examples that the canonical form can be exploited to determine directly and algebraically the failure probability of the Top Event of the PDFT without resorting to the corresponding Markov model. The advantage of the approach is that it provides a complete qualitative description of the system, and that any failure distribution can be accommodated.

Quantitative Analysis of Dynamic Fault Trees based on the Structure Function

This paper presents a probabilistic model of dynamic gates which allows to perform the quantitative analysis of any Dynamic Fault Tree (DFT) from its structure function. Both these probabilistic models and the quantitative analysis which can be performed thanks to them can accommodate any failure distribution of basic events. We illustrate our approach on a DFT example from the literature.

Algebraic determination of the structure function of Dynamic Fault Trees

This paper presents an algebraic framework allowing to algebraically model dynamic gates and determine the structure function of any Dynamic Fault Tree (DFT). This structure function can then be exploited to perform both the qualitative and quantitative analysis of DFTs directly, even though this latter aspect is not detailed in this paper. We illustrate our approach on a DFT example from the literature.

FAULT DETECTION OF DISCRETE EVENT SYSTEMS USING AN IDENTIFICATION APPROACH

In this paper, we focus on the identification of large-scale discrete-event systems for the purpose of fault detection. The properties of a model to be useful for fault detection are discussed. As appropriate model basis the nondeterministic autonomous automaton is chosen and metrics to evaluate the accuracy of the identified model are defined. An identification algorithm which allows setting the accuracy of the identified model is presented. Results are given for two case studies, one of a laboratory and another one of an industrial plant.

Black-box identification of discrete event systems with optimal partitioning of concurrent subsystems

This paper proposes a data-driven method to determine concurrent parts in Discrete Event Systems (DES). The aim is to improve the results of black-box identification methods without considering any system information except of observed data. To allow an analysis of the collected data, the impact of concurrency on the exhibited system data is determined by two criteria. We propose to use an optimization algorithm that isolates concurrent parts of the system by minimizing concurrency expressed by the two proposed criteria within the determined subsystems. A lab-size application shows the potential of the method for real-world manufacturing systems. The aim is to deliver optimal identified models for fault detection and isolation.

A Comparative Analysis of Recent Identification Approaches for Discrete-Event Systems

Analogous to the identification of continuous dynamical systems, identification of discrete-event systems (DESs) consists of determining the mathematical model that describes the behaviour of a given ill-known or eventually unknown system from the observation of the evolution of its inputs and outputs. First, the paper overviews identification approaches of DES found in the literature, and then it provides a comparative analysis of three recent and innovative contributions.

Fault detection and isolation in manufacturing systems with an identified discrete event model

In this article a generic method for fault detection and isolation (FDI) in manufacturing systems considered as discrete event systems (DES) is presented. The method uses an identified model of the closed-loop of plant and controller built on the basis of observed fault-free system behaviour. An identification algorithm known from literature is used to determine the fault detection model in form of a non-deterministic automaton. New results of how to parameterise this algorithm are reported. To assess the fault detection capability of an identified automaton, probabilistic measures are proposed. For fault isolation, the concept of residuals adapted for DES is used by defining appropriate set operations representing generic fault symptoms. The method is applied to a case study system.

Analytic Calculus of Response Time in Networked Automation Systems

This paper presents a novel approach to evaluate the response time in networked automation systems (NAS) that use a client/server protocol. The developments introduced are derived from modeling the entire architecture in the form of timed event graphs (TEGs), as well as from the resulting state representation in Max-Plus algebra. The various architectural stages are actually modeled in a very abstract pattern, which yields just those TEG models where local delays are sufficient to perform the overall evaluation. In this manner, linear Max-Plus equations are obtained. A thorough analysis of these equations has led to analytical formulas for direct calculus of NAS response time. As a final step, experimental measurements taken on a laboratory facility have been used to verify the validity of the results. In conclusion, the benefit and effectiveness of this novel method have been demonstrated.

Overview of discrete event systems opacity: Models, validation, and quantification

Abstract Over the last decade, opacity of discrete event systems (DES) has become a very fertile field of research. Driven by safety and privacy concerns in network communications and online services, much theoretical work has been conducted in order to design opaque systems. A system is opaque if an external observer in unable to infer a “secret” about the system behavior. This paper aims to review the most commonly used techniques of opacity validation for deterministic models and opacity quantification for probabilistic ones. Available complexity results are also provided. Finally, we review existing tools for opacity validation and current applications.