Outils statistiques de traitement d'indicateurs pour le diagnostic et le pronostic des moteurs d'avions

Identifying early signs of failures in an industrial complex system is one of the main goals of preventive maintenance.It allows to avoid failure and reduce the degradation on a component by doing an earlier maintenance operation. Health monitoring for aircraft engines is one of the industrial fields for which this anomaly detection is very important and meaningful. Aircraft engine manufacturers such as Snecma collect large amount of engine related data during each flight.The idea is to be able to automatically detect when the engine is deviating from its normal behavior.Thus Snecma is developing applications allowing people to prevent engine failures by detecting early signs of anomaly.This doctoral thesis is introdulcing how the experts' knowledge is used to process this engine related data.This first step has pointed out the difficulties in handling the data whether relating to their storage or relating to processing algorithms themselves.After that, this thesis offers a method to combine experts' knowledge with machine learning processes which follow Snecma needs such as the combination of various informations, error control or the interpretability of diagnostics results.To do that the method is focusing directly on the data from the algorithms developed by the experts themselves.This is done by homogenizing the data and then by merging these data.This step allows for the use of supervised classification algorithms whom goal are to to group the items (here the engines) of a similar nature in the same class without losing the temporal component of the information.The homogenization of the data also allows the use of monitoring applications developed by experts in order to detect anomalies.Before merging the data, a selection algorithm is used. This thesis describes how the selection process allows the monitoring algorithms to calibrate themselves.Moreover, this selection follows the first constraint imposed by Snecma concerning the interpretability of the results.Eventually, the method introduced in this thesis aims at helping Snecma make the anomalies' labels converge for all its users. It also aims at incitating to gather all the data on a single database containing : the raw and the processed data from the engine and the engine related data that could be useful such as the results from experts analysis, etc.Using this database, this thesis can then offer a labelisation tool that can be used to improve selection and classification algorithms.Détecter les signes d'anomalies dans un système complexe est l'un des principaux objectifs de la maintenance préventive dans l'industrie. Cela permet d’éviter une défaillance ou de limiter les dégradations d'un composant en avançant une opération de maintenance. Le \textit{Health Monitoring} des moteurs d'avions fait partie des domaines industriels pour lesquels cette détection d'anomalies est un enjeu fort.Ainsi, les motoristes, tels que Snecma, collectent de grandes quantités de données relatives au moteur durant chaque vol.Il s'agit de détecter automatiquement, à partir de ces données, les cas où un moteur dévie de son comportement normal. Plus précisément, Snecma développe des applications permettant de prévenir les pannes moteurs en détectant les anomalies.Cette thèse présente comment le savoir des experts de Snecma est exploité pour traiter ces données moteurs.Ce premier travail a permis de mettre en avant les difficultés liées aux traitements des données : qu'il s'agisse des difficultés concernant le stockage des données ou bien des difficultés liées à la définition des algorithmes de traitement eux-mêmes. Ensuite, la thèse propose une méthodologie permettant de combiner le savoir expert à des méthodes d'apprentissage automatique tout en respectant les exigences d'un motoriste tel que Snecma. Parmi celles-ci, on peut citer le besoin de fusionner des informations variées, le contrôle des erreurs et l'interprétabilité des résultats de diagnostic. Pour cela, la méthodologie exploite directement les données issues des algorithmes de traitement développées par les experts eux-mêmes. Cela est rendu possible par une nécessaire homogénéisation des données, autrement dit par une mise en forme commune de celles-ci permettant alors de procéder à leur fusion. L'homogénéisation des données rend possible l'utilisation des algorithmes de classification (supervisée) dont le but est de regrouper automatiquement, en classe, les individus (ici les moteurs) de même nature à partir des informations fournies et sans perdre l'information temporelle.L'homogénéisation des données permet également d'exploiter directement les applications de surveillance mises en place par les experts métier pour détecter les anomalies.De cette façon, la méthodologie mise à disposition par la thèse reste compréhensible par les experts métier.Avant de procéder effectivement à la fusion, un algorithme de sélection de variables est utilisé. La thèse décrit comment le processus de sélection permet une calibration automatique des applications de surveillance développées par les experts métier. De plus, cette sélection permet de répondre en partie à la première exigence de Snecma concernant l'interprétabilité des résultats. En définitive, la méthodologie présentée dans cette thèse a pour but d'aider Snecma à faire converger les labels des anomalies pour l'ensemble de ses utilisateurs. Elle vise également à faciliter et à inciter la mise en place d'une seule et même base de données regroupant : d'une part toutes les mesures et leurs transformations prélevées sur les moteurs et d'autre part les informations relatives aux moteurs pouvant être pertinentes telles que les résultats d'analyse des experts ou les dates de changement de pièces.La base de données ainsi exploitable, cette thèse peut alors proposer un outil de labellisation qui pourra être utilisé pour améliorer, à travers la labellisation des données, les algorithmes de sélection et de classification supervisés

Anomaly Detection Based on Indicators Aggregation

Automatic anomaly detection is a major issue in various areas. Beyond mere detection, the identification of the source of the problem that produced the anomaly is also essential. This is particularly the case in aircraft engine health monitoring where detecting early signs of failure (anomalies) and helping the engine owner to implement efficiently the adapted maintenance operations (fixing the source of the anomaly) are of crucial importance to reduce the costs attached to unscheduled maintenance. This paper introduces a general methodology that aims at classifying monitoring signals into normal ones and several classes of abnormal ones. The main idea is to leverage expert knowledge by generating a very large number of binary indicators. Each indicator corresponds to a fully parametrized anomaly detector built from parametric anomaly scores designed by experts. A feature selection method is used to keep only the most discriminant indicators which are used at inputs of a Naive Bayes classifier. This give an interpretable classifier based on interpretable anomaly detectors whose parameters have been optimized indirectly by the selection process. The proposed methodology is evaluated on simulated data designed to reproduce some of the anomaly types observed in real world engines.Comment: International Joint Conference on Neural Networks (IJCNN 2014), Beijing : China (2014). arXiv admin note: substantial text overlap with arXiv:1407.088

Anomaly Detection Based on Aggregation of Indicators

Automatic anomaly detection is a major issue in various areas. Beyond mere detection, the identification of the origin of the problem that produced the anomaly is also essential. This paper introduces a general methodology that can assist human operators who aim at classifying monitoring signals. The main idea is to leverage expert knowledge by generating a very large number of indicators. A feature selection method is used to keep only the most discriminant indicators which are used as inputs of a Naive Bayes classifier. The parameters of the classifier have been optimized indirectly by the selection process. Simulated data designed to reproduce some of the anomaly types observed in real world engines.Comment: 23rd annual Belgian-Dutch Conference on Machine Learning (Benelearn 2014), Bruxelles : Belgium (2014

Search Strategies for Binary Feature Selection for a Naive Bayes Classifier

We compare in this paper several feature selection methods for the Naive Bayes Classifier (NBC) when the data under study are described by a large number of redundant binary indicators. Wrapper approaches guided by the NBC estimation of the classification error probability out-perform filter approaches while retaining a reasonable computational cost

Interpretable Aircraft Engine Diagnostic via Expert Indicator Aggregation

Detecting early signs of failures (anomalies) in complex systems is one of the main goal of preventive maintenance. It allows in particular to avoid actual failures by (re)scheduling maintenance operations in a way that optimizes maintenance costs. Aircraft engine health monitoring is one representative example of a field in which anomaly detection is crucial. Manufacturers collect large amount of engine related data during flights which are used, among other applications, to detect anomalies. This article introduces and studies a generic methodology that allows one to build automatic early signs of anomaly detection in a way that builds upon human expertise and that remains understandable by human operators who make the final maintenance decision. The main idea of the method is to generate a very large number of binary indicators based on parametric anomaly scores designed by experts, complemented by simple aggregations of those scores. A feature selection method is used to keep only the most discriminant indicators which are used as inputs of a Naive Bayes classifier. This give an interpretable classifier based on interpretable anomaly detectors whose parameters have been optimized indirectly by the selection process. The proposed methodology is evaluated on simulated data designed to reproduce some of the anomaly types observed in real world engines.Comment: arXiv admin note: substantial text overlap with arXiv:1408.6214, arXiv:1409.4747, arXiv:1407.088