Génération de chemins de couverture pour des opérations automatisées de contrôle non destructif appliquées dans l'industrie aérospatiale

RESUME L’industrie aerospatiale accorde un role majeur au controle non destructif (CND) dans le processus de fabrication et de maintenance des structures et il est utilise, entre autres, pour detecter des defauts tels que des fissures a un stade precoce. Cependant, les techniques de CND sont encore principalement operees manuellement, en particulier sur des structures aerospatiales complexes. Plusieurs inconvenients en resultent tels que la penibilite et le temps d’operation des techniques. De plus, la fiabilite et la repetabilite des resultats d’inspection est susceptible de varier de maniere significative puisqu’elles dependent de l’experience et de la dexterite de chaque operateur. Dans le cadre du projet MANU-418 du Consortium de recherche et d’innovation en aerospatiale au Quebec (CRIAQ) dans lequel s’inscrit le present travail de recherche, il a ete propose de developper un systeme muni d’un bras manipulateur a 6 DDL permettant d’automatiser trois techniques particulieres de CND utilisees dans l’industrie aerospatiale : l’inspection par courants de Foucault (ECT), l’inspection par ressuage fluorescent (FPI) et l’inspection par thermographie infrarouge (IRT). L’objectif global du projet MANU-418 est de demontrer que ce systeme automatise permet d’obtenir des resultats de detection de defauts (des fissures generalement) en surface et legerement sous la surface au moins aussi acceptables en termes de fiabilite et de repetabilite que ceux obtenus manuellement. Un des objectifs specifiques qui decoule de ce projet est de developper une methodologie et un outil logiciel de generation de chemins de couverture adaptes aux trois techniques de CND mentionnees precedemment pour l’inspection de surfaces complexes de structures aerospatiales. Le present travail de recherche s’attache a la realisation de cet objectif specifique. Dans un premier temps, les proprietes de geometrie et de topologie du type de surfaces considerees dans ce projet sont definies (surfaces planes, conges, bords droits, surfaces cylindriques, trou dans la surface). Il est egalement suppose que le modele 3D de la surface a inspecter est connu a l’avance. Aussi, l’automatisation de l’inspection ECT etant prioritaire devant celles des techniques FPI et IRT dans le cadre du projet MANU-418, la methodologie developpee se base sur les proprietes de chemin qu’une sonde differentielle a courants de Foucault (appelee ici sonde EC) suit habituellement lors d’une inspection manuelle, tout en permettant de rester utilisable pour les autres techniques. Le chemin d’inspection d’une sonde EC est defini par un balayage en zigzag et cette sonde est generalement en contact leger avec la surface durant le balayage. Aussi, l’axe de la sonde doit en tout temps etre normal a la surface et, l’alignement de ses deux bobines doit toujours etre oriente le long de sa direction de deplacement. Une premiere methodologie est alors proposee pour generer des chemins de couverture sur toute la surface a inspecter en respectant les contraintes de la sonde EC. ----------ABSTRACT Non destructive testing (NDT) plays an important role in the aerospace industry during the fabrication and maintenance of the structures built and is used, among other useful applications, to detect flaws such as cracks at an early stage. However, NDT techniques are still mainly done manually, especially on complex aeronautical structures, which then results in several drawbacks. In addition to be difficult and time-consuming, reliability and repeatability of inspection results are likely to be affected, since they rely on each operator’s experience and dexterity. The present thesis is part of a larger project (MANU-418) of the Consortium for Research and Innovation in Aerospace in Quebec (CRIAQ). In this project, it has been proposed to develop a system using a 6-DOF manipulator arm to automate three particular NDT techniques often needed in the aerospace industry: eddy current testing (ECT), fluorescent penetrant inspection (FPI), and infrared thermography (IRT). The main objective of the MANU-418 project is to demonstrate the efficiency of the developed system and provide inspection results of surface and near surface flaws (cracks usually) at least as reliably and repeatably as inspection results from a human operator. One specific objective stemming from the main objective of the project is to develop a methodology and a software tool to generate covering paths adapted for the three forementioned NDT techniques to inspect the complex surfaces of aerospace structures. The present thesis aims at reaching this specific objective. At first, geometrical and topological properties of the surfaces considered in this project are defined (flat surfaces, round and straight edges, cylindrical or near cylindrical surfaces, holes). It is also assumed that the 3D model of the surface to inspect is known in advance. Moreover, it has been decided within the framework of the MANU-418 project to give priority to the automation of ECT compared with the other techniques (FPI and IRT). As a result, the methodology developed to generate inspection paths is more closely focused on path constraints relative to the manual operations of ECT using a differential eddy current probe (named here EC probe), but it is developed to be flexible enough to be used with the other techniques as well. Common inspection paths for ECT are usually defined by a sweeping motion using a zigzag pattern with the EC probe in mild contact with the inspected surface. Moreover, the main axis of the probe must keep a normal orientation with the surface, and the alignment of its two coils must always be oriented along the direction of its motion. A first methodology is then proposed to generate covering paths on the whole surface of interest while meeting all EC probe motion constraints. First, the surface is meshed with triangular facets, and then it is subdivided into several patches such that their geometry and topology are simpler than the whole surface.