Geometrical inspection of flexible parts using intrinsic geometry

Abstract

The tolerancing of mechanical parts is one of the major problems in mode mindustry . It's economic consequences are important to the manufacturing sector which sustains major transformations imposed by market globalization and technology evolution (CAD, CMM, 3D Scanners, etc.). Today, we know that product performance optimization requires a consideration of the inherent variations in manufacturing processes, hence quality control throughout the development process and manufacturing. Currently, the geometric inspection oiflexible (or nonrigid) mechanical parts, such as thin-walled skins of airplane or car bodies is still limited to the use of relatively expensive special inspection fixtures, which simulate the use state, applying the same constraints that reflect assembly information. Subsequently, contact measuring or scanning is performed. Simulating this use state means that, deformation effects due to flexibility are eliminated. In this way, defects in the manufacturing process are detectable. The goal of this thesis is to facilitate the dimensional and geometrical inspection of flexible components from a point cloud without using a jig or secondary conformation operation. More specifically, we aim to develop a methodology to localize and quantify the profile defects in the case of thin shells which are typical to the aerospace and automotive industries. To this end, we implemented an idea that we call Numerical Inspection Fixtures. We use geodesic distances to detect the intrinsic similarities between a part in a free state which includes the effects of gravity, intemal constraints and manufacturing defects, and the same part as nominally defined by a CAD model. This thesis develops the theoretical foundation of the proposed methods and related algorithms. We used an approach already used in medical image processing to identify minimum geodesic distance and statistics (Multidimensional Scaling) to analyze the similarities and dissimilarities between two objects, as well as the finite element method to reach a general approach for the inspection of nonrigid parts. Two methods are proposed with numerical validations.

Date	14 Jul 2010
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Antoine Tahan (Supervisor) & Jean-François Chatelain (Co-supervisor)