Optical-based techniques have found merit in measuring displacement and strain for decades. These techniques are commonly used in numerous applications ranging from large displacements in wind tunnel experiments to displacement measurements on the submicron scale. Projection Moiré Interferometry (PMI) is an out-of-plane displacement measurement technique, and consists of capturing reference and deformed images of a grid pattern projected on the test object. By differencing the reference and deformed images of the projected grid pattern, a fringe pattern is generated from which the displacement field can be extracted. This computation requires calibration procedures that analyze a number of fringe patterns from known displacements to compute the fringe sensitivity constant (FSC) values. This process can be time consuming and for large-scale applications, very costly. In addition, due to the projection-oriented nature of this technique, measuring displacements in applications with non-viewable, hidden, or inaccessible reference surfaces excludes the use of PMI. In this thesis, a technique is developed which eliminates calibration procedures through implementation of virtual calibration methods, and typical PMI measurement processes are extended to include digital reference images in determining displacements from inaccessible surfaces. Using camera calibration routines and ray tracing techniques, each major component of the PMI arrangement is modeled as virtual components within a computer simulation where the entire calibration process can be performed. A CAD model of the inaccessible surface is then converted to a point cloud and a surface interpolation function is implemented to generate a displacement field, which can be correlated and differenced from the displacement field of the actual object. Many potential applications exist in the automobile, aerospace, and other manufacturing industries. These industries provide numerous large-scale applications where conventional calibration is not cost-effective. In addition, these applications provide instances where differences between the deformed and reference images represent the manufacturing errors due to dimensional variations and assembly processes. An automated, self-calibrating, whole-field projection measuring system would greatly increase inspection efficiency of large production parts and final assemblies. It is in these types of circumstances that the developed techniques would be of most use.
College and Department
Ira A. Fulton College of Engineering and Technology; Mechanical Engineering
BYU ScholarsArchive Citation
Kimber, Mark Lee, "Development of a Virtually Calibrated Projection Moire Interferometry Technique Capable of Inaccessible Surface Measurements" (2004). Theses and Dissertations. 192.
Moire, optics, measurements, interferometry, CAD