UBC Theses and Dissertations
Multi-axis ESPI interferometer for 3-D displacement measurements Zanini Broetto, Filipe
Small displacement measurements have several applications in engineering. Deformations ranging from nanometric scale to micrometric scale are very often related to mechanical stresses, materials phase transformations, residual stresses, biological processes, etc. It is common that these deformations occur in three dimensions and are not easily measured with simple equipment. Electronic speckle pattern interferometry (ESPI) systems use interference of light and laser properties to measure such small displacements in a very reliable way. The ESPI technique is a full-field non-contact technique capable of 3D measurements but the arrangement can get very complicated when it comes to number of components, size, cost, assembly complexity and operation. Among the many factors contributing for the complexity, the most important ones are the number of light beams and optical elements, and the laser itself. High quality lasers offer very high coherence – which is a measure of purity of spectrum and therefore allow for very high quality measurements with very low noise – at a very high cost, and usually are bulky, requiring many extra components to split light beams and direct the light to the region of interest. The aim of this project is to use special components to eliminate the need for an expensive laser and simplify the arrangement for a 3D ESPI measurement. The introduction of a dual diffraction grating system makes it possible to replace a high quality laser with a low coherence, compact and cheap laser diode. Moreover, with this new proposed arrangement it is possible to obtain the 3D ESPI information using two in-plane ESPI systems combined in one, reducing complexity and offering up to 6 different measurement possibilities. Based on the fact that only 3 different measurements are required for solving a complete 3D displacement field, the remaining measurements can be used for data averaging and to increase the accuracy and reduce uncertainties. The new design is presented and a portable device is developed. The arrangement is explored to test the robustness against exterior factors such as temperature and ambient light, and the accuracy of the measurement is verified with a controlled sample and finite element analysis/analytical solutions.
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