Narrow band frequency analysis for laser-based glass thickness measurement

International audienceThis paper presents a narrow-band frequency analysis approach for a new laser interferometric heterodyne system, which is used for noncontact glass bottle wall thickness measurement. The measurement signal consists of a number of spectral components, the strongest of which is a reliable representation of the above-mentioned thickness. A fast method for searching and locating this frequency is vital for real-time implementations. As the standard fast Fourier transform (FFT) proved to be ineffective for the given problem, we use a combination of a zero-padding discrete Fourier transform (DFT) with a coarse-to-fine technique to locate this frequency at a smaller processing cost. Considering also the Chirp-z transform, a comparison of the different methods under investigation demonstrates the effectiveness of the proposed approach for online thickness estimation

Caracterización de los cambios en las películas plásticas multicapa en procesos de termodeformación usando fotoelasticidad digital

Este trabajo propone una metodología para la caracterización de los cambios en secuencias de imágenes de fotoelasticidad. Las películas plásticas multicapa fueron deformadas a diferentes temperaturas (20°C y 60°C). El análisis de la variación se observó en un polariscopio plano ya que las muestras presentan comportamiento birrefringente lo que genera colores de interferencia en las imágenes capturadas. La evolución temporal de intensidades de color se analizaron usando métricas de similitud, demodulación del color, desplazamiento de fase, algoritmos de aprendizaje del color-espesor y mapa de esfuerzos. Se encontró que las películas presentan cambios en el retardo de fase, espesor y esfuerzo, así la fotoelasticidad describe variaciones espaciales y temporales no homogéneas sobre la superficie de las muestras analizadasThis paper proposes a methodology for the characterization of the temporal behavior of photoelasticity image sequences. The multilayer plastic films were deformed at different temperatures (20°C y 60°C). The analysis of the variation was observed in a plane polariscope because the specimen present birefringent behavior which generates colors of interference in the images captured. The evolution temporal intensities were analyzed using similarity metrics, color demodulation, phase shifting, color-thickness learning algorithms and stress maps. It was found that the films show changes in phase retardation, thickness and stress, thus the photoelasticity describes non-homogeneous spatial and temporal variations on the surface of the specimens analyzedMagister en Automatización y Contro