Search

©2003 The British Institute of Non-Destructive Testing., Structured light techniques (Moiré, projected fringes and other pattern projection techniques) have been used for many years in the aerospace and other industries for external defect location and characterization, 3D shape, deformation measurements and the like. The application of digital image processing methods to the images generated by these techniques has made possible the realization of fast and automatic systems for quantitative NDT measurements. This work is divided in two parts. First, the principal approaches to structured light-based NDT are reviewed, presenting the basis, performance characteristics as well as their expected ranges and resolutions. The second part concentrates on the digital image processing techniques of interest in the field of structured light-based NDT. As the images produced by these techniques are often in the form of phase-modulated fringe patterns, the branch of image processing that deal with this kind of images is denominated fringe pattern processing. Among the many existing fringe pattern processing techniques, the paper will concentrate on the phase-shifting methods (spatial and temporal) and the regularization and natural demodulation methods. It will be shown how when acquisition time is not critical, and several phase-shifted images can be acquired, phase-shifting techniques are well-suited for phase demodulation. Related with these techniques is the so-called phase unwrapping problem that will be discussed. Finally, fringe pattern processing techniques are discussed which can be applied in cases when acquisition time or the optical set-up only allows the use of one fringe pattern. In this case the problem of demodulating the phase is ill-posed from a mathematical point of view and special techniques as regularization and the so-called natural demodulation are needed., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 Society of Photo-Optical Instrumentation Engineers., A method for sensing wavefronts is presented. The method is based on the resolution of the irradiance transport equation, which relates the irradiance distribution and the shape of the wavefront of a light beam propagating along a given direction. The method presents no restrictions in the locations of the measurement planes and incorporates an improved procedure to geometrically correct the acquired images to take into account the effect of ray deflection in the propagation of the irradiance distributions. With the proposed technique, we measure the wavefront at the exit pupil of a progressive addition lens and find good agreement with an alternative deflectometric method., Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

We provide a simple solution for the particular problem of the in-service inspection of aeronautic surfaces in order to detect bumps that otherwise it is made visually and usually less reliably. Bumps and other surface defects can be a symptom of a more serious internal damage. We have extended the use of the well know shadow Moire technique to be implemented in convex curved surfaces. The use of flexible Ronchi grating allows its adaptation to a convex general surface. The effect is the contrast enhancement of only the small defects sweeping-off other misleading height profile fringes. The result obtained are quite satisfactory compared to the use of flat reference gratings. The experimental set- up consists of a plastic foil with a printed Ronchi grating stretched between three points which adapts to nay cylindrical or conical convex surface independently of the relative grating-surface orientation. Static quantification of defects profiles is also possible by means of with an attached CCD camera. Visual detectability of local surface structures lye in the range of approximately 30 micrometers in depth.

We have developed a prototype for in-line detection of surface defects in metallic wires, specially for scratches. A simple geometrical relationship between surface topography and conical reflection, permits to correlate the defects with intensity patterns in a simple way. The presented apparatus consists basically in a grating-divided laser beam incident on angular equidistant points. A CCD and an associated optics capture the information of the whole wire perimeter at once. Analytic rudiments are provided in agreement with the experimental results.

We improve the known results on interpolation of strictly singular operators and strictly co-singular operators in several directions. Applications are given to embeddings between symmetric spaces., DGES, Programa Praxis XXI da Fundaçao para a Ciencia e Tecnologia, Instituto Politécnico de Leiria, Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

We estimate the ideal measure of certain interpolated operators in terms of the measure of their restrictions to the intersection. The dual situation is also studied.: Special attention is paid to the ideal of weakly compact operators., Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

We investigate the behaviour of the measure of Iron-compactness of an operator under real interpolation. Our results refer to general Banach couples. An application to the essential spectral radius of interpolated operators is also given., Dirección General de Investigación Científica y Técnica (España), Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub