Conventional methods used to inspect the molten pool surface induced by arc welding processes are based on post-welding evaluation using destructive or semi-destructive testing methods. Many attempts were performed to develop alternative and nondestructive tests. In this context, a polarimetric vision methodology is evaluated. The polarimetric parameters are measured from the thermal radiations emitted by the hot liquid metal at a wavelength within an arc plasma blind spectral window. The Stokes parameters and their segmentation within a Gaussian mixture model allow to discriminate artifacts at the surface of the liquid metal. After weld pool solidification, the use of scanning electron microscopy and energy dispersive spectroscopy allow to identify the artifacts, i.e., floating alumina particles.
This paper presents a passive polarimetry method using a division of aperture optical device in order to segment the weld pool surface of the welding. Due to the high specularity of the surface of the weld pool, we use polarimetric data in order to facilitate it’s segmentation in the liquid state. In this paper, we propose to combine two segmentation methods: Watershed Transform and the Level Set to ensure a better result. Our ultimate goal of this study is to provide real-time quality control of the surface of molten metal during the welding process while utilizing the additional information provided by the polarimetric data.
KEYWORDS: Polarization, Polarimetry, Stereoscopy, 3D image processing, Far infrared, Near infrared, Metals, 3D metrology, Dielectric polarization, Cameras, Glasses, 3D modeling, Infrared radiation, Polarizers
This paper describes the use of polarization information to estimate the shape of emissive objects in the field of nonconventional imaging techniques for 3D digitization. Using “Shape from Polarization” method which is applied in the far infrared for transparent object and in the near infrared for the molten metal. Our study shows that by studying the state of polarization of the emitted radiation from the object, normal of the surface can be determined and subsequently the 3D shape.
In the domain of 3D measurement for inspection purposes, standard systems based on triangulation approaches, can be limited by the nature of the observed surface. When the surface is not lambertian, i.e. highly reflective or transparent, other strategies to ease the measurement need to be developed. The idea of using the polarization property of the light is one of them. This was explored to be a complementary modality, in triangulation or shape from distortion methods, or used in a standalone system through the concept of "shape from polarization". In this paper we propose a short state of the art of the usage of polarimetric imaging for the study of surface and the measurement of 3D data. We focus on recent development applied to the industrial domain, or the health domain.
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