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RESEARCH PRODUCT

3D Displacements and Strains Solid Measurement based on the Surface Texture with a Scanner Laser

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International audience; The developments of non-contact measurement are today widely due to the unprecedented progress of optronic. The applications of these techniques are wide and varied for the 3D measurement of industrial products. In addition to the forms and dimensions, we show in this paper that the devices of laser scanning permit to measure displacements and deformations. In this case, it is necessary to follow a solid particle in its motion. It is then necessary to identify the particle between two configurations of the body before and after displacement. The method of greyscale patterns, obtained by applying a spray, is generally used. The originality of the proposed method is based on the fact that the pairing between two configurations is carried out with micro-geometrical patterns, detected directly by the laser sensor. The measurement process is described in the paper. The first step consists to acquire a point cloud of the surface before and after the movement. This point cloud must be sufficiently dense to be able to obtain a characterization of the micro-geometrical texture. The point cloud is regularized to extract the form and to obtain images of the surface texture. A point and its neighbourhood are then linked to a pixel and its neighbours. The pairing of two points on the both images corresponding to the configurations before and after displacement is then performed with the traditional tools of image analysis. Finally, the displacement between the two points belonging to the real object can be determined. The advantages of this method are numerous, for example to track movement or to quantify deformation of objects presenting natural surface textures without having to change them. It is adapted for soft objects for which it is not possible to apply a contrast agent. Various applications of measurement of displacements and deformations illustrate our approach. When the surface texture is too fine to be detected by the scanner, a spray can be applied. A camera associated with the scanning device permits to track the patterns in gray level associated with a point of the object. So, the laser scanning becomes a basic instrument to measure solids deformation in 3D and contributes to aid the engineers in the development of manufacturing process