For the past two decades, the need for three-dimensional (3-D) scanning of industrial objects has increased significantly and many experimental techniques and commercial solutions have been proposed. However, difficulties remain for the acquisition of optically non-cooperative surfaces, such as transparent or specular surfaces. To address highly reflective metallic surfaces, we propose the extension of a technique that was originally dedicated to glass objects. In contrast to conventional active triangulation techniques that measure the reflection of visible radiation, we measure the thermal emission of a surface, which is locally heated by a laser source. Considering the thermophysical properties of metals, we present a simulation model of heat exchanges that are induced by the process, helping to demonstrate its feasibility on specular metallic surfaces and predicting the settings of the system. With our experimental device, we have validated the theoretical modeling and computed some 3-D point clouds from specular surfaces of various geometries. Furthermore, a comparison of our results with those of a conventional system on specular and diffuse parts will highlight that the accuracy of the measurement no longer depends on the roughness of the surface.
The Scanning From Heating is a 3D scanning approach initially developed to realise 3D acquisition of transparent or
specular surfaces. A laser source is used to create a local heating point. An infrared camera is used to observe the IR
radiation emitted by the scene. The 2D coordinates of the heated point are computed in the 2D image of the camera.
Knowing the parameters of the system (which are obtained by a previous calibration), the 3D coordinates of the point are
computed using triangulation method. In this article we will present an extension of this technique. We propose here to
analyse the shape of the hot spot observed by the IR camera, and, from the analysis to determine information on the local
orientation of the surface at each measured point.
This paper presents a simulation of automatic 3D acquisition and post-processing pipeline. The proposed methodology
is applied to a LASER triangulation based scanner and a 6 degrees of freedom (DOF) robotic arm simulation.
The viewpoints are computed by solving a set covering problem to reduce the number of potential
positions. The quality of the view plan is determined by its length and the percentage of area of the object's
surface it covers. Results are presented and discussed on various shapes. The article also presents future work
concerning the implementation of the proposed method on a real system.
During industrial forging of big hot metallic shells, it is necessary to regularly measure the dimensions of the parts,
especially the inner and outer diameters and the thickness of the walls, in order to decide when to stop the forging
process. The inner and outer diameters of the shells range from 4 to 6 meters and to measure them a large ruler is placed
horizontally at the end of the shell. Two blacksmiths standing on each side of the ruler at about ten meters from it
visually reads the graduations on the ruler in order to determine the inner and outer diameters from which the thickness
of the wall is determined. This operation is carried out several times during a forging process and it is very risky for the
blacksmiths due to the high temperature of the shell when the measurement is done. Also, it is error prone and the result
is rather inaccurate. In order to improve the working conditions, for the safety of the blacksmiths, and for a faster and
more accurate measurement, a system based on two commercially available Time Of Flight (TOF) laser scanners for the
measurement of cylindrical shell diameters during the forging process has been developed. The advantages of using laser
scanners are that they can be placed very far from the hot shell, more than 15 meters, while at the same time giving an
accurate point cloud from which 3D views of the shell can be reconstructed and diameter measurements done.
Moreover, better dimensional measurement accuracy is achieved in less time with the laser system than with the
conventional method using a large ruler. The system has been successfully used to measure the diameter of cold and hot
cylindrical metallic shells.