Object digitalization using a scanning fringe projection system
The advantage of optical 3D measurement systems like triangulation based fringe projection systems compared with tactile working systems is their contactless and fast 3D surface data acquisition. The results in the form of point clouds can be processed regarding a mathematical surface description for CAD data generation. In many cases the optical 3D surface data acquisition of complex workpieces cannot be achieved in one measuring process so that it is necessary to merge different measuring fields. This approach is essential when the object is larger than the measuring range or the object cannot be measured in one measuring process in consequence of reflections or shadings. According to these problems a fringe projection system was integrated in a coordinate measuring machine with 5 axes (3 linear axes and 2 rotation axes). By using these axes, every region of the workpiece can be reached with the optical 3D sensor for digitalization. To get the complete point cloud of the object surface the different measuring fields must be transformed in one coordinate system by using the relative axes positions of the coordinate measuring machine. Results concerning Reverse Engineering applications and considerations of the measurement uncertainty of the scanning fringe projection system are presented.
Automatic registration method for multisensor datasets adopted for dimensional measurements on cutting tools
Multisensor systems with optical 3D sensors are frequently employed to capture complete surface information by measuring workpieces from different views. During coarse and fine registration the resulting datasets are afterward transformed into one common coordinate system. Automatic fine registration methods are well established in dimensional metrology, whereas there is a deficit in automatic coarse registration methods. The advantage of a fully automatic registration procedure is twofold: it enables a fast and contact-free alignment and further a flexible application to datasets of any kind of optical 3D sensor. In this paper, an algorithm adapted for a robust automatic coarse registration is presented. The method was originally developed for the field of object reconstruction or localization. It is based on a segmentation of planes in the datasets to calculate the transformation parameters. The rotation is defined by the normals of three corresponding segmented planes of two overlapping datasets, while the translation is calculated via the intersection point of the segmented planes. First results have shown that the translation is strongly shape dependent: 3D data of objects with non-orthogonal planar flanks cannot be registered with the current method. In the novel supplement for the algorithm, the translation is additionally calculated via the distance between centroids of corresponding segmented planes, which results in more than one option for the transformation. A newly introduced measure considering the distance between the datasets after coarse registration evaluates the best possible transformation. Results of the robust automatic registration method are presented on the example of datasets taken from a cutting tool with a fringe-projection system and a focus-variation system. The successful application in dimensional metrology is proven with evaluations of shape parameters based on the registered datasets of a calibrated workpiece.
Numerical Simulation of Induction Heating Process of Continuous Casting Slab
Compared with traditional blazing furnace, the Continuous Casting-Direct Rolling is an advanced manufacturing steel technology, which can reduce energy waste, decrease pollution and enhance efficiency. The characteristics of steels during induction heating are complex, the change of material properties with temperature makes exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite difference analysis) is selected to numerically model the induction heating process in this paper. The mathematic model coupling with electromagnetic field and thermal field was established, and it was solved by finite difference method (FDM), thus the slab temperature distribution and its variation with time were obtained, and the characteristics in whole induction heating process were studied. To validate the program feasible, the results were evaluated and compared with experiment results, which showed that the simulation results are reliable and effective. The skin effect in heating process from the two results was studied and demonstrated, the temperature change caused by different parameters such as the induced power intensity and the corner radian were also presented, which indicate that the slab temperature can be heated uniformly through adjusting these parameters, thus the continuous casting slab can meet the rolling requirement.