A new method for the accuracy evaluation of a manufactured piece

To evaluate the accuracy of a manufactured piece, it must be measured and compared with a reference model, namely the designed 3D model, based on geometrical elements. In this paper a new method for the precision evaluation of a manufactured piece is proposed, which implies the creation of the piece digital 3D model based on digital images and its transformation into a 3D mesh surface. The differences between the two models, the designed model and the new created one, are calculated using the Hausdorff distance. The aim of this research is to determine the differences between two 3D models, especially CAD models, with high precision, in a completely automated way. To obtain the results, a small piece has been photographed with a digital camera, that was calibrated using a 3D calibration object, a target consisting of a number of 42 points, 36 placed in the corners of 9 wood cubes with different heights and 6 of them placed at the middle of the distance between the cubes, on a board. This target was previously tested, the tests showing that using this calibration target instead of a 2D calibration grid, the precision of the final 3D model is improved with approximatly 50%. The 3D model of the manufactured piece was created using two methods. First, based on digital images, a point cloud was automatically generated and after the filtering process, the remaining points were interpolated, obtaining the piece 3D model as a mesh surface. Second, the piece 3D model was created using also the digital images, based on its characteristic points, resulting a CAD model, that was transformed into a mesh surface. Finally, the two 3D models were compared with the designed model, using the CloudCompare software, thus resulting the imperfections of the manufactured piece. The proposed method highlights the differences between the two models using a color palette, offering at the same time a global comparison.