Reflection grating method for 3D measurement of reflecting surfaces

Within the recent years, 3D measurement of shape has gained importance due to increasing tolerance requirements in quality assurance. Optical methods are well suited for this task since they provide 3D-shape of surfaces with high density of information while working contactless and fast. In many cases, the surfaces of the inspected workpieces are reflecting and may not be modified for measurement purposes. If so, common methods such as fringe-projection-systems cannot be used since they require a non-reflecting surface. In this paper, an optical measurement technique is presented that unlike known optical methods allows the direct and unambiguous determination of 3D-coordinates of reflecting surfaces based on the observation of a separate reference grid structure and its image reflected by the inspected surface. For the calculation of 3D-coordinates from the recorded images of the reference grid, photogrammetric methods and phase shifting techniques are applied. Finally, application examples are given, depicting the potential of the presented measuring method.