Object-orientated registration method for surface inspection of automotive windshields

In this paper we introduce a new point cloud registration strategy for 3D surface inspection, named object-oriented method. Traditionally, the registration methods use a fitting based algorithm, which is a recursive process and too time consuming to do quality inspection. Moreover, the fitting based algorithms require that the measured data and the CAD model have same shapes. Photogrammetry and ICP-based fitting algorithms are commonly used in this area. However, both of them cannot be applied directly to online point cloud registration for quality inspection. Since it requires: 1.) no markers on the object surface; 2.) a very limited inspection period of time for each part on an assembly line; and 3.) the measured work piece can not be assumed as same as the CAD model. The online registration is currently demanded by 3D surface inspection in automotive glasses manufacturing industry. The object-oriented registration method is developed based on matching the invariant geometric features between two data sets instead of the artificial markers and the recursive fitting algorithms. Therefore the registration speed is much higher. A datum filter is developed to extract the invariant features from the measured point cloud, based on the information that the CAD model carries. The curvature information and moment values are used as characteristic features to design the filter. The registration matrix is calculated by the invariance parts in both data sets. The new online registration method has been applied to the quality inspection in the windshield manufacturing industry. Experimental results are presented in this paper to demonstrate the effectiveness of the developed strategy.