In soldering, the position of parts assembled perpendicularly to each other has to be estimated accurately to achieve high quality attachment. Image processing can be applied to inspect soldering positions in two dimensions, but it is hardly ever used to inspect positions of assembled parts in three dimensions. We have developed a method to recognize a three-dimensional object using the information of three-dimensional computer aided design (3D-CAD). Therefore, we propose an inspection method for soldering robots, which enables the measurement of an opening angle formed by two base metals which intersect in a straight line and the discrepancy of their position by comparing the standard figure made by 3 D-CAD with the input image. First, an assembly drawing written by three-dimensional CAD is projected onto a virtual plane in order to obtain a projection drawing which can be used as the two-dimensional standard assembly figure. After an image of actual boards is input and processed, the straight-line intersection of the two boards is detected and set as a reference line. Second, the standard figure is rotated, zoomed and moved in a virtual plane in order to set the two reference lines of the standard figure and input image superimposed precisely on each other. Finally, the standard figure and input image are compared to detect errors of the opening angle and the position of the actual base metals assembled. An experimental application proved that the proposed method is able to inspect three-dimensional objects soldered less in than one second.
View full abstract