Rotation estimation for printed circuit board recycling

Electronic devices are nowadays an integral part of everyday life. The number of discarded electronic items has grown significantly over the last years. Due to the amount of precious materials used in the manufacturing of these devices recycling of electronic devices is becoming more and more important. Currently, the processes to regain some of these precious materials such as gold, copper, scarce elements etc. are not able to differentiate electronic waste according to its material composition. To enhance these processes, as much information as possible needs to be retrieved per electronic waste item. In particular, information used for the classification of the processed printed circuit boards (PCBs) is important as PCBs are extensively used in electronic devices. One key aspect of this classification process is the estimation of the orientation of the PCBs in this process (e.g. on a conveyor belt). In this paper typical properties of PCBs with respect to orientation estimation are introduced and three different orientation estimation algorithms are evaluated and discussed. These approaches comprise the Hough transform, structure tensors and orientation estimation via Fourier transform. Finally, all presented algorithms are evaluated based on images of PCBs with known orientation. The results indicate, that the Hough transform yields the best results for completely visible PCBs while structure tensors performed best on partially visible PCBs.