Heightmap generation for printed circuit boards (PCB) using laser triangulation for pre-processing optimization in industrial recycling applications

Electronic devices are nowadays an integral part of our everyday lives. The number of discarded electronical items has grown significantly over the last years. As the amount of precious materials used in the manufacturing of these devices has increased over the last years recycling of these devices is becoming more and more important. Currently the processes to regain some of these precious materials like gold, copper, scarce elements etc. do not differentiate much the input material composition. To enhance these processes as much information about the input material as possible is needed. Especially information used for the classification of the processed printed circuit boards (PCBs) is important as PCBs have been used extensively in electronic devices. One key aspect of this classification process is the acquisition of geometrical properties of the processed PCBs. In this paper employing laser triangulation to gain the height profile of PCBs is discussed. The basic principles of laser triangulation are introduced as well as several laser line detection algorithms. The variability of shapes of the components mounted on PCBs is limited. Due to this limitation the correction of geometrical distortions (called rise extension slope contraction (RESC)) resulting in a systematic error is feasible and discussed in this paper as well. Finally all algorithms presented are evaluated in a comprehensive testing environment and the results are shown in the end.