Detecting residuals at plastic samples to optimize laser cutting processes

Abstract

When using a molding machine to produce plastic samples, unwanted residuals can occur. Within this study two image processing methods for the detection of residuals at plastic samples are evaluated. The aim of the two suggested methods is to detect the position of the residuals at the plastic sample reliable and to transform the image-based information into laser machine coordinates. By using the transferred coordinates, the laser machine can remove the detected residuals by laser cutting accurately without damaging the sample. The measurement setup for both methods is identical, the difference is in the processing of the captured raw image. The first method compares the raw image with the image masking template to determine the residual. The second method processes the raw image directly by comparing the light intensity transmitted through the sample to distinguish the residual from the main sample. Once the residuals can be detected, binary shifting are then performed to locate the cut lines for the residuals. The lines obtained from the image in pixel scale must then be accurately converted into millimeter-scale so that the laser machine can use them. By comparing the two methods mentioned above, the method that uses template images has more accurate and detailed results, leaving no small residuals on the sample. Meanwhile, in the method that compares the intensity of the transmitted light through the sample, there were undetectable residuals that did not produce the desired straight line. However, using the image template-matching method has some drawbacks, such as requiring each measurement to be in the same position. And thus, a more detailed design process is needed to stabilize the measurement process. In this study, a design has been made in terms of hardware as well as software with a GUI that can set several important parameters for measurement. From the results of this study, we obtained a system that can cut the residuals on the sample without damaging the sample.