Automated Foreign Object Detection on Conveyor Belts

Abstract: Ore is transported using belt conveyor systems. The transported ore has various anomalous objects that must be removed to prevent damage to the system. Currently anomalies are detected manually using humans. This leads to increased costs of wages and damage to the system overmissed anomalies. The thesis aims to solve this problem via the use of trained neural networks which can run on relatively cheap systems with a greater accuracy than humans. A set of neural networks were trained on both the BCS dataset consisting of data collected from the belt conveyor system and on the MVTec dataset. The latter dataset was used as a way of checking the correctness of the implementation of the models. As training neural networks usually requires large datasets, this thesis also focuses on the effect of the portion of labelled versus unlabelled data on the models. Labelling data can be time consuming and expensive so investigating if or how much data can be unlabelled without any or minimal loss to accuracy could lead to further cost reductions. The convolutional autoencoder (CAE) performed best on the classification based task on the BCS dataset where it managed to classify most of the dataset correctly, with an F1-score of 0.94 on data without anomalies and an F1-score of 0.86 on data with anomalies, as long as suitable thresholds were set. ResNet performed somewhat well with a 0.91 F1-score in detecting anomaly free data and a 0.50 F1-score in detecting anomaly containing data. The SimCLR and SimCLRv2 models were unable to learn from the data and defaulted to always assuming the data contained anomalies. The CAE model trained using the L1 loss function performed best with an IoU of 0.272 and performed worst with the SSIM based loss function with an IoU of 0.160. The effect of labelled versus unlabelled data using the MVTec dataset was tested using the SimCLR and SimCLRv2 models and the models performed best with the fully labelled dataset which was expected. The SimCLR model was able to identify all categories with an F1-score greater than 0.67 whereas the other splits performed worse overall with two or more categories completely misclassified. The SimCLRv2 was able to classify six categories with an F1-score greater than 0.0 which was significantly better than all other labelled and unlabelled splits.