Anomaly Detection in Automated Fibre Placement: Learning with Data Limitations

Current defect detection systems for Automated Fibre Placement (AFP) are mostly based on end-to-end supervised learning methods requiring abundant labelled defective samples, which are not easily generated in sufficient numbers. To address this data scarcity problem, we introduce an autoencoder-based approach compatible with small datasets. Fortunately, the problem from a foundational point of view can be simplified as a binary classification between normal and abnormal samples. The proposed approach uses a depth map of the fibre layup surface, split into small windows aligned to each composite strip (tow). A subset of these windows that do not contain anomalies is passed to an autoencoder to reconstruct the input. Because the autoencoder is trained with normal samples, it produces more accurate reconstructions for these samples than for abnormal ones. Therefore, the value of reconstruction error is used as a quantitative metric for whether there are potential anomalies. These values are combined to produce an anomaly map, which can localize the manufacturing defects in the depth map. The results show that although the autoencoder is trained with a very limited number of scans, the proposed approach can produce sufficient binary classification accuracy and specify the location of the defects.