Automatic detection of defects in as-built parts is a challenging task due to the large number of potential manufacturing flaws that can occur. X-Ray computed tomography (CT) can produce high-quality images of the parts in a non-destructive manner. The images, however, are grayscale valued, often have artifacts and noise, and require expert interpretation to spot flaws. In order for anomaly detection to be reproducible and cost effective, an automated method is needed to find potential defects. Traditional supervised machine learning techniques fail in the high reliability parts regime due to large class imbalance: there are often many more examples of well-built parts than there are defective parts. This, coupled with the time expense of obtaining labeled data, motivates research into unsupervised techniques. In particular, we build upon the AnoGAN and f-AnoGAN work by T. Schlegl et al. and created a new architecture called PandaNet. PandaNet learns an encoding function to a latent space of defect-free components and a decoding function to reconstruct the original image. We restrict the training data to defect-free components so that the encode-decode operation cannot learn to reproduce defects well. The difference between the reconstruction and the original image highlights anomalies that can be used for defect detection. In our work with CT images, PandaNet successfully identifies cracks, voids, and high z inclusions. Beyond CT, we demonstrate PandaNet working successfully with little to no modifications on a variety of common 2-D defect datasets both in color and grayscale.
Recent advances in deep learning have shown promising results for anomaly detection that can be applied to the problem of defect detection in electronic parts. In this work, we train a deep learning model with Generative Adversarial Networks (GANs) to detect anomalies in images of X-ray CT scans. The GANs detections can then be reviewed by an analyst to confirm the presence or absence of a defect in a scan, significantly reducing the amount of time required to analyze X-Ray CT scans. We employ a trained GAN via a system referred to in the literature as an AnoGAN. We train the AnoGAN on images of X-Ray CT scans from normal, non-defective components until it is capable of generating images that are indistinguishable from genuine part scans. Once trained, we query the AnoGAN with an image of an X-ray CT scan that is known to contain a defect, such as a crack or a void. By sampling the GANs latent space, we generate an image that is as visually close to the query image as possible. Because the AnoGAN has learned a distribution over non-defective parts, it can only produce images without defects. By taking the difference between the query image and the generated image, we are able to highlight anomalous areas in the defective part. We hypothesize that this work can be used to improve speed and accuracy for quality assurance of manufactured parts by applying machine learning to non-destructive imaging.
Conference Committee Involvement (1)
Applications of Machine Learning 2020
23 August 2020 | Online Only, California, United States
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