Contextual Auto-Encoder Anomaly Detection for Micro-Fractures

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Solution Overview

Problem

Detecting small and faint anomalies in images, such as micro-fractures in x-ray images of metallic objects, is difficult for both humans and automated systems due to low contrast with surrounding pixel intensities, necessitating improved automation for quality assurance and quality control.

Innovation Solution

A computer-implemented method using a Contextual Auto-Encoder (CAE) model for unsupervised back-propagation training, followed by supervised training of a classifier model, to normalize and detect defective products by reconstructing defect-free images and contrasting them with original images to identify anomalies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional anomaly detection methods are used, then the system can detect anomalies, but the detection accuracy is low for small and faint anomalies with low contrast

Engineering Contradiction:
Improveanomaly detection accuracyVSAvoiddifficulty of detecting small and faint anomalies
Core Design Contradiction:
Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent applies preliminary action by training the autoencoder model in advance using only defect-free images to learn the normal characteristics of products. This pre-trained model then serves as the basis for anomaly detection, where deviations from the learned normal pattern indicate defects. This approach prepares the system beforehand with knowledge of normality, enabling more accurate detection of subtle anomalies without requiring labeled defect data during training.

Inventive Principle:
Principle #10Preliminary action

2Measurement precision

If more training data including defective products is collected, then detection accuracy may improve, but the complexity and cost of data collection and labeling increases

Engineering Contradiction:
Improvedetection accuracyVSAvoidcomplexity of data collection and labeling
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements self-service by using the autoencoder model to automatically learn normal product characteristics from defect-free images without requiring manual labeling of defective samples. The model self-trains by reconstructing normal images and identifying deviations as anomalies, eliminating the need for complex data annotation processes and expert labeling of defect types, thereby reducing both complexity and cost.

Inventive Principle:
Principle #25Self-service

3Reliability

If conventional supervised learning is used, then the model can be trained with labeled data, but it requires abundant defective product images which are often scarce

Engineering Contradiction:
Improvemodel training reliabilityVSAvoidquantity of defective product images
Core Design Contradiction:
ReliabilityVSQuantity of substance

Solution Approach 1:

The patent applies inversion by reversing the conventional supervised learning approach. Instead of training a model to recognize defects directly using labeled defective images, the autoencoder is trained to reconstruct only defect-free images. The model learns what normal products should look like, and any significant deviation from this learned pattern is flagged as an anomaly. This inverted approach enables reliable training with abundant normal images while detecting rare defects without requiring scarce labeled defective data.

Inventive Principle:
Principle #13The other way round (Inversion)

Data Source

PatentUS10964011B2Anomaly detection with predictive normalization
Publication Date: 2021.03.30 NEC CORP
  • US10964011B2 patent drawing
  • US10964011B2 patent drawing
  • US10964011B2 patent drawing

AI summary

A method is provided for model training to detect defective products. The method includes sampling training images of a product to (i) extract image portions therefrom made of a center patch and its context and (ii) black-out the center patch. The method further includes performing unsupervised back-propagation training of a Contextual Auto-Encoder (CAE) model using (i) the image portions with the blacked-out center patch as an input and, (ii) the center patch as a target output and, (iii) an image-based loss function, to obtain a trained CAE model. The method also includes sampling positive and negative center-patch-sized portions from the training images. The method additionally includes normalizing, using the trained CAE model, the positive and negative center-patch-sized portions. The method further includes performing supervised training of a classifier model using the normalized positive and negative center-patch-sized portions to obtain a trained supervised classifier model for detecting the defective products.