Anomaly Detection for Small Defects in Optical Inspection

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Solution Overview

Problem

Current optical inspection systems are inadequate for detecting minor optical defects in high-resolution images of large, non-reflective surfaces with complex patterns, and existing deep learning models are not suited for classifying small anomalies, while the imbalance in training data between good and bad images complicates the detection of optical defects.

Innovation Solution

A method using a supervised learning approach with an artificial neural network that generates bad images by introducing image errors into good images, allowing for the training of the network with pairs of good and bad images, enabling the detection of small anomalies and handling imbalanced data sets effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If known optical inspection systems with open source software are used, then inspection of labeling and configuration can be performed, but detection of minor optical defects on large-area objects is not suitable

Engineering Contradiction:
Improvedetection capabilityVSAvoidapplicability to different inspection tasks
Core Design Contradiction:
Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent segments the inspection task into two distinct processing paths: one for structural inspection (labeling, configuration) using traditional image analysis, and another for defect detection using deep learning anomaly detection. This segmentation allows each path to be optimized for its specific purpose, resolving the contradiction between precision for different inspection types and system versatility.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent introduces a new dimension to the inspection system by integrating deep learning-based anomaly detection alongside traditional optical inspection methods. This additional dimension enables the system to handle both structured inspection tasks (labeling, configuration) and unstructured defect detection tasks simultaneously, thereby improving both measurement precision and adaptability.

Inventive Principle:
Principle #17Another dimension (Dimensionality change)

2Measurement precision

If current deep learning models are used for anomaly detection, then medium to large pixel area features can be detected, but smallest anomalies in high-resolution images with complex patterns cannot be classified

Engineering Contradiction:
Improveanomaly detection accuracyVSAvoidcomputational resources
Core Design Contradiction:
Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent segments the image processing into two resolution levels: high-resolution imaging for capturing detailed defect information, and then segmentation of processing tasks where anomaly detection operates on the high-resolution data. This allows detection of smallest anomalies while managing computational resources through targeted application of deep learning only where needed.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by using anomaly detection specifically for defect identification in regions where it is most needed, rather than uniformly processing entire high-resolution images. This localized application of computational resources improves detection accuracy for small anomalies while reducing overall computational burden.

Inventive Principle:
Principle #3Local quality

3Ease of operation

If manual inspection by human inspectors is performed, then evaluation of objects can be carried out, but minor defects are overlooked and quality fluctuates

Engineering Contradiction:
Improveinspection process simplicityVSAvoidinspection quality consistency
Core Design Contradiction:
Ease of operationVSReliability

Solution Approach 1:

The patent implements feedback mechanisms where the anomaly detection system continuously learns from inspection results and adjusts its detection parameters. This feedback loop ensures consistent quality assessment by maintaining objective detection criteria, eliminating the variability inherent in manual inspection while preserving operational simplicity through automated decision-making.

Inventive Principle:
Principle #23Feedback

Solution Approach 2:

The inspection system performs self-service by automatically detecting and classifying defects without requiring human inspectors. The anomaly detection algorithm autonomously evaluates objects, ensuring consistent quality assessment while reducing reliance on human judgment, thereby improving reliability without sacrificing ease of operation.

Inventive Principle:
Principle #25Self-service

4Measurement precision

If training data for deep learning is collected from production, then real defect examples are obtained, but the proportion of defective objects is considerably smaller than non-defective objects

Engineering Contradiction:
Improvetraining data qualityVSAvoidavailable training data volume
Core Design Contradiction:
Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent applies preliminary action by using anomaly detection to identify potential defects in non-defective objects during the training phase. This allows the system to proactively generate training examples of defects that would otherwise be rare in production data, thereby improving training data quality and volume balance before the model is deployed for actual inspection.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The patent converts the scarcity of defective samples (a harmful condition for training) into a benefit by using anomaly detection to synthetically generate defect training data from non-defective objects. This approach transforms the imbalance problem into an opportunity to create diverse training examples, improving both the quality and volume of training data available.

Inventive Principle:
Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS20240096059A1Method for classifying images and method for optically examining an object
Publication Date: 2024.03.21 FRESENIUS MEDICAL CARE DEUTSCHLAND GMBH
  • US20240096059A1 patent drawing
  • US20240096059A1 patent drawing
  • US20240096059A1 patent drawing

AI summary

A method for classifying images, in which the images are classified according to good images and bad images, comprises the following steps:capturing image data of an image, andclassifying the image as a good image (GB) or a bad image (SB, SB2),wherein the classification is made using an artificial neural network trained by supervised learning using training data from a plurality of good images (GB) and a plurality of bad images (SB), wherein each bad image (SB) of at least a subset of the plurality of bad images (SB) of the training data corresponds to a respective good image (GB) of at least a subset of the plurality of good images (GB) of the training data, into which at least one image error (11) is inserted, and wherein the artificial neural network is trained using respective pairs of a respective good image (GB) from the subset of the plurality of good images (GB) and a respective bad image (SB) from the subset of the plurality of bad images (SB), wherein a respective bad image (SB) corresponds to the good image (GB) belonging to the same pair, into which the at least one image error (11) is inserted. The method according to the invention makes it possible, in particular, to identify small defects (defective areas from 1 pixel) on large areas.