Automatic Inspection of Metallic Structures

     Rust dept measurement industrial system using image processing.
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Corrosion recognition system

AIMS -

Automatic Inspection of Metallic Structures

  City University - London

 

AIMS Management Handbook

 

Table of contents              

1. Task description.

2. Executive Summary.

3. Video Library for Feature Extraction.

3.1.    Introduction.

3.2.    Visual Library and initial conditions.

3.2.1.        Video Library images requirements.

3.2.2.Video Library Optimization.

3.2.3.Size optimization process.

3.2.4.Labeling (Naming) and storing the pictures in database.

3.2.5.Video Library Automation data support system..

3.2.6.User Interface and functionality.

4. Mathematical Approaches for features extraction.

4.1     Introduction and basic requirements.

4.2     Image processing possibility for mathematical approaches.

5. Feature Extraction and Classification Methods.

5.1.1. Color distribution methods.

5.1.1.1.  RGB Method.

5.1.2. Texture analyzing methods.

5.1.2.1. Histograms.

5.1.2.2.Moments.

5.1.2.3.Co-occurrence matrix 32*32 pixels.

5.1.2.4.Co-occurrence matrix 64*64 pixels.

5.1.2.5.Markov Random Fields- Energy Distribution.

5.1.2.6.Markov Random Fields Gibbs middle intensity-Energy Distribution.

5.1.2.7.Threshold.

5.1.2.8.MRF-Threshold.

5.2.Classification of information extracted from the methods.

5.3.Weights according to the probability and the time of processing.

5.4.CONCLUSIONS..

6. Neural Network.

6.1.Theoretical description of neural nets method calculation.

 6.1.1.Introduction.

6.1.2.Cellular neural network.

6.1.3.Self- organizing mechanism system..

6.1.4.Basic Profits of using Cellular Neural Networks.

6.1.5.Profits from a self organizing mechanism..

6.1.6.General Description of used Cellular Neuronal Network

6.1.7.Brief description of the layers.

6.1.7.1.Layer 1.

6.1.7.2. Layer 2.

6.1.7.3.Layer 3.

6.1.7.4.Layer 4.

6.1.8.Decision Cells.

6.1.9. Database of Knowledge.

7. The block scheme of the system and user interface.

8. Conclusions.

8.1.Mathematics models and data processing.

8.2.Software.

8.3.Industrial realization.

 

 

CONCLUSIONS

We can make some conclusions in order to complete this final report

This task represents a complicated research work cross-section between mathematics, software, and engineering.

Using this can be extracted several classes conclusions according to the task requirements.

8.1.Mathematics models and data processing

 

·        The result form corrosion zone separating shows that between 0 and 1500 hours the recognition is more precise than in 1500-8000 hours zones.

·        The mathematical models should be combined to be able to produce data in 0-8000 hours corrosion range.

·        The calculation time is not proportional always to the probability of the result.

·        The Cellular Network is the optimum approach combining self-organizing system and reducing total calculation time.

·        The model is very sensitive to initial learning process and initial data library

8.2.Software

 

·      Exclude the interface (prepared for scientific purposes) the basic functions and principles are ready for industrial application.

·      The realized program proves the idea for probabilistic corrosion categorizing using the chosen methods and self-organizing mechanism.

·      The recognition speed is reliable for industrial purposes.

·      The system is independent according to light source intensity

8.3.Industrial realization

·        For industrial application the software should be rewritten in full C++ program, combining learning process from video library and recognition process from Frame grabber and real camera.

·        User interface should be prepared depending how the system will be used (robotic or manual realization).


TASK 2:     Non-destructive Testing strategies for CLASSIFICATION OF EXISTING COATED and prepared steel SURFACES

  

Objectives: Development of non-destructive testing (NDT) methods which will enable quantified classification of the condition of existing coated and prepared steel surfaces as an intrinsic component of an automated man-machine system. For the existing surfaces, these methods will include classification of substrate corrosion and coating defects such as disbonding and delamination.

 

Three main design criteria are crucial for these systems:

 

Large surface areas must be covered quickly.

The sensor systems must be suitable for use in an automated man-machine system.

Currently recognised international standards for surface condition are to be used as references.

 

Rationale: Currently, photographic standards are used for classification of the level of corrosion of coated steel surfaces. Similarly, photographic standards are available for levels of cleanliness achieved by the established surface preparation methods i.e. hand cleaning with tools and dry, slurry and ultra-high pressure water blasting. These methods of testing have the following disadvantages [24]:

·      Both sets of visual standards are difficult to use due to differing appearance of steel, hue and lighting effects.

·      Destructive testing methods must also be used to support coating condition assessment.

·      Only spot inspection is practical.

 

This task overcomes these disadvantages by developing a non-destructive, non-contact automated surface classification system that improves classification reliability and enables large surface areas to be quickly tested.

Task Description: The main classification methods will be grey scale and colour image processing techniques [6,8] and infrared thermography synchronised with a controllable heat source [7,19,20,21,22,23]. Artificial intelligence techniques will be applied to the interpretation and quantifying classification problems. A comprehensive set of manually classified (to international standards) reference samples (80 - 100) will be made available for this work, representing levels of substrate corrosion and corresponding levels of surface cleanliness with different preparation methods. The approaches in the investigation will be:

(i) Application of colour segmentation to the detection of the pigmentation anomalies which are frequently symptoms of substrate corrosion and coating failure. Quantification is expected to be mainly on the basis of affected area and location.

 

(ii) The textural properties of the range of samples will be studied. Texture analysis, including statistics and signal processing and filtering methods, will be applied and the most reliable sets of discriminating features identified for each class of surface. Features such as uniformity of energy entropy, contrast, homogeneity and roughness will be extracted from cooccurrence, grey level dependence, grey level gap length and grey level run length matrices of the textured images. Features thus obtained will be tested for reduction using techniques such as principle component analysis and neural networks. The optimum basis for classification will be investigated using classification schemes such as regression trees, neural networks, genetic algorithms and bayesian classification. Controlled lighting and techniques for invariance with illumination will be tested.

 

(iii) Lockin thermography with modulated lamps will be used to inspect samples representing delaminations, paint disbondings and corrosion. Measurements of paint thickness and corrosion thickness will also be performed with lockin thermography on the base of reference samples. Depending on the kind of problem, validation techniques such as ultrasonics and eddy currents will be used in order to assess the quality of results obtained using the lockin thermography technique. The partner responsible for providing the samples (see Task 1) will know in advance the level of corrosion of every sample. This "a priori" knowledge will allow the validation of lockin thermography results for determination of corrosion levels, thus avoiding the need of highly expensive destructive tests. Porosity evaluation even if possible, will not be performed due to the high costs related to the validation procedure.

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