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Home Programming 2008 Fissure recognition and CNC controlled electron-beam welding

Fissure recognition and CNC controlled electron-beam welding

Fissure recognition and CNC controlled electron-beam welding
Kodok Márton
final year project, Sapientia - Hungarian University of Transylvania
2008, Targu Mures, Romania 

      In this paper the author used intensity pictures for recognizing fissures trajectories, the pictures were made by electron-beam machine, projected and developed by PhD. Dávid László.

These images have been enhanced with complex filters and image recognition procedures used in digital processing industry, to extract fissure’s trajectories in a thin and continuous format. Based on the digital information from the filtered images, another program, called postprocessor, generated CNC numerical algorithm for following fissure trajectory.

One deficiency of the electron-beam machinery is the missing precise and modern positioning system. Based on the industry requirements of electron-beam processing under vacuum has been chosen an XY linear positioning stage to hold the metal and move under the beam. Graphical user interface software has been created to transcript CNC numerical codes into the industrial language understood by the motion controllers. Therefore the piece holding table can be controlled using CNC algorithm codes.

      Electron-beam applications are used more and more in the automotive manufacturing industry. The exiting electron jet from electron-gun is focused on the metal piece with electro-magnetic lens. Because of it’s great focusing feature, and the amount of energy density that can be achieved in a small spot, it leads precise manufacturing process compared to universal method. Electron-beam installations are equipped with image recording equipment; the retro diffused electrons from the surface are used for analog processing and converted to digital data, so a digital picture is created on the computer.

      Nowadays in our digital and automatic way of life, use of computer to extract information from digital source to be used for industry process is a common and modern fact. From the images, taken with the electron-beam machine, with image processing techniques the fissure trajectory can be extracted. OpenCV is an open source computer vision library, it is focused mainly on real-time image processing. A few years ago programmers must code thousand of lines in order to get the results they wanted, now with the OpenCV library this is reduced to one line of codes, making programmers life easy and growth of the image processing usage in industry. From the machine taken intensity pictures, with well chosen filters and structural elements the noises can be removed. The filtered image with morphological image pattern recognition instructions can be altered, so finally we get a thin and continuous trajectory of the fissure.

            For usage, a graphical user interface desktop application has been created. In the desktop you are able to fine tune the parameters used in image processing. On a metal piece fissures can occur near important edges. In this situation on the picture among the fissure path can be seen the edge path too. In order to get good results, the user is able to define an area on the image that will be omitted. Recognized fissure data in vector format, is used for the CNC postprocessor part of the desktop, where CNC numerical codes are generated to follow the fissure’s trajectory.

            One deficiency of the electron-beam machinery is the missing precise and modern positioning system. Based on CNC machine tools idea, it’s a great upgrade to consider a positioning system in 2 axes configuration which moves the metal under the electron-beam. This stage is considered to be controlled numerically with CNC codes.

            The e-gun welding process is in a closed vacuum chamber. The presence of vacuum justifies the construction of the stage from a special material, the outgasing effect attention, demagnetization and degreasing. In the chamber high temperatures, splash of material micro parts, and roentgen rays are to be considered when choosing operating devices. The selection of the stage must also be based on important geometrical and technological factors, like usage of vacuum compatible lubricants or assure optimal performance of motors.

            The manufacturer assures motion controller for the 2 axes XY stage. The motion controller can be programmed from a personal computer via serial RS-232 standard. The created graphical user interface desktop program, generates CNC codes based on the extracted trajectory of fissures but is able to transcript CNC codes into the industrial language understood by the motion controllers.

The results of the presented paper is the fissure recognition, generation of CNC codes to follow the path, selection process of a stage for specific environment conditions, and ability to numerical control this stage with CNC codes. For future is considered achievability the whole system as a CNC machine-tool and enhancing the image recognition algorithm to extract more complex forms.

Table of contents

Romanian table of contents page 1
Hungarian table of contents 4
English table of contents 7
Romanian abstract 10
Hungarian abstract 12
English abstract 14

1. Introduction 16

2. Presentation and usage of the electron-beam machine 17

2.1. Importance of electron-beam applications in manufacturing industry 17
2.2. Theory of electron-beam process 19
2.2.1. Acceleration of electrons 19
2.2.2. Surface heating and particles vapors in e-gun process 20
2.3. Structure of electron gun machines 22
2.4. The used electron-beam machine 25
2.5. Electron-gun 27
2.6. Vacuum creating system 29
2.7. Image converters 31
2.8. Dimension of images on the piece surface 32

3. Processing of the images, with own algoritm, made by the electron-beam machine 34

3.1. Image processing with computers 34
3.2. Digital images in computers 35
3.3. Image recognition theory bases 36
3.4. Aritmetical operations with digital images 37
3.5. Tthresholding 38
3.6. Translation 39
3.7. Vector type operations – average intensity 39
3.8. Convolution filters 40
3.8.1. Low pass filter 41
3.8.2. High  pass filter 41
3.9. Morfological operations 41
3.9.1. Dilation 42
3.9.2. Erosion 43
3.9.3. Opening and closing 43
3.9.4. Object’s skeleton 44
3.10. Structure of the own image processing program 46
3.10.1. The aim of the image data and program input 48
3.10.2. Idea of preprocessing 50
3.10.3. Tried analises on the filtered image 54
3.10.4. Dilation of the filtered image 56
3.10.5. Searching of the skeletion 57
3.10.6. Postprocessing - conclusions 60

4. The metal holding XY stage selection process and planning of the CNC numerical control 61

4.1. The current position system of the welding machine 61
4.2. Upgrading of the position system 63
4.3. Review of numericaly controlled machines 64
4.4. Selection of the 2 axes XY stage 65
4.4.1. The used geometric and process parameters for selection 65
4.4.2. Ability to working in vacuum environment 66
4.4.3. Ability to work in high temperature environment 66
4.4.4. Demagnetization and degreasing factors 68
4.5. Technical sheet of the selected stage 69
4.6. Subparts of the linear stage 70
4.6.1. Linear guides 70
4.6.2. Ball screws 71
4.6.3. Encoders 71
4.6.4. Stepper motors 71
4.7. CAD modell of the XY stage 72
4.8. Comunication between the stage and motion controller 74
4.9. Motion controller’s interpollation system 77
4.10. The place of the CNC control  in the system 78

5. Usage of vectorized images to control the stage motion 79

5.1. Presentation of the developed graphical user interface application 79
5.2. Fissure trajectory transformation in vector list structure 80
5.3. Bases of CNC programming 80
5.4. Generationg with own software the CNC numerical control codes to follow the fissure path 82
5.5. Transcripting  the CNC codes into the industrial language understood by the motion controller with own developed application 83

6. Results and development opportunities 85
7. Bibiliography 86
Thank you page 87
Appendix 88