Oram Embedded Technology     Real-Time and Embedded Systems Software Development
 
             

Automatic Inspection System for Perspex Sheets with Rule Based Defect Classification

This project involved a laser scanning system for scanning perspex sheets on a production line. It used a custom hardware board for defect feature extraction and three Force 68000 boards for data processing. My responsibility was for the defect classification software on one of the 68000 boards, and for the PC rule-compiler software, both written in 'C'. The processing of the data from the laser scanner was done in the following steps -
  • Feature Extraction. The signal from the laser scanner was processed by a custom hardware board called a "feature extractor" that calculated the size and location of defects on the sheet.
  • Master Processor.The defect parameters were then read by the first 68000 board which logged the raw data to a PC and passed the data to the other two 68000 boards (display and defect classification).
  • Graphics Display.One of the 68000 boards was responsible for producing a real-time colour display of the sheet, showing the location and type of the defects.
  • Rule-based Classification.The third 68000 board used the size, shape and location of the defects to classify them. This information was then passed to the display board, to allow the type of defect to be displayed in colour, and to the master 68000 board for logging to the PC. I was responsible for developing the software for this board, including the defect classifier software and the PC software for the rule compiler.
The rule compiler allowed the user to write simple "IF .. THEN .. ELSE .." type rules to classify defects. An example of a very simple rule to detects scratches (which tend to be long and thing) might be -

IF length > 10 and width < 2 THEN
    type = scratch

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© 2006 Oram Embedded Technology Ltd.