Automated Optical Inspection System for O-Ring Based on Photometric Stereo and Machine Vision

Abstract

This research developed an AOI (automated optical inspection) system for the O-Ring inspection. First, an AOI system was implemented to detect surface scratches, flow marks, non-fills, and indentations on elastomer O-Rings with high surface reflection coefficients. The proposed system employed multiple light source structures to realize the photometric stereo. This method eased the identification of the O-Ring contour and Bézier control points. Then, by applying an interpolation process on these control points, we estimated the paths of the object surface. Simultaneously, regression analysis was conducted to produce a new smooth surface and then a constructed surface was compared with the model built by the photometric stereo method. The difference was deemed the candidate defect location. Overall, the detection recall rate was 100% and accuracy reached 96.56%. This paper also developed an AOI system for the O-Ring dimension measurement. The system analyzed the contour of the O-Ring and reversely calculated the Bézier curve control points. Then, those control points were used with De Casteljau’s algorithm to estimate the O-Ring dimension with high accuracy.

Keywords

• photometric stereo
• AOI
• Bézier curve
• rubber
• homography
• defect detection