Machine vision system for surface inspection on brushed industrial parts

Abstract

This work aims at detecting defects on metallic industrial parts with streaked surface. The orientation of those parallel streaks is totally random. The searched defects are scratch and lack of machining. A specific machine vision system has been designed to deal with the particular inspected surface features. One image is acquired with an annular lighting in bright field and six images are acquired with a rotating lighting in dark field. A particular image processing is applied on the six images in order to get one image that represents all the revealed imperfections. A thresholding processing is then applied on this image in order to segment the imperfections. A trained classification, created with well known typical objects of each class, is performed. The classification has to recognize the different defects and the small imperfections that are not defects. The decision phase is used to know if the defects are acceptable, and therefore if the inspected part is acceptable. Some acceptability rules are defined for every defect class. The developed machine vision system has been implemented on an experimental industrial production line and it gives 2% of sub-detection and 16% of over-detection.