Inspection technology identifies surface defects
Automated surface defect inspection technology from Nissan identifies potential defects on a painted surface so that they can be remedied. In this way, products with the highest quality finish leave the factory. The inspection system greatly improves the rate of defect detection over those defects found by visual inspection and provides data to a database so that the size, location, quality and other aspects of production line defects can be tracked over time to improve production quality. The system is applicable for inspection of dots/dust from 0.1mm or greater on coated film such as automobile bodies. It uses a series of LED lights configured in stripes, and CCD cameras. The cameras provide images for analysis to a tracking system. If there is a defect, the angle of reflection from the lights shining on the product produces brightness different from the average brightness of the area. The tracking software identifies defects that pass a preset threshold. The tracking software tests the possible defect location several times before it identifies the location as a defect candidate. Information about type, location, and size automatically enters a statistical database for quality control analysis. The system may have additional applications in detecting surface defects on other materials and parts that have surface-quality issues, such as stamped parts and plastic-molded parts, even if they are not painted. The system is already in commercial use, and a later version including lights and camera has been mounted on an articulated arm for robotic inspection of parts smaller than a completed automobile.
Nissan’s surface defect detection system provides high accuracy of defect detection — close to 100% for defect sizes 0.3mm and above, and can detect defects as small as 0.1mm in the surface. An automated surface defect detection system overcomes the natural tendency of the human eye to tire and miss defects as the shift progresses, thus greatly improving the quality of the painted surfaces leaving the factory. The Nissan detection system reduces the number of inspectors required, and makes the remaining inspectors more efficient.
In order to reliably detect a defect on an inspected surface, electronic pictures of the inspected surface are formed at different positions by moving an imaging area relative to the inspected surface. Defect candidate regions are extracted from a series of the pictures. The system examines whether a movement from one candidate region to another candidate region is proportional to the movement of the imaging area. If the movement between the candidate regions is in proportion to the movement of the imaging area, the system judges that the candidate regions are imagery of a defect on the inspected surface.
The system consists of relatively low-cost equipment, but offers high reliability both in terms of equipment and in terms of detecting imperfections. The system records data about defect location, size, quality, and other information to facilitate continuous paint quality control on the production line.
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