Development of Shape Meter Employing LED Dot Pattern Projection Method for Hot Strip Finishing Mill

In recent years, in order to improve the fuel efficiency of automobiles by reducing their weight with maintaining strength, the thinner thickness and higher strength steel sheets tends to be used as their construction materials. For stable and accurate production of these sheets, it is very important for these to be flattened at hot strip rolling process. Therefore, to realize accurate AFC (Automatic Flatness Control), a new shape meter which employed LED dot pattern projection method was developed. This is consist of LED dot pattern projector which can project the staggered periodic dot pattern, formed of 1200 power LED chips, on the rolled strip and area camera which captures the image of projected pattern. Then, instantaneous strip flatness is measured by analyzing the pattern pitch correlative with inclination angle. The shape meter was installed at the hot strip finishing mill exit and evaluated its measurement accuracy and stability. As a result, its inclination angle measurement error was within 0.45 degrees (two sigma) by comparing with the set angle of standard target and the measured flatness of rolling strip was consistent with the visually observed one. Its measurement success rate per entire coil was exceeded above 98.5%. These results indicated that the developed shape meter would be able to apply to the AFC. In addition, applying the measured flatness to the AFC of the work roll bender and leveling, it was confirmed that the strip flatness was improved in a short time.