26 April 2008 Metal sheet thickness profile measurement method based on two-side line triangulation and continuous vibration compensation
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Dimension measurements in metal production are getting increasingly important to improve quality and yield. One important measurement is thickness profile, in this case of copper strip. Knowing the strip profile in entrance and exit side of milling line helps optimizing the milling depth and give information about tool wearing. In this study a comparative measurement method was traversing point measurement system. It gives profile as a series of points which take a relatively long time to measure. Now presented method is based on two-side optical triangulation formed by line illuminators and CMOS-cameras and enables instantaneous thickness profile measurement. Results from both sides are fixed together using reference plates on both ends of the measurement area. From 1.3 m stand-off distance, 1.4 m wide measurement area is achieved. This paper presents the measurement method and results of laboratory and on-line tests. Using laser line illumination the accuracy of thickness was 150 μm when measuring 9 mm thick test plate. Accuracy was limited by laser speckle during static calibration. Other illumination method based on white light was therefore tested and the accuracy was 12 μm correspondingly. Measurement time for one profile was 1 second and resolution in cross machine direction 50 mm after averaging. Now presented method enables thickness profile measurement of copper and other metal sheets. Using white light the accuracy is at same level as the present traversing point measurement. Method has also continuous reference measurement to compensate errors caused by vibration; therefore the system can be realized at reasonable cost.
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Petri Lehtonen, Petri Lehtonen, Jari Miettinen, Jari Miettinen, Heimo Keränen, Heimo Keränen, Tapio Vaarala, Tapio Vaarala, } "Metal sheet thickness profile measurement method based on two-side line triangulation and continuous vibration compensation", Proc. SPIE 7003, Optical Sensors 2008, 70030P (26 April 2008); doi: 10.1117/12.780800; https://doi.org/10.1117/12.780800

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