New shapemeter roll technology based on Fiber Bragg Grating technology for on-line flatness monitoring of thin cold rolled metal sheets

The shape of laminated products is a crucial parameter in high-speed and high-volume finishing lines where they must fulfill tight tolerances. Latent defects are detected by flatness rolls (or shapemeter rolls) inserted in the manufacturing line for online flatness control. A prototype of flatness roll has been developed with high spatial resolution (5 mm) and measurement capability over a thickness range of 0.1–1 mm to evaluate flatness and residual stresses of flat metal strip products manufactured by continuous cold rolling (ultra-thin sheets for packaging and automotive markets). The flatness roll prototype relies on pressure-induced strain sensing on segmented blades using Fiber Bragg Grating technology. Synchronous measurement of the flatness profile across strip width rejects disturbances of strip tension during rolling. We provide a proof-of-concept on pilot lines in both static and dynamic conditions (e.g., roll in rotation and in contact with a strip under tension) and the sensing mechanism shows a capability above 3. This combination of performances remains unique up to now. Interblade crosstalk appears to be an important issue. We propose a crosstalk model that agrees with experimental coupling coefficients. A crosstalk matrix inversion yields the distribution in contact pressure from strain data measured on the reverse side. Additional work will be required to use the flatness roll in industrial conditions.