Flatness measurement system based on a nonlinear optical triangulation technique

This paper describes the development of a flatness measurement system, integrated in the control process of a hot strip mill in the steel industry. The objective of the system is to calculate flatness indexes for every rolled strip, comparing the length of its lateral profiles with the central length. The reconstruction of the profiles is based on a nonlinear triangulation technique. Images of laser spots over the steel strip, at high temperature and high speed, are sampled every two milliseconds at five different points and are processed online in order to calculate height displacement values of the strip, so that final flatness indexes for the steel strip can be calculated. The measurement method developed introduces an innovative geometry in the disposition of the optic elements which increases the measurement range of the system without reducing its accuracy. It also includes a tracking system to compensate for the effects of lateral displacements of the strip. The flatness measurement system has been implemented using a heterogeneous distributed computer system.