You are here : Control System Design - Index | Simulations | Rolling Mill | Part 4 ## Rolling Mill Tutorial - Part 4The sinusoidal variations in exit thickness are due to the fact that
the rolls are not perfectly round, but contain various "bumps"
or imperfections. These imperfections are known as the The model of the system can then be modified to include the effect of
eccentricity. The eccentricity signal
We then find that the exit thickness is given by
Note that the eccentricity signal is attenuated by a factor of in the uncontrolled, open-loop system (i.e. the effect of eccentricity on the output is one third of the input value). The actual system is shown in the diagram below.
This has severe implications for the BISRA gauge, since the estimated exit thickness is actually
So the controller thinks that the eccentricity variations are disturbances in the output and compensates for them. This explains why the eccentricity appears unattenuated on the output of the system. Next, we look at the use of a Kalman filter (another "virtual sensor", "soft sensor" or "observer") to estimate the eccentricity and remove it from the thickness measurement. |