The use of basis function expansions to analyse the robustness of cross-directional control systems

One of the major difficulties in designing cross directional (CD) control systems for web processes is to make the control design robust to the high levels of uncertainty in the shape of the cross-directional response of the actuators. This paper shows how a number of approaches to minimum variance control can be regarded as versions of the same underlying control strategy but using different basis function expansions. These basis function expansions can be used to analyse the robustness of the CD control systems to modelling errors. Results from a typical response for controlling basis weight on a paper machine indicate that spline based methods (including the commonly used technique of averaging CD variations over zones) are significantly less robust than controllers that use other basis function expansions