Two-dimensional methods for MD and CD estimation and control: Recent progress - An outline of developments and how they relate to sensor research

The paper describes recent progress in two-dimensional estimation and control methods for web forming processes such as paper making. In particular, it outlines some of the developments in two-dimensional methods that have taken place in the Control Systems Centre since the Control '92 Conference [1] and relates them to recent sensor research. The basic premise for this paper is that continuous web forming (such as takes place at the wet-end of a paper machine) or related coating processes are two-dimensional dynamical processes in which the machine direction (MD) and cross direction (CD) form the two dimensions. The two-dimensional paradigm leads to a set of techniques with which to estimate, predict and potentially regulate the MD/CD process in a way which acknowledges and accounts for the mutual dependence of the machine and cross machine directions.