Dynamic modeling of cross-directional actuators: Implications for control

Actuators that bend slice lips are commonly used in cross-directional (CD) control systems for paper making and plastic film extrusion. A dynamic mode l of these actuators is developed which is used to investigate their spatia l modes and dynamic responses. The model shows that both the shape and the amplitude of the spatial response depend upon the stiffness of the slice li p. The design of most practical CD control systems is simplified by assumin g that the spatial and dynamic responses are separable in the sense that ea ch of the spatial modes has the same dynamics. The validity of this assumpt ion is examined and it is shown that subject to conditions that are likely to be satisfied in practice, the responses can be taken as separable, The m odel is verified using data from plastic film extrusion line and the conseq uences of separability for the design of CD control systems are discussed.