The cross-directional problem is to control variations in the profile across the strip, orthogonal to the direction of production.
Typically the profile is controlled with an array of evenly spaced actuators with near identical response. The actuators are usually subject to hard physical constraints, and may have a limited dynamic range.
The cross-directional profile is usually subject to disturbances which are constant or slowly varying in time. The main aim of the control system is to remove such disturbances; limitations in actuator configuration as well as robustness requirements usually restrict the control action to low spatial bandwidths across the web.
We have been involved in the analysis, design and implementation of such control systems, in particular for plastic film extrusion. Our main current interest is the ability to guarantee robust stability and performance under both dynamic and steady state constraints. We are also interested in the more general class of spatially varying control systems.
Modelled profile response on a paper Fourdrinier machine
- J.A.G. Akkermans, A.G. Wills and W.P. Heath. Robust cross-directional control of paper making machines with saturating actuators. Control Systems 2004, Québec, June 14-17th, 2004.
- W.P. Heath and A.G. Wills Design of cross-directional controllers with optimal steady state performance. European Journal of Control, 10, pp15-27 with discussion pp28-29, 2004.
- A.G. Wills and W.P. Heath: Analysis of steady state performance for cross-directional control. I.E.E. Proc.-Control Theory Appl., 149, pp433-440, 2002.
- S.O.R. Moheimani and W.P. Heath: Model correction for a class of spatio-temporal systems. Automatica, 38, pp147-155, 2002.
- S.R. Duncan, J.M. Allwood, W.P. Heath and K.W. Corscadden: Dynamic modelling of cross-directional actuators: implications for control. IEEE Trans. on Control Systems Technology, 8, pp667-675, 2000.
- W.P. Heath: Orthogonal functions for cross-directional control of web forming processes. Automatica, 32, pp183-198, 1996.