Robust Cross-Machine Control on Dilution Profiling Headboxes, 2001 Papermakers Conference Proceedings

The introduction of dilution profiling headboxes in recent years has significantly changed the control of cross-machine sheet profiles. Issues associated with slice actuators such as the bending limit of the slice lip, the wide response width of an actuator zone, and the impacts on fiber orientation are now completely replaced by a different set of challenges related to the characteristics of dilution valves. Although narrower actuator and narrower response of dilution valves enable headboxes to produce more uniform profiles, a different set of process issues have become new challenges for the application of cross-machine direction (CD) control. Specifically, the spatial relationship between the dilution actuators and the CD profile, also known as CD mapping, drifts or varies more often. To achieve consistent profile control, it is crucial to maintain a good CD mapping dynamically and adjust CD control to accommodate unavoidable process uncertainty. This paper describes a new approach that addresses this specific need of dilution profiling headboxes and shows the benefits of the new control solution. The described new control solution can also be easily applied to other CD controls, such as watersprays, that have similar needs.