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Modeling paper machine cross direction slice lip responses close to sheet edges Yang, David Wei

Abstract

The design of paper machine cross directional (CD) control systems is normally based on actuator response models obtained in the centre rather than the machine edges. However process characteristics near the sheet edges are different from those in the centre of the sheet. Even with good CD control, the edge profile often shows the greatest variations from the target level. The application of control algorithms more suited to the centre of the machine reduces controller effectiveness at sheet edges. Control close to the sheet edge is normally carried out using a variety of assumptions concerning the expected response, however, these assumptions are often made for mathematical convenience rather than on the basis of physical principles. This work involves the comparison of edge response of the cross directional slice lip actuators with the response at the centre of the paper machine. The performance of a typical industrial CD actuator centre response model is tested and found to be inadequate when modeling the edge response. A new physical model, using surface wave theory of the slurry is investigated, tested and later modified in an attempt to better model the edge response. The new edge model is found to generate an improved edge response prediction, based on the centre response, but in general will be computationally expensive. Several variants of the proposed model are put to the test and one particular model with a fixed parameter is proposed, based on physical principles to replace the centre model when modeling the edge response of heavy grade papers. The performance of this new model is evaluated and found to be more effective at modeling edge response than the conventional model. In addition, this edge model can be applied in conjunction with typical industrial control software without difficulty. Superposition and linearity in actuator response are successfully evaluated and found to hold for the test responses.

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