The identification of mapping parameters for paper machine cross direction control

Abstract

Quality controls of a paper machine can be divided into cross- (CD) and machine directional (MD) controls according to the characteristics of the measurements and actuators. -The CD measurement is a scanner that traveses from one edge to another of a sheet during the paper production. The measurement gauge samples all the time during the scan, and samples across the sheet are stored in a vector called profile. The fundamental problem in vector based CD control is mapping. The mapping is an alignment information of the error profile position that has to be mapped into the correct actuator that can eliminate the error. The mapping is one of the most important tuning parameter during the commisioning of the CD controls. -The mapping can be modelled with first order equation. The constant and slope has to be tuned with a "bump" test. The bump test is a step response test of a CD actuator. The response data has to be collected and analyzed with some numerical computation program. This procedure takes too long and is sensitive for errors. -This work includes the development of an automated on-line method for identifying the, mapping parameters. The reader is first familiarized into the paper machine CD controls, actuators and circuits. The model of mapping is derived that can compensate the mapping errors caused by the unlinear shrinkage. -The whole concept of automatic on-line mapping identification includes many functional parts and the basic structure was tested in a board machine last summer. The MD variation was found to disturb the testing and for that reason MD filtering was added. The implemented filter was boxcar average type, but also Wiener filters were implemented and tested later in the analysis part. -The results of the test application were stored while the data was also collected. The data was analyzed using a numerical program called Octave. The aim was to develop further methods for determining the final mapping parameters from intermediate results. A set of tools was developed and the best combination was found. The final results were good and the application can be implemented with present tools.

Paperikoneiden laatusäädöt voidaan jakaa konesuuntaisiin (MD) ja koneen poikkisuuntaisiin (CD) säätöihin. Tässä työssä tutkittiin CD-säätöjen automaattista on-line kohdistusta. - Työssä tutkittiin automaattista kohdistusparametrien idenfiointia. - Esitetään käytetty on-line ratkaisu, jota testattiin kesällä eräällä kartonkikoneella. - Automaattisen kohdistuksen kokonaisratkaisu on moniosainen ja tehdaskokeissa tutkittiin peruskonseptin toimivuutta. Kokonaissovellus vaatii kuitenkin saatujen välitulosten lisäanalyysimenetelmiä, joita kehitettiin Octavella, mikä on numeerinen laskentaohjelmisto. Erilaisia algoritrneja ja niiden toteutettavuutta tutkittiin. Kriteereinä oli toteutuksen helppous, robustisuus ja suorituskyky. Lopputuloksena löytyi menetelmien kombinaatio, jolla pystyttiin varsin tarkasti määrittämään kohdistusparametrit. /Kir10