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Thesis for the Degree of Master of Science

 

Year 2005
Tapio Jokinen

OPTIMIZATION OF PROFILE CONTROLS OF A PAPER MACHINE


Quality of paper is one of the most important objectives of a paper mill. Cross Direction variations of Basis Weight and Moisture of paper, also called Cross Directional profiles, have a great impact on quality seen by the customer.

In the literature review, on-line quality control of the paper machine is discussed with the main emphasis in Cross Direction control. The actuators, on-line quality measurements and control systems related to Cross Direction control of Basis Weight and Moisture are studied.

The target of the experimental part was to optimize the current profile control system of Basis Weight and Moisture by using an industrial tuning program in order to be sure that the system is used in an optimal way. The optimization also includes application of laboratory measured shrinkage curve to the profile control system. Additionally, a comparison of three cross direction Basis Weight actuators is included in the experimental part. The target of the comparison is to predict how much the current Dry Basis Weight profile can be improved by using

different actuators

After profile control system optimization, the Dry Basis Weight and Moisture profile variations become smaller on controllable wavelengths, which can be seen in the power spectrums of profile errors. The industrial standard 2σ value does not describe the performance of a profile control system very well: the 2σ value can be high although the profile control system removes all the profile error on the controllable wavelengths due to profile variation on uncontrollable wavelengths. The actual width of actuator response is more important than spacing of actuators, which can be seen in the Moisture profile control.


This info last modified 22 Nov 2017 by Jerri Kämpe-Hellenius