METHOD AND APPARATUS FOR CONTROL OF THE DRY LINE OR FOR CONTROL BASED ON THE DRY LINE IN A FOURDRINIER PAPER MACHINE

摘要

The system effects an automatic observation of the dry line on wire of the Fourdrinier paper machine and the control actions based on it. In order to produce an image of the dry line range on wire this is illuminated by means of a large, diffusely illuminating surface (20) of even luminosity. The material on moving wire (10) is imaged by an optoelectric camera (40) on a detector whereby the pulp surface preceding the dry line and being specularly reflecting is found homogeneous and bright while the web surface following it and being diffusely reflecting is found homogeneous but matter and darker. The electric image signal delivered by the detector is conducted to a computer (50) in which the dry line is identified as the borderline of said surfaces of different brightness. Its deviations from target values are determined for both the average value and different values in cross direction and the corresponding actuators are adjusted in order to control the paper web on basis of deviations observed for its different parts or for its whole breath. Dry line and values of quantities and deviations characterizing it are also presented on a display terminal, whereby said controls can alternatively be effected by a human observer.