Optics: measuring and testing – By monitoring of webs or thread
Reexamination Certificate
2000-04-20
2001-10-02
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
By monitoring of webs or thread
C242S563000
Reexamination Certificate
active
06297882
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for measuring paper color, whereby paper color is measured from the surface of a paper roll on a winder during the winding of the paper in such a way that the angle between a measuring device and the surface of the paper roll is kept substantially constant.
BACKGROUND OF THE INVENTION
The invention further relates to an apparatus for measuring paper color, the apparatus comprising a measuring device which is arranged to measure paper color from the surface of a paper roll on a winder during, the winding of the paper, and to means for keeping the angle between the measuring device and the paper roll constant.
The article “An on-line sensor for the measurement of paper colour” in the publication “Appita Vol. 44 No. 2” describes a method and apparatus in which paper color is measured on the winder. In this case the caliper of the paper to be measured and its background color cannot affect the measurement result because a thick layer of paper is very quickly formed on the winder, and the paper provides for the color measurement an even backing which also has the same color as the sample to be measured. The measuring device is immovably arranged at a distance from the winder, therefore background light easily interferes too much with the measurement result, and the measuring device is also difficult to calibrate. As the circumference of the paper roll grows, distance to the roll surface must be measured and the measurement angle adjusted on the basis of the measurement, which makes the apparatus complex and cumbersome. Further, the growing circumference of the paper roll changes the distance between the measuring device and the paper surface, which in turn changes the measurement geometry of the apparatus, i.e., the focusing of a light beam directed from the measurement apparatus on the surface of the paper, whereby the measurement provided is inaccurate.
An object of the invention is to provide a method and apparatus allowing the above mentioned drawbacks to be avoided.
SUMMARY OF THE INVENTION
The method of the invention is characterized in that as the size of the paper roll grows, a measuring device is moved in such a way that the distance of the measuring device from the surface of the paper roll remains substantially constant.
The apparatus of the invention is further characterized in that the apparatus comprises means for keeping the distance of the measuring device from the surface of the paper roll constant as the size of the paper roll grows.
An essential idea of the invention is that paper color is measured on a winder, the angle between a measuring device and the paper surface remaining substantially constant and the measuring device being moved, as the roll size grows, in such a way that the distance of the measuring device from the roll surface also remains substantially constant. An idea of a preferred embodiment is that the measuring device is arranged to move in line with the central axis of the roll. An idea of another preferred embodiment is that the measuring device is arranged to move in relation to two joints in such a way that as the roll size grows the measuring device turns, thus keeping the measurement angle substantially constant.
An advantage of the invention is that since paper is very quickly formed on the winder, the paper provides for the color measurement an even surface which also has the same color as the sample to be measured. In this case neither the backing nor the opacity of the paper to be measured affects the result of the color measurement. In addition, because the distance of the measuring device from the paper on the roll surface is small, the disturbing effect of background light can be eliminated and an accurate measurement is obtained. Likewise, the measurement geometry remains unchanged. In addition, since the measuring device moves as the roll size grows, the angle between the measuring device and the paper surface is simple to adjust. The measuring device being arranged to move in line with the central axis of the roll, the measurement angle can be kept constant all the way without turning the measuring device. The invention is particularly well suited for measuring the color of thin paper grades.
REFERENCES:
patent: 4715715 (1987-12-01), Howarth et al.
patent: 4865456 (1989-09-01), Mast et al.
patent: 5047652 (1991-09-01), Lisnyansky et al.
patent: 5082529 (1992-01-01), Burk
patent: 5592294 (1997-01-01), Ota et al.
patent: 5758982 (1998-06-01), Yoshida et al.
patent: 0 710 569 A1 (1996-05-01), None
patent: 95 323 (1995-09-01), None
Bradford et al; An on-line sensor for the measurement of paper colour; Appita; Mar., 1991; pp 139-143; vol. 44, No. 2.
Alston & Bird LLP
Metso Paper Automation Oy
Rosenberger Richard A.
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