Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-04-19
1990-12-18
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356371, G01N 2186
Patent
active
049788612
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for the continuous determination of a surface state index for a moving creped sheet, particularly for a sheet of creped paper.
By a "surface state index" is meant a value which indicates the undulatory variations of the surface of a material in the form of sheet along one of its dimensions, in comparison with the plane surface of the same material.
The paper-making industry produces large quantities of paper described as quilted or creped, i.e. papers having undulations that are difficult to see with the naked eye. This type of paper is mainly used for its absorbent qualities that are due to the increase in its surface density when undulations are present. It is generally "bonded" a variable number of times to paper of the same type in order to obtain the thickness required for the intended use (kitchen paper, table napkin, etc.).
In a known way, creped or microcreped paper is continuously manufactured in rolls using a rotating cylinder 10 to 30 meters per second at its periphery) of considerable size (4 to 7 meters in diameter and several meters in width) known in the trade as a "yankee". The paper is deposited on the rotating yankee while still very wet (two to three times more water than fibers), thus enabling it to be partially dried. A doctor of dimension equal to that of the generatrix of the yankee is maintained in contact with it. The function of the doctor is to produce the creping of the sheet of paper, i.e. to produce undulations which are more or less perpendicular to the direction of motion of the sheet of paper and which have dimensions depending on the intended use.
The doctor generally consists of a replaceable steel blade. In fact, with the yankee being made from cast iron and because it rotates at high speed and the doctor is pressed permanently onto it, the doctor is observed to wear very rapidly; if the doctor is not changed frequently, the edge in contact with the yankee becomes bevelled, thus producing irregular creping or even none at all.
At present, no methods for monitoring the quality of the paper are known other than visual, and therefore subjective, observation.
One of the criteria for the quality of the creping is the depth of the undulations, the magnitude of which is directly related to three parameters: quality of the paper pulp, which covers the yankee and acts as an adhesive for the paper during the creping phase. In fact, the absence of this layer is observed to produce as well as accelerate wear in the doctor, irregular creping of the paper or even its break-up.
One of the aims of the present invention, when applied in the paper-making industry, is to guarantee the quality of the creped paper and to provide a way of monitoring the wear in the doctor.
Another aim of the present invention is to carry out continuous measurement of the amplitude of the undulations in any type of sheet material subjected to creping or similar treatment.
The present invention proposes a device for the continuous determination of a surface state index for a moving sheet, creped in the form of undulations, of the type comprising: creped sheet; source and to form a luminous spot on the surface of the sheet to be analyzed; arranged on the same side of the sheet as the first optical system;
In this device: shape of the laser beam in such a way that, at the point where it meets the sheet, the luminous spot is adapted to the direction of the undulations and to the dimensions of the average pitch of the undulations; least part of the back-scattered light, concentrated by a second convergent optical system, the optoelectronic cell delivering at least one electrical signal depending on the position of the point of impact of the back-scattered light beam delivered by the convergent optical system onto the sensitive surface; index for the creped sheet from the electrical signals.
In other words, the invention comprises firstly the production of an electrical signal by the optical proximity detection method and then, by suitable means, the production of directly u
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Bauduin Serge
Kerneis Jean C.
Sabater Jacques
Allen Stephone B.
Centre Technique de l'Industrie des Papiers, Cartons et Cellulos
Nelms David C.
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