JPH0523382B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a device for measuring the moisture content of sheet-like paper, and more specifically, it relates to a device for measuring the moisture content of sheet-like paper, and more specifically, it is applicable regardless of the type of paper or even in the case of the same type of paper. This invention relates to a paper moisture measuring device that can always perform measurements with the same sensitivity without being affected by basis weight.

<Prior Art> The moisture content of paper is an important control item in maintaining the quality of paper, for example in paper machines or coating machines.

Figures 9 and 10 are conventional devices for measuring the moisture content of paper. Figure 9 shows a single transmission method moisture content measurement device, and Figure 10 shows a multiple scattering method moisture content measurement device. Show the device.

In Fig. 9, 1 and 2 are paper 3 which is the object to be measured.
A pair of heads are arranged opposite to each other with the upper head 1 constituting an irradiating section, and the lower head 2 constituting a detecting section.

In the irradiation unit 1, numeral 4 denotes a light source, and the light from this source is converted into parallel rays by a lens 5 and applied to a rotary filter 6. The rotary filter 6 is provided with two types of optical filters 6a and 6b.The optical filter 6a generates reference light in a spectral band (for example, wavelength 1.95 μm) that is not absorbed by moisture, and the optical filter 6b spectral bands that are absorbed depending on the water content (e.g.
1.80μm) measurement light is generated.

These reference light and measurement light are time-divisionally irradiated onto the paper 3 from the irradiation window 7 as the rotary filter 6 rotates.

The light transmitted through the paper 3 enters the detection section 2 through the entrance window 8, and is focused by the condenser lens 9, then passes through the light detector 10.
detected by. 11 is a computing unit, detector 1
A measurement signal M based on the measurement light given in a time-division manner from 0 and a reference signal R based on the reference light are held and a calculation M/R is performed. By taking the ratio of the signals M and R, changes in the characteristics of the light source 4 and the photodetector 10 are canceled out, and a signal is obtained that compensates for the effects of temperature fluctuations.

However, in the case of such a single transmission method, the sensitivity varies depending on the paper quality, and in the case of a paper quality that causes little scattering on the surface, there is a drawback that the moisture sensitivity decreases significantly. Figure 11 is a characteristic diagram showing this state, where the vertical axis f (MW) represents the device output and the horizontal axis
MW represents water content. In addition, f(MW) is expressed by the relational expression f(MW)=Z+S・(M/R)...(1), and the bias Z for zero point adjustment is
and the output (M/R) of the arithmetic unit 11 multiplied by a coefficient S for Subang adjustment.

In the figure, the curve GP is a GP whose main raw material is mechanical pulp.
This represents the case of paper with a quality that scatters light well, and the curve CGP shows the case where mechanical pulp and chemical pulp are 50/50.
This represents the case of CGP paper with less light scattering, and the curve SP represents the case of SP (sulfide pulp) paper with even less light scattering.

In this way, moisture sensitivity varies depending on the paper quality.
SP paper, such as Tateshiyu paper, which scatters very little light, had the disadvantage of significantly lower sensitivity.

In contrast, Japanese Patent Publication No. 58-7938 proposes a scattering type moisture content measuring device as shown in FIG. In the figure, the same elements as those in FIG. 9 are given the same reference numerals, and explanations thereof will be omitted. Reference numeral 12 denotes a rotating body that cuts off the light from the light source 4, and an optical filter as shown in FIG. 9 is not provided in this part. The irradiation window 7 of the irradiation section 1 and the entrance window 8 of the detection section 2 are provided offset from each other, and a reflective film 1 is provided on the opposing surface of the irradiation section 1 and the detection section 2.
3 and 14 are provided. The intermittent light from the irradiation section 1 is diffusely reflected between the reflective films 13 and 14 and guided to the detection section 2.

The light from the entrance window 8 is split into two by a light splitter 15,
One is guided to the photodetector 18 via the M signal system, that is, the optical filter 16 and the lens 17, and the other is
R signal system, that is, optical filter 19, lens 20
The light is guided to the photodetector 21 through the. photodetector 18,
The signal from 21 is applied to arithmetic unit 22, and M/R
The following calculation is performed.

In the case of such a scattering method, since light is multiple-reflected between the reflective films 13 and 14 with the paper 3 in between, there are advantages that the optical path length can be long, the sensitivity is increased, and the reflection is less affected by the paper quality.

However, when such a method is used, the moisture sensitivity slightly changes depending on the basis weight even for the same type of paper. Figure 12 is a characteristic diagram showing this state, where the vertical axis f (MW) represents the device output and the horizontal axis
MP represents moisture content. Curve BW1 has a basis weight of 90g/
m ² , curve BW2 represents the case where the basis weight is 60 g/m ² , and curve BW3 represents the case where the basis weight is 30 g/m ² .

In this way, the moisture sensitivity changes depending on the basis weight, so in conventional equipment, a basis weight meter is installed in addition to the moisture meter, and the signal obtained from this basis weight meter is used to remove the influence of the basis weight. Ta.

Further, reflective films 13 and 14 are provided with the paper 3 in between, and the surfaces of these films are easily stained by paper dust from the paper 3, and the paper dust may adhere unevenly to the surface, or these reflective films may If it adheres to one of the two sides, it is not possible to sufficiently compensate for the error caused by this.

<Problems to be Solved by the Invention> The technical problems to be solved by the present invention are that it is not affected by paper quality, does not require compensation using a basis weight signal as in the above-mentioned scattering method, and The object of the present invention is to realize a paper moisture content measuring device that fundamentally does not cause the problem of surface stains.

<Means for Solving the Problems> The configuration of the present invention is to time-divisionally irradiate measuring light in a spectral band that is absorbed according to the amount of water and reference light in a spectral band that is not absorbed by water. a light source, a means for reflecting the light guided from the light source on an internal reflective surface to form a closed loop of light with a sheet of paper in between, a means for varying the amount of reflected light provided within the closed loop of light; and a light detection means provided outside the closed loop of light, to which the light within the closed loop of light is applied via the reflected light amount variable means, and the reference light detected by the light detection means is fixed. The reflection amount variable means is controlled to obtain a signal related to the paper and moisture content from a measurement signal based on the measurement light and a reference signal based on the reference light.

<Operation> The technical means described above operates as follows. That is,
Paper types that scatter light very little, such as Tateshi paper and condenser paper, have low moisture sensitivity, while paper types that scatter light well have inherently high moisture sensitivity. On the other hand, when the same type of paper differs only in basis weight, thin paper with a small basis weight has low moisture sensitivity, while thick paper with a large basis weight has inherently high moisture sensitivity. The device of the present invention is constructed with attention to such points.

That is, in the case of a paper quality that causes little light scattering, the reflected light amount variable means is controlled to increase the amount of reflected light in the closed loop of light based on the output of the light detection means, increasing the amount of light incident on the paper to reduce moisture. Increase sensitivity.

In the case of a paper quality that scatters light well, the reflected light amount variable means is controlled to reduce the amount of reflected light in the closed loop of light, reducing the amount of light incident on the paper to the same level as in the case of a paper quality that does not scatter light well. Achieving a degree of moisture sensitivity.

On the other hand, in the case of thin paper of the same type of paper with a small basis weight, a large amount of transmitted light is transmitted, and the reflected light amount variable means is controlled to increase the amount of reflected light within the closed loop of light based on the output of the light detection means. , increasing the amount of light incident on the paper to increase moisture sensitivity.

In the case of paper with a large basis weight, the transmitted light is small, and the reflected light amount variable means is controlled to reduce the amount of reflected light in the closed loop of light, reducing the amount of light incident on the paper, and in the case of paper with a small basis weight. Achieves moisture sensitivity similar to that of

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an apparatus according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the plane A--A in FIG. In the figures, the same elements as in FIGS. 9 and 10 are given the same reference numerals. Upper head 23 and lower head 24 forming the detection section
and are placed opposite to each other with the paper 3 in between.

Reference numeral 25 denotes light passages formed in the upper head 23 and lower head 24, respectively, and the inner wall surfaces thereof are finished in a mirror finish. Windows 25a and 25b are provided in the light path 25 of the upper head 23, and windows 25a and 25b are provided in the light path 25 of the lower head 24, opposite to these.
c and 25d are provided, respectively.

The light path 25 of the upper head 23 is provided with a small irradiation window 25e for alternately guiding the reference light and measurement light into the light path, and a part of the internal reflection surface of this light path is provided with a reflection window 25e. A light quantity variable means 26 is provided.

3 and 4 are perspective views showing specific examples of this incident light amount variable means. In the case of FIG. 3, two mirrors 26a and 26b are provided with a plurality of slits.
The areas of the slit portion and the mirror surface portion can be changed by superimposing the mirrors 26b on one side in the direction of arrow B1. In the device shown in Fig. 4, two semicircular mirrors 26c and 26d are overlapped, and one mirror 26d is rotated in the direction of arrow B2 to change the area of the mirror surface and change the amount of reflected light. ing.

An integrating sphere 27 is placed outside the light path 25 and behind the incident light amount variable means 26, and averages the light that has passed through the incident light amount variable means 26. integrating sphere 27
The averaged light is detected by a photodetector 28.
Note that instead of the integrating sphere 27, a scattering element such as an opal may be used for averaging.

29 is a sample/hold circuit, and the irradiation window 25
In synchronization with the measurement light and reference light given in a time-sharing manner from e, a measurement signal M based on the measurement light and a reference signal R based on the reference light are held, and these are given to a central processing unit (CPU) A reference signal R based on the reference light is provided to the control circuit 30.

With this configuration, the light guided from the irradiation window 25e is reflected within the light path 25 as shown by the arrow, and a closed loop of light is formed with the paper 3 in between. A part of the light in this closed loop passes through the reflected light amount variable means 26 and the integrating sphere 27, and then passes through the photodetector 28.
given to. A reference signal R is given to the control circuit 30 from the sample and hold circuit 29,
The reflected light amount variable means 26 is controlled so that the value of this signal is constant.

By the way, in the case of a paper quality that scatters very little light, such as tissue paper or condenser paper, the moisture sensitivity is low, and in the case of a paper quality that scatters light well, the moisture sensitivity is inherently high. On the other hand, when the same type of paper differs only in basis weight, thin paper with a small basis weight has low moisture sensitivity, while thick paper with a large basis weight has inherently high moisture sensitivity.

For paper types that scatter less light, the amount of light in the closed loop of light increases. As a result, the photodetector 2
The amount of light detected at 8 also increases, but the reference signal R
The reflected light amount variable means 26 is controlled so that the amount of reflected light is constant, and the amount of light incident on the photodetector 28 is narrowed down. As a result, the amount of reflected light in the closed loop of light increases, increasing the amount of light incident on the paper 3 and increasing moisture sensitivity.

In the case of paper that scatters light well, the amount of light in the closed loop of light will be small and the value of the reference symbol R detected by photodetector 28 will be small. Based on this, the reflected light amount variable means 26 is controlled so that the reference symbol R detected by the photodetector 28 is a constant value, and the amount of reflected light within the closed loop of light is controlled to be reduced. As a result, the amount of light incident on the paper 3 decreases, but since the paper quality that scatters light well has inherently high moisture sensitivity, the same level of moisture sensitivity as the paper quality that scatters less light is achieved. .

On the other hand, in the case of thin paper of the same type of paper with a small basis weight, a large amount of transmitted light is transmitted, and the amount of light in the closed loop of light increases. As a result, the amount of light detected by the photodetector 28 also increases, but the reflected light amount variable means 26 is controlled so that the reference symbol R remains constant, and the amount of light incident on the photodetector 28 is narrowed down. . As a result, the amount of reflected light in the closed loop of light increases, increasing the amount of light incident on the paper 3 and increasing moisture sensitivity.

For paper with a higher basis weight, less light will be transmitted and the amount of light in the closed loop of light will be less. The value of the reference signal R detected by the photodetector 28 becomes smaller,
The reflected light amount variable means 26 is controlled so that the reference signal R detected by the photodetector 28 has a constant value, and is controlled so that the amount of reflected light within the closed loop of the light is reduced. As a result, although the amount of light incident on the paper 3 is reduced, since thick paper with a large basis weight inherently has high moisture sensitivity, moisture sensitivity comparable to that of thin paper with a small basis weight is achieved.

5 and 6 show another embodiment of the present invention. FIG. 5 is a schematic sectional view of the embodiment device, and FIG. 6 is a sectional view taken along the C--C plane in FIG. In the figure, the same elements as those in FIGS. 1 and 2 are given the same reference numerals. In the case of the device of this embodiment, the upper head 23 and the lower head 24
Rectangular windows 25e and 25f are provided on opposing surfaces of the paper 3 to form a closed loop of light with the paper 3 in between.

Even with such a configuration, the same effects as the apparatus according to the embodiment of the present invention shown in FIGS. 1 and 2 can be obtained.

<Effects of the Invention> According to the present invention, the moisture content can be measured with the same sensitivity regardless of the type of paper to be measured, and even when the paper is of the same type, it is not affected by the basis weight, making it possible to measure moisture content with the same sensitivity. There is no need to use a basis weight signal to ensure moisture content when measuring moisture content, as in

Furthermore, the method of the present invention differs from the conventional scattering method in which a reflective film is provided with a sheet of paper 3 interposed and multiple reflections are performed between these reflective films. 7 and 8 are characteristic diagrams showing the effects of the apparatus according to the present invention. As shown in FIG. 7, the same characteristics can be obtained regardless of the type of paper, and as shown in FIG. 8, the same characteristics can be obtained even when the same type of paper differs only in basis weight.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an apparatus according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the apparatus according to an embodiment taken along the A-A plane in FIG. 1, and FIGS. FIG. 5 is a schematic cross-sectional view showing another embodiment of the device of the present invention, and FIG. 6 is a perspective view showing a specific example of the incident light amount variable means in FIG. A cross-sectional view of an example device,
7 and 8 are characteristic diagrams showing the effects of the apparatus according to the embodiment of the present invention, FIGS. 9 and 10 are schematic sectional views of the conventional apparatus, and FIGS. 11 and 12 are characteristic diagrams of the conventional apparatus. 3... Sheet of paper, 4... Light source, 6... Rotating filter, 23... Upper head, 24... Lower head, 25... Light path, 26... Reflected light amount variable means, 27... ...integrating sphere, 28...photodetector.

Claims (1)

[Claims] 1. A light source that time-divisionally irradiates measurement light in a spectral band that is absorbed depending on the moisture content and reference light in a spectral band that is not absorbed by moisture, and a light source that irradiates the light guided from this light source with an internal reflection surface. reflect,
A means for forming a closed loop of light by sandwiching a sheet of paper, a means for varying the amount of reflected light provided within the closed loop for light, and a means for varying the amount of reflected light provided outside the closed loop for light. and a light detection means to which light in a closed loop is applied, the reflection amount variable means is controlled so that the reference light detected by the light detection means is constant, and the measurement signal based on the measurement light and the reference light are controlled. A paper moisture content measuring device configured to obtain a signal related to the paper and moisture content using a reference signal based on light.