JP2932783B2 - Equipment for measuring characteristics of sheet-like objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the amount of water contained in a sheet-like object.

[0002]

2. Description of the Related Art FIGS. 7 to 9 show a conventional example of a moisture meter for measuring the moisture content of a sheet-like object in a paper machine or the like.

In FIG. 7, reference numeral 1 denotes a light projecting unit, 2 denotes a light receiving unit, and these are arranged to face each other with a paper 3 to be measured interposed therebetween. In the light projecting unit 1, the light from the light source 6 is converted into parallel light by the lens 7, and is turned into intermittent light by the chopper wheel 8, and then is irradiated on the paper 3 through the irradiation window 4. 1.94μ to be absorbed by water in chopper wheel 8
A filter 9 that transmits light of m (measurement light) and a filter 10 that transmits light of 1.8 μm (comparison light) that is not absorbed by moisture are provided. Irradiate paper 3. In the light receiving unit 2, the light transmitted through the paper 3 from the entrance window 5 enters, is focused by the lens 11, and is focused on the light receiving element 12. In this light receiving element 12, the measuring light M
And the comparison light R are detected in time series,
/ M is calculated and output.

In the conventional example shown in FIG. 8, light from a light source 6 in a light projecting section 1 is made parallel by a lens 7 and
After making the light intermittent with the wheel 8 ′, the paper 3 is irradiated from the irradiation window 4. This chopper wheel does not include a filter as in the conventional example of FIG. 7, and the wheel is used only for removing the effect of stray light. The white light emitted from the irradiation window 4 is interposed between the paper 3 and the light emitting portion 1 and the light receiving portion 2.
Are multiple-reflected on the irregular reflection surfaces 16 and 17 provided on the opposite surfaces of the light-receiving portion 2 and enter the light receiving portion 2 through the entrance window 5 provided at a position shifted from the irradiation window 4.

In the light receiving section 2, the incident light is split into two by a beam splitter 18, one of which is guided to a light receiving element 12 through a filter 9 which transmits a measuring light and a lens 11, and the other is a filter which transmits a comparative light. 10. The light is guided to the light receiving element 12 'through the lens 11'. The measuring light M detected by the light receiving element 12 and the comparison light R detected by the light receiving element 12 'are simultaneously supplied to an arithmetic unit 13, where R / M is calculated and output.

FIG. 9 shows still another conventional example.
Spherical mirrors 20 and 21 whose openings are covered with dustproof glasses 22 and 23 are disposed with the glass mirrors interposed therebetween. In this example, the light emitted from the light source 6 and turned into intermittent light by the chopper wheel 8 having the two types of filters is applied to the paper 3 through the irradiation window 5. The light transmitted through the paper 3 or scattered by the paper is reflected on the inner surface of the sphere and irradiates the paper again, so that the light passes through the paper a plurality of times and reaches the light receiving element 12. The detected light is R / R output by a computing unit (not shown) in the same manner as in the example shown in FIG.
The calculation of M is performed, and an electric signal related to the water content of the paper is output.

[0007]

In the above-mentioned conventional apparatus, the apparatus shown in FIG. 7 has the advantages that the structure is simple and the amount of light attenuation is small, but the object to be measured is one sheet of paper. If the thickness of the paper is small, there is a problem that a high-sensitivity product cannot be obtained. In addition, in the configuration shown in FIG. 8, the optical axes of the light projecting unit and the light receiving unit are shifted from each other. Although the number of times of association with paper increases, the light scattered by paper has a maximum spread of 180 °. Considering that light that is associated only once with paper is included, sensitivity is not always satisfactory. Was. In addition, there is a problem that the light amount decreases when the shift amount of the optical axis is increased in order to reduce the influence of the light transmitted once. The distance between the upper and lower reflectors is designed to be about 6 to 8 mm).

In the configuration shown in FIG. 9, the light that is transmitted and scattered by paper a small number of times (low-sensitivity light that is not sufficiently associated with water molecules) occupies most of the detection light. There is a problem that the sensitivity is low. Further, in this method, there is a problem that the sensitivity is different between thin paper and thick paper, so that the influence of paper quality increases.

[0009]

According to the present invention, there is provided a sheet-like object that irradiates at least light having a wavelength that is absorbed by moisture and light having a wavelength that is not absorbed by moisture to a sheet-like object. A characteristic measurement of a sheet-like object having a light-receiving element for receiving light scattered and transmitted by the sheet-like object, and measuring a physical characteristic of the sheet-like object based on a signal from the light-receiving element In the apparatus, an upper reflector and a lower reflector having a folded portion around the sheet-like object are disposed, and a shielding plate having both surfaces mirror-finished is disposed between the sheet-like object and the lower reflector. In addition, a wavelength at an iso-absorption point having no temperature dependency is used as a wavelength to be absorbed by the water.

[0010]

The light incident from the light transmitting portion transmits through the paper or is scattered by the paper, and spreads between the upper reflector and the shield in the outer peripheral direction. The light further propagates in the outer peripheral direction while repeatedly transmitting and scattering between the upper reflector, the paper, and the lower reflector, and is reflected at the folded portion, and further travels toward the center while repeating transmission and scattering. After a part of this light is reflected by the lower reflector, it goes to the back side of the shield plate and is reflected between the lower reflector and the shield plate to reach the light receiving element. Since the absorbance of the measurement light having the wavelength at the isosbestic point does not depend on the temperature of the paper, more accurate moisture measurement can be performed.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a sectional perspective view of a main part showing an embodiment of the apparatus of the present invention.
In the figure, reference numeral 30 denotes an upper reflector having a mirror-finished surface facing the paper, a light emitting hole 30a formed in the center, and a folded ring 30b formed in the outer peripheral portion. The folded ring 30b is a convex ring, and the inner periphery has a hypotenuse whose cross section is about 60 ° with respect to a perpendicular line of a mirror surface. Reference numeral 31 denotes a lower reflector having a mirror-finished surface facing the paper, a light receiving hole 31a formed in the center, and a folded ring 31 formed on the outer peripheral portion.
b is formed. The folded ring 31b is a convex ring, and its inner periphery has a hypotenuse with a cross section of about 60 ° with respect to a perpendicular to the mirror surface.

Numeral 32 is a shielding plate having mirror-finished projections (conical mirrors) 33 whose both surfaces are mirror-finished and whose surface is mirror-finished at the center of one surface. The shielding plate 32 has a plurality of columns (not shown) in a space between the lower reflecting plate 31 and the paper 3.
And is fixed at the same height as the upper part of the folded ring 31b of the lower reflecting plate, and the conical mirror 33 is arranged facing the light receiving hole 31a. It is preferable that the center of the shielding plate 32 be aligned with the axes of the upper and lower reflecting plates 30 and 31.

The upper and lower reflectors 30 and 31 are arranged as close as possible in consideration of a necessary allowable width across the paper 3 whose moisture content is to be measured. To form Although not shown in the drawing, 1.94 is absorbed by moisture above the light emitting hole 30a.
A light source that emits measurement light having a center wavelength of μm and comparative light of 1.8 μm that is not absorbed by moisture is disposed. At the subsequent stage of the light receiving element 12, the calculation of the water content based on the output of this element is performed. Components required as a moisture measuring device, such as a calculation unit, are provided.

In such a configuration, of the light emitted from the light projecting unit onto the paper surface, the light scattered on the paper surface is reflected by the upper reflector 30 and the transmitted light is reflected by the shield plate 32 and is again reflected on the paper 3. Is returned to. The light transmitted and scattered by the paper 3 and propagated to the surroundings in this manner is mainly reflected by the reflection surface of the upper reflector 30 and returned to the center. Reach Conical mirror 3 under the shielding plate 32
Reference numeral 3 functions to effectively guide the arrived light to the light receiving element.

It should be noted that the present applicant has applied the upper and lower reflectors 3
The outer diameter of 0, 31 is 60 mm, the height h1 of the upper turn ring 30a is 2.5 mm, and the lower turn ring 31
The height h2 of the ring b is 5.0 mm and the folded ring 30
1. The gaps h3 and h4 from a, 30b to the paper are set to 2.
A prototype was made with 0 mm, the diameter of the light shielding plate was 30 mm, the gap from the surface of the light shielding plate to the paper was 2.0 mm, the diameter of the light emitting hole was 3 mm, and the diameter of the light receiving hole was 18 mm. Was done.

FIGS. 2 and 3 show MW (moisture weight per unit area) obtained from measurement signals (R / M) of six types of paper using the conventional apparatus shown in FIG. 8 and the apparatus of the present invention. Shows the calibration curve when the moisture content of the paper (MW / BW × 100%... BW = weight of paper per unit area) is calculated from the value of and the measurement can be performed within the accuracy of ± 0.1%. (In this case, the accuracy of ± 0.1% means that when the water content is, for example, 5%, the measurement error is 4.9%.
(R / M) N is standardized with reference to a signal when there is no paper). That is, in the conventional device, as shown in FIG.
Although five calibration curves were required to obtain 0.1% accuracy, the apparatus of the present invention can measure with three calibration curves as shown in FIG.

Incidentally, it is known that water has a temperature dependence of an absorption spectrum. FIG. 4 shows the temperature dependence of the near-infrared absorption spectrum of ice and water known in the art (published by Kyoritsu Shuppan Co., Ltd., March 1982; water and aqueous solution), showing the relationship between wavelength and absorbance. . The portion indicated by the dotted line in the figure is the portion at a wavelength of 1.94 μm, which has the highest absorbance at any temperature of water, and it is necessary to select around this wavelength in order to improve the sensitivity as a moisture meter (accordingly, In the conventional example shown in FIGS. 7 to 9, 1.94 μm (5150 cm
^{-1 to} 5155 cm ^-1 ). At this wavelength, the absorbance at each temperature is different, as is clear from the figure. Therefore, when the paper temperature changes, the absorbance of water changes and a measurement error occurs.

Further, in the present invention, the upper reflector and the lower reflector having a folded portion in the periphery are disposed, and the shielding plate whose both surfaces are mirror-finished is disposed between the sheet-like object and the lower reflector. The sensitivity is remarkably improved as compared with the related art, and the measurement error is further affected by the above-mentioned temperature change. For example, a basis weight of 70 using a wavelength of 1.94 μm.
When the moisture of a bleached kraft of about g / m ² is measured, it is said that when the paper temperature is 13 ° C. and 40 ° C., the moisture content error is about 0.3% (a true value of 10% becomes 10.3%). There was a problem. Therefore, the present inventors set the center wavelength of the measurement to 5150 cm ⁻¹ which is the isosbestic point of water based on the above-mentioned known literature.
(Wavelength: 1.957 μm), and experiments were carried out at paper temperatures of 13 ° C. and 40 ° C., but it was not possible to reduce the water content error at this wavelength. This is presumably because the water contained in the paper is composed of bound water and free water, so that the isosbestic point shifts to shorter wavelengths than in the case of free water.

FIG. 5 shows three measurement wavelengths and a basis weight of 70 g / m.
^Using about ² bleached kraft, paper temperature 13 ℃ and 40 ℃
FIG. 4 is a diagram showing the temperature dependence of the center wavelength and the calibration curve when moisture is measured. In this experiment, three wavelengths, (M), the wavelength absorbed by paper moisture (C), the wavelength absorbed by paper fiber (C), and the wavelength (R), which is not affected by moisture or fiber, were used. The calculation was performed using the three-wavelength method used. In the figure, MW is the moisture weight per unit area, and CW is the fiber weight per unit area. According to the figure, 1.92
13 ° C to 40 for wavelengths of 6 μm and 1.549 μm
When the temperature changes by 27 ° C. and the temperature changes by 27 ° C., the calibration curve changes as shown by the arrow, and the deviation of the calibration curve becomes large. However, when the wavelength is 1.936 μm, the calibration curves almost overlap each other, and the influence of the temperature does not occur.

FIG. 6 shows the relationship between the center wavelength and the water content error caused by the difference in paper temperature. According to the figure, the measurement accuracy is ±
The wavelength falling within the range of 0.2 is 1.933 to 1.939 μm.
You can see that it is in the range. Therefore, in the present invention, the center wavelength used for the measurement is in the range of 1.933 to 1.939 μm. In addition to the method of selecting the measurement wavelength using a filter, it is also possible to use monochromatic light such as a laser.

[0021]

According to the present invention, as described above in detail with the embodiments, the light incident from the light projecting hole transmits or scatters the paper at first, but these lights are transmitted through the shielding plate and the upper reflecting plate. Reflects between and meets the paper multiple times. Then, when the light reaches the outer periphery of the shielding plate, a part of the light goes to the back side of the lower reflecting plate and the shielding plate and reaches the light receiving element while repeating reflection. On the other hand, the light that has repeatedly associated with the paper further toward the outer periphery of the reflector is returned by the folding ring and reaches the outer periphery of the shielding plate again, and a part of the light reaches the back side of the shielding plate and reaches the light receiving element while repeating transmission and scattering. . As a result, the light having low moisture detection sensitivity that has passed through the paper, for example, only once does not reach the light receiving element side, so that the sensitivity is improved. For the structure to return the light to the light receiving element side (toward the center) by the return rings, confinement effect of light becomes high, high basis weight from many low basis weight paper detected light (e.g. 30 g / m ² or so) (e.g. 150g / M
^Two To the extent) can be measured with the same optical system. Since light that is sufficiently associated with water molecules and sufficiently transmitted and scattered by paper from thin paper to thick paper is detected,
The effect of paper quality is reduced. Since the light is folded by the folding ring, a small measurement area is required to obtain light having the same optical path length as in the past. The measurement wavelength is 1.933 to 1.939 μm
0.2% moisture error due to changes in paper temperature
Can be suppressed to the extent. And so on.

[0022]

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of a physical quantity measuring device for a sheet-like object according to the present invention.

FIG. 2 is a diagram showing a relationship between a measurement signal (R / M), MW, and a calibration curve in a conventional apparatus.

FIG. 3 shows a measurement signal (R / M) and M in the apparatus of the present invention.
It is a figure showing the relation between W and a calibration curve.

FIG. 4 is a diagram showing the temperature dependence of near infrared absorption spectra of ice and water.

FIG. 5 is a diagram showing the temperature dependence of a calibration curve using three types of wavelengths.

FIG. 6 is a diagram showing a relationship between a center wavelength and a moisture content error caused by a difference in paper temperature.

FIG. 7 is a configuration diagram showing an embodiment of a conventional apparatus.

FIG. 8 is a configuration diagram showing another embodiment of the conventional device.

FIG. 9 is a configuration diagram showing another embodiment of the conventional device.

[Explanation of symbols]

 3 Sample Paper 30 Upper Reflector 30a Light Emitting Hole 30b Folding Ring 31 Lower Reflector 31a Light Receiving Hole 31b Folding Ring 32 Shielding Plate 33 Conical Mirror

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-34342 (JP, A) JP-A-64-32152 (JP, A) JP-A-56-7050 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) G01N 21/00-21/01 G01N 21/17-21/61

Claims (1)

(57) [Claims] A light receiving element for irradiating a sheet-like object with at least light having a wavelength that is absorbed by moisture and light having a wavelength that is not absorbed by moisture, and receiving light scattered and transmitted by the sheet-like object. A sheet-like object characteristic measuring device for measuring physical characteristics of the sheet-like object based on a signal from the light-receiving element, wherein a folded portion is provided around the sheet-like object around the sheet-like object. An upper reflector and a lower reflector having the same, and a shielding plate having both surfaces mirror-finished between the sheet-like object and the lower reflector. An apparatus for measuring characteristics of a sheet-like object, wherein a wavelength at an absorption point is used.