JP2018189659A - Infrared moisture meter - Google Patents

Abstract

An infrared moisture meter capable of measuring moisture content with high accuracy even for extremely thin paper.
An infrared moisture meter including a light source unit and a light receiving unit that move synchronously with a paper to be measured interposed therebetween, the light source unit including an optical element that diffuses light in which infrared rays of a plurality of wavelengths are mixed, and A diaphragm plate in which a minute through-hole for allowing light diffused by the optical element to pass through and irradiating the paper is formed, and a surface on the light receiving unit side is a reflecting surface, and the light receiving unit is a diaphragm plate The light-shielding plate is arranged to transmit light outside the outer periphery, the reflective plate on both sides, and the farther from the paper than the light-shielding plate, the light source side surface is the reflective surface And a reflection plate having a larger outer diameter than the light shielding plate and guiding light to the detector.
[Selection] Figure 1

Description

  The present invention relates to an infrared moisture meter used in a papermaking process, and more particularly, to an infrared moisture meter capable of performing highly accurate moisture content measurement even on extremely thin paper.

  It is important to control the moisture content in order to maintain the quality of products in the papermaking process for manufacturing paper. For this reason, a moisture measuring device that measures the moisture content of the paper moving on the paper making line online is used. By measuring the moisture content online and feeding back the measurement results to the upstream paper machine, it becomes possible to produce products with stable quality. Several types of moisture measuring devices have been put to practical use, but infrared moisture meters using near infrared rays are widely used as moisture measuring devices used online.

  In the infrared moisture meter, light having a wavelength that is absorbed by moisture and not absorbed by cellulose, which is a main component of paper, and light having a wavelength that is not absorbed by moisture but absorbed by cellulose are transmitted through the paper to be measured. Then, the moisture content in the paper is calculated based on the absorption rate of light of each wavelength measured by the light receiving unit. At this time, in order to eliminate the influence of paper scattering, mixture, basis weight, ash, lignin, colorant, coating, etc., light having a wavelength that is not absorbed by moisture or cellulose is also used as reference light. Yes.

  The infrared moisture meter is mounted as one of the sensors on the measuring head of the measuring apparatus 300 that performs various measurements essential for the paper making process such as moisture content, basis weight, color, thickness, ash content, etc. as shown in FIG. . The measurement head includes an upper measurement head 310 and a lower measurement head 320. A light source is mounted on one head and a light receiver is mounted on the other head. In general, a light source is mounted on the upper measurement head 310 and a light receiver is mounted on the lower measurement head 320.

  The upper measurement head 310 and the lower measurement head 320 are movably attached to the frame 330, and the heads perform measurement while reciprocally moving in the direction orthogonal to the moving direction A of the paper 200. For this reason, the measurement region draws a zigzag locus as shown by the line in the figure.

  In an infrared moisture meter, an index value obtained from the absorption rate of each wavelength is converted into a moisture content and output as a measurement result. A calibration curve is used for conversion from the index value to the moisture content. The calibration curve defines the correspondence between the index value and the moisture content. The calibration curve was obtained by measuring the moisture content measured using an electronic balance or the like for each sample having a different moisture state, and measuring the infrared moisture meter for each sample before shipping the infrared moisture meter. It is created by associating with an index value.

JP 2012-173249 A

  In FIG. 9, the light from the light source mounted on the upper measurement head 310 is applied to the paper 200, and the light that has passed through the paper 200 is measured by a light receiver mounted on the lower measurement head 320. Since the upper measurement head 310 and the lower measurement head 320 move synchronously, the light receiver is normally positioned on the optical axis of the light source. However, the position of the upper measurement head 310 and the position of the lower measurement head 320 are relatively shifted due to running characteristics of the measurement heads (310, 320), poor adjustment of the frame 330, and the like, and light is received from the optical axis of the light source. The vessel may come off. This deviation is referred to as an optical system alignment error.

  Since the general paper 200 has a certain thickness, as shown in FIG. 10A, the light emitted from the light source 311 mounted on the upper measurement head 310 is diffused when transmitted. For this reason, even if an optical alignment error as shown in FIG. 10B occurs, the amount of light received by the light receiver 321 mounted on the lower measurement head 320 does not change so much, and the measurement accuracy has a great influence. I do not receive it.

  However, in the case of the ultrathin paper 200 typified by tissue paper, as shown in FIG. For this reason, when an optical alignment error as shown in FIG. 11B occurs, the amount of light received by the light receiver 321 changes greatly, and the measurement accuracy decreases. Although it is conceivable to perform correction according to the amount of deviation, it is undeniable that the accuracy is reduced at that time.

  Even if no optical alignment error occurs, the paper thickness is small, so the amount of light absorbed at the time of transmission becomes very small, the amount of light absorption information when calculating the absorption rate is reduced, and the accuracy is also lowered.

  Then, an object of this invention is to provide the infrared moisture meter which can perform a moisture content measurement with high precision also to the ultra-thin paper represented by the tissue paper.

In order to solve the above problems, an infrared moisture meter of the present invention is an infrared moisture meter including a light source unit and a light receiving unit that move in synchronization with a paper to be measured interposed therebetween, and the light source unit has a plurality of wavelengths. The aperture plate is formed with a fine through-hole for passing the light mixed with the infrared rays and irradiating the paper, and the light-receiving portion side surface is a reflection surface. A light-shielding plate that is disposed so as to transmit light outside the outer periphery and that has both surfaces as reflection surfaces, and a surface that is located farther from the paper than the light-shielding plate, and that faces the light source unit Is a reflecting surface, has a larger outer diameter than the light shielding plate, and includes a reflecting plate that guides light to a detector.
Here, it is desirable that the minute through hole of the diaphragm plate is located on the central axis of the light shielding plate when there is no positional shift during the synchronous movement of the light source unit and the light receiving unit.
In addition, it is desirable that the detector and the minute through hole of the diaphragm plate are shielded by the light shielding plate when there is no positional deviation during the synchronous movement of the light source unit and the light receiving unit. .
The infrared rays having a plurality of wavelengths may include infrared rays having a wavelength that is easily absorbed by cellulose and infrared rays having a wavelength that is easily absorbed by water.
A light source side window may be provided on the light receiving unit side of the light source unit, and a light receiving side window having an outer diameter larger than that of the light shielding plate may be provided on the light source unit side of the light receiving unit.
At this time, the light shielding plate may be formed integrally with the light receiving side window.
The reflector may have an annular shape with a through hole formed in the center, and light may be guided from the through hole to the detector.

  ADVANTAGE OF THE INVENTION According to this invention, the infrared moisture meter which can perform a moisture content measurement with high precision also to ultra-thin paper is provided.

It is a figure which shows the structure of the optical system of the infrared moisture meter which concerns on this embodiment. It is a figure which shows an aperture plate, a shielding board, and a reflecting plate. It is a figure explaining the behavior of infrared light. It is a figure explaining the behavior of infrared light. It is a figure explaining the behavior of infrared light. It is a figure explaining the behavior of infrared light. It is a figure explaining the influence of the optical system alignment error in the optical system of the infrared moisture meter which concerns on this embodiment. It is a figure explaining the influence of the pass line fluctuation | variation in the optical system of the infrared moisture meter which concerns on this embodiment. It is a figure which shows the on-line measuring apparatus for papermaking processes carrying an infrared moisture meter. It is a figure explaining the influence of the optical system alignment error in the case of normal paper. It is a figure explaining the influence of the optical system alignment error in the case of ultra-thin paper.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an optical system of an infrared moisture meter according to the present embodiment. As shown in the figure, the optical system of the infrared moisture meter includes a light source unit 110 and a light receiving unit 120, and the measurement target paper 200 is conveyed between the light source unit 110 and the light receiving unit 120 at high speed. . In the present embodiment, the light source unit 110 is mounted on the upper measurement head and the light receiving unit 120 is mounted on the lower measurement head.

  The light source unit 110 includes a mounting substrate 111, a semiconductor light emitting element 112 as a light source, a light uniformizing member 113, a diffusion sheet 114, a diaphragm plate 115, and a light source side window 116. These are preferably arranged so that the central axes overlap.

  The semiconductor light emitting device 112 includes a light emitting device that emits a wavelength that is easily absorbed by water (for example, 1.94 μm), a light emitting device that emits a wavelength that is easily absorbed by cellulose that is the main component of paper (for example, 2.1 μm), Light-emitting elements that emit a wavelength that is not easily absorbed by water or cellulose (for example, 1.7 μm) are formed on the mounting substrate 111 with high density. The light emitting surface of the semiconductor light emitting device 112 is disposed toward the incident end of the light uniformizing member 113.

  The light uniformizing member 113 is a member that uniformly mixes light of three wavelengths output from the semiconductor light emitting element 112 and emits it as light with uniform spatial uniformity. The light homogenizing member 113 can be a light pipe made of a material with good near-infrared transmittance, a hollow mirror surface tube made of a reflective material with good near-infrared reflection, or the like. Polygonal pyramids such as quadrangular columns, hexagonal pyramids, hexagonal columns, and polygonal columns are preferable.

  The diffusion sheet 114 is a sheet-like or plate-like optical element that diffuses and transmits light, and is disposed at the emission end of the light uniformizing member 113. As the diffusion sheet 114, a non-woven fabric or an optical filter whose surface is roughened to enhance the diffusibility can be used, and a material that absorbs less light and does not absorb water is preferable.

  The diaphragm plate 115 is a disk-shaped member, and a small through hole 115a (pin hole) of about 1 to 5 mm, for example, is formed in the center portion. The light diffused by the diffusion sheet 114 passes through the through hole 115a. The number of through holes is not limited to one and may be plural. Further, the diaphragm plate 115 is a reflecting surface on the light receiving part side, and reflects light of three wavelengths in the direction of the paper 200 efficiently.

The light source side window 116 is a transparent member having a diameter of about 20 to 60 mm, for example, and prevents inflow of a high-temperature atmosphere or paper powder from the outside. The light source side window 116 is made of a material having high wear resistance and high near-infrared transmittance. For example, sapphire (AL ₂ O ₃ ), rigid quartz, BK7, B270 or the like is used after being thinly formed. it can.

  The light receiving unit 120 includes a detector 121, a light receiving side window 122, a light shielding plate 123, and a reflecting plate 124. These are also preferably arranged so that the central axes overlap with each other, and coincide with the central axis of the light source unit 110 in a state where no optical system alignment error occurs.

  The detector 121 can be composed of an InGaAs PIN photodiode that is sensitive to the three wavelengths output from the light source unit 110. The light-receiving side window 122 is a transparent member having a diameter of about 20 to 60 mm, for example, and can be configured similarly to the light source-side window 116.

  The light shielding plate 123 is a disk-shaped member, and both surfaces are reflecting surfaces. The light shielding plate 123 is disposed so as to face the diaphragm plate 115 so that the light that has passed through the through hole 115 a and transmitted through the paper 200 does not directly enter the detector 121. The light shielding plate 123 is formed in a slightly smaller size than the light receiving side window 122, and light is transmitted through the outer peripheral region of the light receiving side window 122. The diameter of the light shielding plate 123 is preferably about 75 to 95% of the diameter of the light receiving side window 122, for example. If the diameter of the light-receiving side window 122 is 40 mm, it can be about 30 to 38 mm.

  The light shielding plate 123 may be an independent member using a mirror surface material made of aluminum, a mirror formed by depositing a highly reflective metal such as aluminum, gold, silver, or a dielectric thin film on a glass substrate, or a light receiving side window. A highly reflective metal may be integrally formed with the light receiving side window 122 by vapor-depositing a highly reflective metal or a dielectric thin film in the inner region of 122. At this time, the light shielding plate 123 may be configured by forming a large number of small areas such as reflective dots.

  The reflection plate 124 is an annular member in which a through hole having a diameter of about 20 to 60 mm is formed, for example, and the light source portion side is a reflection surface. The light that has passed through the through hole enters the detector 121.

  FIGS. 2A to 2C are views of the diaphragm plate 115, the light shielding plate 123, and the reflection plate 124 as viewed from the upper surface (the light source unit 110 side), respectively, and FIG. It shows the situation when In FIG. 2D, for convenience, the area of the diaphragm plate 115 is indicated by dots, the outline of the light shielding plate 123 is indicated by a broken line, and the outline of the reflection plate 124 is indicated by an alternate long and short dash line.

  As shown in this figure, the light shielding plate 123 is formed larger than the through hole of the reflecting plate 124, and the through hole 115 a of the diaphragm plate 115 is formed sufficiently smaller than the light shielding plate 123. When viewed from the detector 121, the diaphragm plate 115 has a size and a positional relationship that are completely hidden by the light shielding plate 123.

  The behavior of infrared light in the optical system of the infrared moisture meter according to this embodiment will be described. Here, it is assumed that the measurement target paper 200 is an extremely thin paper typified by tissue paper. Ultrathin paper is characterized by a small amount of diffusion during light transmission and a small amount of light absorption.

  As shown in FIG. 3, the light mixed by the light uniformizing member 113 is diffused by the diffusion sheet 114 and applied to the diaphragm plate 115.

  Part of the light irradiated to the diaphragm plate 115 passes through the through hole 115a of the diaphragm plate 115 and is irradiated to the paper 200. As shown in FIG. 4, since the paper 200 is extremely thin, the irradiation light is transmitted without diffusing so much and reaches the light shielding plate 123. At this time, some light is absorbed depending on the moisture content, but the amount of absorption is small. Further, since the light shielding plate 123 exists, the light that has passed through the paper 200 does not reach the detector 121 directly.

  Since both sides of the light shielding plate 123 are reflecting surfaces, the light is reflected in the direction of the paper 200 and is irradiated again on the paper 200. At this time, part of the light is absorbed according to the moisture content, and the remaining light reaches the diaphragm plate 115. Since the light receiving side of the diaphragm plate 115 is a reflecting surface, the light is reflected in the direction of the paper 200 and irradiated onto the paper 200. At this time, part of the light is absorbed according to the moisture content, and the remaining light reaches the light shielding plate 123.

  As shown in FIG. 5, this behavior is repeated, and light passes through the paper 200 many times. Each time, a part of the light is absorbed according to the moisture content. For this reason, even if the amount of absorption at one time is small, the amount of absorption is accumulated, so that a sufficient amount of light absorption information can be obtained.

  When light is repeatedly reflected, the light spreads in the outer circumferential direction. When the outer edge of the light shielding plate 123 is exceeded, the light advances from the outer peripheral region of the light receiving side window 122 toward the reflecting plate 124. Since the light source side of the reflection plate 124 is a reflection surface, and both sides of the light shielding plate 123 are reflection surfaces, light is reflected between the reflection plate 124 and the light shielding plate 123 as shown in FIG. Repeat and progress in the inner circumference direction. Then, the light passes through the through hole of the reflecting plate 124 and enters the detector 121.

  In the optical system of the infrared moisture meter according to the present embodiment, the light irradiated from the light source unit 110 and passing through the paper 200 does not directly enter the detector 121 but repeatedly reflects a plurality of times with the paper 200 interposed therebetween. For this reason, as shown in FIG. 7, even if an optical alignment error occurs, the amount of light received by the detector 121 does not change so much, and the measurement accuracy is not greatly affected.

  Further, in the optical system of the infrared moisture meter according to the present embodiment, since the paper 200 passes a plurality of times, the amount of absorbed light that is absorbed according to the moisture content is accumulated, and a sufficient amount of light absorption information is obtained. become.

  Therefore, with the optical system of the infrared moisture meter according to the present embodiment, it is possible to measure the moisture content with high accuracy even for extremely thin paper typified by tissue paper. Of course, the moisture content can be measured with high accuracy even on ordinary paper.

Furthermore, in the optical system of the infrared moisture meter according to the present embodiment, irradiation from the light source side and irradiation from the light receiving side to the paper 200 are repeated many times. For this reason, as shown in FIG. 8, even when a pass line variation, which is a fluctuation in the distance between the measurement head and the paper 200, occurs, the variation is averaged. Therefore, it becomes possible to measure accurately without being affected by the pass line fluctuation. Since the ultrathin paper 200 causes more frequent pass line fluctuations than normal paper, the optical system of the infrared moisture meter according to this embodiment is also suitable for measuring the moisture content of ultrathin paper. It is.
In addition, in the optical system of the infrared moisture meter according to the present embodiment, as described above, near-infrared rays are subjected to multiple reflection. However, since near infrared rays have a longer wavelength than visible light, the energy level is relatively low. Furthermore, in general, the paper making process is in an environment filled with near infrared rays (heat rays) to dry the paper, and the near infrared signal used for measurement becomes relatively weak. There is a risk of being drowned out by environmental noise.

  As a measure for preventing the influence of environmental noise under such conditions, it is conceivable to increase the amount of light source. However, if the light source light quantity is increased, the light source becomes a heat source and the measurement location is locally dried, which affects the moisture content measurement. This problem becomes significant when the moisture content is statically measured using sample paper or the like.

  Therefore, the optical system of the infrared moisture meter according to the present embodiment desirably has the following configuration. That is, in the semiconductor light emitting device 112, light of three wavelengths is modulated and emitted with different frequencies. Then, a lock-in amplifier that detects and amplifies a signal of a specific frequency is arranged at the subsequent stage of the detector 121 so that three wavelength light components are extracted from the frequency-modulated signal. Any device that detects an original signal wave from a frequency-modulated signal can be used without being limited to a lock-in amplifier.

  By adopting such a configuration, it becomes possible to detect a minute signal buried in noise and to detect a signal with higher sensitivity, and to prevent the influence of environmental noise on the multiple reflected near-infrared signal. It becomes possible.

  By the way, tissue paper is substantially composed only of cellulose and moisture, and does not contain impurities such as lignin and ash. For this reason, if a cellulose weight and a moisture weight are measured, the basic weight of tissue paper can also be measured. Conventionally, radiation has been used to measure the basis weight. However, in the optical system of the infrared moisture meter according to this embodiment, near-infrared light having a wavelength that is easily absorbed by cellulose and near-red light having a wavelength that is easily absorbed by water. Since external light is used, it is possible to measure cellulose weight and moisture weight. Here, the weight of cellulose and the weight of water can be calculated based on wavelength light that is easily absorbed by water emitted from the light source unit 110 and attenuation characteristics of wavelength light that is easily absorbed by cellulose.

  In the optical system of the infrared moisture meter according to this embodiment, since the basis weight of tissue paper can be measured without using radiation, there is no need to separately install a basis weight measuring device on the measuring head, and miniaturization and saving can be achieved. Cost can be promoted. Furthermore, there is no need for registration of radiation use, setting of radiation area, securing of personnel handling radiation, etc. for basis weight measurement.

  The paper type capable of measuring the basis weight is not limited to tissue paper. The basis weight can be measured as long as the paper is substantially composed of only cellulose and moisture and does not contain impurities such as lignin and ash. For example, kraft paper or the like can be used.

DESCRIPTION OF SYMBOLS 110 ... Light source part, 111 ... Mounting board, 112 ... Semiconductor light emitting element, 113 ... Light uniformizing member, 114 ... Diffusion sheet, 115 ... Diaphragm plate, 116 ... Light source side window, 120 ... Light receiving part, 121 ... Detector, 122 Light receiving side window 123 Light shielding plate 124 Reflecting plate 200 Paper

Claims (8)

An infrared moisture meter having a light source unit and a light receiving unit that move synchronously across a paper to be measured,
The light source unit is
An optical element that diffuses light mixed with infrared rays of multiple wavelengths;
A diaphragm plate in which a minute through hole for passing the light diffused by the optical element and irradiating the paper is formed, and the surface on the light receiving unit side is a reflecting surface;
The light receiving unit is
A light-shielding plate that faces the diaphragm plate and is disposed so as to transmit light outside the outer periphery, both surfaces being reflective surfaces;
The reflector is disposed at a position farther from the paper than the light shielding plate, the surface on the light source unit side is a reflection surface, has a larger outer diameter than the light shielding plate, and a light guide plate that guides light to a detector; An infrared moisture meter characterized by comprising:   The minute through hole of the diaphragm plate is located on the central axis of the light shielding plate when there is no positional shift during the synchronous movement of the light source unit and the light receiving unit. Infrared moisture meter according to 1.   The detector and the minute through hole of the diaphragm plate are blocked by the light shielding plate when there is no positional shift during the synchronous movement of the light source unit and the light receiving unit. The infrared moisture meter according to claim 1 or 2.   The infrared moisture according to any one of claims 1 to 3, wherein the infrared of the plurality of wavelengths includes an infrared having a wavelength that is easily absorbed by cellulose and an infrared having a wavelength that is easily absorbed by water. Total. A light source side window is provided on the light receiving unit side of the light source unit;
5. The infrared moisture meter according to claim 1, wherein a light receiving side window having an outer diameter larger than that of the light shielding plate is provided on a light source unit side of the light receiving unit.   The infrared moisture meter according to claim 5, wherein the light shielding plate is formed integrally with the light receiving side window.   The infrared moisture meter according to any one of claims 1 to 6, wherein the reflecting plate has an annular shape with a through hole formed in the center, and guides light from the through hole to the detector. .   The infrared moisture meter according to any one of claims 1 to 7, wherein the diaphragm plate has an outer diameter larger than that of the light shielding plate and smaller than that of the reflection plate.

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