JPS6123500B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention irradiates a sheet of paper with near-infrared rays, detects the near-infrared rays that interact with the paper, and obtains a signal related to the amount of water contained or adsorbed in the sheet of paper. The present invention relates to a method and apparatus for obtaining quantity-related signals and using these signals to measure moisture content, moisture content, etc. Signal related to moisture content (hereinafter simply referred to as moisture content signal)
There are transmission methods and multiple scattering methods as means for obtaining this. The former has an irradiating part and a light receiving part which are arranged facing each other so that the optical axis of the irradiating optical system and the optical axis of the receiving optical system almost coincide, and a sheet of paper is passed between them. , infrared rays of approximately 1.95 μm (light in the wavelength region absorbed by moisture. Hereinafter, this wavelength light is referred to as measurement light) and infrared rays of approximately 1.80 μm (light in the wavelength region not absorbed by moisture. Hereinafter, this wavelength A signal corresponding to the measurement light (hereinafter referred to as the M signal) and a signal corresponding to the reference light (hereinafter referred to as the R signal) are detected by the light receiving section. However, the quotient of these M signal and R signal (hereinafter referred to as M/R signal) is configured to be a water amount signal. The latter differs from the former in the following points. The optical axis of the irradiation-side optical system and the optical axis of the light-receiving side optical system are configured so that they do not match, and the measurement light and reference light from the irradiation section interact with the paper multiple times (much more times than the former). It is designed so that the light reaches the light receiving section. By the way, since the moisture content signal is a function of basis weight, a moisture meter is often provided with a basis weight detection section. As the basis weight detection unit, radiation, for example,
Those using β-rays are in practical use. The measurement principle utilizes the fact that when β rays pass through paper, the amount of attenuation is related to the basis weight. In the transmission method or multiple scattering method described above,
When the raw material composition of paper changes, or when the so-called optical conditions of paper such as whiteness, basis weight, press pressure, etc. change,
An influence appears on the M/R signal, that is, the water content signal. In order to reduce these effects, paper machine operators had to change the constants in the moisture calculation formula depending on the paper type (brand), but this operation was not only complicated, but also Even for different brands, the optical conditions mentioned above may change (without the operator's knowledge), so with conventional methods, it is difficult to continuously and accurately measure paper moisture content, moisture content, etc. It was difficult. In order to solve these drawbacks, an apparatus having a structure as described below has been attempted, focusing on the following facts (see Japanese Patent Laid-Open No. 154439/1983). The creation of this device is based on the fact that the R and M signals in the transmission mode and the multiple scattering mode are functions of the variables that govern the optical properties of the paper, namely the number of layers n, the transmittance f, the reflectance r and the moisture content MW. This was done by focusing on the fact that these variables exhibit sensitivities to each signal as shown in the table below. In the table, Rt,
Mt indicates the R signal and M signal in the transmission type moisture meter, and Rn and Mn indicate the R signal and M signal in the multiple scattering type moisture meter.

[Table] The above device uses the Mn/Rn signal (a signal with high moisture content sensitivity and is the same as the Rn/Mn signal) as the moisture content signal, and automatically compensates for error factors included in this signal with other signals. It is configured to perform calculations. A specific example of this is a device for measuring moisture content, moisture content, etc. of newspaper. Newspaper is manufactured by incorporating waste paper into the raw material pulp, but the transmittance f varies greatly depending on the content of waste paper, which is a cause of error. Therefore, the water content signal Mn/Rn signal is the Rn/Rt signal (a signal with high transmittance sensitivity;
The same applies to the Rn signal). In such equipment, Mn/Rn
The signal and Rn/Rt signal must be stably obtained. However, in actual measurement equipment, dust (paper powder and carbon) adheres to the scattering surface, irradiation window, entrance window, etc. over time, and the effects of this are reduced.
This appears in the Rn, Mn, Rt, and Mt signals, and is a factor that reduces measurement accuracy. The influence of dust will be explained with reference to FIG. FIG. 3 shows the relationship between dust and signal, based on experimental data obtained by applying zero samples to the detection head (see FIG. 1) described below. The vertical axis in Figure 3 is the K value (=Mn/Rn signal value),
The horizontal axis shows the dust amount d, and the graph is a graph obtained by installing a zero sample in the upper head. Note that in the environment in which the detection head is installed, the amount of dust adhesion increases relatively with time, so in FIG. 3, the amount of dust adhesion and the number of calibrations are shown in correspondence. In the graph, point A is Kzo, which is the K value when no dust is attached to the scattering surfaces of the upper and lower heads, each window, etc. Point B is a plot of the value in the calibration after a certain period of time (this is called the first calibration), and the dust amount d = d ₁ , K
The value = Kz ₁ . Similarly, point C is due to the second calibration, dust amount d = d ₂ , K value =
Kz ₂ , and point D is due to the third calibration, dust amount d=d ₃ and K value=Kz ₃ . On the other hand, grapho was drawn based on data obtained by actually placing a sheet sample with the same physical properties as those used in the graph above at the position where the sheet of paper, which is the object to be measured, is flowed. . Point A, point B, point C, and point D in the grapho may be made to correspond to point A, point B, point C, and point D in the graph. The reason why the K value differs depending on the position where the sample is placed (graphs 1 and 2) is that when the sample is placed at the position where the paper is actually flowed, the degree of multiple scattering is higher than the upper head. This seems to be because it is extremely large compared to when the sample is placed inside. We have just explained the K value, but the Rn/Rt signal (this is called the M value) and
The Mt/Rt signal (this is called the L value) is similarly affected by the amount of dust adhering to the scattering surface and each window surface. The present invention has been made in view of these points,
The purpose of this is to automatically compensate for the effects of dust adhering to the scattering surfaces, which are the opposing surfaces of the upper and lower heads, each window surface, etc., using a signal with high dust contamination detection sensitivity, and to adjust the moisture content and moisture percentage. the corresponding signal,
An object of the present invention is to provide a method and apparatus for obtaining higher accuracy. Hereinafter, the present invention will be explained in detail with reference to the drawings. Figure 1 shows the water content,
FIG. 2 is an explanatory diagram of the configuration of a detection head of a device for measuring moisture content, etc. In FIG. 1, the detection head is located at the irradiation window 1.
An upper head 10 having windows 1 and 12 and a lower head 20 having an entrance window 21 are arranged facing each other with a sheet of paper 30 sandwiched therebetween. The opposing surfaces of the upper and lower heads constitute a scattering surface consisting of reflective coatings 13 and 22. Further, the upper head 10 has through holes 42 and 43 formed in a disc-shaped plate 41, and each of these through holes supports an optical filter 42 for reference light and an optical filter 43 for measurement light, and rotates continuously. Rotating sector 40 and disk-shaped plate 61
A standard sample is buried in several through-holes, and a standard sample is buried in some of the through-holes.
Or, if necessary, it has a wheel 60 that rotates intermittently at a predetermined rotation angle, and an optical path created by the lamp 50 and lens 51 by the rotating sector 40 and having the irradiation window 11 as a path; lamp 50,
The irradiation window 12 is created by a mirror 53 and a lens 52.
It is designed to intermittently block the light passing through the passageway. On the other hand, the lower head 20 includes a lens 23 and a sensor 2.
5, and is configured to detect light passing through the entrance window 21 and send a detection signal to the next stage calculation section (not shown). Incidentally, the relationship between the window of each head and the rotating sector 40 and the relationship between the window of each head and the wheel 60 are as shown in FIG. Figure 2 A,
Figures B, C, and D represent A, B, and B in Figure 1.
It is a sectional view of Ro-Ro, Ha-Ha, and Ni-Ni (dimensions do not necessarily match). The irradiation windows 11 and 12 in the upper head 10 are as shown in FIG.
The irradiation window 12 is provided at a distance in the paper flow direction (indicated by the arrow), and the irradiation window 12 and the entrance window 21 of the lower head 20 shown in FIG. On the other hand, the through holes 42 and 43 of the rotating sector 40
(same as optical filters 42 and 43) and irradiation window 1
1 and 12, as shown in FIG.
In other words, the irradiation light is not emitted to the paper 30 from the irradiation windows 11 and 12 at the same time. The wheel 60 also has a through hole 6 in the peripheral edge of the plate 61, as shown in FIG.
2, 65, 67, 63 and 64 are provided at equal intervals,
A zero sample 65 for multiple scattering, a span sample 66,
A check sample 67 and a zero sample 64 for transmission are buried and supported. During normal measurement, the through holes 62 and 63 correspond to the irradiation window 11 and the irradiation window 12, respectively, and are in a stopped state. During calibration, the wheel 60 is rotated by a predetermined angle using the first control signal, and a zero sample 65 for multiple scattering is placed in the irradiation window 11, and a zero sample 64 for transmission is placed in the irradiation window 12.
A span sample 66 for multiple scattering is sequentially arranged in the irradiation window 11 according to the second control signal, and a check sample 67 for multiple scattering is sequentially arranged in the irradiation window 11 according to the third control signal. Note that when the second and third control signals are generated, the irradiation window 12 is configured to be shielded from light (the light shielding means is not shown). The time series detected by such a detection head
Give each signal Rn, Mn, Rt, Mt to the calculation section,
By creating the Mn/Rn signal and the Rn/Rt signal and performing desired calculations, it is possible to obtain the moisture content and moisture content with the influence of transmittance f corrected. In addition, the measuring device is
Before starting the measurement operation, calibration is automatically performed periodically or as needed using standard samples such as samples 64 to 67 to maintain the accuracy of the apparatus. By the way, as explained earlier with reference to FIG. 3, the K value, that is, the Mn/Rn signal is affected by dust, and the detection head exhibits the characteristics shown in graphs 1 and 2 in FIG. I understand. Therefore, the present inventors calculated the correction calculation formula for K as (1)
In addition to detecting dirt due to dust adhesion on the scattering surface, each window surface, etc., and automatically correcting it using the detection signal, based on experiments, we calculated Rn/Rt as the detection signal. It was concluded that the signal was optimal. K=Kon-a・D (1) However, Kon...K value (Mn/Rn signal) in the measurement state (online) a...Constant determined based on experiment D...Signal indicating the amount of dust attached Equation (1) , a and D are the correction amounts. The basis for reaching the above conclusion will be explained below. As a result of repeated experiments, the present inventors found that the sensitivity to the amount of dust adhesion (stain) differs depending on the type of detection signal. An example of this is shown in the 4th section.
As shown in FIG. Figures 4 and 5 are obtained by adhering adsorbent dust to the scattering surfaces of the upper and lower heads, each window surface, etc., and the vertical axis in Figure 4 is K.
The amount of correction of the value, the horizontal axis is ΔK, the vertical axis in FIG. 5 is the amount of correction of the K value, and the horizontal axis is ΔM. Here, ΔK and Δ
M is defined by equations (2) and (3). ΔK=Mnd/Rnd-Mno/Rno (2) ΔM=Rnd/Rtd-Rno/Rto (3) However, Mno, Rno, and Rto... When no dust is attached to the scattering surface, etc., zero sample 66 or 64 is Values of signals Mn, Rn, and Rt obtained using Mnd, Rnd, and Rtd... Signals obtained using zero sample 66 or 64 when daite is attached to the scattering surface etc.
Values of Mn, Rn, and Rt Comparing the characteristics in FIG. 4 and FIG. 5, one has a positive characteristic and the other has a negative characteristic for the following reasons. When adsorbent dust adheres to the scattering surfaces of the upper and lower heads, the signals Mt and Rt hardly change, but the signals Mn and Rn change significantly (signal Rn changes more greatly), and the characteristics of the dust It has a negative characteristic in that the signal value decreases as the amount of adhesion increases. Therefore, as the amount of attached dust increases, Mnd/Rnd tends to increase and ΔK shows a positive value, and Rnd/Rtd tends to decrease and ΔM shows a negative value. Now, in the above detection head, the amount of correction of K required for changes in the amount of attached dust is set to 0.05.
ΔK and ΔK with reference to FIGS. 4 and 5.
When M is determined, ΔK=0.0042 and ΔM=0.32. Therefore, the sensitivity ratio of the dust adhesion detection signals in the two graphs is approximately 0.0042/0.32≒
It becomes 1/80. In other words, the sensitivity of the dust adhesion detection signal is that the Rn/Rt signal is approximately 80 times more sensitive than the Mn/Rn signal.
This is twice as good, and it can be seen that it is more advantageous to use the Rn/Rt signal for the K value correction calculation. The apparatus according to the present invention is configured to apply a detection signal from the detection head to an electronic computer to determine the moisture content and moisture content without performing the operations described below. Prior to measurement, the dust zero signal values Rno and Rn of the signals Rn and Rt are determined using a zero sample with no dust attached to the scattering surface of the detection head, etc.
Find and memorize Rto. In the measurement state, perform a calibration operation using zero samples periodically or as necessary, detect the signal values Rnd and Rtd of the signals Rn and Rt each time, and calculate ΔM by calculating based on equation (3). Find this ΔM
A correction calculation is performed based on equation (1) using as a signal corresponding to the amount of dust adhesion. There are two ways to perform the correction calculation: one is to assume that the signal ΔM is constant until the next calibration operation is applied, and the other is to assume that the signal ΔM changes over time, that is, as a function of time. The relationship is determined by experiment. In this way, the corrected Mn/Rn signal corrects the influence of other error factors, such as paper transmittance f (this is also automatically calculated using the Rn/Rt signal), and calculates the moisture content. It is output as a signal corresponding to water content and moisture content. In the above embodiments, the calibration operation is performed using zero samples, but the present invention is not limited to this, and other samples, such as span samples and check samples, may be used. In addition, since the scattering surface of the detection head is heated up and is difficult to form condensation, the dust adhesion amount detection signal can be replaced with the above Rn/Rt signal.
The above correction calculation may be performed using the Mn/Mt signal. As explained above, according to the method or apparatus of the present invention, the Rn/Rt signal that can detect the amount of dust attached to the scattering surface of the detection head with high sensitivity, that is,
Since the correction calculation is performed using the dust adhesion amount detection signal with a good S/N ratio, the correction calculation can obtain highly accurate results. Therefore, the moisture content and moisture content of paper can be measured with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a detection head of an apparatus according to an embodiment of the present invention, and FIG. 3 is a K value-dust characteristic diagram, FIG. 4 is a K correction amount-ΔK characteristic diagram, and FIG. 5 is a K correction amount-ΔM characteristic diagram. 10... upper head, 11 and 12... irradiation window,
13 and 22... Reflective coating (scattering surface), 20...
Lower head, 21... Entrance window, 25... Photosensitive element, 30... Measured object (paper), 40... Rotating sector, 60... Wheel, 50... Lamp, 51,
52 and 23...lens, 53...mirror.

Claims (1)

[Claims] 1. An upper head and a lower head are disposed facing each other to constitute a multiple scattering type optical system and a transmission type optical system, and a sheet of paper is placed in the gap formed by the upper and lower heads. The paper is irradiated with measurement light that is light in a wavelength range that is absorbed by moisture and reference light that is light in a wavelength range that is not absorbed by moisture, and the measurement that interacts with the paper is performed. The light and the reference light are guided to and detected by a photosensitive element, and the information contained in the paper is calculated by using a measurement signal and a reference signal output from the photosensitive element in response to the measurement light and the reference light, respectively. In the method of measuring moisture content or moisture percentage, when no dust is attached to any of the scattering surfaces, the irradiation window, and the incident window formed on the opposing surfaces of the upper and lower heads, a sheet-shaped sheet is removed from the gap. Detection signal values Mno and Rno of the measurement signal Mn and reference signal Rn for the multiple scattering optical system obtained by removing the paper and using a standard sample placed in the upper head or lower head, and measurement for the transmission optical system. Each detected signal value of signal value Mt and reference signal Rt
The detection signal Rno, Rto related to the reference light or the detection signal value related to the measurement light from Mto and Rto.
Mno and Mto are memorized in advance, a sheet of paper is removed from the gap, and a measurement signal Mn regarding the multiple scattering optical system is obtained by performing a calibration operation periodically or as necessary using the standard sample. and each detection signal value Mnd and reference signal Rn.
Rnd and measurement signals related to the transmission type optical system
Detection signal related to the reference light selected from detection signal values Mtd and Rtd of Mt and reference signal Rt
Rnd, Rtd or detection signal value related to the measurement light
Mnd, Mtd and the detection signal value Rno related to the reference light,
(Rnd/Rtd−Rno/Rto) or (Mnd/Mtd
- Mno/Mto) A method for measuring the moisture content or moisture percentage of paper, characterized in that a signal is created as a function of Mno/Mto), and the signal is used to correct an error due to dust adhesion. 2. An upper head and a lower head are arranged facing each other to configure a multiple scattering type optical system and a transmission type optical system, and a sheet of paper is poured into the gap formed by the upper and lower heads, and moisture is applied to the paper. The measuring light, which is light in a wavelength range that is absorbed by water, and the reference light, which is light in a wavelength range that is not absorbed by water, are irradiated, and the measuring light and reference light that interact with the paper are illuminated. The moisture content or moisture content of the paper is determined by a calculation using a measurement signal and a reference signal output from the photosensitive element corresponding to the measurement light and the reference light, respectively. In the measuring device, a standard sample is provided in the upper head or the lower head and inserted into the optical path of the multiple scattering optical system or the transmission optical system by a calibration operation signal from the outside, and the upper and lower The multiple scattering was determined using the standard sample by removing the sheet of paper from the gap when no dust was attached to any of the scattering surfaces formed on the opposing surfaces of the head, the irradiation window, and the entrance window. Detection related to the reference light from among the detection signal values Mno and Rno of the measurement signal Mn and reference signal Rn related to the transmissive optical system and the detection signal values Mto and Rto of the measurement signal Mt and reference signal Rt related to the transmissive optical system. Means for storing the signals Rno, Rto or the detected signal values Mno, Mto related to the measurement light in advance, and removing the sheet of paper from the gap and performing a calibration operation periodically or as necessary using the standard sample. from the detection signal values Mnd and Rnd of the measurement signal Mn and reference signal Rn regarding the multiple scattering optical system obtained by Detection signal related to the selected reference light
Rnd, Rtd or detection signal value related to the measurement light
Using Mnd, Mtd and the stored signal values Rno, Rto or Mno, Mto, (Rnd/Rtd−Rno/
means for creating a signal that is a function of Rto) or (Mnd/Mtd-Mno/Mto) and using the signal to perform a correction calculation for an error caused by dust adhesion. Or a device that measures moisture content.