JPH0545137B2 - - 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, to a device for measuring the moisture content of sheet-like paper, and more specifically, a device for measuring the moisture content of paper sheets, which has a simple configuration, a small measurement area, and excellent sensitivity. Related to a moisture content measuring device. .

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

Figures 6 and 7 are conventional devices for measuring the moisture content of paper. Figure 6 shows a single transmission method moisture content measurement device, and Figure 7 shows a multiple scattering method moisture content measurement device. Show the device.

In Fig. 6, 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, and the optical filter 6a generates reference light in a spectral band (wavelength 1.80 μm) that is not absorbed by moisture. 6b generates measurement light in a spectral band (1.95 μm) that is absorbed by moisture.

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 condensing lens 9 into the halo detection section 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 unaffected by temperature fluctuations is obtained.

However, in the case of such a single transmission method, the sensitivity changes depending on the paper quality, and when measuring paper such as paper with little scattering on the surface, there is a drawback that the sensitivity decreases significantly.

In contrast, Japanese Patent Publication No. 7938/1983 proposed a scattering type moisture content measuring device as shown in FIG. In the figure, the same elements as those in FIG. 6 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. 6 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 window 1 is diffusely reflected between the reflective films 13 and 14 and reaches the detection unit 2.
be led to.

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 in that the optical path length can be long, the sensitivity is increased, and the S/N ratio is improved.

However, in the case of such a system, the irradiation window 7 and the entrance window 8 are disposed at different positions, which has the disadvantage that the apparatus becomes large and complicated.

Furthermore, since the entrance window 8 has a considerable area for guiding diffusely reflected light, there is a drawback that measurements cannot be performed near the edge of the paper 3.

Furthermore, dirt, paper dust, etc. from the paper 3 adhere to the reflective films 13 and 14, which has the disadvantage that the measurement results are greatly affected.

<Problems to be Solved by the Invention> The technical problems to be solved by the present invention are to have sensitivity equivalent to that of the multiple scattering method, to have a simple and compact configuration, and to solve the problem of contamination of the reflective film. The purpose of the present invention is to realize a paper moisture content measuring device that does not generate moisture.

<Means for Solving the Problems> The present invention has a light source that time-divisionally irradiates measurement light in a spectral band that is absorbed by moisture and reference light in a spectral band that is not absorbed by moisture. , a transmitted light detection means disposed on the opposite side of the light source with a sheet of paper in between, and detecting transmitted light T1 from the light source that has passed through the paper once; reflected light detection means arranged on the same side and detecting the reflected light R1 from the light source that has been reflected once by the paper, and the formula inf=K1・T1+K2・T2... expressing the detected light in the multiple scattering method. ...+Km・Tm (where Iinf: detected multiple scattered light, Tm: transmitted light that has met the paper m times, Km: probability coefficient),
The formula expressing each luminous flux of the transmitted light and reflected light, Tm=T(m-1)・R1+R(m-1)・T1 Rm=T(m-1)・T1+R(m-1)・R1 (However, Rm: reflected light that met the paper m times)
is transformed into a formula expressed by transmitted light T1, reflected light R1, and probability coefficient Km, and based on this formula, when the measurement light is irradiated, the one-time transmission detected by the transmitted light detection means A measurement signal is calculated from the light T1 signal and the once-reflected light R1 signal detected by the reflected light detection means, and based on this formula, when the reference light is irradiated, the one-time reflected light R1 signal detected by the transmitted light detection means is calculated. A reference signal is calculated from the twice-transmitted light T1 signal and the once-reflected light R1 signal detected by the reflected light detection means, and a moisture content signal of the paper is obtained from the ratio of these measurement signals and the reference signal. .

<Operation> The technical means described above operates as follows. That is,
In the formula representing the detected light in the multiple scattering method,
The probability coefficients K1, K2...Km are constants determined by the geometrical conditions of the measurement system of the multiple scattering method, and if these constants are given and the once-transmitted light T1 and the once-reflected light R1 are detected and given, the multiple scattering As with the scattering method, a highly sensitive signal can be obtained.

That is, when the measurement light is irradiated using the equations representing the respective luminous fluxes of the transmitted light and the reflected light, and the equation representing the detection light in the multiple scattering method,
Single transmitted light T1 detected by the transmitted light detection means
A measurement signal is calculated from the signal and the once-reflected light R1 signal detected by the reflected light detection means, and using these formulas, when the reference light is irradiated, the measurement signal is detected by the transmitted light detection means. One-time transmitted light
A reference signal is calculated from the T1 signal and the once-reflected light R1 signal detected by the reflected light detection means, and a paper moisture content signal is obtained from the ratio of these measurement signals and the reference signal.

Furthermore, since the measurement system of the present invention detects once-transmitted light and once-reflected light, the measurement area can be reduced, and the entire apparatus can be made simple and compact. Furthermore, since there is no need for a reflective film or a scattering film, there is no fundamental problem that the characteristics change due to changes in the state of these parts.

<Examples> Examples of the present invention will be described below with reference to the drawings. First, before explaining in detail the specific configuration of the apparatus according to the embodiment of the present invention, the principle of the present invention will be explained. FIG. 4 is an explanatory diagram showing a state in which multiple scattered light is received in the multiple scattering type water content measuring device shown in FIG. In the figure, the same elements as those in FIG. 7 are given the same reference numerals. The light emitted from the irradiation window 7 reaches the entrance window 8 through various routes as shown in the figure. The light is diffusely reflected by the reflective films 13 and 14 and collides with the paper 3 from once to infinite times, and these lights are detected by the photodetector through the entrance window 8. The detected multiple scattered light is generally expressed by the following equation.

inf=K1・T1+K2・T2……+Km・Tm……(1) (however, inf: detected multiple scattered light, Tm: transmitted light that met the paper m times, Km: probability coefficient) On the other hand, each luminous flux is As shown in FIG. 5, the transmitted light Tm that has met the paper 3 m times is the light that has met the paper 3 (m-1) times, the once transmitted light T1 and the once reflected light R1.
is the product of Tm=T(m-1)・R1+R(m-1)・T1...(2), and the reflected light that met the paper 3 m times.
Rm is the product of the light that has met the paper 3 (m-1) times, the once-transmitted light T1, and the once-reflected light R1, Rm=T(m-1)・T1+R(m-1)・R1 ...It is expressed as (3).

By the way, in equation (1), m is not infinite, and diffusely reflected light more than a predetermined number of times can be ignored. According to experiments, the distance between the reflective films 13 and 14 is 10
mm, the distance L between the optical axis of the light source 4 and the optical axis of the photodetector 21 (see Figure 4) is 60 mm, and when the paper 3 is newsprint, the light is almost attenuated when m=4. Therefore,
In this case, m≧5 among Tm and Rm can be ignored.

For m = 1 to 4, Tm, Rm from equations (2) and (3)
seek.

When m=1, T1=T1...(4) R1=R1...(5) When m=2, T2=T1・R1+R1・T1=2R1・T1...(6) R2=T1・T1+R1・R1 = T1 ² + R1 ² ...(7) When m = 3, T3 = T2・R1+R2・T1 =3R1 ²・T1+T1 ³ ...(8) R3=T2・T1+R2・R1 =3R1・T1 ² +R1 ³ ... …(9) When m=4, T4=T3・R1+R3・T1 =4R1・T1 ³ +4R1 ³・T1 …(10) R4=T3・T1+R3・R1 =T1 ⁴ +6R1 ²・T1 ² +R1 ⁴ … (11) When formula (1) is transformed using these, formula (1) can be expressed only by once transmitted light T1, once reflected light R1, and probability coefficient Km. Furthermore, the probability coefficient Km is a constant determined by the geometrical conditions of the measurement system of the multiple scattering method, and it is possible to specify this.

In the present invention, the detection signal of the once-transmitted light T1 and the detection signal of the once-reflected light R1 are given to the equation obtained in this way, and the measurement system remains in the once-transmitted light configuration and the once-reflected light configuration. This method obtains a highly sensitive signal similar to the multiple scattering method.

FIG. 1 is a sectional view of a device according to a first embodiment of the present invention. In the figure, the same elements as those in FIGS. 6 and 7 are given the same reference numerals. Reference numeral 23 denotes a light source that irradiates the paper 3 obliquely with measurement light and reference light in a time-division manner. 24 is a transmitted light detector that detects transmitted light T1 from the light source 23 that has passed through the paper 3 once. A reflected light detector 25 is arranged on the same side of the paper 3 as the light source 23 and detects the reflected light R1 from the light source 23 that is reflected once on the paper 3.

With this configuration, signals corresponding to the once-transmitted light T1 and the once-reflected light R1 detected by the transmitted light detector 24 and the reflected light detector 25 are processed by a calculation means using a computer, which is not shown in this figure. is given, and the operation of equation (1) is performed. That is, when the measurement light is irradiated, a measurement signal is calculated from the once transmitted light T1 signal detected by the transmitted light detector 24 and the once reflected light R1 signal detected by the reflected light detector 25. When the reference light is irradiated, a reference signal is calculated from the once transmitted light T1 signal detected by the transmitted light detector 24 and the once reflected light R1 signal detected by the reflected light detector 25, respectively.

The measurement signal and reference signal obtained by such calculation are then ratioed to obtain an output signal that compensates for changes in the characteristics of the light source 23 and the detectors 23 and 24.

FIGS. 2 and 3 are sectional views showing second and third embodiments of the present invention. In these figures, elements that are the same as those in FIG. 1 are given the same reference numerals. In the embodiment shown in FIG. 2, a light source 23' is attached around the once-reflected light detector 25, so that a plurality of light sources are provided. In the case of the embodiment shown in FIG. 3, the light source 23 and the single-reflection light detector 24
The light source 23 is arranged to face the paper 3, and the light from the light source 23 is irradiated perpendicularly to the paper 3.

The signals detected in these embodiment devices are subjected to arithmetic processing using equation (1), as in the case of the embodiment device shown in FIG. In the embodiment shown in FIG. 1, the ratio between the measured signal obtained by calculation and the reference signal is used as the output signal, but if the paper 3 is newsprint, The optical condition of the paper, that is, the transmittance of the paper changes depending on the amount of waste paper, resulting in an error. As a way to compensate for this, JP-A-56-
The method shown in No. 138240 can be used. That is, according to this method, the ratio of the reference signal detected by the multiple scattering method and the reference signal detected by the transmission method is obtained as a signal related to the amount of waste paper, and compensation is performed using this signal. There is. Also in the present invention,
The ratio of a reference signal that has been subjected to the calculation of equation (1) and has characteristics similar to those of the multiple scattering method and a single-transmission reference signal that has not been subjected to this calculation is calculated, and this signal is used to compensate the output signal. By doing this, the influence of waste paper can be removed.

<Effects of the Invention> According to the present invention, the ideal measurement state of the multiple scattering method can be achieved while maintaining a simple structure that detects the once-transmitted light T1 and the once-reflected light R1 without using the multiple scattering method. (a state in which paper is sufficiently scattered) is realized by software using calculation means using a computer.
It has the same sensitivity as the multiple scattering method, has a simple and compact structure, and fundamentally does not cause the problem of contamination of the reflective film.

[Brief explanation of drawings]

FIGS. 1 to 3 are cross-sectional views showing an embodiment of the present invention, FIGS. 4 and 5 are explanatory views for explaining the principle of the present invention, and FIGS. 6 and 7 are cross-sectional views of a conventional device. It is a diagram. 1, 2...Head, 3...Paper, 23, 23'...
...Light source, 24...Single transmitted light detector, 25...Single reflected light detector.

Claims (1)

[Scope of Claims] 1. A light source that time-divisionally irradiates measurement light in a spectral band that is absorbed by moisture and reference light in a spectral band that is not absorbed by moisture; placed on the opposite side of the light source,
Transmitted light T1 from the light source that passes through the paper once
and reflected light detection means, which is arranged on the same side of the sheet-like paper as the light source and detects reflected light R1 from the light source that has been reflected once by the paper. However, the formula representing the detected light in the multiple scattering method is inf=K1・T1+K2・T2...+Km・Tm (where, Iinf: detected multiple scattered light, Tm: transmitted light that has met the paper m times, Km: probability coefficient )of,
The formula expressing each luminous flux of the transmitted light and reflected light, Tm=T(m-1)・R1+R(m-1)・T1 Rm=T(m-1)・T1+R(m-1)・R1 (However, Rm: reflected light that met the paper m times)
is transformed into a formula expressed by transmitted light T1, reflected light R1, and probability coefficient Km, and based on this formula, when the measurement light is irradiated, the one-time transmission detected by the transmitted light detection means A measurement signal is calculated from the light T1 signal and the once-reflected light R1 signal detected by the reflected light detection means, and based on this formula, when the reference light is irradiated, the one-time reflected light R1 signal detected by the transmitted light detection means is calculated. A reference signal is calculated from the twice-transmitted light T1 signal and the once-reflected light R1 signal detected by the reflected light detection means, and a water content signal of the paper is obtained from the ratio of these measurement signals and the reference signal. moisture content measuring device.