JPH02259409A - Beta-ray thickness gage - Google Patents

Abstract

PURPOSE:To enable execution of frame correction when a sheet is interposed, by a method wherein a sample having a basis weight in proximity to the basis weight of the sheet is inserted into a gap between a ray source element and a detecting element and basis weight values of the sample at a calibration reference point and each measuring point are determined. CONSTITUTION:A sheet flows in the direction vertical to the surface of paper in the region of a measuring width L. An arithmetic control element 22 drives a motor 19 through a drive circuit 20 and thereby a ray source element 17 and a detecting element 17 are driven rightward. Said control element 22 always monitors the positions of the ray source element 17 and the detecting element 18 by taking in outputs of an encoder. When the ray source element 17 and the detecting element 18 come to a measuring point set within the measuring width L, the control element 22 opens a gate circuit 23. A beta-ray detection data signal from the detecting element 18 is taken in the control element 22 through an A/D converter 24. Using the beta-ray detection data signal picked up at each detecting point and a correction value obtained from frame correction, subsequently, the basis weight of the sheet at the detecting point is computed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention includes a radiation source section that generates β-rays, a detection section that faces each other with a sheet in between, and a radiation source section and a detection section that are connected to each other by a width of the sheet. The present invention relates to a β-ray thickness meter that measures the basis weight (weight per unit area) and thickness of the sheet, and includes a drive unit that scans in the direction.

(Conventional technology) First, the β-ray thickness meter will be explained using drawings.

FIG. 2 is a block diagram of the β-ray thickness meter.

In the figure, 1 and 2 are vertical frames, 3 and 4 are horizontal frames, and these constitute an O-shaped frame 5. 6 is a sheet (for example, paper or plastic film sheet),
7 is a radiation source section that generates β rays, and 8 is a detection section. The radiation source section 7 and the detection section 8 are mounted on the horizontal frame 3 with an appropriate gap.
and Ll and L2 on the horizontal frames 3 and 4.
It is designed to travel back and forth synchronously.

Here, the principle of basis weight detection using β rays will be explained. The intensity of the β-rays emitted from the radiation source section 7 and detected by the detection section 8 is attenuated by passing through the sheet 6, but the rate of this attenuation is compared to the intensity of the β-rays without the sheet 6. There is a correlation as shown below.

1ml,,e-'°1...
■Here, ■...Transmitted β-ray intensity 101...β-ray intensity when sheet 6 is not present μ...Absorption coefficient p...Basic weight of sheet 6■Using a correlation such as the formula the set measurement point (
For example, the basis weight (weight per unit area) of the sheet 6 is measured at several hundred points in the width direction of the sheet. Further, the thickness of the sheet 6 can be obtained by dividing the basis weight of the sheet 6 by the density.

(Problems to be Solved by the Invention) In the conventional example with the above configuration, when the length of the horizontal frames 3 and 4 of the O-shaped frame 5 becomes long, the gap between the horizontal frames 3 and 4 is not constant due to bending or the like.

Therefore, the gap (measurement gap) between the radiation source section 7 and the measurement section 8 is not necessarily constant over the entire width. When the size of the measurement gap changes, an error occurs in the measured value of the sensor due to reasons such as changes in the thickness of the air layer in the measurement gap. Therefore, at each measurement point, a process (frame correction) that adds correction to the obtained measurement value is required.

Conventionally, such frame correction was performed by obtaining the measured value at each measurement point with only an air layer in the measurement gap, and calculating the difference between that value and the measurement value at the calibration reference point at each measurement point. It was used as a frame correction amount. This is because it was thought that errors caused by changes in the size of the measurement gap were mainly caused only by changes in the thickness of the air layer.

However, when the sheet 6 actually exists in the measurement gap, the amount of frame correction performed only with the air layer is
There is a problem in that it may not be possible to correctly correct the amount of error that actually occurs.

This example will be explained using FIG. This figure shows the Z characteristics for sheets of each basis weight.

(a) when the sheet is Og/Go, (b) when the sheet is 1
In the case of 02g/rrr, (c) the sheet is 504g/r
The case of rr is shown, and the line segment E shows the prescribed measurement gap. Further, 2 is the frame direction when the flow direction of the sheet is X1 and the width direction of the sheet is Y, and BW is the basis weight. Therefore, FIG. 3 shows the change in two directions, ie, the change in the basis weight indication value with respect to the change in the measurement gap.

As in (a), when the sheet is Og/nf (when there is no intervening sheet), the initially defined measurement gap E
, and the measurement gap that optimizes the Z characteristics are almost the same, but as the sheet actually intervenes in (b) and (C) and the basis weight increases, the measurement gap E that was specified at the beginning becomes different. , it can be seen that there is a difference from the measurement gap at which the Z characteristic becomes optimal.

In other words, if there is a sheet in the measurement gap,
The amount of error caused by changing the size of the measurement gap is different from the amount of error when there is no intervening sheet. Therefore,
The amount of correction obtained using the air layer is not an appropriate correction.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a β-ray thickness meter that can perform appropriate frame correction when a sheet is present.

(Means for Solving the Problems) The present invention for solving the above problems has a radiation source section that generates β-rays, a detection section that faces each other with a sheet in between, and a radiation source section and a detection section that are connected to each other by a width of the sheet. In the β-ray thickness meter, which is equipped with a drive unit that scans in the direction, and measures the basis weight (weight per unit area) and thickness of the sheet, a sample having a basis weight close to the basis weight of the sheet to be actually measured is The sample is inserted into the gap between the radiation source section and the detection section, the basis weight value of the sample at the calibration reference point and each measurement point is determined, and the basis weight value of the sample at each measurement point and the basis weight value at the calibration point are calculated. The difference between the measured value of the sample basis weight and the sample basis weight is calculated, and during actual basis weight measurement, the basis weight values at each of the measurement points are corrected using the respective differences.

(Function) In the β-ray thickness meter of the present invention, the basis weight value of the sample at the calibration reference point and each measurement point is determined, and the measured value of the basis weight of the sample at each measurement point and the sample at the calibration point are calculated. Calculate the difference between the measured value of basis weight and use it during actual basis weight measurement.
The basis weight values at each of the measurement points are corrected using each of the differences.

(Example) Next, one embodiment of the present invention will be described using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, 11 and 12 are vertical frames, 13 and 1
Reference numeral 4 indicates a horizontal frame, which constitutes a type 0 frame 15. 17 is a radiation source section that generates β rays, and 18 is a detection section. The radiation source section 17 and the detection section 18 are installed on the horizontal frames 13 and 14 with a suitable gap between them, and are moved back and forth synchronously across the measurement width on the horizontal frames 13 and 14 by a motor 19. .

20 is a drive circuit for the motor 19; 21 is an encoder that generates pulses as the motor 19 rotates; 22 is various data (β-ray detection data from the detector 18, rotational deviation data of the motor 19 from the encoder 21, etc.); ) and performs calculations (calculation of the basis weight and thickness of the sheet, calculation of the positions of the radiation source section 17 and detection section 18, etc.). 23
is the radiation source section 17. a gate circuit that passes β-ray detection data from the detection unit 18 when the detection unit 18 reaches a predetermined measurement point;
4 is an A/D converter that converts the β-ray detection data (analog signal) output from the gate circuit 23 into a digital signal.

Next, frame correction will be explained.

First, the radiation source section 17. is placed at the calibration reference point B. When the detection section 18 is present, the sample 26 placed on the sample holder 25 is set in the measurement gap G. The basis weight value of this sample 26 is preferably near the middle value of the basis weight measurement range of the device.

Next, at point B, sample 2 is
The basis weight of No. 6 is defined as n1, and its average value is defined as MB.

With the sample 26 placed thereon, the radiation source section 17. The detection unit 18 is moved back and forth, and the basis weight of the sample is measured at each of a large number of measurement points within the measurement width. At this time, if the type 0 frame 15 has structural deflection or the like, the basis weight at the configuration reference point B will be a different value.

The difference between the measured value obtained for each measuring point and the measured value MB at the calibration reference point is stored in a memory within the arithmetic control section.

Difference on the outward trip...MBI MP Difference on the return trip...MBI M11 With the sample 26 on it, repeat the round trip many times (20 times in this example), and measure the outward trip at each measurement point. , and the difference between the return bone and the return bone are accumulated for each measurement point and stored in the arithmetic control unit 22 . Here, the reason for taking the difference is to save memory.

Outbound portion...Σ (M B I M p + )...
・■ Return bone Σ (M a r M a +)...
■Next, taking into account drift, the radiation source section 17. Detection section 18
is moved to the configuration reference point B again, and the sample 26 is held for a certain period of time.
are measured, and the average value is defined as MB2.

Then, calculate Σ MF, ...■ Σ MB, ...■ from formulas ■ and ■, and as the frame correction amount for each measurement point, (M
Bl + MB2) / 2-1 / n -Σ MF,
−・・■(MBI+MB2)/2 1/n・Σ M
B, -.-■No.■l are determined, stored in the arithmetic control unit 22, and used as the correction amount for each n1 fixed point thereafter.

Next, the operation during actual basis weight measurement will be explained.

The sheet flows in a direction perpendicular to the plane of the paper in an area of the measured width. The arithmetic control section 22 drives the motor 19 via the drive circuit 20, and drives the radiation source section 17 and the detection section 18 rightward in the figure from the state shown in FIG. Arithmetic control unit 22
constantly monitors the positions of the radiation source section 17 and the detection section 18 by taking in the encoder output. Then, when the radiation source section 17 and the detection section 18 come to a measurement point set within the measurement width, the calculation control section 22 opens the gate circuit 23, and the β-ray detection data signal from the detection section 18 is /D converter 24
The data is taken into the arithmetic control section 22 via.

The calculation control unit 22 calculates the basis weight of the sheet at the detection point using the β-ray detection data signal read at each detection point and the correction amount obtained by frame correction.

According to the above configuration, as compared to conventional frame correction, it is possible to perform appropriate frame correction in the measurement range actually used. Also, the lower limit of the measurement basis weight range.

Although an excess or deficiency occurs between the correct frame correction amount near the upper limit, this amount is small compared to the difference between the frame correction amount and the conventional frame correction amount performed using only the air layer, and there is no problem in practical use.

(Effects of the Invention) As explained above, according to the present invention, the difference between the measurement value of the sample at the calibration reference point and each measurement point and the sample basis weight value at the calibration point is calculated, and the actual basis weight is calculated. A sheet basis weight measuring device that can perform appropriate frame correction when a sheet is present by correcting the basis weight value at each measurement point using each of the differences when measuring the quantity. can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of a sheet basis weight measuring device, and FIG. 3 is a diagram showing Z characteristics for sheets of various basis weights. In these figures: 1.2.11.12...vertical frame 3.4.13.
14...Horizontal frame 5.15...0 type frame 6...Seat 7.17...Radiation source part 8.
18...Detection unit 19...Motor 20...Drive circuit 21...Encoder 22...Arithmetic control unit 24...A/D converter 23...Gate circuit

Claims (1)

[Scope of Claims] A radiation source unit that generates β-rays, a detection unit that faces each other with the sheet in between, and a drive unit that scans the radiation source unit and the detection unit in the width direction of the sheet, In a β-ray thickness meter that measures the basis weight (weight per unit area) and thickness of a sheet, a sample having a basis weight close to the basis weight of the sheet to be actually measured is inserted into the gap between the radiation source section and the detection section. Then, determine the basis weight value of the sample at the calibration reference point and each measurement point, and calculate the difference between the measurement value of the sample basis weight at each measurement point and the measurement value of the sample basis weight at the calibration point. The β-ray thickness meter is characterized in that, during actual basis weight measurement, each of the differences is used to correct the basis weight value at each of the measurement points.