JPH01155204A - Method for calibrating thickness measuring device - Google Patents

Abstract

PURPOSE:To remove the effect of a gap, by performing zero measurement by upper and lower detection heads at the time of calibration and giving a definite gap to again perform zero measurement to calculate the detection characteristic to the gap and correcting the measured value on the basis of the detection characteristic value at the time of measurement. CONSTITUTION:At first, the interval between an upper detection head 2 and a lower detection head 3 is measured by the gap sensor 5 mounted on the base 301 of the lower detection head 3. Next, zero measurement is performed in a usual state and in such a state that the head interval is widened by definite quantity as compared with the usual state to calculate a characteristic in a Z-direction. The gap Z between the upper and lower detection heads 2, 3 imparts different values like C1, C2 at the time of the first calibration and at the time of this calibration, and an error (d) is generated between an initial gap Z0 and the value by the zero measurement when the lower head 3 is lowed, for example, by DELTAZ as shown a chart. Therefore, a correction signal dm is calculated from the gap measured value Zm between the heads 2, 3 and a newly formed Z-direction characteristic curve C2 at the time of measurement by the gap sensor 5 and the value detected by a sensor coil 304 is corrected using the signal dm.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thickness measuring device for online measuring the thickness of a sheet-like object such as paper.

<Prior Art> Conventionally, an apparatus as shown in FIG. 4 has been used as an apparatus for measuring the thickness of a sheet-like object such as paper or film. That is, an upper detection head 2 and a lower detection head 3 are disposed facing each other on a frame 1, and a sheet-like object 4 is run between them in the direction of arrow X, and the upper detection head 2 and lower detection head 3 are are moved back and forth in the width direction (direction of arrow Y) of this sheet-like object while maintaining the facing positional relationship, and the distance between the upper detection head 2 and the lower detection head 3, which are floating with a certain gap from the sheet-like object 4, is Devices are known for measuring the thickness of sheet-like objects 4 based on this method.

FIG. 5 shows a cross section of the detection head of such a conventional device. In the upper detection head 2, a tank cab 202 is attached to the base 201, and the base 2
A diaphragm 205 made of, for example, rubber is fixed to the periphery of the opening 203 provided in 01 via a retainer ring 204.

A conductive target 206 is attached to the center of this diaphragm, and has a chamber inside and a plurality of air blowing holes on its surface. 207 is air pressure P
, to the target 206.

A coil spring 208 is fixed to the diaphragm 205, and the other end of the spring is fixed to a support part provided on the base 201 inside the tank cap 202. Air pressure P2 is applied within tank cap 202.

In the lower detection head 3, the body 30 is attached to the base 301.
2 is installed. A case 305 housing a sensor coil 304 is attached to a diaphragm 303 attached to the periphery of the base 301 . In addition, 306
is a glass attached to the top surface of the case 305 and forming a reference surface.

P3 is air pressure introduced into the body 302 to raise and lower the sensor coil 304 portion.

Next, the operation of the thickness measuring device having such a configuration will be explained. When the detection head 2.3 is on the sheet material 4, the internal pressure of the tank cap 202 and the body 302 is increased, and the target 206 and the sensor coil 304 are
case 305 is brought close to sheet-like object 4.

At this time, the glass 306 of the case 305 comes into contact with the lower surface of the sheet-like object 4 and serves as a reference surface for thickness measurement. On the other hand, the target 206 is supplied with air pressure P1 through the tube 207, and the target's own weight, the restoring force of the coil spring 208, the pressing force of the diaphragm 205 due to the air pressure P2,
The floating blade is balanced by air blowing and floats a certain amount above the sheet-like object 4.

A high frequency current is passed through the sensor coil 304 in the lower detection head 3 to generate magnetic flux. Sensor coil 304
The target 206, which is placed opposite the target 206, is a good conductor, and the eddy current generated in this part
4 magnetic flux decreases and the coil impedance changes.

This change corresponds to the distance between the sensor coil 304 and the target 206, which is the distance between the sheet-like object 4
The thickness of the sheet-like object 4 can be measured by detecting the impedance change using a bridge circuit or the like.

<Problems to be Solved by the Invention> When such a device is installed at a measurement site, the head position is adjusted in the X and Y directions, and the upper output head 2 and lower detection head 3 are aligned. will be held. Further, the upper detection head 2 is floating above the sheet-like object 4, and the spacing between the heads 2 and 3 in two directions (see FIG. 4) changes due to irregularities in the middle of the frame 1, and accordingly, the target 206
The flying height from the sheet-like object 4 changes slightly, causing a measurement error. Therefore, as shown in the explanatory diagram of FIG. The flying height G, , G2°, G3 . d3・
... is obtained and used to perform zero correction for each point.

Once the characteristics in the X and Y directions are adjusted, they are unlikely to go out of order, but in the two directions, the flying height of the target 206, which should be constant, changes depending on the distance between the heads 2.3. The distance between the levers itself changes depending on the temperature difference between the time of calibration and the time of measurement (the temperature is higher during measurement). Further Z
The directional characteristics change under the influence of aging of the rubber diaphragm used in the detection head. For this reason, correct measurements could not be performed only by performing zero calibration at each measurement point during the initial calibration.

A technical problem to be solved by the present invention is to prevent the measurement results from being influenced by changes in the characteristics in the two directions in the floating thickness measuring device for sheet-like objects.

Means for Solving the Problems> The method of the present invention is characterized by performing the following steps a to e.

a1. At the time of calibration, performing zero measurement by bringing the upper detection head and the lower detection head close together in the same state as during measurement, and b. At the time of said calibration, moving said upper detection head and lower detection head to From the step of performing zero measurement by changing the gap more constant in step a, and the measurement results obtained in steps a and b, the detection characteristics for the gap between the upper detection head and the lower stacking head are determined. d. During measurement, a step of measuring the gap between the upper detection head and the lower detection head and determining a correction amount from this measurement value and the detection characteristic; e. A step of performing correction by adding the correction amount obtained in step d above to the measurement output.

Function> The above technical means works as follows. That is, during calibration, after performing zero measurement under normal conditions, for example, lowering the lower detection head by a certain amount from the normal state and widening the head-to-rad interval, performing zero measurement, and then performing zero measurement under these two different conditions. A two-way characteristic curve is obtained from the measurement results.

At the time of measurement, the distance between the upper detection head and the lower detection head is measured, and a correction signal is obtained from this measurement value and the two-way characteristic curve. This correction signal is added to the measurement signal to perform correction.

<Example> The method of the present invention will be explained below with reference to the drawings. FIG. 1 is a flowchart showing the method of the present invention, and FIG. 2 is an apparatus for carrying out the method of the present invention. In FIG. 1, the same elements as those in FIG. Omitted. First, in FIG. 2, 5 is a gap sensor attached to the base 301 of the lower detection head 3, which measures the distance from the upper detection head 2. For example, a magnetic sensor such as sensor coil 304 is used as this sensor. The configuration of the pond is the same as that in Figure 5.

In steps (1) and (2), zero measurements are performed in a normal state and in a state in which the head spacing is increased by a certain amount from the normal state. In step (3), two-way characteristics are determined from the measurement results at the two points.

This process will be explained in detail with reference to FIG. In Figure 3, C1 represents the two-way characteristic curve obtained during the first calibration, and C2 (dotted line) represents the two-way characteristic curve obtained during the current calibration.
Represents a directional characteristic curve.

The horizontal axis represents the gap Z between the upper detection head 2 and the lower detection head 3, and the vertical axis represents the error d from the standard value of the spacing between the heads.6 At the time of calibration, only an air layer was present, and the head Zero measurement is performed by setting the initial gap between the two to the same interval as in the normal measurement state.The gap at this time is set to Zo.Next, in the same state where there is only an air layer, for example, the lower detection head 3 is moved by a predetermined amount ΔZ. Lower the gap between the heads by 2.
Set to 0+Δ2 and perform zero measurement.

No matter how gap 2 is set, target 20
6 moves to a position that is a certain amount floating above the glass 306, which is the reference surface, and the error d should not originally occur. However, as can be seen from FIG. 3, the error d has a characteristic that increases as the gap Z increases, and this characteristic changes from 01 to 02 with time. A two-point calibration is performed every time the calibration is performed to recreate the two-direction characteristic curve.

During measurement, in step (4), the inter-head cap is measured by the gap sensor 5, and a correction signal d is obtained from this measured value 2 and a newly created two-way characteristic curve C2. In step (5), a correction is made to the measurement signal detected by the sensor coil 304 using the correction signal d.

<Effects of the Invention> According to the present invention, in the thickness measuring device, the measurement results are not affected by changes in the characteristics in the two directions.

[Brief explanation of the drawing]

Figure 1 is a flowchart showing the method of the present invention, Figure 2 is an apparatus for carrying out the method of the present invention, Figure 3 is an explanatory diagram for explaining the method of the present invention, and Figure 4 is the thickness of the sheet-like object. FIG. 5 is a perspective view showing the overall configuration of the measuring device, FIG. 5 is a sectional view of a detection head used in the conventional device, and FIG. 6 is an explanatory diagram for explaining a calibration method in the conventional device. 2... Upper detection head, 205... Diaphragm,
206...Target, 3...Lower detection head, 3
04...Sensor coil, 306...Glass, 4.
...Sheet-like object Figure 1 wc2 Figure 13 Figure 5 Figure 6

Claims (1)

[Scope of Claims] An upper detection head having a target floating a certain amount from a sheet-like object that is fed in one direction, and a lower detection head that is disposed opposite to the upper detection head with the sheet-like object sandwiched between the objects. A method for calibrating an apparatus that measures the thickness of the sheet-like object by reciprocating these heads in the width direction of the sheet-like object, characterized by performing the following steps a to e. How to calibrate a thickness measuring device. a. At the time of calibration, a step of performing zero measurement by bringing the upper detection head and the lower detection head close together in the same state as during measurement; b. At the time of calibration, the step of bringing the upper detection head and the lower detection head c. From the measurement results obtained in steps a and b, detecting the gap between the upper detection head and the lower detection head. determining a characteristic; d. during measurement, measuring a gap between the upper detection head and the lower detection head, and determining a correction amount from this measurement value and the detection characteristic; e. A step of performing correction by adding the correction amount obtained in step d to the measurement output during the measurement.