JPH0524162Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The invention consists of an upper detection head that floats a certain amount above a sheet-like material by air blowing, and a sensor coil arranged below the sheet-like material. The present invention relates to an apparatus for on-line measuring the thickness of the sheet-like material, comprising a lower detection head and a lower detection head.

<Prior Art> FIG. 6 is a sectional view of a conventional device. In the figure, A is the upper detection head, and a diaphragm 3 is fixed to the periphery of the opening 2 of the tank cap 1, and a conductive target 4 is attached to the center of this diaphragm. Inside this target is the seventh
As shown in the figure, a chamber 4a is provided, and a plurality of air blowing holes 4b are provided on the surface of the target 4, as shown in FIG. 5 is a tube that guides air to the target 4, and 6 is a tube that guides air into the tank cap 1.

B is a lower detection head, and a sensor coil 7 is provided inside thereof. 8 is a detection circuit.

C is a sheet-like material that is fed in contact with the detection head B on the lower side.

With this configuration, the sheet-like material C is indicated by the arrow D ₁
When the material is fed in the direction, the upper detection head A and the lower detection head B reciprocate in the width direction of the sheet material C (perpendicular to the plane of the paper).

The thickness is measured using the detection head A of the sheet-like material C.
and B, the internal pressure of the tank cap 1 is increased, and the target 4 is pressed perpendicularly to the surface of the sheet material C.

Air is supplied to the target 4 through a tube 5, and the target 4's own weight, the restoring force of the diaphragm 3, and the tank cap 1 are supplied through the tube 6.
Pressure force due to air pressure P ₂ guided inside, air pressure P ₁
The levitation force due to air blowing is balanced, and the target 4 is levitated by a certain amount ε above the sheet material C. For a predetermined air pressure P2, the flying height ε
The air pressure P1 supplied from the outside of the tank cap 1 is set so that P1 becomes a predetermined value.

A high frequency current is passed through the sensor coil 7 in the lower detection head B, and a magnetic flux is generated. Target 4 placed opposite sensor coil 7
is a good conductor, and eddy currents occur in this part.
This eddy current reduces the magnetic flux of the sensor coil 7 and changes the coil impedance. This impedance change corresponds to the distance between the target 4 and the sensor coil 7, and this distance is also expressed as the sum of the thickness a of the sheet material C and a constant flying height ε. Therefore, if the change in impedance is detected by the detection circuit 8 using a bridge circuit or the like, and the flying height ε is subtracted from this signal, the thickness a of the sheet material C can be detected online. I can do it.

However, the tension of the sheet material C changes depending on the position in the width direction. Generally, the tension is large in the center of the sheet-like material C, and the tension is small at both ends because the edges are open. When the sheet material C is fibrous, such as paper, when the tension changes, the state of the fibers on the surface of the paper changes, and the flow of air blown out by the air pressure _P1 changes. Due to this change in airflow, the flying height ε changes.

FIG. 9 shows the relationship between tension and flying height, with the horizontal axis representing the tension T of the sheet material C and the vertical axis representing the target 4.
and the sensor coil 7 (a+ε). Note that the thickness a of the sheet material C is constant.
As is clear from the figure, as the tension T increases, the distance a+ε becomes smaller. Since the thickness a of the sheet material C is constant, this indicates that the flying height ε of the target 4 decreases as the tension T increases.

The thickness measuring device for sheet-like materials requires that the flying height ε be constant, and if the flying height changes during measurement, an error in the indication will occur, making it difficult to obtain the correct profile for the thickness of the sheet-like material C. could not be measured.

The applicant is Japanese Patent Application No. 61-95148 (filing date:
(April 24, 1985) proposed a device that could solve these problems. This device detects the air pressure blown from the target and detects the flying height ε based on this. In order to detect the air pressure blown out, a pressure guide hole is provided on the surface of the target, and this hole is connected to a pressure gauge through a tube to detect the air pressure blown out from the target.

However, in the case of such a structure, air is not blown out from the pressure guiding hole provided on the surface of the target, and the pressure guiding hole is simply used to guide the blown air pressure from the target to the pressure gauge. Therefore, if the sheet-like material is paper, there is a risk that dust such as paper powder may adhere to the holes and block the holes, making measurement impossible. Further, in such a structure, the tube is passed through the target and connected to the pressure guiding hole, which makes the structure complicated.

<Problem to be solved by the invention> The technical problem to be solved by the invention is to prevent measurement errors caused by changes in the tension of the sheet-like material C from appearing in a device for measuring the thickness of a sheet-like material. The object of the present invention is to realize a device capable of doing this without providing a pressure guiding hole for detecting the flying height ε on the surface of the target.

<Means for Solving the Problems> The configuration of the present invention is such that an upper detection head A and a lower detection head B are arranged opposite to each other with a sheet-like material C interposed therebetween, and a sensor is attached to the lower detection head B. A coil 7 is provided, and a conductive target 4 having a plurality of air blowing holes 4b on its surface is elastically supported by a diaphragm 3 attached to the periphery of the opening of the tank cap 1 in the upper detection head A. Air pressure P1 is introduced into the target 4, and air pressure P2 is introduced into the tank cap 1 to increase the internal pressure of the diaphragm 3. By balancing the pressing pressure in the vertical direction with respect to C, the air pressure P2 is determined in advance.
, the air pressure P1 is set to the target 4.
The sensor coil 7 is set such that the flying height ε from the surface of the sheet material C becomes a predetermined value.
A signal corresponding to the sum (a+ε) of the thickness a of the sheet-like material C and the flying height ε is obtained based on the change in impedance of By doing so,
In the apparatus for measuring the thickness a of the sheet-like material C, a compensation signal generating section detects the internal pressure of the target 4, performs calculations on this detection signal, and outputs a compensation signal Sc corresponding to the actual flying height ε. 10,
The flying height ε stored in the arithmetic processing unit is rewritten with this compensation signal Sc, and the sum of the thickness a of the sheet material C obtained based on the change in impedance of the sensor coil 7 and the actual flying height ε (a+ε)
The rewritten flying height ε signal was subtracted from the signal to obtain a signal that accurately corresponded to the thickness a of the sheet material C.

<Operation> The technical means described above operates as follows. That is,
When the flying height of the target changes, the back pressure of the air blown from the target toward the sheet material changes, and the internal pressure of the target changes accordingly. That is, the change in the internal pressure of the target corresponds to the change in the flying height. Therefore, the internal pressure of the target is detected, and based on this detection signal, for example, the flying height ε that has been read in advance in the arithmetic processing unit is rewritten based on this signal, and this signal and the thickness of the sheet material, which is the detection signal, are rewritten. The thickness a of the sheet-like material is calculated from the sum signal (a+ε) of the flying height and the flying height.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the main parts. In the figure, the same elements as those in FIGS. 6 to 8 are designated by the same reference numerals, and explanations thereof will be omitted. 9 is a conduit for measuring the internal pressure of the target 4, and 10 is a compensation device that detects the internal pressure _P3 of the target 4 guided by this conduit, performs P/I calculation on the detected signal, and then outputs a compensation signal Sc. This is a signal generator.

In such a configuration, if the influence of the tension T is not taken into consideration, and if the air P ₂ guided into the tank cab 1 through the tube 6 and the air pressure P ₁ applied to the target 4 through the tube 5 are constant, the flying height ε is constant. However, the flying height ε of the target 4 is determined by the tension T as shown in FIG.
changes with changes in

On the other hand, the target 4 detected through the conduit 9
The internal pressure P ₃ corresponds to the change in the flying height ε. Figure 3 shows the relationship between target internal pressure _P3 and tension.
In the case of Fig. 9, the flying height ε decreases as the tension T increases, and in the case of Fig. 3, the internal pressure of the target 4 decreases.
P ₃ increases as the tension T increases.

FIG. 4 shows the relationship between the internal pressure _P3 of the target and the distance a+ε derived from the results of FIGS. 3 and 9. A compensation signal Sc is obtained from the target internal pressure _P3 ,
Based on this, the flying height ε that has been read in advance by an arithmetic processing unit (not shown) is rewritten. The output of the detector 8 corresponds to the sum of the thickness a of the sheet material C and the actual flying height ε, and by subtracting the rewritten flying height ε signal from the detection signal in the arithmetic processing section, A signal that accurately corresponds to the thickness a of the sheet material C can be obtained.

FIG. 5 is a sectional view showing another embodiment of the device of the present invention. In the figure, the same elements as those in FIG. 1 are given the same reference numerals, and explanations thereof will be omitted. In this embodiment, an independent means for measuring the internal pressure of the target 4 is omitted. That is, the structure is such that the internal pressure of the target 4 is detected by detecting changes in the air pressure _P1 for levitation of the target 4, and it has improved sensitivity and linearity compared to the embodiment shown in FIG. Although it is inferior, the conduit 9 is not required and the configuration is simplified.

<Effects of the invention> According to the invention, no indication errors occur due to changes in the tension of the sheet material. Furthermore, unlike the applicant's earlier application, Japanese Patent Application No. 61-95148, there is no need to provide a pressure-conducting hole on the surface of the target to detect the flying height ε, so there may be problems such as the adhesion of dust to this part. No problems occur.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the device according to the present invention;
The figure is a sectional view of the main parts, FIGS. 3 and 4 are explanatory diagrams of the operation of the device according to the embodiment of the present invention, FIG. 5 is a sectional view showing another embodiment of the device of the present invention, and FIG. 6 is a sectional view of the conventional device. 7 is a cross-sectional view of the main part of the conventional device shown in FIG. 6, FIG. 8 is a plan view of the main part of the conventional device shown in FIG. 6, and FIG. 9 is an explanatory diagram of the operation of the conventional device shown in FIG. 6. . A...Upper detection head, B...Lower detection head, C...Sheet material, 1...Tank cap, 4...Target, 4b...Air blowout hole, 5
...Tube that guides air pressure _P1 to target 4,
6...Tube guiding air pressure P1 to tank cap ₁ , 7...Sensor coil, 8...Detection circuit, 9
...A conduit for measuring the internal pressure _P3 of the target 4,
10... Compensation signal generation section, ε... Flying height, a...
Thickness of sheet material.

Claims (1)

[Claims for Utility Model Registration] Detection head A on the upper side across the sheet-like substance C
and a lower detection head B are arranged to face each other, the lower detection head B is provided with a sensor coil 7, and the upper detection head A is provided with a conductive target 4 having a plurality of air blowing holes 4b on its surface. Tank cap 1
The tank cap 1 is elastically supported by a diaphragm 3 attached to the periphery of the opening of the tank cap 1, and air pressure P1 is introduced into the target 4.
Introducing air pressure P2 into the diaphragm 3 to increase the internal pressure of the diaphragm 3, and balancing the pressure with which the target 4 is pressed against the sheet material C in a vertical direction;
With respect to the predetermined air pressure P2, the air pressure P1 is adjusted such that the flying height ε of the target 4 from the surface of the sheet material C becomes a predetermined value.
and obtain a signal corresponding to the sum (a+ε) of the thickness a of the sheet material C and the flying height ε based on the change in the impedance of the sensor coil 7.
In the apparatus for measuring the thickness a of the sheet-like material C, the internal pressure of the target 4 is detected by subtracting the flying height ε signal stored in advance in the arithmetic processing section from this signal, and a calculation is performed on this detection signal. A compensation signal generator 10 is provided which outputs a compensation signal Sc corresponding to the actual flying height ε,
The flying height ε stored in the arithmetic processing unit is rewritten with this compensation signal Sc, and the sum of the thickness a of the sheet material C obtained based on the change in impedance of the sensor coil 7 and the actual flying height ε (a+ε)
An apparatus for measuring the thickness of a sheet-like material, characterized in that the rewritten flying height ε signal is subtracted from the signal to obtain a signal that accurately corresponds to the thickness a of the sheet-like material C.