JPH0431527Y2 - - 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. 5 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 6th
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 such a configuration, the sheet-like material C is indicated by the arrow D1.
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 the tube 5, and includes the weight of the target 4, the restoring force of the elastic support means, the pressing force due to the air pressure _P2 introduced into the tank cap 1 through the tube 6, and the air at the air pressure _P1 . The buoyancy force due to the blowout is balanced,
The target 4 is levitated above the sheet material C by a certain amount ε.

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 material C, and the tension is small at both ends because the edges are open. If the sheet material C is fibrous, such as paper, when the tension changes, the orientation of the fibers on the surface of the paper changes,
The flow of the blown air changes depending on the air pressure P ₁ . Due to this change in airflow, the flying height ε changes.

Figure 8 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). In addition, in the experiment, the thickness a of the sheet material C was assumed to be constant. As is clear from the figure, as the tension T increases, the distance a+ε decreases. Since the thickness a of the sheet material C is constant, the target 4
This indicates that the flying height ε 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 proposed a method for solving this problem in Japanese Patent Application No. 61-9514 (filing date: April 24, 1985). This application proposes an alternative, more specific solution.

<Problems to be solved by the invention> The technical problem to be solved by the invention is to prevent indication errors caused by changes in the tension of the sheet material C from appearing in the output in such a device. It is in.

<Means for Solving the Problems> The configuration of the present invention is that in the apparatus for measuring the thickness of the sheet-like material, a small hole is provided in the target, air is introduced into the small hole, and the sheet is removed through the hole. A compensation signal corresponding to the flying height of the target is obtained by blowing air toward the surface of the target material, and a compensation signal corresponding to the flying height of the target is obtained by changing the back pressure of this airflow. Based on this compensation signal, an indication error due to a change in the flying height is compensated. I decided to do so.

<Operation> The technical means described above operates as follows. That is,
When the flying height of the target changes, the air flow blown out from the small holes provided in the target toward the surface of the sheet-like material changes, and the back pressure changes. That is, the change in back pressure corresponds to the change in the flying height of the target. A compensation signal is generated based on this change in back pressure, and, for example, the flying height previously read into the arithmetic processing unit is rewritten, and this is combined with the thickness of the sheet material detected by the detection circuit and the flying height. The thickness of the sheet-like material is calculated from the sum signal of .

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view of the main part, and FIG. 3 is a plan view of the main part. In the figure,
Elements that are the same as those in FIGS. 5 to 7 are given the same reference numerals, and explanations thereof will be omitted. 4c is a small hole provided in the center of the surface of the target 4. Note that this hole does not necessarily need to be located at the center of the surface of the target 4. 9 is small hole 4c
tube for guiding air P ₃ to , 10 is a constriction, 1
Reference numeral 1 denotes a detection/calculation section that detects the back pressure _P4 led through the branch 12 from the tube 9, performs proportional/integral calculations on it, and outputs the result.

In such a configuration, if the influence of the tension T is not taken into consideration, and the air pressure P ₂ introduced into the tank cap 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 will be ε is always constant. However, the flying height ε of the target 4 changes as the tension T changes.

Air P ₃ led to small hole 4c via tube 9
is blown out toward the sheet-like material C from this hole. When the flying height ε changes, the flow rate of the air flow F blown out from the small hole 4c changes, and the back pressure _P4 changes. FIG. 4 shows the relationship between back pressure P ₄ and distance a+ε. In the experiment, a sheet-like material C with a constant thickness a
is used, indicating that the back pressure P ₄ increases proportionally with changes in the flying height ε.

The back pressure P ₄ is guided to the detection/calculation section 11 and proportional/
An integral operation is performed to generate a compensation signal _S1 . This signal corresponds to the flying height ε, and thereby rewrites the flying height ε previously read into an arithmetic processing section (not shown). The output of the detection circuit 8 corresponds to the sum of the thickness a of the sheet material C and the actual flying height ε, and the arithmetic processing section subtracts the rewritten flying height ε signal from the output of the detection circuit 8. By this,
A signal that accurately corresponds to the thickness a of the sheet material C can be obtained.

In the case of the apparatus according to the embodiment of the present invention shown in _FIG .
The air pressure _P2 is returned to the means for supplying air pressure P2 to the floating height ε
may be controlled so that it is always constant. Furthermore,
The small hole 4c may be used in common with the air outlet 4b for target levitation, and the air supply is also used for target levitation and for detection of the levitation height ε, so that changes in the back pressure of this blown air can be A compensation signal _S1 may also be generated.

<Effects of the invention> According to the invention, no indication errors occur due to changes in the tension of the sheet material.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the device according to the present invention;
The figure is a cross-sectional view of the main part of the device according to the embodiment of the present invention shown in FIG. 1, and FIG. 3 is a plan view of the main part of the device according to the embodiment of the invention shown in FIG.
4 is an explanatory diagram of the operation of the device according to the embodiment of the present invention shown in FIG. 1, FIG. 5 is a sectional view of the conventional device, FIG. FIG. 8 is a plan view of a main part of the conventional device shown in the figure, and FIG. 8 is an explanatory diagram of the operation of the conventional device shown in FIG. A...Upper detection head, B...Lower detection head, C...Sheet material, 1...Tank cap, 4...Target, 4b...Air blowout hole, 4
c...Small hole, 5...Tube leading air pressure _P1 to target 4, 6...Air pressure to tank cap 1
Tube guiding P ₂ , 7...sensor coil, 8...
...Detection circuit, 9...Tube for guiding air _P3 , 1
0...Aperture, 11...Detection/calculation unit, ε...Flying height, a...Thickness of sheet material.

Claims (1)

[Scope of utility model registration request] A pair of detection heads are arranged opposite to each other with a sheet of material in between, the lower detection head is provided with a sensor coil, and the upper detection head elastically supports a conductive target having a plurality of air blow holes on its surface. Pressing the surface of the sheet material in a direction perpendicular to the surface of the sheet material, balancing the levitation force caused by the air blowing of the target with the target's own weight and the pressing force, so as to levitate the target a certain amount above the surface of the sheet material. In the device, the thickness of the sheet-like material is measured from the change in impedance of the sensor coil, wherein a small hole is provided in the target, air is introduced into the hole, and the surface of the sheet-like material is measured from the hole. A compensation signal corresponding to the flying height of the target is obtained from a change in the back pressure of this air flow, and an indication error due to a change in the flying height is compensated based on this compensation signal. A device for measuring the thickness of a sheet-like material.