JPH0668441B2 - Sheet thickness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention provides an upper detection head that is levitated from a sheet-like substance by a certain amount by air blowing, and a sensor coil disposed below the sheet-like substance. An apparatus for measuring the thickness of the sheet-shaped substance online, which comprises a lower detection head having the same.

<Prior Art> FIG. 7 is a sectional view of a conventional device. In the figure, A is an upper detection head, a diaphragm 3 is fixed to the periphery of the opening 2 of the tank cap 1, and a conductor target 4 is attached to the center of the diaphragm. A chamber 4a is provided inside the target as shown in FIG. 8, and a plurality of air outlets 4b are provided on the surface of the target 4 as shown in FIG. Reference numeral 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, inside of which a sensor coil 7 is provided. Reference numeral 8 is a detection circuit.

C is a sheet-like substance transferred in contact with the lower detection head B.

With such a configuration, when the sheet material C is transported in the direction of the arrow D1, the upper detection head A and the lower detection head B are arranged in the width direction of the sheet material C (perpendicular to the paper surface).
Travel back and forth.

To measure the thickness, the sheet-shaped substance C is sandwiched between the detection heads A and B, the internal pressure of the tank cap 1 is increased, and the target 4
Is pressed in the direction perpendicular to the surface of the sheet-like substance C.

Air is supplied to the target 4 through the tube 5, and the weight of the target 4 and the restoring force of the elastic support means
Air pressure introduced into the tank cap 1 through the tube 6.
The pressing force of P ₂ and the levitation force of the air pressure P _{1 due to} the air blowing balance, and the target 4 is levitated from the sheet-like substance C by a certain amount ε.

A high frequency current is applied to the sensor coil 7 in the lower detection head B, and a magnetic flux is generated. The target 4 arranged so as to face the sensor coil 7 is a good conductor, and an eddy current is generated in this portion. 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 represented by the sum of the thickness a of the sheet-like substance C and the constant flying height ε.
Therefore, the change in the impedance is detected by the detection circuit 8 using a bridge circuit or the like, and the flying height ε is detected from this signal.
The thickness a of the sheet-like substance C can be detected online by performing the subtraction calculation.

However, the tension of the sheet material C changes depending on the position in the width direction. Generally, the tension is high in the central portion of the sheet-like material C and the edges are open at both ends, so the tension is low. When the sheet-like substance C is a fibrous material such as paper, when the tension is changed, the blending condition of the fibers on the surface portion of the paper is changed, and the flow of the air P ₁ is changed. Due to the change in the air flow, the flying height ε changes.

FIG. 10 shows changes in the flying height, the horizontal axis represents the tension T of the sheet-like material C, and the vertical axis represents the distance (a + ε) between the target 4 and the sensor coil 7. The thickness a of the sheet-shaped substance C is constant. As is clear from the figure, the distance a + ε decreases as the tension T increases. Since the thickness of the sheet-like material C is constant, the flying height ε of the target 4 is equal to the tension T.
It shows that it decreases with the increase of.

In the thickness measuring device for the sheet-like material, the flying height ε is constant, and if the flying height changes during the measurement, an instruction error occurs. Therefore, in such a device, a high error is indicated at both ends of the sheet-like material C, and a correct profile cannot be measured. <Problems to be solved by the invention> Technical problem to be solved by the present invention In such a device, an instruction error caused by a change in the tension of the sheet-shaped material C is prevented from appearing in the output.

<Means for Solving Problems> In the device for measuring the thickness of the sheet-like material, the structure of the present invention is provided with a means for detecting air blowing air pressure near the center of the target, and based on this detection signal. The pointing error caused by the change in the tension of the sheet material is compensated.

<Operation> The above-mentioned technical means operates as follows. That is, the change in the air blowing pressure of the target corresponds to the change in the flying height. A pressure gauge is provided on the target to detect the blowout pressure, and based on this detection signal, for example, the flying height read in advance by the arithmetic processing unit is rewritten with this signal, and this signal is detected with the detection circuit. The thickness of the sheet-shaped substance is calculated from the signal of the sum of the thickness of the sheet-shaped substance and the flying height.

<Example> An example of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view of an essential part, and FIG. 3 is a plan view of an essential part. In the figure, the same elements as those in FIGS. 7 to 9 are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 4c is a pressure guiding hole provided near the center of the surface of the target 4. The holes may be provided at a plurality of places near the center. Reference numeral 9 is a tube connected to the pressure guide hole 4c, and 10 is a pressure gauge for detecting the blown air pressure P ₃ of the target 4 guided from the tube 9.

In such a configuration, if the effect of the tension T is not considered, if 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 is increased. ε is always constant. However, the flying height ε of the target 4 changes as the tension T changes. The blown air pressure P ₃ detected by the pressure gauge 10 through the pressure guiding hole 4c corresponds to the change in the flying height ε. That is, FIG. 4 shows the experimental results under the same conditions as FIG. 10, in which the horizontal axis represents the tension T and the vertical axis represents the blown air pressure P ₃ . First
In the case of FIG. 10, the flying height ε decreases as the tension T increases.
On the other hand, in the case of FIG. 4, the blown air pressure P ₃ increases as the tension T increases. The blowout pressure P ₃ is the target 4
It is a value obtained by measuring near the center of.

Here, assuming that the pressure P ₁ is constant, the decrease in the distance a + ε with the increase in the tension T occurs because the average blowout pressure between the target 4 and the substance C increases with the increase in the tension T (loss of the blowout resistance). This loss is target 4 though
This is considered to be a decrease in the amount of outflow resistance when the air flowing out from the plurality of air outlets 4b escapes into the atmosphere around the target.

Considering the details, the largest change in this loss is the part that flows into the atmosphere around the target. This is because the air from the blowout holes 4b has a larger contact area with the paper as it flows to the periphery and is easily affected by the surface of the paper.

In other words, it is considered that the levitation pressure is decreased more than ε is decreased due to the decrease in the average blowout pressure at the peripheral portion.

On the other hand, considering the central part of the target, the blown air stagnates and the flow is small, and even if the surface condition of the paper changes, the influence on the outflow resistance is small. That is, it is considered that the loss due to the increase in tension is smaller than that in the peripheral portion.

Since the amount of air blown out from the small holes 4b is almost constant, the pressure P ₃ in the vicinity of the center increases as the distance ε with the paper decreases (see FIG. 4).

FIG. 5 shows the relationship between the blowout air pressure P ₃ , the tension T (straight line C ₁ ), and the distance a + ε derived from the results of FIGS. 4 and 10, and the distance a + ε decreases as the tension T increases. At the same time, the blowout air pressure P ₃ is rising.

Using the detected blown air pressure P ₃ , the flying height ε that has been read in advance by an arithmetic processing unit (not shown) is rewritten. The output of the detection circuit 8 is the thickness a of the sheet material C and the actual flying height ε.
It corresponds to the sum of, from the detection signal in the arithmetic processing unit,
By subtracting the rewritten flying height ε signal, a signal that accurately corresponds to the thickness a of the sheet-shaped material C can be obtained.

FIG. 6 is a sectional view showing an apparatus according to another embodiment of the present invention.
In the figure, the same elements as the elements in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. 11 is blown air pressure
It is a differential pressure converter that compares P ₃ with a reference pressure Ps and outputs a pressure corresponding to the difference between these pressures. A subtracter 12 subtracts the output pressure of the differential pressure converter 11 from the air pressure P ₂ supplied to the tank cap 1.

In the case of the device of the first embodiment of the present invention shown in FIG. 1, the compensation of the error due to the change of the flying height ε is performed by software in the arithmetic processing unit, but the outlet air pressure P ₃ is detected and the tank cap 1
The flying height ε may be controlled so that the flying height ε is always constant by returning to the circuit that supplies the air pressure P ₂ . That is, the sheet-like substance C
When the tension of No. 1 increases, the flying height ε decreases, and the blown air pressure P ₃ increases, the differential pressure converter 11 outputs a differential pressure k (P ₃ −Ps) (where k is a gain).

This pressure signal is applied to the subtractor 12 as a subtraction input, and the air pressure P ₂ ′ = P ₂ −k (P ₃ −Ps) (1) is supplied to the tank cap 1. As a result,
The pressing force from the inside to the outside of the target 4 is reduced, and the flying height ε is kept constant. Even with such a method, it is possible to compensate the pointing error due to the change in the tension of the sheet-shaped material C.

<Effects of the Invention> According to the present invention, an indication error due to a change in the tension of the sheet-like substance does not occur.

[Brief description of drawings]

FIG. 1 is a sectional view showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a sectional view of an essential part of the device according to the present invention in FIG. 3, FIG. 3 is a plan view of the essential part of the device according to the present invention in FIG. 1, and FIGS. 4 and 5 are views of the device according to the present invention in FIG. FIG. 6 is a sectional view showing an apparatus according to another embodiment of the present invention, FIG. 7 is a sectional view of a conventional apparatus, FIG. 8 is a sectional view of a main portion of the conventional apparatus of FIG. 7, and FIG. FIG. 7 is a plan view of a main part of the conventional device shown in FIG. 7, and FIG. A: upper detection head, B: lower detection head, C
...... Sheet-like material, 1 ... Tank cap, 4 ... Target, 4b ... Air outlet hole, 4c ... Pressure guide hole, 5 ... Tube that guides air pressure P ₁ to the target 4, 6 ... Tank cap 1 Tube that guides air pressure P ₂ to, 7 ... Sensor coil, 8
...... Detection circuit, 9 ...... Tube that guides blown air pressure P ₃ , 10
…… Pressure gauge, 11 …… Differential pressure converter, 12 …… Subtractor, ε ...
… Float, a …… Thickness of sheet material

Claims (1)

[Claims] 1. A pair of detection heads are arranged to face each other with a sheet-like substance sandwiched therebetween, a sensor coil is provided on the lower detection head, and a conductor target having a plurality of air blowout holes on the surface is provided on the upper detection head. While elastically supporting, pressing in a direction perpendicular to the surface of the sheet-like substance, the levitation force by the air blowing of the target, the weight of the target and the pressing force are balanced, the target from the sheet-like substance surface. In a device that floats a certain amount and measures the thickness of the sheet-like material from the change in impedance of the sensor coil, a means for detecting the air blowing pressure of the target is provided, and based on this detection signal, A sheet characterized by compensating an indication error due to a change in the flying height caused by a change in the tension of the sheet-like substance Thickness measuring device materials.