JPS5944567B2 - Thickness measuring device for thin plate materials - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION This invention relates to the use of acoustic vibrations for automatic inspection, and more particularly to apparatus for measuring sheet-like materials using acoustic vibrations.

[Technical background of the invention and its problems]

The present invention is applicable to automatic control devices for rolling mills in metallurgy of ferrous and nonferrous metals, machine assembly, polymer industry, pulse industry, and paper manufacturing industry for thin plate materials (with a thickness of 0.5 to 1 mm or less).
It can also be applied to devices for automatically inspecting the thickness of thin film materials in a non-contact manner.

Methods for automatically measuring the thickness of thin sheet materials are known (
V. I. "Electronic and Semiconductor Equipment in the Metallurgical Industry" by Feighin
rOvOdnikOvyeprivOryvmetal
lurghii)) Metalurg in Moscow
Published by Hiya Publishing, reference). According to this method, penetrating radiation is irradiated into a thin plate-like material to be inspected, and the degree of attenuation of the radiation that has passed through the thin plate-like material is measured. The value thus obtained indicates the thickness of the measured material. However, this method can only be applied to a narrow thickness range because the degree of attenuation of radiation is exponentially related to the thickness of the material.

Additionally, this method introduces considerable errors when measuring the thickness of thin materials.

This is because the attenuation of radiation in thin materials is small and comparable to the attenuation by a protective screen of the radiation source. A thickness gauge that implements the above method is also known (information magazine "NTY-495 and NTY-496 type thickness gauge")
IzmeritelltOlshinNTY-4951
NTY-496), Isotope Publishing House, (Moscow)
Published in 1963, see). This thickness gage comprises a radioisotope radiation source, a radioisotope radiation detector and a measuring unit connected to this detector, the radiation source and the radiation detector being placed on either side of the material to be examined. for example,
When using thickness gauges to check the thickness of steel sheets being rolled, it is prohibited from placing a radioactive isotope source next to the rolls of the rolling mill for safety reasons.

This results in considerable delays in getting information about the thickness of the material to be inspected into the automatic rolling mill control, with consequent negative effects on the quality of the rolled sheet.

In addition, when using such a thickness gauge, use of protective equipment,
Requires special storage for storing measuring instruments or radioisotope radiation sources during repair or adjustment.

The radioisotope radiation source used in this type of thickness gage is expensive and has a short service life due to the short half-life of the radioisotope.

This requires periodic replacement of the radioactive isotope, which is a tedious process, making the use of such a thickness gauge expensive. A method of inspecting the thickness of a thin plate-like material using acoustic vibration is also known (V.S.
"Physical Principles of Ultrasonic Thickness Measurement" by Grebennik
(Phyzicheskiye OsnOvyultra
zvukOvykhmetdOvizmereniya
11-12, published by MachinOstrOyeniye Publishing House (Moscow), 1968).

According to this method, an acoustic vibration source placed in a sound-conducting medium, such as a liquid stream, periodically sends acoustic vibrations into the lamellar material being tested.

Acoustic vibrations are transmitted approximately perpendicular to the surface of the material. The time taken for acoustic vibrations to pass through the medium and material is measured using, for example, a phase meter, and the thickness of the material is determined from the measurement results.
However, when measuring the thickness of very thin plate-like materials, this method also produces considerable measurement errors.

The reason for this is that the absolute transit time of acoustic vibrations passing through a very thin material is extremely short (on the order of 10-8 seconds). In addition, in this method, acoustic vibrations are reflected by the surface of the acoustic vibration receiver (hereinafter referred to as the acoustic receiver), the surface of the acoustic vibration receiver (hereinafter referred to as the acoustic receiver), and the surface of the material being inspected. The reflected acoustic vibrations are superimposed on the acoustic vibrations that have passed through the material, resulting in a standing number and an error.

To reduce this error, the material whose thickness is to be measured must be placed on the vibration node. This is done by special equipment that automatically moves the acoustic generator and receiver relative to the material. This requires sophisticated and expensive equipment. At the same time, a significant error associated with thickness measurements is the dependence of the propagation speed, and therefore the propagation time, of acoustic vibrations in the liquid stream on the temperature of the liquid stream.

Changes in the temperature of the liquid stream change the propagation velocity of the acoustic vibrations, which causes errors in thickness measurements. The reason is that, for an operating gap (distance between acoustic generator and receiver) selected to meet manufacturing requirements, the propagation time of acoustic vibrations in the liquid is This is because the recorded time of an acoustic vibration passing through a thin or thin material is twice as long.

Therefore, even if the relative propagation time of the acoustic vibrations in the liquid stream changes slightly due to temperature changes, the total travel time of the acoustic vibrations through the thin film material being examined is comparable to the recorded transit time. The absolute value of the propagation time will change significantly. For example, for a foil with a thickness of 0.06 mm and a working gap of 60 mm, the propagation time of an acoustic vibration in the liquid is 40 ms, whereas the recorded propagation of an acoustic vibration in the foil is The time is 0.03 milliseconds. 1.5CTn/
The propagation time of acoustic vibrations in the liquid is O,04 due to the temperature change rate of the speed of the ultrasound in water equal to Sec/℃.
Mcsec/°C, which amounts to an error of 130% per °C.

Although temperature compensation can reduce the error, it is not possible to obtain the required accuracy due to the non-uniform distribution of temperature along the length of the liquid dinit.

This non-uniform distribution changes over time. As a result, this method can only be used when changes in ambient air temperature are small. A device for measuring the thickness of sheet-like materials according to this method is also known (USSR Inventor's Certificate No. 270261). The device comprises an acoustic generator and an acoustic receiver, between which the material to be inspected is placed.

The operating planes of the generator and receiver are approximately parallel to the surface of the material. An excitation voltage generator is connected to the acoustic generator. The device also includes a measuring unit, which has an amplifier connected to the receiver, a time measuring unit of oscillograph or phase meter type, and a recorder. These components of the measuring unit are connected in series with each other. The device also includes a delay unit connected to the measurement unit and the excitation voltage generator. However, this device cannot be used to measure the thickness of sheet-like materials that are significantly curved in the longitudinal direction.

The reason for this is that the operating gap, which is the distance between the acoustic generator and the receiver, is narrow. As the operating gap increases, the error in the thickness measurement increases rapidly because the measuring unit records the change in the total propagation time between the generator and the receiver. Such changes in propagation time are due to changes in the thickness of the material being tested and the operating gap. As a result, even negligible changes in the width of the gap during measurement will result in large measurement errors. For example, if the gap is 60mm,
Even if the gap changes by 1/10000 of that, or 0.006 mm, an error of about 100/) will occur in the measured thickness of a 0.06 mm thick foil. [Object of the Invention] Therefore, an object of the present invention is to provide a method for inspecting the thickness of a thin plate-like material using acoustic vibration, and an apparatus that enables thickness measurement over a wide range.

Another object of the present invention is to increase the accuracy of thickness measurement of sheet-like materials.

Another object of the invention is to accurately measure the thickness of sheet-like materials that have significant longitudinal curvature.

Yet another object of the invention is to facilitate maintenance of a device for testing the thickness of sheet-like materials.

[Summary of the Invention] An object of the present invention is to provide an acoustic generator, an oscillator that periodically generates a group of acoustic vibrations, an acoustic receiver,
a measuring unit connected to the acoustic receiver, the sheet material to be inspected being placed between the acoustic generator and the acoustic receiver, the working surface of the acoustic generator and the acoustic receiver being the surface of said material. In a device that performs a method of testing the thickness of a thin sheet material using acoustic vibrations that are approximately parallel to The distance that the traveling wave travels in
That is, the length of the emitted acoustic vibration is given by the product of the propagation velocity of the acoustic vibration in the medium surrounding the lamellar material being tested and the duration of the group of emitted acoustic vibrations. The wavelength of the traveling wave selected and resulting from such a distance relationship is greater than four times the thickness of the sheet-like material, and the measuring unit includes an amplifier, a peak value detector, a reference signal setter and a tester. a unit for comparing a signal having information about the thickness of the material to be used with a reference signal, and a recorder connected to an output terminal of the comparison unit,
The human power terminal of the amplifier is connected to the output terminal of the acoustic receiver,
The input terminal of the peak value detector is connected to the output terminal of the amplifier, one input terminal of the comparison unit is connected to the output terminal of the peak value detector, and the other input terminal is connected to the reference signal setter. This is achieved by a device for measuring the thickness of a thin sheet material using an acoustic signal characterized by:

The reference signal setter, whose function is performed by a traveling wave through a sheet-shaped material having a predetermined thickness, is conveniently configured as a variable DC power supply.

It is also convenient to configure the comparison unit as a subtracter and connect it directly to the variable DC power supply. A further acoustic generator may be provided for injecting acoustic vibrations into the sheet-like material having a predetermined thickness.

A reference signal setter whose function is performed by a traveling wave passing through a thin plate-like material having a predetermined thickness is configured as a separate acoustic receiver receiving acoustic vibrations passing through the material, and between the acoustic generator and the another acoustic receiver;
The surface of the material is arranged so that it is approximately parallel to the working plane of the generator and the receiver, and the distance between the working planes of the generator and receiver is the same as the distance between the working planes of the main generator and the main receiver. It is convenient to make them equal. Conveniently, the comparison unit is configured as a divider, which divider is connected to said further receiver via a further series-connected receiver and a further peak value detector. A reference signal setter whose function is performed by a traveling wave transmitted into the lamellar material being tested is such that a portion of the traveling wave passing through the material to the main acoustic receiver passes through the material to another receiver. The comparison unit can be configured as a further acoustic receiver which is arranged in a bypass manner across the path of the traveling wave between the acoustic generator and the material to be examined, and the comparison unit is configured as a dividing unit.

The further receiver is connected to the divider unit via a further amplifier and a further peak detector in series. [Effects of the Invention] The method and apparatus for inspecting the thickness of thin sheet materials using acoustic vibrations of the present invention has several advantages over conventional ones.

First of all, the method and apparatus of the present invention are characterized by the weight of the acoustic vibrations reflected from the surface of the acoustic generator, the surface of the receiver, and the surface of the material being inspected, as well as the acoustic vibrations that have passed through the material. Measurement errors caused by the formation of standing waves are completely eliminated.

This is because the acoustic vibrations are transmitted in the form of traveling waves into the material being tested. In the device of the invention, the distance between the working plane of the acoustic generator and the working plane of the receiver is checked, i.e. the distance traveled by the traveling wave during the duration of the traveling wave per measurement. The length of the emitted acoustic vibration is selected to be greater than or equal to the product of the propagation velocity of the acoustic vibration in the medium surrounding the lamellar material and the duration of the group of emitted acoustic vibrations. , a traveling wave is generated. Here, an example of a traveling wave used in the present invention is shown in FIG. In FIG. 5, T, , T2, and T3 indicate each measurement period, and a indicates a traveling wave output from the acoustic vibration generator. In this a, LO is the above-mentioned [distance traveled by the traveling wave during the duration of the traveling wave per measurement], and AO is the amplitude of the traveling wave before passing through the thin plate material, λ. indicate the wavelength of the traveling wave. b is a waveform diagram showing the traveling wave after it passes through the thin plate material, A is its amplitude, λo is the wavelength, and H
is the distance between the working surfaces of the acoustic vibration generator and the receiver.
C and d indicate states in which A and b decay exponentially, respectively. Note that the distance L. and the wavelength λ of the traveling wave
. Between, LO=nλ. /2 (n is an integer) holds true. As a result of using traveling waves as described above, the acoustic vibrations reflected from the surface of the material being tested and the heated surface of the receiver are
No standing waves are generated because they are not superimposed on the acoustic vibrations that have passed through the material.

Because of these advantages, the device of the invention requires special equipment for automatically moving the acoustic generator and the receiver relative to the material to be inspected in order to place the material at the node of the standing wave. does not require. This simplifies maintenance of the device according to the invention. Secondly, the device of the invention is free from errors caused by changes in the width of the motion interval and by changes in the propagation velocity of acoustic vibrations in the acoustically conductive medium, and hence the dependence of the propagation time on the temperature of that medium. This greatly reduces the errors that occur.

Reducing such errors is important when measuring the thickness of very thin materials or thin films. The second advantage is
According to the invention, the parameter representing the thickness of the material is the amplitude of the acoustic vibrations introduced into the sheet material, measured by the device of the invention.

This amplitude is independent of changes in the width of the working gap and depends only on the propagation speed of the acoustic vibrations in the acoustic propagation medium. As a result, errors due to changes in the propagation velocity of acoustic vibrations in the acoustic propagation medium are reduced by a factor of 5 to 10.

This can be explained by the following equation. Here, δD,
is the thickness D of the material to be inspected.

, the propagation velocity C of acoustic vibrations in the acoustic propagation medium. The measurement error when measured using the conventional method is caused by a change in ΔC, H is the width of the movement interval, and KO is a constant. When using the present invention, the propagation velocity C.

A thicker D occurs due to a change in ΔC. The measurement error δ
D2 is determined by the following equation. Furthermore, by selecting the frequency of the acoustic vibration so that the wavelength of the traveling wave in the material to be inspected is four times or more the thickness of the material, the accuracy of measuring the thickness of the thin plate material is increased.

This is because the dependence of the amplitude of a traveling wave passed through a sheet-like material on the thickness of the material is linear only in the first part.

As the thickness of the thin plate material increases, the wavelength of the traveling wave in the material increases by 4
As the value approaches a factor of 1, the dependence becomes non-linear.
Furthermore, beyond that value, the dependence is no longer a single value. If the frequency is selected such that the maximum thickness of the material under test exceeds one quarter of the wavelength of the traveling wave in the material, the amplitude of the change in material thickness over the linear part of the single value dependence can be measured. This increases measurement accuracy. Due to the high measurement sensitivity of the device of the present invention, it is possible to extend the thickness measurement range of thin sheet materials in thin thickness regions.

The reason for this is that the parameter indicating the thickness of the material to be inspected is the amplitude of acoustic vibration. The amplitude of acoustic vibrations passed through the material under test is inversely proportional to the thickness of the material and is virtually independent of the width of the working gap. As a result, the magnitude of the change in the amplitude of acoustic vibrations passed through very thin materials is usually sufficient to be measured by the measuring unit of the device according to the invention. The device of the present invention, in which the reference signal is a traveling wave that has passed through a thin plate-like material having a predetermined thickness, and the reference signal setting device is a variable DC power supply, can reduce the noise by 20 to 40% of the predetermined thickness.
You can easily and accurately measure the thickness of materials within the thickness range.

In order to expand the measurement range, the DC power supply must be readjusted. The function of the reference signal is performed by a traveling wave passing through a material having a preselected thickness, the function of the reference signal setter is performed by another receiver receiving acoustic vibrations passing through the material, and the function of the reference signal setter is performed by a separate receiver receiving the acoustic vibrations passing through the material, and Because the function is performed by the dividing unit, it is possible to measure the thickness over a wide range without readjusting the reference signal setter.

Now, the present invention and apparatus reduce errors caused by the instability of the transmission coefficient of acoustic vibrations in the material to be inspected.

The reason for this is that the instability of said coefficient due to changes in the density of the surrounding air, i.e. temperature or atmospheric pressure, for example, is the same for materials under test that are close to each other and for materials with a given thickness. It is. Furthermore, the above-described embodiment of the device according to the invention makes it possible to increase the measurement accuracy by making the dependence of the output signal of the dividing unit linear and directly proportional to the thickness of the material to be inspected.

This is because the amplitude of acoustic vibrations passing through the material under test is inversely proportional to its thickness. Therefore, the quotient is directly proportional to the thickness when it is used as a divisor. Since the function of the reference signal is performed by a traveling wave passed through the material under test, and the function of the reference signal setter is performed by a separate receiver, measurement errors due to instability of the output of the acoustic oscillator and , measurement errors due to instability of the acoustic generator are eliminated.

In this case, these instabilities equally affect the acoustic vibrations that are passed through the material under test and the acoustic vibrations that have already passed through the material. Such an embodiment of the device according to the invention ensures that the output signal of the dividing unit is directly proportional to the thickness of the material to be tested.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The apparatus for measuring the thickness of a thin plate-like material according to the present invention shown in FIG. 1 has an acoustic generator 1 and an acoustic receiver 3. The apparatus shown in FIG. An oscillator 2 is connected to this acoustic generator 1 . The acoustic generator 1 is a known piezoelectric transducer. The oscillator 2 is constructed using a known shock oscillator. The receiver 3 is also known and similar to the acoustic generator 1. Generator 1 and receiver 3
A sheet material 4 to be inspected is placed between them.

The material 4 is placed in an acoustically conductive medium 5. In the case described here, the medium 5 is water heated to a temperature of 70-80<0>C. This water is supplied in the form of a stream flowing in the direction indicated by arrow L. The operating planes of the acoustic generator 1 and the acoustic receiver 3 are approximately parallel to the surface of the sheet-like material 4.

This makes it possible to send an acoustic signal into the material 4 through the medium 5 so as to be substantially perpendicular to the surface of the material 4. The distance between the operating planes of the generator 1 and the receiver 3 is selected to be equal to or greater than the distance traveled by the traveling wave during its duration per measurement (see FIG. 5).

This makes it possible to send acoustic vibrations from the generator 1 into the material 4 in the form of a traveling wave. As a result, generation of standing waves can be prevented. Therefore, thickness measurement errors caused by the presence of standing waves can be eliminated. At the same time, it is possible to dispense with special equipment for automatically moving the generator 1 and the receiver 3 relative to the material 4 in order to place the material 4 on the node of the standing wave. Become. As a result, the device of the invention is easy to maintain. A measuring unit 6 is connected to the acoustic receiver 3.

The measurement unit 6 includes an amplifier 7 constructed using transistors, a peak value detector 8 connected to the output terminal of this amplifier 7, and a comparison unit whose one input terminal is connected to the output terminal of this detector. 9, a reference signal setter 11 configured as a variable DC power supply connected to the other input terminal of this unit 9, and a known recorder (US Pat. No. 3,345) connected to the output terminal of the comparison unit 9. , No. 861). The input terminal of amplifier 7 is connected to the output terminal of receiver 3.

The peak value detector 8 is composed of a known transistor diode circuit, and its detection constant is one order of magnitude larger than the period of the generated acoustic vibration. than the amplitude of the acoustic vibration that has passed through the material 4 and has been repeatedly reflected by the peak detector 8 from the surface of the generator 1, the surface of the receiver 1, and the surface of the material 4. Peak value detection rather than amplitude detectors or amplitude single-phase detectors used in conventional devices for measuring the thickness of thin sheet materials, since it is possible to avoid recording acoustic vibrations with small amplitudes. It is preferable to use a container. The comparison unit 9 is a unit for comparing a signal containing information about the thickness of the material 4 to be inspected with a reference signal, and in the embodiment described here is configured as a subtraction unit.

The subtraction unit 9 is constructed using a known discrimination circuit.
The signal containing information about the thickness of the material 4 is a traveling wave that has passed through the material.

According to this embodiment, the reference signal is a material 10 of a predetermined thickness.
This is a traveling wave that has passed through (Figure 2). Prior to measuring the thickness of the material 4, the material 4 is placed between the generator 13 and the receiver 14 in the same manner as the material 4 is placed. The acoustic vibrations generated by the generator 1 are sent into the material 10 in the form of a traveling wave, and then their amplitude is measured. The output voltage of the variable DC power supply 11 is directly proportional to the measured amplitude of the traveling wave passing through the material 10 having a given thickness.

The scale of the recorder 12 is graduated in units of thickness. Although the embodiment described above is the simplest one, it is possible to measure the thickness only within a relatively narrow range of 20 to 40% of the preset thickness.

In order to expand the measurement range, it is necessary to change the output voltage of the DC power supply. To this end, this embodiment can be employed in automatic equipment for controlling manufacturing processes that only requires information about the variation in thickness of the sheet-like material being inspected over a given thickness.

In order to increase the reliability of the test, it is necessary to stabilize the properties of the acoustic transmission medium 5 and generate stable sound.
This objective is achieved by using a temperature-controlled liquid as medium 5, for example water, and by using a very stable acoustic generator 1. Another embodiment of the device of the invention is shown in FIG.

With this embodiment, the thickness measurement range of the thin plate material can be expanded, and the effects of changes in the properties of the acoustic transmission medium 5 and instability of the generator 1 on the measurement results can be reduced. In addition to the components 1, 2, 3, 7, 8, 12, 13 described above, the embodiment shown in FIG. Contains container 13. This generator 13 is connected to the oscillator 2. This other generator 13
This makes it possible to reduce errors due to instability of the generator 1. In the embodiment shown in FIG. 2, the setter of the reference signal, which is a traveling wave passed through a material 10 having a preselected thickness, is a separate receiver 14.

The receiver 14, like the receiver 3, is of a known type. The material 10 is placed in sufficient proximity to the material 4 to be inspected by another generator 1.
3 and another receiver 14. As a result, the temperature, pressure and density of the acoustic transmission medium 5 (air in this case) is the same or very similar to that of the air in the part sandwiched by the generators 1, 13 and the main receivers 3, 14. do.
Therefore, errors due to changes in the properties of the medium 5 are reduced. The plane of operation of the generator 13 and receiver 14 is approximately parallel to the surface of the material 10.

The operational spacing between the generator 13 and the receiver 14 is close to the operational spacing between the main generator 13 and the main receiver 14. As a result, the acoustic vibrations generated by the generator 13 are transmitted into the material 10 in the form of traveling waves. In the embodiment shown in FIG. 2, the unit for comparing the signal containing information about the thickness of the material 4 with the reference signal is constructed as a known dividing unit 15.

A further receiver 14 is connected to one input of the divider unit 15 via a further amplifier 16 and a peak value checker 17 in series. The other input terminal of the unit 15 is connected to the output terminal of the peak value checker 8, and the output terminal of the dividing unit 15 is connected to the recorder 12. The further amplifier 16 is similar to the main amplifier 7 and the peak checker 17 is similar to the main peak checker 8. The embodiment shown in FIG. 2 includes a stable acoustic transmission medium;
It can operate without using a precise and highly stable acoustic generator 1. Consequently, the acoustic transmission medium can be a gaseous medium, but preferably a liquid medium is used. The use of a gaseous medium increases the response speed of the device, since the attenuation of acoustic vibrations reflected from the surfaces of the generators 1, 13 and receivers 3, 14 is accelerated in the gaseous medium. The gaseous medium also eliminates the instability of the acoustic contact between the generator 1, 13 and the receiver 3, 14 and the material 4 to be examined and the material 10 of a given thickness. This can be explained by remembering that contact is lost when the flow of liquid ceases. Furthermore, by using a gaseous medium, the measuring range can be expanded considerably. The reason is that the density of the sheet material 4 is several times higher than the density of the gaseous medium. At the same time, since the propagation velocity of acoustic vibrations in a gaseous medium is an order of magnitude lower than that in a liquid medium, in order to generate a traveling wave, the generators 1, 13 and the receivers 3, 1 are required.
It is necessary to shorten the respective distances between the four. The use of gaseous media also prevents corrosion of parts of the equipment to be controlled, for example rolling mills. The device of the invention can be employed to measure the absolute thickness of sheet material during its manufacturing process without readjusting the reference signal setter.

In this embodiment, the unit for comparing the signal containing information about the thickness of the sheet material to be inspected with the reference signal is a subtraction unit ( (not shown).

In this case, the device can be employed in a device that automatically controls the manufacturing process, providing the actuator of the device with a control signal proportional to the deviation of the thickness of the material being inspected from a specified value. . In the embodiment shown in FIG.
The setter of the reference signal, whose function is performed by a traveling wave passing through the material 4 to be examined, can be configured as a separate receiver 18 .

This receiver 18 is a small piezoelectric microphone (see US Pat. No. 3,109,111). The receiver 18 is located between the acoustic generator 1 and the material 4 to be inspected so that the majority of the traveling wave passes through the material 4 to be inspected and reaches the main receiver 3. placed across the path. The unit for comparing the reference signal with a signal containing information about the thickness of the material 4 to be examined is configured as a division unit 15.

This dividing unit 15 is connected to a peak value detector 8 and a recorder 12 and to a further receiver 18 via an amplifier 19 and a peak value detector 17 connected in series. The amplifier 19 is provided with a temperature controller (not shown) that adjusts the gain. This temperature regulator helps reduce errors due to temperature changes in the air, which in this example is the acoustic transmission medium 5. The embodiment shown in FIG. 3 makes it possible to eliminate errors in measuring the thickness of the thin plate material 4 to be inspected, which are caused by the instability of the output of the oscillator 2 and the instability of the acoustic generator 1. In this case, these instabilities have no effect on the output voltage of the dividing unit 15, since they equally affect the acoustic vibrations passing through the material 4 and the acoustic vibrations that have already passed through the material 4. . As a result, the accuracy of measuring the thickness of the material 4 becomes extremely high. This device can be used to measure the thickness of a wide range of sheet materials during the entire manufacturing process without readjusting the reference signal setter.

FIG. 4 shows the amplitude A of acoustic vibrations passed through a material and the amplitude A of acoustic vibrations passed through the material in the method of the present invention. 2 is a graph showing the relationship between the ratio of d and the product of the thickness d of the material 4 (FIG. 1) and the frequency f of acoustic vibration. Curves I, l, show their ratios for aluminum, copper and tungsten, respectively. Amplitude A. :5A0 ratio can be expressed by the following formula.

~ − VV here, ρo and C.

are the density of the acoustic transmission medium 5 and the propagation velocity of acoustic vibrations in the medium, respectively, and ρ and C are the density of the thin plate material 4 to be tested and the propagation velocity of acoustic vibrations therein, respectively. From equation (1) and the graph in FIG. 4, it is clear that the amplitude A of the acoustic vibration passing through the material 4 is inversely proportional to the thickness d of the material 4. The thickness measuring method of the present invention is carried out as follows using the apparatus described above.

The sheet material 4 to be tested is placed between the acoustic generator 1 and the receiver 3, which are placed in water heated to 70-80°C.

The oscillator 2 generates electrical pulses which are applied to the generator 1 at a constant repetition period.

This pulse repetition period is selected depending on the required thickness measurement accuracy which depends on the number of measurements per unit time. Generator 1 is excited by a pulse given from generator 2,
It sends short, narrow-spectrum acoustic vibration pulses into the water in the form of traveling waves.

By using acoustic vibrations in the form of traveling waves, thickness measurement errors due to the generation of standing waves can be completely eliminated. This standing wave operating condition is ensured by choosing the distance between the generator 1 and the receiver 3 to be greater than or equal to the distance traveled by the traveling wave during its duration per measurement. .

The frequency of the acoustic vibrations is selected such that the wavelength of the traveling wave within the sheet material 4 is at least four times the thickness of that material.

As a result, the amplitude of the traveling wave of the acoustic vibration that has passed through the material 4 and the thickness of the material 4 are linearly related, and therefore the measurement range within a narrow thickness range can be expanded.
The ratio between the wavelength of the traveling wave and the maximum thickness of the thin plate material to be inspected is determined by the thickness of the thin film material (in this case, the thickness is several tenths of
1L1L) by using ultrasonic vibrations and acoustic vibrations with a frequency between the lower part of the ultrasonic frequency range and the upper part of the audio frequency range. Audible sound frequencies are used to measure the thickness of thick materials. The traveling wave of the acoustic vibration pulse passing through the sheet material 4 to be inspected is approximately perpendicular to the surface of the material 4;
It enters the water on both sides of the material 4 as a pulse with attenuated amplitude as shown in equation (1) above.

A traveling wave passing through the material 4 to be inspected enters the surface of the material 4 perpendicularly.

The reason is that the operating planes of the generator 1 and the receiver 3 were parallel to the surface of the material 4. The traveling wave pulse that has passed through the sheet material 4 to be inspected is applied to a receiver 3. This receiver 3 converts these pulses into electrical pulses with a carrier frequency equal to the frequency of the acoustic vibrations. These electrical pulses contain information about the thickness of the material 4 to be tested and are applied via an amplifier 7 to a peak value tester 8 . The peak detector 8 generates a voltage equal to the amplitude of the envelope of the pulse applied to its input terminal. From the output of the peak detector 8, a voltage is applied to one input of the subtraction unit 9, which is inversely proportional to the thickness of the material being tested.

A constant voltage is applied to the other input terminal of the subtraction unit 9 from the output terminal of the DC power supply 11. This voltage is inversely proportional to the preselected thickness of the sheet material 10. At the output terminal of the subtraction unit 9 appears a voltage equal to the sum of the voltages applied to its two input terminals and which is inversely proportional to the difference between the preselected thickness of the sheet material 10 and the thickness of the material to be examined. . The output voltage of subtraction unit 9 is applied to recorder 12.

This output voltage indicates the value of the deviation of the thickness of the material 4 being tested from a preselected thickness of the material 10. Before starting the operation of the device shown in FIG. 1, the DC power supply 11, which functions as a reference signal setter, is suitably adjusted.

For this purpose, instead of the material 4 to be examined, a material 10 of a predetermined thickness is placed between the generator 1 and the receiver 3.
An acoustic vibration traveling wave passes through this material 10, and the DC power source 1
Adjust the output voltage of 1 so that the recorder 12 shows zero. Usually the preselected value is at the beginning of the measurement band.

During operation, the output voltage of the DC power supply 11 is constant. Although the method explained above is simple, it is possible to
It is possible to make measurements within a relatively narrow range of %. As the thickness to be measured becomes larger, the relationship of the register 12 reading to the material thickness becomes non-linear and the DC power supply 11 must be readjusted for a different measurement band. The range of thicknesses to be measured can also be extended using the method for testing the thickness of sheet-like materials, which is carried out using the apparatus shown in FIG. According to this method, a sheet-like material 4 to be tested is placed between a generator 1 and a receiver 3, which are placed in an acoustic transmission medium 5 (in this case air).

Also, a thin plate-like material 10 of a preselected thickness is placed close to the material 4 between another generator 13 and another receiver 14 . This reduces errors caused by changes in the properties of the acoustic transmission medium. The oscillator 2 generates electrical pulses and applies them to the main generator 1 and the further generator 13 with a constant repetition period.

The main generator 1 sends acoustic vibration pulses into the air in the form of traveling waves.

These pulses pass through the material 4 to be inspected. After passing, the amplitude of these pulses decreases according to equation (6) above. Density ρ of air, which is the acoustic propagation medium. is about four orders of magnitude smaller than the density ρ of the material 4 to be inspected.

Furthermore, in order to prevent the amplitude A of the acoustic vibration from being excessively attenuated, the frequency f of the acoustic vibration is selected such that 2πFd/C is significantly smaller than π/2.

Therefore, equation (6) can be expressed as the following equation. If λo is the wavelength of a traveling wave in the air, then C.

Since /f=λo, equation (8) can be expressed as the following equation. Here, K=AOρ.

λo/πρ. Material 4 to be inspected from this (expression)
It will be appreciated that the amplitude of acoustic vibrations passed through the material 4 is directly proportional to the thickness of the material 4, and that this is applicable to practically any range of thicknesses.

The acoustic vibrations that have passed through the material 4 to be examined enter the receiver 3 and are thereby converted into electrical pulses.

These electrical pulses are amplified by an amplifier 7 and then applied to a peak detector 8. This peak detector 8 then generates a constant voltage equal to the amplitude of the envelope of the electrical pulse applied to its input terminal. This constant voltage is applied to one input terminal of divider unit 15. On the other hand, the auxiliary generator 13 sends acoustic vibration pulses into the air in the form of traveling waves.

The pulses pass through a sheet-like material 10 having a predetermined thickness, so that the amplitude of the pulses is attenuated according to the relationship .

Here, A is the amplitude of acoustic vibration passing through the material 10 of a predetermined thickness. Receiver 14 receives the weakened pulses, converts them into electrical pulses with a carrier frequency equal to the frequency of the acoustic vibrations, and amplifies the electrical pulses with amplifier 16 prior to peak detection. Add to bowl 17.

The peak detector 17 receiving the pulses generates a constant voltage equal to the amplitude of the envelope of those pulses. This constant voltage is applied to the second input terminal of divider unit 15. As a result, the output terminal of this dividing unit 15 receives the voltage applied from the output terminal of the peak value detector 17 to its second input terminal, and the voltage applied from the output terminal of the peak value detector 8 to the dividing unit 15. A voltage appears which is equal to the ratio of the voltage applied to the first input terminal of . The output voltage appearing at the output terminal of the dividing unit 15 is proportional to the thickness of the material 4 to be examined. This output voltage is applied to a recorder 12, which indicates the thickness of the material 4 being inspected. The apparatus shown in FIG. 2 is calibrated prior to beginning operation.

For this purpose, instead of the material 4 to be examined, a sample of material 4 (not shown) with a known thickness is placed between the generator 1 and the receiver 3. Acoustic vibrations in the form of traveling waves are transmitted through the sample and the material 10. A voltage then appears at the output of the divider unit 15 which is directly proportional to the known thickness of the sample and adjusts the gain of the auxiliary amplifier 16 so that the reading of the recorder 12 corresponds to that thickness. In this thickness measurement method, the output signal of the dividing unit 15 is directly proportional to the thickness of the material being inspected, so that the thickness measurement accuracy can be increased over a wide range.

At the same time, due to the instability of the transmission coefficient of acoustic vibrations as they pass through the material being examined by this method, as well as the instability of the output of oscillator 2 and the fact that generators 1, 13 Errors caused by instability can be reduced. However, this method requires precise equipment for its implementation. This can be easily done using the apparatus shown in FIG. In this case, acoustic vibrations are sent into the sheet material 4 to be tested, the vibrations passing through the material are received by a receiver 3 and converted into electrical pulses, which are amplified by an amplifier 7. It is then applied to a peak detector 8 whose output is applied to the input terminal of the divider unit 5.

At the same time, the signal sent into the air by the generator 1 serves in this case as a reference signal.

The traveling wave of acoustic vibrations is received by another receiver 18 .
Receiver 18 converts the pulses into electrical pulses with a repetition frequency equal to the frequency of the acoustic vibrations. These electrical pulses are amplified by an amplifier 19. By providing an amplifier 19 whose gain is temperature adjusted, errors due to changes in air temperature are reduced. The amplified electrical pulse is applied to a peak value detector 17;
Detector 17 generates a voltage equal to the amplitude of the envelope of the electrical pulse applied to the input terminal of divider unit 15.
As a result, one input terminal of the dividing unit 15 receives the amplitude A of the traveling wave of acoustic vibrations transmitted through the material 4 to be examined.

A voltage is applied to the other input terminal which is directly proportional to the amplitude A of the traveling wave of acoustic vibrations passing through the material 4 to be examined. The output terminal of the dividing unit 15 receives the amplitude A of the traveling wave passing through the material 4. A voltage appears which is equal to the ratio of the voltage directly proportional to A and the voltage directly proportional to the amplitude A of the traveling wave through the material 4. According to equation (8), a voltage appears at the output terminal of the dividing unit 15 which is directly proportional to the thickness of the material 4 to be inspected. This voltage is recorder 1
Added to 2. This recorder 12 indicates the thickness of the material being examined. The apparatus shown in FIG.
It is adjusted in a manner similar to the device shown in the figure.

The method of the invention for testing the thickness of sheet-like materials carried out by the apparatus shown in FIGS. Density can be measured automatically without contact.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out the method of the present invention for inspecting the thickness of a sheet material, FIG. 2 is a block diagram of another embodiment of the apparatus of the present invention, and FIG. 3 is a block diagram of an apparatus according to the present invention. A block diagram of a further embodiment of the apparatus, FIG. 4, shows the relationship between the amplitude of the acoustic vibrations passing through the material to be inspected, the amplitude of the acoustic vibrations passing through the material, and the thickness of the material and the frequency of the acoustic vibrations. Graphs showing the dependence on the product, FIGS. 5A to 5D are waveform diagrams showing examples of the traveling wave used in the present invention. 1, 13... Sound generator, 2... Oscillator, 3, 14... Sound receiver, 4...
5. Acoustic transmission medium; 5. Acoustic transmission medium;
6...Measurement unit, 7,16...Amplifier, 8,17...Peak value detector, 12...
...Recorder.

Claims (1)

[Scope of Claims] 1. A system comprising: an acoustic vibration generator, an oscillator that periodically generates a group of acoustic vibrations, an acoustic vibration receiver, and a measurement unit connected to the acoustic vibration receiver; A thin plate material whose thickness is to be tested is placed between the generator and the acoustic vibration receiver, and a working surface of the acoustic vibration generator and a working surface of the acoustic vibration receiver are substantially parallel to the surface of the thin sheet material. In an apparatus for measuring the thickness of a thin sheet material, the distance between the working surface of the acoustic vibration generator and the working surface of the acoustic vibration receiver is determined by the distance between the working surface of the acoustic vibration generator and the working surface of the acoustic vibration receiver. The wavelength of the traveling wave generated from such a distance relationship is greater than the length of the radiated acoustic vibration given by the product of the propagation velocity of the wave and the duration of a group of radiated acoustic vibrations. the measuring unit comprises an amplifier, a peak value detector, a reference signal setter and a reference signal for comparing the reference signal with a signal having information about the thickness of the sheet material to be tested. and a recorder connected to the output terminal of the comparator,
The input terminal of the amplifier is connected to the output terminal of the acoustic vibration receiver, the input terminal of the peak value detector is connected to the output terminal of the amplifier, and one input terminal of the comparison unit is connected to the output terminal of the peak value detector. 1. An apparatus for measuring the thickness of a thin plate material, characterized in that the other input terminal is connected to the reference signal setting device. 2. In the device according to claim 1, the setter for the reference signal, which is a traveling wave passed through a thin plate-like material having a predetermined thickness, is made as a variable DC power source, and the reference signal is tested. 1. An apparatus for measuring the thickness of a thin plate-shaped material, characterized in that a unit for comparing with a signal having information about the thickness of the thin plate-shaped material is configured as a subtraction unit and is directly connected to a variable DC power source. 3. In the device according to claim 1, a separate acoustic vibration generator is provided for generating acoustic vibrations that are passed through a thin plate-like material having a predetermined thickness. The reference signal setter, whose function is performed by the passed traveling wave, is made as another acoustic vibration setter passed through a sheet-like material having a predetermined thickness, and this material disposed between the generator and the other receiver, and the operating plane of the other acoustic vibration generator and the operating plane of the other receiver are substantially parallel to one surface of the thin plate-like material having a predetermined thickness. , their distance is approximately equal to the distance between the working planes of the main acoustic vibration generator and the main receiver, and the reference signal is compared with the signal having information about the thickness of the material being examined divided by the unit unit, this division unit is connected to said another receiver via another amplifier and another peak detector, and another amplifier and another peak detector are connected to said another receiver. A thickness measuring device for thin plate-like materials characterized by being connected in series. 4. In the device according to claim 1, the setter for the reference signal, which is a traveling wave passed through the sheet material to be inspected, is configured as a separate acoustic vibration receiver, and this receiver between the main acoustic vibration generator and the lamellar material being tested, so that the part of the traveling wave that reaches the main receiver through the material being tested bypasses another receiver. The unit arranged across the path and comparing the reference signal with a signal having information about the thickness of the lamellar material to be examined is made as a dividing unit, which divider unit has a separate amplifier and a separate tip. A device for measuring the thickness of a thin plate material, characterized in that the device is coupled to the other receiver via a value detector, and that another amplifier and another peak value detector are connected in series to the other receiver. .