KR101794716B1

KR101794716B1 - Non-contact type system and method for measuring thickness using laser

Info

Publication number: KR101794716B1
Application number: KR1020160031024A
Authority: KR
Inventors: 박관규; 박준홍; 최원영
Original assignee: 한양대학교 산학협력단
Priority date: 2016-03-15
Filing date: 2016-03-15
Publication date: 2017-11-07
Also published as: KR20170107274A; WO2017160082A1

Abstract

The present invention relates to a non-contact thickness measurement system and method using a laser, and more particularly, to a system and method for measuring non-contact thickness using a laser, including a light irradiating unit for irradiating a target with a laser by using a light source, A receiving unit for receiving a secondary photoacoustic signal and a secondary photoacoustic signal generated while the laser is traveling inside the object, a measurement for measuring a response waveform of the primary photoacoustic signal and the secondary photoacoustic signal received, And analyzing means for analyzing response characteristics of the measured response waveform to derive the thickness of the object. The analyzing unit analyzes the tendency of the first photoacoustic signal and the second photoacoustic signal generated by irradiating the laser to the object, A non-contact thickness measurement system using a laser capable of measuring the thickness of a target object &Lt; / RTI >

Description

[0001] NON-CONTACT TYPE SYSTEM AND METHOD FOR MEASURING THICKNESS USING LASER [0002]

The present invention relates to a system and method for measuring the thickness of an object from acoustic signals originating from an object using optical pulses from the laser.

When producing a product, it is not easy for the physical properties of the member to be homogeneous due to various internal and external factors and to have uniform thickness. Since the heterogeneity of these members is a direct cause of deteriorating the performance of the products, the homogeneity of the members is one of the very important characteristics that determine the quality.

Generally, in the fields of household appliances, automobiles, civil engineering and architecture, as the technology develops, the products are manufactured by thinning the plates and lighter weight. At this time, a phenomenon that a thickness of a specific part becomes thin in the process of metal processing of a metal plate or the like may occur, which causes a deterioration of the quality of the product.

Therefore, it is necessary to check the thickness non-uniformity in order to reduce the defect rate of the product or predict the life of the product.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating a system for measuring the thickness and refractive index of a conventional material.

Referring to FIG. 1, interference signals of a measurement material are measured and analyzed by using a light-irradiating unit that provides a pulsed laser oscillating at periodic intervals and laser light emitted from the light-irradiating unit, And a spectrum analyzing interferometer for simultaneously calculating the spectrum analyzer.

Since the above technology is a system that measures the thickness of a substance by passing the light passing through the substance through the laser to the interferometer, an expensive equipment called an interferometer is additionally required. It is limited to the mirror surface material having a smooth surface and excellent optical transparency The range of applicable materials is limited.

In addition, the above technology can measure only a very thin thickness, and it is impossible to measure in a range of several mm thickness. In order to measure a large wiper in real time at once, the spectrum analyzing interferometer is configured for measuring a large optical system And there is a need to further include an area photodetector.
Related prior art is Japanese Patent Application Laid-Open No. 2002-213936 (Jul. 31, 2002).

According to an aspect of the present invention, there is provided a non-contact thickness measurement system using a laser capable of measuring a thickness of a target object by analyzing a tendency of a first photoacoustic signal and a second photoacoustic signal generated by irradiating a laser to a target object. And a method thereof.

According to an aspect of the present invention, there is provided a non-contact thickness measurement system, comprising: a light irradiating unit for irradiating a target with a laser using a light source; A receiver for receiving a first photoacoustic signal and a second photoacoustic signal generated while the laser is traveling inside the object, a second controller for measuring a response waveform of the received first photoacoustic signal and the second photoacoustic signal, And an analyzer for analyzing the response characteristic of the measurement unit and the measured response waveform to derive the thickness of the object.

Further, the second photoacoustic signal according to an embodiment of the present invention is generated by physical vibration of the object.

The non-contact thickness measuring system according to an embodiment of the present invention includes an angle adjusting unit for adjusting an irradiation angle of the laser generated in the light irradiating unit.

In addition, the angle adjusting unit according to an embodiment of the present invention adjusts an irradiation angle at which the laser is irradiated to the object depending on the position of the receiving unit.

Further, the measuring unit according to an embodiment of the present invention is characterized in that the response waveform of the first photoacoustic signal and the second photoacoustic signal is stably measured by triggering the laser irradiation point of the light irradiation unit.

In addition, the response characteristic according to an embodiment of the present invention may include a difference between a generation time of the first photoacoustic signal and the second photoacoustic signal, a maximum amplitude of each of the first photoacoustic signal and the second photoacoustic signal Size and duration of time.

In the non-contact thickness measurement system according to an embodiment of the present invention, as the thickness of the object increases, the generation time difference between the first photoacoustic signal and the second photoacoustic signal decreases.

Further, in the non-contact thickness measurement system according to an embodiment of the present invention, as the thickness of the object increases, the maximum amplitude magnitude of the first photoacoustic signal decreases and the maximum amplitude magnitude of the second photoacoustic signal increases .

In the non-contact thickness measurement system according to an embodiment of the present invention, the duration of the first photoacoustic signal decreases and the duration of the second photoacoustic signal increases as the thickness of the object increases. do.

According to another aspect of the present invention, there is provided a non-contact thickness measuring method comprising: irradiating a laser to a reference specimen using a light source; irradiating the reference specimen with a laser beam, Receiving a photoacoustic signal and a second photoacoustic signal generated while the laser proceeds in the reference specimen, measuring a first response waveform of the received first photoacoustic signal and the second photoacoustic signal, A step of irradiating a laser to a target using a light source, a step of receiving a first photoacoustic signal generated by a direct collision of the laser with the surface of the object and a second photoacoustic signal generated while the laser proceeds inside the object, Measuring a second response waveform of the received first photoacoustic signal and the second photoacoustic signal, And comparing the response characteristic indicated by the first response waveform with the response characteristic indicated by the second response waveform to derive the thickness of the target object.

Also, the rms ratio of the response waveform according to an embodiment of the present invention can be expressed by Equation 1, and the rms ratio increases as the thickness of the object increases.

[Equation 1]

rms ratio = rms value of the second photoacoustic signal / rms value of the first photoacoustic signal

The maximum value ratio of the response waveform according to an exemplary embodiment of the present invention may be expressed by Equation 2, and the maximum value ratio increases as the thickness of the object increases.

[Equation 2]

Maximum value ratio = maximum value of the second photoacoustic signal / maximum value of the first photoacoustic signal

The non-contact thickness measurement system and method according to the present invention can be applied to various materials such as rubber, wood, plastic or metal, and has a thickness measurement range from several hundred micrometers to several millimeters.

In addition, there is an advantage in that the thickness of various materials having vibration characteristics can be measured by only a light emitting device, a sound wave detecting device, and a waveform measuring device.

In addition, it is possible to perform measurement in a short period of time by using a laser galvanometer system even in a wide area scanning, and it can be used in a noncontact manner in the air, so that there is an effect that use restriction is small.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating a system for measuring the thickness and refractive index of a conventional material.
2 is a block diagram of a non-contact thickness measurement system using a laser according to an embodiment of the present invention.
3 is an A-scan graph of a 0.5 mm thick PS (polystyrene) plate according to an embodiment of the present invention.
4 is an A-scan graph of a 1 mm thick PS (polystyrene) plate according to an embodiment of the present invention.
5 is an A-scan graph of a 1.5 mm thick PS (polystyrene) plate according to an embodiment of the present invention.
6 is a first graph illustrating a thickness of a target object and a tendency of a photoacoustic signal according to an exemplary embodiment of the present invention.
FIG. 7 is a second graph illustrating a thickness of a target object and a tendency of a photoacoustic signal according to an exemplary embodiment of the present invention. Referring to FIG.
8 is a flowchart of a non-contact thickness measurement method using a laser according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving it will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings.

The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a configuration of a non-contact thickness measurement system using a laser according to an embodiment of the present invention.

2, the non-contact type thickness measurement system using a laser according to an exemplary embodiment of the present invention includes a light irradiation unit 100, a reception unit 200, a measurement unit 300, and an analysis unit 400 .

The light irradiation unit 100 is a device for generating a laser 10 using a light source and irradiating the laser 10 to the object 20. The light irradiation unit 100 irradiates the laser 10 to a target object 20 in order to acquire a photoacoustic signal by photoacoustic effect 20). At this time, the photoacoustic effect means a phenomenon in which a material absorbing electromagnetic wave energy such as light or radio wave generates a sound wave by thermal expansion.

The light irradiation unit 100 includes a light source for generating the laser 10, and a YAG laser using YAG (Yttrium Aluminum Garnet) may be used as the oscillating material. At this time, it is preferable to use Nd-doped Nd-YAG laser to increase the laser oscillation efficiency. However, the Nd-YAG laser may include all the devices that emit light of a specific frequency such as a laser and a diode.

It is a matter of course that the wavelength of the laser 10 may include both the ultraviolet ray, the infrared ray and the visible ray range.

The receiving unit 200 corresponds to an acoustic signal detecting device for detecting the photoacoustic signal 40. The receiving unit 200 receives the photoacoustic signal 40 generated by irradiating the object 40 with the laser 40 generated from the light irradiating unit, Range microphone, and the like, but it is not limited thereto, and may include all the equipment from low-frequency detection devices in kHz to high-frequency detection devices in MHz.

As a power supply source of the apparatus for detecting a signal of a steady state, the receiving unit may be connected to a separate power supply source 210 for supplying power.

The object 20 corresponds to an object to be used for thickness measurement, inspection, and may include plastic, wood, metal, and rubber sheet.

The photoacoustic signal 40 may include a primary photoacoustic signal generated by a direct collision between the laser and the surface of the object and a secondary photoacoustic signal generated while the laser travels inside the object.

The measuring unit 300 measures a response waveform of the received first photoacoustic signal and the second photoacoustic signal, and is a device for displaying a voltage waveform over time, You can use an oscilloscope that corresponds to the basic measuring equipment to be used.

The measuring unit 300 can be triggered by the light irradiating unit 100. Specifically, the measuring unit 300 triggers the laser irradiation point of the light irradiating unit 100 to detect the response of the primary photoacoustic signal and the secondary photoacoustic signal It is possible to measure the waveform stably.

The analysis unit 400 may be a device for deriving the thickness of the object 20 by analyzing the response characteristic of the measured response waveform, and may be a computer capable of controlling or measuring signals.

The first photoacoustic signal corresponds to a shock wave generated when the laser 40 comes into contact with the object 20 for the first time at a point reached when the laser 40 reaches the surface of the object 20, It shows a tendency to become a large waveform and gradually decrease in intensity.

The second photoacoustic signal is generated at a slight time interval from the first photoacoustic signal and corresponds to a surface wave generated through mechanical excitation after the laser 10 collides with the surface of the object 20.

The response waveform by the first photoacoustic signal and the response waveform by the second photoacoustic signal have a tendency depending on the thickness of the object 20. The thickness of the object 20 can be measured by using this tendency Do.

Particularly, it shows similar tendency regardless of materials such as low hardness and rigidity and materials with high hardness and rigidity mainly used in industry, and it can be applied to various materials such as rubber, wood, plastic and metal , The range of thickness measurements can be measured from hundreds of micrometers to several millimeters.

The response characteristic of the measured response waveform indicates the difference between the generation time of the first photoacoustic signal and the second photoacoustic signal and the maximum amplitude magnitude and duration of each of the first photoacoustic signal and the second photoacoustic signal .

Specifically, the second photoacoustic signal occurs with a slight temporal gap after the generation of the first photoacoustic signal. As the thickness of the object increases, the first photoacoustic signal and the second photoacoustic signal The occurrence time difference shows a tendency to decrease.

In the oscilloscope corresponding to the measuring unit 300, a voltage waveform with respect to time can be measured. Here, the first photoacoustic signal and the second photoacoustic signal each have a maximum amplitude value. The thickness of the object 20 The maximum amplitude magnitude of the first photoacoustic signal decreases and the maximum amplitude magnitude of the second photoacoustic signal increases.

In addition, when the laser 10 collides with the object 20 for the first time, a first photoacoustic signal is generated. As time passes, intensity gradually decreases. As the laser 10 advances into the object 20 As the thickness of the object 20 increases, the duration of the first photoacoustic signal decreases and the duration of the second photoacoustic signal increases, .

The non-contact type thickness measuring system using laser according to an embodiment of the present invention may include an angle adjusting unit 500 for adjusting the irradiation angle of the laser generated in the light irradiating unit 100.

The angle adjusting unit 500 is preferably positioned between the light irradiating unit 100 and the object 20 and may be a galvano mirror or the like. All possible mirrors, and the like.

The angle adjusting unit 500 can control the irradiation angle of the laser 10 to the target 20 according to the position of the receiving unit 200 installed therein. The degree of freedom of design of the thickness measurement system can be greatly improved.

Hereinafter, a non-contact type thickness measurement system using a laser according to the present invention will be described in detail with reference to embodiments of the present invention. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

The light source used was a YAG laser for generating light and was set at a frequency of 10 Hz, a wavelength of 532 nm, and a pulse duration of 7 ns. PS (polystyrene) plate was used as the target, Photoacoustic signals were measured.

FIG. 3 is a graph showing an A-scan graph of a 0.5 mm thick PS (polystyrene) plate according to an embodiment of the present invention. FIG. -scan graph, and Figure 5 shows an A-scan graph of a 1.5 mm thick PS (polystyrene) plate according to one embodiment of the present invention.

In general, there are A-scan, B-scan, and C-scan techniques for photoacoustic signals. A-scan is a pulse-echo or pitch- .

3 to 5, the duration time of the first photoacoustic signal is about 170 to 360 μm when the object is 0.5 mm, about 160 to 320 μm when the object is 1 mm, and about 165 to 320 μm when the object is 1.5 mm , It can be seen from this measurement result that the duration of the first photoacoustic signal decreases as the thickness of the object increases.

The duration of the second photoacoustic signal was measured to be about 430 μm to 650 μm when the object was 0.5 mm, about 350 μm to 780 μm when the object was 1 mm, and about 330 μm to 1260 μm when the object was 1.5 mm. It can be seen that the duration of the second photoacoustic signal increases.

Also, it can be seen that as the thickness of the object increases, the maximum amplitude magnitude of the first photoacoustic signal decreases and the maximum amplitude magnitude of the second photoacoustic signal increases, and that the first photoacoustic signal and the second photoacoustic signal The difference in the generation time of the signal decreases.

As mentioned above, there is a very strong correlation between the thickness of the object and the response characteristics of the photoacoustic signal. By analyzing this correlation, it is possible to measure the absolute thickness of the object or the thickness relative to the reference specimen.

FIG. 6 is a first graph illustrating a thickness of a target object and a tendency of a photoacoustic signal according to an exemplary embodiment of the present invention. FIG. 7 is a graph illustrating the thickness of a target object and the tendency of a photoacoustic signal according to an exemplary embodiment of the present invention. Is a second graph for representing the <

Here, the rms ratio is defined by the following equation (1), and the maximum ratio can be defined by the following equation (2).

[Equation 1]

[Equation 2]

Here, rms represents the root mean square (rms) value of the photoacoustic signal.

Referring to the figure, it can be seen that both the rms ratio and the maximum value ratio show a tendency to increase as the thickness of the object increases, and the thickness of the object can be estimated from this tendency.

8 is a flowchart of a non-contact thickness measurement method using a laser according to an embodiment of the present invention.

Referring to FIG. 8, a laser beam can be irradiated to a reference specimen using a light source (S10).

Next, a first photoacoustic signal generated by a direct collision between the laser and the reference specimen surface and a second photoacoustic signal generated while the laser proceeds through the reference specimen are received (S20).

Thereafter, the first response waveform of the received first photoacoustic signal and the second photoacoustic signal can be measured (S30).

After measuring the response waveform of the reference specimen, the response waveform of the subject can be measured as follows. Of course, the order of measurement of the reference specimen and the subject can be changed.

Specifically, the laser can be irradiated to the subject using the light source (S40).

Then, a first photoacoustic signal generated by a direct collision between the laser and the surface of the object and a second photoacoustic signal generated while the laser proceeds through the object are received (S50).

Thereafter, the second response waveform of the received first photoacoustic signal and the second photoacoustic signal can be measured (S60).

Finally, the thickness of the object can be derived by comparing and analyzing the response characteristic indicated by the first response waveform and the response characteristic indicated by the second response waveform (S70).

At this time, the response characteristic may include a difference in generation time of the first photoacoustic signal and the second photoacoustic signal, and a maximum amplitude magnitude and a duration of the first photoacoustic signal and the second photoacoustic signal, respectively .

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. Furthermore, the terms "comprises", "comprising", or "having" described above mean that a component can be implanted unless otherwise specifically stated, But should be construed as including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

10: Laser
20: object
30: Waveform of vibration wave
40: photoacoustic signal
100:
200: Receiver
210: power source
300:
400: Analytical Department
500:

Claims

A light irradiating unit for irradiating a target object with a laser by using a light source;
A receiver for receiving a first photoacoustic signal generated by a direct collision between the laser and the surface of the object and a second photoacoustic signal generated while the laser travels inside the object;
A measuring unit for measuring a response waveform of the received first photoacoustic signal and the second photoacoustic signal; And
And an analysis unit for analyzing a response characteristic indicated by the measured response waveform to derive a thickness of the object,
The response characteristic may be,
A difference between a generation time of the first photoacoustic signal and the second photoacoustic signal and a maximum amplitude magnitude and duration of each of the first photoacoustic signal and the second photoacoustic signal,
As the thickness of the object increases, the generation time difference between the first photoacoustic signal and the second photoacoustic signal decreases, the maximum amplitude magnitude of the first photoacoustic signal decreases, and the maximum amplitude of the second photoacoustic signal decreases Wherein the amplitude magnitude increases and the duration of the first photoacoustic signal decreases and the duration of the second photoacoustic signal increases.

The method according to claim 1,
Wherein the second photoacoustic signal is generated by physical vibration of the object.

The method according to claim 1,
And an angle adjusting unit for adjusting an irradiation angle of the laser generated in the light irradiating unit.

The method of claim 3,
Wherein the angle adjusting unit adjusts an irradiation angle at which the laser is irradiated to the object according to the position of the receiving unit.

The method according to claim 1,
Wherein the measurement unit stably measures a response waveform of the first photoacoustic signal and the second photoacoustic signal by triggering a laser irradiation point of time of the light irradiation unit.

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Irradiating a reference specimen with a laser using a light source;
Receiving a first photoacoustic signal generated by a direct collision between the laser and the surface of the reference specimen and a second photoacoustic signal generated while the laser proceeds inside the reference specimen;
Measuring a first response waveform of the received first photoacoustic signal and the second photoacoustic signal;
Irradiating a laser to a target using a light source;
Receiving a first photoacoustic signal generated by a direct collision between the laser and the surface of the object and a second photoacoustic signal generated while the laser travels inside the object;
Measuring a second response waveform of the received first photoacoustic signal and the second photoacoustic signal; And
And comparing the response characteristic indicated by the first response waveform with the response characteristic indicated by the second response waveform to derive the thickness of the object,
The response characteristic may be,
A difference between a generation time of the first photoacoustic signal and the second photoacoustic signal and a maximum amplitude magnitude and duration of each of the first photoacoustic signal and the second photoacoustic signal,
The rms ratio of the response waveform can be expressed by Equation 1, and the rms ratio increases as the thickness of the object increases,
Wherein the maximum value ratio of the response waveform is expressed by Equation (2), and the maximum value ratio increases as the thickness of the object increases.
[Equation 1]
rms ratio = rms value of the second photoacoustic signal / rms value of the first photoacoustic signal
[Equation 2]
Maximum value ratio = maximum value of the second photoacoustic signal / maximum value of the first photoacoustic signal

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