KR102814087B1 - Low power laser scanning system and thereof method - Google Patents

Abstract

One embodiment of the present invention provides a low-power laser scanning system and method capable of reducing energy applied to an inspection and measurement target object by implementing low-power laser scanning and calculating an optimal excitation point using constructive interference, thereby minimizing damage to the inspection and measurement target object. The low-power laser scanning system according to one embodiment of the present invention includes an excitation unit that non-contactly excites a measurement target object using ultrasonic waves, a diffraction optical unit that is provided between the measurement target object and the excitation unit and disperses and diffracts light incident on the measurement target object from the excitation unit in a preset direction, a measuring unit that measures an excitation point distance (a) between excitation points generated by the excitation of the measurement target object, a vibrator that detects sound pressure transmitted from the measurement target object, and a control unit that sets an excitation point distance using a wavelength (λ) of ultrasonic waves transmitted from the excitation unit to the measurement target object, calculates a distance (x) between the measurement target object and the diffraction optical unit according to a preset calculation formula, and sets a constructive interference point at which sound pressure detected by the vibrator is maximized in a range of excitation point distances measured by the measuring unit as an optimal point.

Description

{LOW POWER LASER SCANNING SYSTEM AND THEREOF METHOD}

The present invention relates to a low power laser scanning system and method.

Laser scanning systems using pulsed lasers have been developed in various ways as non-destructive testing devices for detecting structural defects. Pulsed laser scanning systems are known as systems that irradiate a laser on a structure to be tested to generate thermal stress, thereby generating ultrasonic waves, and then scan the area to be tested to detect defects.

When performing non-destructive testing using a pulsed laser, there is a risk that the test piece may be damaged by heat if a high energy laser is used per unit area. To avoid such damage, a laser in the thermal elastic range must be used, and if the energy used is low, ultrasound may not be generated in the test piece.

Structures such as petrochemical plants contain flammable materials inside, so there is a risk of fire when they are excited by pulse lasers, and there is a risk that a large fire can occur due to a small mistake. Therefore, care must be taken to prevent safety accidents caused by fire when using pulse lasers, and the development of a system that can detect structural defects using low-power laser scanning is required.

As a related prior art document, Korean Patent No. 788,823 discloses “Laser-ultrasonic inspection device and method for extracting surface defect information.”

Korean registered patent 788,823

One embodiment of the present invention provides a low-power laser scanning system and method capable of minimizing damage to an inspection and measurement target by reducing energy applied to the target by calculating an optimal point using constructive interference and implementing low-power laser scanning.

In addition to the above tasks, embodiments according to the present invention can be used to achieve other tasks not specifically mentioned.

According to one embodiment of the present invention, a low-power laser scanning system includes: an excitation unit that non-contactly excites a measurement target using ultrasonic waves; a diffraction optical unit that is provided between the measurement target and the excitation unit and disperses and diffracts light incident on the measurement target from the excitation unit in a preset direction; a measurement unit that measures an excitation point distance (a) between excitation points generated by the excitation of the measurement target; a vibrator that detects sound pressure transmitted from the measurement target; and a control unit that sets the excitation point distance using the wavelength (λ) of ultrasonic waves transmitted from the excitation unit to the measurement target, calculates the distance (x) between the measurement target and the diffraction optical unit according to a preset calculation formula, and sets an optimal point having a constructive interference point at which sound pressure detected by the vibrator is maximized in a range of excitation point distances measured by the measurement unit.

A low-power laser scanning method according to one embodiment of the present invention includes an excitation point distance (a) initial value setting step of setting an initial value of an excitation point distance (a) between excitation points and points generated by excitation of a measurement object, an excitation step of maintaining a distance (x) between the measurement object and a diffraction optical unit using an excitation unit and exciting the measurement object, an excitation point distance (a) measuring step of measuring the excitation point distance (a) between the excitation points and points generated by excitation of the measurement object using a measurement unit, and an excitation optimum point setting step of setting an optimum point having a constructive interference point at which sound pressure detected by a vibrometer is maximized in a range of excitation point distances measured by the measurement unit while adjusting the set distance (x).

One embodiment of the present invention has the effect of reducing damage to a test object due to heat by using a low-energy laser per unit area through constructive interference when performing a non-destructive test using a pulsed laser.

For this reason, it is effective in preventing fire accidents that may occur during non-destructive testing of petrochemical plants.

FIG. 1 is a schematic diagram illustrating a low-power laser scanning system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a state in which an optimal point is set by measuring sound pressure to optimize the distance between points according to an embodiment of the present invention.
Figure 3 is a diagram illustrating changes in signal size and excited area according to laser energy irradiated on the surface of an aluminum material.
FIG. 4 is a diagram schematically illustrating a low-power laser scanning method according to an embodiment of the present invention.
FIG. 5 is a diagram schematically illustrating an application example of a low-power laser scanning system according to an embodiment of the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein. In order to clearly describe the present invention in the drawings, parts that are not related to the description are omitted, and the same or similar components are designated by the same reference numerals throughout the specification. In addition, in the case of widely known known technologies, their detailed descriptions are omitted.

Throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

Hereinafter, a low-power laser scanning system and method are described in detail with reference to the drawings.

FIG. 1 is a schematic diagram illustrating a low-power laser scanning system according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a state in which an optimum excitation point is set by measuring sound pressure for optimizing the distance between excitation points according to an embodiment of the present invention. Referring to FIGS. 1 and 2, the low-power laser scanning system according to an embodiment of the present invention includes an excitation unit (110), a diffraction optical unit (120), a measurement unit (130), a vibrometer (140), and a control unit (150), and calculates an optimum excitation point using constructive interference and implements low-power laser scanning, thereby using a low-energy laser per unit area on a measurement target (10), which is an inspection chain, so as to reduce damage to the measurement target (10) due to heat. Here, the low-energy laser means a laser in the thermoelastic range. In non-destructive testing using laser ultrasound, the conditions are divided into the thermoelastic regime, the ablation regime, and the intermediate regime, and can be classified according to the laser intensity irradiated on the material surface. In the thermoelastic regime, relatively low-power beam energy is irradiated, and ultrasound can be generated by thermal expansion. In contrast, in the ablation regime, some of the material is lost due to high-power beam energy, and relatively strong ultrasound can be generated compared to the thermoelastic regime.

Fig. 3 is a diagram illustrating changes in signal size and excited area according to laser energy irradiated on the surface of an aluminum material. Referring to Fig. 3, the thermoelastic region, intermediate region, and ablation region according to laser energy are shown for an aluminum material. In the ablation region, it can be seen that damage occurs on the surface when it becomes about 75 MW/cm ² . Conservatively, no damage occurs to the specimen when it is about 50 MW/cm ² or less. However, this may vary somewhat depending on the material. That is, since in the thermoelastic region, unlike the ablation region, micro-damage is not induced on the material surface, an analysis is possible by considering only the thermal expansion phenomenon without considering material loss.

The excitation unit (110) has a function of non-contactingly exciting the measurement target (10) using ultrasonic waves. The excitation unit (110) can be driven in a preset low-power energy range to transmit excitation for calculating the optimal excitation point on the surface of the measurement target (10). The excitation unit (110) can irradiate a low-power laser, including an excitation laser or an excimer laser. In the case of a low-power laser, since the optical energy is not large, the straightness unique to the laser is utilized, and the heat generation of the laser can be minimized in the process of irradiating a laser with low output to transmit optical energy to the measurement target (10). Therefore, the problem (fire) that occurs when using a high-energy laser when using a general pulse laser can be resolved.

A low-power laser scanning system according to an embodiment of the present invention may further include a base (12) supporting a driving unit (110), and a moving unit (14) provided on the base (12) to support a preset longitudinal movement of the driving unit (110). Here, the moving unit (14) may include a rail.

The diffractive optical unit (120) (DOE; Diffractive Optical Element) is provided between the measurement target (10) and the excitation unit (110) and has the function of dispersing and diffracting light incident on the measurement target (10) from the excitation unit (110) in a preset direction. The diffractive optical unit (120) can be integrally provided at the tip of the excitation unit (110). The diffractive optical unit (120) has a light distribution function of diffracting light incident on the excitation unit (110) and dividing it into a plurality of split beams. Therefore, low-power laser energy can be induced by using the diffractive optical unit (120).

The measuring unit (130) measures the distance (a) between the excitation points generated by the excitation of the measurement object (10). The measuring unit (130) may include a camera.

The vibrometer (140) has a function of detecting sound pressure transmitted from the measurement target (10). The vibrometer (140) may include a laser vibrometer (LDV; Laser Doppler Vibrometer). The laser vibrometer can detect elastic wave signals unique to each measurement target (10) that are generated due to micro-cracks or corrosion, etc.

The control unit (150) can detect a signal related to low-power laser scanning using constructive interference and perform a control operation corresponding to the detected signal. The control unit (150) can include a DAQ board that converts analog signals input from the excitation unit (110) and the vibrator (140) into digital values and acquires related data. The control unit (150) can analyze input information related to low-power laser scanning control and set an optimal excitation point while maintaining low power when driving the excitation unit (110). The control unit (150) can implement an overall control operation related to low-power laser scanning control based on information stored in a memory.

For example, the control unit (150) sets the excitation point distance by using the wavelength (λ) of the ultrasonic wave transmitted from the excitation unit (110) to the measurement object (10), calculates the distance (x) between the measurement object (10) and the diffraction optical unit (120) according to a preset calculation formula, and can set the optimum point having the constructive interference point where the sound pressure detected by the vibrator (140) is maximum in the excitation point distance range measured by the measurement unit (130). In addition, the control unit (150) can calculate the wavelength transmitted by the ultrasonic wave generated from the excitation unit (110) through preset dispersion diagram calculation, and set the initial value of the excitation point distance (a) to be a multiple of the transmitted wavelength (λ).

As described above, the embodiment of the present invention can eliminate the concern that the measurement target (10) may be damaged by heat by using a low-energy laser per unit area when performing a non-destructive inspection using a pulse laser through a low-power laser scanning system using a constructive interference method.

FIG. 4 is a diagram schematically illustrating a low-power laser scanning method according to an embodiment of the present invention. Referring to FIGS. 1 to 4, the low-power laser scanning method using the low-power laser scanning system according to the embodiment of the present invention described above includes an initial value setting step (S10) of the excitation point distance (a), an excitation step (S20), an excitation point distance (a) measuring step (S30), and an excitation optimum point setting step (S40).

The initial value setting step (S10) of the excitation point distance (a) is a step of setting the initial value of the excitation point distance (a) between excitation points and points generated by the excitation of the measurement object (10). By setting the initial value of the excitation point distance (a), high ultrasonic propagation energy can be obtained. In the initial value setting step (S10) of the excitation point distance (a), the initial value of the excitation point distance (a) can be set to be a multiple of the wavelength (λ) propagated by calculating the wavelength of the ultrasonic wave generated from the excitation unit (110) through a preset dispersion diagram calculation.

When the initial value of the distance (a) between the excitation point is set, the distance (x) between the measurement object (10) and the diffraction optical unit (120) can be calculated by calculation. This can be set as the initial value (x ₁ ) of the distance between the measurement object (10) and the diffraction optical unit (120). While the measurement object (10) is excited with the set distance initial value (x 1 ), the excitation point distance (a) between the excitation points is measured using the measurement unit (130).

The excitation step (S20) is a step of exciting the measurement object (10) while maintaining the distance (x) between the measurement object (10) and the diffraction optical unit (120) using the excitation unit (110).

The step (S30) of measuring the distance (a) between the excitation points generated by the excitation of the measurement target (10) using the measuring unit (130) is a step of measuring the distance (a) between the excitation points.

The optimum point setting step (S40) is a step of setting the constructive interference point at which the sound pressure detected by the vibrator (140) is maximum in the excitation point distance range measured by the measuring unit (130) while adjusting the set distance (x) as the optimum point. In the optimum point setting step (S40), the excitation unit (110) is moved back and forth to find the point at which the sound pressure of the vibrator (140) is maximum. For example, when the distance (x) between the measurement object (10) and the diffraction optical unit (120) increases, the excitation point distance (a) becomes longer, and when the distance (x) between the measurement object (10) and the diffraction optical unit (120) decreases, the excitation point distance (a) becomes shorter. The point at which the sound pressure of the vibrator (140) is maximum is the point at which constructive interference occurs, and this point can be regarded as the optimum point for inspection. In other words, the optimum point for excitation can be set as the point at which the average amplitude exhibits the maximum amplitude. As described above, by setting the optimal point, the energy to the measurement object (10) can be reduced by half compared to when at least one point is present, thereby minimizing damage to the measurement object (10).

The step of setting the optimal point (S40) may further include a laser scanning step (S50) of scanning the measurement target (10) while reducing the energy applied to the measurement target (10) by using the optimal point set.

The low-power laser scanning method according to an embodiment of the present invention can also be used in a 4-point, 8-point, 16-point, and 2D array shape by using various types of diffractive optical parts (120).

FIG. 5 is a drawing schematically illustrating an application example of a low-power laser scanning system according to an embodiment of the present invention. As described above, by combining a low-power laser scanning system using a constructive interference method with a general laser scanning system, a low-power laser scanning system setup such as that shown in FIG. 5 is possible.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

10; Measurement object 12; Base
14; Moving part 110; Possessed part
120; Diffraction optics section 130; Measurement section
140 ; Vibration system 150 ; Control unit

Claims (10)

A vibrating unit that uses ultrasonic waves to vibrate the measurement target without contact.
A diffraction optical section provided between the measurement object and the excitation section to disperse and diffract light incident on the measurement object from the excitation section in a preset direction.
A measuring unit that measures the distance (a) between excitation points generated by the excitation of the above measurement object,
A vibrator that detects the sound pressure transmitted from the above measurement object, and
A control unit that sets the distance between the excitation point using the wavelength (λ) of the ultrasonic wave transmitted from the excitation unit to the measurement target and calculates the distance (x) between the measurement target and the diffraction optical unit according to a preset calculation formula, and sets the optimal point having the constructive interference point where the sound pressure detected by the vibrator is maximum in the excitation point distance range measured by the measurement unit.
A low power laser scanning system comprising: In paragraph 1,
The above-mentioned excitation unit is a low-power laser scanning system that is driven by a preset low-power energy range and delivers an excitation for calculating an optimal point on the surface of the measurement target. In paragraph 1,
The above measuring unit is a low-power laser scanning system including a photographing unit. In paragraph 1,
The above vibrometer is a low-power laser scanning system including a laser vibrometer. In paragraph 1,
A low-power laser scanning system in which the above diffractive optical section is integrally provided at the tip of the above excitation section. In paragraph 1,
A base part supporting the above-mentioned part, and
A low-power laser scanning system further comprising a moving part provided on the base part and supporting a preset longitudinal movement of the excitation part. In paragraph 1,
The above control unit
A low-power laser scanning system that calculates the wavelength of the ultrasonic wave generated from the above-described excitation unit through a preset dispersion curve calculation and sets the initial value of the distance (a) between the excitation points to be a multiple of the propagating wavelength (λ). The initial value setting step of the excitation point distance (a) is to set the initial value of the excitation point distance (a) between the excitation points and the points generated by the excitation of the measurement target.
An excitation step for maintaining the distance (x) between the measurement target and the diffraction optical section using the excitation section and exciting the measurement target,
A step of measuring the distance (a) between the excitation points and the excitation points generated by the excitation of the measurement object using a measuring unit, and
The optimum excitation point setting step is to set the optimum point with the reinforcement interference point where the sound pressure detected by the vibrator is maximum in the excitation point distance range measured by the measuring unit while adjusting the above-mentioned set distance (x).
A low power laser scanning method comprising: In Article 8,
A low-power laser scanning method further comprising a laser scanning step of scanning the measurement object while reducing energy applied to the measurement object by using the optimum point set in the optimum point setting step. In Article 8,
A low-power laser scanning method in which, in the step of setting the initial value of the above-mentioned distance from the excitation point (a), the initial value of the distance from the excitation point (a) is set to be a multiple of the wavelength (λ) propagated by calculating the wavelength of the ultrasonic wave generated from the excitation unit through a preset dispersion diagram calculation.