CN111537564B - Metal micro-crack depth detection system and method based on transmission laser thermal imaging - Google Patents

Abstract

The invention relates to a metal surface microcrack depth detection technology, in particular to a transmission type laser thermal imaging-based metal microcrack depth detection system and method. The invention solves the problems of low detection precision, low detection speed and poor detection result intuition of the traditional metal surface microcrack depth detection technology. The metal microcrack depth detection system based on transmission type laser thermal imaging comprises a metal workpiece to be detected, a focusing lens, a semiconductor laser, an amplifier, a digital potentiometer, a single chip microcomputer, an upper computer and a thermal infrared imager; the exit end of the semiconductor laser is opposite to the incident end of the focusing lens; the exit end of the focusing lens is opposite to the front surface of the metal workpiece to be detected; the signal output end of the amplifier is connected with the signal input end of the semiconductor laser; and the signal output end of the digital potentiometer is connected with the signal input end of the amplifier. The method is suitable for detecting the depth of the microcracks on the metal surface.

Description

Metal micro-crack depth detection system and method based on transmission laser thermal imaging

technical field

The invention relates to a metal surface micro-crack depth detection technology, in particular to a metal micro-crack depth detection system and method based on transmission laser thermal imaging.

Background technique

Metals are widely used in the manufacture of aero-engines, automobiles, and ships because of their advantages such as high strength, good heat resistance, and strong corrosion resistance. During the use of metal workpieces, surface micro-cracks are prone to appear due to fatigue aging or harsh environments, which will affect the mechanical properties, vibration and noise, and service life of metal workpieces. Therefore, in order to ensure the mechanical properties, vibration and noise, and service life of metal workpieces, it is necessary to detect the depth of micro-cracks on the surface of metal workpieces. However, due to the limitation of its own principle, the traditional metal surface micro-crack depth detection technology generally has the problems of low detection accuracy, slow detection speed, and poor intuition of detection results. Based on this, it is necessary to invent a metal micro-crack depth detection system and method based on transmission laser thermal imaging to solve the problems of low detection accuracy, slow detection speed, and poor visibility of detection results in traditional metal surface micro-crack depth detection technology.

Contents of the invention

In order to solve the problems of low detection accuracy, slow detection speed, and poor intuitiveness of detection results of the traditional metal surface micro-crack depth detection technology, the present invention provides a metal micro-crack depth detection system and method based on transmission laser thermal imaging.

The present invention is realized by adopting the following technical solutions:

Metal microcrack depth detection system based on transmission laser thermal imaging, including metal workpiece to be tested, focusing lens, semiconductor laser, amplifier, digital potentiometer, single-chip microcomputer, host computer, infrared thermal imager;

Among them, the outgoing end of the semiconductor laser is facing the incident end of the focusing lens; the outgoing end of the focusing lens is facing the front of the metal workpiece to be tested; the signal output end of the amplifier is connected to the signal input end of the semiconductor laser; the signal output end of the digital potentiometer is connected to the amplifier The signal input terminal of the single-chip microcomputer is connected to the signal input terminal of the digital potentiometer; the signal output terminal of the host computer is connected to the signal input terminal of the single-chip microcomputer; the detection terminal of the infrared thermal imager is facing the back of the metal workpiece to be tested.

It also includes a stabilized power supply and a power supply; the output end of the stabilized power supply is connected to the voltage end of the digital potentiometer; the output end of the power supply is respectively connected to the power supply end of the single chip microcomputer, the power supply end of the digital potentiometer, and the power supply end of the amplifier.

The digital potentiometer is an X9C103 digital potentiometer; the fifth pin of the X9C103 digital potentiometer is connected to the signal input end of the amplifier; the signal output end of the single-chip microcomputer is respectively connected to the first pin, the second pin, The seventh pin is connected; the output end of the regulated power supply is respectively connected to the third pin and the sixth pin of the X9C103 digital potentiometer; the output end of the power supply is respectively connected to the fourth pin and the eighth pin of the X9C103 digital potentiometer pin connection.

Metal microcrack depth detection method based on transmission laser thermal imaging (this method is realized based on the metal microcrack depth detection system based on transmission laser thermal imaging of the present invention), the method is realized by the following steps:

Step 1: For a microcrack that appears on the front of the metal workpiece to be tested, select a laser heating point on the front of the metal workpiece to be tested, and select two temperature collection points on the back of the metal workpiece to be tested; the laser heating point and the two The temperature collection point meets the following conditions:

The laser heating point is located 2mm directly below the micro-crack, the first temperature collection point is located directly above the corresponding position on the back of the laser heating point and directly above the corresponding position on the back of the micro-crack, and the second temperature collection point is located at the laser heating point Directly below the corresponding position on the back, the vertical distance from the two temperature collection points to the laser heating point is equal;

Step 2: Set the working parameters of the semiconductor laser and the thermal imaging camera; then, start the semiconductor laser and the thermal imaging camera, the semiconductor laser emits a pulsed laser beam, the pulsed laser beam is focused by the focusing lens and irradiated vertically on the laser heating point, In this way, the laser heating point is heated; during the heating process, the infrared thermal imaging camera detects the temperature field change on the back of the measured metal workpiece in real time, and generates a thermal infrared image in real time according to the detection results;

Step 3: Select the coordinate point with the highest temperature value in the thermal infrared image, and define the coordinate point as the corresponding point of the laser heating point in the thermal infrared image;

Step 4: Calculate the number n of pixels corresponding to the vertical distance from the two temperature collection points to the laser heating point in the thermal infrared image; the specific calculation formula is as follows:

In the formula: d represents the vertical distance from the two temperature collection points to the laser heating point; d ₁ represents the vertical shooting range of the infrared thermal imager; f represents the focal length of the infrared thermal imager; u represents the infrared thermal imager and the measured Object distance between metal workpieces; V represents the vertical resolution of the infrared thermal imager; d, d ₁ , f, u, V are all known quantities;

Then, according to the calculation results, two coordinate points are selected in the thermal infrared image; the two coordinate points meet the following conditions:

The first coordinate point is located directly above the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image;

The second coordinate point is located directly below the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image;

Then, the first coordinate point is defined as the corresponding point of the first temperature collection point in the thermal infrared image, and the second coordinate point is defined as the corresponding point of the second temperature collection point in the thermal infrared image;

Step 5: Continuously record the temperature values of the corresponding points of the two temperature collection points in the thermal infrared image, and draw the temperature value change curve according to the recording results;

Step 6: By observing the temperature value change curve, it is obtained that when the temperature value of the corresponding point of the first temperature collection point in the thermal infrared image is 50°C, the temperature of the corresponding point of the second temperature collection point in the thermal infrared image temperature value T(x,y,z,t);

Step 7: According to the temperature value T(x, y, z, t) of the corresponding point of the second temperature collection point in the thermal infrared image, calculate the depth of the micro-crack; the specific calculation formula is as follows:

In the formula: x represents the abscissa coordinate value of the corresponding point of the second temperature collection point in the thermal infrared image; y represents the vertical axis coordinate value of the corresponding point of the second temperature collection point in the thermal infrared image; z represents the The vertical axis coordinates of the corresponding points of the two temperature collection points in the thermal infrared image; t indicates the corresponding moment when the temperature value of the corresponding point of the first temperature collection point in the thermal infrared image is 50°C; g(x, y, z) represents the heat source function; ρ represents the density of the tested metal workpiece; c _p represents the constant pressure heat capacity of the measured metal workpiece; k represents the thermal conductivity of the measured metal workpiece; α represents the temperature conductivity of the measured metal workpiece ; ρ _d represents the density at the microcrack; k _d represents the thermal conductivity at the microcrack.

In the second step, the working parameter setting process of the semiconductor laser is as follows: the upper computer generates code instructions, and sends the code instructions to the single-chip microcomputer; the single-chip computer converts the code instructions into level signals, and sends the level signals to the digital potentiometer , thereby setting the output voltage of the digital potentiometer; the output voltage of the digital potentiometer is amplified by the amplifier and then loaded to the semiconductor laser, thereby setting the working parameters of the semiconductor laser.

Compared with the traditional metal surface micro-crack depth detection technology, the metal micro-crack depth detection system and method based on transmission laser thermal imaging in the present invention is based on laser heating technology and infrared temperature measurement technology, and uses a double-point sampling strategy , to realize the depth detection of surface micro-cracks on metal workpieces, thereby not only effectively improving the detection accuracy, effectively speeding up the detection speed, but also making the detection results more intuitive.

The invention effectively solves the problems of low detection accuracy, slow detection speed, and poor visibility of detection results in the traditional metal surface micro-crack depth detection technology, and is suitable for the detection of the metal surface micro-crack depth.

Description of drawings

Fig. 1 is a schematic structural diagram of the system of the present invention.

Fig. 2 is a schematic diagram of microcracks, laser heating points, and temperature collection points in the method of the present invention.

Fig. 3 is a graph showing the relationship between the temperature value of the corresponding point in the thermal infrared image and the depth of the microcrack at the second temperature collection point in the method of the present invention.

In the figure: 1-metal workpiece under test, 2-focusing lens, 3-semiconductor laser, 4-amplifier, 5-digital potentiometer, 6-single-chip microcomputer, 7-host computer, 8-infrared thermal imager, 9-voltage regulator Power supply, 10-power supply.

Detailed ways

Metal microcrack depth detection system based on transmission laser thermal imaging, including metal workpiece 1, focusing lens 2, semiconductor laser 3, amplifier 4, digital potentiometer 5, single-chip microcomputer 6, host computer 7, infrared thermal imager 8;

Wherein, the outgoing end of semiconductor laser 3 is facing the incident end of focusing lens 2; The signal output terminal of 5 is connected with the signal input terminal of amplifier 4; the signal output terminal of single-chip microcomputer 6 is connected with the signal input terminal of digital potentiometer 5; the signal output terminal of upper computer 7 is connected with the signal input terminal of single-chip microcomputer 6; The detection end of the instrument 8 faces the back side of the metal workpiece 1 to be tested.

Also comprise stabilized voltage power supply 9, power supply 10; The output end of stabilized voltage power supply 9 is connected with the voltage end of digital potentiometer 5; The power supply terminal of the amplifier 4 is connected.

Described digital potentiometer 5 is X9C103 digital potentiometer; The 5th pin of X9C103 digital potentiometer is connected with the signal input end of amplifier 4; pin and the seventh pin; the output terminal of the regulated power supply 9 is respectively connected to the third pin and the sixth pin of the X9C103 digital potentiometer; the output terminal of the power supply 10 is respectively connected to the fourth pin of the X9C103 digital potentiometer Pin, eighth pin connection.

Metal microcrack depth detection method based on transmission laser thermal imaging (this method is realized based on the metal microcrack depth detection system based on transmission laser thermal imaging of the present invention), the method is realized by the following steps:

Step 1: For a certain microcrack that appears on the front of the metal workpiece 1 to be tested, select a laser heating point on the front of the metal workpiece 1 to be tested, and select two temperature collection points on the back of the metal workpiece 1 to be tested; the laser heating point and two temperature collection points meet the following conditions:

The laser heating point is located 2mm directly below the micro-crack, the first temperature collection point is located directly above the corresponding position on the back of the laser heating point and directly above the corresponding position on the back of the micro-crack, and the second temperature collection point is located at the laser heating point Directly below the corresponding position on the back, the vertical distance from the two temperature collection points to the laser heating point is equal;

Step 2: Set the operating parameters of the semiconductor laser 3 and the thermal imaging camera 8; then, start the semiconductor laser 3 and the thermal imaging camera 8, the semiconductor laser 3 emits a pulsed laser beam, and the pulsed laser beam is focused by the focusing lens 2 and vertical The laser heating point is irradiated, thereby heating the laser heating point; during the heating process, the infrared thermal imager 8 detects the temperature field change on the back side of the metal workpiece 1 to be tested in real time, and generates a thermal infrared image in real time according to the detection result;

Step 3: Select the coordinate point with the highest temperature value in the thermal infrared image, and define the coordinate point as the corresponding point of the laser heating point in the thermal infrared image;

Step 4: Calculate the number n of pixels corresponding to the vertical distance from the two temperature collection points to the laser heating point in the thermal infrared image; the specific calculation formula is as follows:

In the formula: d represents the vertical distance from the two temperature collection points to the laser heating point; _d1 represents the vertical shooting range of the infrared thermal imager 8; f represents the focal length of the infrared thermal imager 8; u represents the infrared thermal imager 8 and the object distance between the measured metal workpiece 1; V represents the vertical resolution of the thermal imaging camera 8; d, d ₁ , f, u, and V are all known quantities;

Then, according to the calculation results, two coordinate points are selected in the thermal infrared image; the two coordinate points meet the following conditions:

The first coordinate point is located directly above the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image;

The second coordinate point is located directly below the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image;

Then, the first coordinate point is defined as the corresponding point of the first temperature collection point in the thermal infrared image, and the second coordinate point is defined as the corresponding point of the second temperature collection point in the thermal infrared image;

Step 5: Continuously record the temperature values of the corresponding points of the two temperature collection points in the thermal infrared image, and draw the temperature value change curve according to the recording results;

Step 6: By observing the temperature value change curve, it is obtained that when the temperature value of the corresponding point of the first temperature collection point in the thermal infrared image is 50°C, the temperature of the corresponding point of the second temperature collection point in the thermal infrared image temperature value T(x,y,z,t);

Step 7: According to the temperature value T(x, y, z, t) of the corresponding point of the second temperature collection point in the thermal infrared image, calculate the depth of the micro-crack; the specific calculation formula is as follows:

In the formula: x represents the abscissa coordinate value of the corresponding point of the second temperature collection point in the thermal infrared image; y represents the vertical axis coordinate value of the corresponding point of the second temperature collection point in the thermal infrared image; z represents the The vertical axis coordinates of the corresponding points of the two temperature collection points in the thermal infrared image; t indicates the corresponding moment when the temperature value of the corresponding point of the first temperature collection point in the thermal infrared image is 50°C; g(x, y, z) represents the heat source function; ρ represents the density of the tested metal workpiece 1; c _p represents the constant pressure heat capacity of the measured metal workpiece 1; k represents the thermal conductivity of the tested metal workpiece 1; The thermal conductivity; ρ _d represents the density at the micro-crack; k _d represents the thermal conductivity at the micro-crack.

In said step 2, the working parameter setting process of the semiconductor laser 3 is as follows: the host computer 7 generates a code instruction, and sends the code instruction to the single-chip microcomputer 6; the single-chip computer 6 converts the code instruction into a level signal, and sends the level signal To the digital potentiometer 5, thereby setting the output voltage of the digital potentiometer 5; the output voltage of the digital potentiometer 5 is amplified by the amplifier 4 and then loaded to the semiconductor laser 3, thereby setting the working parameters of the semiconductor laser 3.

Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and the protection scope of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principle and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims (4)

1. A metal microcrack depth detection method based on transmission laser thermal imaging, characterized in that: the method is based on a metal microcrack depth detection system based on transmission laser thermal imaging, the system includes the measured metal Workpiece (1), focusing lens (2), semiconductor laser (3), amplifier (4), digital potentiometer (5), single-chip microcomputer (6), upper computer (7), infrared thermal imager (8); Wherein, the outgoing end of the semiconductor laser (3) is facing the incident end of the focusing lens (2); the outgoing end of the focusing lens (2) is facing the front of the metal workpiece (1) to be tested; The signal input terminal of (3) is connected; The signal output terminal of digital potentiometer (5) is connected with the signal input terminal of amplifier (4); The signal output terminal of single-chip microcomputer (6) is connected with the signal input terminal of digital potentiometer (5) The signal output end of the host computer (7) is connected with the signal input end of the single-chip microcomputer (6); the detection end of the infrared thermal imager (8) is facing the back side of the metal workpiece (1) to be tested; This method is realized by adopting the following steps: Step 1: For a microcrack that appears on the front side of the metal workpiece (1) to be tested, select a laser heating point on the front side of the metal workpiece (1) to be tested, and select two temperature points on the back side of the metal workpiece (1) to be tested. Collection point; laser heating point and two temperature collection points meet the following conditions: The laser heating point is located 2mm directly below the micro-crack, the first temperature collection point is located directly above the corresponding position on the back of the laser heating point and directly above the corresponding position on the back of the micro-crack, and the second temperature collection point is located at the laser heating point Directly below the corresponding position on the back, the vertical distance from the two temperature collection points to the laser heating point is equal; Step 2: set the operating parameters of the semiconductor laser (3) and the thermal imaging camera (8); then, start the semiconductor laser (3) and the thermal imaging camera (8), and the semiconductor laser (3) sends a pulsed laser beam, pulse The laser beam is focused by the focusing lens (2) and then irradiated vertically on the laser heating point, thereby heating the laser heating point; during the heating process, the infrared thermal imager (8) detects in real time The temperature field changes, and thermal infrared images are generated in real time according to the detection results; Step 3: Select the coordinate point with the highest temperature value in the thermal infrared image, and define the coordinate point as the corresponding point of the laser heating point in the thermal infrared image; Step 4: Calculate the number n of pixels corresponding to the vertical distance from the two temperature collection points to the laser heating point in the thermal infrared image; the specific calculation formula is as follows:

In the formula: d represents the vertical distance from two temperature collection points to the laser heating point; d ₁ represents the vertical shooting range of the thermal imager (8); f represents the focal length of the thermal imager (8); u represents the infrared Object distance between thermal imager (8) and measured metal workpiece (1); V represents the vertical resolution of infrared thermal imager (8); d, d ₁ , f, u, V are all known quantities ; Then, according to the calculation results, two coordinate points are selected in the thermal infrared image; the two coordinate points meet the following conditions: The first coordinate point is located directly above the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image; The second coordinate point is located directly below the corresponding point of the laser heating point in the thermal infrared image, and there are n pixels between the coordinate point and the corresponding point of the laser heating point in the thermal infrared image; Then, the first coordinate point is defined as the corresponding point of the first temperature collection point in the thermal infrared image, and the second coordinate point is defined as the corresponding point of the second temperature collection point in the thermal infrared image; Step 5: Continuously record the temperature values of the corresponding points of the two temperature collection points in the thermal infrared image, and draw the temperature value change curve according to the recording results; Step 6: By observing the temperature value change curve, it is obtained that when the temperature value of the corresponding point of the second temperature collection point in the thermal infrared image is 50°C, the temperature of the corresponding point of the first temperature collection point in the thermal infrared image temperature value T(x,y,z,t); Step 7: According to the temperature value T(x, y, z, t) of the corresponding point of the first temperature collection point in the thermal infrared image, calculate the depth of the micro-crack; the specific calculation formula is as follows:

In the formula: x represents the abscissa coordinate value of the corresponding point of the first temperature collection point in the thermal infrared image; y represents the vertical axis coordinate value of the corresponding point of the first temperature collection point in the thermal infrared image; z represents the first temperature collection point The vertical axis coordinate value of the corresponding point of a temperature collection point in the thermal infrared image; t indicates the corresponding moment when the temperature value of the corresponding point of the second temperature collection point in the thermal infrared image is 50°C; g(x, y, z) represents the heat source function; ρ represents the density of the tested metal workpiece (1); c _p represents the constant pressure heat capacity of the measured metal workpiece (1); k represents the thermal conductivity of the measured metal workpiece (1); Indicates the thermal conductivity of the tested metal workpiece (1); ρ _d indicates the density at the micro-crack; k _d indicates the thermal conductivity at the micro-crack. 2. the metal microcrack depth detection method based on transmission laser thermal imaging according to claim 1, is characterized in that: in the described step 2, the working parameter setting process of semiconductor laser (3) is as follows: upper computer (7 ) generates a code command, and sends the code command to the single-chip microcomputer (6); the single-chip microcomputer (6) converts the code command into a level signal, and sends the level signal to the digital potentiometer (5), thereby setting the digital potentiometer (5); the output voltage of the digital potentiometer (5) is amplified by the amplifier (4) and then loaded to the semiconductor laser (3), thereby setting the operating parameters of the semiconductor laser (3). 3. the metal microcrack depth detection method based on transmission laser thermal imaging according to claim 1, characterized in that: said a kind of metal microcrack depth detection system based on transmission laser thermal imaging also includes a stabilized power supply ( 9), the power supply (10); the output terminal of the stabilized power supply (9) is connected with the voltage terminal of the digital potentiometer (5); The power supply terminal of the device (5) and the power supply terminal of the amplifier (4) are connected. 4. The metal microcrack depth detection method based on transmission laser thermal imaging according to claim 3, characterized in that: the digital potentiometer (5) is an X9C103 digital potentiometer; the fifth pin of the X9C103 digital potentiometer Connect with the signal input end of the amplifier (4); the signal output end of the single-chip microcomputer (6) is respectively connected with the first pin, the second pin, the seventh pin of the X9C103 digital potentiometer; the output of the regulated power supply (9) The terminals are respectively connected with the third pin and the sixth pin of the X9C103 digital potentiometer; the output terminals of the power supply (10) are respectively connected with the fourth pin and the eighth pin of the X9C103 digital potentiometer.

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