CN111323480B - A handheld auto-focus laser ultrasonic nondestructive testing system - Google Patents

Abstract

The invention provides a handheld automatic focusing laser ultrasonic nondestructive testing system, in particular to the field of laser ultrasonic nondestructive testing, excitation light is led into an optical fiber collimator, the optical fiber collimator corrects a beam divergence angle to obtain a beam of parallel light, and the parallel light is divided into two beams by a beam splitter; the parallel light can be expanded by a beam expander consisting of a concave lens and a first convex lens, then focused by a second convex lens controlled by an electric control motor through a light outlet window to form spot light on a workpiece to be detected, scattered and then sequentially reflected by the second convex lens, the first convex lens and the concave lens, passed through a sleeve lens by the beam splitter, and captured by a high-speed CCD camera arranged on the sleeve lens to form an image; the coordinate tracking camera can transmit the updated focusing light spot position to the control and signal processing module; and finally reconstructing the captured data by a high-performance computer to obtain a test result. The invention can improve the detection efficiency and is more humanized in detection.

Description

A handheld auto-focus laser ultrasonic nondestructive testing system

Technical Field

The invention belongs to the field of laser ultrasonic nondestructive testing, and in particular relates to a handheld automatic focusing laser ultrasonic nondestructive testing system.

Background Art

Nondestructive testing technology (NDT) refers to a method of detecting and testing the performance parameters of the surface and internal structure, properties, state, etc. of a specimen by means of physical or chemical methods, with the help of advanced technology and equipment without damaging the specimen. At present, the conventional detection methods mainly include: 1. Visual method. 2. Fracture fatigue tensile test. 3. X-ray detection and 4. Ultrasonic detection.

Although the visual method refers to the manual observation of the defects and cracks on the surface of the workpiece, this method can see some larger cracks on the surface (relative to laser ultrasound), but it cannot obtain the defects inside the workpiece. Moreover, the information obtained is relatively single, and it is impossible to predict the physical properties of the workpiece, such as stress and strain. As the name suggests, the fracture fatigue tensile test is a destructive experiment. For some "precious" workpieces, it cannot meet the requirements of non-destructive testing. Although X-ray detection can see some cracks inside the workpiece, it cannot reach the detection accuracy of laser ultrasound and is not sensitive to some tiny crack holes. At the same time, X-rays have certain radiation and are difficult to achieve online integration. Ultrasonic method is the mainstream method of non-destructive testing at present. Its basic idea is to transmit and receive ultrasound through ultrasound. When ultrasound propagates between heterogeneous media, it produces reflection, transmission, scattering and other phenomena. People analyze and process the signals after the interaction between ultrasound and matter, and finally extract the relevant characteristics of the defects. Ultrasonic testing has the characteristics of being able to detect defects of different types of materials, high tolerance for the depth of defects, accurate positioning of defects, high detection sensitivity, and easy use of the technology, fast detection speed, harmless to the human body, and easy to implement at the fault site. However, this technology is a contact detection and cannot be applied under some extreme conditions (for example, high temperature, high pressure, toxic and other harsh environments).

Laser ultrasound, as a non-contact non-destructive testing technology, is gaining more and more attention. Its basic idea is to generate ultrasonic signals through pulsed laser excitation and then receive ultrasonic signals through a vibrometer or transducer. This method can achieve large-area and rapid scanning and testing of the workpiece without contacting the surface of the test piece, and the detected signal has high resolution both in time and space. However, this method requires an additional set of scanning galvanometer systems, and the scanning path is relatively simple. In addition, for some complex workpieces, if you want to scan other surfaces after scanning one side, you have to flip and translate the workpiece, which will greatly reduce the scanning efficiency, and the entire experimental environment (positioning, equipment stability, etc.) will also have slight changes.

Summary of the invention

In view of the above-mentioned shortcomings, the purpose of the present invention is to provide a handheld auto-focus laser ultrasonic non-destructive testing system, which can not only perform real-time online monitoring of workpieces in high temperature and high pressure environments, but also greatly improve the detection efficiency and be more user-friendly due to the convenience of its handheld laser probe.

The present invention provides the following technical solutions:

A handheld auto-focus laser ultrasonic nondestructive testing system, comprising a laser ultrasonic nondestructive testing probe, a nanosecond pulse laser, a high-speed signal acquisition card, a photoelectric detector, a fiber coupler, high-performance computer software, a multimode optical fiber, a coordinate tracking camera and a vibrometer;

The laser ultrasonic nondestructive testing probe includes a shell, and a variable focus long focal length combined lens, a photoelectric detector, a beam splitter, an electronically controlled motor, a high-speed CCD camera, a fiber collimator, a double convex lens, a sleeve lens, and a lead screw integrated in the shell; the variable focus long focal length combined lens includes a concave lens, a first convex lens, and a second convex lens;

The photoelectric detector and the high-speed CCD camera are located on both sides of the beam splitter, and a double convex lens is arranged between the photoelectric detector and the beam splitter, and a sleeve lens is arranged between the high-speed CCD camera and the beam splitter; both ends of the beam splitter are respectively provided with a fiber collimator and a concave lens, a first convex lens and a second convex lens arranged in sequence; the outer side of the second convex lens is provided with a light exit window on the shell;

The laser ultrasonic nondestructive testing probe is connected to the nanosecond pulse laser through a multimode optical fiber, and the two ends of the multimode optical fiber are connected to a fiber collimator and a fiber coupler respectively; the excitation light of the nanosecond pulse laser is coupled to the fused silica optical fiber through the fiber coupler, and the excitation light is introduced into the fiber collimator. The fiber collimator corrects the divergence angle of the light beam to obtain a beam of parallel light, and then the parallel light is divided into two beams by a beam splitter;

Among them, part of the parallel light passing through the beam splitter is focused by the double convex lens and received by the photodetector, which is used for signal triggering and for calibration of single pulse laser energy;

Another part of the parallel light passing through the beam splitter can be expanded by a beam expander composed of a concave lens and a first convex lens, and then by a second convex lens controlled by an electronic motor, the second convex lens can be translated back and forth in the transmission guide rail to control the focus position, and then focused on the workpiece to be inspected through the light exit window to form a point light spot. After being scattered, the point light spot passes through the second convex lens, the first convex lens, and the concave lens in turn, and then is reflected by the beam splitter through the sleeve lens, and is captured by a high-speed CCD camera installed on the sleeve lens.

Among them, the high-speed CCD camera can feed back the captured focus spot size to the control and signal processing module, and the control and signal processing module sends commands to the electronic motor; the coordinate tracking camera can transmit the updated focus spot position to the control and signal processing module; finally, the captured data is reconstructed by a high-performance computer to obtain the test results.

Preferably, a transmission guide rail is provided on the periphery of the second convex lens, a transmission wheel is connected to the side of the transmission guide rail, a lead screw passes through the center of the transmission wheel, and the end of the lead screw is connected to the driving shaft of the electronically controlled motor; the bonding method between the transmission wheel and the transmission guide rail is a precise gear meshing, and the transmission error is less than 300 microns.

Preferably, the high-speed signal acquisition card has a bandwidth of hundreds of MHz and a sampling rate of GSa/S, which can restore the original signal with high fidelity.

Preferably, the high-performance computer software is MATLAB, and the principle of the image visualization algorithm used is based on the reciprocity between the excitation and reception of ultrasonic waves. The vibrometer is a double-glass hybrid interferometer with a sensitivity better than 10 nanometers.

Preferably, the multimode optical fiber is a fused silica optical fiber with a fiber diameter of 200 microns and a SMA interface at both ends.

Preferably, according to the actual amplitude of the hand shaking up and down during the scanning process, the maximum distance that the transmission guide rail moves back and forth is ±20mm.

Preferably, the coordinate tracking camera is mounted on a sturdy and stable tripod to prevent the coordinates of the laser focus spot from being distorted by unstable factors such as shaking.

Preferably, when the light exit window is excited by a point light source, a high-transmittance plane mirror is installed in the window to protect the optical elements inside the housing. When excited by a line light source, it is only necessary to replace the lens with a circular plano-convex cylindrical lens, which is very convenient to operate.

Beneficial effects of the present invention:

(1) The present invention relates to a "light-acoustic-light" detection technology that generates ultrasonic waves through light excitation and then detects ultrasonic waves through "light". Therefore, non-destructive detection of workpieces under high temperature and high pressure can be performed.

(2) The present invention does not require a galvanometer scanning system, and only requires a handheld laser excitation probe to perform all-round and multi-angle scanning of the workpiece, which is easy to operate.

(3) In the present invention, the focus deviation caused by hand shaking during the scanning process is compensated in real time by a feedback correction circuit composed of a high-speed CCD camera and a control motor, making the experimental results more accurate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

FIG1 is a schematic diagram of the overall system of the present invention;

FIG2 is a schematic diagram of the structure of a laser ultrasonic nondestructive testing probe according to the present invention;

Fig. 3 is a structural block diagram of the present invention;

Figure numerals: 1. nanosecond laser; 2. fiber coupler; 3. fused silica multimode optical fiber; 4. laser ultrasonic nondestructive testing probe; 5. workpiece; 6. filter; 7. vibrometer; 8. high-speed acquisition card; 9. coordinate tracking camera; 10. tripod; 11. high-performance computer; 12. laser module; 13. coordinate tracking module; 14. handheld probe module; 15. detection module; 16. control signal processing module; 17. housing; 18. fiber collimator; 19. double convex lens; 20. photodetector; 21. beam splitter; 22. sleeve lens; 23. high-speed CCD camera; 24. electric control motor; 25. lead screw; 26. concave lens; 27. first convex lens; 28. transmission wheel; 29. transmission guide rail; 30. second convex lens; 31. light exit window; 32. circular plano-convex cylindrical lens.

DETAILED DESCRIPTION

Example 1:

Referring to Figures 1 and 2 of the present application, the device system includes a nanosecond laser 1, a fiber coupler 2, a fused silica multimode optical fiber 3, a laser ultrasonic nondestructive testing probe 4, a workpiece 5, a filter 6, a vibrometer 7, a high-speed acquisition card 8, a coordinate tracking camera 9, a tripod 10, and a high-performance computer 11; the nanosecond pulse laser pulse 1 has a pulse width of 8ns, a single pulse energy of less than 5mJ, and a repetition frequency of less than 50Hz. The two ends of the fused silica multimode optical fiber 3 are SMA connectors connected to the fiber coupler 2 and the fiber collimator 18 respectively. There are three wires at the rear end of the laser ultrasonic nondestructive testing probe 4, of which two wires connected to the high-speed CCD camera 23 and the electric control motor 24 are connected to the high-performance computer 11. Another wire connects the photodetector 20 to the high-speed acquisition card 8 for triggering the signal. The coordinate tracking camera 9 is fixed on the tripod. A 532nm filter 6 is placed in front of the vibrometer 7 to prevent the excitation light in the nanosecond pulse laser pulse 1 from leaking into the vibrometer 7, thereby interfering with the measurement signal and causing damage to the vibrometer 7 itself;

When the system is working, the excitation light emitted by the nanosecond pulse laser 1 is coupled to the fused silica multimode optical fiber 3 through the fiber coupler 2, and then transmitted to the laser ultrasonic nondestructive testing probe 4 to focus the light spot on the workpiece 5 to be tested. Since the nanosecond pulse and the surface material of the workpiece 5 have a very short action time, the local area on the surface of the workpiece 5 will be heated and expanded, and the local temperature will not have time to diffuse to the surroundings, which will produce a temperature gradient, and then generate ultrasonic waves according to the stress balance principle. The ultrasonic wave mainly includes three different modes of waves: surface acoustic wave, longitudinal wave, and transverse wave. When the ultrasonic wave propagates on the surface and inside of the workpiece 5, it will cause a tiny vibration on its surface, which can be sensed by the vibration meter 7, and the vibration signal is converted into an electrical signal and synchronously transmitted to the high-speed signal acquisition card 8 and the signal is transmitted to the high-performance computer 11. At the same time, the coordinate tracking camera 9 records the position of the excitation light spot in real time, and the automatic focusing system built into the laser ultrasonic nondestructive testing probe 4 will automatically adjust the focus according to the size of the light spot in real time to ensure that the focused light spot is on the workpiece 5. And transmit it to the high-performance high-performance computer 11. Finally, the high-performance high-performance computer 11 processes the data in time according to the visualization algorithm to obtain a three-dimensional dynamic image, and determines the position and size of the internal and surface defects of the workpiece 5 and gives a detailed analysis report.

Embodiment 2:

Referring to Figure 3 of the present application, a handheld auto-focus laser ultrasonic non-destructive testing system includes: a laser module 12, a coordinate tracking module 13, a handheld probe module 14, a control and signal processing module 16 and a detection module 15. The function of the laser module 12 is to provide a stable nano-pulse light source, the function of the coordinate tracking module 13 is to determine the position of the final excitation light spot in real time, the function of the handheld probe module 14 is to associate the coordinate tracking module 13 and the control and signal processing module 16, automatically focus the light spot and trigger the signal, the function of the control and signal processing module 16 is to control the electric control motor 24 and collect the signals fed back by the vibrometer 7 and the photoelectric detector at high speed, and the function of the detection module 15 is to capture the tiny vibrations on the surface of the workpiece 5 and convert the mechanical signal into an electrical signal.

Embodiment 3:

1 and 2 of the present application, the laser ultrasonic nondestructive testing probe includes a housing 17, and a variable focus long focal length combination lens integrated in the housing, a photodetector 20, a beam splitter 21, an electronically controlled motor 24, a high-speed CCD camera 23, a fiber collimator 18, a biconvex lens 19, a sleeve lens 22, a lead screw 25, a transmission wheel 28 and a transmission guide rail 29.

The variable focal length combined lens includes a concave lens 26 , a first convex lens 27 , and a second convex lens 30 .

The excitation light emitted by the nanosecond pulse laser 1 is coupled to the fused silica multimode optical fiber 3 through the optical fiber coupler 2, and the excitation light is introduced into the optical fiber collimator 18. The optical fiber collimator 18 corrects the divergence angle of the light beam to obtain a beam of parallel light, and then the parallel light is divided into two beams by the beam splitter 21. A part of the reflected light is focused by the double convex lens 19 and received by the photodetector 20. On the one hand, it is used to trigger the signal, and on the other hand, it is used to calibrate the energy of a single pulse laser.

The other part of the transmitted light first passes through a beam expander composed of a concave lens 26 and a first convex lens 27 to expand the light spot, and then passes through a second convex lens 30 controlled by an electronic motor 24. The second convex lens 30 can be translated back and forth in a transmission guide rail 29 to control the focus position, and then is focused on the workpiece to be inspected through a light exit window 31 to form a point light spot. After being scattered, the point light spot passes through the second convex lens 30, the first convex lens 27, and the concave lens 26 in turn, and is then reflected by the beam splitter 21 through the sleeve lens 22, and is captured by a high-speed CCD camera 23 installed on the sleeve lens.

The high-speed CCD camera 23 feeds back the captured focus spot size to the control and signal processing module 16 in real time, and the control and signal processing module 16 immediately sends a command to the electric motor 24 to make a left or right rotation command control, and then the electric motor 24 drives the lead screw 25 to rotate and drive the transmission guide rail to move forward or backward. At the same time, the coordinate tracking camera 9 is also constantly updating the position of the focus spot and recording it in real time to feed back to the control and signal processing module 16, and finally the captured data is quickly reconstructed through a specific algorithm to obtain the dynamic change image of the ultrasonic wave propagating on the surface and inside the workpiece and the position and size of the defects on the surface and inside the workpiece.

The high-speed signal acquisition card has a bandwidth of hundreds of MHz and a sampling rate of GSa/S, which can restore the original signal with high fidelity.

The high-performance computer software is MATLAB, and the image visualization algorithm used is based on the reciprocity between the excitation and reception of ultrasonic waves. The vibrometer is a double-glass hybrid interferometer with a sensitivity better than 10 nanometers.

The multimode optical fiber is a fused silica optical fiber with a fiber diameter of 200 microns and SMA interfaces at both ends.

According to the actual amplitude of the hand shaking up and down during the scanning process, the maximum distance the transmission guide rail moves forward and backward is ±20mm.

The keying mode between the transmission wheel and the transmission guide rail is a precise gear meshing, and the transmission error is less than 300 microns.

The coordinate tracking camera is installed on a sturdy and stable tripod to prevent the coordinates of the laser focus spot from being affected by unstable factors such as shaking.

When the light exit window is excited by a point light source, a high-transmittance plane mirror is installed in the window to protect the optical elements inside the shell. When excited by a line light source, it is only necessary to replace the lens with a circular plano-convex cylindrical lens, which is very convenient to operate.

The implementation steps are as follows:

S1. Assemble each device according to FIG. 1 , turn on each device, and adjust the signal of the vibration meter 7 to reach the strongest;

S2. Select the required lens (point source excitation or line source excitation) and scan according to the scanning path required by the experiment;

S3. After scanning, the data is reconstructed into three-dimensional dynamic visualization and a detailed inspection report is obtained;

S4. After the experiment, turn off each experimental device in turn.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (5)

1. A handheld auto-focus laser ultrasonic nondestructive testing system, characterized by: comprising a laser ultrasonic nondestructive testing probe, a nanosecond pulse laser, a high-speed signal acquisition card, a photodetector, a fiber coupler, high-performance computer software, a multimode optical fiber, a coordinate tracking camera and a vibrometer; The laser ultrasonic nondestructive testing probe includes a shell, and a variable focus long focal length combined lens, a photoelectric detector, a beam splitter, an electronically controlled motor, a high-speed CCD camera, a fiber collimator, a double convex lens, a sleeve lens, and a lead screw integrated in the shell; the variable focus long focal length combined lens includes a concave lens, a first convex lens, and a second convex lens; The photoelectric detector and the high-speed CCD camera are located on both sides of the beam splitter, and a double convex lens is arranged between the photoelectric detector and the beam splitter, and a sleeve lens is arranged between the high-speed CCD camera and the beam splitter; both ends of the beam splitter are respectively provided with a fiber collimator and a concave lens, a first convex lens and a second convex lens arranged in sequence; the outer side of the second convex lens is provided with a light exit window on the shell; The laser ultrasonic nondestructive testing probe is connected to the nanosecond pulse laser through a multimode optical fiber, and the two ends of the multimode optical fiber are connected to a fiber collimator and a fiber coupler respectively; the excitation light of the nanosecond pulse laser is coupled to the fused silica optical fiber through the fiber coupler, and the excitation light is introduced into the fiber collimator. The fiber collimator corrects the divergence angle of the light beam to obtain a beam of parallel light, and then the parallel light is divided into two beams by a beam splitter; Part of the parallel light passing through the beam splitter is focused by the double convex lens and then received by the photodetector, which is used for signal triggering and for calibration of the energy of a single pulse laser. Another part of the parallel light passing through the beam splitter can be expanded by a beam expander composed of a concave lens and a first convex lens, and then by a second convex lens controlled by an electric motor. The second convex lens can be translated back and forth in the transmission guide rail to control the focus position, and then focused on the workpiece to be inspected through the light exit window to form a point light spot. After being scattered, the point light spot passes through the second convex lens, the first convex lens, and the concave lens in turn, and then is reflected by the beam splitter through the sleeve lens, and is captured by a high-speed CCD camera installed on the sleeve lens. The high-speed CCD camera can feed back the captured focus spot size to the control and signal processing module, which then sends commands to the electronically controlled motor; the coordinate tracking camera can transmit the updated focus spot position to the control and signal processing module; finally, the captured data can be reconstructed by a high-performance computer to obtain the test results; A transmission guide rail is arranged on the periphery of the second convex lens, a transmission wheel is connected to the side of the transmission guide rail, a lead screw runs through the center of the transmission wheel, and the end of the lead screw is connected to the driving shaft of the electric control motor; the bonding method between the transmission wheel and the transmission guide rail is gear engagement; The coordinate tracking camera is set up on a tripod. 2. A handheld auto-focus laser ultrasonic non-destructive testing system according to claim 1, characterized in that the distance that the transmission guide rail moves forward and backward is ±20mm. 3. A handheld auto-focus laser ultrasonic nondestructive testing system according to claim 1, characterized in that: the bandwidth of the high-speed signal acquisition card is 100 to 600 MHz, and the sampling rate is 1 to 10 GSa/S; the high-performance computer software is MATLAB, and the vibrometer is a double-glass hybrid interferometer. 4. A handheld auto-focus laser ultrasonic nondestructive testing system according to claim 1, characterized in that the multimode optical fiber is a fused silica optical fiber with a fiber diameter of 200 microns, and the connection method at both ends of the multimode optical fiber is an SMA interface. 5. A handheld auto-focus laser ultrasonic nondestructive testing system according to claim 1, characterized in that: when the light exit window is excited by a point light source, a high-transmittance plane mirror is installed in the window, or when excited by a line light source, a circular plano-convex cylindrical lens is used.