Air coupling ultrasonic detection system based on multiple optical encoders and working method thereof

Abstract

The invention relates to an air coupling ultrasonic detection system based on multiple optical encoders and a working method thereof. The system comprises a main body device, a coding device, a detection device and a control device, the coding device and the detection device are respectively connected with the main body device and are respectively connected with the control device through a wireless network; the encoding device comprises a plurality of optical encoder groups and is used for monitoring the translation and rotation movement of the system so as to obtain the position information of the ultrasonic guided wave signal; each optical encoder group consists of a displacement optical encoder and a distance optical encoder; the detection device comprises an air coupling ultrasonic probe used for collecting ultrasonic guided wave signals. Compared with the prior art, the method has the advantages of high reliability, accurate detection result and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic detection, and in particular to an air-coupled ultrasonic detection system based on a multi-optical encoder and a working method thereof. Background Art

[0002] Composite materials refer to a new material formed by combining two or more materials with different physical and chemical properties through specific process methods. The performance of this material is generally better than that of a single component material, and it has the advantages of light weight, high specific strength, high specific stiffness, corrosion resistance, fatigue resistance, etc., and is widely used in the aerospace field. Since composite materials have the characteristics of multiple component materials, the interface between different materials is extremely unstable due to the existence of surface energy, and various forms of defects are very likely to occur. The service environment of composite materials in the aerospace field is harsh, and the structure and shape are complex. At the same time, the integration of the load-bearing function of aerospace structures places higher requirements on the quality and reliability of composite materials. It is of great significance to develop non-destructive testing technology that can be applied to the quality inspection of complex-shaped structures to improve the application level of composite structures in the aerospace field.

[0003] Currently, air-coupled ultrasonic testing (AUT) of composite structures typically utilizes manual A (amplitude) scanning or automated C (constant depth) scanning. Manual A-scanning is often used in the early stages of testing due to its ease of operation and adaptability. However, this method has limitations in data recording and result consistency, and inspection quality often depends on the operator's skill level.

[0004] In contrast, C-scan imaging technology provides more comprehensive defect information. While manual raster scanning can meet this requirement to a certain extent, it is cumbersome and reliability is difficult to guarantee. Automated C-scanning significantly improves inspection accuracy and stability through mechanized operation, but its high equipment cost and limited scanning range, particularly due to the limited motion capabilities of the robotic arm, pose certain challenges to its application.

[0005] In recent years, manual C-scan systems have emerged. These systems use devices such as rollers to collect position data. However, these systems can only provide one-dimensional coding positioning and still face problems such as requiring linear grating scanning and insufficient reliability.

[0006] In addition, to meet connection requirements, it is often necessary to make holes and grooves on the surface of the composite material, which can easily cause the surface of the composite material to be uneven. The current common optical encoders require a relatively constant distance to the surface. When imaging uneven small-curvature surface structures, the distance between the optical encoder and the surface to be measured changes, resulting in positioning errors in the ultrasonic detection results, which in turn leads to inaccurate overall detection results and low reliability. In addition, this type of optical encoder cannot verify the validity of the displacement data obtained.

[0007] In summary, in the existing non-destructive testing technology of composite materials, there are common problems such as high cost, low efficiency, and poor versatility of automated C-scanning, and high operation requirements and poor reliability of manual raster ultrasonic scanning. Summary of the Invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide an air-coupled ultrasonic detection system based on a multi-optical encoder and a working method thereof.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] According to one aspect of the present invention, an air-coupled ultrasonic detection system based on a multi-optical encoder is provided, the system comprising a main device, an encoding device, a detection device and a control device;

[0011] The encoding device and the detection device are respectively connected to the main device, and are respectively connected to the control device via a wireless network;

[0012] The encoding device includes multiple optical encoder groups for monitoring the translation and rotational motion of the system to obtain the position information of the ultrasonic guided wave signal; each optical encoder group is composed of a displacement optical encoder 10 and a distance optical encoder 11;

[0013] The detection device includes an air-coupled ultrasonic probe 9 for collecting ultrasonic guided wave signals.

[0014] As a preferred technical solution, the main device is a detection cart body 1, and a plurality of universal wheels 2 are fixedly connected to the bottom of the detection cart body 1.

[0015] As a preferred technical solution, the displacement optical encoder 10 and the distance optical encoder 11 are both equipped with an internal laser emitter 12 and an internal CMOS sensor 13; wherein, the displacement optical encoder 10 is fixedly mounted on the bottom of the detection cart body 1, and the distance between it and the inspected plane is 2 mm, and is used to obtain the two-dimensional moving distance of the system; the distance optical encoder 11 is fixedly mounted on the side of the detection cart body 1, and is used to detect the distance between the displacement encoder and the test piece.

[0016] As a preferred technical solution, the detection device includes an air-coupled ultrasonic probe 9, a signal generator, a preamplifier and a signal receiver; one side of the air-coupled ultrasonic probe 9 is connected to the signal generator, and the other side is connected to the preamplifier, and the output end of the preamplifier is connected to the signal receiver.

[0017] As an optimal technical solution, the control device includes two working modes: a single host computer mode and a coordinated upper and lower computer mode. In the single host computer mode, the host computer is directly connected to the encoding device and the detection device through a wireless network, and independently completes the full process of signal processing, feedback and result display; while in the coordinated upper and lower computer mode, the lower computer is responsible for signal processing and detection process feedback, its input end is wirelessly connected to the encoding device and the detection device, and the output end of the lower computer is connected to the host computer, and the upper computer completes the visualization presentation of the final ultrasonic detection results.

[0018] According to another aspect of the present invention, a method for operating an air-coupled ultrasonic detection system based on a multi-optical encoder is provided, the method comprising the following steps:

[0019] S1. Select the surface area of ​​the composite material structure to be tested and adjust the position of the detection device so that the acoustic wave focus of the air-coupled ultrasonic probe 9 falls on the surface of the structure to be tested;

[0020] S2. Perform system self-check. If any error is found, the control device will be used to feedback abnormal information; otherwise, execute S3;

[0021] S3, pushing the detection system to move along the surface of the structure to be tested, and performing real-time displacement validity determination. If the displacement is invalid, repeat S3; if the displacement is valid, execute S4;

[0022] S4. Collecting ultrasonic guided wave signals using a detection device and simultaneously obtaining ultrasonic probe position information using an encoding device;

[0023] S5. Calculate the inverse of the maximum amplitude within the preset time gate for the ultrasonic guided wave signal, so that the ultrasonic guided wave signal corresponds to the ultrasonic probe position information, thereby generating an ultrasonic C-scan result graph as the final ultrasonic detection result.

[0024] As a preferred technical solution, system self-check includes hardware self-check and communication self-check.

[0025] As a preferred technical solution, in S4, if two optical encoders (l, r) are used, and the ultrasonic probes are measured as (sl, sr) respectively, and the initial coordinates of the sl probe are (0, 0), the corresponding initial coordinates of the l optical encoder are (-s0, 0); and the initial coordinates of the sl probe are (s1+s2, 0), the corresponding initial coordinates of the l optical encoder are (s1, 0); then the specific process of obtaining the ultrasonic probe position information through the encoding device is: first, obtain the corresponding initial coordinates of the ultrasonic probe and the optical encoder, then use the two-dimensional moving distance and the initial coordinates to calculate the steering angle of the probe, and then determine the rotation matrix from the steering angle of the probe; finally, based on the rotation matrix, the two-dimensional moving distance and the initial coordinates, calculate the position information of the ultrasonic probe (sl_final, sr_final); its specific formula is:

[0026]

[0027] Where (xl, yl) is the two-dimensional movement distance detected by the l optical encoder; (xr, yr) is the two-dimensional movement distance detected by the r optical encoder; α is the probe steering angle; R is the rotation matrix; sl_final and sr_final are the position information of the ultrasonic probe; s0, s1, and s2 are the initial coordinate parameters.

[0028] As a preferred technical solution, in S3, the basis for determining the effectiveness of displacement is as follows:

[0029] The first judgment condition: There is any displacement encoder whose x or y direction movement distance exceeds 0.01mm;

[0030] Second determination condition: there is at least one displacement encoder that meets the first determination condition, and the distance between the displacement encoder and the surface of the measured structure is within a preset distance error range;

[0031] When the second determination condition is satisfied, it is determined that the displacement is valid.

[0032] As a preferred technical solution, when any optical encoder group only meets the first judgment condition but does not meet the second judgment condition, it is determined that the optical encoder group is interfered with. At this time, the distance sensor detects the abnormality and transmits the abnormality information back to the control device. The control device uses other optical encoder group data with valid displacement to correct the interfered optical encoder group data.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The encoding device in the present invention includes multiple optical encoder groups, which can effectively monitor the translation and rotational motion of the detection system to obtain the position information of the ultrasonic guided wave signal; and each optical encoder group is composed of a displacement optical encoder and a distance optical encoder; by setting up multiple optical encoder groups for displacement positioning, two-dimensional small curvature surface displacement non-contact portable positioning air-coupled ultrasonic scanning real-time encoding can be realized, and the encoding device is used in conjunction with the detection device and the control device. In the optical encoder group, by combining the displacement optical encoder and the distance optical encoder, the method has strong versatility and simple operation. The encoding device can quickly and accurately obtain position information, verify the validity of the obtained displacement data, and enable automatic position correction of the air-coupled ultrasonic scanning, thereby improving the accuracy and reliability of the detection.

[0035] 2. The detection device efficiently collects ultrasonic guided wave signals, the encoding device obtains the location information of the ultrasonic guided wave signals, and the control device precisely regulates and manages the entire detection process. The close cooperation between the detection device, the control device, and the encoding device forms a highly efficient detection process, resulting in high overall detection efficiency.

[0036] 3. Both the displacement optical encoder and the distance optical encoder in this invention are equipped with internal laser emitters and internal CMOS (Complementary Metal-Oxide–Semiconductor) sensors. The displacement optical encoder is fixedly mounted on the bottom of the inspection cart, with a distance of 2 mm from the inspected surface, and is used to obtain the system's two-dimensional movement distance. The distance optical encoder is fixedly mounted on the side of the inspection cart and is used to detect the distance between the displacement encoder and the test piece. The overall detection accuracy can be adjusted according to the optical encoder's DPI (Dots Per Inch), achieving a resolution of 0.01 mm. The displacement and distance optical encoders work together to ensure high-precision position information acquisition during ultrasonic testing, making the test results more reliable. Furthermore, the rational installation layout and functional division of labor optimize the structural design of the inspection cart, enhance the equipment's adaptability in different testing scenarios, and enable the entire inspection system to operate stably and efficiently even in complex environments.

[0037] 4. In the present invention, the first judgment condition and the second judgment condition are used to judge the validity of the displacement. When it is detected in the judgment process that a certain optical encoder group is interfered, the data of other optical encoder groups with valid displacement are used to correct the interfered optical encoder group data. A method of using multiple optical encoders (positioning and distance two-in-one) to locate defects is proposed, which can effectively solve the problems of defect positioning errors caused by single optical encoder positioning and positioning errors caused by signal interference of multiple optical encoders (positioning error in a certain optical encoder, etc.), thereby improving the accuracy of detection.

[0038] 5. In the present invention, the corresponding initial coordinates of the ultrasonic probe and the optical encoder are first obtained, and then the steering angle of the probe is calculated using the two-dimensional moving distance and the initial coordinates, and then the rotation matrix is ​​determined by the steering angle of the probe; finally, based on the rotation matrix, the two-dimensional moving distance and the initial coordinates, the position information of the ultrasonic probe is calculated. The calculation based on the two-dimensional moving distance can adapt to various movement modes of the probe in the plane, has high flexibility, and the rotation state of the probe is intuitively represented by the rotation matrix, which is convenient for debugging and optimization in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the structure of an air-coupled ultrasonic detection system based on a multi-optical encoder of the present invention;

[0040] Figure 2 Schematic diagram of the structure of the distance optical encoder and the displacement optical encoder of the present invention;

[0041] Figure 3 Schematic diagram of the steps of an air-coupled ultrasonic detection method based on a multi-optical encoder in the present invention;

[0042] Figure 4 A flowchart of collaborative testing of positions obtained by multiple optical encoders and ultrasonic signals in an embodiment;

[0043] Figure 5 Schematic diagram of the test specimen in the embodiment;

[0044] Figure 6 This is a comparison diagram of ultrasonic guided waves with and without delamination defects in the embodiment;

[0045] FIG7( a ) is an imaging diagram of a defect moving along the y direction in an embodiment;

[0046] FIG7( b ) is an imaging diagram of a defect moving along the x direction in an embodiment;

[0047] FIG7( c ) is an overlay image of defect imaging in the xy direction in the embodiment;

[0048] FIG7( d ) is a threshold processing diagram of the overlay image of the defect imaging in the xy direction in the embodiment;

[0049] In the figure, 1 is the detection cart body, 2 is the universal wheel, 3 is the first optical encoder group, 4 is the second optical encoder group, 5 is the third optical encoder group, 6 is the fourth optical encoder group, 7 is the air-coupled ultrasonic probe fixture lifter, 8 is the free-style air-coupled ultrasonic probe fixture, 9 is the air-coupled ultrasonic probe; 10 is the displacement optical encoder, 11 is the distance optical encoder, 12 is the laser emitter inside the optical encoder, and 13 is the CMOS sensor inside the optical encoder. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0051] Composite materials refer to a new material formed by combining two or more materials with different physical and chemical properties through specific process methods. The performance of this material is generally better than that of a single component material, and it has the advantages of light weight, high specific strength, high specific stiffness, corrosion resistance, fatigue resistance, etc., and is widely used in the aerospace field. Since composite materials have the characteristics of multiple component materials, the interface between different materials is extremely unstable due to the existence of surface energy, and various forms of defects are very likely to occur. The service environment of composite materials in the aerospace field is harsh, and the structure and shape are complex. At the same time, the integration of the load-bearing function of aerospace structures places higher requirements on the quality and reliability of composite materials. It is of great significance to develop non-destructive testing technology that can be applied to the quality inspection of complex-shaped structures to improve the application level of composite structures in the aerospace field.

[0052] Non-destructive testing (NDT) is an important quality verification method that can detect internal defects in materials without damaging or slightly damaging structural functions. Guided wave air-coupled ultrasonic testing is a commonly used NDT method with the advantages of being contactless, non-invasive, highly penetrating, and efficient. Compared to traditional ultrasonic testing methods, air-coupled ultrasonic testing is more flexible and is not affected by factors such as environmental coupling agents. It can quickly and conveniently change the test object. Because air is used as a coupling agent, air-coupled ultrasound can fundamentally avoid coupling agent contamination. It can also avoid errors caused by different coupling agent thicknesses during testing, and has the potential for far-field online testing.

[0053] Currently, air-coupled ultrasonic testing (A-scan) of composite structures typically utilizes manual A-scanning or automated C-scanning. Manual A-scanning is often used in the initial stages of inspection due to its ease of operation and adaptability. However, this method has limitations in data recording and result consistency, and inspection quality often depends on the operator's skill level. In contrast, C-scan imaging technology provides more comprehensive defect information. While manual raster scanning can meet C-scanning requirements to a certain extent, it is cumbersome and reliability is difficult to guarantee. Automated C-scanning significantly improves inspection accuracy and stability through mechanized operation, but its high equipment cost and limited scanning range, particularly due to the limited motion capabilities of the robotic arm, pose challenges to its application. In recent years, manual C-scan systems have emerged that utilize devices such as rollers to collect position data. However, these systems still only provide one-dimensional coded positioning and still face challenges such as the requirement for linear raster scanning and insufficient reliability.

[0054] Furthermore, to meet connection requirements, holes and grooves often need to be made on the surface of composite materials, which can easily cause the composite surface to be uneven. Conventional optical encoders require a relatively constant distance to the surface, and such optical encoders cannot verify the validity of the displacement data obtained. Therefore, it is urgent to develop an ultrasonic imaging method that is simple to operate, capable of self-correcting displacement positioning, and can adapt to imaging of uneven, small-curvature surfaces. This method should use an improved optical encoder for two-dimensional position encoding to avoid the limitations of mechanical encoding methods.

[0055] Example 1

[0056] In this embodiment, an air-coupled ultrasonic detection system based on a multi-optical encoder is used, and the system includes a main device, an encoding device, a detection device, and a control device;

[0057] The encoding device and the detection device are respectively connected to the main device, and are respectively connected to the control device via a wireless network;

[0058] The encoding device includes multiple optical encoder groups for monitoring the translation and rotational motion of the system to obtain the position information of the ultrasonic guided wave signal; each optical encoder group is composed of a displacement optical encoder 10 and a distance optical encoder 11;

[0059] The detection device includes an air-coupled ultrasonic probe 9 for collecting ultrasonic guided wave signals.

[0060] Devices such as Figure 1As shown, in this embodiment, four optical encoder groups are arranged around the detection cart body 1, including a first optical encoder group 3, a second optical encoder group 4, a third optical encoder group 5, and a fourth optical encoder group 6. An air-coupled ultrasonic probe 9 is clamped by a free-style air-coupled ultrasonic probe fixture 8, and the fixture is raised and lowered by an air-coupled ultrasonic probe fixture lifter 7.

[0061] In this embodiment, the device is used to perform ultrasonic testing, and the process is as follows: Figure 4 As shown, the process begins with the power-on operation. After powering on, a hardware self-test is first performed. If the self-test fails, "Display 0" is displayed; if it passes, a communication self-test is performed. If the communication self-test fails, "Display 1" is displayed; if the communication self-test passes, "Display 2" is displayed. After display 2, the system is manually moved along the plane. Multiple displacement optical encoders 10 monitor the position movement of the present invention. A real-time check is performed to see if any displacement encoder moves more than 0.01mm in the X and Y directions. If not, the system returns to continue monitoring the displacement; if so, a check is performed to see if at least one displacement encoder with a displacement exceeding 0.01mm is within the error range from the specimen surface (the encoder obtains this data). If not, the system returns to continue monitoring the displacement; if so, data processing and signal manipulation are performed, namely, the multi-displacement optical encoder interpolation algorithm is used to obtain the two-dimensional spatial position of the two ultrasonic probes. The ultrasonic probe transmits and receives signals. The inverse of the maximum amplitude within the specific gate of the guided wave A scan is calculated, and the ultrasonic probe position matches the amplitude and phase points to form a C scan. Finally, the encoder displacement and position data are transmitted back to the host computer.

[0062] The specific steps for its implementation are as follows:

[0063] Step 1: Select the surface area of ​​the composite material structure to be inspected and determine the manual movement route.

[0064] Step 2: Select an air-coupled ultrasonic probe 9 with a suitable center frequency according to the detection requirements and place it in the fixture. Adjust the position of the fixture so that the acoustic wave focus of the air-coupled ultrasonic probe 9 is located on the surface of the structure to be tested;

[0065] Step 3: Based on the selected composite material surface area, select the number and position of the enabled optical encoders and input them into the computer.

[0066] Step 4: Hardware self-check. If any error is found, the lower computer screen will display 0. If no error is found, proceed to the next step.

[0067] Step 5: Two-way communication test between the lower computer and the upper computer. If an error is found, 1 will be displayed on the lower computer screen. If no error is found, proceed to the next step.

[0068] Step 6: When the lower computer screen displays 2, use a manual push method to push the present invention to move horizontally or rotate, and use multiple optical displacement encoders to synchronize test data to monitor the displacement of the air-coupled ultrasonic probe 9. When the displacement of any encoder in the X or Y direction exceeds 0.01 mm, proceed to the next step;

[0069] Step 7: Use the air-coupled ultrasonic probe 9 selected in step 2 to collect ultrasonic guided wave signals, and simultaneously display the results on the host computer monitoring page;

[0070] Step 8: Use the test results of the multi-optical displacement encoder to interpolate and obtain the position information of the air-coupled ultrasonic probe 9, and correspond it with the ultrasonic guided wave data code.

[0071] Step 9: Calculate the inverse of the maximum amplitude within a specific time gate for the ultrasonic guided wave signal collected in step 7, and generate an ultrasonic C-scan result map synchronously with the position information.

[0072] In step 1, the maximum scanning rectangular area is determined based on the location where defects may occur in the composite material, and the length and width data are input into the computer.

[0073] In step three, at least two optical encoders should be selected to ensure that the scanner's translational and rotational motion can be monitored. The principle for selecting optical encoders is to ensure that at least two optical encoders maintain a fixed distance from the test piece surface at all times during the scanning process. If the moving optical encoder experiences interference (e.g., a change in distance from the test piece surface) during scanner motion, the distance sensor will detect the anomaly and transmit this information to the host computer. The remaining optical encoders 10, which are functioning normally, will then use the data from the abnormal displacement sensor to correct the abnormal displacement.

[0074] In step 4, the air-coupled ultrasonic probe 9 can be freely moved, including but not limited to translation and rotation, while ensuring that the acoustic wave focal point is located on the surface of the structure being measured. The hardware self-test includes but is not limited to a single slave device as a master device and multiple optical encoders as slave devices, or a single slave device as a master device and multiple slave devices connected to multiple optical encoders, communicating with each other, such as SPI communication.

[0075] In step 5, bidirectional communication involves communication between multiple optical encoders and the master device's slave computer, or between multiple optical encoders and multiple slave device slave computers, or between slave device slave computers and the master device's slave computer. The displacement information from the optical encoders is transmitted to the host computer via a wireless transmitter. Wires are used to connect the signal generator to the air-coupled ultrasonic transmitter probe, the air-coupled ultrasonic receiver probe to the preamplifier, and the preamplifier to the signal receiver. The signal generator, signal receiver, and signal processor are then connected together, and finally, the computer and signal processor are connected to form the experimental data collection system.

[0076] In step 6, when one or more displacement optical encoders 10 are detected to have displaced more than 0.01 mm, a simultaneous check is performed to determine whether the distance between at least one displacement optical encoder 10 and the specimen surface is within 2 ± 0.1 mm. If this is within the error range, the displacement is determined to be valid and the subsequent steps are performed. Assume that two optical encoders (l, r) are enabled, arranged on either side of the device, and two ultrasonic probes (sl, sr) are aligned with the optical encoders. That is, the initial coordinates sl_init of the sl probe are (0, 0). Then, the initial coordinates l_init of the l optical encoder are (-s0, 0), the initial coordinates r_init of the r optical encoder are (s1+s2, 0), and the initial coordinates sr_init of the sr probe are (s1, 0). When the device moves a certain distance on the specimen surface (assuming translation and rotation), the l optical encoder detects a two-dimensional movement distance of (xl, yl), and the r optical encoder detects a two-dimensional movement distance of (xr, yr). Then the final coordinates of the two ultrasonic probes, sl_final and sr_final, are:

[0077]

[0078] In step 7, the abscissa of the ultrasonic A scan represents the time series of acquisition, and the ordinate represents the amplitude information of the ultrasonic signal. The abscissa of the ultrasonic C scan represents the horizontal coordinate points of the scanning area, and the ordinate represents the vertical coordinate points of the scanning area. The brightness represents the defect probability of the current scanning area (the higher the brightness, the greater the defect probability).

[0079] This embodiment utilizes a system using multiple optical encoders (displacement + distance encoders) for two-dimensional, portable, non-contact positioning of small-curvature surfaces, combined with air-coupled ultrasonic testing equipment for defect detection, location, and characterization. This technology has been validated on ABS additive manufacturing composite material specimens.

[0080] In this embodiment, a composite material containing delamination defects is used as a test sample; the test sample is as follows: Figure 5 As shown; the surface of the sample is flat and the dimensions are 200 mm long × 200 mm wide × 0.6 mm thick, among which three square layer-missing holes with plane dimensions of 8 mm × 8 mm, 12 mm × 12 mm, and 5 mm × 5 mm and a thickness of 0.2 mm are evenly distributed parallel to the center axis of the sample plane and 0.2 mm away from the surface in the thickness direction.

[0081] First, build the model Figure 1 and Figure 2The experimental system shown has a detection range of 136 mm × 136 mm. Multiple optical encoders interactively monitor the displacement of the air-coupled ultrasonic probe 9. When the displacement of the air-coupled ultrasonic probe 9 exceeds 0.01 mm, the computer controls the air-coupled ultrasonic excitation probe to emit ultrasonic waves with a center frequency of 100 kHz. The ultrasonic waves propagate through the coupling medium air into the test sample and propagate in the sample in the form of guided waves. After the ultrasonic waves have an effect on the expected action area and the sample, they are received by the air-coupled receiving probe, amplified by the pre-receiving amplifier, and input into the computer. The signal processing and data analysis are controlled by the signal processing software.

[0082] In this embodiment, when the ultrasonic probe scans an area without defects and an area with delamination defects, the received ultrasonic guided waves take on different forms, such as Figure 6 As shown. It can be seen that when the ultrasonic guided wave passes through the delamination defect, due to the discontinuity of the acoustic impedance, it will generate obvious reflection waves at the defect boundary. Part of the guided wave will penetrate the delamination defect, but its amplitude will be reduced. Therefore, this experiment uses the reciprocal of the maximum value within the first arrival wave range of the collected ultrasonic guided wave transmission signal As the characterization coefficient of delamination defects, Figure 6 Delamination and defect-free They are 0.0031 and 0.0014 respectively.

[0083] Next, the ultrasonic scanning device is scanned in the x-direction and y-direction of the specimen (i.e., scanned twice), and the positioning is performed by the optical encoder. The results are normalized as follows Figure 7a , b. Figure 7a It can be seen that large bright stripes appear near y=8, 58, and 103 mm, indicating that the probability of delamination defects occurring at these three locations is relatively high. Figure 7b It can be seen that a large bright strip appears near x=52mm, indicating that the probability of delamination defects is high here. Figure 7a The data of b are fused together to form Figure 7c , it can be seen Figure 7c The interference is too great to clearly determine the location of the defect. Figure 7c Update the threshold and get Figure 7d .exist Figure 7d There are three obvious bright spots, namely delamination defects, with the center positions at (52, 8), (52, 58), and (52, 103) mm, which are the same as the positions of the delamination defects of 5, 12, and 8 mm in the actual test specimens used.

[0084] Example 2

[0085] In this embodiment, a working method of an air-coupled ultrasonic detection system based on a multi-optical encoder is applied. The method is applied to an air-coupled ultrasonic detection system based on a multi-optical encoder as in Example 1. The method steps are as follows: Figure 3 As shown, specifically including:

[0086] S1. Select the surface area of ​​the composite material structure to be tested and adjust the position of the detection device so that the acoustic wave focus of the air-coupled ultrasonic probe 9 falls on the surface of the structure to be tested;

[0087] S2. Perform system self-check. If any error is found, the control device will be used to feedback abnormal information; otherwise, execute S3;

[0088] S3, pushing the detection system to move along the surface of the structure to be tested, and performing real-time displacement validity determination. If the displacement is invalid, repeat S3; if the displacement is valid, execute S4;

[0089] S4. Collecting ultrasonic guided wave signals using a detection device and simultaneously obtaining ultrasonic probe position information using an encoding device;

[0090] S5. Calculate the inverse of the maximum amplitude within the preset time gate for the ultrasonic guided wave signal, so that the ultrasonic guided wave signal corresponds to the ultrasonic probe position information, thereby generating an ultrasonic C-scan result graph as the final ultrasonic detection result.

[0091] Among them, system self-test includes hardware self-test and communication self-test.

[0092] In S4, if two optical encoders (l, r) are used, and the ultrasonic probes are measured as (sl, sr), and the initial coordinates of the sl probe are (0, 0), the corresponding initial coordinates of the l optical encoder are (-s0, 0); and the initial coordinates of the sl probe are (s1+s2, 0), the corresponding initial coordinates of the l optical encoder are (s1, 0); then the specific process of obtaining the ultrasonic probe position information through the encoding device is: first, obtain the corresponding initial coordinates of the ultrasonic probe and the optical encoder, then use the two-dimensional moving distance and the initial coordinates to calculate the steering angle of the probe, and then determine the rotation matrix from the steering angle of the probe; finally, based on the rotation matrix, the two-dimensional moving distance and the initial coordinates, the ultrasonic probe position information (sl_final, sr_final) is calculated; the specific formula is:

[0093]

[0094] Where (xl, yl) is the two-dimensional movement distance detected by the l optical encoder; (xr, yr) is the two-dimensional movement distance detected by the r optical encoder; α is the probe steering angle; R is the rotation matrix; sl_final and sr_final are the position information of the ultrasonic probe; s0, s1, and s2 are the initial coordinate parameters.

[0095] In S3, the basis for determining the validity of displacement is as follows:

[0096] The first judgment condition: There is any displacement encoder whose x or y direction movement distance exceeds 0.01mm;

[0097] Second determination condition: there is at least one displacement encoder that meets the first determination condition, and the distance between the displacement encoder and the surface of the measured structure is within a preset distance error range;

[0098] When the second determination condition is satisfied, it is determined that the displacement is valid.

[0099] When any optical encoder group only meets the first judgment condition but does not meet the second judgment condition, it is determined that the optical encoder group is interfered with. At this time, the distance sensor detects the abnormality and transmits the abnormality information back to the control device. The control device uses other optical encoder group data with valid displacement to correct the interfered optical encoder group data.

[0100] In summary, this method enables real-time encoding of two-dimensional, small-curvature surface displacements using non-contact, portable air-coupled ultrasonic scanning, as well as automatic position correction for air-coupled ultrasonic scanning. This addresses the high cost, low efficiency, and poor versatility of automated C-scanning, and the high operational requirements and poor reliability of manual raster ultrasonic scanning. One method, displacement positioning based on an optical encoder, effectively detects planar motions such as translation and rotation, with accuracy adjustable based on the optical encoder's DPI, achieving a resolution of 0.01mm.

[0101] Moreover, the method of defect positioning using multiple optical encoders (positioning and distance two-in-one) can effectively solve the problems of defect positioning errors caused by single optical encoder positioning and positioning errors caused by signal interference of multiple optical encoders (positioning error in a certain optical encoder, etc.).

[0102] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. An air-coupled ultrasonic detection system based on multiple optical encoders, characterized in that: The system includes a main device, an encoding device, a detection device and a control device; The encoding device and the detection device are respectively connected to the main device, and are respectively connected to the control device via a wireless network; The encoding device includes a plurality of optical encoder groups for monitoring the translation and rotational motion of the system to obtain position information of the ultrasonic guided wave signal; each optical encoder group is composed of a displacement optical encoder (10) and a distance optical encoder (11); The detection device comprises an air-coupled ultrasonic probe (9) for collecting ultrasonic guided wave signals.

2. The air-coupled ultrasonic detection system based on multiple optical encoders according to claim 1, characterized in that: The main device is a detection cart body (1), and a plurality of universal wheels (2) are fixedly connected to the bottom of the detection cart body (1).

3. The air-coupled ultrasonic detection system based on multiple optical encoders according to claim 2, characterized in that: The displacement optical encoder (10) and the distance optical encoder (11) are both equipped with an internal laser emitter (12) and an internal CMOS sensor (13); wherein the displacement optical encoder (10) is fixedly mounted on the bottom of the detection cart body (1), and the distance between it and the inspected plane is 2 mm, and is used to obtain the two-dimensional moving distance of the system; the distance optical encoder (11) is fixedly mounted on the side of the detection cart body (1), and is used to detect the distance between the displacement encoder and the test piece.

4. The air-coupled ultrasonic detection system based on multiple optical encoders according to claim 1, characterized in that: The detection device comprises an air-coupled ultrasonic probe (9), a signal generator, a preamplifier and a signal receiver; one side of the air-coupled ultrasonic probe (9) is connected to the signal generator, and the other side is connected to the preamplifier, and the output end of the preamplifier is connected to the signal receiver.

5. The air-coupled ultrasonic detection system based on multiple optical encoders according to claim 1, characterized in that: The control device includes two working modes: single host computer mode and upper and lower computer collaborative mode. In the single host computer mode, the host computer is directly connected to the encoding device and the detection device through a wireless network, and independently completes the whole process of signal processing, feedback and result display; while in the upper and lower computer collaborative mode, the lower computer is responsible for signal processing and detection process feedback, its input end is wirelessly connected to the encoding device and the detection device, and the output end of the lower computer is connected to the host computer, and the upper computer completes the visualization presentation of the final ultrasonic detection results.

6. A working method of an air-coupled ultrasonic detection system based on a multi-optical encoder, characterized in that: The method is applied to an air-coupled ultrasonic detection system based on a multi-optical encoder as described in any one of claims 1 to 5, and the method steps include: S1. Select the surface area of ​​the composite material structure to be tested and adjust the position of the detection device so that the acoustic wave focus of the air-coupled ultrasonic probe falls on the surface of the structure to be tested; S2. Perform system self-check. If any error is found, the control device will be used to feedback abnormal information; otherwise, execute S3; S3, pushing the detection system to move along the surface of the structure to be tested, and performing real-time displacement validity determination. If the displacement is invalid, repeat S3; if the displacement is valid, execute S4; S4. Collecting ultrasonic guided wave signals using a detection device and simultaneously obtaining ultrasonic probe position information using an encoding device; S5. Calculate the inverse of the maximum amplitude within the preset time gate for the ultrasonic guided wave signal, so that the ultrasonic guided wave signal corresponds to the ultrasonic probe position information, thereby generating an ultrasonic C-scan result graph as the final ultrasonic detection result.

7. The working method of the air-coupled ultrasonic detection system based on multiple optical encoders according to claim 6, characterized in that: The system self-check includes hardware self-check and communication self-check.

8. The working method of the air-coupled ultrasonic detection system based on multiple optical encoders according to claim 6, characterized in that: In S4, if two optical encoder groups (l, r) are used, and the ultrasonic probes are measured as (sl, sr), and the initial coordinates of the sl probe are (0, 0), corresponding to the initial coordinates of the l optical encoder are (-s0, 0); and the initial coordinates of the sl probe are (s1+s2, 0), corresponding to the initial coordinates of the l optical encoder are (s1, 0); then the specific process of obtaining the ultrasonic probe position information through the encoding device is: first, obtaining the corresponding initial coordinates of the ultrasonic probe and the optical encoder, then using the two-dimensional moving distance and the initial coordinates to calculate the steering angle of the probe, and then determining the rotation matrix from the steering angle of the probe; finally, based on the rotation matrix, the two-dimensional moving distance and the initial coordinates, the ultrasonic probe position information (sl_final, sr_final) is calculated; its specific formula is: Where (xl, yl) is the two-dimensional movement distance detected by the l optical encoder; (xr, yr) is the two-dimensional movement distance detected by the r optical encoder; α is the probe steering angle; R is the rotation matrix; sl_final and sr_final are the position information of the ultrasonic probe; s0, s1, and s2 are the initial coordinate parameters.

9. The working method of the air-coupled ultrasonic detection system based on multiple optical encoders according to claim 6, characterized in that: In S3, the displacement validity is determined based on the following: The first judgment condition: There is any displacement encoder whose x or y direction movement distance exceeds 0.01mm; Second determination condition: there is at least one displacement encoder that meets the first determination condition, and the distance between the displacement encoder and the surface of the measured structure is within a preset distance error range; When the second determination condition is satisfied, it is determined that the displacement is valid.

10. The working method of the air-coupled ultrasonic detection system based on multiple optical encoders according to claim 9, characterized in that: When any optical encoder group only meets the first judgment condition but does not meet the second judgment condition, it is determined that the optical encoder group is interfered with. At this time, the distance sensor detects the abnormality and transmits the abnormality information back to the control device. The control device uses other optical encoder group data with valid displacement to correct the interfered optical encoder group data.

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