A full-field non-contact health monitoring method and device for large structures

Abstract

A full-field non-contact health monitoring method for large structures mainly includes: S1: Divide the monitoring sub-areas; divide the area to be monitored into multiple sub-areas to be measured; arrange multiple distributed channel-separated speckle interferometers to synchronously image and monitor each sub-area to be measured respectively; S2: Obtain speckle interferograms and dual-channel color images; make the object to be monitored deformed; collect the speckle interferograms and dual-channel color images before and after the deformation of the sub-areas to be measured respectively; S3: Process the speckle interferograms; process the speckle interferograms before and after deformation, extract the phase fringe pattern reflecting the defect information of the sub-areas to be measured, and determine the defect morphology; S4: Stitch the monitoring data; stitch the dual-channel images captured for each sub-area to be measured; use the stitching parameters of the dual-channel images obtained before and after stitching to perform geometric transformation and fusion on the phase change information to generate full-field monitoring data, and obtain the defect positions and damage evolution of the object to be monitored.

Description

Technical Field

[0001] The present invention relates to structural health monitoring technology, and particularly to a full-field non-contact health monitoring method and device for large structures. Background Art

[0002] Structural health monitoring technology is a technical means for evaluating the health status and safety of a structure by real-time monitoring and analyzing the physical parameters of the structure. Large structures such as murals, wings, bridges, etc. are often affected by natural environments and various loads, etc., and defects such as cracks, deformations, and corrosion will occur. The health monitoring of large structures is crucial for ensuring public safety and the long-term stability of the structure. Therefore, it is necessary to timely and accurately monitor the potential damage of the structure, take repair measures in advance, and avoid accidents.

[0003] The large measured area is the main difficulty in the health monitoring of large structures. Traditional contact monitoring methods have problems such as low spatial resolution, weak static monitoring ability, and temperature sensitivity. For example, health monitoring methods based on optical fiber sensing (CN202411018913.6, CN202323077267.4) are easily affected by multiple parameters such as temperature, stress, and light during use and have low spatial resolution, making it difficult to ensure the measurement accuracy and damage location accuracy; monitoring methods based on piezoelectric sensing (CN201910160196.3) are often used for dynamic signal monitoring, difficult to measure static strain, and the defect location accuracy depends on the sensor layout density; acoustic emission-based monitoring methods (CN202410327181.2) are often used for post-damage detection and difficult to achieve early warning at the time of damage initiation; ultrasonic guided wave (CN202410868821.0) technology has material and geometric dependence and is sensitive to temperature changes.

[0004] Full-field non-contact optical detection technology can avoid direct contact with the object to be measured, reduce human damage, and can perform rapid scanning of the entire surface, which is an ideal method for structural health monitoring. However, structural health monitoring methods that solely rely on algorithms such as image matching and recognition (CN202311817843.6) usually have their deformation measurement resolution limited by the physical resolution of digital cameras and face problems such as massive data transmission and calculation during full-field monitoring. Shearing speckle interferometry technology (for example, patents with application numbers CN202010237587.3 and CN202410138923.7) is a full-field non-contact optical measurement method based on laser speckle interferometry. It obtains the deformation information of the object to be measured by calculating the phase difference in the speckle patterns before and after the deformation of the object to be measured, and has advantages such as high deformation measurement resolution and small calculation amount. However, limited by factors such as laser power and measurement field of view, existing shearing speckle interferometry technology is often used for defect detection of small components or small areas such as tires and steel structure solder joints and cannot be applied to the health monitoring of large structures. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the present invention provides a full-field non-contact health monitoring method and device for large structures, realizing high-resolution, full-field, non-contact health monitoring of large structures.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A full-field non-contact health monitoring method for large structures, comprising the following steps:

[0008] S1. Divide the sub-areas to be measured; divide the area to be monitored into a plurality of the sub-areas to be measured; arrange a plurality of distributed channel-separated speckle interferometers to synchronously image and monitor each of the sub-areas to be measured;

[0009] S2. Obtain speckle interferograms and dual-channel color images; cause the object to be monitored to deform; respectively collect the speckle interferograms and dual-channel color images before deformation of the sub-areas to be measured; respectively collect the speckle interferograms and dual-channel color images after deformation of the sub-areas to be measured;

[0010] S3. Process the speckle interferograms; process the speckle interferograms before deformation and the speckle interferograms after deformation, extract the phase fringe pattern reflecting the defect information of the sub-areas to be measured, and determine the defect morphology;

[0011] S4. Stitch the monitoring data; stitch the dual-channel color images captured by each of the sub-areas to be measured; use the stitching parameters of the dual-channel color images obtained before and after stitching to perform geometric transformation and fusion on the phase change information, generate full-field monitoring data, locate the defect, and obtain the evolution of the damage of the object to be monitored.

[0012] Preferably, the channel-separated speckle interferometer (hereinafter uniformly referred to as the speckle interferometer) has a plurality of color channels, one of the color channels records the speckle interferogram generated by the interferometer, and the other color channels record images of other bands except the color of the laser band of the speckle interferometer (hereinafter uniformly referred to as dual-channel color images); the speckle interferogram is used for defect monitoring, and the dual-channel color image is used to guide the stitching of monitoring data.

[0013] Preferably, the step S1 includes:

[0014] S1.1. Divide the area to be monitored into a plurality of the sub-areas to be measured, arrange the speckle interferometers at equal intervals, turn on each of the speckle interferometers, and adjust the angle and position so that the speckle interferometer vertically observes the surface of the sub-areas to be measured, and there is partial overlap between the images of adjacent sub-areas to be measured;

[0015] S1.2. Adjust the optical lens and the first mirror to ensure that the imaging of the sub-region to be measured is clear and has no ghosting;

[0016] S1.3. Turn on the laser and adjust the second mirror to misalign the image in the channel where the laser speckle is located.

[0017] Preferably, the step S2 specifically includes:

[0018] S2.1. According to the equal-step long-time phase-shifting method, synchronously control the piezoelectric ceramics to achieve multiple phase shifts, and synchronously record the speckle interference pattern and the dual-channel color pattern before deformation of the area to be monitored each time after phase shift;

[0019] S2.2. Make the area to be monitored deformed by a non-contact method;

[0020] S2.3. Again, according to the equal-step long-time phase-shifting method, synchronously control the piezoelectric ceramics to achieve multiple phase shifts, and synchronously record the speckle interference pattern and the dual-channel color pattern after deformation of the area to be monitored each time after phase shift.

[0021] Preferably, the step S3 includes: Using the time phase-shifting algorithm to solve the phase diagram before deformation and the phase diagram after deformation of each sub-region to be measured, and performing subtraction calculation to obtain the phase change diagram (also known as the phase fringe pattern) caused by the deformation of the sub-region to be measured, and determining the defect morphology.

[0022] Preferably, the step S4 includes:

[0023] S4.1. Perform image registration on the dual-color channel maps corresponding to each area to be monitored, obtain the image geometric transformation model, and search for the optimal stitching line;

[0024] S4.2. Use the geometric transformation model and the optimal stitching line to stitch the phase fringe patterns corresponding to each area to be monitored to obtain the global monitoring data, and locate the defect based on this.

[0025] A distributed full-field non-contact health monitoring device, comprising:

[0026] Multiple said speckle interferometers, and the monitoring areas of adjacent said speckle interferometers partially overlap;

[0027] A synchronous control module, used to trigger the speckle interferometers to synchronously collect images;

[0028] The speckle interferometer includes a laser, a beam expander, a first imaging lens, a second imaging lens, a convex lens, a beam splitter prism, a first mirror, a second mirror, an optical adjustment mount, a piezoelectric ceramic, a band-pass filter, and a color camera. The laser beam emitted by the laser is expanded by the beam expander and then irradiated onto the surface of the object to be measured. After diffuse reflection from the surface of the object to be measured, it enters the beam splitter prism through the first imaging lens and the convex lens. After the beam splitter prism divides the laser beam into two beams, they are respectively transmitted to the color camera through the first mirror and the second mirror. The first mirror is connected to the piezoelectric ceramic. The second mirror is connected to the optical adjustment mount. The band-pass filter is provided on the optical path between the second mirror and the beam splitter prism.

[0029] Preferably, the first imaging lens and the second imaging lens are used to expand the field of view of the speckle interferometer. The convex lens is provided between the equivalent optical paths of the first imaging lens and the second imaging lens. The first imaging lens is used for focusing the speckle interferometer.

[0030] Preferably, the transmission band of the band-pass filter matches the wavelength of the laser, and reflects light other than the transmission band. The transmission band range includes the band of the light generated by the laser.

[0031] Preferably, the first mirror is connected to the piezoelectric ceramic, and the first mirror generates displacement by adjusting the voltage applied to the piezoelectric ceramic. The second mirror is mounted on the optical adjustment mount, and the reflection direction and reflection angle of the transmitted light can be changed by angle adjustment, thereby adjusting the shear direction and shear amount of the speckle interferometer.

[0032] Since the area to be monitored of large structures (such as murals, building structures, etc.) is very large, using only a single speckle interferometer will not be able to ensure full coverage of the area to be measured and high spatial resolution simultaneously due to the limitation of the field of view. The entire area to be measured is divided into several smaller sub-areas, and each sub-area corresponds to a speckle interferometer. The speckle interferometer is used to synchronously image and monitor each sub-area respectively, which can ensure that the defects and diseases of each sub-area can be monitored, and avoid the loss of monitoring information due to the limitation of the field of view. When imaging each sub-area, the images of adjacent sub-areas need to partially overlap. The above overlap helps with image registration during subsequent image stitching, ensuring that there are no gaps, misalignments, or other stitching errors in the stitched image.

[0033] Therefore, the full-field non-contact health monitoring device for distributed large structures of the present invention includes multiple sets of identical speckle interferometers. The areas photographed between adjacent speckle interferometers partially overlap, and the image acquisition signals between each speckle interferometer are synchronized, and can synchronously record the images of each sub-area to be measured.

[0034] Since the speckle image dislocation is a necessary condition for real - time speckle shearing interference, and the dislocation of the image will cause difficulties in image registration during image stitching, which will lead to image stitching errors. Separating the channels of the images recorded by the color camera in the speckle interferometer according to the wavelength of the laser can ensure that image stitching and defect monitoring do not interfere with each other.

[0035] Since different color cameras use different methods to record image colors, in order to make the technical means, creative features, and achieved purposes of the present invention easy to understand, the present invention is described by taking the Bayer array color camera as an example. However, the color cameras, image channels, etc. involved in the present invention are not limited to the Bayer array type. The following will further describe the present invention by taking the Bayer array color camera as the photosensitive element of the speckle interferometer.

[0036] The Bayer array image sensor is a commonly used color digital image sensor. It realizes the acquisition of color information (images) by arranging micro - filters of different colors (usually red, green, and blue) on the image sensor. In a Bayer array color camera, the photosensitive units of green (G) account for 50% of the total area of the camera's photosensitive chip, and the photosensitive units of red (R) and blue (B) each account for 25%. This means that the G - channel image has a higher effective spatial resolution. By selectively transmitting green light and using the G - channel for defect monitoring, the high - resolution characteristics of the G - channel can be fully utilized to effectively capture the defect information in the image and accurately identify the defect location. A band - pass filter can selectively transmit light within a specific wavelength range and reflect light of other wavelengths. In the present invention, the selected band - pass filter can transmit green light and reflect red and blue light. It should be noted that the selection of the band - pass filter depends on the image channel for defect monitoring. For non - Bayer array type color cameras, other color channels can be selected for defect monitoring, and correspondingly, the band - pass filter should be able to transmit the light of that color and reflect the light of other colors.

[0037] Although the RB channels in the Bayer array only account for 50% of the total area of the image sensor, they can collect red and blue information simultaneously. Therefore, the RB - channel images collected by the Bayer array color camera can provide accurate edge information, stably reflect the overall structure of the image, help the algorithm better perform image registration, reduce stitching errors, ensure the accuracy of image stitching, and provide reliable stitching parameters for monitoring data stitching.

[0038] During the instrument layout stage of actual monitoring, the area to be monitored is divided into multiple sub - areas to be measured, the speckle interferometers are arranged at equal intervals, each speckle interferometer is turned on, and the angle and position are adjusted so that the speckle interferometer vertically observes the surface of the sub - area to be measured, and there is partial overlap between the images of adjacent sub - areas to be measured.

[0039] After determining the arrangement positions of the speckle interferometers, adjust the mirrors in the speckle interferometers so that the images captured by the speckle interferometers have no ghosting. Adjust the angles or positions of the mirrors so that the images collected by the speckle interferometers completely overlap (no image misalignment), ensuring that all color channels (R, G, B) in the imaging system are aligned with the same target area, avoiding image stitching errors caused by subsequent image ghosting, reducing imaging errors, and improving the stability and reliability of the system.

[0040] Turn on the laser of the speckle interferometer, adjust the tilt angle and tilt direction of the mirror in the optical path behind the band-pass filter, change the propagation path of part of the green light, and cause ghosting (overlapping images with slight misalignment) in the speckle interferogram of the G channel, that is, cause image dislocation in the speckle interferogram of the G channel.

[0041] When irradiating the measured sub-region with coherent light, the rough surface of the measured sub-region will diffusely reflect the incident coherent light and form speckles in space. These speckles form a speckle interferogram through the interferometer, and the phase information in the interferogram contains the information of the measured surface. By extracting and processing the speckle information before and after the deformation of the measured surface, the deformation information of the measured surface can be obtained. In interference measurement, piezoelectric ceramics are usually used to precisely control the optical path difference. Connect the piezoelectric ceramics to the optical element (the above-mentioned mirror), and by applying different voltages, the piezoelectric ceramics can precisely move the mirror, thereby introducing a specific optical path difference (phase change) in the optical path. In order to accurately extract the phase information in the speckle interferogram, multiple phase shifts are required. Then, combined with relevant algorithms (such as the four-step phase shift algorithm), the phase information in the speckle interferogram can be extracted. By comparing the phase information before and after the deformation of the measured sub-region, quantitative analysis of the surface micro-deformation, defect position and morphology of the measured sub-region can be realized.

[0042] During the monitoring process, perform non-contact deformation such as infrared heating on the measured area to cause micro-deformation of the measured area. Infrared heating will cause a certain deformation of the measured area, resulting in a change in the phase of its diffusely reflected light, correspondingly causing a change in the speckles. The surface deformation information of the measured sub-region after deformation can be extracted by the phase shift method.

[0043] After the measured area is deformed, control the piezoelectric ceramics to achieve multiple equal-step phase shifts, and collect the deformed speckle interferograms after each phase shift. Extract the phase information after deformation (phase map after deformation) through the phase shift algorithm; the deformed speckle interferogram contains the deformed G-channel image and RB-channel image.

[0044] Subtract the phase diagram before deformation and the phase diagram after deformation, where each measured sub-region corresponds to a pair of phase diagrams before and after deformation. The result of the subtraction is called the "phase fringe pattern" or "phase change diagram". The phase fringe pattern reflects the deformation of the surface of the measured area, and it can quantitatively display the surface deformation amount and local deformation degree of the measured area. Since defects on the surface or near-surface of the measured area will cause sudden changes in the deformation at the location of the defects, which is reflected as sudden changes in the phase change on the phase fringe pattern, the size and location of the defects can be determined by observing the phase fringe pattern.

[0045] The pixel coordinates between the color channels of the images captured by the color camera correspond one by one. Therefore, the pixel coordinate positions of the RB channel image and the G channel image collected by the interferometer also completely correspond. Since the phase fringe pattern is obtained by calculating the speckle interferogram of the G channel, the pixel coordinates of the phase fringe pattern corresponding to each measured sub-region and the RB channel image completely correspond. For example, the monitoring result corresponding to the pixel coordinate position (a, b) in the RB channel image is the monitoring data corresponding to the pixel coordinate position (a, b) in the phase fringe pattern.

[0046] Therefore, the change relationship of the coordinate positions of each pixel point before and after the RB image splicing is the change relationship of the coordinate positions of each pixel point before and after the splicing of the phase fringe pattern (corresponding to the G channel image). First, perform image registration on the RB channel images corresponding to each measured area, obtain the image geometric transformation model, and search for the optimal stitching line to complete the image stitching of the RB channel. Using the above geometric transformation model and the optimal stitching line, stitch the corresponding phase fringe pattern (corresponding to the G channel image) to realize the stitching of the monitoring data.

[0047] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0048] The present invention adopts a special optical design for a single speckle interferometer, and simultaneously realizes the acquisition of the speckle interferogram (G channel) and the dual-channel color image (RB channel) of the measured object synchronously; on this basis, a distributed large-scale structural health monitoring device is constructed by using multiple speckle interferometers, breaking through the field of view limitation of a single interferometer; a method of guiding the stitching of monitoring data by stitching color images is proposed, reducing the computational complexity of the stitching of monitoring data, and realizing non-contact full coverage of the large-scale structure to be monitored while ensuring the detection resolution, and solving the problem of low efficiency of traditional monitoring methods. Through the collaborative innovation of optics and computing, the present invention overcomes the contradiction between "high precision" and "large field of view" in large-scale structural health monitoring, and provides an efficient and reliable technical means for the health assessment of infrastructure, cultural heritage and other fields. Description of the Drawings

[0049] Figure 1 It is a schematic flowchart of the method in Embodiment 2;

[0050] Figure 2 It is a schematic structural diagram of a single-channel separated speckle interferometer in Embodiment 1;

[0051] Figure 3 It is a schematic optical path diagram of a single-channel separated speckle interferometer in Embodiment 1;

[0052] Figure 4 It is a scene illustration diagram of a multi-channel separated speckle interferometer for monitoring the health of murals in Embodiment 2;

[0053] Figure 5 It is a schematic diagram of separating Bayer array color images into two types of channel data in Embodiment 2;

[0054] Figure 6 It is a schematic flow diagram of stitching the guiding monitoring data (phase fringe pattern) of the RB channel image in Embodiment 2.

[0055] Among them:

[0056] 1. Laser; 2. Beam expander; 3. First imaging lens; 4. Lens; 5. Beam splitting prism; 6. First mirror; 7. Piezoelectric ceramic; 8. Band-pass filter; 9. Second mirror; 10. Optical adjustment mount; 11. Second imaging lens; 12. Color camera. Specific implementation manners

[0057] In order to make the technical means, creative features, achieved purposes and effects of the invention easy to understand, the present invention is further described below in conjunction with specific drawings. However, the present invention is not limited to the following implemented cases.

[0058] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the implementable conditions of the present invention. Therefore, they do not have technical essence. Any modification of the structure, change of the ratio relationship or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0059] Embodiment 1 (Channel-separated speckle interferometer):

[0060] A channel-separated speckle interferometer is constructed by using a laser, a beam splitter, a mirror, a band-pass filter, an imaging module, a control module, etc.; the interferometer can respectively record the RB channel image and the G channel image of the object to be monitored; among them, the G channel image is used for defect monitoring, and the RB channel image is used for guiding the stitching of monitoring data.

[0061] As Figure 2 shown is a channel-separated speckle interferometer, Figure 3The corresponding optical path diagram is as follows: The laser emitted by the laser 1, after passing through the beam expander 2, irradiates the object to be measured, and then enters the beam splitter prism 5 after being diffusely reflected by the surface of the object to be measured; the beam splitter prism 5 divides the laser into two beams, which are projected onto the color camera 12 after being reflected by the first mirror 6 and the second mirror 9 respectively; the first mirror 6 is connected to the piezoelectric ceramic 7; a band-pass filter 8 is provided on the optical path between the second mirror 9 and the beam splitter prism 5, which is used to transmit green light and reflect blue light and red light.

[0062] The laser 1 is used to emit green laser light. The beam expander 2 is used to expand the laser beam emitted by the laser 1 to cover a larger surface to be measured. The rough surface of the object to be measured will diffusely reflect the irradiated laser, and the diffusely reflected light will interfere with each other in space to form speckles. The first imaging lens 3 is responsible for focusing the interferometer to adapt to different measurement distances. The lenses 4 and the lens 11 are used to expand the field of view of the interferometer so that it can observe a larger area. The beam splitter prism 5, in this embodiment, a beam splitter prism with a transmission-to-reflection ratio of 1:1 is adopted, which divides the transmitted laser into two beams with equal light intensities. One beam of light is projected onto the first mirror 6; the other beam of light is projected onto the band-pass filter 8. After that, the red and blue partial lights are reflected by the band-pass filter, and the green partial light passes through the band-pass filter and is reflected by the second mirror 9. In this device, we choose a narrow-band band-pass filter that only allows green light within a specific wavelength range to pass through, while effectively reflecting blue and red light. This can ensure that only green light of a specific wavelength participates in the speckle interference, improving the accuracy of the interference. The first mirror 6 can reflect red, green, and blue light. The piezoelectric ceramic 7 is connected to the first mirror 6, and by applying a voltage, the first mirror 6 can be precisely pushed to introduce a specific phase (optical path difference) change in the optical path. The second mirror 9 only reflects the green light beam. The optical adjustment mount 10 is connected to the second mirror 9 and is used to adjust the tilt angle and tilt direction of the second mirror 9, correspondingly adjusting the shear amount and shear direction, so that the system can adapt to different measurement requirements and improve the flexibility and accuracy of its measurement. The above two beams of coherent light (G channel) passing through different optical paths are reflected by the first mirror 6 and the second mirror 9, and then converge again through the beam splitter prism 5 and finally reach the imaging target surface of the color camera 12 at the same time to form a speckle interference image. The color camera 12 is used to record the RB channel map of the object to be measured and the speckle interference map of the G channel. Among them, the speckle interference map records the phase information of the surface of the object to be measured, providing data support for subsequent defect monitoring and analysis. By using the speckle interference maps before and after the object to be measured is loaded, combined with a suitable phase-shifting algorithm, the phase distribution maps before and after loading can be extracted. By subtracting the phases, a phase fringe map reflecting the surface deformation of the measurement object can be obtained. This phase fringe map can be directly used for the health monitoring of the object to be measured.

[0063] Embodiment 2 (Distributed large-scale structure health monitoring method and device):

[0064] In this embodiment, taking the monitoring of the health status of a large mural as an example, as Figure 1 shown:

[0065] S1: Divide the monitoring sub-areas; divide the area to be monitored into multiple sub-areas to be measured; arrange multiple interferometers to synchronously image and monitor each sub-area to be measured respectively.

[0066] As Figure 4 shown, in this embodiment, the mural to be monitored is divided into three sub-areas to be measured. Arrange the three interferometers at equal intervals, turn on the interferometers, adjust the angles and positions of the devices so that the interferometers vertically observe the surface of the mural, and adjust the optical lens and the first mirror to ensure that the sub-areas to be measured of the mural recorded by the interferometers are clear and have no double images, and there is partial overlap between the images of adjacent sub-areas to be measured. Synchronously record the images of the three sub-areas to be measured respectively. Adjust the second mirror in each interferometer to cause a certain displacement in the G-channel image.

[0067] S2: Obtain speckle interferometry images; cause the object to be monitored to produce micro-deformation; collect the speckle interferometry images before and after the deformation of each sub-area to be measured respectively.

[0068] Turn on the lasers in each interferometer, uniformly irradiate each sub-area to be measured, and use the interferometer to record the speckle interferometry images. Through four-step phase shift with equal step size, collect two sets of speckle interferometry images before and after the deformation of each sub-area to be measured. Specifically: the three interferometers simultaneously drive the first mirror through controlling the piezoelectric ceramics to achieve phase shift, and record the speckle interferometry images after each phase shift.

[0069] In the initial stage, the three interferometers respectively record the images of their respective RB channels and G channels, where the G channel is the speckle interferometry image, and are respectively denoted as: I A1 , I B1 , I C1 (where the subscript letter represents the corresponding interferometer label, and the number represents the image serial number taken). For each subsequent phase shift, the three interferometers respectively synchronously record the speckle interferometry images of the G channel, and the speckle interferometry images recorded by each interferometer are respectively denoted as: I A2 , I A3 , I A4 ; I B2 , I B3 , I B4 ; I C2 , I C3 , I C4。

[0070] Use an infrared heat lamp to irradiate the surface of the mural to cause it to produce micro-deformation. Then, control the interferometer to repeat the above phase shift steps, and record the speckle interferometry images after each phase shift. The speckle interferometry images corresponding to each interferometer are respectively: P A1 , PA2 , P A3 , P A4 ; P B1 , P B2 , P B3 , P B4 ; P C1 , P C2 , P C3 , P C4 .

[0071] S3: Process the speckle interference images; process the speckle interference images before and after deformation to obtain the defects and their evolution information of each sub-region to be measured.

[0072] Using the four-step phase-shifting algorithm, extract the phase diagrams corresponding to the two sets of speckle interference images recorded before and after the deformation of the mural painting. Taking the speckle interference image collected by interferometer A as an example, the intensity of the speckle interference image before the deformation of the mural painting can be expressed as:

[0073]

[0074] where a ( x , y ) is the background light intensity, b ( x , y ) is the light wave amplitude, φ( x , y ) is the phase to be determined, and Δ is the phase shift amount. Through the four-step phase-shifting method, the phase diagram can be obtained:

[0075]

[0076] Subtract the phase diagrams before and after loading to obtain the phase fringe diagram for health monitoring, as shown in the formula:

[0077]

[0078] Perform the same processing on the speckle interference images before and after deformation collected by interferometers B and C respectively to obtain the phase fringe diagrams of the corresponding sub-regions to be measured.

[0079] S4: Stitch the monitoring data; stitch the dual-color channel images taken of each sub-region to be measured; use the stitching parameters of the dual-color channel images obtained before and after stitching to guide the stitching of the monitoring data.

[0080] Such as Figure 5 , Figure 6As shown, the RB channel images are separated from the images collected by each interferometer for image stitching. First, image registration is performed: the image recorded by interferometer B is defined as the reference image, and then feature detection and matching are carried out on each RB channel image. According to the matching features, the optimal geometric transformation model is established between the images recorded by interferometers A and C and the reference image. Based on this, each image is transformed into the coordinate system of the reference image, so that the overlapping regions of the images are aligned pixel by pixel. Then, image fusion is performed: the optimal stitching line is searched through existing algorithms, and the RB channel images are stitched along the stitching line. Similarly, taking the phase fringe pattern obtained by interferometer B as the reference, using the above geometric transformation model, the phase fringe patterns obtained by interferometers A and C are transformed into the coordinate system of the reference phase fringe pattern, and according to the above optimal stitching line, each phase fringe pattern is stitched to obtain the phase fringe pattern of the entire mural area.

[0081] Finally, a phase fringe pattern corresponding to the entire monitored area of the mural is established to achieve real-time full-field non-destructive health monitoring of the mural.

Claims

1. A full-field non-contact health monitoring method for large structures, characterized in that: The following steps are involved: S1, dividing the sub-area to be measured; dividing the area to be monitored into a plurality of the sub-areas to be measured; arranging a plurality of distributed channel separation speckle interferometers to synchronously image and monitor each of the sub-areas to be measured; S2, obtaining a speckle interferogram and a dual-channel color image; causing the monitored object to deform; respectively collecting the speckle interferogram and the dual-channel color image of the sub-region to be measured before deformation; respectively collecting the speckle interferogram and the dual-channel color image of the sub-region to be measured after deformation; S3, processing the speckle interferogram; processing the speckle interferogram before deformation and the speckle interferogram after deformation, extracting a phase fringe diagram reflecting defect information of the sub-region to be measured, and determining the defect morphology; S4, splicing monitoring data; splicing the dual-channel color images captured in each of the sub-areas to be tested; using the dual-channel color image splicing parameters obtained before and after splicing, geometrically transforming and fusing the phase change information, generating full-field monitoring data, locating defects, and obtaining the evolution of damage to the monitored object; the channel separation speckle interferometer has multiple color channels, one of which records the speckle interferogram of the laser emitted by the channel separation speckle interferometer, and the other color channels record the dual-channel color images of other bands outside the band where the laser is located; the speckle interferogram is used for defect monitoring, and the dual-channel color image is used to guide the splicing of monitoring data; the step S1 comprises: S1.

1. Arrange the channel separation speckle interferometers at equal intervals, turn on each of the channel separation speckle interferometers, and adjust the angle and position so that the channel separation speckle interferometers observe the measured surface vertically and the images of adjacent sub-areas to be measured partially overlap; S1.2, adjust the optical lens and the first reflector to ensure that the image of the sub-area to be measured is clear and has no ghosting; S1.3, turning on the laser, adjusting the second reflector, so that the image of the channel where the laser speckle is located is dislocated; Step S4 includes: S4.1, performing image registration on the dual-channel color images corresponding to each of the areas to be monitored, obtaining an image geometric transformation model, and searching for an optimal stitching line; S4.

2. Using the geometric transformation model and the optimal stitching line, the phase fringe diagrams corresponding to the areas to be monitored are stitched together to obtain global monitoring data, and thereby locate defects.

2. The full-field non-contact health monitoring method for large structures according to claim 1 is characterized in that: The step S2 specifically includes: S2.

1. According to the equal-step time phase shift method, the piezoelectric ceramics are synchronously controlled to realize multiple phase shifts, and the speckle interferogram and the dual-channel color image of the monitored area before deformation after each phase shift are synchronously recorded; S2.2, deforming the area to be monitored by a non-contact method; S2.

3. Again according to the equal-step time phase shift method, synchronously control the piezoelectric ceramics to achieve multiple phase shifts, and synchronously record the speckle interference pattern and dual-channel color image of the deformed area to be monitored after each phase shift.

3. The full-field non-contact health monitoring method for large structures according to claim 1 is characterized in that: The step S3 includes: using a time phase shift algorithm to solve the phase diagram before and after deformation of each sub-region to be measured, and performing a subtraction calculation to obtain the phase fringe diagram caused by the deformation of the sub-region to be measured, and determining the defect morphology.

4. A distributed full-field non-contact health monitoring device for implementing the full-field non-contact health monitoring method for large structures as described in any one of claims 1 to 3, characterized in that: include: A plurality of the channel separation speckle interferometers, wherein the monitoring areas of adjacent channel separation speckle interferometers partially overlap; A synchronization control module, used for triggering the channel separation speckle interferometer to synchronously collect images; The channel separation speckle interferometer comprises a laser (1), a beam expander (2), a first imaging lens (3) and a second imaging lens (11), a convex lens (4), a beam splitter prism (5), a first reflector (6), a second reflector (9), an optical adjustment frame (10), a piezoelectric ceramic (7), a bandpass filter (8), and a color camera (12); the laser light emitted by the laser (1) is expanded by the beam expander (2), irradiated onto the surface of the object to be measured, diffusely reflected by the surface of the object to be measured, and enters the beam splitter prism (5) through the first imaging lens (3) and the convex lens (4); the beam splitter prism (5) splits the laser light into two beams, which are respectively transmitted to the color camera (12) through the first reflector (6) and the second reflector (9); the first reflector (6) is connected to the piezoelectric ceramic (7); the second reflector (9) is connected to the optical adjustment frame (10); and the bandpass filter (8) is provided on the optical path between the second reflector (9) and the beam splitter prism (5).

5. The distributed full-field non-contact health monitoring device according to claim 4, characterized in that: The first imaging lens (3) and the second imaging lens (11) are used to expand the field of view of the channel separation speckle interferometer; the convex lens (4) is provided between the equivalent optical paths of the first imaging lens (3) and the second imaging lens (11); and the first imaging lens (3) is used for focusing the channel separation speckle interferometer.

6. The distributed full-field non-contact health monitoring device according to claim 4, characterized in that: The transmission wavelength band of the bandpass filter (8) matches the wavelength of the laser (1), and reflects light outside the transmission wavelength band; the transmission wavelength band range includes the wavelength band of light generated by the laser (1).

7. The distributed full-field non-contact health monitoring device according to claim 4, characterized in that: The first reflector (6) is connected to the piezoelectric ceramic (7), and the first reflector (6) is displaced by adjusting the voltage applied to the piezoelectric ceramic (7); the second reflector (9) is mounted on the optical adjustment frame (10), and the shearing direction and shearing amount of the transmitted light are changed by angle adjustment.

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