Full-field non-contact health monitoring method and device for large-scale structure

Abstract

The invention discloses a full-field non-contact health monitoring method for a large-scale structure. The method mainly comprises the following steps: S1, dividing monitoring sub-regions; dividing the to-be-monitored area into a plurality of to-be-monitored sub-areas; arranging a plurality of distributed channel discrete speckle interferometers to respectively and synchronously image and monitor each to-be-detected sub-region; s2, acquiring a speckle interferogram and a dual-channel color map; the monitored object is deformed; respectively collecting speckle interferograms and dual-channel color maps before and after deformation of the to-be-detected sub-region; s3, processing a speckle interferogram; processing the speckle interferograms before and after deformation, extracting a phase fringe pattern reflecting defect information of the to-be-detected sub-region, and determining a defect form; s4, splicing the monitoring data; splicing the two-color channel images shot by the sub-regions to be detected; and performing geometric transformation and fusion on the phase change information by using the two-color channel image splicing parameters obtained before and after splicing to generate full-field monitoring data, and obtaining the defect position and damage evolution of the monitored object.

Description

Technical Field

[0001] The present invention relates to structural health monitoring technology, and in particular 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 to evaluate the health and safety of a structure by real-time monitoring and analyzing its physical parameters. Large structures such as murals, wings, bridges, etc. are often affected by factors such as the natural environment and various loads, and will produce defects such as cracks, deformation, and corrosion. The health monitoring of large structures is crucial to ensuring public safety and the long-term stability of the structure. Therefore, it is necessary to monitor the potential damage of the structure in a timely and accurate manner, take repair measures in advance, and avoid accidents. The large area to be measured is the main difficulty in health monitoring of large structures. Traditional contact monitoring methods have problems such as low spatial resolution, weak static monitoring capabilities, and temperature sensitivity. For example, the health monitoring method based on fiber optic sensing (CN202411018913.6, CN202323077267.4) is easily affected by multiple parameters such as temperature, stress, and light during use, and has low spatial resolution, making it difficult to ensure measurement accuracy and damage location accuracy; the monitoring method based on piezoelectric sensing (CN201910160196.3) is often used for dynamic signal monitoring, and it is difficult to measure static strain, and the defect location accuracy depends on the sensor layout density; the monitoring method based on acoustic emission (CN202410327181.2) is often detected after the damage occurs, and it is difficult to achieve early warning when the damage is initiated; the ultrasonic guided wave (CN202410868821.0) technology is material and geometric dependent and sensitive to temperature changes.

[0003] Full-field non-contact optical detection technology can avoid direct contact with the object to be measured, reduce human damage, and can quickly scan the entire surface, which is an ideal method for structural health monitoring. However, the structural health monitoring method that relies solely on image matching, recognition and other algorithms (CN202311817843.6) usually has a deformation measurement resolution limited by the physical resolution of the digital camera, and faces problems such as massive data transmission and calculation when performing full-field monitoring. Shearing speckle interferometry technology (such as 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 pattern before and after the deformation of the object to be measured, and has the advantages of high deformation measurement resolution and small calculation amount. However, due to factors such as laser power and measurement field of view, the existing shearing speckle interferometry technology is often used for defect detection of small components or small areas such as tires and steel structure welds, and cannot be applied to health monitoring of large structures. Summary of the invention

[0004] 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, so as to realize high-resolution, full-field, non-contact health monitoring of large structures.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A full-field non-contact health monitoring method for large structures includes the following steps: 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, stitching monitoring data; stitching the dual-channel color images captured in each of the sub-areas to be tested; using the stitching parameters of the dual-channel color images obtained before and after stitching, 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.

[0006] Preferably, the channel separation speckle interferometer (hereinafter referred to as speckle interferometer) has multiple color channels, one of which records the speckle interference pattern generated by the interferometer, and the other color channels record other band images except the color of the band where the speckle interferometer laser is located (hereinafter referred to as dual-channel color images); the speckle interference pattern is used for defect monitoring, and the dual-channel color image is used to guide the splicing of monitoring data.

[0007] Preferably, the step S1 comprises: S1.1. Divide the area to be monitored into a plurality of 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 interferometers vertically observe the surface of the sub-areas to be measured, and the images of adjacent sub-areas to be measured partially overlap; S1.2, adjusting 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. Turn on the laser and adjust the second reflector to cause the image of the channel where the laser speckle is located to be misaligned.

[0008] Preferably, 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.

[0009] Preferably, step S3 includes: using a time phase shift algorithm to solve the phase image before and after deformation of each sub-area to be measured, and performing subtraction calculation to obtain a phase change image (also called a phase fringe image) caused by the deformation of the sub-area to be measured, and determining the defect morphology.

[0010] Preferably, the step S4 comprises: S4.1. performing image registration on the two-color channel 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.

[0011] A distributed full-field non-contact health monitoring device, comprising: There are a plurality of the speckle interferometers, and the monitoring areas of adjacent speckle interferometers partially overlap; A synchronization control module, used for triggering the speckle interferometer to synchronously collect images; The speckle interferometer comprises a laser, a beam expander, a first imaging lens and a second imaging lens, a convex lens, a beam splitter prism, a first reflector, a second reflector, an optical adjustment frame, a piezoelectric ceramic, a bandpass filter, and a color camera; the laser emitted by the laser is expanded by the beam expander, 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 through the first imaging lens and the convex lens; the beam splitter prism splits the laser into two beams, which are respectively transmitted to the color camera through the first reflector and the second reflector; the first reflector is connected to the piezoelectric ceramic; the second reflector is connected to the optical adjustment frame; the bandpass filter is arranged on the optical path between the second reflector and the beam splitter prism.

[0012] 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; and the first imaging lens is used for focusing the speckle interferometer.

[0013] Preferably, the transmission band of the bandpass filter matches the wavelength of the laser and reflects light other than the transmission band; the transmission band range includes the band of light generated by the laser.

[0014] Preferably, the first reflector is connected to the piezoelectric ceramic, and the first reflector is displaced by adjusting the voltage applied to the piezoelectric ceramic; the second reflector is mounted on the optical adjustment frame, 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.

[0015] Since the area to be monitored for large structures (such as murals, building structures, etc.) is very large, using only a single speckle interferometer will not be able to simultaneously ensure full coverage of the area to be tested and high spatial resolution due to field of view limitations. The entire area to be tested is divided into several smaller sub-areas, each of which corresponds to a speckle interferometer. The speckle interferometer is used to synchronously image and monitor each sub-area separately, which can ensure that the defects and diseases of each sub-area can be monitored, avoiding the loss of monitoring information due to field of view limitations. When imaging each sub-area, the images of adjacent sub-areas need to overlap partially. The above overlap helps with image registration during subsequent image stitching, ensuring that the stitched images have no gaps, misalignments or other stitching errors.

[0016] Therefore, the distributed large-scale full-field non-contact health monitoring device of the present invention includes multiple sets of identical speckle interferometers, the areas photographed by adjacent speckle interferometers partially overlap, the image acquisition signals between the various speckle interferometers are synchronized, and the images of each sub-area to be measured can be synchronously recorded.

[0017] Since speckle image dislocation is a necessary condition for real speckle shearing interferometry, and image dislocation will lead to difficulty in image registration when stitching images, which will cause image stitching errors. Channel separation 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.

[0018] Since different color cameras realize image color recording in different ways, in order to make the technical means, creative features, and purpose of the present invention easy to understand, the present invention is described by taking the Bayer array color camera as a representative. However, the color camera, image channel, etc. involved in the present invention are not limited to the Bayer array type. The present invention will be further described below by taking the Bayer array color camera as the photosensitive element of the speckle interferometer.

[0019] The Bayer array image sensor is a commonly used color digital image sensor, which realizes the acquisition of color information (image) by arranging micro filters of different colors (usually red, green and blue) on the image sensor. In the Bayer array color camera, the green (G) photosensitive unit accounts for 50% of the total area of ​​the camera photosensitive chip, and the red (R) and blue (B) photosensitive units 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. The bandpass filter can selectively transmit light within a specific wavelength range and reflect light of other wavelengths. In the present invention, the selected bandpass filter can transmit green light and reflect red and blue light. It should be noted that the selection of the bandpass 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 the corresponding bandpass filter should be able to transmit light of this color and reflect light of other colors.

[0020] Although the RB channel in the Bayer array only occupies 50% of the total area of ​​the image sensor, it can collect red and blue information at the same time. Therefore, the RB channel image collected by the Bayer array color camera can provide accurate edge information, stably reflect the overall structure of the image, help the algorithm to better perform image registration, reduce stitching errors, ensure the accuracy of image stitching, and provide reliable stitching parameters for monitoring data stitching.

[0021] During the instrument arrangement stage of actual monitoring, the area to be monitored is divided into multiple sub-areas to be measured, and 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 observes the surface of the sub-area to be measured vertically and the images of adjacent sub-areas to be measured partially overlap.

[0022] After determining the layout of each speckle interferometer, adjust the reflector in the speckle interferometer so that there is no ghosting in the image taken by the speckle interferometer. Adjust the angle or position of the reflector so that the images collected by the speckle interferometer are completely overlapped (no image misalignment), ensuring that all color channels (R, G, B) in the imaging system are aligned with the same target area, avoiding subsequent image stitching errors caused by image ghosting, reducing imaging errors, and improving the stability and reliability of the system.

[0023] Turn on the laser of the speckle interferometer, adjust the tilt angle and tilt direction of the reflector in the optical path behind the bandpass filter, change the propagation path of part of the green light, and make the speckle interferogram of the G channel produce ghosting (slightly misaligned overlapping images), that is, the generated image of the speckle interferogram of the G channel is misaligned.

[0024] When the sub-area to be measured is illuminated with coherent light, the rough surface of the sub-area to be measured will diffusely reflect the incident coherent light and form speckles in space. These speckles form a speckle interference pattern through the interferometer, and the phase information in the interference pattern 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 interferometry, piezoelectric ceramics are usually used to accurately control the optical path change in the optical path. Piezoelectric ceramics are connected to optical elements (the above-mentioned reflectors). By applying different voltages, piezoelectric ceramics can accurately move the reflectors, 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, the phase information in the speckle interferogram can be extracted by combining relevant algorithms (such as the four-step phase shift algorithm). By comparing the phase information before and after the deformation of the sub-area to be measured, quantitative analysis of the position and morphology of small deformations and defects on the surface of the sub-area to be measured can be achieved.

[0025] During the monitoring process, the measured area is subjected to non-contact deformation such as infrared heating 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, which will cause a corresponding change in the speckle pattern. The surface deformation information of the measured sub-area after deformation can be extracted through the phase shift method.

[0026] After the measured area is deformed, the piezoelectric ceramic is controlled to achieve multiple equal-step phase shifts, and the post-deformation speckle interferogram after each phase shift is collected. The post-deformation phase information (post-deformation phase map) is extracted through the phase shift algorithm; the post-deformation speckle interferogram includes the post-deformation G channel image and RB channel image.

[0027] The phase image before deformation and the phase image after deformation are subtracted, where each sub-area under test corresponds to a pair of phase images before and after deformation. The result of the subtraction is called a "phase fringe image" or "phase change image". The phase fringe image 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 shallow surface of the measured area will cause a sudden change in deformation at the location of the defect, this is reflected in the phase fringe image as a sudden change in phase change. Therefore, the size and location of the defect can be determined by observing the phase fringe image.

[0028] The pixel coordinates of each color channel of the image taken by the color camera correspond one to one. Therefore, the pixel coordinate positions of the RB channel image and the G channel image collected by the interferometer are also completely corresponding. Since the phase fringe diagram is obtained by calculating the speckle interferogram of the G channel, the pixel coordinates of the phase fringe diagram and the RB channel image corresponding to each measured sub-area completely correspond. For example, the monitoring result corresponding to the pixel coordinate (a, b) position in the RB channel image is the monitoring data corresponding to the pixel coordinate (a, b) position in the phase fringe diagram.

[0029] Therefore, the coordinate position change relationship of each pixel before and after the RB image is stitched is the coordinate change relationship of each pixel before and after the phase fringe image (corresponding to the G channel image) is stitched. First, the RB channel images corresponding to each measured area are registered, the image geometric transformation model is obtained, and the optimal stitching line is searched to complete the image stitching of the RB channel. Using the above geometric transformation model and the optimal stitching line, the corresponding phase fringe image (corresponding to the G channel image) is stitched to achieve monitoring data stitching.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention adopts a special optical design for a single speckle interferometer, and simultaneously realizes the acquisition of speckle interference pattern (G channel) and dual-channel color image (RB channel) of the measured object; on this basis, multiple speckle interferometers are used to construct a distributed large-scale structural health monitoring device, breaking through the field of view limitation of a single interferometer; a method of color image splicing to guide monitoring data splicing is proposed to reduce the computational complexity of monitoring data splicing, and achieve non-contact full coverage of the monitored area of ​​large structures while ensuring the detection resolution, solving the problem of low efficiency of traditional monitoring methods. Through optical-computing collaborative innovation, the present invention overcomes the contradiction between "high precision" and "large field of view" in large-scale structural health monitoring, and provides efficient and reliable technical means for health assessment in infrastructure, cultural heritage and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic flow chart of the method of Example 2; Figure 2 is a schematic structural diagram of a single channel separation speckle interferometer of Example 1; Figure 3 is a schematic diagram of the optical path of a single channel separated speckle interferometer of Example 1; Figure 4 is a scene illustration of monitoring the health of a mural by using a multiple channel separation speckle interferometer in Example 2; Figure 5 Schematic diagram of separating a Bayer array color image into two types of channel data in Example 2; Figure 6 The figure is a schematic diagram of the process of stitching the RB channel image in Example 2 to guide the stitching of the monitoring data (phase fringe diagram).

[0032] in: 1. Laser; 2. Beam expander; 3. First imaging lens; 4. Lens; 5. Beam splitter; 6. First reflector; 7. Piezoelectric ceramics; 8. Bandpass filter; 9. Second reflector; 10. Optical adjustment frame; 11. Second imaging lens; 12. Color camera. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, objectives and effects of the invention easier to understand, the invention is further described with reference to specific diagrams. However, the invention is not limited to the following implementation cases.

[0034] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0035] Example 1 (Channel Separation Speckle Interferometer): A channel-separated speckle interferometer is constructed by using a laser, a beam splitter, a reflector, a bandpass filter, an imaging module and a control module; the interferometer can respectively record the RB channel image and the G channel image of the object to be monitored; the G channel image is used for defect monitoring, and the RB channel image is used to guide the splicing of monitoring data.

[0036] like Figure 2 A channel-separated speckle interferometer is shown. Figure 3 The corresponding optical path diagram is as follows: the laser emitted by the laser 1 irradiates the object to be measured after passing through the beam expander 2, and then enters the dichroic prism 5 after diffuse reflection from the surface of the object to be measured; the dichroic prism 5 divides the laser into two beams, which are respectively reflected by the first reflector 6 and the second reflector 9 and projected onto the color camera 12; the first reflector 6 is connected to the piezoelectric ceramic 7; a bandpass filter 8 is provided on the optical path between the second reflector 9 and the dichroic prism 5 for transmitting green light and reflecting blue light and red light.

[0037] Laser 1 is used to emit green laser. Beam expander 2 is used to expand the laser beam emitted by 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 interferes with each other in space to form speckle. The first imaging lens 3 is responsible for focusing the interferometer to adapt to different measuring distances. Lens 4 and lens 11 are used to expand the field of view of the interferometer so that it can observe a larger area. Beam splitter prism 5, this embodiment uses a beam splitter prism with a transmission-reflection ratio of 1:1 to split the transmitted laser into two beams of equal light intensity. One beam of light is projected onto the first reflector 6; after the other beam of light is projected onto the bandpass filter 8, the red and blue parts of the light are reflected by the bandpass filter, and the green part of the light is reflected by the second reflector 9 through the bandpass filter. In this device, we choose a narrow-band bandpass 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, thereby improving the accuracy of interference. The first reflector 6 can reflect red, green and blue light. The piezoelectric ceramic 7 is connected to the first reflector 6, and can accurately push the first reflector 6 by applying voltage to introduce a specific phase (optical path difference) change in the optical path. The second reflector 9 only reflects the green light beam. The optical adjustment frame 10 is connected to the second reflector 9, which is used to adjust the tilt angle and tilt direction of the second reflector 9, and correspondingly adjust the shear amount and shear direction, so that the system can adapt to different measurement requirements and improve its measurement flexibility and accuracy. After the above two beams of coherent light (G channel) passing through different optical paths are reflected by the first reflector 6 and the second reflector 9, they are converged again by 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. 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 interferogram of the measured object before and after loading, combined with a suitable phase shift algorithm, the phase distribution map before and after loading can be extracted, and by phase subtraction, a phase fringe map reflecting the surface deformation of the measured object can be obtained. This phase fringe map can be directly used for health monitoring of the measured object.

[0038] Embodiment 2 (distributed large-scale structural health monitoring method and device): This embodiment takes monitoring the health status of a large mural as an example. Figure 1 As shown: S1: Divide the monitoring sub-area; 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.

[0039] like Figure 4As shown, in this embodiment, the wall to be monitored is divided into three sub-areas to be measured. The three interferometers are arranged at equal intervals, turned on, and the angle and position of the device are adjusted so that the interferometer can observe the surface of the mural vertically. The optical lens and the first reflector are adjusted to ensure that the sub-areas to be measured of the mural recorded by the interferometer are clear and have no ghosting, and that the images of adjacent sub-areas to be measured overlap partially. The images of the three sub-areas to be measured are recorded synchronously respectively. The second reflector in each interferometer is adjusted to produce a positioning difference in the G channel image.

[0040] S2: Acquire a speckle interferometer image; cause the monitored object to produce a slight deformation; and respectively collect the speckle interferometer image of the sub-region to be measured before the deformation and the speckle interferometer image after the deformation.

[0041] Turn on the laser in each interferometer, evenly illuminate each sub-area to be measured, and use the interferometer to record the speckle interference image. Through four-step phase shift with equal step length, collect two sets of speckle interference patterns before and after the deformation of each sub-area to be measured. Specifically: the three interferometers simultaneously control the piezoelectric ceramic to drive the first reflector to achieve phase shift, and record the speckle interference pattern after each phase shift.

[0042] In the initial stage, the three interferometers record the images of their respective RB channels and G channels, where the G channel is the speckle interference pattern, which are recorded as: I A1 , I B1 , I C1 (The letters in the subscripts represent the corresponding interferometer numbers, and the numbers represent the image numbers.) At each subsequent phase shift, the three interferometers synchronously record the speckle interferogram of the G channel. The speckle interferograms recorded by each interferometer are recorded as: I A2 ,I A3 ,I A4 ;I B2 ,I B3 ,I B4 ;I C2 ,I C3 ,I C4。

[0043] Use an infrared heat lamp to illuminate the surface of the mural to cause it to deform slightly. Then, control the interferometer to repeat the above phase shift steps and record the speckle interference pattern after each phase shift. The speckle interference patterns corresponding to each interferometer are: P A1 , P A2 , P A3 , P A4 ;P B1 , P B2 , P B3 , P B4 ;P C1 , P C2 , P C3 , P C4 .

[0044] S3: Processing the speckle interference image; processing the speckle interference image before deformation and the speckle interference image after deformation to obtain the defects of each sub-region to be measured and the information on their evolution.

[0045] The four-step phase shift algorithm is used to extract the phase images corresponding to the two sets of speckle interferograms recorded before and after the mural is deformed. Taking the speckle interferogram collected by interferometer A as an example, the intensity of the speckle interferogram before the mural is deformed can be expressed as: in, 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. Through the four-step phase shift method, the phase diagram can be obtained: By subtracting the phase images before and after loading, the phase fringe image used for health monitoring can be obtained, as shown in the formula: The same processing is performed on the speckle interferograms before and after deformation collected by interferometers B and C, respectively, to obtain the phase fringe diagram of the corresponding sub-area to be measured.

[0046] S4: stitching monitoring data; stitching the two-color channel images captured in each sub-area to be tested; and guiding the stitching of monitoring data using stitching parameters of the two-color channel images obtained before and after the stitching.

[0047] like Figure 5 , Figure 6 As 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 performed on each RB channel image. The optimal geometric transformation model between the images recorded by interferometers A and C and the reference image is established based on the matching features. Based on this, each image is transformed into the coordinate system of the reference image so that the overlapping areas of each image are aligned pixel by pixel; then image fusion is performed: the optimal stitching line is searched through the existing algorithm, and the RB channel images are stitched along the stitching line. Similarly, with the phase fringe pattern obtained by interferometer B as a reference, the phase fringe patterns obtained by interferometers A and C are transformed into the coordinate system of the reference phase fringe pattern using the above-mentioned geometric transformation model. According to the above-mentioned optimal stitching line, each phase fringe pattern is stitched to obtain the phase fringe pattern of the entire mural.

[0048] Finally, a phase fringe diagram 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, stitching monitoring data; stitching the dual-channel color images captured in each of the sub-areas to be tested; using the stitching parameters of the dual-channel color images obtained before and after stitching, 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.

2. The full-field non-contact health monitoring method for large structures according to claim 1 is characterized in that: The channel separation speckle interferometer has multiple color channels, one of which records the speckle interference pattern 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 interference pattern is used for defect monitoring, and the dual-channel color image is used to guide the splicing of monitoring data.

3. The full-field non-contact health monitoring method for large structures according to claim 1 is characterized in that: 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. Turn on the laser and adjust the second reflector to cause the image of the channel where the laser speckle is located to be misaligned.

4. 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.

5. 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.

6. The full-field non-contact health monitoring method for large structures according to claim 1 is characterized in that: The step S4 comprises: S4.

1. performing image registration on the two-color channel 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.

7. 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 6, 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; and the bandpass filter (8) is provided on the optical path between the second reflector (9) and the beam splitter prism (5).

8. The distributed full-field non-contact health monitoring device according to claim 7, 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.

9. The distributed full-field non-contact health monitoring device according to claim 7, 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).

10. The distributed full-field non-contact health monitoring device according to claim 7, 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 can be changed by adjusting the angle.

Images