A full-field dynamic three-dimensional deformation measurement method and system based on polarization multiplexing

Abstract

The application discloses a kind of full-field dynamic three-dimensional deformation measurement method and system based on polarization multiplexing, by the polarization state of object light and reference light is adjusted to circularly polarized light and 45 ° linearly polarized light respectively, polarization CCD is used, the synchronous recording of speckle field and speckle interference phase shift field before and after the three-dimensional deformation of measured object occurs is realized.The speckle interference phase shift map recorded by the pixel of polarization direction 0 and 90 on polarization CCD is used to restore off-plane deformation, and the speckle map recorded by the pixel of polarization direction 135 is used to carry out DIC calculation and restore in-plane deformation.The problems that direct speckle map and interference phase shift map cannot be recorded synchronously and dynamic measurement demand is not easy to meet in the related technology of three-dimensional deformation dynamic measurement combining DSPI and DIC are solved.

Description

Technical Field

[0001] This invention belongs to the field of high-precision measurement technology of dynamic three-dimensional deformation of rough surfaces, specifically involving a full-field dynamic three-dimensional deformation measurement method and system based on polarization multiplexing. Background Technology

[0002] In practical engineering applications, full-field, high-precision real-time monitoring of the three-dimensional deformation of key components is an important means of analyzing their dynamic stress-strain distribution and mechanical properties under different loads, which is of great significance for ensuring system safety and reliability. Combining digital speckle interferometry (DSPI) and digital speckle correlation (DSC) techniques can meet the requirements for high-precision, non-contact measurement of three-dimensional deformation of rough surfaces, and is therefore widely studied.

[0003] Both DSPI and DSC can perform full-field non-destructive measurements on optically rough surfaces. DSPI is an interferometric technique with wavelength-level detection accuracy, primarily measuring out-of-plane deformation by analyzing the phase changes of speckle interferograms. DSC, on the other hand, measures in-plane deformation based on the correlation between speckle patterns, essentially belonging to digital image correlation (DIC) technology. Therefore, combining the two can simultaneously measure both out-of-plane and in-plane deformations, and the system structure is simple and compact.

[0004] The key to achieving 3D deformation measurement based on DSPI lies in obtaining the deformation phases in at least three different sensitivity directions to solve for the 3D deformation. This means the system must contain at least three illumination or imaging directions. Common system layouts currently include: three cameras + single-wavelength illumination, single camera + three-wavelength illumination, and single-color camera + dual-wavelength illumination. The latter two, because they record multiple interferometric fields on the same camera, must simultaneously utilize carrier wave technology to separate deformation information in different directions in the frequency domain. Therefore, the problem with DSPI-based 3D deformation measurement is that overly complex structural designs make the interferometric measurement system increasingly sensitive to environmental interference, resulting in poor stability, and high setup and maintenance costs.

[0005] Therefore, combining DSPI and DIC technologies to achieve three-dimensional deformation measurement has become a research hotspot. The advantage of this measurement method is that its structure is based on the DSPI one-dimensional out-of-plane deformation measurement system, requiring only a single camera and a single illumination wavelength. Therefore, the system layout is simple and compact, meeting the needs of practical engineering. However, the difficulty of this measurement technology lies in how to simultaneously acquire speckle interferograms and speckle maps containing only the light intensity information of the measured object, and then use them for interferometric phase retrieval and DIC calculations to obtain out-of-plane and in-plane deformations, respectively.

[0006] Currently, there are two main approaches to solving this problem: one is to recover the object-side light intensity information through numerical calculation based on the speckle interferometric field information acquired by the camera. In 2015, Redouane Zemmamouche et al. calculated the background or modulation term of the interferometric field based on a four-step time-phase-shifted speckle interferogram sequence, treating it as an approximate solution of the real speckle pattern for DIC in-plane deformation analysis, and compared the differences between the two. Meanwhile, out-of-plane deformation was recovered through phase-shifted interferograms with high accuracy, but dynamic three-dimensional deformation measurement could not be achieved due to the time-phase-shifting process. In 2014, Yan et al. adopted an off-axis interferometric measurement system layout, based on the Fourier transform phase demodulation process, treating the extracted +1 order information as an approximation of the object-side light field complex amplitude, taking the real part (i.e., the modulation term) for DIC calculation, and the imaginary part for out-of-plane deformation phase recovery, thus achieving dynamic measurement of three-dimensional deformation, but with lower measurement accuracy. Although such methods yield speckle intensity maps (hereinafter referred to as numerical speckle maps) usable for DIC calculations through numerical computation, a key issue remains: both the background and modulation terms of the interferometric field simultaneously contain reference light intensity information, and the numerical computation process itself introduces numerous errors, leading to a decrease in speckle contrast and affecting the accuracy of DIC calculation results. In 2016, Giancarlo Pedrini et al. compared the computational accuracy of directly recorded speckle maps (hereinafter referred to as direct speckle maps) and numerical speckle maps for in-plane deformation analysis of DIC, concluding that DIC calculations based on direct speckle maps have higher accuracy, and that the reference light is a key factor affecting the poor accuracy of DIC calculations using numerical speckle maps. In 2018, Zhao et al. proposed that when combining Fresnel digital holographic interferometry with DIC for three-dimensional deformation measurement, the reference light wavefront error and speckle size also affect the quality of numerical speckle map reconstruction, reducing the accuracy of in-plane deformation solutions in DIC. Another approach is to incorporate an optical switch in the reference optical path of the measurement system. When the switch is closed (blocking the reference light), the camera acquires a speckle pattern; when the switch is open, it acquires a speckle interferogram. While this method completely avoids the influence of the reference light and obtains an ideal speckle pattern to ensure the accuracy of DIC calculations, it cannot meet the needs of dynamic measurements.

[0007] In summary, in the study of combining DSPI and DIC for three-dimensional dynamic deformation measurement, the most ideal solution is to directly record the speckle interference field and speckle pattern with a camera for solving out-of-plane and in-plane deformation respectively. The challenge lies in how to achieve the synchronous recording of the phase-shifted speckle interference pattern sequence and the speckle pattern without reference light information, so as to meet the dynamic measurement requirements while ensuring high-precision three-dimensional deformation measurement results. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a full-field dynamic three-dimensional deformation measurement method and system based on polarization multiplexing to address the shortcomings of the prior art. This method and system solve the technical problems that direct speckle patterns and interferometric phase shift patterns cannot be recorded synchronously and that dynamic measurement requirements are not easily met in the combination of DSPI and DIC for three-dimensional dynamic deformation measurement.

[0009] The present invention adopts the following technical solution:

[0010] A full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing includes the following steps:

[0011] S1. Adjust the angles of the polarizer and quarter-wave plate to ensure that the polarization states of the reference light and the object light satisfy polarization multiplexing. Adjust the aperture of the adjustable stop according to the pixel size of the polarization CCD.

[0012] S2. During the deformation of the surface of the object being measured, a speckle pattern I is simultaneously recorded using a polarized CCD. 135 And speckle interference phase shift diagram I 0 I 45 I 90 ;

[0013] S3. Sequence I of speckle interference phase shift diagrams recorded before and after deformation of the object under test. 0 I 90 By performing pairwise subtraction, a deformed fringe pattern is obtained. A multi-frame phase-shift demodulation algorithm is then used to obtain the deformed phase information. The wrapped phase diagram is used to perform unwrapping calculations on the wrapped phase diagram, recover the out-of-plane deformation phase information, and convert it to obtain the out-of-plane deformation amount Δz;

[0014] S4. Speckle pattern I recorded based on pixels with a polarization direction of 135° on the polarized CCD. 135 DIC calculation is performed to obtain the in-plane deformation of the object under test. Combined with the out-of-plane deformation Δz obtained in step S3, dynamic three-dimensional deformation measurement is realized.

[0015] Specifically, in step S1, the relationship between the aperture D of the adjustable aperture and the speckle size δ is as follows:

[0016]

[0017] Where M and f are the magnification and focal length of the imaging system, λ is the laser wavelength, and pixelsize is the CCD pixel size.

[0018] Specifically, in step S2, light intensity maps in four polarization directions are extracted from the raw data recorded by the polarization CCD through downsampling. Then, interpolation is performed on the four light intensity maps to obtain speckle map I. 135 And speckle interference phase shift diagram I 0I 45 I 90 .

[0019] Furthermore, speckle pattern I 135 And speckle interference phase shift diagram I 0 I 45 I 90 They are respectively:

[0020]

[0021]

[0022]

[0023] I 135 =A 2

[0024] o

[0025] Among them, A r , A represents the amplitude and phase of the reference light, respectively. o , These represent the amplitude and phase of the object light, respectively.

[0026] Specifically, in step S3, the out-of-plane deformation Δz is as follows:

[0027]

[0028] in, λ represents the deformed phase information, and λ is the laser wavelength.

[0029] Specifically, step S4 is as follows:

[0030] Select the speckle pattern I collected before deformation 135 Using the reference image and selecting the region of interest (ROI), a reference sub-region Ref with dimensions of (2m+1)*(2m+1) is set with the measurement point as the center. Then, the corresponding target sub-region Def is searched in the deformed image to determine the displacement of the measurement point at the center of the reference sub-region Ref. The above search process is performed on each measurement point in the ROI to obtain the total in-field deformation of the measured surface.

[0031] Using the correlation operations of the reference subregion Ref and the target subregion Def as the objective function, and by establishing and setting the shape function relationship and initial parameter value p0, the inverse synthesis Gaussian-Newton algorithm is used for iterative optimization to find the local optimum and determine the displacement vector (u,v) of the measured point. T The displacement vector (u,v) of the measured point is determined based on the imaging magnification M and the pixel size. T Convert to actual physical displacement (Δx, Δy)T This process is extended to the remaining test points to obtain the overall displacement assessment results.

[0032] Furthermore, Δx is:

[0033] Δx = u * M * pixel size

[0034] Where pixelsize is the CCD pixel size.

[0035] Secondly, embodiments of the present invention provide a full-field dynamic three-dimensional deformation measurement system based on polarization multiplexing, including a depolarizing beam splitter prism BS. The object to be measured is placed on one side of the depolarizing beam splitter prism BS, and a laser is placed on the other side of the depolarizing beam splitter prism BS. A reflector M is placed on the upper side of the depolarizing beam splitter prism BS, and a polarizing CCD is placed on the lower side of the depolarizing beam splitter prism BS. A first attenuator, a pinhole filter, a collimating lens, and a first polarizer P1 are sequentially arranged between the laser and the depolarizing beam splitter prism BS. A third polarizer P3 is arranged between the object to be measured and the depolarizing beam splitter prism BS. A second attenuator and a second polarizer P2 are sequentially arranged between the reflector M and the depolarizing beam splitter prism BS. A quarter-wave plate QWP, a second lens L2, an adjustable aperture, and a first lens L1 are sequentially arranged between the polarizing CCD and the depolarizing beam splitter prism BS. The depolarizing beam splitter splits the linearly polarized light emitted by the laser, which has been adjusted to 0° by the first polarizer P1, into object light and reference light, while maintaining the polarization state of the beam unchanged.

[0036] Specifically, the fast axis of the quarter-wave plate QWP is parallel to the transmission direction of the second polarizer P2.

[0037] Specifically, the adjustable aperture is located at the Fourier surface of the imaging system.

[0038] Compared with the prior art, the present invention has at least the following beneficial effects:

[0039] A full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing is proposed. This method adjusts the polarization states of the object light and reference light to circularly polarized light and 45° linearly polarized light, respectively. Using a polarization-controlled CCD, it achieves simultaneous recording of the speckle field and speckle interference phase shift field before and after the measured object undergoes three-dimensional deformation. The speckle interference phase shift map recorded by pixels with polarization directions of 0° and 90° on the polarization-controlled CCD is used to recover out-of-plane deformation, while the speckle map recorded by pixels with a polarization direction of 135° is used for DIC calculation to recover in-plane deformation. This method solves the problems in related technologies combining DSPI and DIC for dynamic three-dimensional deformation measurement, such as the inability to synchronously record direct speckle maps and interference phase shift maps, and the difficulty in meeting dynamic measurement requirements.

[0040] Furthermore, the aperture of the adjustable stop is adjusted according to the pixel size of the polarization CCD so that the average speckle size covers at least four pixels, thereby improving the speckle correlation within a polarization unit and ensuring the accuracy of the phase calculation results.

[0041] Furthermore, intensity maps in four polarization directions are extracted from the raw data recorded by the polarization CCD through downsampling. Then, interpolation is performed on the four intensity maps to obtain speckle map I. 135 And speckle interference phase shift diagram I 0 I 45 I 90 Downsampling reduces the resolution of the intensity map, but this can be compensated for by interpolation.

[0042] Furthermore, based on the speckle interference phase shift sequence I recorded before and after the deformation of the object under test... 0 I 45 I 90 The out-of-plane deformation phase is calculated based on the principle of speckle interference. Based on speckle pattern I 135 Based on the theory of correlation dimension in digital images, we can calculate in-plane deformation.

[0043] Furthermore, the speckle pattern I collected before deformation was selected. 135 Using the reference image as a reference, and selecting the region of interest (ROI), a reference sub-region Ref with a size of (2m+1)*(2m+1) is set with the measurement point as the center. Then, the corresponding target sub-region Def is searched in the deformed image to determine the displacement of the measurement point at the center of the reference sub-region Ref. The above search process is performed on each measurement point in the region of interest (ROI) to obtain the in-field deformation (Δx, Δy) of the measured surface. Together with the out-of-field deformation obtained in the previous step, they constitute the three-dimensional deformation distribution of the measured object.

[0044] A full-field dynamic three-dimensional deformation measurement system based on polarization multiplexing is disclosed. In this system, an attenuator is used to adjust the intensity of the light source or reference light; a pinhole filter and a collimating lens are used to expand and collimate the light emitted from a laser; a polarizer P1 is used to adjust the incident light to be linearly polarized at 0°; a depolarizing beam splitter BS not only achieves beam refraction and splitting but also ensures that the polarization state remains unchanged; a combination of P3 and a QWP is used to adjust the object light to circularly polarized light, and a combination of P2 and a QWP is used to adjust the reference light to linearly polarized light, thus satisfying the polarization multiplexing design of this scheme. L1 and L2 are used to image the object under test onto the CCD target surface, and an adjustable aperture is used to control the speckle size to satisfy speckle correlation.

[0045] Furthermore, the fast axis of the quarter-wave plate QWP is parallel to the transmission direction of the polarizer P2. Therefore, after passing through QWP, the polarization state of the reference light remains unchanged, while the polarization state of the object light is converted into circularly polarized light.

[0046] Furthermore, the adjustable aperture is located at the Fourier surface of the imaging system and is used to adjust the speckle size.

[0047] In summary, the present invention features a simple and compact structure, enabling full-field, high-precision measurement of dynamic three-dimensional deformation of objects with rough surfaces, thus meeting the real-time and accuracy requirements of practical engineering measurement applications.

[0048] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the optical path of the measurement system of the method of the present invention;

[0050] Figure 2 The distribution of polarization units on the polarization CCD target surface, and the phase-shifted interferogram and object-side light intensity map synchronously acquired in four polarization directions when the object under test is a resolution plate;

[0051] Figure 3 This is a flowchart illustrating the measurement process of the method of the present invention;

[0052] Figure 4 The diagram shows the phase shift fringe pattern of the out-of-plane deformation of the tested object and the measurement results of the out-of-plane deformation.

[0053] Figure 5 The image shows the in-plane deformation measurement results of the object based on the speckle pattern DIC calculation, where (a) is the x-direction and (b) is the y-direction.

[0054] Among them: BS. depolarizing beam splitter, P. polarizer, M. mirror, L. lens, CCD. camera. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0057] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0058] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" relationship.

[0059] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0060] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0061] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0062] This invention provides a full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing. By adjusting the polarization states of the object light and reference light to circularly polarized light and 45° linearly polarized light, respectively, a polarized CCD is used to simultaneously record the speckle field and speckle interference phase shift field before and after the three-dimensional deformation of the measured object. The speckle interference phase shift map recorded by pixels with polarization directions of 0° and 90° on the polarized CCD is used to recover out-of-plane deformation, while the speckle map recorded by pixels with a polarization direction of 135° is used for DIC calculation to recover in-plane deformation. This solves the problems in related technologies combining DSPI and DIC for dynamic three-dimensional deformation measurement, such as the inability to synchronously record direct speckle maps and interference phase shift maps, and the difficulty in meeting dynamic measurement requirements. Therefore, the speckle map does not need to be calculated from the interference field, thus avoiding the decrease in accuracy of DIC in-plane deformation calculation caused by this problem. Simultaneously, the synchronous acquisition of multi-step phase shift interferograms based on polarization phase shift technology ensures the measurement accuracy of out-of-plane deformation.

[0063] Please see Figure 3 The present invention discloses a full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing, comprising the following steps:

[0064] S1. Build a dynamic three-dimensional deformation high-precision measurement system based on polarization multiplexing, adjust the angles of the polarizer and quarter-wave plate to ensure that the polarization states of the reference light and the object light meet the polarization multiplexing requirements, and adjust the aperture of the adjustable aperture according to the size of the CCD pixel to make the speckle size meet the design requirements.

[0065] Please see Figure 1 The dynamic three-dimensional deformation high-precision measurement system includes a laser, a polarizing CCD, a reflector M, and a depolarizing beam splitter BS. The laser is set on one side of the depolarizing beam splitter BS, the object to be measured is set on the other side of the depolarizing beam splitter BS, the polarizing CCD is located on the lower side of the depolarizing beam splitter BS, and the reflector M is set on the upper side of the depolarizing beam splitter BS.

[0066] A first attenuator, a pinhole filter, a collimating lens, and a first polarizer P1 are sequentially arranged between the laser and the depolarizing beam splitter BS. A third polarizer P3 is arranged between the object under test and the depolarizing beam splitter BS. A second attenuator and a second polarizer P2 are sequentially arranged between the reflector M and the depolarizing beam splitter BS. A quarter-wave plate QWP, a second lens L2, an adjustable aperture, and a first lens L1 are sequentially arranged between the polarizing CCD and the depolarizing beam splitter BS.

[0067] The light emitted by the laser is expanded and collimated, and then adjusted to 0° linearly polarized light by the first polarizer P1. The depolarizing beam splitter separates the beam into object light and reference light, and can maintain the polarization state of each beam without change.

[0068] In this process, the reference light is polarized at 45° after passing through the second polarizer P2, while the polarization state of the object light remains unchanged at 0°. At the same time, the second polarizer P2 and the third polarizer P3 can prevent the polarization state of the reference light and the object light from changing after being reflected by the mirror M or the surface under test.

[0069] The fast axis of the quarter-wave plate QWP is parallel to the transmission direction of the second polarizer P2. Therefore, after passing through QWP, the polarization state of the reference light remains unchanged, while the polarization state of the object light is converted into circularly polarized light.

[0070] The first lens L1 and the first lens L2 together form an imaging system that images the object under test onto the target surface of a polarization CCD.

[0071] The adjustable aperture is located at the Fourier surface of the imaging system and is used to adjust the speckle size.

[0072] The second attenuator is used to match the intensity of the object parameter light to produce a high-contrast interference fringe pattern.

[0073] According to the Jones matrix, the complex amplitude of the incident light after passing through the first polarizer P1 is expressed as: After being split by BS, since the angles between the transmission directions of P2, P3 and P1 are 45° and 0° respectively, the reference beam E... r1 、physical light E o1 The complex amplitudes are expressed as follows:

[0074]

[0075]

[0076] The angles between the fast axis direction of the QWP and the transmission directions of P2 and P3 are 0° and 45°, respectively. Therefore, after modulation by the QWP, the reference light E... r2 、physical light E o2 The complex amplitudes are expressed as follows:

[0077]

[0078]

[0079] At this point, the reference light is 45° linearly polarized, while the object light is circularly polarized.

[0080] A polarization CCD is an imaging device capable of simultaneously recording polarization information at 0°, 45°, 90°, and 135°. This camera uses 2x2 pixels as a polarization unit, and the layout within each polarization unit is as follows: Figure 2 As shown.

[0081] When the reference light and object light are imaged onto the CCD target surface, the complex amplitude distributions of the reference light and object light in the four polarization directions are as follows:

[0082]

[0083]

[0084] Since the reference light is polarized at 45°, the pixels on the polarized CCD with a polarization direction of 135° do not contain reference light information and can only capture the object light intensity, i.e., the speckle pattern. The pixels in the other three polarization directions can capture the interference information between the object light and the reference light. Because the object light is circularly polarized, according to the principle of polarization phase shift, there is a 45° phase shift between the corresponding interference fields in the three polarization directions.

[0085] make A r , A o , Let A and B be the amplitude and phase of the reference light and the object light, respectively. Then, the light intensity distributions recorded by the polarization CCD in the four polarization directions are as follows:

[0086]

[0087]

[0088]

[0089] I 135 =A 2

[0090] o

[0091] This enables the simultaneous recording of speckle patterns and speckle interference phase shift patterns, meeting the requirements for dynamic high-precision measurement.

[0092] To clearly demonstrate the principle of the method of this invention, an imaging experiment was conducted using a resolution plate as the object under test. The light intensity maps in four polarization directions extracted from the raw data recorded by a single frame of a polarization CCD are shown below. Figure 2 As shown, phase-shifted interferograms are recorded in the polarization directions from 0 to 90°, and object-side light intensity diagrams are recorded at 135°, consistent with the aforementioned analysis, thus verifying the rationality of the invention method.

[0093] S2. During the continuous change of the surface state of the object being measured, the polarization CCD synchronously records the speckle pattern I at a certain frame rate. 135 And speckle interference phase shift diagram I 0 I 45 I 90 ;

[0094] Because of I 0 I 45 I 90 I 135Since the light intensity maps are distributed across different pixels, before calculating the 3D deformation, it is necessary to first extract the light intensity maps in four polarization directions from the raw data recorded by the polarization CCD through downsampling. This process reduces the image resolution to half that of the CCD. Therefore, to ensure that the measurement resolution is not lost, interpolation operations need to be performed on the four light intensity maps. There has been much research on image interpolation algorithms. Bicubic spline interpolation was used in the experiment, but it is not limited to this method.

[0095] S3, Given A o 2 Under the condition, I 45 Represented as I 0 I 90 A linear combination of, i.e.: I 45 -A o 2 =I 0 +I 90 -2A o 2 Therefore, the effective phase shift interferogram used to solve for out-of-plane deformation is only I. 0 I 90 When the object being measured undergoes deformation, the intensity distribution of the phase-shifted interferogram is represented as follows:

[0096]

[0097]

[0098] Subtracting the phase-shifted interference intensity diagram pairwise from the original diagram yields a three-step phase-shifted fringe pattern that includes information about out-of-plane deformation:

[0099]

[0100]

[0101]

[0102] It can be seen that the phase shift between the three phase-shifted fringe patterns is refer to Figure 4 Based on the three phase-shifted fringe patterns mentioned above, a multi-frame phase-shift demodulation algorithm can be used to obtain the distorted phase information. The enclosed phase map is obtained. The enclosed phase obtained based on multi-frame phase shift demodulation has high accuracy and low speckle noise, which can ensure the accuracy of out-of-surface deformation measurement. There are many multi-frame phase shift demodulation methods that can be adopted, such as matrix decomposition-based demodulation methods, which will not be elaborated here.

[0103] After unwrapping the wrapped phase map, the out-of-plane deformation phase information can be recovered and converted into the out-of-plane deformation amount Δz using the following formula:

[0104]

[0105] It should be noted that when obtaining the stripe patterns sub1 and sub3, I df 0 -I 90 I df 90 -I 0 This is a process of subtracting light intensity between different pixels. Therefore, to ensure the generation of high-contrast fringes, each polarization unit must be covered by the same speckle pattern. At this point, the changes in background light intensity and phase in the four polarization directions are minimized, and the correlation is maximized. That is, the speckle size should be 4 times the pixel size. The speckle size δ can be controlled by adjusting the aperture D of the variable aperture.

[0106]

[0107] Where M and f are the magnification and focal length of the imaging system, and λ is the laser wavelength.

[0108] S4. Based on the speckle pattern recorded by the pixels with a polarization direction of 135° on the polarization CCD, DIC calculation is performed to obtain the in-plane deformation of the measured object, thereby realizing high-precision measurement of dynamic three-dimensional deformation.

[0109] The high-precision DIC algorithm is now very mature, and its calculation accuracy can reach the sub-pixel level. Here, we will only briefly describe its general steps.

[0110] Select the speckle pattern I collected before deformation 135 Using the reference image and selecting a region of interest (ROI), to determine the displacement of each measurement point in the ROI, a reference sub-region Ref with a size of (2m+1)*(2m+1) needs to be set with that point as the center. Then, the position and shape of the most similar target sub-region Def are searched in the deformed image to determine the displacement of the center measurement point of the reference sub-region Ref. The above search process is performed for each measurement point in the ROI to obtain the total in-field deformation of the measured surface.

[0111] The similarity evaluation between the reference subset Ref and the target subset Def adopts the zero-mean normalized minimum squared distance standard, which is highly resistant to environmental interference and has high accuracy.

[0112]

[0113] Among them, (x i ,y i ) and (x i ′,y i′) represent the coordinate positions of the reference sub-region and the target sub-region, respectively. and This represents the average intensity.

[0114] For a certain area of ​​the surface being measured, the deformation within that area can be represented by a mathematical model, i.e., a shape function.

[0115] Let the shape function be expressed as S(p), where p = (u, u x ,u y ,v,v x ,v y Let ) represent displacement and displacement gradient. Then, corresponding to the reference sub-region and the target sub-region, we have:

[0116] (x i ′,y i ′)=S((x i ,y i ),p)

[0117] Therefore, the correlation operations between the reference sub-region and the target sub-region are taken as the objective function. By establishing and setting reasonable shape function relations and initial parameter values ​​p0, the classic and efficient inverse synthesis Gauss-Newton algorithm is used for iterative optimization to find local optimal solutions, thereby determining the displacement vector (u,v) of the measured point. T This can be extended to other points to be measured, resulting in a high-precision full-field displacement assessment. It is important to note that the displacement (u,v) calculated by DIC... T The results are usually in pixels, so they need to be converted into actual physical displacements (Δx, Δy) based on the imaging magnification M of the measurement system and the pixel size. T More precise calibration methods can also be adopted to further improve measurement accuracy.

[0118] Δx = u * M * pixel size

[0119] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0120] To demonstrate the actual measurement effect of the method of the present invention, a system was constructed according to the description in step S1. Figure 1 The three-dimensional measurement system shown was used to measure the three-dimensional deformation of a coin. The coin was fixed on a horizontal displacement stage, which was moved 50 micrometers along the x-axis to simulate in-plane deformation. Simultaneously, the coin was rotated a small angle around the x-axis to produce out-of-plane deformation. A polarizing CCD recorded the speckle pattern and speckle interferogram of the coin before and after deformation. Based on the descriptions in steps S2 to S4, out-of-plane deformation and in-plane deformation were calculated respectively to obtain the three-dimensional deformation distribution of the coin.

[0121] Figure 4 To correspond to the three-frame phase-shifted interference fringe pattern of out-of-plane deformation, the phase diagram and the true phase distribution are included. The fringe contrast of the three-frame interference fringe pattern is relatively consistent. Thanks to the design step of using an adjustable aperture to control the speckle size to improve speckle correlation, the measurement results verify the feasibility of the scheme of using a polarized CCD to achieve synchronous phase shift for dynamic out-of-plane deformation measurement.

[0122] Figure 5 To correspond with the in-plane deformation distribution calculated based on DIC, it can be seen that the deformation in the x-direction of the measurement results is basically consistent with the displacement of the displacement stage, while the deformation in the y-direction is very small (caused by the coin surface and the displacement direction of the displacement stage not being perpendicular to the optical axis), which is consistent with the actual in-plane deformation.

[0123] In summary, this demonstrates the feasibility and practicality of applying the method of this invention to the field of dynamic high-precision measurement.

[0124] In summary, this invention provides a full-field dynamic three-dimensional deformation measurement method and system based on polarization multiplexing. By adjusting the polarization states of the object light and reference light to circularly polarized light and 45° linearly polarized light, respectively, and utilizing a polarization CCD, the speckle field and speckle interference phase shift field of the measured object before and after three-dimensional deformation are simultaneously recorded. Specifically, the speckle interference phase shift map recorded by pixels with polarization directions of 0° and 90° on the polarization CCD is used to recover out-of-plane deformation, while the speckle map recorded by pixels with a polarization direction of 135° is used for DIC calculation to recover in-plane deformation. This solves the problems in related technologies combining DSPI and DIC for dynamic three-dimensional deformation measurement, such as the inability to synchronously record direct speckle maps and interference phase shift maps, and the difficulty in meeting dynamic measurement requirements. Therefore, the speckle map does not need to be calculated from the interference field, thus avoiding the decrease in accuracy of DIC in-plane deformation calculation caused by this problem. Simultaneously, based on polarization phase shift technology, the synchronous acquisition of multi-step phase shift interferograms is achieved, ensuring the measurement accuracy of out-of-plane deformation.

[0125] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0126] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing, characterized in that, This measurement is performed using a polarization-multiplexed full-field dynamic three-dimensional deformation measurement system. The system includes a depolarization-splitting beam splitter prism (BS), with the object being measured positioned on one side of the BS. A laser is positioned on the other side of the BS. A reflector M is positioned above the BS, and a polarizing CCD is positioned below it. A first attenuator, a pinhole filter, a collimating lens, and a first polarizing filter are sequentially arranged between the laser and the BS. A third polarizer P3 is placed between the object under test and the depolarizing beam splitter BS. A second attenuator and a second polarizer P2 are sequentially placed between the reflector M and the depolarizing beam splitter BS. A quarter-wave plate QWP, a second lens L2, an adjustable aperture, and a first lens L1 are sequentially placed between the polarizing CCD and the depolarizing beam splitter BS. The depolarizing beam splitter splits the linearly polarized light emitted by the laser, which has been adjusted to 0° by the first polarizer P1, into object light and reference light, while maintaining the polarization state of the beam unchanged. This includes the following steps: S1. Adjust the angles of the first polarizer P1, the second polarizer P2, the third polarizer P3 and the quarter-wave plate so that the polarization states of the reference light and the object light satisfy polarization multiplexing. Adjust the aperture of the adjustable stop according to the pixel size of the polarization CCD. S2. During the deformation of the surface of the object being measured, a speckle pattern is simultaneously recorded using a polarizing CCD. and speckle interference phase shift diagram , , speckle pattern and speckle interference phase shift diagram , , They are respectively: in, , These represent the amplitude and phase of the reference light, respectively. , These represent the amplitude and phase of the object beam, respectively. S3. A sequence of speckle interference phase shift images recorded before and after deformation of the object under test. , By performing pairwise subtraction, a deformed fringe pattern is obtained. A multi-frame phase-shift demodulation algorithm is then used to obtain the deformed phase information. The enclosed phase map is used to perform unwrapping calculations to recover the out-of-plane deformation phase information and convert it to obtain the out-of-plane deformation amount. ; S4. Speckle pattern recorded based on pixels with a polarization direction of 135° on a polarized CCD. Perform DIC calculations to obtain the in-plane deformation of the measured object, and combine this with the out-of-plane deformation obtained in step S3. To achieve dynamic three-dimensional deformation measurement, specifically: Select the speckle pattern acquired before deformation As a reference image, and selecting the region of interest (ROI), the size is set with the measurement point as the center. Reference subregion , The integer is positive, and then the corresponding target sub-region is searched in the deformed image. Determine the reference sub-region The displacement of the central measurement point; the above search process is performed on each measurement point in the region of interest (ROI) to obtain the total in-field deformation of the measured surface. Reference sub-region and target sub-region The relevant operations are used as the objective function, and the formal functional relations and initial parameter values ​​are established and set. The inverse Gaussian-Newton algorithm is used for iterative optimization to find local optima and determine the displacement vector of the measured point. According to the imaging magnification And pixel size is the displacement vector of the measured point Converted to actual physical displacement This process is extended to the remaining test points to obtain the overall displacement assessment results.

2. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 1, characterized in that, In step S1, the aperture of the adjustable aperture... and speckle size The relationship is as follows: in, , For the magnification and focal length of the imaging system, The wavelength of the laser. This refers to the CCD pixel size.

3. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 1, characterized in that, In step S2, light intensity maps in four polarization directions are extracted from the raw data recorded by the polarization CCD through downsampling. Then, interpolation is performed on the four light intensity maps to obtain the speckle map. and speckle interference phase shift diagram , , .

4. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 1, characterized in that, In step S3, the amount of out-of-plane deformation Specifically: in, For deformed phase information, is the laser wavelength.

5. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 4, characterized in that, for: in, This refers to the CCD pixel size.

6. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 1, characterized in that, The fast axis of the quarter-wave plate QWP is parallel to the transmission direction of the second polarizer P2.

7. The full-field dynamic three-dimensional deformation measurement method based on polarization multiplexing according to claim 1, characterized in that, The adjustable aperture is located at the Fourier surface of the imaging system.

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