Structured light digital speckle interferometry apparatus and method for in-plane deformation measurement

Abstract

This invention discloses a structured light digital speckle interferometry device and method for in-plane deformation measurement. The device includes a structured light illumination generation module, an imaging module, and a data processing module. The structured light illumination generation module includes a laser, a spatial light modulator, a TIR prism, and a spatial mask. The spatial light modulator is used to load fringe modulation patterns with different phase shifts along a first direction and a second direction, respectively, to modulate the illumination beam, forming multiple diffracted beams propagating in different directions and achieving phase shift operation. The spatial mask only selects +1... st -1 st A diffraction-level beam is interfered with to generate structured illumination light; an imaging module is used to record digital speckle phase-shift images corresponding to structured illumination light with different directions and phase shifts; a data processing module is used to obtain deformation information of the sample along different in-plane directions. This invention can achieve high-precision in-plane deformation measurement, is less affected by environmental disturbances, and has a compact device and high stability.

Description

Technical Field

[0001] This invention belongs to the field of non-contact optical detection technology, specifically relating to a structured light digital speckle interferometer device and method for in-plane deformation measurement. Background Technology

[0002] Material mechanical property testing and structural reliability analysis play a crucial role in engineering applications. Since deformation parameters serve as a direct representation of material mechanical behavior, their accurate acquisition is directly related to key aspects such as stress-strain analysis and strength / stiffness calculations, thus becoming a core observation indicator in modern experimental mechanics research. Precise deformation measurement is not only a fundamental prerequisite for constructing stress and strain field distributions of structures but also directly determines the effectiveness of engineering processes such as strength and stiffness analysis. Therefore, the development of high-precision deformation measurement technology has become a focal point of widespread research interest.

[0003] Depending on the testing conditions, deformation measurement methods can be divided into contact measurement methods and non-contact measurement methods. The former mainly involves the measuring instrument directly contacting the object being measured to achieve deformation measurement, such as the coordinate measuring machine (CMM), which is a typical example. Although it has high repeatability, it can damage the surface of the object being measured and has a slow measurement speed. The latter mainly involves optical testing methods, including holography, speckle method, structured light measurement, and image matching method. These methods have advantages such as non-contact, full-field measurement, high accuracy, and high speed, and are gradually gaining attention from researchers.

[0004] Electron speckle interferometry (ESPI) is a well-developed modern full-field non-contact optical measurement technique. It boasts advantages such as versatility, high measurement accuracy, wide frequency range, ease of measurement, and minimal susceptibility to environmental interference, and has been widely applied to the measurement of displacement, slope, curvature, torsion, vibration, and morphology of objects. Furthermore, depending on the different interference optical paths constructed, ESPI can be used to measure in-plane deformation, out-of-plane deformation, and in-plane / out-of-plane coupled deformation. With the continuous maturation of the theory of corresponding one-dimensional deformation, researching and developing methods for measuring multi-dimensional deformation of objects using ESPI has become a new trend.

[0005] Currently, various multi-sensitivity vector interferometric optical paths exist for measuring the static deformation of objects, but the measurement of different deformations often cannot be performed in a common path. For example, Takatsuji et al. used three object beams and one reference beam to form three interferometric optical paths to measure the three displacement components of three-dimensional deformation. Zhang Xi et al. used three lasers, a large misaligned prism, and a PZT phase shifter to form a three-dimensional phase-shifting ESPI system for measuring the three-dimensional displacement of a diesel engine fuselage. This method, using a large misaligned prism, eliminates the need for three separate reference optical paths placed in front of the camera, thus greatly simplifying the optical path. Subsequently, Flynn et al. used three different wavelengths of light to form a three-dimensional displacement field measurement interferometric optical path to measure the three-dimensional displacement components. Although the above techniques can all achieve the measurement of object deformation, the phase-shifting operation often uses devices such as piezoelectric ceramics (PZT). Due to their inherent delay, repeatability is poor, resulting in slow imaging speed and low phase-shifting accuracy, which in turn affects the measurement accuracy. Furthermore, when generating digital speckle interference, different beams take different paths, leading to low device stability and complex imaging optical paths. Summary of the Invention

[0006] To address the problems of complex structure, poor stability, and low phase shift accuracy in traditional digital speckle interferometry optical paths, this invention provides a structured light digital speckle interferometry device and method for in-plane deformation measurement, enabling measurement of samples in the first in-plane direction. x and the direction within the second face y In-plane deformation measurement in a specific direction offers advantages such as high precision, high stability, fast imaging speed, and simple imaging device. The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] One aspect of the present invention provides a structured light digital speckle interferometer capable of measuring in-plane deformation, comprising a structured light illumination generation module, an imaging module, and a data processing module, wherein...

[0008] The structured light illumination generation module includes a laser, a spatial light modulator, a TIR prism, and a spatial mask. The laser generates a laser beam. The spatial light modulator loads fringe modulation patterns with different phase shifts along a first direction and a second direction, respectively, to modulate the laser beam and achieve phase shift operation, forming multiple diffracted beams propagating in different directions under the modulation of each fringe modulation pattern. The TIR prism ensures that the diffracted beams modulated by the spatial light modulator propagate along the optical axis. The spatial mask selects only +1 when loading fringe modulation patterns along the first direction and the second direction onto the spatial light modulator. st -1 st The diffraction-level beams interfere to generate structured illumination light, wherein the first direction and the second direction are both located on the working surface of the spatial light modulator and are perpendicular to each other;

[0009] The imaging module is used to illuminate the sample with the structured illumination light and record digital speckle phase shift images corresponding to structured illumination light with different directions and different phase shifts under different directions and phase shifts.

[0010] The data processing module is used to obtain the deformation information of the sample along different in-plane directions using digital speckle phase shift images corresponding to structured illumination light with different directions and phase shift amounts.

[0011] Another aspect of the present invention provides a structured light digital speckle interferometry method for measuring in-plane deformation, the method comprising:

[0012] S1: Load the spatial light modulator with stripe modulation patterns having different phase shifts along the first direction and stripe modulation patterns having different phase shifts along the second direction, respectively, to obtain multiple digital speckle phase shift images of the sample under structured illumination light conditions with different directions and different phase shifts before deformation;

[0013] S2: Obtain in-plane deformation information of the sample along different directions using digital speckle phase-shift images corresponding to structured illumination with different directions and phase shift amounts.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] This invention proposes a structured light illumination digital speckle interferometer device and method for in-plane deformation measurement, enabling high-precision in-plane deformation measurement. First, by loading fringe modulation patterns with different phase shifts along a first direction and a second direction onto an SLM (spatial light modulator), and combining this with a spatial mask, a +1... st and -1 st The diffraction-level beam is used to generate fast structured illumination and phase shift, offering advantages such as fast imaging speed, high phase shift accuracy, and accurate reconstruction results. Secondly, compared to traditional digital speckle interferometry paths, the common-path mode (+1) is utilized... st and -1 st When the diffraction-level beam travels along the same path, it is less affected by environmental disturbances, the device is compact, and the stability is high, which can further ensure measurement accuracy. In summary, this deformation measurement device and method have the advantages of simple structure, high precision, and high stability, and can be widely used in various fields such as modern material property research.

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a structured light digital speckle interferometer device for in-plane deformation measurement provided in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the modulated images loaded in the first and second directions of the spatial light modulator and the corresponding spatial mask.

[0019] Figure 3 This is a schematic diagram of digital speckle interferometry under structured illumination light in the first direction.

[0020] Figure 4 It is a digital speckle phase-shift image of the sample in the direction in the first surface under structured illumination and a reconstructed phase distribution map;

[0021] Figure 5 It is a digital speckle phase-shift image of the sample in the direction in the second surface under structured illumination, and a reconstructed phase distribution map;

[0022] Figure 6 It is a diagram showing the phase difference relationship caused by the displacement in different planes in the first plane direction and the second plane direction, and the correspondence between theoretical displacement and actual displacement.

[0023] Explanation of reference numerals in the attached figures:

[0024] 1-Laser; 2-Fiber optic cable; 3-Linear polarizer; 4-First thin lens; 5-TIR prism; 6-Spatial light modulator; 7-Second thin lens; 8-Spatial mask; 9-Third thin lens; 10-Beam splitter; 11-Sample; 12-Industrial lens; 13-Camera. Detailed Implementation

[0025] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, describes the structured light digital speckle interferometer device and method for in-plane deformation measurement proposed according to the present invention.

[0026] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes said element.

[0028] Example 1

[0029] This embodiment provides a structured light digital speckle interferometer capable of measuring in-plane deformation. The structured light digital speckle interferometer includes a structured light illumination generation module, an imaging module, and a data processing module arranged sequentially. The structured light illumination generation module includes a laser 1, a spatial light modulator 6, a TIR (Total Internal Reflection) prism 5, and a spatial mask 8. The laser 1 generates a laser beam. The spatial light modulator 6 loads fringe modulation patterns with different phase shifts along a first or second direction onto the working surface to modulate the laser beam from the laser 1 and achieve phase shifting, i.e., multiple diffracted beams propagating in different directions are formed under the modulation of each fringe modulation pattern. The TIR prism 5 ensures that the diffracted beam modulated by the spatial light modulator 6 propagates along the optical axis. The spatial mask 8 selects only +1 when loading fringe modulation patterns along the first and second directions onto the spatial light modulator 6. st -1 st The diffraction-level beams are interfered to generate structured illumination light, wherein the first direction and the second direction are both located on the working surface of the spatial light modulator 6 and are perpendicular to each other; the imaging module is used to illuminate the sample with structured illumination light and record digital speckle phase shift images corresponding to structured illumination light under different directions and different phase shifts; the data processing module is used to obtain the deformation information of the sample along different in-plane directions using the digital speckle phase shift images corresponding to structured illumination light under different directions and different phase shifts.

[0030] Further, please see Figure 1 , Figure 1This is a schematic diagram of a structured light illumination digital speckle interferometer device for in-plane deformation measurement provided by an embodiment of the present invention. The structured light illumination generation module of this embodiment further includes an optical fiber 2, a linear polarizer 3, a first thin lens 4, a second thin lens 7, and a third thin lens 9. The linear polarizer 3 is used to polarize the laser beam generated by the laser 1 to obtain linearly polarized light with the same polarization direction as the spatial light modulator 6. The first thin lens 4 is used to collimate and expand the linearly polarized light. The TIR prism 5 is used to reflect the linearly polarized light collimated and expanded by the first thin lens 4 while simultaneously transmitting the diffracted beam generated by the spatial light modulator 6, ensuring that the diffracted beam propagates along the optical axis. The second thin lens 7 is used to converge multiple diffracted beams propagating in different directions from the spatial light modulator 6 and illuminate a spatial mask plate 8. The spatial mask plate 8 is disposed on the back focal plane of the second thin lens 7, enabling selective filtering of the diffracted beam after passing through the spatial light modulator 6, retaining only the +1 values ​​in the first and second directions. st -1 st The diffraction-level beams interfere; the front focal plane of the third thin lens 9 coincides with the rear focal plane of the second thin lens 7, and is used to image the structured illumination light filtered by the space mask plate 8 onto the sample 11.

[0031] The imaging module of this embodiment includes a beam splitter 10, an industrial lens 12, and a camera 13. The beam splitter 10 is used to reflect the structural illumination light from the third thin lens 9 and illuminate the sample 11, while simultaneously transmitting the scattered light beam from the sample 11 to the industrial lens 12. The sample 11 is disposed on the front focal plane of the industrial lens 12, and the rear focal plane of the third thin lens 9 coincides with the front focal plane of the industrial lens 12. The camera 13 is disposed on the side of the industrial lens 12 away from the beam splitter 10.

[0032] Specifically, the laser emitted by laser 1 is coupled into optical fiber 2 and emitted out. Linear polarizer 3 acts on the laser generated by laser 1 to change its polarization characteristics and adjust its polarization direction, ultimately making it linearly polarized light with the same polarization direction as spatial light modulator 6. After being converted into linearly polarized light by linear polarizer 3, it is expanded and collimated by first thin lens 4, and then reflected by TIR prism 5 to spatial light modulator 6. This illumination beam can cover the effective working surface of spatial light modulator 6.

[0033] In this embodiment, the spatial light modulator 6 is specifically used to: load stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain the in-plane direction (corresponding to) the deformation front of the sample 11 on the camera 13. Figure 1 In xThree digital speckle phase-shifted images (corresponding to the second direction) are obtained; stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain the in-plane direction (corresponding to the second plane direction) of the sample 11 at the deformation front on camera 13. Figure 1 In y Three digital speckle phase-shifted images of sample 11 in the first in-plane direction are obtained on camera 13; stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase-shifted images of sample 11 in the first in-plane direction after deformation; stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase-shifted images of sample 11 in the second in-plane direction after deformation on camera 13, wherein the first in-plane direction and the second in-plane direction are both located in the sample surface of sample 11 and are perpendicular to each other.

[0034] When a fringe modulation pattern is applied to the spatial light modulator 6, the laser beam is modulated by the current fringe modulation pattern to form multiple diffracted beams propagating in different directions. The second thin lens 7 converges the multiple diffracted beams from the spatial light modulator 6 in different propagation directions and illuminates the spatial mask plate 8. After selective filtering by the spatial mask plate 8, only +1 is retained. st -1 st The diffraction beam interferes and is then imaged onto sample 11 by the third thin lens 9.

[0035] Specifically, please see Figure 2 By loading stripe modulation patterns with corresponding phase shifts of 0, 2π / 3, and 4π / 3 in the first and second directions respectively onto the spatial light modulator 6, such as... Figure 2 As shown in (b) and 2(d). Simultaneously, the generated multiple diffracted beams are converged by the second thin lens 7 and irradiate the spatial mask 8, which is shown in... Figure 1 , 2 As shown in (a) and 2(c), it should be noted that the actual spatial mask 8 is as follows: Figure 1 As shown, Figure 2 (a) and Figure 2 (c) The superposition of structures can be achieved by selecting only +1 when loading the stripe modulation pattern along the first direction and the stripe modulation pattern along the second direction. st -1 st A diffraction-level beam is used to generate structured illumination. Finally, digital speckle phase-shift images corresponding to structured illumination with different directions and phase shifts are acquired sequentially.

[0036] Preferably, the laser 1 has a wavelength in the visible light range, stable output laser power, and an appropriate coherence length. In this embodiment, the wavelength of the laser 1 is 561 nm; the linear polarizer 3 has a wavelength range of 400-700 nm and an extinction ratio of 500:1. The first thin lens 4, the second thin lens 7, and the third thin lens 9 are all achromatic cemented doublet lenses. The focal length of the first thin lens 4 is 200 mm; the focal length of the second thin lens 7 is 100 mm; and the focal length of the third thin lens 4 is 150 mm. The spatial light modulator 6 has 2716 × 1600 pixels, and the pixel size is 5.4 μm.

[0037] Beam splitter 10 is used to reflect the structured illumination light and transmit the scattered light from sample 11. Industrial lens 12 has a focal length of 25mm, a pixel count of 10MP, and an image size of 1 / 1.8 inch. Camera 13 is a standard monochrome sCMOS camera with specific gain, grayscale levels, pixel size, and pixel count. Preferably, the beam splitter 10 has a beam splitting ratio of 50:50 (transmission:reflection); the sCMOS camera 13 has 4096×3000 pixels and a pixel size of 3.45 μm.

[0038] Specifically, the +1 after filtering by the spatial mask 8 st -1 st The diffractive beam passes through the third thin lens 9 and forms parallel structured light propagating in different directions. It is then reflected by the beam splitter 10 onto the sample 11. Subsequently, the scattered light reflected from the sample is transmitted by the beam splitter 10 and collected by the industrial lens 12. The resulting digital speckle phase-shift image is received by the camera 13.

[0039] It should be noted that the light propagation distance from the spatial light modulator 6 to the sample surface of the sample 11 is the same as the distance from the sample surface of the sample 11 to the image surface of the camera 13, which is used to make the image surfaces of the sample, structured light, and camera consistent to obtain the best imaging effect.

[0040] Furthermore, the data processing module in this embodiment is specifically used for:

[0041] Using three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the first direction before deformation and three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the first direction after deformation, the phase distribution of sample 11 before and after deformation along its first in-plane direction is obtained. Based on the correspondence between the phase difference and the optical path difference caused by deformation, the in-plane deformation information of sample 11 along its first in-plane direction is obtained. Using three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the second direction before deformation and three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the second direction after deformation, the phase distribution of sample 11 before and after deformation along its second in-plane direction is obtained. Based on the correspondence between the phase difference and the optical path difference caused by deformation, the in-plane deformation information of sample 11 along its second in-plane direction is obtained.

[0042] Specifically, loading a corresponding fringe modulation pattern onto the spatial light modulator 6 can achieve three-step phase shifts in the first direction: 0, 2π / 3, and 4π / 3. By recording three (six in total) digital speckle phase shift images generated before and after sample deformation, and combining them with the corresponding reconstruction algorithm, the phase distribution of sample 11 before and after deformation in the first in-plane direction can be solved. Finally, based on the correspondence between the phase difference and the optical path difference caused by deformation, the in-plane deformation information of sample 11 in the first in-plane direction can be obtained. Then, loading a corresponding fringe modulation pattern onto the spatial light modulator 9 can achieve... The three-step phase shifts of 0, 2π / 3, and 4π / 3 in the second direction are recorded by taking three digital speckle phase shift images (a total of six) before and after the sample deformation. Combined with the corresponding reconstruction algorithm, the phase distribution of the sample 11 before and after deformation in the second in-plane direction is solved. Finally, based on the correspondence between the phase difference and the optical path difference caused by the deformation, the in-plane deformation information of the sample 11 in the second in-plane direction can be obtained. Finally, the in-plane deformation information of the sample in two mutually perpendicular directions can be obtained. For the specific data processing and solution process, please refer to the following implementation case two.

[0043] This invention proposes a structured light-illuminated digital speckle interferometer for in-plane deformation measurement, enabling high-precision deformation measurement. First, a corresponding fringe modulation pattern is loaded onto an SLM (spatial light modulator), and then a spatial mask is selected with a +1... st and -1 st Interference of diffraction-level beams to generate rapid structured light illumination and phase shifting offers the advantage of high imaging speed while avoiding the poor repeatability issues encountered when using devices such as PZT for phase shifting. High phase shift repeatability further ensures the accuracy of the reconstruction results. Secondly, compared to traditional digital speckle interferometry paths, utilizing a common-path mode (+1...) st and -1 stWhen the diffraction-level beam travels along the same path, it is less affected by environmental disturbances, resulting in high device stability and ensuring measurement accuracy. Finally, compared to traditional in-plane deformation measurement optical paths, this method utilizes phase-shift patterns applied by the SLM in the first and second directions, simplifying the optical path and enabling in-plane deformation measurement. In summary, this deformation measurement device and method possess advantages such as high precision, high stability, and high integration, and can be widely applied in various fields, including industrial inspection.

[0044] Example 2

[0045] Based on Embodiment 1, this embodiment provides a structured light illumination digital speckle interferometry method for in-plane deformation measurement, including:

[0046] S1: The spatial light modulator 6 is loaded with stripe modulation patterns with different phase shifts along the first direction and stripe modulation patterns with different phase shifts along the second direction, respectively, to obtain multiple digital speckle phase shift images corresponding to structural illumination light conditions with different directions and different phase shifts before and after sample deformation.

[0047] Specifically, laser 1 is turned on; stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are respectively applied to spatial light modulator 6 to obtain three digital speckle phase shift images of sample 11 in the first plane direction at the deformation front of its sample 11 on camera 13; stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are respectively applied to obtain three digital speckle phase shift images of sample 11 in the second plane direction at the deformation front of its sample 11 on camera 13. After the sample is moved, stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are applied respectively to obtain three digital speckle phase-shifted images of the sample 11 after deformation along its first in-plane direction on camera 13; stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are applied respectively to obtain three digital speckle phase-shifted images of the sample 11 after deformation along its second in-plane direction on camera 13, wherein the first in-plane direction (corresponding to Figure 1 In x Direction) and the direction within the second plane (corresponding) Figure 1 In x The directions are all located within the sample surface of sample 11 and are perpendicular to each other.

[0048] S2: Obtain in-plane deformation information of the sample along different directions using digital speckle phase-shift images corresponding to structured illumination with different directions and phase shift amounts.

[0049] Specifically, using three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the first direction before deformation and three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the first direction after deformation, the phase distribution of sample 11 before and after deformation along its first in-plane direction is obtained, and the in-plane deformation information of sample 11 along its first in-plane direction is obtained according to the correspondence between the phase difference and the optical path difference caused by deformation; using three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the second direction before deformation and three digital speckle phase-shift images of sample 11 under structured illumination with different phase shifts in the second direction after deformation, the phase distribution of sample 11 before and after deformation along its second in-plane direction is obtained, and the in-plane deformation information of sample 11 along its second in-plane direction is obtained according to the correspondence between the phase difference and the optical path difference caused by deformation.

[0050] In this embodiment, an aluminum disk is used as a sample to illustrate the deformation measurement capability of the structured light digital speckle interferometry device and method provided by the present invention. The in-plane deformation of the aluminum disk is simulated by the radial movement of the aluminum disk. During the experiment, fringe modulation patterns with phase shifts of 0, 2π / 3, and 4π / 3 corresponding to the first direction and the second direction are sequentially loaded onto the spatial light modulator 6. Six digital speckle phase shift images (twelve in total) are recorded sequentially before and after the radial displacement of the aluminum disk causes deformation. Then, the phase difference before and after deformation (including the phase difference in the first in-plane direction) is calculated using a corresponding reconstruction algorithm. Figure 1 In x Phase difference (direction) In the direction of the second plane (corresponding) Figure 1 In y Phase difference (direction) Finally, the in-plane deformation information of the sample (including in-plane deformation information in the first in-plane direction) is obtained by the correspondence between the position difference and the optical path difference caused by deformation. In-plane deformation information in the second in-plane direction ).

[0051] Specifically, taking the example of loading stripe modulation patterns with three phase shifts corresponding to 0, 2π / 3, and 4π / 3 in the first direction onto the spatial light modulator 6, the +1 generated by the structured illumination light... st and -1 st The digital speckle phase-shift image produced by diffraction-order beam interference can be represented as:

[0052] (1)

[0053] in, , and The complex amplitudes and phase shifts of sample 11 before deformation are the 0th, -1st, and +1st orders, respectively. =2 m π / 3 ( m =0, 1, 2).

[0054] Before the sample is displaced, record the speckle intensity images at phase shifts of 0, 2π / 3, and 4π / 3 in the first direction. I 1. I 2. I 3. From equation (1), we can obtain:

[0055] (2)

[0056] By numerically processing the matrix equation (2), the complex amplitudes of the 0th and ±1st orders before displacement can be obtained.

[0057] Similarly, after the sample is displaced, the speckle intensity images at phase shifts of 0, 2π / 3, and 4π / 3 in the first direction are recorded. I 4. I 5. I 6. We can obtain:

[0058] (3)

[0059] in, , and These represent the complex amplitudes of sample 11 at orders 0, -1, and +1 after deformation. The complex amplitudes at orders 0 and ±1 after deformation were obtained using the same method. By selecting... or This allows us to obtain the change in complex amplitude before and after sample displacement. Furthermore, it allows us to obtain the phase difference in the direction within the first plane before and after sample displacement (i.e. before and after deformation). :

[0060] (4)

[0061] Similarly, the phase difference in the direction within the second plane before and after sample displacement (i.e., before and after deformation) can be obtained based on the above process. .

[0062] In deformation measurement using digital speckle interferometry, the deformation information of the sample can be obtained by utilizing the correspondence between the phase difference and the optical path difference caused by deformation. For example... Figure 3 As shown, Figure 3 (a) is a schematic diagram of in-plane deformation measurement. The enlarged area in the diagram is the in-plane area in the first direction +1. st and -1 st Interference fringes formed after diffraction-order interference; Figure 3(b) is a schematic diagram of the sample before and after deformation in the first plane.

[0063] The specific relationship is derived as follows: +1 st Diffraction-order beam 1-1 passes through the sample before deformation P After the point, move the sample along the coordinate axes from point 1-3 to the camera target surface. x Displacement in direction (corresponding to the direction within the first plane) Then, +1 st Diffraction-order beams 1-4 P If point 1 is followed by a path from 1 to 6 to the camera target surface, then +1 is applied. st The optical path difference of the diffraction beam before and after sample deformation is ,in According to geometric relationships, we can obtain... Furthermore, At this point, based on the relationship between phase difference and optical path difference, we can obtain:

[0064] (5)

[0065] in, The illumination wavelength of laser 1 Indicates +1 st The phase difference generated in the diffraction-order beam before and after deformation Indicates +1 st The incident angle of a diffraction-order beam.

[0066] -1 st Diffraction beam 1-2 passes through the sample before deformation P After the point, move the sample along the coordinate axes from point 1-3 to the camera target surface. x Directional displacement After that, -1 st Diffraction-grade beams 1-5 P If the line from point 1 to point 6 extends to the camera target surface, then -1... st The optical path difference before and after the diffraction-order beam deformation is P 1 B ,in According to geometric relationships, we can obtain... Furthermore, At this point, based on the relationship between phase difference and optical path difference, we can obtain:

[0067] (6)

[0068] in, Represents -1 st The phase difference generated by the diffraction beam before and after deformation.

[0069] The relationship between the total phase difference and the optical path difference is:

[0070] (7)

[0071] y The deformation principle of direction (inside the second plane) and x The same applies to the direction.

[0072] This embodiment utilizes a spatial light modulator to achieve phase shifting, avoiding the problems of poor repeatability when using devices such as PZT to perform phase shifting operations. The phase shifting repeatability is high, further ensuring the accuracy of the reconstruction results.

[0073] To verify the accuracy of the structured light digital speckle interferometry device and method proposed in this invention, the actual displacement was compared with the theoretical displacement value. The process is as follows: [The text abruptly ends here, likely due to an incomplete sentence or a missing section.] x and y The direction adds an actual displacement to the sample, and phase reconstruction is performed using the captured digital speckle phase-shift image to obtain a phase difference image, which yields the phase difference value corresponding to the actual displacement. This is then compared with the phase difference value calculated from the theoretical formula. x and y The theoretical displacement values ​​in the direction are compared.

[0074] Please see Figure 4 , Figure 4 This is a phase-shifted image of the SLM in the first direction when the aluminum disk is used as the sample. Figure 2 (b) The digital speckle phase-shift image and the reconstructed phase distribution image at time (b). Among them, the aluminum disk is directed towards... x Increase displacement by 3μm in the direction (inside the first plane), i.e. It is 3μm. Figure 4 (a) and 4(c) are digital speckle phase-shift images acquired by an sCMOS camera before and after deformation, with phase shifts of 0, 2π / 3, and 4π / 3, respectively. Figure 4 (b) and 4(d) are the phase distribution diagrams obtained before and after deformation. , ); Figure 4 (e) represents the phase difference between before and after deformation. - )distributed; Figure 4 (f) shows the phase difference statistics and Gaussian fitting for 4(e). The phase difference of the peak of the fitted curve is 0.9 rad, which means that the phase difference before and after deformation is 0.9 rad. The theoretical displacement is calculated according to formula (5). It is 3.07 μm, using The relative displacement measurement accuracy was calculated to be 0.023.

[0075] Please see Figure 5 , Figure 5This is a phase shift image of the second direction under SLM loading when the aluminum circular plate is used as the sample. Figure 2 (d) The digital speckle phase-shift image and the reconstructed phase distribution image at time (d). Among them, the aluminum disk is directed towards... y An increase of 6 μm displacement in the direction (inside the second plane), i.e. It is 6μm. Figure 5 (a) and 5(c) are digital speckle phase-shift images acquired by an sCMOS camera before and after deformation, with phase shifts of 0, 2π / 3, and 4π / 3, respectively. Figure 5 (b) and 5(d) are the phase distributions obtained before and after deformation by solving the equation. , ); Figure 5 (e) represents the phase difference between before and after deformation. - )distributed; Figure 5 (f) shows the phase difference statistics and Gaussian fitting for 4(e). The phase difference of the peak of the fitted curve is 1.78 rad, which means that the phase difference before and after deformation is 1.78 rad. The theoretical displacement is calculated according to formula (5). For 6.07μm utilization The relative displacement measurement accuracy was calculated to be 0.012.

[0076] Please see Figure 6 , Figure 6 These represent the phase difference relationship caused by in-plane displacements in different directions and the correspondence between theoretical and actual displacements. Figure 6 (a) and 6(b) represent the actual displacement of the aluminum disk in the direction in the first plane and the direction in the direction in the second plane. x and y The linear relationship of phase difference caused by direction ( and ), fitting linear coefficients k x =0.291, k y =0.297; The sample surface area was calculated based on the interference fringe pattern captured when the aluminum disk of the sample was replaced with a reflector. x or y Direction +1 st Diffraction-order beam, -1 st The angle between the diffraction order beam and the normal is 0.75°, according to the formula... We can obtain, =3.4106, Figure 6 Multiplying the phase difference in both (a) and 6(b) by 3.4106 yields the theoretical displacement value. and . Figure 6 (c) represents the theoretical displacement. and actual displacement Correspondence ( The linear coefficients of the fit are k x= 0.992±0.008; Figure 6 (d) is the theoretical displacement and actual displacement Correspondence ( The linear coefficients of the fit are k y= 1.014±0.008. For example, when an aluminum disk is moved axially... y Directional displacement The phase difference introduced when the theoretical displacement is 6 μm is: = - =1.78 rad The corresponding displacement change can be calculated using the above relationship. =3.4106 The result is obtained. =6.07μm (actual displacement). At this point, using... The relative displacement measurement accuracy was calculated to be 0.012, indicating that the present invention has the advantage of high-precision deformation measurement.

[0077] This invention proposes a structured light illumination digital speckle interferometer device and method for in-plane deformation measurement, enabling high-precision in-plane deformation measurement. First, by loading fringe modulation patterns with different phase shifts along a first direction and a second direction onto an SLM (spatial light modulator), and combining this with a spatial mask, a +1... st and -1 st The diffraction-level beam is used to generate fast structured illumination and phase shift, offering advantages such as fast imaging speed, high phase shift accuracy, and accurate reconstruction results. Secondly, compared to traditional digital speckle interferometry paths, the common-path mode (+1) is utilized... st and -1 st When the diffraction-level beam travels along the same path, it is less affected by environmental disturbances, the device is compact, and the stability is high, which can further ensure measurement accuracy. In summary, this deformation measurement device and method have the advantages of simple structure, high precision, and high stability, and can be widely used in various fields such as modern material property research.

[0078] In the several embodiments provided by this invention, it should be understood that the apparatus and methods disclosed in this invention can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For example, the division of modules is merely a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0079] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated module can be implemented in hardware or in the form of hardware plus software functional modules.

[0080] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A structured light digital speckle interferometer capable of measuring in-plane deformation, characterized in that, It includes a structured light illumination generation module, an imaging module, and a data processing module, among which, The structured light illumination generation module includes a laser (1), a spatial light modulator (6), a TIR prism (5), and a spatial mask (8). The laser (1) is used to generate a laser beam. The spatial light modulator (6) is used to load stripe modulation patterns with different phase shifts along a first direction and a second direction, respectively, to modulate the laser beam and achieve phase shift operation, forming multiple diffracted beams propagating in different directions under the modulation of each stripe modulation pattern. The TIR prism (5) is used to ensure that the diffracted beam modulated by the spatial light modulator (6) propagates along the optical axis. The spatial mask (8) is used to select only +1 when loading stripe modulation patterns along the first direction and stripe modulation patterns along the second direction onto the spatial light modulator (6). st -1 st The diffraction-level beams interfere to generate structured illumination light, wherein the first direction and the second direction are both located on the working surface of the spatial light modulator (6) and are perpendicular to each other; The imaging module is used to illuminate the sample (11) with the structured illumination light and record the digital speckle phase shift images corresponding to the structured illumination light in different directions and with different phase shifts. The data processing module is used to obtain the deformation information of the sample (11) along different in-plane directions using digital speckle phase shift images corresponding to structured illumination light with different directions and different phase shift amounts; The structured light illumination generation module further includes an optical fiber (2), a linear polarizer (3), a first thin lens (4), a second thin lens (7), and a third thin lens (9), wherein, The linear polarizer (3) is used to polarize the laser beam generated by the laser (1) to obtain linearly polarized light with the same polarization direction as the spatial light modulator (6); The first thin lens (4) is used to collimate and expand the linearly polarized light; The TIR prism (5) is used to reflect the linearly polarized light collimated and expanded by the first thin lens (4) and simultaneously transmit the diffracted beam generated by the spatial light modulator (6), ensuring that the diffracted beam propagates along the optical axis. The second thin lens (7) is used to converge multiple diffracted beams from the spatial light modulator (6) that propagate in different directions and illuminate the spatial mask plate (8), which is disposed on the back focal plane of the second thin lens (7). The front focal plane of the third thin lens (9) coincides with the rear focal plane of the second thin lens (7), and is used to image the structured illumination light filtered by the space mask plate (8) onto the sample (11). The imaging module includes a beam splitter (10), an industrial lens (12), and a camera (13), wherein, The beam splitter (10) is used to reflect the structural illumination light from the third thin lens (9) onto the sample (11), and at the same time transmit the scattered beam from the sample (11) to the industrial lens (12). The sample (11) is placed on the front focal plane of the industrial lens (12), and the rear focal plane of the third thin lens (9) coincides with the front focal plane of the industrial lens (12); the camera (13) is placed on the side of the industrial lens (12) away from the beam splitter (10).

2. The structured light digital speckle interferometer device for in-plane deformation measurement according to claim 1, characterized in that, The light propagation distance from the spatial light modulator (6) to the sample surface of the sample (11) is the same as the distance from the sample surface of the sample (11) to the image surface of the camera (13).

3. The structured light digital speckle interferometer device for in-plane deformation measurement according to claim 2, characterized in that, The spatial light modulator (6) is specifically used for: Stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase shift images of the sample (11) in the first plane direction at the deformation front of the sample (11) on the camera (13); Stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 were loaded respectively to obtain three digital speckle phase shift images of the sample (11) in the direction of its second surface at the deformation front on the camera (13); Stripe modulation patterns along the first direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase shift images of the sample (11) after deformation along the direction in the first plane on the camera (13); Stripe modulation patterns along the second direction with corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase shift images of the sample (11) after deformation along its second in-plane direction on the camera (13). The first in-plane direction and the second in-plane direction are both located in the sample plane of the sample (11) and are perpendicular to each other.

4. The structured light digital speckle interferometer device for in-plane deformation measurement according to claim 3, characterized in that, The data processing module is specifically used for: Using three digital speckle phase shift images of sample (11) under structured illumination with different phase shifts in the first direction before deformation and three digital speckle phase shift images of sample (11) under structured illumination with different phase shifts in the first direction after deformation, the phase distribution of sample (11) before and after deformation along its first in-plane direction is obtained, and the in-plane deformation information of sample along its first in-plane direction is obtained according to the correspondence between phase difference and optical path difference caused by deformation. Using three digital speckle phase shift images of sample (11) under structured illumination with different phase shifts in the second direction before deformation and three digital speckle phase shift images of sample (11) under structured illumination with different phase shifts in the second direction after deformation, the phase distribution of sample (11) before and after deformation along its second in-plane direction is obtained, and the in-plane deformation information of sample (11) along its second in-plane direction is obtained according to the correspondence between the phase difference and the optical path difference caused by deformation.

5. A structured light digital speckle interferometry method for measuring in-plane deformation, characterized in that, The method comprises: using the structured light digital speckle interferometer capable of in-plane deformation measurement as described in any one of claims 1 to 4; S1: The spatial light modulator (6) is loaded with stripe modulation patterns with different phase shifts along the first direction and stripe modulation patterns with different phase shifts along the second direction, respectively, to obtain multiple digital speckle phase shift images corresponding to structural illumination light conditions with different directions and different phase shifts before sample deformation; S2: Obtain in-plane deformation information of the sample along different directions using digital speckle phase-shift images corresponding to structured illumination with different directions and phase shift amounts.

6. The structured light digital speckle interferometry method for in-plane deformation measurement according to claim 5, characterized in that, S1 includes: The spatial light modulator (6) is loaded with stripe modulation patterns along the first direction and corresponding phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase shift images of the sample (11) in the first plane direction at the deformation front of the sample (11) on the camera (13); The spatial light modulator (6) is loaded with stripe modulation patterns along the second direction and corresponding phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase shift images of the sample (11) in the direction of its second surface at the deformation front on the camera (13); The spatial light modulator (6) is loaded with stripe modulation patterns along the first direction and corresponding phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase shift images of the sample (11) after deformation along the direction in the first plane on the camera (13); The spatial light modulator (6) is loaded with stripe modulation patterns along the second direction and corresponding phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase shift images of the sample (11) after deformation along its second in-plane direction on the camera (13), wherein the first in-plane direction and the second in-plane direction are both located in the sample plane of the sample (11) and are perpendicular to each other.

7. The structured light digital speckle interferometry method for in-plane deformation measurement according to claim 6, characterized in that, S2 includes: Using three digital speckle phase-shift images of the sample (11) in the first in-plane direction before deformation and three digital speckle phase-shift images of the sample (11) in the first in-plane direction after deformation, the phase distribution of the sample (11) in the first in-plane direction before and after deformation is obtained according to the reconstruction algorithm, and the in-plane deformation information of the sample (11) in the first in-plane direction before and after deformation is obtained according to the correspondence between the phase difference and the optical path difference caused by deformation. Using three digital speckle phase-shift images of the sample (11) in the direction of its second surface before deformation and three digital speckle phase-shift images of the sample (11) in the direction of its second surface after deformation, the phase distribution of the sample (11) in the direction of its second surface before and after deformation is obtained according to the reconstruction algorithm, and the in-plane deformation information of the sample (11) in the direction of its second surface before and after deformation is obtained according to the correspondence between the phase difference and the optical path difference caused by deformation.

Images