Structured light digital speckle interference device and method capable of realizing in-plane deformation measurement

Abstract

The invention discloses a structured light digital speckle interference device and method capable of realizing in-plane deformation measurement, the device comprises a structured light illumination generation module, an imaging module and a data processing module, the structured light illumination generation module comprises a laser, a spatial light modulator, a TIR prism and a spatial mask plate, and the spatial light modulator is connected with the imaging module. The spatial light modulator is used for loading stripe modulation patterns which are in the first direction and the second direction and have different phase shift amounts so as to modulate the illumination light beam, multiple diffraction light beams propagating in the different directions are formed, and phase shift operation is achieved. The spatial mask plate only selects + 1st and-1st diffraction order light beams for interference so as to generate structural illumination light; the imaging module is used for recording corresponding digital speckle phase shift images under the structural illumination light with different directions and different phase shift amounts; and the data processing module is used for obtaining deformation information of the sample along different in-plane directions. The in-plane deformation measuring device can realize high-precision in-plane deformation measurement, is slightly influenced by environmental disturbance, and is compact and high in stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of non-contact optical detection, and particularly relates to a structured light digital speckle interferometer device and method capable of realizing in-plane deformation measurement. BACKGROUND

[0002] Material mechanical property testing and structure reliability analysis play an important role in engineering application practice. As the deformation parameter is a direct representation of the material mechanical behavior, its accurate acquisition is directly related to key links such as stress and strain analysis and strength and stiffness calculation, and thus becomes a core observation index of modern experimental mechanics research. Precise deformation measurement is not only a core prerequisite for constructing stress and strain field distribution of a structure, but also can directly determine the effectiveness of strength and stiffness analysis and other engineering. Therefore, developing high-precision deformation measurement technology has become a focus problem widely concerned by researchers.

[0003] According to different test conditions, the deformation measurement method can be divided into contact measurement method and non-contact measurement method. The former is mainly to measure the deformation by directly contacting the measured object with a measuring instrument, such as a coordinate measuring machine (CMM), which is a typical representative, although it has high repeatability, but it will damage the surface of the measured object, and the measurement speed is slow; the latter is mainly an optical testing method, including holography, speckle method, structured light measurement method, image matching method, etc., which has the advantages of non-contact, full-field measurement, high precision, fast speed, etc., and gradually attracts the attention of researchers.

[0004] Among them, electronic speckle pattern interferometry (ESPI) is a relatively mature modern full-field non-contact optical measurement technology, which has the advantages of strong universality, high measurement accuracy, wide frequency range, simple measurement and small environmental interference, and has been widely used in object displacement, slope, curvature, torsion, vibration and topography measurement. Moreover, according to the construction of different interference light paths, ESPI can be used to measure in-plane deformation, out-of-plane deformation and in-plane and out-of-plane coupled deformation. With the continuous maturity of the one-dimensional deformation theory, it has become a new trend to research and develop methods for measuring more dimensional deformations of objects by ESPI.

[0005] At present, there are various interferometric optical paths for measuring the multi-sensitivity vector of the static deformation of an object, but the measurement of each deformation cannot be performed in a common path. For example, Takatsuji et al. measured three displacement components of three-dimensional deformation by using three object beams and one reference beam to form three interferometric optical paths. Zhang Xi et al. used three lasers, a large-displacement prism and a PZT phase shifter to form a three-dimensional phase shift ESPI system and used it for three-dimensional displacement measurement of a diesel engine body. This method uses a large-displacement prism to avoid placing three separate reference light paths in front of the camera, thereby greatly simplifying the optical path. Thereafter, Flynn et al. used three different wavelengths of light to form a three-dimensional displacement field measurement interferometric optical path to measure three-dimensional displacement components. Although the above techniques can achieve object deformation measurement, when performing phase shifting, a piezoelectric ceramic (PZT) device is often used. Due to its own delay, the repeatability is poor, the imaging speed is slow, the phase shifting precision is low, and the measurement precision is affected. When digital speckle interference is generated, the paths of different beams are different, resulting in low device stability and complex imaging optical path. SUMMARY

[0006] In order to solve the problems of complex structure, poor stability and low phase shifting precision of the traditional digital speckle interference optical path, the present application provides a structured light digital speckle interference device and method capable of measuring in-plane deformation, which can realize in-plane deformation measurement in a first in-plane direction x and a second in-plane direction y of a sample, has the advantages of high precision, high stability, fast imaging speed, simple imaging device, etc. The technical problem to be solved by the present application is solved by the following technical scheme: One aspect of the present application provides a structured light digital speckle interference device capable of measuring in-plane deformation, comprising a structured light illumination generation module, an imaging module and a data processing module, wherein, the structured light illumination generation module comprises a laser, a spatial light modulator, a TIR prism and a spatial mask plate, the laser is used to generate a laser beam, the spatial light modulator is used to load a fringe modulation pattern along a first direction and a second direction respectively and with different phase shifting amounts, to modulate the laser beam and realize phase shifting operation, and to form a plurality of diffracted beams propagating in different directions under the modulation of each fringe modulation pattern; the TIR prism is used to ensure that the diffracted beams modulated by the spatial light modulator propagate along the optical axis, and the spatial mask plate is used to select only +1 st , -1 st diffracted order beams for interference to generate structured illumination light when the spatial light modulator loads the fringe modulation pattern along the first direction and loads the fringe modulation pattern along the second direction, wherein the first direction and the second direction are both on the working surface of the spatial light modulator and perpendicular to each other; The imaging module is used to illuminate the sample with the structured illumination light and record the corresponding digital speckle phase-shift images under the structured illumination light in different directions and with different phase shift amounts; The data processing module is used to obtain deformation information of the sample along different in-plane directions using digital speckle phase-shift images corresponding to structured illumination lights in different directions and with different phase shift amounts.

[0007] Another aspect of the present invention provides a structured light digital speckle interferometry method capable of realizing in-plane deformation measurement, the method comprising: S1: Loading fringe modulation patterns with different phase shifts along a first direction and fringe modulation patterns with different phase shifts along a second direction to the spatial light modulator, respectively, to obtain a plurality of digital speckle phase shift images corresponding to structured illumination light conditions in different directions and with different phase shifts before deformation of the sample; S2: The in-plane deformation information of the sample along different directions is obtained using the corresponding digital speckle phase shift images under structured illumination light with different directions and different phase shift amounts.

[0008] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a structured light illumination digital speckle interferometry device and method for in-plane deformation measurement, which can achieve high-precision in-plane deformation measurement. First, by loading fringe modulation patterns with different phase shifts along the first direction and the second direction on the SLM (spatial light modulator), the spatial mask is combined to select +1 st and -1 st The diffraction order beams are interfered to generate fast structured illumination light and phase shift, which has the advantages of fast imaging speed, high phase shift accuracy and accurate reconstruction results. Secondly, compared with the traditional digital speckle interferometry optical path, the common path mode (+1 st and -1 st The diffraction-order beams (which follow the same path) are less affected by environmental disturbances, resulting in a compact and highly stable device that further ensures measurement accuracy. In summary, this deformation measurement device and method boasts a simple structure, high precision, and high stability, and can be widely applied in various fields, including modern material performance research.

[0009] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of a structured light digital speckle interferometry device capable of realizing in-plane deformation measurement provided by an embodiment of the present invention; Figure 2 Schematic diagram of the modulated images loaded in the first direction and the second direction of the spatial light modulator and the corresponding spatial mask; Figure 3is a schematic diagram of digital speckle interferometry under the condition of the structured illumination light in the first direction; Figure 4 is a digital speckle phase shift image of the sample in the first in-plane direction under the structured illumination light and a reconstructed phase distribution map; Figure 5 is a digital speckle phase shift image of the sample in the second in-plane direction under the structured illumination light and a reconstructed phase distribution map; Figure 6 is a phase difference relationship caused by different in-plane displacements in the first in-plane direction and the second in-plane direction and a corresponding relationship between the theoretical displacement and the actual displacement.

[0011] Explanation of reference signs: 1 - laser; 2 - optical fiber; 3 - linear polarizer; 4 - first thin lens; 5 - TIR prism; 6 - spatial light modulator; 7 - second thin lens; 8 - spatial mask plate; 9 - third thin lens; 10 - beam splitter; 11 - sample; 12 - industrial lens; 13 - camera. DETAILED DESCRIPTION

[0012] In order to further illustrate the technical means and effects taken by the present application to achieve the predetermined object, the structure light digital speckle interferometry device and method for realizing in-plane deformation measurement according to the present application are described in detail below in combination with the drawings and specific embodiments.

[0013] The foregoing and other technical contents, features and effects of the present application can be clearly presented in the detailed description of the specific embodiments below in combination with the drawings. Through the description of the specific embodiments, the technical means and effects taken by the present application to achieve the predetermined object can be understood more deeply and specifically. However, the attached drawings are provided for reference and illustration only, and are not intended to limit the technical solutions of the present application.

[0014] It should be noted that in this document, relational terms such as first and second and the like can only be used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations exist in any such actual relationship or order. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a product or device that includes a list of elements does not exclude other elements not explicitly listed. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the product or device that includes the element.

[0015] Example one The embodiment provides a structured light digital speckle interferometer device capable of realizing in-plane deformation measurement, which comprises a structured light illumination generation module, an imaging module and a data processing module arranged in sequence, wherein the structured light illumination generation module comprises a laser 1, a spatial light modulator 6, a TIR (Total Internal Reflection) prism 5 and a spatial mask plate 8; the laser 1 is used for generating a laser beam; the spatial light modulator 6 is used for respectively loading a stripe modulation pattern along a first direction or a second direction and having different phase shift amounts on a working surface, so as to modulate the laser beam from the laser 1 and realize a phase shift operation, that is, to form a plurality of diffraction beams propagating along different directions under the modulation of each stripe modulation pattern; the TIR prism 5 is used for ensuring that the diffraction beams modulated by the spatial light modulator 6 propagate along an optical axis; and the spatial mask plate 8 is used for selecting only +1 st , -1 st diffraction order beams to interfere to generate structured illumination light when the spatial light modulator 6 loads the stripe modulation pattern along the first direction and loads the stripe modulation pattern along the second direction, wherein the first direction and the second direction are both located on the working surface of the spatial light modulator 6 and perpendicular to each other; the imaging module is used for irradiating a sample by using the structured illumination light and recording corresponding digital speckle phase shift images under the condition of the structured illumination light in different directions and different phase shift amounts; and the data processing module is used for obtaining deformation information of the sample along different in-plane directions by using the corresponding digital speckle phase shift images under the condition of the structured illumination light in different directions and different phase shift amounts.

[0016] Further, referring to Figure 1 , Figure 1 is a schematic diagram of a structured light illumination digital speckle interferometer device capable of realizing in-plane deformation measurement. The structured light illumination generation module of the embodiment further comprises a fiber 2, a linear polarizer 3, a first thin lens 4, a second thin lens 7, a third thin lens 9, wherein the linear polarizer 3 is used for performing a polarization action on the laser beam generated by the laser 1 to obtain linearly polarized light having the same polarization direction as the spatial light modulator 6; the first thin lens 4 is used for collimating and expanding the linearly polarized light; the TIR prism 5 is used for reflecting the linearly polarized light collimated and expanded by the first thin lens 4 and transmitting the diffraction beams generated by the spatial light modulator 6, so as to ensure that the diffraction beams propagate along the optical axis; the second thin lens 7 is used for converging the plurality of diffraction beams propagating along different directions from the spatial light modulator 6 and irradiating the spatial mask plate 8; and the spatial mask plate 8 is arranged on the back focal plane of the second thin lens 7 and can selectively filter the diffraction beams after the spatial light modulator 6, so as to only retain +1 st , -1 stThe diffraction order beams interfere; the front focal plane of the third thin lens 9 coincides with the back focal plane of the second thin lens 7, for imaging the structure illumination light filtered by the spatial mask 8 onto the sample 11.

[0017] The imaging module of the embodiment comprises a beam splitter 10, an industrial lens 12 and a camera 13, wherein the beam splitter 10 is used for reflecting the structure illumination light from the third thin lens 9 to irradiate the sample 11, while transmitting the scattered light beams from the sample 11 to the industrial lens 12; the sample 11 is arranged on the front focal plane of the industrial lens 12, and the back focal plane of the third thin lens 9 coincides with the front focal plane of the industrial lens 12; the camera 13 is arranged on the side of the industrial lens 12 away from the beam splitter 10.

[0018] Specifically, the laser emitted by the laser 1 is coupled into the optical fiber 2 and emitted, the linear polarizer 3 acts on the laser generated by the laser 1 to change its polarization characteristics, and then adjusts its polarization direction, and finally makes it become linearly polarized light with the same polarization direction as the spatial light modulator 6; after becoming linearly polarized light by the linear polarizer 3, it is expanded and collimated by the first thin lens 4, and then reflected to the spatial light modulator 6 by the TIR prism 5. The illumination light beam can cover the effective working surface of the spatial light modulator 6.

[0019] The spatial light modulator 6 of the embodiment is specifically used for: loading a stripe modulation pattern along a first direction and corresponding to a phase shift amount of 0, 2π / 3 and 4π / 3 respectively, so as to obtain three digital speckle phase shift images of a first in-plane direction of the sample 11 before deformation (corresponding to the direction in the Figure 1 x direction in the Figure 1 direction in the y direction in the

[0020] ​When the spatial light modulator 6 is loaded with a fringe modulation pattern, the laser beam forms a plurality of beams of diffracted light propagating in different directions under the modulation of the current fringe modulation pattern, and the second thin lens 7 converges the plurality of beams of diffracted light from the spatial light modulator 6 in different directions of propagation and irradiates the spatial mask plate 8; after selective filtering of the spatial mask plate 8, only the +1 st , -1 st order diffracted light beams interfere, and then are imaged onto the sample 11 by the third thin lens 9.

[0021] Specifically, referring to Figure 2 , by loading the spatial light modulator 6 with fringe modulation patterns corresponding to phase shifts of 0, 2π / 3, and 4π / 3 in the first direction and the second direction respectively, as shown in Figure 2 (b) and 2(d), meanwhile, the plurality of beams of diffracted light generated are converged by the second thin lens 7 and irradiated onto the spatial mask plate 8, which is shown in Figure 1 , 2 (a) and 2(c), it should be noted that the actual spatial mask plate 8 is shown in Figure 1 , which is a superposition of the structures of Figure 2 (a) and Figure 2 (c), and can only select the +1 st , -1 st order diffracted light beams to generate structured illumination light when loading the fringe modulation pattern in the first direction and loading the fringe modulation pattern in the second direction. Finally, the digital speckle phase shift images corresponding to the structured illumination light in different directions and different phase shift amounts are obtained in sequence.

[0022] Preferably, the wavelength of the laser 1 is in the visible light range, the output laser power is stable, and the coherence length is appropriate. In the present embodiment, the wavelength of the laser 1 is 561 nm; the wavelength range of the linear polarizer 3 is 400-700 nm, and the extinction ratio is 500:1. The first thin lens 4, the second thin lens 7, and the third thin lens 9 are all achromatic 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 number of pixels of the spatial light modulator 6 is 2716×1600, and the pixel size is 5.4 μm.

[0023] The beam splitter 10 is used to reflect the structured illumination light and transmit the scattered light from the sample 11. The focal length of the industrial lens 12 is 25 mm, the pixel is 10 MP, the image size is 1 / 1.8 inch, and the camera 13 is a common black and white sCMOS camera with certain gain, gray scale, pixel size, and pixel number. Preferably, the splitting ratio of the beam splitter 10 is 50:50 (transmission:reflection); the number of pixels of the sCMOS camera 13 is 4096×3000, and the pixel size is 3.45 μm.

[0024] Specifically, the filtered +1 st , -1 st diffraction order beams pass through the third thin lens 9 to form parallel structured light propagating in different directions, and then are reflected by the beam splitter 10 to the sample 11. Subsequently, the scattered light reflected by the sample is transmitted by the beam splitter 10, collected by the industrial lens 12, and the digital speckle phase shift images formed are received by the camera 13.

[0025] 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, the structured light and the camera consistent to obtain the best imaging effect.

[0026] Further, the data processing module of the embodiment is specifically used for: using the three digital speckle phase shift images of the sample 11 before deformation under the structured illumination light of different phase shifts in the first direction and the three digital speckle phase shift images of the sample 11 after deformation under the structured illumination light of different phase shifts in the first direction to obtain the phase distributions of the sample 11 before and after deformation along the first in-plane direction thereof, and obtaining the in-plane deformation information of the sample along the first in-plane direction thereof according to the corresponding relationship between the phase difference and the optical path difference caused by deformation; using the three digital speckle phase shift images of the sample 11 before deformation under the structured illumination light of different phase shifts in the second direction and the three digital speckle phase shift images of the sample 11 after deformation under the structured illumination light of different phase shifts in the second direction to obtain the phase distributions of the sample 11 before and after deformation along the second in-plane direction thereof, and obtaining the in-plane deformation information of the sample 11 along the second in-plane direction thereof according to the corresponding relationship between the phase difference and the optical path difference caused by deformation.

[0027] Specifically, the corresponding stripe modulation pattern loaded on the spatial light modulator 6 can realize 0, 2π / 3, 4π / 3 three-step phase shifts in the first direction, by recording each three (a total of six) digital speckle phase shift images generated by the sample before and after deformation, combined with the corresponding reconstruction algorithm, the phase distribution of the sample 11 in the first in-plane direction before and after deformation is solved, and finally according to the corresponding relationship between the phase difference and the optical path difference caused by the deformation, the in-plane deformation information of the sample 11 in the first in-plane direction can be obtained. Then, the corresponding stripe modulation pattern loaded on the spatial light modulator 9 can realize 0, 2π / 3, 4π / 3 three-step phase shifts in the second direction, by recording each three (a total of six) digital speckle phase shift images generated by the sample before and after deformation, combined with the corresponding reconstruction algorithm, the phase distribution of the sample 11 in the second in-plane direction before and after deformation is solved, and finally according to the corresponding relationship 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 the two perpendicular directions can be obtained, and the specific data processing and solving process is described in the following embodiment two.

[0028] The application provides a structured light illumination digital speckle interferometer device capable of realizing in-plane deformation measurement and high-precision deformation measurement. First, by loading a corresponding stripe modulation pattern on an SLM (spatial light modulator), combined with spatial mask selection +1 st and-1 st order diffracted beams to interfere to produce fast structured light illumination and phase shift, which has the advantage of fast imaging speed, and avoids the problems of poor repeatability when using PZT and other devices to realize phase shift operation, and has high phase shift repeatability, which further ensures the accuracy of the reconstruction result; secondly, compared with the traditional digital speckle interferometer optical path, the common path mode (+1 st and-1 st order diffracted beams pass through the same path) is used, which is less affected by environmental disturbances, has high stability, and can ensure the measurement accuracy; finally, compared with the traditional in-plane deformation measurement optical path, the optical path uses the phase shift pattern loaded on the SLM in the first direction and the second direction, and the optical path is simple and can realize in-plane deformation measurement. In summary, the deformation measurement device and method have the advantages of high precision, high stability, high integration, etc., and can be widely applied in many fields such as industrial detection.

[0029] Embodiment two On the basis of embodiment one, the application provides a structured light illumination digital speckle interferometer method capable of realizing in-plane deformation measurement, comprising: S1: loading the spatial light modulator 6 with fringe modulation patterns with different phase shift amounts in the first direction and fringe modulation patterns with different phase shift amounts in the second direction respectively, to obtain a plurality of digital speckle phase shift images corresponding to the sample before and after deformation under different directions and different phase shift amounts of the structured illumination light.

[0030] Specifically, the laser 1 is turned on; the spatial light modulator 6 is loaded with fringe modulation patterns in the first direction and corresponding phase shift amounts of 0, 2π / 3, 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample 11 before deformation along its first in-plane direction on the camera 13; the spatial light modulator 6 is loaded with fringe modulation patterns in the second direction and corresponding phase shift amounts of 0, 2π / 3, 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample 11 before deformation along its second in-plane direction on the camera 13; after the sample is moved, the spatial light modulator 6 is loaded with fringe modulation patterns in the first direction and corresponding phase shift amounts of 0, 2π / 3, 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample 11 after deformation along its first in-plane direction on the camera 13; the spatial light modulator 6 is loaded with fringe modulation patterns in the second direction and corresponding phase shift amounts of 0, 2π / 3, 4π / 3 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, wherein the first in-plane direction (corresponding to the direction in the formula (1)) and the second in-plane direction (corresponding to the direction in the formula (2)) are both in the sample plane of the sample 11 and perpendicular to each other. Figure 1 x Figure 1 x

[0031] S2: obtaining the in-plane deformation information of the sample in different directions by using the corresponding digital speckle phase shift images under different directions and different phase shift amounts of the structured illumination light.

[0032] Specifically, the phase distributions of the sample 11 before and after deformation along its first in-plane direction are obtained by using the three digital speckle phase shift images of the sample 11 before deformation under different phase shift amounts of the structured illumination light in the first direction and the three digital speckle phase shift images of the sample 11 after deformation under different phase shift amounts of the structured illumination light in the first direction, and the in-plane deformation information of the sample 11 along its first in-plane direction is obtained according to the corresponding relationship between the phase difference and the optical path difference caused by deformation; the phase distributions of the sample 11 before and after deformation along its second in-plane direction are obtained by using the three digital speckle phase shift images of the sample 11 before deformation under different phase shift amounts of the structured illumination light in the second direction and the three digital speckle phase shift images of the sample 11 after deformation under different phase shift amounts of the structured illumination light in the second direction, and the in-plane deformation information of the sample 11 along its second in-plane direction is obtained according to the corresponding relationship between the phase difference and the optical path difference caused by deformation.

[0033] ​​​​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, wherein the in-plane deformation of the aluminum disk is simulated by the movement of the aluminum disk along its radial direction. During the experiment, fringe modulation patterns corresponding to three phase shifts of 0, 2π / 3, and 4π / 3 in the first direction and fringe modulation patterns corresponding to three phase shifts of 0, 2π / 3, and 4π / 3 in the second direction are loaded on the spatial light modulator 6, and the camera 13 sequentially records six (twelve in total) digital speckle phase shift images before and after the deformation caused by the radial displacement of the aluminum disk. Afterwards, the phase difference before and after the deformation (including the first in-plane direction (corresponding to the phase difference before and after the deformation) is solved by the corresponding reconstruction algorithm. Figure 1 in x direction) phase difference and the second in-plane direction (corresponding to Figure 1 in y direction) phase difference ), and finally the in-plane deformation information of the sample (including the in-plane deformation information of the first in-plane direction) is obtained through the correspondence between the position difference and the optical path difference caused by the deformation and the in-plane deformation information in the second in-plane direction ).

[0034] Specifically, taking the fringe modulation patterns of three phase shift amounts of 0, 2π / 3, and 4π / 3 in the first direction as an example, the +1 st and -1 st The digital speckle phase-shift image generated by the interference of diffraction-order beams can be expressed as: , (1) in, 、 and They are the complex amplitudes of level 0, level -1 and level +1 of sample 11 before deformation, and the phase shift =2 m π / 3( m =0, 1, 2).

[0035] Before the sample is displaced, the speckle intensity images are recorded at the phase shifts of 0, 2π / 3, and 4π / 3 in the first direction. I 1. I 2. I 3, from formula (1) we can get: , (2) By numerically processing the matrix equation (2), the complex amplitudes of the 0th and ±1st orders before displacement can be obtained.

[0036] After the sample is displaced, the speckle intensity images of the sample are recorded at 0, 2π / 3, and 4π / 3 phase shifts in the first direction. I 4. I 5. I 6, we can get: , (3) in, 、 and are the complex amplitudes of 0, -1 and +1 after deformation of sample 11. The same method is used to obtain the complex amplitudes of 0 and ±1 after deformation. or , the complex amplitude change before and after the sample displacement can be obtained, and further, the phase difference in the first plane direction before and after the sample displacement (i.e. before and after deformation) can be obtained. : , (4) Similarly, the phase difference in the second plane direction before and after the sample displacement (i.e. before and after deformation) can be obtained according to the above process. .

[0037] In the deformation measurement of digital speckle interferometry, the deformation information of the sample can be obtained by using the corresponding relationship between the phase difference and the optical path difference caused by the deformation. Figure 3 As shown, Figure 3 (a) is a schematic diagram of in-plane deformation measurement. The enlarged area in the figure is +1 in the first direction. st and -1 st Interference fringes formed after diffraction orders interfere; Figure 3 (b) Schematic diagram of the sample before and after deformation in the first in-plane direction.

[0038] The specific relationship is derived as follows: +1 st Diffraction order beam 1-1 is passed through P Point 1-3 to the camera target surface, and move the sample along the coordinate axis x Direction (corresponding to the first in-plane direction) displacement After, +1 st Diffraction order beams 1-4 P After 1 point, along 1-6 to the camera target surface, then +1 st The optical path difference of the diffraction order beam before and after the sample deformation is ,in According to the geometric relationship, we can get , further, At this time, according to the relationship between phase difference and optical path difference, we can get: , (5) in, for the illumination wavelength of the laser 1, represents +1 st phase difference generated by the diffractive order beams before and after deformation, represents +1 st incident angle of the diffractive order beams.

[0039] -1 st diffractive order beam 1-2 is incident on the sample before deformation P point after 1-3 to the camera target surface, the sample is displaced along the coordinate axis x direction after, -1 st diffractive order beam 1-5 is incident on the sample P 1 point after 1-6 to the camera target surface, then -1 st optical path difference of the diffractive order beams before and after deformation is P 1 B wherein According to the geometric relationship, it can be obtained that further, At this time, according to the relationship between the phase difference and the optical path difference, it can be obtained that: , (6) wherein, represents -1 st phase difference generated by the diffractive order beams before and after deformation.

[0040] The relationship between the total phase difference and the optical path difference is: , (7) y deformation principle in the direction (the second in-plane direction) is the same as that in the direction. x

[0041] The embodiment utilizes a spatial light modulator to realize phase shift, avoiding problems such as poor repeatability when using a PZT or the like to realize phase shift operation, and the phase shift has high repeatability, further ensuring the accuracy of the reconstruction result.

[0042] In order to verify whether the structured light digital speckle interferometer device and method proposed in the application have accuracy, the actual displacement is compared with the theoretical displacement value, and the process is as follows: respectively in x and y directions, actual displacement is added to the sample, and the phase difference image is obtained by using the captured digital speckle phase shift image to perform phase reconstruction, that is, the corresponding phase difference value under the actual displacement is obtained, and then compared with the theoretical displacement value of the sample in x and y directions calculated according to the theoretical formula.

[0043] Please refer to Figure 4 , Figure 4 ​Digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the first direction phase shift images (d) for the aluminum disc sample. Figure 2 (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. x (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. Figure 4 (a) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. Figure 4 (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. , Figure 4 Figure 4 (f) is the phase difference statistics and Gaussian fitting of 4(e), and the phase difference of the peak value of the fitting curve is 0.9 rad, that is, the phase difference between before and after deformation is 0.9 rad, and the theoretical displacement amount calculated according to formula (5) is 3.07 μm, and the relative displacement measurement accuracy is 0.023.

[0044] Figure 5 , Figure 5 Digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the first direction phase shift images (d) for the aluminum disc sample. Figure 2 (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. y (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. Figure 5 (a) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. Figure 5 (b) and 4(c) are the digital speckle pattern phase shift images and reconstructed phase distribution images when the SLM loaded the second direction phase shift images (d) for the aluminum disc sample. Figure 5 Figure 5 (f) is the phase difference statistics and Gaussian fitting of 4(e), and the phase difference of the peak value of the fitting curve is 1.78 rad, that is, the phase difference between before and after deformation is 1.78 rad, and the theoretical displacement amount calculated according to formula (5) is 6.07 μm, and the relative displacement measurement accuracy is 0.012. ​​​​​​​​​​​​​​

[0045] See Figure 6 , Figure 6 They are the phase difference relationship caused by the displacement in different directions and the corresponding relationship between the theoretical displacement and the actual displacement. Figure 6 (a) and (b) are the corresponding displacements of the aluminum disk in the first and second plane directions. x and y The phase difference caused by the direction is linearly related to ( and ), fitting linear coefficient k x =0.291, k y =0.297; The sample surface is calculated based on the interference fringe pattern taken when the sample aluminum disk is 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 Available, =3.4106, Figure 6 The theoretical displacement value can be obtained by multiplying the phase difference in (a) and 6(b) by 3.4106. and . Figure 6 (c) is the theoretical displacement and actual displacement The corresponding relationship ( ), the fitting linear coefficient is k x= 0.992±0.008; Figure 6 (d) is the theoretical displacement and actual displacement The corresponding relationship ( ), the fitting linear coefficient is k y= 1.014±0.008. For example, when an aluminum disk is y Directional displacement =6 μm (theoretical displacement) the phase difference introduced is = - =1.78 rad , the corresponding displacement change can be calculated by the above relationship =3.4106 The result is =6.07μm (actual displacement). At this time, 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.

[0046] The application provides a structured light illumination digital speckle interferometry device and method capable of realizing in-plane deformation measurement and high-precision in-plane deformation measurement. st st The device has the advantages of fast imaging speed, high phase shift precision and accurate reconstruction result; compared with a traditional digital speckle interferometry optical path, the device has small environmental disturbance, compact structure and high stability when using a common path mode (+1 st st and -1diffracted light beams pass through the same path), and can further ensure measurement precision.

[0047] In the several embodiments provided in the application, it should be understood that the disclosed device and method can be implemented in other ways. For example, the device embodiments described above are merely illustrative, for example, the division of the modules is only a logical function division, and actual implementation can have another division manner, for example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0048] In addition, each function module in each embodiment of the application can be integrated in a processing module, or each module can exist physically, or two or more modules can be integrated in one module. The integrated module can be realized in the form of hardware or in the form of hardware plus software function module.

[0049] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, several simple deductions or substitutions can be made without departing from the concept of the application, and all should be regarded as falling within the protection scope of the application.​

Claims

1. A structured light digital speckle interferometry device 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, wherein: The structured light illumination generation module comprises a laser (1), a spatial light modulator (6), a TIR prism (5) and a spatial mask (8), wherein the laser (1) is used to generate a laser beam, and the spatial light modulator (6) is used to load stripe modulation patterns with different phase shift amounts along a first direction and a second direction respectively, so as to modulate the laser beam and realize a phase shift operation, and form multiple diffracted light beams propagating along different directions under the modulation of each stripe modulation pattern; the TIR prism (5) is used to ensure that the diffracted light beam modulated by the spatial light modulator (6) propagates along the optical axis, and the spatial mask (8) is used to select only +1 when the spatial light modulator (6) loads the stripe modulation pattern along the first direction and the stripe modulation pattern along the second direction. st 、-1 st The diffraction order light 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) using the structured illumination light and record the corresponding digital speckle phase shift images under the structured illumination light in different directions and with different phase shift amounts; The data processing module is used to obtain deformation information of the sample (11) along different in-plane directions using corresponding digital speckle phase-shift images under structured illumination light of different directions and different phase shift amounts.

2. The structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to claim 1, characterized in that: 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 having the same polarization direction as that of 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 transmit the diffracted light beam modulated by the spatial light modulator (6) to ensure that the diffracted light beam propagates along the optical axis; The second thin lens (7) is used to converge multiple diffracted light beams propagating in different directions from the spatial light modulator (6) and irradiate the light onto the spatial mask plate (8), and the spatial mask plate (8) is arranged on the back focal plane of the second thin lens (7); The front focal plane of the third thin lens (9) coincides with the back focal plane of the second thin lens (7), and is used to image the structured illumination light filtered by the spatial mask plate (8) onto the sample (11).

3. The structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to claim 2, characterized in that: 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 structured illumination light from the third thin lens (9) and then illuminate the sample (11), while transmitting the scattered light beam from the sample (11) to the industrial lens (12); The sample (11) is arranged on the front focal plane of the industrial lens (12), and the back focal plane of the third thin lens (9) coincides with the front focal plane of the industrial lens (12); the camera (13) is arranged on a side of the industrial lens (12) away from the beam splitter (10).

4. The structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to claim 3, 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 plane of the camera (13).

5. The structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to claim 4, characterized in that: The spatial light modulator (6) is specifically used for: Loading fringe modulation patterns along the first direction and corresponding to phase shifts of 0, 2π / 3, and 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample (11) in the first in-plane direction at the deformation front on the camera (13); Loading fringe modulation patterns along the second direction and corresponding to phase shifts of 0, 2π / 3, and 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample (11) in the second in-plane direction at the deformation front on the camera (13); Loading fringe modulation patterns along a first direction and corresponding to phase shifts of 0, 2π / 3, and 4π / 3 respectively, to obtain three digital speckle phase shift images of the sample (11) along a first in-plane direction after deformation on a camera (13); Stripe modulation patterns along the second direction and corresponding phase shifts of 0, 2π / 3, and 4π / 3 are loaded respectively to obtain three digital speckle phase shift images along the second in-plane direction of the sample (11) after deformation 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.

6. The structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to claim 5, characterized in that: The data processing module is specifically used for: By using three digital speckle phase-shift images of the sample (11) before deformation under structured illumination light with different phase shift amounts in the first direction and three digital speckle phase-shift images of the sample (11) after deformation under structured illumination light with different phase shift amounts in the first direction, the phase distribution of the sample (11) before and after deformation along the first in-plane direction is obtained, and the in-plane deformation information of the sample along the first in-plane direction is obtained based on the corresponding relationship between the phase difference and the optical path difference caused by the deformation; By using three digital speckle phase-shift images of the sample (11) under structured illumination light with different phase shift amounts in the second direction before deformation and three digital speckle phase-shift images of the sample (11) under structured illumination light with different phase shift amounts in the second direction after deformation, the phase distribution of the sample (11) before and after deformation along the second in-plane direction is obtained, and the in-plane deformation information of the sample (11) along the second in-plane direction is obtained based on the corresponding relationship between the phase difference and the optical path difference caused by the deformation.

7. A structured light digital speckle interferometry method capable of achieving in-plane deformation measurement, characterized in that: The method is implemented using the structured light digital speckle interferometry device capable of realizing in-plane deformation measurement according to any one of claims 3 to 6, and comprises: S1: loading the spatial light modulator (6) with fringe modulation patterns having different phase shift amounts along a first direction and fringe modulation patterns having different phase shift amounts along a second direction, respectively, to obtain a plurality of digital speckle phase shift images corresponding to structured illumination light conditions in different directions and with different phase shift amounts before the sample is deformed; S2: The in-plane deformation information of the sample along different directions is obtained using the corresponding digital speckle phase shift images under structured illumination light with different directions and different phase shift amounts.

8. The structured light digital speckle interferometry method capable of realizing in-plane deformation measurement according to claim 7, characterized in that: Said S1 comprises: The spatial light modulator (6) is loaded with fringe modulation patterns along a first direction and corresponding to 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 a first in-plane direction at the deformation front on the camera (13); The spatial light modulator (6) is loaded with fringe modulation patterns along the second direction and corresponding to 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 second in-plane direction at the deformation front on the camera (13); The spatial light modulator (6) is loaded with fringe modulation patterns along a first direction and corresponding to phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase-shift images of the sample (11) along a first in-plane direction after deformation on a camera (13); The spatial light modulator (6) is loaded with fringe modulation patterns along the second direction and corresponding to phase shifts of 0, 2π / 3, and 4π / 3, respectively, so as to obtain three digital speckle phase-shifted images of the sample (11) along the second in-plane direction after deformation 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.

9. The structured light digital speckle interferometry method capable of realizing in-plane deformation measurement according to claim 8, characterized in that: The S2 includes: Using three digital speckle phase-shift images of the sample (11) in a 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, a phase distribution of the sample (11) in the first in-plane direction before and after deformation is obtained according to a reconstruction algorithm, and in-plane deformation information of the sample (11) in the first in-plane direction before and after deformation is obtained according to a corresponding relationship between the phase difference and the optical path difference caused by the deformation; Using three digital speckle phase-shift images of the sample (11) in its second in-plane direction before deformation and three digital speckle phase-shift images of the sample (11) in its second in-plane direction after deformation, the phase distribution of the sample (11) in the second in-plane direction before and after deformation is obtained according to a reconstruction algorithm, and the in-plane deformation information of the sample (11) in the second in-plane direction before and after deformation is obtained according to the corresponding relationship between the phase difference and the optical path difference caused by the deformation.

Images