CN110068283A - A kind of digital speckle sensor-based system applied to face internal strain - Google Patents
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Abstract
The present invention relates to a kind of digital speckle sensor-based systems applied to face internal strain, including light-source system, digital speckle pattern interferometry system, image capturing system, electric loading system device and computer, the light-source system includes two different wavelength laser sources, issues different wavelength laser for the detection sample on electric loading system device；The electric loading system device detects sample for clamping, and can be to detection sample on-load pressure；The test speckle interference image of sample is detected when the digital speckle pattern interferometry system is used to generate non-on-load pressure when the reference speckle interference image and on-load pressure of detection sample；Described image acquisition system is for obtaining with reference to speckle interference image and test speckle interference image；The computer calculates separately the phase of two speckle interference images by frequency spectrum isolation technics, and goes out material face internal strain information according to Phase-Resolved Analysis.The present invention synchronizes record without multiple CCD, can substantially reduce sensor-based system cost.
Description
Technical Field
The invention relates to the technical field of strain measurement, in particular to a digital speckle sensing system applied to in-plane strain.
Background
In order to eliminate the annoyance of amputees and help them restore their normal lives, it is necessary to design and install a prosthesis or perform a total hip replacement. There are various difficulties in improving the performance of prostheses for those patients with amputated lower extremities and for those with total joint replacement. Currently, the most important problem is the adaptation of the biological interface interaction forces of the harder metal and the softer bone surface. When a dynamic load is applied to such a structure, the structure not only has out-of-plane stresses, but also has the potential for transient, abrupt in-plane high strain forces, which is dangerous for biological or biomimetic structural materials with low yield strength. Determination of the dynamic strain profile at the biomaterial interface and assessment of potential pressure mismatch at the interface are critical to avoid potential infection of loosening, misalignment and interface gaps. Although current CAD software and finite element analysis play an important role in the estimation of strain, the creation of these models requires that the correct boundary conditions (constraints) and mechanical parameters of their materials be known in advance and verified by accurate measurements. Therefore, it is important to achieve a measurement of the strain induced by the transient load at the bone-implant interface. Bone is anisotropic heterogeneous biomaterial, and besides the evaluation of out-of-plane stress at the material interface, the measurement of the microscopic level of in-plane tension is also of crucial importance for understanding the biomechanical properties between bone and implant. However, in the conventional strain measurement methods, it is difficult to accurately identify and measure various strains caused by dynamic loads on the bioactive material. Especially due to the influence of unstructured test environment factors in the test process, no ideal in-plane strain measurement sensing system can meet the detection requirement so far.
Disclosure of Invention
The invention aims to provide a digital speckle sensing system applied to in-plane strain, which can conveniently, accurately and quickly detect the in-plane strain of a detected object.
The technical scheme adopted by the invention for solving the technical problems is as follows: the digital speckle sensing system comprises a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, wherein the light source system comprises two different-wavelength laser light sources which are used for emitting different-wavelength laser to a detection sample on the electric loading device; the electric loading device is used for clamping a detection sample and loading pressure to the detection sample; the digital speckle interference system is used for generating a reference speckle interference image of a detection sample when pressure is not loaded and a test speckle interference image of the detection sample when pressure is loaded; the image acquisition system is used for acquiring a reference speckle interference image and a test speckle interference image; the computer respectively calculates the phases of the two speckle interference images through a frequency spectrum separation technology, and analyzes strain information in the material surface according to the phases.
The digital speckle interference system comprises an aperture diaphragm, an imaging lens, a semi-reflecting and semi-transmitting mirror, a first adjustable reflector and a second adjustable reflector; the diffuse reflection light on the surface of the detection sample sequentially comprises an aperture diaphragm, an imaging lens and a semi-reflecting and semi-transmitting lens, and a first adjustable reflective mirror and a second adjustable reflective mirror are arranged on two sides of the semi-reflecting and semi-transmitting lens to form an interference system; and after the diffuse reflection light on the surface of the detection sample is reflected by the first reflector and the second reflector with adjustable inclination angles, the diffuse reflection light is sheared by the interference system, and sheared interference images in two directions are recorded in the same image acquisition system at the same time.
When the computer calculates the phases of the two speckle interference images, the characteristic that the positions of the spectral patterns of the two different-wavelength laser sources are different in wavelength and the speckle interference images are cut in two directions is utilized, and the phase information in the two cutting directions is extracted by intercepting the window frequency spectrum information at different positions and carrying out complex operation.
The computer specifically extracts the phase information in the two shearing directions as follows: if the shear direction is along the x-axis, then the measured wavefront is at k1And k is2The expression in direction is noted as:wherein u is11、u12Is the wavefront, u, through the first and second adjustable mirrors in the sensitive direction k1, respectively21And u22Respectively passing through the first adjustable reflector and the second adjustable reflector in the sensitive direction k2The wavefront of (a);andis the phase of the wavefront, and f1And f2Then two different spatial frequencies are generated by clipping, denoted as:λ1and λ2The obtained speckle interference image I is expressed as I ═ u (u) by the wavelength of the two different-wavelength laser light sources and the inclination angle of the second adjustable reflector β11u11 *+u12u12 *)+(u21u21 *+u22u22 *)+(u11u12 *+u12u11 *)+(u21u22 *+u22u21 *) Wherein u is11 *、u12 *、u21 *、u22 *Are each u11、u12、u21、u22In the sensitive direction k1And k is2The wave front conjugate term of (2) is obtained by Fourier transformWherein,representing a convolution operation, let: u shape11(fx,fy)＝FT(u11)，U12(fx+f1,fy)＝FT(u12)，U21(fx,fy)＝FT(u21)，U22(fx+f2,fy)＝FT(u22) A fourier spectrogram distribution in which speckle images are recorded is obtained, wherein the 8 terms are divided into 5 parts, wherein (U)11+U11 *+U12+U12 *) And (U)21+U21 *+U22+U22 *) The terms are low-frequency terms, respectively occupying the center of the frequency domain and having a width of 2fc1And 2fc2；(U12+U11 *) Is positioned at (f)10) is central, and (U)11+U12 *) Is positioned at (-f)10) as centers, they are all 2f wide in the frequency spectrumc1The two terms comprise k1Phase information of direction shearing; (U)22+U21 *) The item is located at (f)20) is central, and (U)21+U22 *) Is positioned at (-f)20), their widths in the frequency spectrum are all2fc2The two items are recorded at k2Phase information of the directional shear; wherein f isc1And fc2By selecting appropriate slit size control, in the spectral region (f)10) and (f)20), by applying a windowed inverse fourier transform, the phase distribution is calculated using the complex amplitude, which is calculated by the formula:where Im and Re represent the real and imaginary parts of the complex number, respectively, and phi1And phi2The phase difference of the two oblique beams respectively; after deformation of the loaded sample, it can be obtained by using the same method
The computer analyzes the strain information in the material surface according to the phase specifically as follows: and subtracting the phase before and after deformation to obtain a phase distribution diagram reflecting the out-of-plane strain in the two illumination directions, and calculating the in-plane strain information of the detection surface according to the out-of-plane strain phase information in the two directions.
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
the invention provides a simpler and faster method for measuring in-plane strain caused by dynamic loading. The traditional complex in-plane strain detection method needs to take 16 frames of time phase shift images and transform 4 times of lens switches in the strain detection process, and the whole detection process is simplified into the process of only acquiring two frames of interference images by the space phase shift shearing system provided by the prior art. In particular, only one frame of image is needed to calculate the relative phase change after deformation in the detection process. Because the detection speed of the whole measuring system is only limited by the CCD frame rate, the frame rate of the current advanced CCD camera can reach 15000 frames/second, so that the novel sensor system is very suitable for dynamic strain tests which require high sensitivity of dozens of micro-strain levels.
In addition, current spatial phase shift digital shear systems for in-plane strain measurement are typically implemented with dual information channels, dual beams. However, the inventors of the present application found experimentally that by using laser illumination of different wavelengths, the resulting two shear speckle spectra differ in position on the frequency domain image. Therefore, the laser speckle interference system with different wavelengths and double light sources can realize the simultaneous recording of two shearing speckle patterns in a single channel, and the separation of the two shearing frequency spectrograms is possible by selecting proper system parameters. Because the whole sensing system only needs one CCD camera to record images, the system cost can be greatly reduced, and simultaneously, the measurement process can be simpler, because the pixel registration, synchronous trigger recording and the like of the images of a plurality of channels are not needed any more.
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FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a flow chart of in-plane strain detection in the present invention;
FIG. 3 is a schematic diagram of the speckle interference spectrum recorded by the interference system of the present invention;
in the figure: the device comprises a first laser 1, a second laser 2, a first beam expander 3, a second beam expander 4, an aperture diaphragm 5, an imaging lens 6, a semi-reflecting and semi-transmitting mirror 7, a first adjustable reflective mirror 8, a second adjustable reflective mirror 9, a loading support 10, a voice coil motor 11, a CCD camera 12, a display 13, a computer 14 and a detection sample 15.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The embodiment of the invention relates to a digital speckle sensing system applied to in-plane strain, which comprises a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, wherein the light source system comprises two different-wavelength laser light sources used for emitting different-wavelength laser to a detection sample on the electric loading device; the electric loading device is used for clamping a detection sample and loading pressure to the detection sample; the digital speckle interference system is used for generating a reference speckle interference image of a detection sample when pressure is not loaded and a test speckle interference image of the detection sample when pressure is loaded; the image acquisition system is used for acquiring a reference speckle interference image and a test speckle interference image; the computer respectively calculates the phases of the two speckle interference images through a frequency spectrum separation technology, and analyzes strain information in the material surface according to the phases.
In the detection process, two different-wavelength lasers project laser and irradiate the surface of an object simultaneously, two frames of speckle interference patterns are generated in an improved Michelson interference system, and the two frames of speckle interference patterns are recorded on the same CCD imaging array surface simultaneously through different channels; then, the phases of the speckle interferograms in the two shearing directions are respectively calculated through a frequency spectrum separation technology, and finally, the in-plane strain information of the material is analyzed.
As shown in fig. 1, the light source system includes a different-wavelength laser 1, a laser 2, a beam expander 3 and a beam expander 4; the digital speckle interference system is an improved Michelson speckle interference device and mainly comprises an aperture diaphragm 5, an imaging lens 6, a semi-reflecting and semi-transmitting mirror 7, an adjustable reflective mirror 8 and an adjustable reflective mirror 9, the image acquisition system comprises a CCD camera 12 and other devices, and the electric loading system comprises a loading support 10, a voice coil motor 11 and the like.
The electric loading system is used for realizing the installation and loading of the detection sample 15; the digital speckle interference system and the image acquisition system are arranged in front of a detection area of a detection sample 15; the two different-wavelength laser light sources 1 and 2 project laser light, and the laser light is respectively expanded by the beam expander 3 and the beam expander 4 and simultaneously irradiated on the surface of the detection sample 15; the diffuse reflection light beam on the surface of the detection sample 15 passes through an aperture diaphragm 5, an imaging lens 6, a semi-reflecting and semi-transmitting mirror 7, an adjustable reflecting mirror 8 and an adjustable reflecting mirror 9 to finally form shearing speckle images on the array surface of a CCD camera 12, and the CCD camera 12 performs image acquisition control through a computer 14; the CCD imaging array surface 12 acquires speckle images, frequency spectrum separation and complex operation are carried out through the computer 14, the phases of the shearing speckle patterns in two directions are respectively calculated, and finally the in-plane dependent variables of the material are analyzed. The two lasers respectively illuminate an object to be detected, reflected light of the two lasers is respectively reflected by the adjustable reflective mirror 8 and the adjustable reflective mirror 9 with adjustable inclination angles and then is cut by the Michelson interference device, and cut interference images in two directions are recorded into the image sensor at the same time.
This embodiment may employ the following:
(1) a computer: the model is Mowa IPC-610L-701VG, the processor inter i5-2400 supports JPEG hardware coding and decoding, and the memory is 4Gbits DDR 3. Supporting RGB 24Bit interface and TVOUT video output;
(2) a display: type samsung C27F390FHC, resolution 1920 x 1080;
(3) laser light source 1: a solid laser with wavelength of 532nm and 200mw and a single longitudinal mode;
(4) laser light source 2: a 200mw solid-state laser with a wavelength of 632nm, a single longitudinal mode;
(5) the beam expander 3: f is 16mm, phi is 20.4 mm;
(6) the beam expander 4: f is 16mm, phi is 20.4 mm;
(7) aperture stop 5: an electric adjustable aperture diaphragm HGEMD52, the aperture change is 3-52 mm;
(8) the CCD camera 12: the method adopts a Basler acA2400-50gm area array CCD, 2048 x 1536 pixels, the size of an imaging area is 3626 mu m x 2709 mu m, the size of the pixel is 1.75 mu m x 1.75 mu m, and the highest speed can reach 50 frames per second;
(9) imaging lens 6: brand great, Φ 25.4K9 biconvex lens, f 100mm, clear aperture: 90 percent;
(10) and (3) a half-reflecting half-transmitting mirror 7: brand identity, GCC-4011 series broadband beam splitter prism, transmittance/reflectance: 50/50, respectively; material K9; the external dimension is as follows: 25.4 mm;
(11) voice coil motor 11: the SMAC voice coil motor LAL series has rated power of 10-50(kW), rated voltage of 24-48(V), stroke of 15mm and displacement resolution of 5 μm;
(12) mirrors 8 and 9, a loading stand 10, etc.
As shown in fig. 2, the in-plane strain detection process includes: the CCD imaging array surface respectively acquires speckle interference images I before and after deformation1And I2Fourier Transform (FFT) is respectively carried out to obtain frequency spectrum images F (I) before and after loading1) And F (I)2) (ii) a Because the two laser light sources have different wavelengths, the positions of the frequency spectrums of the obtained speckle images are different (as shown in fig. 3), so the frequency f before and after deformation is adjusted1And f2Windowing (WIFT) and complex operation are carried out on the frequency spectrum bands of the fixed neighborhoods, and phase information phi in two illumination directions before and after deformation is obtained in sequence1，φ2And phi1'，φ2' phase profile △ reflecting out-of-plane strain in two illumination directions is obtained by phase subtraction1And △2And through the phase information △ of out-of-plane strain in two directions1And △2And calculating in-plane strain information of the detection surface.
Therefore, the phase evaluation of the two laser light sources to cut the speckle patterns is realized by performing spectrum separation and correlation operation on the speckle interference images simultaneously recorded in the same image sensor. The positions of spectral patterns of speckle interference images sheared in two directions are different due to the fact that the wavelengths of the two laser light sources are different, and phase information of the two shearing directions is extracted by intercepting window spectral information of different positions and performing complex operation. The method comprises the following specific steps:
if the shear direction is along the x-axis, then the measured wavefront is at k1And k is2The expression in direction can be written as:
u11、u12the wavefronts in the sensitive direction k1 through the adjustable mirror 8 and the adjustable mirror 9, respectively, and u21And u22Respectively through an adjustable reflector 8 and an adjustable reflector 9 in the sensitive direction k2The wavefront of (a);andis the phase of the wavefront, and f1And f2Then two different spatial frequencies are generated by clipping, which can be expressed as:
f1＝(sinβ/λ1) (5)
f2＝(sinβ/λ2) (6)
λ1and λ2The wavelengths of the two light sources, β, respectively, are the tilt angle of the adjustable mirror 9, so that the speckle image I recorded on the CCD can be expressed as:
I＝(u11+u12)(u11 *+u12 *)+(u21+u22)(u21 *+u22 *)
＝(u11u11 *+u12u12 *+u11u12 *+u12u11 *)+(u21u21 *+u22u22 *)(u21u22 *+u22u21 *)
＝(u11u11 *+u12u12 *)+(u21u21 *+u22u22 *)+(u11u12 *+u12u11 *)+(u21u22 *+u22u21 *) (7)
the fourier transform yields:
whereinRepresenting a convolution operation, let: u shape11(fx,fy)＝FT(u11)，U12(fx+f1,fy)＝FT(u12)，U21(fx,fy)＝FT(u21)，U22(fx+f2,fy)＝FT(u22) FIG. 3 shows the Fourier image recorded under ideal conditionsDistribution of the inner leaf frequency spectrum.
In the fourier domain, there are 6 spectral bins corresponding to the 8 sub-terms in the above equation. As can be seen from the spectrogram, these 8 terms can be divided into 5 parts. Wherein (U)11+U11 *+U12+U12 *) And (U)21+U21 *+U22+U22 *) The terms, low-frequency terms, mainly background light, occupy the center of the frequency domain and have widths of 2fc1And 2fc2。(U12+U11 *) Is positioned at (f)10) is central, and (U)11+U12 *) Is positioned at (-f)10) as centers, they are all 2f wide in the frequency spectrumc1The two terms comprise k1Phase information of direction shear. (U)22+U21 *) The item is located at (f)20) is central, and (U)21+U22 *) Is positioned at (-f)20), their widths in the spectrum are all 2fc2The two items are recorded at k2Phase information of directional shear. Wherein f isc1And fc2Can be controlled by selecting an appropriate slit size. In the spectral region (f)10) and (f)20), by applying a Windowed Inverse Fourier Transform (WIFT), the phase distribution can be calculated by using the complex amplitude. The calculation formula is as follows:
[φ1+2πxf1]＝arctan{Im[u12u11*]/Re[u12u11*]} (9)
[φ2+2πxf2]＝arctan{Im[u22u21*]/Re[u22u21*]} (10)
where Im and Re represent the real and imaginary parts of the complex number, respectively, and phi1And phi2Respectively the phase difference of the two oblique beams,in the process of loading sampleAfter the formation, by using the same method, it is possible to obtain:
[φ1′+2πxf1]＝arctan{Im[u12u11 *]/Re[u12u11 *]} (11)
[φ2′+2πxf2]＝arctan{Im[u22u11 *]/Re[u22u21 *]} (12)
therefore, the relative phase difference caused by the deformation can be calculated by the following formula:
Δ1＝φ1′-φ1(13)
Δ2＝φ2′-φ2(14)
thereby obtaining a phase profile △ reflecting out-of-plane strain information1And △2。
The in-plane strain of the biological material is calculated by calculating phase information △ of out-of-plane strain in two directions1And △2Calculated, the calculation flow is as follows:
based on the relationship between the phase difference and the in-plane strain, the following can be obtained:
simultaneous and simplified to obtain:
similarly, the in-plane strain component in other directions will be expressed in the same manner as:
thereby finally obtaining the in-plane strain information of the detection surface.
The invention can be applied to the in-plane strain detection of biological materials, is convenient to know and detect potential stress mismatching of the artificial limb contact interface, uneven pressure or stress distribution and the like, is beneficial to comprehensively mastering and knowing stress distribution and matching conditions of the broken limb patient and the hip joint integral replacement patient, and provides the most direct information for diagnosis, treatment and recovery of the patient.
Claims (5)
1. A digital speckle sensing system applied to in-plane strain comprises a light source system, a digital speckle interference system, an image acquisition system, an electric loading device and a computer, and is characterized in that the light source system comprises two different-wavelength laser light sources which are used for emitting different-wavelength laser to a detection sample on the electric loading device; the electric loading device is used for clamping a detection sample and loading pressure to the detection sample; the digital speckle interference system is used for generating a reference speckle interference image of a detection sample when pressure is not loaded and a test speckle interference image of the detection sample when pressure is loaded; the image acquisition system is used for acquiring a reference speckle interference image and a test speckle interference image; the computer respectively calculates the phases of the two speckle interference images through a frequency spectrum separation technology, and analyzes strain information in the material surface according to the phases.
2. The digital speckle sensing system applied to in-plane strain of claim 1, wherein the digital speckle interference system comprises an aperture stop, an imaging lens, a semi-reflective semi-transparent mirror, a first adjustable mirror and a second adjustable mirror; the diffuse reflection light on the surface of the detection sample sequentially comprises an aperture diaphragm, an imaging lens and a semi-reflecting and semi-transmitting lens, and a first adjustable reflective mirror and a second adjustable reflective mirror are arranged on two sides of the semi-reflecting and semi-transmitting lens to form an interference system; and after the diffuse reflection light on the surface of the detection sample is reflected by the first reflector and the second reflector with adjustable inclination angles, the diffuse reflection light is sheared by the interference system, and sheared interference images in two directions are recorded in the same image acquisition system at the same time.
3. The digital speckle sensing system applied to in-plane strain according to claim 1, wherein the computer extracts the phase information of the two shearing directions by intercepting the window spectrum information of different positions and performing complex operation by using the characteristics that the two different wavelength laser sources have different wavelengths and the positions of the spectral patterns shearing the speckle interference images in the two directions are different when calculating the phases of the two speckle interference images.
4. The digital speckle sensing system applied to in-plane strain according to claim 3, wherein the computer extracts the phase information of two shearing directions specifically as follows: if the shear direction is along the x-axis, then the measured wavefront is at k1And k is2The expression in direction is noted as:wherein, therein，u11、u12Is the wavefront, u, through the first and second adjustable mirrors in the sensitive direction k1, respectively21And u22Respectively passing through the first adjustable reflector and the second adjustable reflector in the sensitive direction k2The wavefront of (a);andis the phase of the wavefront, and f1And f2Then two different spatial frequencies are generated by clipping, denoted as:λ1and λ2The obtained speckle interference image I is expressed as I ═ u (u) by the wavelength of the two different-wavelength laser light sources and the inclination angle of the second adjustable reflector β11u11 *+u12u12 *)+(u21u21 *+u22u22 *)+(u11u12 *+u12u11 *)+(u21u22 *+u22u21 *) Wherein u is11 *、u12 *、u21 *、u22 *Are each u11、u12、u21、u22In the sensitive direction k1And k is2The wave front conjugate term of (2) is obtained by Fourier transformWherein,representing a convolution operation, let: u shape11(fx,fy)＝FT(u11)，U12(fx+f1,fy)＝FT(u12)，U21(fx,fy)＝FT(u21)，U22(fx+f2,fy)＝FT(u22) A fourier spectrogram distribution in which speckle images are recorded is obtained, wherein the 8 terms are divided into 5 parts, wherein (U)11+U11 *+U12+U12 *) And (U)21+U21 *+U22+U22 *) The terms are low-frequency terms, respectively occupying the center of the frequency domain and having a width of 2fc1And 2fc2；(U12+U11 *) Is positioned at (f)10) is central, and (U)11+U12 *) Is positioned at (-f)10) as centers, they are all 2f wide in the frequency spectrumc1The two terms comprise k1Phase information of direction shearing; (U)22+U21 *) The item is located at (f)20) is central, and (U)21+U22 *) Is positioned at (-f)20), their widths in the spectrum are all 2fc2The two items are recorded at k2Phase information of the directional shear; wherein f isc1And fc2By selecting appropriate slit size control, in the spectral region (f)10) and (f)20), by applying a windowed inverse fourier transform, the phase distribution is calculated using the complex amplitude, which is calculated by the formula:where Im and Re represent the real and imaginary parts of the complex number, respectively, and phi1And phi2The phase difference of the two oblique beams respectively; after deformation of the loaded sample, it can be obtained by using the same method
5. The digital speckle sensing system applied to in-plane strain according to claim 1, wherein the computer analyzes the strain information in the material plane according to the phase specifically as follows: and subtracting the phase before and after deformation to obtain a phase distribution diagram reflecting the out-of-plane strain in the two illumination directions, and calculating the in-plane strain information of the detection surface according to the out-of-plane strain phase information in the two directions.
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| CN113551984A (en) * | 2020-04-24 | 2021-10-26 | 株式会社岛津制作所 | Material testing machine and display method in material testing machine |
| CN114324359A (en) * | 2021-12-30 | 2022-04-12 | 合肥工业大学 | Object double-end-face out-of-plane deformation gradient distribution synchronous measurement system |
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