Compact measurement device, method and medium for three-dimensional displacement in holographic range of scattered light field

Abstract

The present invention provides a compact measurement device, method and medium for three-dimensional displacement in a holographic range of a scattered light field, comprising a first laser, a second laser, a first beam splitter, a second beam splitter, a converging lens, a pinhole, a first plane mirror, a second plane mirror, a third beam splitter and a camera. By combining holographic measurement of scattered light fields and digital image correlation and other technologies, dynamic measurement of three-dimensional vector displacement of highly scattering objects is achieved. The measuring device of the present invention adopts dual wavelengths to achieve optical path multiplexing, has a compact structure, is suitable for integration, is simple and practical, and has a larger displacement measurement range than a single wavelength. The present invention combines digital image correlation technology and holographic measurement technology of scattered light fields, has the advantages of non-contact, high measurement accuracy, fast measurement speed, large measurement range, synchronous measurement of three-dimensional vector displacement, compact device, etc., and has broad application prospects in high-precision measurement occasions such as aerospace and micro medical robots.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and in particular to a compact device, method and medium for measuring three-dimensional displacement in a scattered light field holographic range, and in particular to a compact device and method for measuring large-scale three-dimensional displacement in a scattered light field holographic range. Background Art

[0002] With the rapid development of precision machining technology in industries such as machinery manufacturing and semiconductor industry, the corresponding process requirements for various ultra-precision devices or optical components are increasing. For many occasions that require precise matching of various components, such as aerospace, micro medical robots, etc., how to obtain the displacement or deformation of precision components is a very critical issue.

[0003] Among the existing measurement methods, the traditional contact displacement measurement method has a slow measurement speed, introduces artificial force interference, and may also cause wear on the surface of the object due to the contact force, so it is not suitable for the measurement of precision components. Among the non-contact measurement methods, digital holography technology has the advantages of non-contact measurement and full-field measurement of nanometer-level high precision, and is an ideal high-precision displacement detection method. However, digital holography technology is generally used for the measurement of objects on mirror surfaces, and fails for objects on scattering surfaces. At the same time, a single digital holographic device is not suitable for the measurement of three-dimensional vector displacement. If you want to achieve synchronous three-dimensional vector displacement measurement, you often need three sets of digital holographic devices, each of which is responsible for the measurement of one dimension of displacement. However, the installation of three sets of digital holographic devices is relatively complicated. At the same time, the utilization efficiency of information is not high, only the phase map is used, and the intensity maps of the three devices are all discarded. At the same time, the measurement range of single-wavelength holography is limited, usually at the level of hundreds of nanometers, and the single-wavelength holographic method fails for occasions with higher measurement range requirements.

[0004] A new laser displacement measurement method based on the digital speckle correlation method is disclosed in the patent document with publication number CN102967261A, which is specifically as follows: the laser is focused and vertically incident on the surface of the moving object to be measured; the scattered light at the incident light point on the surface of the object to be measured is received, and the scattered light spot is imaged on the sensitive surface of the CCD through an imaging lens; when the signal bandwidth of the scattered light spot is less than or equal to the bandwidth threshold, it indicates that the surface of the object to be measured is a weak scattering interface, and the displacement of the scattered light spot on the CCD is measured by the average weighted centroid method; when the signal bandwidth of the scattered light spot is greater than the bandwidth threshold, it indicates that the surface of the object to be measured is a strong scattering cross-section, and the correlation method is used to measure the displacement of the scattered light spot on the CCD; the displacement of the object to be measured is calculated based on the displacement of the scattered light spot on the CCD.

[0005] In addition, among the existing optical measurement methods, the digital image correlation method has been widely studied and applied due to its comprehensive advantages such as simple installation, rich measurement indicators and information, a wide range of measurable material types, suitability for measurement at various scales and under various conditions, and high accuracy. In the field of experimental mechanics, two-dimensional digital image correlation is a widely used method for quantitatively measuring the displacement of a plane object in the x and y directions. It obtains the displacement and strain information of the object's area of ​​interest in the image plane by analyzing the digital image of the surface of the object before and after deformation, and achieves sub-pixel accuracy. However, two-dimensional digital image correlation is limited to the measurement of displacement in the x and y directions of the plane, and cannot obtain the displacement in the z direction of the optical axis.

[0006] Therefore, how to quickly and easily obtain the three-dimensional vector displacement of an object in a larger measurement range through a simple device is an urgent problem to be solved, and a technical solution needs to be proposed to improve the above technical problems. Summary of the invention

[0007] In view of the defects in the prior art, the object of the present invention is to provide a compact device, method and medium for measuring three-dimensional displacement in a holographic range of a scattered light field.

[0008] According to the present invention, a scattered light field holographic range three-dimensional displacement compact measurement device includes a first laser, a second laser, a first beam splitter, a second beam splitter, a converging lens, a pinhole, a first plane mirror, a second plane mirror, a third beam splitter and a camera;

[0009] The first beam splitter is directly opposite to the laser emission ports of the first laser and the second laser to combine the two laser beams, the second beam splitter is located on the combined light path of the first beam splitter, the converging lens, the pinhole and the first plane mirror are arranged in a row in sequence and are located on the reflected light path of the second beam splitter, the second plane mirror is located on the reflected light path of the first plane mirror, the third beam splitter is located at the intersection of the transmitted light path of the second beam splitter and the reflected light path of the second plane mirror, the object to be measured is located on the transmitted light path of the third beam splitter, and the reflected light of the camera located on the combined light path of the third beam splitter with the reflected light of the object to be measured and the reflected light of the second plane mirror.

[0010] Preferably, a neutral attenuation plate is arranged between the second beam splitter and the converging lens.

[0011] Preferably, an imaging lens is arranged between the third beam splitter and the object to be measured.

[0012] Preferably, a phase shifting device is provided between the second plane mirror and the third beam splitter.

[0013] Preferably, the second beam splitter is replaced by a polarization beam splitter unit, which includes a polarization beam splitter, a first half-wave plate and a second half-wave plate. The polarization beam splitter is located at the position of the second beam splitter, the first half-wave plate is arranged between the first beam splitter and the polarization beam splitter, and the second half-wave plate is arranged between the polarization beam splitter and the converging lens.

[0014] The present invention also provides a method for measuring a compact device for measuring three-dimensional displacement in a scattered light field holographic range, the method using the above-mentioned compact device for measuring three-dimensional displacement in a scattered light field holographic range, and the method comprising the following steps:

[0015] Step S1: The light emitted by the first laser and the second laser is combined by the first beam splitter and then incident on the second beam splitter to be divided into two paths: the light beam transmitted by the second beam splitter is irradiated to the surface of the object to be measured after passing through the third beam splitter, and is reflected by the surface of the object to be measured to form a measuring beam; the light beam reflected by the second beam splitter is reflected by the first plane mirror and the second plane mirror after passing through a converging lens and a pinhole filter to form a reference beam; the measuring beam and the reference beam are combined by the third beam splitter and interfere with each other, and a hologram is formed on the photosensitive surface of the camera;

[0016] Step S2: before the displacement of the object to be measured changes, the object to be measured is irradiated with the first laser and the second laser respectively, and recorded by the camera to obtain two holograms H1 and H2, and the light field is reconstructed by using the two recorded holograms to obtain two single-wavelength phase images of the light field reflected from the surface of the object to be measured before the displacement, and then the morphology of the object to be measured before the displacement is calculated from the two single-wavelength phase images according to the dual-wavelength phase synthesis formula, and the intensity image of the light field reflected from the surface of the object to be measured before the displacement is calculated using the hologram H1 or the hologram H2;

[0017] Step S3: after the displacement of the object to be measured changes, the object to be measured is irradiated with the first laser and the second laser respectively, and recorded by the camera to obtain two holograms H3 and H4, and the light field is reconstructed using the two recorded holograms, thereby obtaining two single-wavelength phase images of the light field reflected from the surface of the object to be measured after the displacement, and then the morphology of the object to be measured after the displacement is calculated from the two single-wavelength phase images according to the dual-wavelength phase synthesis formula; the hologram H3 or H4 obtained by irradiation with the same wavelength laser as in step S2 is used to calculate the intensity image of the light field reflected from the surface of the object to be measured after the displacement;

[0018] Step S4: subtracting the morphology of the object to be measured before and after the displacement to obtain the displacement in the z direction along the optical axis; processing the intensity map of the light field reflected from the surface of the object to be measured before and after the displacement, and calculating the displacement of the object to be measured in the x direction and the y direction perpendicular to the optical axis;

[0019] Step S5: combining the displacement of the object to be measured in the z direction along the optical axis with the displacements in the x direction and the y direction perpendicular to the optical axis to obtain the three-dimensional vector displacement of the object to be measured.

[0020] Preferably, step S2 comprises the following steps:

[0021] Step S2.1: Select the coordinate point P1 to be measured on the intensity map before displacement;

[0022] Step S2.2: With the selected coordinate point P1 to be measured as the center, define a region R1 with a size of (2M+1)×(2M+1) pixels, where M is a positive integer determined by the size of the sub-region of interest;

[0023] Step S2.3: arbitrarily define a region R2 with a size of (2M+1)×(2M+1) centered at the coordinate point Pi on the intensity map after displacement;

[0024] Step S2.4: Calculate the similarity between regions R1 and R2;

[0025] Step S2.5: Change the coordinate value of the coordinate point Pi in step S2.3, and repeat steps S2.3 to S2.4 until i traverses all pixels in the intensity map after displacement and finds the region R2 with the highest similarity to region R1;

[0026] Step S2.6: Calculate the center coordinate P2 of region R2;

[0027] Step S2.7: Subtract the coordinates of P2 from those of P1 to obtain the displacement of point P1 in the x-direction and the y-direction perpendicular to the optical axis;

[0028] Step S2.8: Repeat steps S2.1 to S2.7 until all pixel points in the intensity map before displacement are traversed, that is, the displacements in the x-direction and y-direction perpendicular to the optical axis corresponding to all pixel points are obtained.

[0029] Preferably, the inclination angles of the first plane mirror and the second plane mirror are adjusted so that an angle is formed between the reflected reference beam and the measuring beam, and the scattered light field is extracted from the hologram by Fourier transform method.

[0030] Preferably, a phase shift device is added to the optical path before the light beam is reflected by the first plane mirror and incident on the third beam splitter to shift the phase of the reference beam, and the scattered light field is extracted from the hologram by a multi-step phase shift calculation method.

[0031] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program implements the steps of the above method when executed by a processor.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The measuring device of the present invention solves the problem that the existing three-dimensional vector displacement measurement technology uses multiple sets of measuring devices to measure displacements of different dimensions respectively, resulting in a complex system optical path structure and high cost. A measurement method that uses only one multiplexed measuring beam is proposed, which is combined with a two-dimensional digital image correlation technology to efficiently utilize all the information of a set of measurement systems, effectively reduce costs, and greatly simplify the complexity of the measurement system and operation process;

[0034] 2. The present invention adopts a dual-wavelength optical path structure to achieve optical path multiplexing, which can effectively expand the measurement range of off-plane displacement;

[0035] 3. Compared with the existing measuring devices, the measuring device of the present invention has a more scientific and reasonable structural design, is simpler and more convenient to use, has a more compact optical path, and is more suitable for integration;

[0036] 4. The measuring device of the present invention adopts a single lens, which not only realizes the light spot magnification but also realizes the imaging function. The light spot can be magnified according to actual needs to achieve a larger light spot measurement range;

[0037] 5. The measuring method of the present invention has the characteristics of full-field and non-contact measurement, and can realize non-destructive testing of the test piece;

[0038] 6. The measurement method of the present invention combines nanometer-level high-precision scattered light field measurement technology with sub-pixel-level high-precision digital image correlation technology, and has the advantages of high efficiency, rapidity, high measurement accuracy, and dynamic measurement; first, the present invention integrates two independent technologies into one hardware system. The previous two technologies each had their own hardware systems, including independent cameras and optical imaging systems. The present invention is based on only one set of holographic hardware systems, and does not use an additional hardware system of independent digital image correlation technology. Instead, it uses digital image correlation technology to process the speckle intensity image that was not used by the previous digital holography, so the two independent technologies are organically integrated into one hardware system. Secondly, the digital image correlation technology in the present invention processes laser speckle images. The previous digital image correlation technology processes intensity images under natural light or white light, and the key content of the processing is the texture of the object in the intensity image or the artificially sprayed speckle. There are differences in the characteristics of laser speckle and the above digital image correlation technologies.

[0039] 7. The measurement method of the present invention can realize the synchronous measurement of the three-dimensional vector displacement of scattering surface objects, which solves the limitation that traditional optical measurement methods can only measure mirror surface objects. The three-dimensional displacement measurement of curved surface objects requires the three-dimensional morphology information of the object. However, the three-dimensional morphology measurement of scattering surface objects is more difficult than that of mirror objects. This is mainly because the height variation of particles on scattering surface objects has exceeded the laser wavelength, which is difficult to measure with a simple digital holographic system. An additional three-dimensional morphology measurement system is often required, which not only makes the measurement scheme complicated, but also makes the data fusion of multiple systems difficult and further complicated. However, the three-dimensional morphology of mirror objects with a height of microns and below can be measured using a laser holographic system. Therefore, it is difficult to measure the three-dimensional vector displacement of scattering surface objects. The present invention solves this problem by reusing the same set of optical paths and using a holographic system of two lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0041] Figure 1 It is a schematic diagram of a compact device for measuring scattered light field holographic large-range three-dimensional displacement of the present invention;

[0042] Figure 2 It is a structural diagram of a compact device for measuring scattered light field holographic large-range three-dimensional displacement in Example 1 of the present invention;

[0043] Figure 3A The hologram recorded by the CCD in Embodiment 1 of the present invention before the object to be measured is moved and irradiated by the first laser;

[0044] Figure 3B The holograms recorded by the CCD in Embodiment 1 of the present invention before the object to be measured is moved and respectively illuminated by the second laser;

[0045] Figure 4A The hologram recorded by the CCD in Embodiment 1 of the present invention after the object to be measured is displaced and irradiated by the first laser;

[0046] Figure 4B The hologram recorded by the CCD in Embodiment 1 of the present invention after the object to be measured is displaced and irradiated by the second laser;

[0047] Figure 5 The dual-wavelength synthetic wrapped phase image of the object to be measured before displacement in Example 1 of the present invention;

[0048] Figure 6 This is a diagram of the measurement results of the object to be measured along the optical axis z direction in Example 1 of the present invention;

[0049] Fig. 7A is an intensity diagram of the object to be measured recorded by the CCD before displacement under the irradiation of the first laser in Example 1 of the present invention;

[0050] Figure 7B is an intensity diagram of the object to be measured recorded by the CCD before displacement under the irradiation of the second laser in Example 1 of the present invention;

[0051] Fig. 8A Graph showing the measurement result of the in-plane displacement of the object to be measured along the x direction perpendicular to the optical axis in Example 1 of the present invention;

[0052] Figure 8B Graph showing the measurement result of the in-plane displacement of the object to be measured along the y direction perpendicular to the optical axis in Example 1 of the present invention;

[0053] Fig. 9 This is a structural diagram of a compact device for measuring scattered light field holographic large-range three-dimensional displacement in Example 2 of the present invention;

[0054] Fig.10 is a diagram showing the internal structure of the polarization splitting unit in the present invention;

[0055] Fig.11 This is a structural diagram of a compact device for measuring scattered light field holographic large-range three-dimensional displacement in Example 3 of the present invention;

[0056] Fig.12 This is a structural diagram of the compact measurement device for scattered light field holographic large-range three-dimensional displacement in Example 4 of the present invention.

[0057] in:

[0058] First laser 1 Camera 11

[0059] Second laser 2 Neutral attenuator 12

[0060] First beam splitter 3 Imaging lens 13

[0061] Second beam splitter 4 Polarization beam splitting unit 14

[0062] Converging lens 5 First half-wave plate 141

[0063] Pinhole 6 Polarization beam splitter 142

[0064] First plane mirror 7 Second half-wave plate 143

[0065] Second plane mirror 8 beam splitter plate 15

[0066] The third beam splitter 9 phase shift device 16

[0067] Object to be tested 10 DETAILED DESCRIPTION

[0068] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0069] The present invention provides a compact device, method and medium for measuring three-dimensional displacement in a scattered light field holographic range. The present invention is based on the scattered light field measurement technology and combines the two-dimensional digital image correlation technology to dynamically and synchronously measure the three-dimensional vector displacement of an object. The present invention can be applied to the displacement measurement of objects with mirror or rough surfaces to achieve synchronous measurement of the three-dimensional vector displacement or deformation of the object.

[0070] Example 1

[0071] like Figure 2 As shown, the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a second beam splitter 4, a converging lens 5, a pinhole 6, a first plane mirror 7, a second plane mirror 8, a third beam splitter 9, an object to be measured 10, a camera 11, a neutral attenuation plate 12, and an imaging lens 13.

[0072] The first laser 1 generates laser light 1 a , and the second laser 2 generates laser light 2 a . The laser light 1 a and the laser light 2 a are input to the first beam splitter 3 and then combined.

[0073] The first laser 1 and the second laser 2 are coherent light sources. In the specific design of the present invention, the first laser 1 provides spatial light with a central wavelength of 532 nm, and the second laser 2 provides spatial light with a central wavelength of 526.5 nm.

[0074] The first beam splitter 3, the second beam splitter 4 and the third beam splitter 9 are optical devices that can split a light beam into two, achieving 50% transmission and 50% reflection. The first beam splitter 3, the second beam splitter 4 and the third beam splitter 9 have the same structure and function, and the second beam splitter 4 is used as an example for explanation. The second beam splitter 4 is used to receive the spatial light 3a after the first beam splitter 3 combines the light, and split it into spatial light 4a and 4b for output. The transmitted light 4b enters the measurement light path, and the reflected light 4a enters the reference light path.

[0075] The neutral attenuation plate 12 is used to adjust the strength of the reference light path, and then adjust the light intensity ratio between the measurement light and the reference light to obtain a high-quality hologram.

[0076] The converging lens 5 and the pinhole 6 together form a spatial filtering unit. The converging lens 5 converges the spatial light 5a attenuated by the neutral attenuation plate 12 to a point, and a pinhole is set at the converging point to eliminate stray light and make the point closer to an ideal point light source, wherein the front focus of the converging lens coincides with the point.

[0077] The first plane mirror 7 and the second plane mirror 8 are used to reflect the light beam and deflect the light propagation direction. In this embodiment, the first plane mirror 7 and the second plane mirror 8 have the same structure. The first plane mirror 7 is used to deflect the reference light 7a from the spatial filter unit by about 90° in space so that it is reflected after passing through the second plane mirror 8. With an off-axis digital holographic structure, the second plane mirror 8 is used to adjust the angle between the reference light and the measurement light beam.

[0078] The imaging lens 13 is used for magnification and imaging. First, the spatial light 11a transmitted through the third beam splitter 9 will be magnified after passing through the imaging lens 13, thereby increasing the range of the light spot covering the object to be measured 10. Then, the measuring light 12b carrying the target information passes through the imaging lens 13 and forms an image behind it, and is recorded by the camera 11 after being reflected by the third beam splitter 9.

[0079] The camera 11 is used to record the hologram, and the camera 11 includes but is not limited to CCD or CMOS.

[0080] In this embodiment, the spatial light 4b transmitted by the second beam splitter 4 passes through the third beam splitter 9, the imaging lens 13, and the object to be measured 10, and then reflects through the imaging lens 13 and the third beam splitter 9. This part can be called a measurement beam.

[0081] In this embodiment, the spatial light 4a reflected by the second beam splitter 4 passes through the neutral attenuation plate 12, the converging lens 5, the pinhole 6, the first plane mirror 7, the second plane mirror 8, and the third beam splitter 9. This part can be called a reference beam.

[0082] The reference beam interferes with the measuring beam, and the formed hologram is recorded by the photosensitive surface of the camera 11 to obtain a digital hologram.

[0083] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment is as follows: the laser 1 generates laser 1a, and the laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and then incident on the second beam splitter 4 and is divided into two beams of light: one beam of light 4b is transmitted through the third beam splitter 9 to become 11a, and the light spot is magnified by the imaging lens 13 and then irradiates the object to be measured 10. The light 12b reflected back from the surface of the object to be measured 10 is focused by the imaging lens 13, and then reflected by the third beam splitter 9 to the photosensitive surface of the digital camera 11 and recorded by the camera 11; the other beam of reflected light 4a is attenuated by the neutral filter 12, and then converged by the converging lens 5. Placing a pinhole 6 at the convergence point of the light can effectively improve the light beam quality to obtain 7a, and then 7a is reflected by the first plane mirror 7 and the second plane mirror 8 to become 9a and reach the third beam splitter 9. After 9a is transmitted through the third beam splitter 9, it reaches the photosensitive surface of the camera 11, interferes with the measurement light beam, and is recorded by the camera 11.

[0084] The scattered light field holographic large-range three-dimensional displacement compact measurement device provided in this embodiment can dynamically measure the synchronous three-dimensional deformation or displacement of an object. The specific measurement method thereof has the following steps:

[0085] Step 1: Place the object to be measured 10 in the measuring light path.

[0086] Step 2: Before the object 10 to be measured is displaced, the holograms of the object 10 to be measured when irradiated by two laser beams of different wavelengths are recorded by CCD, as shown in FIG. 3 .

[0087] Step 3: applying a displacement to the object 10 to be measured. In this embodiment, PZT is used to apply a load of 5 microns along the optical axis direction to the object 10 to be measured.

[0088] Step 4: Using CCD to record the holograms of the object 10 to be measured after displacement when irradiated with two laser beams of different wavelengths, as shown in FIG. 4 .

[0089] Step 5: Calculate the scattered light field of the object to be tested 10 under dual wavelength illumination: Perform Fourier transform on the hologram before displacement, intercept the primary spectrum through spatial filtering method, shift the frequency to the center, multiply it by the transfer function determined by the corresponding wavelength and reconstruction distance, and perform inverse Fourier transform to obtain the complex amplitude of the scattered light field of the object to be tested at different wavelengths before displacement.

[0090] Step 6: Repeat step 5 to obtain the complex amplitude of the scattered light field of the object under test at different wavelengths after displacement.

[0091] Step 7: Extract the phase distribution of the scattered light field of the object 10 to be measured when irradiated with different wavelengths from the complex amplitude before displacement and

[0092] Step 8: Repeat step 7 to extract the phase distribution of the scattered light field of the object to be measured after 10 displacements when irradiated with different wavelengths from the complex amplitude. and

[0093] Step 9: Obtain the dual-wavelength synthetic wrapping phase ΔΦ1 of the object to be measured before displacement by 10 by using the relationship, as Figure 5 As shown:

[0094]

[0095] Step 10: Repeat step 9 to obtain the dual-wavelength synthetic wrapping phase ΔΦ2 of the object 10 to be measured after displacement according to the following relationship:

[0096]

[0097] Step 11: Using relational expressions: The phase information is converted into height information, so as to obtain the morphology of the object 10 to be measured before and after the displacement.

[0098] Step 12: Subtract the morphology of the object 10 before displacement from the morphology after displacement to obtain the out-of-plane displacement of the object 10 along the z-axis, such as Figure 6 shown.

[0099] Step 13: Extract the intensity distribution I of the scattered light field of the object to be measured 10 before and after displacement under any wavelength irradiation from the complex amplitude 1 and I 2 As shown in Figure 7.

[0100] Step 14: Use 2D-DIC technology to analyze I 1 and I 2 After processing, the in-plane displacement x, y in the direction perpendicular to the normal line of the entire image area is obtained, as shown in FIG8 .

[0101] Step 15: By combining the out-of-plane displacement z along the normal direction and the in-plane displacement x, y in the direction perpendicular to the optical axis, the three-dimensional displacement measurement result of the object can be obtained.

[0102] Example 2

[0103] Different from the first embodiment, the second beam splitter 4 in the first embodiment is replaced by a polarization beam splitting unit 14 in the second embodiment.

[0104] like Fig. 9As shown, the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a polarization beam splitting unit 14, a neutral attenuation plate 12, a converging lens 5, a pinhole 6, a first plane mirror 7, a second plane mirror 8, a third beam splitter 9, an object to be measured 10, a camera 11 and an imaging lens 13.

[0105] The internal structure of the polarization splitting unit 14 is as follows: Fig.10 As shown, it includes a first half-wave plate 141, a polarization beam splitter 142 and a second half-wave plate 143.

[0106] The polarization splitting unit 14 is used to receive the light source 3a emitted from the first beam splitter 3 after beam combination, split it into spatial light 4a and 4b for output, and is responsible for adjusting the light intensity ratio of the two lights, which is generally 1:5 to 5:1.

[0107] The laser light 3a combined by the first beam splitter enters the polarization beam splitting unit 14 and is split into two beams with orthogonal polarization directions: reflected light and transmitted light. The reflected light passes through the second half-wave plate 143 and becomes 4a to enter the reference light path, while the transmitted light 4b enters the measurement light path.

[0108] In this embodiment, the light intensity ratio between the spatial light 4a and 4b can be changed by rotating and adjusting the first half-wave plate 141 in the polarization splitting unit 14, which is generally 1:5-5:1, thereby performing the function of adjusting the light intensity ratio of the measuring beam and the reference beam to obtain a high-quality hologram. By rotating the second half-wave plate 143, the polarization directions of the measuring beam 4a and the reference beam 4b are made consistent, so that the two can interfere with each other.

[0109] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment is as follows: the first laser 1 generates laser 1a, the second laser 2 generates laser 2a which is combined into laser 3a after passing through the first beam splitter 3 and then incident on the polarization beam splitting unit 14 to be divided into two beams of light with adjustable intensity ratio: one beam of light 4b is transmitted through the third beam splitter 9 to become 11a, and the light spot is magnified by the imaging lens 13 to irradiate the object to be measured 10, and the light 12b reflected back from the surface of the object to be measured 10 is focused by the imaging lens 13, reflected by the third beam splitter 9 to the photosensitive surface of the camera 11, and recorded by the camera 11. After the other reflected light 4a passes through the neutral attenuation plate 12 to attenuate the light intensity, it is converged by the converging lens 5. Placing a pinhole 6 at the convergence point of the light can effectively improve the quality of the light beam to obtain 7a. Then 7a is reflected by the first plane mirror 7 and the second plane mirror 8 to become 9a and reach the third beam splitter 9. After 9a is transmitted through the third beam splitter 9, it reaches the photosensitive surface of the camera, interferes with the measuring beam, and is recorded by the camera 11.

[0110] Example 3

[0111] Different from the first embodiment, the third beam splitter in the first embodiment is replaced by a beam splitter plate 15 in the present embodiment.

[0112] like Fig.11 As shown, the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a polarization beam splitting unit 14, a neutral attenuation plate 12, a converging lens 5, a pinhole 6, a first plane mirror 7, a second plane mirror 8, a beam splitter plate 15, an object to be measured 10, a camera 11 and an imaging lens 13.

[0113] The function of the beam splitter plate 15 is to interfere with and combine the measuring beam 13 a and the reference beam 9 a reflected from the object to be measured 10 .

[0114] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment is as follows: the laser 1 generates laser 1a, and the laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and then incident on the second beam splitter 4 to be divided into two beams of light: one beam of light 4b is transmitted through the beam splitter plate 15 to become 11a, and the light spot is enlarged by the imaging lens 13 and then irradiates the object to be measured 10. The light 12b reflected back from the surface of the object to be measured 10 is focused by the imaging lens 13, and then reflected by the beam splitter plate 15 to the photosensitive surface of the digital camera 11 and recorded by the camera 11; the other beam of reflected light 4a is attenuated by the neutral attenuation plate 12, and then converged by the converging lens 5. Placing a pinhole 6 at the convergence point of the light can effectively improve the light beam quality to obtain 7a, and then 7a is reflected by the first plane mirror 7 and the second plane mirror 8 to become 9a and reach the beam splitter plate 15. After 9a is transmitted through the beam splitter plate 15, it reaches the photosensitive surface of the camera 11, interferes with the measuring light beam, and is recorded by the camera.

[0115] Example 4

[0116] Different from the first embodiment, in this embodiment, a phase shift device 16 is added between the first plane mirror 8 and the third beam splitter 9 in the reference light path.

[0117] like Fig.12 As shown, the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a second beam splitter 4, a converging lens 5, a pinhole 6, a first plane mirror 7, a second plane mirror 8, a third beam splitter 9, an object to be measured 10, a camera 11, a neutral attenuation plate 12, an imaging lens 13 and a phase shift device 16.

[0118] The function of the phase shift device 16 is to shift the phase of the reference light, and then extract the scattered light field from the hologram through a multi-step phase shift calculation method.

[0119] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement compact measurement device used in this embodiment is as follows: the laser 1 generates laser 1a, and the laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and then incident on the second beam splitter 4 to be divided into two beams of light: one beam of light 4b is transmitted through the third beam splitter 9 to become 11a, and the light spot is magnified by the imaging lens 13 to irradiate the object to be measured 10, and the light 12b reflected back from the surface of the object to be measured 10 is focused by the imaging lens 13, and then reflected by the third beam splitter 9 to the photosensitive surface of the camera 11 and recorded by the camera 11; the other beam of reflected light 4a is attenuated by the neutral attenuation plate 12, and then converged by the converging lens 5. Placing a pinhole 6 at the convergence point of the light can effectively improve the light beam quality to obtain 7a, and then 7a is reflected by the first plane mirror 7 and the second plane mirror 8 to become 9a, and 9a is phase-shifted by the phase shifter 16 and reaches and transmits through the third beam splitter 9 to reach the photosensitive surface of the camera 11, interferes with the measurement light beam, and is recorded by the camera.

[0120] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program implements the steps of the above method when executed by a processor.

[0121] The measuring device of the present invention solves the problem that the existing three-dimensional vector displacement measurement technology uses multiple sets of measuring devices to measure displacements of different dimensions respectively, resulting in a complex system optical path structure and high cost. A measurement method that only uses one multiplexed measurement light beam is proposed, and it is combined with a two-dimensional digital image correlation technology to efficiently utilize all the information of a set of measurement systems, effectively reduce costs, and greatly simplify the complexity of the measurement system and the operation process; a dual-wavelength optical path structure is used to realize optical path multiplexing, which can effectively expand the measurement range of off-plane displacement.

[0122] Compared with the existing measuring devices, the measuring device of the present invention has a more scientific and reasonable structural design, is simpler and more convenient to use, has a more compact optical path, and is more suitable for integration; the measuring device adopts a single lens, which not only realizes the light spot magnification, but also realizes the imaging function. The light spot can be magnified according to actual needs to achieve a larger light spot measurement range; the measuring method has the characteristics of full-field and non-contact measurement, and can realize non-destructive testing of the test piece.

[0123] The measurement method of the present invention combines nanometer-level high-precision scattered light field measurement technology with sub-pixel-level high-precision digital image correlation technology, and has the advantages of high efficiency, rapidity, high measurement accuracy, and dynamic measurement; first, the present invention integrates two independent technologies into one hardware system. The previous two technologies each have their own hardware systems, including independent cameras and optical imaging systems. The present invention is based on only one set of holographic hardware system, and does not use an additional hardware system of independent digital image correlation technology. Instead, it uses digital image correlation technology to process the speckle intensity image that was not used by the previous digital holography, so the two independent technologies are organically integrated into one hardware system. Secondly, the digital image correlation technology in the present invention processes laser speckle images. The previous digital image correlation technology processes intensity images under natural light or white light, and the key content of the processing is the texture of the object in the intensity image or the artificially sprayed speckle. There are differences in the characteristics of laser speckle and the above digital image correlation technologies.

[0124] The measurement method of the present invention can realize the synchronous measurement of the three-dimensional vector displacement of the scattering surface object, which solves the limitation that the traditional optical measurement method can only measure the mirror surface objects. The three-dimensional displacement measurement of the curved surface object requires the three-dimensional morphology information of the object. However, the three-dimensional morphology measurement of the scattering surface object is more difficult than that of the mirror surface object. This is mainly because the height variation of the particles of the scattering surface object has exceeded the laser wavelength, which is difficult to measure by a simple digital holographic system, and often requires an additional three-dimensional morphology measurement system, which not only makes the measurement scheme complicated, but also makes the data fusion of multiple systems difficult and further complicated. However, the three-dimensional morphology of mirror surface objects with a height of microns and below can be measured using a laser holographic system. Therefore, it is difficult to measure the three-dimensional vector displacement of the scattering surface object. The present invention solves this problem by multiplexing the same set of optical paths and using a holographic system of two lasers.

[0125] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0126] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for measuring a compact device for measuring three-dimensional displacement in a scattered light field holographic range, characterized in that: include: A compact device for measuring three-dimensional displacement in a scattered light field holographic range, the device comprising a first laser (1), a second laser (2), a first beam splitter (3), a second beam splitter (4), a converging lens (5), a pinhole (6), a first plane mirror (7), a second plane mirror (8), a third beam splitter (9) and a camera (11); The first beam splitter (3) faces the laser emission ports of the first laser (1) and the second laser (2) to combine the two laser beams; the second beam splitter (4) is located on the combined light path of the first beam splitter (3); the converging lens (5), the pinhole (6) and the first plane mirror (7) are arranged in a row and are located on the reflected light path of the second beam splitter (4); the second plane mirror (8) is located on the reflected light path of the first plane mirror (7); the third beam splitter (9) is located at the intersection of the transmission light path of the second beam splitter (4) and the reflection light path of the second plane mirror (8); the object to be measured (10) is located on the transmission light path of the third beam splitter (9); and the camera (11) is located on the combined light path of the reflected light of the object to be measured (10) and the reflected light of the second plane mirror (8); The method comprises the following steps: Step S1: The light emitted by the first laser and the second laser is combined by the first beam splitter and then incident on the second beam splitter to be divided into two paths: the light beam transmitted by the second beam splitter is irradiated to the surface of the object to be measured after passing through the third beam splitter, and is reflected by the surface of the object to be measured to form a measuring beam; the light beam reflected by the second beam splitter is reflected by the first plane mirror and the second plane mirror after passing through a converging lens and a pinhole filter to form a reference beam; The measuring beam and the reference beam are combined by the third beam splitter and interfere with each other, and a hologram is formed on the photosensitive surface of the camera; Step S2: before the displacement of the object to be measured changes, the object to be measured is irradiated with the first laser and the second laser respectively, and recorded by the camera to obtain two holograms H1 and H2, and the light field is reconstructed by using the two recorded holograms to obtain two single-wavelength phase images of the light field reflected from the surface of the object to be measured before the displacement, and then the morphology of the object to be measured before the displacement is calculated from the two single-wavelength phase images according to the dual-wavelength phase synthesis formula, and the intensity image of the light field reflected from the surface of the object to be measured before the displacement is calculated using the hologram H1 or the hologram H2; Step S3: after the displacement of the object to be measured changes, the first laser and the second laser are used to illuminate the object to be measured respectively, and the two holograms H3 and H4 are recorded by the camera, and the light field is reconstructed by using the two recorded holograms, thereby obtaining two single-wavelength phase images of the light field reflected from the surface of the object to be measured after the displacement, and then the morphology of the object to be measured after the displacement is calculated from the two single-wavelength phase images according to the dual-wavelength phase synthesis formula; Using the hologram H3 or H4 obtained by irradiating with the laser of the same wavelength as in step S2, an intensity diagram of the light field reflected from the surface of the object to be measured after displacement is calculated; Step S4: subtracting the morphology of the object to be measured before and after the displacement to obtain the displacement in the z direction along the optical axis; processing the intensity map of the light field reflected from the surface of the object to be measured before and after the displacement, and calculating the displacement of the object to be measured in the x direction and the y direction perpendicular to the optical axis; Step S5: combining the displacement of the object to be measured in the z direction along the optical axis with the displacements in the x direction and the y direction perpendicular to the optical axis to obtain a three-dimensional vector displacement of the object to be measured; The step S2 comprises the following steps: Step S2.1: Select the coordinate point P1 to be measured on the intensity map before displacement; Step S2.2: With the selected coordinate point P1 to be measured as the center, define a region R1 with a size of (2M+1)×(2M+1) pixels, where M is a positive integer determined by the size of the sub-region of interest; Step S2.3: arbitrarily define a region R2 with a size of (2M+1)×(2M+1) centered at the coordinate point Pi on the intensity map after displacement; Step S2.4: Calculate the similarity between regions R1 and R2; Step S2.5: Change the coordinate value of the coordinate point Pi in step S2.3, and repeat steps S2.3 to S2.4 until i traverses all pixels in the intensity map after displacement and finds the region R2 with the highest similarity to region R1; Step S2.6: Calculate the center coordinate P2 of region R2; Step S2.7: Subtract the coordinates of P2 from those of P1 to obtain the displacement of point P1 in the x-direction and the y-direction perpendicular to the optical axis; Step S2.8: Repeat steps S2.1 to S2.7 until all pixel points in the intensity map before displacement are traversed, that is, the displacements in the x-direction and y-direction perpendicular to the optical axis corresponding to all pixel points are obtained.

2. The measuring method of the compact measuring device for three-dimensional displacement in the scattered light field holographic range according to claim 1 is characterized in that: A neutral attenuation plate is arranged between the second beam splitter (4) and the converging lens (5).

3. The measuring method of the compact measuring device for three-dimensional displacement of scattered light field holographic range according to claim 1 is characterized in that: An imaging lens is provided between the third beam splitter (9) and the object to be measured (10).

4. The measuring method of the compact measuring device for three-dimensional displacement of scattered light field holographic range according to claim 1 is characterized in that: A phase shift device is provided between the second plane mirror (8) and the third beam splitter (9).

5. The measuring method of the compact measuring device for three-dimensional displacement in the scattered light field holographic range according to claim 1 is characterized in that: The second beam splitter (4) is replaced by a polarization beam splitter unit, which comprises a polarization beam splitter, a first half-wave plate and a second half-wave plate, the polarization beam splitter is located at the position of the second beam splitter (4), the first half-wave plate is arranged between the first beam splitter (3) and the polarization beam splitter, and the second half-wave plate is arranged between the polarization beam splitter and the converging lens (5).

6. The measuring method of the compact measuring device for three-dimensional displacement in the scattered light field holographic range according to claim 1 is characterized by: The tilt angles of the first plane mirror and the second plane mirror are adjusted so that an angle is formed between the reflected reference beam and the measuring beam, and the scattered light field is extracted from the hologram by Fourier transform method.

7. The measuring method of the compact measuring device for three-dimensional displacement in the scattered light field holographic range according to claim 1 is characterized by: A phase shift device is added in the optical path before the light beam is reflected by the first plane mirror and incident on the third beam splitter to shift the phase of the reference beam, and the scattered light field is extracted from the hologram through a multi-step phase shift calculation method.

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