Scattered light field holographic range three-dimensional displacement measurement device, method and medium

Abstract

The present invention provides a device, method and medium for measuring three-dimensional displacement in a holographic range of a scattered light field. The device of the present invention is mainly composed of a first laser, a second laser, a first beam splitter, a beam expansion and collimation unit, a second beam splitter, a third beam splitter, a fourth beam splitter, a plane mirror 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, which is simpler and more practical than the existing three-dimensional displacement and displacement measurement technology based on scattered light fields, and the displacement measurement range is larger than that of a single wavelength. The present invention integrates digital image correlation technology and holographic measurement technology of scattered light fields, and has the advantages of non-contact, high measurement accuracy, fast measurement speed, large measurement range, and synchronous measurement of three-dimensional vector displacement. It 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 scattered light field holographic range three-dimensional displacement measurement device, method and medium, and in particular to a scattered light field holographic large range three-dimensional displacement measurement device and method. 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 synchronous measurement, you often need three sets of digital holographic devices, each of which is responsible for the measurement of one dimensional deformation. 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 patent document with publication number CN110608678A discloses a deep horizontal displacement monitoring device based on Brillouin scattering optical fiber. The monitoring device includes a laser, a distributed sensing optical fiber, an electro-optic modulator, an optical amplifier, a circulator, a coupler, an MZ interferometer, an optical detector, a digital processor, and a data communication and transmission module. The distributed sensing optical fiber and the electro-optic modulator constitute an optical fiber sensing system. The optical signal passing through the optical fiber sensing system is collected by the optical amplifier, the optical filter, and the optical detector. The collected processed data is transmitted to a microcontroller, the digital processor analyzes and processes the data, and the data communication and transmission module transmits the monitoring data results to a cloud platform, or the remote control measurement system sends a control command to perform measurement at any time.

[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 through a simple device is an urgent problem to be solved, and a technical solution needs to be proposed to improve the above technical problem. Summary of the invention

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

[0008] A scattered light field holographic range three-dimensional displacement measuring device provided by the present invention comprises a first laser, a second laser, a first beam splitter, a beam expansion and collimation unit, a second beam splitter, a plane mirror, a third beam splitter, a fourth beam splitter and a camera;

[0009] The first beam splitter faces the laser emission ports of the first laser and the second laser to combine the two laser beams. The beam expansion and collimation unit, the second beam splitter, the third beam splitter, and the object to be measured are arranged in a row in sequence and are located on the combined light path of the first beam splitter. The object to be measured reflects the light irradiated on its surface and then is reflected by the third beam splitter. The plane mirror is located on the reflected light path of the second beam splitter. The fourth beam splitter is located at the intersection of the reflected light paths of the third beam splitter and the plane mirror. The camera is located on the combined light path of the fourth beam splitter.

[0010] Preferably, the beam expansion and collimation unit further comprises a spatial filtering module, and the spatial filtering module performs spatial shaping on the light beam generated by the laser.

[0011] Preferably, a first imaging lens is arranged between the third beam splitter and the fourth beam splitter, and a second imaging lens is arranged between the plane mirror and the fourth beam splitter.

[0012] Preferably, a phase shifting device is provided between the plane mirror and the fourth 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 beam expansion and collimation unit and the polarization beam splitter, and the second half-wave plate is arranged between the polarization beam splitter and the plane mirror.

[0014] The present invention also provides a method for measuring a scattered light field holographic range three-dimensional displacement measuring device, the method using the scattered light field holographic range three-dimensional displacement measuring device mentioned above, 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 incident on the beam expansion and collimation unit, and then divided into two paths by the second beam splitter: the light beam transmitted by the second beam splitter is irradiated to the surface of the object to be measured through the third beam splitter, and the light reflected by the surface of the object to be measured is reflected by the third beam splitter to form a measuring beam; the light beam reflected by the second beam splitter is reflected by a plane mirror to form a reference light, and the measuring beam and the reference light are combined by the fourth 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 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 to obtain two single-wavelength phase images of the light field reflected from the surface of the object to be measured after the displacement, and 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 tilt angle of the plane mirror is adjusted so that the reflected reference light forms an angle with the measuring light, 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 second beam splitter and incident on the fourth beam splitter to phase shift the reference light, 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 synchronous 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 using only one 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. 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;

[0036] 4. 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.

[0037] 5. 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

[0038] 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:

[0039] Figure 1 It is a schematic diagram of the scattered light field holographic large-range three-dimensional displacement measurement device of the present invention;

[0040] Figure 2 It is a structural diagram of the scattered light field holographic large-range three-dimensional displacement measurement device in Example 1 of the present invention;

[0041] Figure 3 is a schematic diagram of a spatial light filtering module in Embodiment 1 of the present invention;

[0042] Figure 4 Schematic diagram of a beam expansion and collimation module in Embodiment 1 of the present invention;

[0043] Figure 5A 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 5B The hologram recorded by the CCD in Embodiment 1 of the present invention before the object to be measured is displaced and irradiated by the second laser;

[0045] Fig. 6A 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 6B 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 7 The dual-wavelength synthetic wrapped phase image of the object to be measured before displacement in Example 1 of the present invention;

[0048] Figure 8 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. 9A 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] Fig. 9B 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] FIG10 is a diagram showing the measurement results of the in-plane displacement of the object to be measured along the x and y directions perpendicular to the optical axis in Example 1 of the present invention;

[0052] Fig.11It is a structural diagram of the scattered light field holographic large-range three-dimensional displacement measurement device in Example 2 of the present invention;

[0053] Fig.12 is a diagram showing the internal structure of a polarization splitting unit in Embodiment 2 of the present invention;

[0054] Fig.13 This is a structural diagram of the scattered light field holographic large-range three-dimensional displacement measurement device in Example 3 of the present invention.

[0055] in:

[0056] First laser 1 Fourth beam splitter 9

[0057] Second laser 2 Camera 10

[0058] First beam splitter 3 First imaging lens 11

[0059] Beam expansion and collimation unit 4 Second imaging lens 12

[0060] Spatial light filtering module 401 Polarization splitting unit 13

[0061] Beam expansion and collimation module 402 First half-wave plate 131

[0062] Second beam splitter 5 Polarization beam splitter 132

[0063] Plane mirror 6 Second half-wave plate 133

[0064] The third beam splitter 7 phase shift device 14

[0065] Object to be measured 8 DETAILED DESCRIPTION

[0066] 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.

[0067] The present invention provides a scattered light field holographic range three-dimensional displacement measurement device, method and medium. 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.

[0068] Example 1

[0069] like Figure 2As shown, the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a spatial light filtering module 401, a beam expansion and collimation module 402, a second beam splitter 5, a plane mirror 6, a third beam splitter 7, an object to be measured 8, a fourth beam splitter 9, a camera 10, a first imaging lens 11 and a second imaging lens 12.

[0070] 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.

[0071] 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.

[0072] The first beam splitter 3, the second beam splitter 5, the third beam splitter 7 and the fourth beam splitter 9 are an optical device that can split a light beam into two, achieving 50% transmission and 50% reflection. The first beam splitter 3, the second beam splitter 5, the third beam splitter 7 and the fourth beam splitter 9 have the same structure and function, and the second beam splitter 5 is used as an example for explanation. The second beam splitter 5 is used to receive the collimated parallel light 4b emitted by the beam expansion and collimation module 402, and divide it into parallel light 5a and 5b for output. The transmitted light 5a enters the measurement optical path, and the reflected light 5b enters the reference optical path.

[0073] The spatial light filtering module 401 is composed of a spatial filter and a plano-convex lens, and its internal structure is as follows: Figure 3 As shown; the spatial filter is composed of a microscope objective lens MO and a pinhole PH. In the spatial light filtering unit 401, the microscope objective lens converges the spatial light 3a after the first beam splitter to a point, and a pinhole PH is set at the convergence point to eliminate stray light so that the point is closer to the ideal point light source. The front focus of the plano-convex mirror L1 coincides with the point, so that the outgoing light after the plano-convex mirror L1 is parallel light.

[0074] The beam expansion and collimation module 402 is used to expand the beam and generate parallel light with uniform light intensity. Figure 3 As shown, the beam expansion and collimation module 402 is composed of two plano-convex lenses, so that the output light 4a is parallel light after the diameter of the light spot is enlarged. The focal length of the plano-convex lens in the present invention is determined according to the demand for light spot enlargement.

[0075] The plane mirror 6 is used to reflect the light beam and deflect the light propagation direction. The plane mirror 6 is used to deflect the reference light 5b from the second beam splitter 5 by about 90° in space, so that it is reflected after passing through the plane mirror 6. With an off-axis digital holographic structure, the plane mirror 6 is used to adjust the angle between the reference light and the measurement light beam.

[0076] The function of the first imaging lens 11 is to form an image. The incident parallel light 7b carrying the target information forms an image behind the first imaging lens 11 and is recorded by the camera 10. In the present invention, the first imaging lens 11 and the second imaging lens 12 are lenses with the same parameters and the distances from the first imaging lens 11 to the camera are the same, which are used to compensate the optical path of the reference optical path so that the interference fringes in the hologram are clearly visible.

[0077] The function of the second imaging lens 12 is to ensure that the curvature of the reference light wavefront is consistent with that of the measurement light wavefront.

[0078] The camera 10 is used to record the hologram, and the camera 10 includes but is not limited to CCD or CMOS.

[0079] In the present invention, the parallel light 5a emitted by the second beam splitter 5 is reflected by the third beam splitter unit 7 and the object to be measured 8, and then passes through the third beam splitter unit 7, the first imaging lens 11 and the fourth beam splitter unit 9. This part can be called a measurement optical path.

[0080] In the present invention, the parallel light 5b emitted by the second beam splitter 5 passes through the plane mirror 6, the second imaging lens 12 and the fourth beam splitting unit 9, and this part can be called a reference light path.

[0081] The reference light interferes with the measuring light, and the formed hologram is recorded by the photosensitive surface of the camera 10 to obtain a digital hologram.

[0082] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment is as follows: laser 1 generates laser 1a, laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and incident on the spatial light filter module 401 and becomes parallel light 4a, which is input into the beam expansion and collimation module 402 for beam expansion and becomes parallel light 4b, and 4b becomes two beams of light after passing through the second beam splitter 5: one of the beams passes through the third beam splitter 7 and irradiates the object to be measured 8, and the light 8a reflected from the surface of the object is reflected by the third beam splitter 7 and becomes 7b, and 7b is imaged behind it after passing through the first imaging lens 11. The measuring light 11a carrying the object information passes through the fourth beam splitter 9, and finally vertically irradiates the photosensitive surface 10 of the digital camera and is recorded by the camera. The other beam of light is reflected by the plane mirror 6 and then passes through the second imaging lens 12 to reach the fourth beam splitter 9, and the reference light 12a is reflected by the fourth beam splitter 9 and reaches the camera photosensitive surface 10, interferes with the measuring light, and is recorded by the camera 10.

[0083] The scattered light field holographic large-range three-dimensional displacement 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:

[0084] Step S1: placing the object to be measured 8 in the measuring light path.

[0085] Step S2: Before the object 8 to be measured is displaced, the holograms of the object 8 to be measured when irradiated by two laser beams with different wavelengths are recorded by using a CCD, as shown in FIG. 5 .

[0086] Step S3: applying a displacement to the object to be measured 8. In this embodiment, PZT is used to apply a load of 5 micrometers along the optical axis direction to the object to be measured 8.

[0087] Step S4: using CCD to record the holograms of the object to be measured 8 after displacement when irradiated with two laser beams of different wavelengths, as shown in FIG. 6 .

[0088] Step S5: Calculate the scattered light field of the object to be measured 8 illuminated by two lasers of different wavelengths: perform Fourier transform on the hologram before displacement, intercept the primary spectrum by 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 measured at different wavelengths before displacement.

[0089] Step S6: Repeat step S5 to obtain the complex amplitude of the scattered light field of the object to be measured at different wavelengths after displacement.

[0090] Step S7: Extracting the phase distribution of the scattered light field of the object to be measured 8 when irradiated with different wavelengths from the complex amplitude before displacement and

[0091] Step S8: Repeat step (7) to extract the phase distribution of the scattered light field of the object to be measured 8 after displacement when irradiated with different wavelengths from the complex amplitude. and

[0092] Step S9: The dual-wavelength synthetic wrapping phase ΔΦ1 of the object to be measured 8 before displacement is obtained by the relational expression, such as Figure 7 As shown:

[0093]

[0094] Step S10: Repeat step S9 to obtain the dual-wavelength synthetic wrapping phase ΔΦ2 of the object to be measured 8 after displacement according to the following relationship:

[0095]

[0096] Step S11: Using the relational expression: The phase information is converted into height information, so as to obtain the morphology of the object to be measured 8 before and after the displacement.

[0097] Step S12: Subtract the morphology of the object 8 before displacement from the morphology after displacement to obtain the out-of-plane displacement of the object 8 along the z-axis direction, such as Figure 8 shown.

[0098] Step S13: extracting the intensity distributions I1 and I2 of the scattered light field of the object to be measured 8 before and after displacement under any wavelength irradiation from the complex amplitude as shown in FIG. 9 .

[0099] Step S14: Use 2D-DIC technology to process I1 and I2 to obtain the in-plane displacement x, y in the direction perpendicular to the normal line of the entire image area, as shown in FIG10 .

[0100] Step S15: 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.

[0101] Example 2

[0102] Different from the first embodiment, the second beam splitter 5 in the first embodiment is replaced by a polarization beam splitting unit 13 in the second embodiment.

[0103] like Fig.11 As shown, the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a spatial light filtering module 401, a beam expansion and collimation module 402, a polarization beam splitter unit 11, a plane mirror 6, a third beam splitter 7, an object to be measured 8, a fourth beam splitter 9, a camera 10, a first imaging lens 11, a second imaging lens 12 and a polarization beam splitter unit 13.

[0104] The internal structure of the polarization splitting unit 13 is as follows: Fig.12 As shown, it includes a first half-wave plate 131, a polarization beam splitter 132 and a second half-wave plate 133.

[0105] The polarization splitting unit 13 is used to receive the parallel light 4b emitted from the beam expansion and collimation module 402, split it into parallel light 5a and 5b for output, and is responsible for adjusting the light intensity ratio of the two lights, which is generally 1:5 to 5:1.

[0106] After the output light 4b of the beam expansion and collimation unit 402 enters the polarization splitting unit 13, it is split into two beams with orthogonal polarization directions: reflected light 5b and transmitted light 5a; the reflected light passing through the polarization splitter 132 passes through the second half-wave plate 133 and becomes 5b to enter the reference light path, and the transmitted light 5a enters the measurement light path.

[0107] In this embodiment, the light intensity ratio between the spatial light 5a and 5b can be changed by rotating and adjusting the first half-wave plate 131 in the polarization splitting unit 13, which is generally 1:5-5:1, thereby performing the function of adjusting the light intensity ratio of the measuring light and the reference light to obtain a high-quality hologram. By rotating the second half-wave plate 133, the polarization directions of the measuring light 5a and the reference light 5b are made consistent, so that the two can interfere with each other.

[0108] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment is as follows: laser 1 generates laser 1a, laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and incident on the spatial light filter module 401 and becomes parallel light 4a, which is input into the beam expansion and collimation module 402 for beam expansion and becomes parallel light 4b, and 4b becomes two beams of light after passing through the polarization beam splitter unit 13: one beam passes through the third beam splitter 7 and irradiates the object to be measured 8, and the light 8a reflected from the surface of the object is reflected by the third beam splitter 7 and becomes 7b, and 7b is imaged behind it after passing through the first imaging lens 11. The measurement light 11a carrying the object information passes through the fourth beam splitter 9, and finally vertically irradiates the photosensitive surface 10 of the digital camera and is recorded by the camera. The other beam of light is reflected by the plane mirror 6 and then passes through the second imaging lens 12 to reach the fourth beam splitter 9, and the reference light 12a is reflected by the fourth beam splitter 9 and becomes 9b, and finally reaches the camera photosensitive surface 10, interferes with the measurement light, and is recorded by the camera 10.

[0109] Example 3

[0110] Different from the first embodiment, in this embodiment, a phase shift device 14 is added between the plane mirror 6 and the fourth beam splitter 9 of the reference light path.

[0111] like Fig.13 As shown, the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment includes: a first laser 1, a second laser 2, a first beam splitter 3, a spatial light filtering module 401, a beam expansion and collimation module 402, a second beam splitter 5, a plane mirror 6, a third beam splitter 7, an object to be measured 8, a fourth beam splitter 9, a camera 10, a first imaging lens 11, a second imaging lens 12 and a phase shift device 14.

[0112] The function of the phase shift device 14 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.

[0113] The optical path working principle of the scattered light field holographic large-range three-dimensional displacement measurement device used in this embodiment is as follows: laser 1 generates laser 1a, laser 2 generates laser 2a, which is combined into laser 3a after passing through the first beam splitter 3 and incident on the spatial light filter module 401 and becomes parallel light 4a, which is input into the beam expansion and collimation module 402 for beam expansion and becomes parallel light 4b, and 4b becomes two beams of light after passing through the second beam splitter 5: one of the beams passes through the third beam splitter 7 and irradiates the object to be measured 8, and the light 8a reflected from the surface of the object is reflected by the third beam splitter 7 and becomes 7b, and 7b is imaged behind it after passing through the first imaging lens 11. The measuring light 11a carrying the object information passes through the fourth beam splitter 9, and finally vertically irradiates the photosensitive surface 10 of the digital camera and is recorded by the camera. The other beam of light is reflected by the plane mirror 6 and then passes through the second imaging lens 12 and then reaches the fourth beam splitter 9 after phase shifting by the phase shift device 14. The reference light 12a is reflected by the fourth beam splitter 9 and reaches the camera photosensitive surface 10, interferes with the measuring light, and is recorded by the camera 10.

[0114] 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.

[0115] The measuring device of the present invention solves the problem that the existing three-dimensional vector displacement synchronous 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 using only one measuring light 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 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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 measurement method for a scattered light field holographic range three-dimensional displacement measurement device, characterized in that: include: A scattered light field holographic range three-dimensional displacement measurement device, the device comprising a first laser (1), a second laser (2), a first beam splitter (3), a beam expansion and collimation unit (4), a second beam splitter (5), a plane mirror (6), a third beam splitter (7), a fourth beam splitter (9) and a camera (10); 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 beam expansion and collimation unit (4), the second beam splitter (5), the third beam splitter (7), and the object to be measured (8) are arranged in a row and located on the combined light path of the first beam splitter (3); the object to be measured (8) reflects the light irradiated on its surface and then is reflected by the third beam splitter (7); the plane mirror (6) is located on the reflected light path of the second beam splitter (5); the fourth beam splitter (9) is located at the intersection of the reflected light paths of the third beam splitter (7) and the plane mirror (6); and the camera (10) is located on the combined light path of the fourth beam splitter; 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 incident on the beam expansion and collimation unit, and then split into two paths by the second beam splitter: 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 the light reflected by the surface of the object to be measured is reflected by the third beam splitter to form a measuring beam; The light beam reflected by the second beam splitter is reflected by a plane mirror to form a reference light, and the measuring light beam and the reference light are combined by a fourth beam splitter to interfere with each other and form a hologram 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 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 to obtain two single-wavelength phase images of the light field reflected from the surface of the object to be measured after the displacement, and the morphology of the object to be measured after the displacement is calculated by solving 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 8 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 scattered light field holographic range three-dimensional displacement measuring device according to claim 1, characterized in that: The beam expansion and collimation unit (4) also includes a spatial filtering module, which performs spatial shaping on the light beam generated by the laser.

3. The measuring method of the scattered light field holographic range three-dimensional displacement measuring device according to claim 1, characterized in that: A first imaging lens is arranged between the third beam splitter (7) and the fourth beam splitter (9), and a second imaging lens is arranged between the plane mirror (6) and the fourth beam splitter (9).

4. The measuring method of the scattered light field holographic range three-dimensional displacement measuring device according to claim 1, characterized in that: A phase shift device is provided between the plane mirror (6) and the fourth beam splitter (9).

5. The measuring method of the scattered light field holographic range three-dimensional displacement measuring device according to claim 1, characterized in that: The second beam splitter (5) is replaced by a polarization beam splitter unit, the polarization beam splitter unit comprising 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 (5), the first half-wave plate is arranged between the beam expansion and collimation unit (4) and the polarization beam splitter, and the second half-wave plate is arranged between the polarization beam splitter and the plane mirror (6).

6. The measuring method of the scattered light field holographic range three-dimensional displacement measuring device according to claim 1, characterized in that: The tilt angle of the plane mirror is adjusted so that the reflected reference light forms an angle with the measurement light, and the scattered light field is extracted from the hologram by Fourier transform method.

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

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