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

Abstract

The present invention provides a scattered light field holographic three-dimensional displacement measurement device, method and medium, belonging to the field of optical precision measurement technology. The device of the present invention is mainly composed of a laser, a beam expansion and collimation unit, a first beam splitter, a second beam splitter, a third beam splitter, a plane mirror and a camera. By combining the holographic measurement of the scattered light field and digital image correlation and other technologies, high-speed synchronous measurement of the three-dimensional vector displacement of a high-scattering object is achieved. The present invention combines 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, 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 scattered light field holographic three-dimensional displacement measurement device, method and medium. 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. Therefore, 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. It 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.

[0004] 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.

[0005] The patent document with the publication number CN109974591A discloses a device for measuring the micro displacement of particles and a method for measuring the displacement of fine particles. The laser emitted by the laser passes through the first reflector with a small hole in the middle, and then focuses on the particle material through the inclined groove surface. The scattered light generated by the sample particles irradiated by the laser beam enters the beam splitter and is split into two to generate two laser beams. One beam of light is reflected by the optical beam splitter and then incident on the second reflector above, and then reflected back to the beam splitter, and then transmitted through the beam splitter and focused by the lens to be received by the CCD camera; the other beam of light is transmitted through the beam splitter and incident on the third reflector on the right, and then reflected back to the beam splitter and reflected again, and focused on the CCD camera through the lens. The CCD camera records the generated laser speckle pattern through the image card and transmits it to the computer for relevant numerical calculation and processing.

[0006] The holographic method can obtain the complex wavefront information of the object surface, but the biggest problem with using a holographic device is that it can only obtain the displacement of an object in one dimension. For the change of the three-dimensional displacement of the object, three sets of holographic devices must be used.

[0007] 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. A technical solution is needed to improve the above technical problem. Summary of the invention

[0008] In view of the defects in the prior art, an object of the present invention is to provide a scattered light field holographic three-dimensional displacement measurement device, method and medium.

[0009] A scattered light field holographic three-dimensional displacement measurement device provided by the present invention comprises a laser, a beam expansion and collimation unit, a first beam splitter, a plane mirror, a second beam splitter, a third beam splitter and a camera;

[0010] The beam expansion and collimation unit is directly opposite to the laser output port, the first beam splitter is directly opposite to the laser output of the beam expansion and collimation unit, the plane mirror is located on the reflected light path of the first beam splitter, the second beam splitter is located on the transmitted light path of the first beam splitter, the third beam splitter is located at the intersection of the reflected light path of the second beam splitter and the reflected light path of the plane mirror, the object to be measured is located on the transmitted light path of the second beam splitter, the object to be measured reflects the light irradiated on its surface and then reflects it by the second beam splitter, and the camera is located on the combined light path of the third beam splitter.

[0011] 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.

[0012] Preferably, a first imaging lens is arranged between the second beam splitter and the third beam splitter, and a second imaging lens is arranged between the plane mirror and the third beam splitter.

[0013] Preferably, a phase shifting device is provided between the plane mirror and the third beam splitter.

[0014] Preferably, the first 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 first 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.

[0015] The present invention also provides a method for measuring a scattered light field holographic three-dimensional displacement measuring device, the method using the scattered light field holographic three-dimensional displacement measuring device mentioned above, the method comprising the following steps:

[0016] Step S1: The light emitted by the laser is expanded by the beam expansion unit and then divided into two paths by the first beam splitter: the light beam transmitted by the first beam splitter is irradiated to the surface of the object to be measured after passing through the second beam splitter, and the light reflected by the surface of the object to be measured is reflected by the second beam splitter to form a measuring beam; the light beam reflected by the first beam splitter is reflected by a plane mirror to form a reference light; the measuring beam and the reference light are combined by the third beam splitter and interfere with each other, and a hologram is formed on the photosensitive surface of the camera;

[0017] Step S2: Using a camera to record the holograms of the object to be measured before and after the displacement, respectively, and using the recorded holograms to perform light field solution, thereby obtaining an intensity map and a phase map of the light field reflected from the surface of the object to be measured before and after the displacement;

[0018] Step S3: subtract the phase diagrams of the light field reflected from the surface of the object to be measured before and after the displacement to obtain the phase difference, and then calculate the displacement of the object to be measured along the z direction of the optical axis; process the intensity diagram of the light field reflected from the surface of the object to be measured before and after the displacement, and calculate the displacement of the object to be measured in the x direction and y direction perpendicular to the optical axis;

[0019] Step S4: 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 S3 comprises the following steps:

[0021] Step S3.1: Select the coordinate point P1 to be measured on the intensity map before displacement;

[0022] Step S3.2: 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 S3.3: 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 S3.4: Calculate the similarity between regions R1 and R2;

[0025] Step S3.5: Change the coordinate value of the coordinate point Pi in step S3.3, and repeat steps S3.3 to S3.4 until i traverses all pixels in the intensity map after displacement, and finds the region R2 with the highest similarity to the region R1;

[0026] Step S3.6: Calculate the center coordinate P2 of region R2;

[0027] Step S3.7: 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 S3.8: Repeat steps S3.1 to S3.7 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 an angle is formed between the reflected reference light and the measurement 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 first beam splitter and incident on the third 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 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;

[0035] 3. 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.

[0036] 4. 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

[0037] 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:

[0038] Figure 1 It is a schematic diagram of the scattered light field holographic three-dimensional displacement measurement device of the present invention;

[0039] Figure 2 is a structural diagram of the scattered light field holographic three-dimensional displacement measurement device in Example 1 of the present invention;

[0040] Figure 3 is a schematic diagram of a spatial light filtering module in Embodiment 1 of the present invention;

[0041] Figure 4 Schematic diagram of a beam expansion and collimation module in Embodiment 1 of the present invention;

[0042] Figure 5 is the interference pattern of the object before deformation collected by the CCD in Example 1 of the present invention;

[0043] Figure 6 is the interference pattern of the object after deformation collected by the CCD in Example 1 of the present invention;

[0044] Figure 7 This is a spectrum result diagram of the two interference patterns before and after deformation in Example 1 of the present invention after Fourier transformation;

[0045] Fig. 8A is a phase image of the object before deformation collected by the CCD in Example 1 of the present invention;

[0046] Figure 8B is a phase image of the object after deformation collected by the CCD in Example 1 of the present invention;

[0047] Fig. 9 This is a diagram of displacement measurement results along the optical axis in Example 1 of the present invention;

[0048] Fig. 10A is an intensity map of the object before deformation collected by the CCD in Example 1 of the present invention;

[0049] Fig. 10B is an intensity map of the object after deformation collected by the CCD in Example 1 of the present invention;

[0050] Fig.11 Graph showing the measurement result of the x-direction displacement of the vertical optical axis in Example 1 of the present invention;

[0051] Fig.12 Graph showing the measurement result of the y-direction displacement of the vertical optical axis in Example 1 of the present invention;

[0052] Fig.13 is a structural diagram of a scattered light field holographic three-dimensional displacement measurement device in Example 2 of the present invention;

[0053] Fig.14 is a diagram showing the internal structure of a polarization splitting unit in Embodiment 2 of the present invention;

[0054] Fig.15 4 is a structural diagram of the scattered light field holographic three-dimensional displacement measurement device in Example 3 of the present invention.

[0055] in:

[0056] Laser 1 Camera 8

[0057] Beam expansion and collimation unit 2 First imaging lens 9

[0058] Spatial light filtering module 201 Second imaging lens 10

[0059] Beam expansion and collimation module 202 Polarization splitting unit 11

[0060] First beam splitter 3 First half-wave plate 111

[0061] Plane mirror 4 Polarization beam splitter 112

[0062] Second beam splitter 5 Second half-wave plate 113

[0063] Object to be measured 6 Phase shift device 12

[0064] The third beam splitter 7 DETAILED DESCRIPTION

[0065] 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.

[0066] The present invention provides a scattered light field holographic 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.

[0067] Example 1

[0068] like Figure 2 As shown, the scattered light field holographic three-dimensional displacement measurement device used in this embodiment includes: a laser light source 1, a spatial light filtering module 201, a beam expansion and collimation module 202, a first beam splitter 3, a plane mirror 4, a second beam splitter 5, a measured object 6, a third beam splitter 7, a camera 8, a first imaging lens 9 and a second imaging lens 10.

[0069] The laser 1 generates laser light 1 a , which is input to the spatial light filtering module 201 .

[0070] The laser 1 adopts a coherent light source. In the specific design of the present invention, the laser 1 provides spatial light with a central wavelength of 532nm.

[0071] The first beam splitter 3, the second beam splitter 5 and the third beam splitter 7 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 5 and the third beam splitter 7 have the same structure and function, and the first beam splitter 3 is used as an example for explanation. The first beam splitter 3 is used to receive the collimated parallel light 3a emitted by the beam expansion and collimation module 202, and divide it into parallel light 4a and 4b for output. The transmitted light 4a enters the measurement optical path, and the reflected light 4b enters the reference optical path.

[0072] The spatial light filtering module 201 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 2, the microscope objective lens converges the spatial light 1a emitted by the laser 1 to a point, and a pinhole PH is set at the convergence point to eliminate stray light and make the point closer to the ideal point light source. The front focus of the plano-convex mirror L1 coincides with the point, so that the emitted light 2a is parallel light.

[0073] The beam expansion and collimation module 202 is used to expand the beam and generate parallel light with uniform light intensity. Figure 3 As shown, the beam expansion and collimation module 202 is composed of two plano-convex lenses, so that the output light 3a is parallel light after the spot diameter is enlarged. The focal length of the plano-convex lens in the present invention is determined according to the demand for spot enlargement.

[0074] The plane mirror 4 is used to reflect the light beam and deflect the light propagation direction. The plane mirror 4 is used to deflect the reference light 4b from the first beam splitter 3 by about 90° in space, so that it is reflected after passing through the plane mirror 4. With an off-axis digital holographic structure, the plane mirror 4 is used to adjust the angle between the reference light and the measurement light beam.

[0075] The function of the first imaging lens 9 is to form an image. The incident parallel light 5b carrying the target information forms an image behind the first imaging lens 9 and is recorded by the camera 8. In the present invention, the first imaging lens 9 and the second imaging lens 10 are lenses with the same parameters and the distances from the first imaging lens 9 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 interference pattern are clearly visible.

[0076] The function of the second imaging lens 10 is to ensure that the curvature of the reference light wavefront is consistent with that of the measurement light wavefront.

[0077] The camera 8 is used to record the hologram, and the camera 8 includes but is not limited to CCD or CMOS.

[0078] In the present invention, the parallel light 4a emitted by the first beam splitter 3 is reflected by the second beam splitter unit 5 and the measured object 6 and then passes through the second beam splitter unit 5, the first imaging lens 9 and the third beam splitter unit 7. This part can be called a measurement optical path.

[0079] In the present invention, the parallel light 4b emitted by the first beam splitter 3 passes through the plane mirror 4, the second imaging lens 10 and the third beam splitting unit 7, and this part can be called a reference light path.

[0080] The reference light interferes with the measuring light, and the formed hologram is recorded by the photosensitive surface of the camera 8 to obtain a digital hologram.

[0081] The optical path working principle of the scattered light field holographic three-dimensional displacement measurement device used in this embodiment is as follows:

[0082] The laser light source 1 generates laser light 1a, which is converted into parallel light 2a after passing through the spatial light filter module 201 and input into the beam expansion and collimation module 202 for beam expansion to become parallel light 3a. After passing through the first beam splitter 3, 3a is converted into two beams of light: one of which passes through the second beam splitter 5 and irradiates the object to be measured 6, and the light 6a reflected from the surface of the object is reflected by the second beam splitter 5 and then becomes 5b, which is imaged behind it after passing through the first imaging lens 9. The measuring light 9a carrying the object information passes through the third beam splitter 7 and finally vertically irradiates the photosensitive surface 8 of the digital camera and is recorded by the camera. The other beam of light is reflected by the plane mirror 4 and then passes through the second imaging lens 10 to reach the third beam splitter 7. The reference light 8a is reflected by the third beam splitter 7 and reaches the camera photosensitive surface, interferes with the measuring light, and is recorded by the camera 8.

[0083] The camera 8 records the holograms of the object to be measured 6 before and after the displacement, respectively, and uses the recorded holograms to perform light field solution, thereby obtaining the intensity diagram and phase diagram of the light field reflected from the surface of the object to be measured 6 before and after the displacement; the phase diagrams of the light field reflected from the surface of the object to be measured 6 before and after the displacement are subtracted to obtain the phase difference, thereby calculating the displacement of the object to be measured 6 in the z direction along the optical axis direction; the intensity diagram of the light field reflected from the surface of the object to be measured 6 before and after the displacement is processed, and the displacement of the object to be measured 6 in the x direction and the y direction perpendicular to the optical axis direction is calculated; the displacements in the three directions of x, y, and z can be combined to obtain the three-dimensional vector displacement of the object to be measured.

[0084] The scattered light field holographic 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:

[0085] Step 1: Place the sample to be tested in the measurement light path.

[0086] Step 2: Use CCD to record the interference pattern at this time. Figure 5 shown.

[0087] Step 3: Apply deformation to the object. In this embodiment, PZT is used to apply a load of 5 microns to the object along the optical axis.

[0088] Step 4: Use CCD to record the interference pattern after deformation. Figure 6 shown.

[0089] Step 5: Calculate the scattered light field of the object before and after deformation: Perform Fourier transform on the interference pattern before and after deformation to obtain the spectrum result as follows Figure 7 As shown, the first-order spectrum is intercepted by the spatial filtering method, shifted to the center, multiplied by the transfer function determined by the corresponding wavelength and reconstruction distance, and inverse Fourier transform is performed to obtain the complex amplitude corresponding to the scattered light field of the object before and after deformation.

[0090] Step 6: Extract the phase distribution of the scattered light field of the object before and after displacement from the complex amplitude and As shown in Figure 8.

[0091] Step 7: Get the phase difference by subtracting

[0092] Step 8: Using relational expressions: By phase difference Calculate the displacement along the optical axis z direction, such as Fig. 9 shown.

[0093] Step 9: Extract the intensity distributions I1 and I2 of the scattered light field of the object under test before and after the displacement from the complex amplitude, as shown in FIG10 .

[0094] Step 10: Use digital image correlation technology to process I1 and I2 to obtain the x and y displacements of the vertical optical axis of the entire image area. The results are as follows: Fig.11 and 12 shown.

[0095] Step 11: By combining the displacement along the z direction of the optical axis and the displacement in the x and y directions perpendicular to the optical axis, the three-dimensional vector displacement synchronous measurement result of the object to be measured 6 can be obtained.

[0096] Example 2

[0097] Different from the first embodiment, the present embodiment adopts a polarization beam splitting unit 11 to replace the first beam splitter 3 in the first embodiment.

[0098] like Fig.13 As shown, the scattered light field holographic three-dimensional displacement measurement device used in this embodiment includes: a laser light source 1, a spatial light filtering module 201, a beam expansion and collimation module 202, a polarization splitting unit 11, a second beam splitter 5, an object to be measured 6, a plane mirror 4, a first imaging lens 9, a second imaging lens 10, a third beam splitter 7 and a camera 8.

[0099] The internal structure of the polarization splitting unit 11 is as follows: Fig.14 As shown, it includes a first half-wave plate 111, a polarization beam splitter 112 and a second half-wave plate 113.

[0100] The polarization splitting unit 11 is used to receive the parallel light 3a emitted from the beam expansion and collimation module 202, split it into parallel 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.

[0101] After the light 3a emitted from the beam expansion and collimation unit 202 enters the polarization splitting unit 11, it is split into two light beams with orthogonal polarization directions: reflected light 4b and transmitted light 4a; the reflected light 4b becomes 4b after passing through the second half-wave plate 113 and enters the reference light path, while the transmitted light 4a enters the measurement light path.

[0102] 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 111 in the polarization splitting unit 11, 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 113, the polarization directions of the measuring light 4a and the reference light 4b are made consistent, so that the two can interfere with each other.

[0103] The optical path working principle of the scattered light field holographic three-dimensional displacement measurement device used in this embodiment is as follows:

[0104] The laser light source 1 generates laser light 1a, which is converted into parallel light 2a after passing through the spatial light filter unit 201 and input into the beam expansion and collimation module 202 for beam expansion to become parallel light 3a. After passing through the polarization beam splitter unit 11, 3a becomes two beams of light: one of which is transmitted through the second beam splitter 5 and then illuminates the object to be measured 6. The light 6a reflected from the surface of the object is reflected by the second beam splitter 5 and then becomes 5b. After passing through the first imaging lens 9, 5b forms an image behind it. The measuring light 9a carrying the object information is transmitted through the third beam splitter 7, and finally vertically illuminates the photosensitive surface of the camera 8 and is recorded by the camera. The other beam of light is reflected by the plane mirror 4 and then passes through the second imaging lens 10 to reach the third beam splitter 7. The reference light 8a is reflected by the third beam splitter 7 and reaches the photosensitive surface of the camera to interfere with the measuring light to form a hologram, which is recorded by the camera 8.

[0105] Example 3

[0106] Different from the first embodiment, in this embodiment, a phase shift device 12 is added between the plane mirror 4 and the third beam splitter 7 of the reference light path.

[0107] like Fig.15 As shown, the scattered light field holographic three-dimensional displacement measurement device used in this embodiment includes: a laser light source 1, a spatial light filtering module 201, a beam expansion and collimation module 202, a first beam splitter 3, a second beam splitter 5, a measured object 6, a plane mirror 4, a first imaging lens 9, a second imaging lens 10, a third beam splitter 7, a camera 8 and a phase shift device 12.

[0108] The function of the phase shift device 12 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.

[0109] The optical path working principle of the scattered light field holographic three-dimensional displacement measurement device used in this embodiment is as follows:

[0110] The laser light source 1 generates laser light 1a, which is converted into parallel light 2a after passing through the spatial light filter module 201 and input into the beam expansion and collimation module 202 for beam expansion to become parallel light 3a. After passing through the first beam splitter 3, 3a is converted into two beams of light: one of which passes through the second beam splitter 5 and irradiates the object to be measured 6, and the light 6a reflected from the surface of the object is reflected by the second beam splitter to become 5b, and 5b is imaged behind it after passing through the first imaging lens 9. The measuring light 9a carrying the object information passes through the third beam splitter 7, and finally vertically irradiates the photosensitive surface of the camera 8 and is recorded by the camera. The other beam of light is reflected by the plane mirror 4 and then passes through the second imaging lens 10. After being phase-shifted by the phase shift device 12, it reaches the third beam splitter 7. The reference light 8a is reflected by the third beam splitter 7 and reaches the photosensitive surface of the camera, interferes with the measuring light, and is recorded by the camera 8.

[0111] 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.

[0112] 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; the measurement method of the present invention has the characteristics of full-field, non-contact measurement, and can realize non-destructive testing of the workpiece to be measured.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 three-dimensional displacement measurement device, characterized in that: include: A scattered light field holographic three-dimensional displacement measurement device, the device comprising a laser (1), a beam expansion and collimation unit (2), a first beam splitter (3), a plane mirror (4), a second beam splitter (5), a third beam splitter (7) and a camera (8); The beam expansion and collimation unit (2) is directly opposite to the laser output port, the first beam splitter (3) is directly opposite to the laser output of the beam expansion and collimation unit, the plane mirror (4) is located on the reflected light path of the first beam splitter (3), the second beam splitter (5) is located on the transmitted light path of the first beam splitter (3), the third beam splitter (7) is located at the intersection of the reflected light path of the second beam splitter (5) and the reflected light path of the plane mirror (4), the object to be measured (6) is located on the transmitted light path of the second beam splitter (5), the object to be measured (6) reflects the light irradiated on its surface and then is reflected by the second beam splitter (5), and the camera (8) is located on the combined light path of the third beam splitter (7); The method comprises the following steps: Step S1: The light emitted by the laser is expanded by the beam expansion and collimation unit and then divided into two paths by the first beam splitter: the light beam transmitted by the first beam splitter is irradiated to the surface of the object to be measured after passing through the second beam splitter, and the light reflected by the surface of the object to be measured is reflected by the second beam splitter to form a measuring beam; the light beam reflected by the first beam splitter is reflected by a plane mirror to form a reference light; the measuring beam and the reference light 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: Using a camera to record the holograms of the object to be measured before and after the displacement, respectively, and using the recorded holograms to perform light field solution, thereby obtaining an intensity map and a phase map of the light field reflected from the surface of the object to be measured before and after the displacement; Step S3: subtract the phase diagrams of the light field reflected from the surface of the object to be measured before and after the displacement to obtain the phase difference, and then calculate the displacement of the object to be measured along the z direction of the optical axis; process the intensity diagram of the light field reflected from the surface of the object to be measured before and after the displacement, and calculate the displacement of the object to be measured in the x direction and y direction perpendicular to the optical axis; Step S4: combining the displacement of the object to be measured in the z direction along the optical axis direction with the displacements in the x direction and y direction perpendicular to the optical axis direction to obtain a three-dimensional vector displacement of the object to be measured; The step S3 comprises the following steps: Step S3.1: Select the coordinate point P1 to be measured on the intensity map before displacement; Step S3.2: 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 S3.3: 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 S3.4: Calculate the similarity between regions R1 and R2; Step S3.5: Change the coordinate value of the coordinate point Pi in step S3.3, and repeat steps S3.3 to S3.4 until i traverses all pixels in the intensity map after displacement, and finds the region R2 with the highest similarity to the region R1; Step S3.6: Calculate the center coordinate P2 of region R2; Step S3.7: 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 S3.8: Repeat steps S3.1 to S3.7 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 three-dimensional displacement measuring device according to claim 1, characterized in that: The beam expansion and collimation unit further comprises 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 three-dimensional displacement measuring device according to claim 1, characterized in that: A first imaging lens is arranged between the second beam splitter (5) and the third beam splitter (7), and a second imaging lens is arranged between the plane mirror (4) and the third beam splitter (7).

4. The measuring method of the scattered light field holographic three-dimensional displacement measuring device according to claim 1, characterized in that: A phase shift device is provided between the plane mirror (4) and the third beam splitter (7).

5. The measuring method of the scattered light field holographic three-dimensional displacement measuring device according to claim 1, characterized in that: The first beam splitter (3) 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 first beam splitter, the first half-wave plate is arranged between the beam expansion and collimation unit (2) and the polarization beam splitter, and the second half-wave plate is arranged between the polarization beam splitter and the plane mirror (4).

6. The measuring method of the scattered light field holographic three-dimensional displacement measuring device according to claim 1, characterized in that: By adjusting the tilt angle of the plane mirror, an angle is formed between the reflected reference light and the measurement light, and the scattered light field is extracted from the hologram through the Fourier transform method.

7. The measuring method of the scattered light field holographic 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 first beam splitter and incident on the third 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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