Surface topography measuring device and method based on polarization structured light

Abstract

The invention discloses a surface topography measurement device and method based on polarization structured light, and the device comprises a monochromatic LED, a collimating lens, a polarization grating, a light beam adjustment lens group, a telecentric imaging lens, a micro-polarization array camera and a surface topography reconstruction module, the light emitted by the monochromatic LED is collimated by the collimating lens, and then collimated parallel light is output; the polarizer converts the collimated parallel light into linearly polarized light; the polarization grating divides incident linearly polarized light into left-handed and right-handed circularly polarized light, and the light beam adjusting lens group images an emergent surface of the polarization grating on a to-be-measured surface to form polarization structured light; the telecentric imaging lens images a surface to be measured to the micro-polarization array camera, and the micro-polarization array camera can synchronously capture polarization state images in four polarization directions; the surface topography reconstruction module carries out phase extraction and phase unwrapping on the polarization state images in the four polarization directions, and the three-dimensional topography of the surface to be measured is obtained through point cloud surface reconstruction. According to the invention, high-precision morphology measurement of parts in a complex environment can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of surface topography measurement of parts, and particularly relates to a surface topography measurement device and method based on polarized structured light. BACKGROUND

[0002] In the whole life cycle of the manufacturing assembly, test and maintenance of an aero-engine, the surface quality of key parts such as turbine blades, combustion chamber liners and bearing raceways directly determines the operation safety and service life of the engine. There are often micron-level or even sub-micron-level micro-defects such as scratches, pits, cracks and wear marks on the surface of such parts. If these defects are not detected and judged in time, they may rapidly expand under extreme conditions of high temperature, high pressure and high speed, causing serious accidents such as blade fracture and fuel leakage.

[0003] Currently, the on-site detection of the above-mentioned micro-defects on the surface of parts mainly relies on two conventional technical means: one is visual method, which is directly observed by the detector with a magnifying glass or a microscope. This method is greatly affected by the experience, vision condition and subjective judgment of the personnel, and the judgment results of the same defect by different detectors or at different detection times by the same person are significantly different, the consistency of the detection results is poor, and the accurate quantification of the defect size cannot be realized. The other is the light cutting method, which projects a light band to the measured surface, obtains the light band deformation image by using an optical system and calculates the topography parameters. However, it is seriously disturbed by the ambient light, and only one-dimensional profile information can be obtained by a single measurement, and two-dimensional topography reconstruction needs to be realized by mechanical scanning. Not only is the detection efficiency low, but also the mechanical vibration in the scanning process easily leads to measurement errors. Although the micro-profile measuring instrument can realize the surface topography measurement with nanometer-level precision, it usually adopts a complex interference optical system and a precise motion platform, and has a large volume and weight, and requires a strict environment. Most of them need to be operated in a laboratory with constant temperature, humidity and no vibration. However, the detection scene of aero-engine parts is usually a production workshop assembly station, a test site or a maintenance workshop. The above-mentioned environmental conditions cannot be met, and the parts are usually large in size and heavy in weight, which are difficult to transfer to the laboratory for detection, so the micro-profile measuring instrument cannot be applied to the on-site detection scene.

[0004] Therefore, a measurement device and method are needed, which can adapt to the complex environment of parts on site, does not need precise environmental control, realizes instantaneous measurement of surface micro-topography (without mechanical scanning), and quickly completes the evaluation of micro-defect size (length, width, depth, area, etc.) parameters, so as to fill the gap of on-site high-precision detection technology and improve the timeliness and reliability of part quality control. SUMMARY

[0005] The purpose of the present application is to provide a surface topography measurement device and method based on polarized structured light, which can realize high-precision topography measurement of parts in complex environments.

[0006] To achieve the above object, one aspect of the present application provides a surface topography measurement device based on polarized structured light, comprising a light source module, a polarized light projection module, a polarized imaging module and a surface topography reconstruction module, The light source module comprises a monochromatic LED, a collimating lens and a polarizer, the light emitted by the monochromatic LED is collimated by the collimating lens and output as collimated parallel light, and the polarizer is used to convert the collimated parallel light into linearly polarized light; The polarized light projection module comprises a polarized grating and a beam adjusting lens group, the polarized grating is used to divide the incident linearly polarized light into left-handed circularly polarized light and right-handed circularly polarized light, and the beam adjusting lens group is used to collimate the left-handed and right-handed circularly polarized light and image the exit surface of the polarized grating on the surface to be measured to form polarized structured light; The polarized imaging module comprises a telecentric imaging lens and a micro-polarization array camera, the telecentric imaging lens is a high-resolution imaging lens, which is used to image the surface to be measured to the micro-polarization array camera, and the micro-polarization array camera is a high-frame-rate camera integrated with a micro-polarization array, which can synchronously capture polarized state images of four polarization directions to realize the collection of the polarized structured light of the surface to be measured; The surface topography reconstruction module is used to extract the phase and unwrap the phase of the polarized state images of the four polarization directions to obtain the absolute phase of the surface to be measured, convert the absolute phase into phase-height, and reconstruct the three-dimensional topography of the surface to be measured through point cloud surface reconstruction.

[0007] Another aspect of the present application provides a surface topography measurement method based on polarized structured light, which realizes surface topography measurement by using the above device, comprising: Step S1, the light emitted by the monochromatic LED becomes a collimated spot after passing through the collimating lens, is converted into linearly polarized light by the polarizer, and is vertically irradiated onto the polarized grating; Step S2, the linearly polarized light is divided into left-handed and right-handed circularly polarized light which are orthogonal and phase-synchronous after passing through the polarized grating; Step S3, the left-handed and right-handed circularly polarized light passes through the beam adjusting lens group to image the exit surface of the polarized grating on the surface to be measured to form polarized structured light; Step S4, the micro-polarization array camera synchronously captures polarized state images of four polarization directions to realize the collection of the polarized structured light of the surface to be measured; Step S5, the phase of the polarized state images of the four polarization directions is extracted and unwrapped by the four-step phase shift method to obtain the absolute phase of the surface to be measured, the absolute phase is converted into phase-height, and the three-dimensional topography of the surface to be measured is obtained through point cloud surface reconstruction.

[0008] According to the surface topography measurement device and method based on polarized structured light of the above aspect of the present application, high-precision topography measurement of parts in complex environments can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the description of the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings: Figure 1 is a light path diagram of a surface topography measurement device based on polarized structured light according to an embodiment of the present application; Figure 2 is a structural schematic diagram of a surface topography measurement device based on polarized structured light according to an embodiment of the present application; Figure 3 is a connection schematic diagram of a circuit board, a power supply and a computer according to an embodiment of the present application; Figure 4 is a light splitting schematic diagram of a polarized grating according to an embodiment of the present application; Figure 5 is an additional phase generation schematic diagram of a polarized grating according to an embodiment of the present application. DETAILED DESCRIPTION

[0010] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort fall within the scope of protection of the present application.

[0011] An embodiment of the present application provides a surface topography measurement device based on polarized structured light. The device performs polarized imaging on a surface to be measured by a polarization camera, collects the illumination of the surface to be measured, reflects four groups of polarization phase shift images, and then obtains the topography data of the surface to be measured through phase recovery, unwrapping algorithm and height-phase conversion, thereby realizing the recovery of three-dimensional topography.

[0012] The surface topography measurement device based on polarized structured light according to the embodiment of the present application comprises a light source module, a polarization light splitting projection module, a polarization imaging module and a surface topography reconstruction module. Figure 1 and Figure 2As shown, the light source module includes a monochromatic LED 1, a collimating lens and a polarizer 2. The light emitted by the monochromatic LED 1 is collimated by the collimating lens to form a uniform light spot with a wavelength of 450 nm. The output light beam is converted into collimated parallel light, and the linearly polarized light is converted by the polarizer 2. The LED light can form a collimated light spot with a diameter of 1-2 cm. The LED light is monochromatic visible light. The collimating lens uses a convex lens with a focal length of 20-50 mm. The polarizer 2 is a dichroic film polarizer, and there is no need to specify the polarization direction.

[0013] The polarization spectrometer projection module includes a polarization grating 3 and a beam adjustment lens group 4. The polarization grating 3 divides the incident linearly polarized light into left and right circularly polarized light. The beam adjustment lens group 4 collimates the left and right circularly polarized light and then forms an image on the surface of the object to be measured 5 through a subsequent lens, so that the exit surface of the polarization grating is imaged on the surface to be measured to form a polarization structured light with a certain magnification. The depth of field of the image is large enough, about 1 cm.

[0014] Preferably, the included angle between the polarization spectrometer projection module and the polarization imaging module is between 5° and 20°. The beam adjustment lens group 4 includes a first lens (projection lens 1), a diaphragm and a second lens (projection lens 2). The left and right circularly polarized light is collimated by the first lens, then the non-overlapping edge part is blocked by the diaphragm, and then the left and right circularly polarized light is imaged on the surface to be measured by the second lens. The light spot diameter of the monochromatic LED 1 on the surface of the object to be measured 5 can be adjusted by the diaphragm.

[0015] The polarization imaging module includes a telecentric imaging lens 6 and a micro-polarization array camera 7. The telecentric imaging lens 6 is a high-resolution imaging lens, which is used to image the surface to be measured to the micro-polarization array camera 7, realizing the collection of the polarization structured light of the surface to be measured. The telecentric imaging lens 6 includes three imaging lenses (imaging lens 1, imaging lens 2 and imaging lens 3). The micro-polarization array camera 7 uses a high-frame-rate camera with integrated micro-polarization array (pixel-level 0°, 45°, 90°, 135° polarization plate array), which can synchronously capture polarization state interference images of 0°, 45°, 90° and 135° polarization directions. Through an interpolation algorithm, the pixel intensity values of each polarization state image are completed, and signal acquisition can be realized.

[0016] The control and reconstruction module extracts phase information based on four polarization state images, eliminates phase jumps through a phase unwrapping algorithm, and combines system calibration parameters to reconstruct the three-dimensional topography of the surface of the object to be measured. Specifically, the wrapped phase is extracted based on the four-step phase shift method, and the phase unwrapping is performed by using the global quality map method. The reference surface is calibrated by using a calibration block and a micro-displacement platform, the phase-height corresponding value is determined, the lateral resolution depends on the imaging lens resolution and the minimum pixel unit size of the polarization camera sensor, and finally the three-dimensional topography reconstruction is realized.

[0017] In this embodiment, a high-resolution imaging lens is used in conjunction with a polarization camera to acquire polarized structured light from the surface under test. The resulting image is a single image containing four polarization directions, with each group of four pixels representing polarization directions of 0°, 45°, 90°, and 135°. Since polarized structured light exists on the surface under test, individual polarization states of each pixel group are extracted to form a separate polarization image.

[0018] Individual polarization images exhibit periodic bright-dark stripes, with a 90° phase shift occurring sequentially between images of different polarization states. For the four polarization state interferometric images, phase extraction and unwrapping algorithms are used to obtain the absolute phase data of the surface morphology under test. Then, a phase-to-height conversion is performed on the absolute phase of the surface under test, converting the phase information into depth / height information. Due to the magnification of the high-resolution imaging lens, the lateral distance between pixels can be calculated as follows: Then, the three-dimensional shape of the surface under test is obtained through point cloud reconstruction and encapsulation.

[0019] Adjusting the aperture of the telecentric imaging lens, camera exposure time, and LED illumination intensity will all cause changes in the light intensity of the surface under test. The grayscale value of the acquired image should be controlled within the range of 0-255. In cases of strong exposure, the light intensity should be reduced, a mask should be applied, and overexposed areas should be stripped away.

[0020] In one embodiment, such as Figure 3 As shown, the device of the present invention also includes an integrated circuit board 8, a computer 9, a mechanical housing 10, and a power adapter 11. The surface topography reconstruction module is integrated into the computer 9 as a software module. Phase extraction, unwrapping algorithm, and three-dimensional reconstruction are all executed by the computer 9. The integrated circuit board 8 controls the power of the monochrome LED 1, the image extraction of the polarization camera 7, exposure adjustment, and other functions. The overall optical path and circuit board 8 can be encapsulated in the mechanical housing 10 and connected to the computer 9 by a network cable. The power adapter 11 provides power and communication in the middle and connects the power supply to the integrated circuit board 8 and the computer 9.

[0021] The fringe density of the polarized structured light acquired by the micro-polarization array camera 7 can be changed by adjusting the grating period of the polarization grating 3, or by changing the position of the beam adjustment mirror group 4 or the curvature of the lens.

[0022] The embodiment of the present application also provides a surface topography measurement method based on polarized structured light, which realizes surface topography measurement by using the above-mentioned surface topography measurement.

[0023] The method for surface topography measurement based on polarized structured light of the embodiment of the present application comprises the following steps: Step S1, LED light collimation and polarized grating light splitting are realized.

[0024] The monochromatic LED 1 is placed on the focal point of the collimation lens, and the 450 nm laser emitted by the LED is converted into linearly polarized light by the polarizer and irradiated onto the polarized grating, since the object plane is located at the focal point of the collimation lens, and the image plane is located at infinity, thereby obtaining collimated LED light spots.

[0025] Step S2, circular polarization generation and geometric phase modulation.

[0026] Combining Figure 4 and Figure 5 , the linearly polarized light is decomposed into two orthogonal and phase-synchronous left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) components after passing through the polarized grating 3. The periodic structure of the polarized grating 3 applies opposite phase gradients to the two components, thereby separating them into different diffraction orders (usually ±1 order) through diffraction, and finally realizing the splitting of linearly polarized light into left-handed and right-handed circularly polarized light.

[0027] Figure 4 The spiral structure of the polarized grating 3 shown is periodically arranged - at different x positions (a plane perpendicular to the light propagation direction z) of the grating, the "initial phase" of the spiral structure is periodically changed (for example, the twist angle of the spiral repeats once in each period d). This periodic structure will make the optical path difference of LCP and RCP change with the position x in a sinusoidal or cosine law, that is: , depending on the initial arrangement of the grating, Δ(x) is the optical path difference at position x, and Δ0 is the maximum optical path difference.

[0028] Here, a liquid crystal polarized grating is used, and the thickness of the liquid crystal layer of the polarized grating 3 is set as , the optical path of the right-handed circularly polarized light is ; and the optical path of the left-handed circularly polarized light RCP is . and respectively. Since the polarization grating 3 is equivalent to an array of half-wave plates, the orientation of the liquid crystal molecules determines the fast axis direction of the micro half-wave plates. The incident left-handed circularly polarized light will be converted into right-handed circularly polarized light and give an additional phase, and the incident right-handed circularly polarized light will be converted into left-handed circularly polarized light and give an additional phase. The additional phase is related to the fast axis direction of the half-wave plate, that is, the orientation of the liquid crystal molecules of the polarization grating. Since the fast axis direction of the liquid crystal molecules along the grating period direction changes continuously and linearly, the outgoing light is converted into left- and right-handed circularly polarized light with a certain angle after the linearly polarized light is incident vertically on the polarization grating. Since only ±1 diffraction light, the angle thereof meets the diffraction formula:

[0029] is the angle between the light and the normal to the plane of the polarization grating, d is the grating period, is the wavelength of the incident light.

[0030] Step S3, light beam adjustment and imaging.

[0031] The left- and right-handed circularly polarized light is collimated and filtered by the first lens and the diaphragm to block the non-overlapping area at the edge, and then the left- and right-handed circularly polarized light is imaged to the surface to be measured by the second lens. The purpose of the light beam adjustment is to project a sinusoidal bright-dark variation stripe on the surface to be measured, which can be imaged by the subsequent polarization imaging module. By moving the distance between the lenses, the magnification of the surface to be measured is changed to control the stripe spacing. In actual operation, the first lens outputs parallel light, and the distance between the two beams is fine-tuned by moving the second lens to change the stripe spacing and the stripe contrast, which is convenient for subsequent image acquisition and calibration.

[0032] Step S4, polarization interference image acquisition.

[0033] The micro polarization array camera 7 synchronously captures the polarization state images of the four polarization directions to realize the collection of the polarization structured light of the surface to be measured. The micro polarization array camera 7 realizes 0°, 90°, 180°, and 270° polarization phase shifts. In the pixel array of the camera, each of the four adjacent pixels saves a pixel of the polarization state, which is 0°, 45°, 90°, and 135°, respectively. The left- and right-handed circularly polarized light separated from the same light source is converted into linearly polarized light of the four directions after passing through the micro polarization plate array of the camera, and the phase shift thereof has a 2-fold relationship with the polarization direction of the micro polarization plate array, that is, the surface to be measured passes through the polarization plates with 0°, 45°, 90°, and 135° to the x-axis to produce 0°, 90°, 180°, and 270° phase shifts. is the light intensity calculation formula of the left- and right-handed circularly polarized light after passing through the polarization plate, is the peak intensity of a single circularly polarized light after passing through the polarization plate, The initial phase difference of two incident circularly polarized light (determined by the light source), the initial phase difference of the same light is unchanged, The optical path difference of two light beams, the optical path difference of two light beams changes periodically along the grating period direction of the polarization grating, and then a spatial bright-dark change stripe image is generated by passing through the polarizer, The angle between the transmission direction of the polarizer and the x-axis (adjustment The phase of the interference stripe can be changed.

[0034] Step S5, phase extraction and unwrapping algorithm.

[0035] The computer acquires four pieces of polarization information in one image of the micro-polarizer array camera. After reconstruction by bilinear interpolation, four phase shift maps are obtained. The wrapped phase of the measured surface is obtained by four-step phase shift method, and the phase extraction is realized by four-step phase shift technology, The light intensity gray value of the four extracted phase shift surfaces.

[0036]

[0037] The wrapped phase of the measured surface is extracted, and then the global phase unwrapping algorithm using the quality map method is used to obtain the absolute phase distribution; the absolute phase distribution is converted into the measured surface topography measurement data. The resolution requirement of the imaging lens is micron level, and the depth of field of the lens is only 1-2mm, so the measured surface needs to face the imaging lens.

[0038] After obtaining the unwrapping information, the phase-height conversion is performed. Through theoretical value calculation, the height / depth information corresponding to the movement of one pixel position of the stripe image can be obtained. In actual measurement, a high-precision displacement platform can be used to move a specified distance, and the proportion of the pixel movement grid number to the actual stripe period is used to determine the phase value corresponding to the movement height.

[0039] In this embodiment, through the 0.5 times magnification imaging lens, the LED collimation forms a light spot diameter of 2cm, which meets the camera acquisition range. The lens has a large acquisition range and the depth of field can reach 1-2mm, so the micro-displacement platform is used for depth measurement calibration.

[0040] Place the calibration block on the micro-displacement platform, place the imaging lens 6 of the light path in front of the block, adjust the polarization imaging module to align the block, and then keep the angle between the projection light path and the imaging light path unchanged. Otherwise, the calibration is invalid. Then move the micro-displacement platform by one period, and determine the phase corresponding to the height value by observing the camera acquisition stripe and the movement distance.

[0041] After the phase-height conversion ratio is determined, based on the focal plane as the reference phase plane and the to-be-measured plane as the actual test phase plane, the absolute phase of the to-be-measured surface is obtained by subtracting the two after unwrapping. That is, the three-dimensional measurement surface of the actual size is obtained. The transverse pixel distance is determined by the magnification of the imaging lens and the size of the CMOS pixel. After the actual point cloud is obtained, the three-dimensional morphology of the to-be-measured surface is obtained through point cloud surface reconstruction.

[0042] Compared with the prior art, the surface morphology measurement device and method based on polarized structured light according to the embodiments of the present application have the following beneficial effects: 1. The test principle of polarized structured light is used, and optical devices such as a polarization grating and a micro-polarization array camera are used to form a measurement method based on polarized structured light, which has the characteristics of rapidness, anti-interference and easy integration. 2. The light path system is built through the polarization grating spectrometer projection principle and the micro-polarization plate array phase shift technology, and the overall system can be integrated into a handheld product through a circuit board and a mechanical shell, thereby meeting the measurement and calibration requirements in complex environments.

[0043] The above only describes some exemplary embodiments of the present application by way of illustration, and it is needless to say that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present application. Therefore, the above figures and descriptions are illustrative in nature and should not be understood as limiting the scope of protection of the claims of the present application.

Claims

1. A surface topography measurement device based on polarized structured light, characterized in that, It includes a light source module, a polarization beam projection module, a polarization imaging module, and a surface topography reconstruction module. The light source module includes a monochrome LED, a collimating lens, and a polarizer. The light emitted by the monochrome LED is collimated by the collimating lens and outputs collimated parallel light. The polarizer is used to convert the collimated parallel light into linearly polarized light. The polarization beam splitting projection module includes a polarization grating and a beam adjustment lens group. The polarization grating is used to split the incident linearly polarized light into left-handed circularly polarized light and right-handed circularly polarized light. The beam adjustment lens group is used to collimate the left-handed and right-handed circularly polarized light and then image the exit surface of the polarization grating onto the surface to be measured to form polarized structured light. The polarization imaging module includes a telecentric imaging lens and a micro-polarization array camera. The telecentric imaging lens is a high-resolution imaging lens used to image the surface under test onto the micro-polarization array camera. The micro-polarization array camera is a high-frame-rate camera with an integrated micro-polarization array, which can simultaneously capture polarization state images in four polarization directions to achieve the acquisition of polarization structured light from the surface under test. The surface topography reconstruction module is used to extract and unwrap the phase of polarization state images in four polarization directions to obtain the absolute phase of the surface under test. The absolute phase is then converted to height, and the three-dimensional topography of the surface under test is obtained through point cloud surface reconstruction.

2. The apparatus according to claim 1, characterized in that, The four polarization directions are 0°, 45°, 90°, and 135°.

3. The apparatus according to claim 1 or 2, characterized in that, The light emitted by the monochromatic LED is monochromatic visible light with a wavelength of 450nm. The collimating lens is a convex lens with a focal length between 20mm and 50mm, and the polarizer is a dichroic thin-film polarizer.

4. The apparatus according to claim 1 or 2, characterized in that, The beam adjustment lens group includes a first lens, an aperture stop, and a second lens. Left and right circularly polarized light is collimated by the first lens, filtered by the aperture stop, and then imaged onto the surface to be measured by the second lens.

5. The apparatus according to claim 1 or 2, characterized in that, The fringe density of the polarized structured light acquired by the micro-polarization array camera can be changed by adjusting the grating period of the polarization grating.

6. The apparatus according to claim 1 or 2, characterized in that, It also includes a mechanical housing, an integrated circuit board, a power adapter, and a computer. The surface topography reconstruction module is integrated into the computer. The integrated circuit board is used to control the monochrome LED and the micro-polarization array camera. The light source module, the polarization beam projection module, the polarization imaging module, and the circuit board are packaged in the mechanical housing. The power adapter connects the power supply to the integrated circuit board and the computer.

7. A surface topography measurement method based on polarized structured light, wherein the surface topography measurement is performed using the apparatus described in any one of claims 1-6, characterized in that, include: Step S1: The light emitted by the monochromatic LED is collimated into a collimated spot after passing through the collimating lens, and then converted into linearly polarized light by the polarizer, which then shines perpendicularly onto the polarization grating. In step S2, the linearly polarized light is split into orthogonal and phase-synchronized left-handed and right-handed circularly polarized light after passing through the polarization grating; Step S3: Left and right circularly polarized light passes through a beam adjustment lens group, and the polarization grating exit surface is imaged onto the surface to be measured to form polarized structured light. Step S4: The micro-polarization array camera simultaneously captures polarization state images in four polarization directions to achieve the acquisition of polarization structured light on the surface under test. Step S5: The phase of the polarization state images in four polarization directions is extracted and unwrapped using a four-step phase-shifting method to obtain the absolute phase of the surface under test. The absolute phase is then converted to height, and the three-dimensional morphology of the surface under test is obtained through point cloud surface reconstruction.

8. The method according to claim 7, characterized in that, In step S4, the four polarization directions of the polarization state image are 0°, 45°, 90°, and 135°, and the phase shift of 0°, 90°, 180°, and 270° is achieved by the micro-polarization array of the micro-polarization array camera.

9. The method according to claim 7 or 8, characterized in that, In step S5, the light intensity grayscale values ​​of the four phase shift surfaces are extracted by the four-step phase shift method, and the wrapping phase of the surface to be measured is obtained. The global phase unwrapping algorithm of the quality map method is used to unwrap the wrapping phase to obtain the absolute phase distribution. The absolute phase distribution is then converted into three-dimensional morphology measurement data of the surface to be measured.

10. The method according to claim 9, characterized in that, Converting the absolute phase distribution into three-dimensional topographic measurement data of the surface under test includes: Place the calibration block on the micro-motion platform, place the imaging lens directly in front of the block, move the micro-motion platform for one cycle, and determine the height value corresponding to the phase by observing the stripes collected by the camera and the moving distance. After the phase-to-height conversion ratio is determined, the focal plane is used as the reference phase plane and the surface under test is used as the actual test phase plane. The absolute phase of the surface under test is obtained by subtracting the two after unwrapping, and thus the actual height is obtained. The lateral pixel distance is determined by the magnification of the imaging lens and the CMOS pixel size. After obtaining the actual point cloud, the three-dimensional shape of the surface under test is obtained by reconstructing the point cloud surface.

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