High-reflective freeform surface detection method based on wide-field multi-aperture synthetic phase deflectometry
By employing wide-field multi-aperture synthetic phase deflection technology, and utilizing a multi-camera system and iterative gradient solution method, the accuracy and efficiency issues of detecting large local slope freeform surfaces were resolved, achieving high-precision 3D topography reconstruction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI TONGXUN OPTOELECTRONICS TECHNOLOGY CO LTD
- Filing Date
- 2023-10-12
- Publication Date
- 2026-06-30
AI Technical Summary
Existing phase deflection techniques have shortcomings when measuring freeform surfaces with large local slopes, such as limited detection surface type, decreased measurement accuracy, complex detection models, and time-consuming measurement, making it difficult to achieve efficient and accurate detection.
Wide-field multi-aperture synthetic phase deflection technique is adopted. Multiple cameras are used to capture the torsion pattern of the surface under test from different angles. The correspondence between the pixels of each camera and the pixels of the display screen is calculated. A reference point is selected to perform three-dimensional absolute coordinate calculation. Combined with iterative gradient solution method and integral reconstruction technology, the complete three-dimensional morphology of the surface under test is synthesized.
It achieves accurate detection of freeform surfaces with large local slopes, and has the advantages of non-scanning rapid detection, high-precision three-dimensional coordinate registration and simple system structure. The measurement accuracy can reach 2.1μm (relative error 0.03%).
Smart Images
Figure CN117570876B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of curved surface inspection, and in particular to a method for inspecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection. Background Technology
[0002] High-performance optical systems fabricated using freeform mirrors are widely used in optical laser processing, semiconductor manufacturing, aerospace, and automotive manufacturing due to their compact structure and excellent image quality. Currently, the main measurement methods for freeform mirrors are coordinate measuring machine (CMM) and interferometry. However, the point-by-point scanning principle limits the measurement speed of CMM, while the zero-position interferometry principle limits the applicability of interferometry.
[0003] Phase deflection, based on the principle of retroreflected ray tracing, measures the gradient distribution on the surface of a component, thereby accurately reconstructing the three-dimensional morphology of the measured mirror component. It offers advantages such as non-zero detection, system simplicity and flexibility, in-situ measurement, and good stability. Currently, the accuracy of phase deflection for plane mirrors is approaching that of interferometry. However, for surfaces with large local slopes, the inverted rays from the camera can easily exceed the physical range of the display screen, leading to measurement failure. Therefore, how to measure freeform surfaces with large local slopes is a significant challenge for the future development of phase deflection.
[0004] To overcome this challenge, researchers have recently explored phase deflection measurements of large-area slope mirror elements using methods such as curved screens, wavefront conversion, surround projection sources (projector arrays / multi-source splicing), and sub-aperture synthesis. These methods include: 1) replacing planar screens with curved screens, using binocular stereo vision to capture the fringe distribution of the curved screen to establish a curved screen model, and then unfolding the curved screen into a large-area, virtual planar screen to expand the measurement range of the curved surface gradient; 2) converting the wavefront reflected by the cylindrical surface under test into a planar wavefront using a 45-degree conical mirror to measure the circle of the cylindrical surface; 3) phase deflection based on surround projection sources (Cavlectometry), using multiple screens or projector arrays to form a surround projection source around the element under test, successfully measuring large-area slope surfaces using the principle of reverse ray tracing; 4) boundaryless phase deflection, fixing the element under test on a precision rotating stage, continuously rotating the element under test, and achieving large-area slope surface measurement through sub-aperture synthesis.
[0005] Although there are currently several phase deflection correction methods that can improve the measurement capability of phase deflection on freeform surfaces to some extent, each method still has shortcomings such as limited detection surface type, decreased measurement accuracy, complex detection model, and time-consuming measurement. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a high-reflectivity freeform surface detection method based on wide-field multi-aperture synthetic phase deflection. This method can achieve accurate detection of freeform surface mirror elements with large local slopes and has the advantages of non-scanning fast detection, low aperture overlap, high-precision three-dimensional coordinate registration, non-zero detection, and simple system structure.
[0007] The objective of this invention can be achieved through the following technical solutions:
[0008] This invention provides a method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection, the method comprising:
[0009] Step S1: A multi-camera phase deflection system is built using the surface to be measured, a screen for projecting a set pattern onto the surface to be measured, and multiple cameras for simultaneously capturing different areas of the surface to be measured, and the system parameters are calibrated; wherein, the area captured by each camera overlaps with the area captured by at least one other camera, and the area captured by each camera serves as a measurement aperture;
[0010] Step S2: After the system parameters are calibrated, collect the distortion patterns reflected by the measured surface from all cameras, and calculate the correspondence between the pixels of each camera and the pixels of the display screen.
[0011] Step S3: Select multiple sets of reference points in the overlapping area of different apertures, calculate the three-dimensional absolute coordinates of the reference points in the overlapping area based on the correspondence between each camera pixel and the display screen pixel, and use the three-dimensional absolute coordinates of the reference points as a reference to solve the gradient distribution in each aperture and reconstruct the three-dimensional absolute coordinates of each point in each aperture through integration, so as to obtain the aperture inner surface shape distribution with absolute depth.
[0012] Step S4: By registering the three-dimensional absolute coordinates of each point within each aperture, the surface shape distribution within all apertures is synthesized to obtain the complete three-dimensional morphology of the measured surface.
[0013] Preferably, the number of cameras is set such that the entire field of view of all cameras completely covers the entire measurement area.
[0014] Preferably, the system parameters to be calibrated in step S1 include the focal length, distortion, and position parameters of each camera, as well as the position parameters of the screen.
[0015] Preferably, the system parameters are calibrated using a flat plate calibration method.
[0016] Preferably, the camera m, the area captured by the camera m, and the screen are used as a single-camera phase deflection subsystem to measure the marked standard plate. A standard world coordinate system is constructed based on the standard plane and the spacing of the marked points to perform secondary correction on the position parameters of the camera m. Here, n is the camera number, 1≤m≤M, and M is the number of cameras.
[0017] Preferably, step S2 specifically involves: projecting two sets of sinusoidal stripe patterns in different directions onto the surface to be measured using the screen, capturing the distorted stripe patterns reflected from the surface to be measured using all cameras, and calculating the correspondence between the pixels of each camera and the pixels of the display screen.
[0018] Preferably, a multi-step phase-shifting algorithm and a spatial phase unwrapping algorithm are used to calculate the correspondence between each camera pixel and the display screen pixel.
[0019] Preferably, step S3 includes the following sub-steps:
[0020] Step S31: Based on the correspondence between each camera pixel and the display screen pixel, multiple sets of reference points are selected in the overlapping area of different apertures using a feature matching algorithm. The absolute height of the reference points in the overlapping area is determined by the stereo phase deflection method, and then the three-dimensional absolute coordinate value of the reference points is determined. This is used as the benchmark for setting the three-dimensional absolute coordinate of the initial surface shape in a single field of view.
[0021] Step S32: Solve the surface gradient of the surface to be measured within each aperture using the iterative gradient solution method, and obtain the three-dimensional surface shape of each aperture after integration.
[0022] Preferably, step S31 specifically includes:
[0023] The search area m is the overlapping area with other M-1 areas; where m is the camera number, 1≤m≤M, and M is the number of cameras;
[0024] Calculate the m-th distorted stripe pattern I using a feature matching algorithm m The homography matrix between the distorted stripe patterns acquired by other cameras is used to transform the other pattern point sets according to the homography matrix and search for their relationship with I. m The intersection region between point sets, and the minimum set of all intersection regions is taken as the overlapping region;
[0025] Multiple reference points are selected within the overlapping area, and the absolute height of each reference point is calculated sequentially using stereo deflection to serve as the basis for setting the initial surface shape within a single field of view.
[0026] Preferably, step S32 specifically includes:
[0027] Calculate the gradient of the measured surface in the x and y directions:
[0028]
[0029]
[0030] Among them, (x S y S ) and (x C y C ) represent the screen coordinate system and the camera coordinate system, respectively, Δz S and Δz C d represents the offset of the screen and camera relative to a point (x, y) on the measured surface in the z-direction. S and d C These represent the distances of the screen and the camera relative to the point (x, y), respectively.
[0031] Then, the surface shape distribution w(x, y) of the measured surface is updated based on the partition integration method;
[0032] After multiple iterations of calculation, w(x, y) will converge to the surface shape distribution of the measured surface. The height of w(x, y) is then corrected a second time based on the three-dimensional absolute coordinates of the reference point to complete the three-dimensional surface shape reconstruction of the current aperture.
[0033] Compared with the prior art, the present invention has the following beneficial effects:
[0034] 1) Multiple cameras placed at different locations are used to capture the distorted stripes reflected from different areas of the test piece. Each camera, screen and the test surface are used as a phase deflection system to measure and reconstruct the three-dimensional shape of the captured area as the detection result of a single aperture. The morphologies of each aperture are accurately synthesized, thereby solving the problem of conventional phase deflection measurement failure caused by excessive curvature of the test piece, and having the ability to measure free-form surfaces.
[0035] 2) Data from each aperture is collected simultaneously, which solves the problem of time-consuming detection in scanning detection methods and provides rapid detection capability.
[0036] 3) To ensure the accuracy of multi-region surface shape synthesis, a small number of reference points are selected in the overlapping areas of different apertures using a feature matching algorithm. The absolute height of the reference points is calculated by stereo deflection to constrain the height distribution of the local surface shape. This method has the advantages of low aperture overlap and high-precision three-dimensional coordinate registration. At the same time, by obtaining the absolute height of the overlapping area and setting it as the reference for single-aperture surface shape reconstruction, the method takes into account both the fast reconstruction capability of single-camera phase deflection and the absolute height reconstruction capability of stereo deflection.
[0037] 4) Wide-field multi-aperture synthetic phase deflection can use the simple measurement model of reverse ray tracing, and the system is simple and does not require auxiliary measurement tools such as binocular stereo vision systems or mechanical motion devices such as precision rotary tables.
[0038] It has the advantages of non-scanning rapid detection, non-zero detection and simple system structure. Attached Figure Description
[0039] Figure 1 is a schematic diagram of the phase deflection technique based on wide-field multi-aperture synthesis; wherein, Figure a is a schematic diagram of the measurement principle of the phase deflection technique based on wide-field multi-aperture synthesis, Figure b is a flowchart of the measurement process of the phase deflection technique based on wide-field multi-aperture synthesis, Figure c shows the three-dimensional absolute coordinates of point P in the overlapping area obtained by the three-dimensional phase deflection technique, and Figure d shows the morphological distribution of region m iteratively solved based on the principle of software-configurable phase deflection technique.
[0040] Figure 2 shows the numerical simulation results of phase deflection based on wide-field multi-aperture synthesis; where, figure a is the simulation model of phase deflection based on wide-field multi-aperture synthesis, figure b is the freeform surface to be measured, figure c is the tortuous fringes acquired by camera 1 and camera 2, figure d is the three-dimensional surface morphology within a single aperture reconstructed by camera 1 (left) and camera 2 (right), figure e is the complete three-dimensional morphology reconstructed by phase deflection based on wide-field multi-aperture synthesis, and figure f is the reconstruction residual map;
[0041] Figure 3 shows the prototype setup and testing of phase deflection based on wide-field multi-aperture synthesis. Figure a is a physical image of the prototype, Figure b is a checkerboard calibration plate (left) and a dot calibration plate (right), Figure c is a tortuous fringe pattern collected within the four apertures, Figure d is the three-dimensional morphology of the spherical mirror reconstructed based on phase deflection based on wide-field multi-aperture synthesis, and Figure e is a residual distribution map of the spherical reconstruction.
[0042] Figure 4 shows the detection results of a curved screen of a mobile phone based on phase deflection based on wide-field multi-aperture synthesis; in which, Figure a is a picture of the actual curved screen of the mobile phone, the upper part of which (about 75.2mm×63.0mm) is the surface under test, and Figure b is the three-dimensional morphology of the curved screen within the apertures of camera 1 (left) and camera 2 (right), as well as the three-dimensional morphology of the complete curved screen after aperture synthesis.
[0043] Figure 5 shows the detection results of the freeform surface based on phase deflection technique using wide-field multi-aperture synthesis; where, figure a shows the slope distribution of the freeform surface in the x and y directions, figure b shows the three-dimensional morphology of the reconstructed freeform surface, figure c shows the coefficients of the first 30 fitted Zernike polynomials of the freeform surface, where displacement and tilt components have been removed, and figure d shows the distribution of the reconstructed freeform surface residuals.
[0044] In the figure, 1 is the screen, 2 is the first camera, 3 is the second camera, 4 is the third camera, 5 is the Mth camera, 6 is the surface being measured, 7 is the absolute depth plane, 8 is the fourth camera, and 9 is the support for the surface being measured. Detailed Implementation
[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.
[0046] Example
[0047] This embodiment provides a method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection, the method comprising:
[0048] Step S1: Using the test surface 6, a screen 1 for projecting a set pattern onto the test surface 6, and multiple cameras for simultaneously capturing different areas of the test surface 6, a multi-camera phase deflection system is constructed, and the system parameters are calibrated; wherein, the area captured by each camera overlaps with the area captured by at least one other camera, and the area captured by each camera serves as a measurement aperture.
[0049] Step S2: After the system parameters are calibrated, collect the distortion patterns reflected by the measured surface 6 from all cameras, and calculate the correspondence between the pixels of each camera and the pixels of the display screen.
[0050] Step S3: Select multiple sets of reference points in the overlapping area of different apertures, calculate the three-dimensional absolute coordinates of the reference points in the overlapping area based on the correspondence between each camera pixel and the display screen pixel, and use the three-dimensional absolute coordinates of the reference points as a reference to solve the gradient distribution in each aperture and reconstruct the three-dimensional absolute coordinates of each point in each aperture through integration, so as to obtain the aperture inner surface shape distribution with absolute depth.
[0051] Step S4: By registering the three-dimensional absolute coordinates of each point within each aperture, the surface shape distribution within all apertures is synthesized to obtain the complete three-dimensional morphology of the measured surface 6.
[0052] Next, the method in this embodiment will be described in further detail.
[0053] Figure 1 shows the principle of a reflective fringe 3D surface shape measurement method based on wide-field multi-aperture synthesis. The pattern projected by the display is reflected by the measured surface 6 and simultaneously captured by M cameras (M is greater than or equal to 2, theoretically there is no upper limit, the specific number depends on whether the field of view of all cameras can completely cover the entire measurement area). Each camera captures the m-th (1≤m≤M) region of the measured surface 6, and each aperture overlaps with one or more other regions. Each camera's field of view serves as a measurement aperture. Figure 1a ).
[0054] The measurement accuracy of the tested surface 6 depends on the calibration accuracy of the system parameters. First, the system parameters, such as the focal length, distortion, position parameters of the M cameras, and the position parameters of screen 1, are calibrated twice. Then, the display projects two sets of sinusoidal fringe patterns in different directions onto the tested surface 6. Next, the M cameras capture the distorted fringe patterns reflected from the tested surface 6, obtaining the correspondence between the pixels of each camera and the pixels of the display screen. Then, a feature matching algorithm is used to select multiple sets of reference points in the overlapping areas of different apertures. The absolute height of the reference points in the overlapping areas of different apertures is determined by the stereo phase deflection technique, thereby obtaining the three-dimensional absolute coordinates of the reference points. These coordinates are used as the basis for setting the initial surface shape within a single aperture. The surface gradient of the tested element in the m-region is then quickly solved using the iterative gradient solution method. After integration, the three-dimensional surface shape within the M apertures is obtained. Finally, the three-dimensional topography data within all M apertures are synthesized to obtain the complete three-dimensional topography of the tested surface 6, realizing the detection of freeform surface mirror elements with large local slopes.
[0055] Before measurement, the focal length, distortion, position parameters of the M cameras, and the position parameters of screen 1 were calibrated using a flatbed calibration method. Then, the Mth camera (5), region m, and screen 1 were used as a single-camera phase-deflection system to measure a marked standard flatbed. A standard world coordinate system was constructed based on the standard plane and the spacing of the marked points to perform secondary correction on the position parameters of the Mth camera (5). After the measurement data acquisition was completed, the pixel values (px) of each camera were calculated using a multi-step phase-shifting phase calculation algorithm and a spatial phase unwrapping algorithm. m py m ) and display pixels (px) S py S The correspondence between ).
[0056] To obtain the complete surface shape of the measured surface 6, it is necessary to reconstruct the surface shape distribution within M apertures and complete the surface shape synthesis, such as... Figure 1b As shown, the complete process includes calculating the three-dimensional absolute coordinates of reference points within the overlapping region, solving for the gradient distribution within M apertures, integrating and reconstructing the three-dimensional surface shape within the M apertures, and synthesizing all surface shapes. When recovering the surface shape of region m, the overlapping region between this region and other M-1 regions is first searched. Feature matching is used to calculate the m-th distorted fringe pattern I. m The homography matrix between other patterns is used to transform the point sets of other patterns according to the homography matrix and then search for their homography with I. m The intersection regions between point sets are identified, and the smallest set of all intersection regions is taken as the overlapping region. Multiple reference points are selected within the overlapping region, and the absolute height of each reference point is calculated sequentially using a stereo deflection method.
[0057] For a reference point P, such as Figure 1c As shown, from display point Sk Light rays with a range of (1≤k≤K) are reflected from reference point P and then reach point C on camera k. k At point S, according to the law of reflection, the incident ray S... k P and reflected light PC k Find the normal vector n of point P. k for
[0058]
[0059] Search for point P on the reflected light from the first camera 2 to satisfy
[0060]
[0061] The three-dimensional absolute coordinates of all reference points are solved sequentially. The initial surface shape w(x, y) of the region m to be solved is set as a plane, with its height being the average of the three-dimensional absolute coordinates of all reference points, such as... Figure 1d The absolute height plane is shown, and then the gradient distribution of region m is iteratively solved based on the principle of software-configurable phase deflection. The gradients of the measured surface 6 in the x and y directions are calculated:
[0062]
[0063]
[0064] Among them, (x S y S ) and (x C y C ) represent the screen coordinate system and the camera coordinate system, respectively, Δz S and Δz C d represents the offset of screen 1 and camera relative to a point (x, y) on the measured surface 6 in the z direction. S and d C Let x and y represent the distances of screen 1 and the camera relative to point (x, y), respectively. Then, the hexahedral distribution w(x, y) of the measured surface is updated based on the partition integration method. After multiple iterations, w(x, y) converges to the hexahedral distribution of the measured surface. The height of w(x, y) is then corrected a second time based on the absolute value of the reference point, thus completing the surface reconstruction of region m. Finally, the surface shapes within the M apertures are accurately synthesized together using the absolute height values of the reference points in the overlapping region.
[0065] To verify the performance of the proposed method, numerical simulations were first performed in this embodiment.
[0066] Taking the synthesis of two cameras as an example, physical models of the display and each camera were constructed in the world coordinate system using point cloud coordinates. Then, the actual calibration process was simulated. In this simulation, a checkerboard calibration board was added to calibrate the camera's intrinsic and extrinsic parameters and the display's coordinate parameters. Figure 2a To simulate the measurement process of phase deflection based on wide-field multi-aperture synthesis, a freeform surface to be measured was generated using the Zernike polynomial fitting method and used as the measured surface in the simulation system. Figure 2b Then, a sinusoidal fringe pattern for measuring the phase in two directions is displayed on the monitor, and a distorted fringe image image of the camera surface after reflection from the measured surface 6 is obtained by geometric ray tracing. Figure 2c Finally, the three-dimensional morphology of the measured surface 6 was analyzed using the calibration results of the internal and external parameters and the display coordinate parameters. The three-dimensional morphology within the field of view of the first camera 2 and the second camera 3 was obtained by iterative solution as follows: Figure 2d As shown in the figure, the measured surface 6 under the field of view of a single camera all have a certain proportion of missing parts, making it difficult to measure the complete three-dimensional morphology. By combining the three-dimensional morphology results measured by two cameras, the following is obtained: Figure 2e The complete three-dimensional shape of the freeform surface is shown, and the residual between the measurement result and the true value is calculated. Figure 2f The root mean square error between the two is 2.1 μm (relative error 0.03%).
[0067] A phase deflection measurement model based on wide-field multi-aperture synthesis was established using optical tracing methods. Numerical simulations demonstrated the effectiveness of this phase deflection method for measuring freeform surfaces, achieving an accuracy of 2.1 μm (relative error 0.03%). Furthermore, an experimental system using wide-field multi-aperture synthesis based phase deflection was constructed, comprising four cameras, to measure a standard spherical mirror with a radius of curvature of 155.04 mm, achieving a root mean square error of 5.3 nm. Further measurements were taken of a curved mobile phone screen with a local slope ranging from -46.1° to 51.3°, and a freeform surface with a local slope ranging from -6.7° to 7.7° and a peak-to-valley value of 5.3 mm.
[0068] Experiment setup and testing:
[0069] Figure 3aThis describes the experimental system for phase deflection based on wide-field multi-aperture synthesis. Structured light projected from screen 1 (1920×1080 pixels, 0.36mm pixel size, S32E360F, Samsung Electronics, South Korea) is perpendicularly incident on a mirror element placed on support 9 of the surface under test. The distorted fringes reflected from four regions of the surface under test 6 are captured by four cameras (1920×1200 pixels, 4.8μm pixel size, acA1920-150um, Basler AG, Germany), each equipped with a lens (MVL-MF2528M-8MP, Hikvision, China) to collect the reflected light from each region of the surface under test 6. The position and orientation of all four cameras can be adjusted using the support brackets, ensuring that the four fields of view cover all reflected light from the surface under test 6.
[0070] Before measuring the mirror element, the intrinsic parameters (focal length, distortion, etc.), extrinsic parameters (position parameters), and screen 1 position parameters of the four cameras were calibrated sequentially. (The following is a list of parameters:) Figure 3b The ceramic checkerboard pattern shown (grid size 10×10mm, accuracy 1μm) was placed near the component under test. Four cameras were used to simultaneously capture images of the checkerboard pattern from different angles. The intrinsic parameter matrix K of each of the four cameras was obtained using Zhang's calibration method. m (m = 1, 2, 3, 4). To accurately calibrate the camera's position parameters, a customized system was developed. Figure 3b The calibration plate shown has a smooth surface and is marked with points. The upper surface of the plate is engraved with a 4×4 array of dots (30×30mm spacing, 1μm accuracy). Using the plate's dot coordinate system as the world coordinate system, and through the intrinsic parameter matrix K... m Calculate the extrinsic matrix of the four cameras [R] m t m Then, an array of dots in 11 rows and 11 columns, each with a diameter of 10 pixels, is displayed on the screen. Photos reflected from the flat calibration plate are captured by four cameras to obtain the camera pixel coordinates corresponding to each dot on the calibration plate. These coordinates are then combined with the intrinsic parameter matrix K of the Mth camera (5th camera). m , extrinsic parameter matrix [R m t m The position parameters of screen 1 are obtained from the pixel size and the pixel size of screen 1. The average values of the four sets of screen position parameters were obtained using the quaternion averaging method [R]. S t S This is to reduce solution errors.
[0071] After system setup and calibration, a spherical lens (GCL-010123N, Daheng Optoelectronics, China) with a radius of curvature of 155.04 mm (nominal value) and an aperture of 76.2 mm was measured using a phase deflection system based on wide-field multi-aperture synthesis. The structured light projected onto the display consisted of a set of horizontal and vertical stripes with a period of 80 pixels. Each set of stripes was composed of four sinusoidal fringe patterns with initial phases of 0, π / 2, π, and 3π / 2. The reflection areas of the four spherical lenses captured by the four cameras are shown below. Figure 3c As shown. After directly synthesizing the three-dimensional topography of the four regions, the complete spherical topography of the lens was obtained. Figure 3d A standard sphere was fitted based on the lens's nominal radius of curvature. The root mean square error between the measured result and the standard sphere was 5.3 μm (relative error of 0.18%). The error distribution is as follows: Figure 3e As shown.
[0072] Mobile phone curved screen testing:
[0073] The three-dimensional morphology of a curved screen on a mobile phone was examined using a phase deflection technique based on wide-field multi-aperture synthesis. The screen 1 of the mobile phone (X80, VIVO, China) is a piece of glass with an approximately flat center and curved edges on both sides. A 75.2mm × 63.0mm area within the curved screen was used as the measured surface 6. Figure 5a Two cameras were used to capture the distorted stripes reflected from the curved screen of the mobile phone, and the topography of the curved screen within the field of view of each camera was reconstructed. Due to the high curvature of the curved screen, each camera could only capture the topography of one side of the screen. By combining the reconstruction results from the two fields of view, a complete three-dimensional topography of the curved screen was obtained. Figure 2b The three-dimensional morphology of the curved screen is as follows: Figure 2c As shown, the local slope distribution of the curved screen within the effective measurement range of the phase deflection technique based on wide-field multi-aperture synthesis is calculated to be -46.1° to 51.3°.
[0074] High-reflectivity freeform surface inspection:
[0075] To enhance the measurement capabilities of wide-field multi-aperture synthetic phase deflection on freeform surfaces, this embodiment fabricated a surface of arbitrary curvature by heating and softening an acrylic sheet. After system layout adjustments and parameter calibration, the freeform surface of the acrylic sheet was measured using wide-field multi-aperture synthetic phase deflection. The slope distribution of the freeform surface in the x and y directions was calculated. Figure 5a Its local slope ranges from -6.7° to 7.7°. Figure 5b The synthesized complete freeform surface is shown, with a peak-to-valley value of 5.3 mm. Figure 5b A Zernike polynomial fit was performed on the freeform surface, and the distribution of the first 30 Zernike coefficients is as follows: Figure 5cAs shown, displacement and tilt components have been removed. Furthermore, the freeform surface shape was fitted using Zernike coefficients, and the residuals between the fitting results and the measurement results are shown below. Figure 5d As shown.
[0076] This invention proposes a method for detecting freeform surface mirror elements based on wide-field multi-aperture synthesis phase deflection. The method involves capturing distorted fringes reflected from multiple regions of the mirror element under multiple apertures, and then synthesizing the reconstructed three-dimensional topography from each aperture with high precision, thereby achieving the detection of surfaces with large local slopes. To ensure measurement accuracy, the camera position parameters are corrected a second time by measuring the surface shape of a marked plate, ensuring accurate calibration of the multi-camera system. To guarantee the accuracy of multi-aperture surface shape synthesis, a feature matching algorithm is used to select reference points in the overlapping areas of different apertures, and the absolute height of the reference points is calculated using stereo deflection to constrain the height distribution of the local surface shape, thus achieving accurate synthesis of the multi-aperture surface shape. A measurement model based on wide-field multi-aperture synthesis phase deflection is established based on optical tracing methods, and numerical simulations demonstrate the effectiveness of this method for freeform surface measurement, achieving an accuracy of 2.1 μm (relative error 0.03%). Furthermore, an experimental system based on wide-field multi-aperture synthesis using phase deflection, comprising four cameras, was constructed to test a standard spherical mirror with a radius of curvature of 155.04 mm, achieving a root mean square error of 5.3 nm. Additionally, measurements were taken on a curved mobile phone screen with a local slope ranging from -46.1° to 51.3°, and a freeform surface with a local slope ranging from -6.7° to 7.7° and a peak-to-valley value of 5.3 mm.
[0077] In summary, the work of this invention provides a new approach to the measurement of freeform surface mirrors. By measuring the surface shape of mirror elements with high precision, it can further improve the imaging quality, energy utilization, and other performance of optical systems, and is expected to promote the development of fields such as biomedical imaging, semiconductor device processing, and optical inspection.
[0078] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A high-reflective freeform surface inspection method based on wide-field multi-aperture synthetic phase deflectometry, characterized in that, The method includes: Step S1: A multi-camera phase deflection system is built using the surface to be measured, a screen for projecting a set pattern onto the surface to be measured, and multiple cameras for simultaneously capturing different areas of the surface to be measured, and the system parameters are calibrated; wherein, the area captured by each camera overlaps with the area captured by at least one other camera, and the area captured by each camera serves as a measurement aperture; Step S2: After the system parameters are calibrated, collect the distortion patterns reflected by the measured surface from all cameras, and calculate the correspondence between the pixels of each camera and the pixels of the display screen. Step S3: Select multiple sets of reference points in the overlapping area of different apertures, calculate the three-dimensional absolute coordinates of the reference points in the overlapping area based on the correspondence between each camera pixel and the display screen pixel, and use the three-dimensional absolute coordinates of the reference points as a reference to solve the gradient distribution in each aperture and reconstruct the three-dimensional absolute coordinates of each point in each aperture through integration, so as to obtain the aperture inner surface shape distribution with absolute depth. Step S4: By registering the three-dimensional absolute coordinates of each point within each aperture, the surface shape distribution within all apertures is synthesized to obtain the complete three-dimensional morphology of the measured surface. The number of cameras is set to ensure that the field of view of all cameras completely covers the entire measurement area. Step S3 includes the following sub-steps: Step S31: Based on the correspondence between each camera pixel and the display screen pixel, multiple sets of reference points are selected in the overlapping area of different apertures using a feature matching algorithm. The absolute height of the reference points in the overlapping area is determined by the stereo phase deflection method, and then the three-dimensional absolute coordinate value of the reference points is determined. This is used as the benchmark for setting the three-dimensional absolute coordinate of the initial surface shape in a single field of view. Step S32: Solve the surface gradient of the surface to be measured in each aperture based on the iterative gradient solution method, and obtain the three-dimensional surface shape of each aperture after integration; Step S31 specifically involves: Search area m overlapping area with other M-1 areas; wherein, m is the camera number, 1≤m≤M, M is the number of cameras; Calculate the first set of points I using a feature matching algorithm m amplitude distorted fringe pattern I m The homography matrix between the distorted fringe pattern I and the other fringe patterns, and search the other pattern point sets according to the homography matrix m The intersection area between the point sets, and the minimum set of all intersection areas as the overlapping area; Multiple reference points are selected within the overlapping area, and the three-dimensional absolute height of each reference point is calculated sequentially using stereo deflection. The three-dimensional absolute coordinate values of the reference points are then determined as the basis for setting the initial surface shape within a single field of view. The system parameter calibration adopts the flat plate calibration method, specifically as follows: The camera m , the camera m The region of shooting and the screen are measured as a single camera phase deflection system, and a standard world coordinate system is constructed according to the standard plane and the distance between the mark points to correct the position parameters of the camera m ; wherein, m m is the camera number, 1≤m≤M, M M is the number of cameras.
2. The method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection as described in claim 1, characterized in that, The system parameters to be calibrated in step S1 include the focal length, distortion, and position parameters of each camera, as well as the position parameters of the screen.
3. The method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection as described in claim 1, characterized in that, Step S2 specifically involves: projecting two sets of sinusoidal stripe patterns in different directions onto the surface to be measured using the screen; capturing the distorted stripe patterns reflected from the surface to be measured using all cameras; and calculating the correspondence between the pixels of each camera and the pixels of the display screen.
4. The method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection as described in claim 3, characterized in that, The correspondence between each camera pixel and the display screen pixel is calculated using a multi-step phase shifting algorithm and a spatial phase unwrapping algorithm.
5. The method for detecting high-reflectivity freeform surfaces based on wide-field multi-aperture synthetic phase deflection as described in claim 1, characterized in that, Step S32 specifically involves: Calculate the measured surface at x and y Gradient of direction: Among them, (x S y S ) and (x C y C ) represent the screen coordinate system and the camera coordinate system, respectively, Δz S and Δz C This represents the screen and camera relative to a point (x, y) on the measured surface. z Directional offset, d S and d C These represent the distances of the screen and the camera relative to the point (x, y), respectively. Then, the surface shape distribution w(x, y) of the measured surface is updated based on the partition integration method; After multiple iterations of calculation, w(x, y) will converge to the surface shape distribution of the measured surface. The height of w(x, y) is then corrected a second time based on the three-dimensional absolute coordinates of the reference point to complete the three-dimensional surface shape reconstruction of the current aperture.