Subaperture stitching detection method and detection device for large-aperture optical element

Abstract

This invention relates to the field of optical inspection technology, and in particular provides a method and apparatus for sub-aperture stitching inspection of large-aperture optical elements. The method includes the following steps: S1, setting up an inspection system, including an electrically controlled rotary table, a display screen, and a camera; S2, establishing a mirror coordinate system with the center of the mirror surface under test as the origin; S3, rotating the mirror under test and transforming the coordinates of sampling points within each sub-aperture to the world coordinate system; S4, ray tracing to calculate the local slope data of the sampling points; S5, uniformly transforming the slope data of each sub-aperture to the mirror coordinate system, and constructing a full-aperture slope field based on a slope stitching fusion method; S6, constructing an overdetermined linear least squares equation system based on Zernike polynomials to obtain the full-aperture reconstructed surface shape of the mirror surface under test. This invention acquires sub-aperture data through rotational scanning and uses a slope stitching fusion method to achieve full-aperture surface shape reconstruction and high-precision complete inspection of the surface of large-aperture optical elements.

Description

Technical Field

[0001] This invention belongs to the field of optical inspection technology, and particularly relates to a method and device for detecting the sub-aperture splicing of large-aperture optical elements. Background Technology

[0002] With the deepening application of large-scale optical engineering, the performance indicators of optical systems are increasingly developing towards extremely large apertures and extremely high surface accuracy. In the new generation of large space telescopes, breakthroughs in primary mirror aperture directly determine the system's resolving power and imaging quality; in high-power laser inertial confinement fusion devices, the surface quality of large-aperture terminal mirrors directly affects the beam focusing efficiency and energy density, while high-precision detection capabilities are the prerequisite and guarantee for achieving ultra-precision manufacturing. Therefore, achieving high-precision detection of large-aperture optical surfaces has become one of the core key technologies for improving the country's high-end equipment manufacturing capabilities and scientific research level.

[0003] Currently, mainstream optical mirror inspection technologies are mainly divided into two categories: contact measurement and non-contact optical measurement. Contact measurement technologies, represented by coordinate measuring machines (CMMs) or profilometers, while possessing good mechanical stability, are limited by the low efficiency of point-by-point scanning and the risk of surface scratches caused by the probe contact process, making them unsuitable for full-aperture non-destructive testing of large-diameter, high-precision optical surfaces. In the non-contact field, interferometry offers extremely high detection accuracy, but its detection principle makes the system highly sensitive to environmental vibrations and airflow disturbances, and it often requires the generation of an ideal reference wavefront that matches the surface being measured, resulting in complex optical path design. This poses significant challenges to interferometry in system integration and in-situ inspection applications, making it difficult to meet the in-situ inspection needs of complex workshop environments.

[0004] In contrast, Phase Measuring Deflectometry (PMD), as a highly promising non-zero-position detection method, is gradually becoming an ideal solution for solving the in-situ detection problem of optical components due to its larger dynamic measurement range, stronger environmental robustness, and easier integration. However, this technology still has significant limitations when applied to the detection of large-aperture optical components. Limited by the physical constraints of the camera's field of view and the size of the illumination display screen, the single measurement range of PMD is often very limited, making it difficult to complete the full-aperture measurement in one go. Simply increasing the display screen size to expand the field of view is not a feasible solution, as there are physical limits to screen size expansion; excessively large screens are prone to significant surface distortion under their own gravity. This distortion causes a shift in the screen pixel coordinates in the reverse ray tracing model, thereby compromising the system's calibration accuracy and measurement precision. Therefore, achieving complete detection of large-aperture components under the premise of limited hardware size and the inability to arbitrarily expand it has become a pressing technical challenge.

[0005] In summary, PMD faces technical challenges in the inspection of large-aperture optical components, including a limited effective inspection aperture and insufficient accuracy in reconstructing the full-view surface of large apertures. Therefore, there is an urgent need to develop a new inspection technology that can reduce reliance on large-aperture display devices and effectively minimize splicing accumulation errors. Summary of the Invention

[0006] In view of this, the present invention aims to provide a sub-aperture stitching detection method and detection device for large-aperture optical elements. The sub-aperture data is obtained by rotational scanning, and a sub-aperture stitching method based on gradient consistency constraints in the overlapping region of the slope domain is adopted. This solves the technical problems of existing PMD in the detection of large-aperture curved surfaces, which is difficult to achieve full-aperture coverage and insufficient accuracy of large-aperture full-view surface shape reconstruction. It realizes high-precision full-aperture detection of large-aperture optical surfaces under limited field of view.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A method for detecting sub-aperture splicing of large-aperture optical elements includes the following steps: S1: Set up the testing system, fix the large-aperture optical element to be tested on the electronically controlled rotating stage, with the rotation axis coinciding with the normal axis of the center of the mirror to be tested, and place the display screen and camera in a preset space above the mirror to be tested, so that the display screen, camera and the center of the mirror to be tested form an asymmetrical triangular geometric layout. S2: Establish a mirror coordinate system with the center of the mirror to be tested as the origin, define the parameters of the mirror to be tested, and obtain the theoretical surface shape of the mirror to be tested; S3: Rotate the mirror to be tested to different preset angles, and use the rotation matrix to transform the mirror coordinates and their theoretical normal vectors collected by the cameras under each sub-aperture to the world coordinate system fixed in space; S4: Use the fringe reflection method to perform ray tracing on the sampling points in each sub-aperture, calculate the coordinates of the intersection point reflected from the camera position through the mirror under test to the display screen, and then calculate the local slope data of the sampling point; S5: Transform the local slope data back to the mirror coordinate system through the inverse rotation matrix, and solve and stitch the slope data of the overlapping area of ​​each sub-aperture to obtain the full aperture slope field; calculate the overlap rate between adjacent sub-apertures and the full aperture coverage. If the overlap rate or full aperture coverage is lower than the preset threshold, return to step S3 to optimize the sub-aperture layout. S6: A system of overdetermined linear least square equations is constructed using normalized Zernike polynomials. The coefficient vector is solved by combining the full-aperture slope field, and the full-aperture reconstructed surface shape is synthesized by weighting. The full-aperture reconstructed surface shape is aligned with the pose of the theoretical surface shape, and the peak-valley values ​​and root mean square error of the residual surface are calculated.

[0008] Furthermore, the large-aperture optical element to be tested includes planar, spherical, aspherical, or freeform reflective optical elements; the mirror parameters to be tested in step S2 include radius of curvature and aperture.

[0009] Furthermore, the ray tracing method in step S4 is as follows: based on the principle of reversibility of light path, the incident light vector is calculated starting from the camera position, the direction of reflected light is calculated according to the law of reflection and the normal vector of the current sampling point, and the coordinates of the intersection point of the reflected light and the display screen plane are solved by analytical geometry.

[0010] Furthermore, the overdetermined linear least squares equation system in step S6 is: , where the matrix A Each column is composed of the partial derivatives of the Zernike polynomial at the sampling points, and the vector... b The Zernike coefficient vector is obtained by cascading slope fields across the entire aperture. c The Zernike coefficient corresponding to the translation term is not considered in the full-caliber reconstruction model.

[0011] A sub-aperture splicing detection device for large-aperture optical elements, comprising: An electrically controlled rotary stage is used to fix the large-aperture optical element to be tested and drive it to rotate around the rotation axis to different preset angles, with the rotation axis coinciding with the center normal axis of the mirror surface to be tested. The display screen serves as a structured light illumination source for projecting modulated patterns onto the mirror under test. At least one camera is used to capture the modulation pattern after reflection from the mirror under test; The display screen and camera are placed in a preset space above the mirror to be tested, so that the display screen, camera and the center of the mirror to be tested form an asymmetrical triangular geometric layout. The theoretical surface shape construction module is used to establish a mirror coordinate system with the center of the mirror to be tested as the origin, define the parameters of the mirror to be tested, and obtain the theoretical surface shape of the mirror to be tested. The coordinate system transformation module is used to transform the mirror coordinates and their theoretical normal vectors obtained in the mirror coordinate system to the world coordinate system fixed in space through a rotation matrix; and to transform the slope data in the world coordinate system back to the mirror coordinate system through an inverse rotation matrix. The local slope calculation module for the mirror is used to perform ray tracing on the sampling points within each sub-aperture using the fringe reflection method in the world coordinate system, calculate the coordinates of the intersection point reflected from the camera position through the mirror under test to the display screen, and then calculate the local slope data of the sampling point. The slope data fusion processing module is used to solve and stitch together the slope data of the overlapping areas of each sub-aperture to obtain the full-aperture slope field; after generating the measurement counting map, it calculates the overlap rate between adjacent sub-apertures and the full-aperture coverage rate. If the overlap rate or full-aperture coverage rate is lower than the preset threshold, a warning is issued. The full-aperture surface reconstruction module uses normalized Zernike polynomials to construct an overdetermined linear least squares equation system, combines it with the full-aperture slope field to solve for the coefficient vector, and then weights and synthesizes the full-aperture reconstructed surface. The full-aperture reconstructed surface is then aligned with the theoretical surface pose, and the peak-valley values ​​and root mean square error of the residual surface are calculated.

[0012] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. This invention uses a rotating scanning method to obtain sub-aperture data based on the PMD principle, which solves the technical problem that existing PMD methods are difficult to achieve full aperture coverage in the detection of large-aperture curved surfaces, and realizes full aperture measurement of large-aperture optical surfaces under limited field of view.

[0013] 2. This invention adopts a sub-aperture stitching method based on slope consistency constraints, which overcomes the uncertainty of the integration constant and low-frequency surface distortion introduced by independent integration of sub-apertures in principle. It also effectively suppresses error propagation and accumulation during the stitching process by utilizing global slope constraints of the mirror surface, and finally realizes continuous and smooth full-aperture surface reconstruction and high-precision complete detection of large-aperture optical elements. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic flowchart of the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 2 A schematic diagram of the spatial layout of the detection system corresponding to the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 3 A schematic diagram of the sub-aperture rotation scanning scheme of the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 4 A schematic diagram of the mirror sub-aperture coverage area distribution in the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 5 A schematic diagram of the system ray tracing and measurement principle simulation model of the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 6 A schematic diagram of the X-direction slope distribution after sub-aperture splicing and fusion of the sub-aperture splicing and detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 7A schematic diagram of the Y-direction slope distribution after sub-aperture splicing and fusion of the sub-aperture splicing and detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 8 A schematic diagram of the ideal surface shape of the mirror to be tested in the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 9 A schematic diagram of the reconstructed surface shape of the mirror under test in the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention; Figure 10 This is a schematic diagram of the residual distribution of the mirror under test in the sub-aperture splicing detection method for large-aperture optical elements described in the embodiments of the present invention.

[0015] The attached figures are labeled as follows: 1. Large-aperture optical element under test; 2. Electrically controlled rotary table; 3. Display screen; 4. Camera. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0018] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] In this embodiment, a large-aperture convex spherical mirror is selected as a typical optical element under test for simulation verification. The mirror surface under test is the convex spherical surface of this optical element under test, with a radius of curvature of 1000 mm and an aperture of 300 mm. This implementation uses numerical simulation software as the verification platform, but the core detection method is also applicable to the corresponding physical hardware system construction.

[0022] like Figure 1 and Figure 2 As shown, the sub-aperture splicing detection method for large-aperture optical elements in this embodiment includes the following steps: S1: Set up the testing system, fix the large-aperture optical element 1 to be tested on the electronically controlled rotating stage 2, with the rotation axis coinciding with the normal axis of the center of the mirror to be tested, and place the display screen 3 and camera 4 in a preset space above the mirror to be tested, so that the display screen 3, camera 4 and the center of the mirror to be tested form an asymmetrical triangular geometric layout.

[0023] The system uses an LCD display 3 as the structured light illumination source, along with a camera 4 for data acquisition. This asymmetrical triangular geometric layout breaks the field-of-view limitations of traditional coaxial measurement, effectively expanding the effective field of view for a single measurement. In terms of motion control, the large-aperture optical element 1 under test is fixed on an electrically controlled rotary table 2, ensuring that the rotation axis (Z-axis) coincides with the normal axis of the mirror surface, and switching between different sub-aperture regions is achieved through rotational motion.

[0024] S2: Establish a mirror coordinate system with the center of the mirror to be tested as the origin, define the parameters of the mirror to be tested, and obtain the theoretical surface shape of the mirror to be tested.

[0025] The radius of curvature (ROC) of the mirror under test is defined as 1000 mm, and the aperture is 300 mm. Since the mirror under test in this embodiment is a convex spherical surface, the equation of the sphere is used... Calculate the theoretical mirror height corresponding to each grid point to form the theoretical surface shape of the mirror to be measured, such as... Figure 5 The blue curved surface is shown in the image.

[0026] S3: Rotate the mirror to be tested to different preset angles, and use the rotation matrix to transform the mirror coordinates and their theoretical normal vectors collected by the camera 4 under each sub-aperture to the world coordinate system fixed in space.

[0027] like Figure 3 and Figure 4 As shown, during measurement, the electrically controlled rotary stage 2 sequentially rotates the mirror under test to six preset angles: 0°, 60°, 120°, 180°, 240°, and 300° (in 60° increments). At each angle, the field of view of the camera 4 collecting data on the mirror under test is the sub-aperture. Different colored areas represent the effective measurement field of view of the sub-aperture at different angles. The sub-apertures overlap, forming a complete detection network covering the entire aperture. For each angle... θ Using rotation matrix Coordinates of the mirror sampling points and its theoretical normal vector in the mirror coordinate system Transform to a fixed world coordinate system, which is consistent with the initial mirror coordinate system before rotation.

[0028] S4: Using the fringe reflection method, ray tracing is performed on the sampling points within each sub-aperture. The coordinates of the intersection point from the position of camera 4 through the mirror of the large-aperture optical element 1 to the display screen 3 are calculated, and then the local slope data of the sampling point is calculated.

[0029] The simulation model of the system's ray tracing and measurement principles in the world coordinate system is as follows: Figure 5 As shown in the figure, this illustrates the geometric modeling process based on inverse ray tracing. For a point on the mirror surface under test... Calculate from camera position 4 Vector to that point And normalize it. According to the law of reflection... Calculate the direction of the reflected light, where Let be the unit normal vector at that point. It is known that display screen 3 is located at... Solve for parameters by solving a plane and a set of equations of the same line. t , This allows us to obtain the coordinates of the screen intersection point. .

[0030] The core of PMD is to transform the phase coordinate mapping relationship on the display screen 3 into the slope distribution of the surface of the mirror under test. In this embodiment, the slope is directly derived from geometric relationships, and the unit direction vector of the reflected light is... The angle bisector vector between the incident and reflected light is the normal deviation vector. Local slope of the mirror sampling point and The relationship is .

[0031] S5: Transform the local slope data back to the mirror coordinate system using an inverse rotation matrix, and solve and stitch together the slope data of the overlapping areas of each sub-aperture to obtain the full-aperture slope field. Figure 6 and Figure 7 These are the slope distribution maps of the full aperture in the X and Y directions, obtained after stitching and fusing the sub-apertures. The overlap rate between adjacent sub-apertures and the full aperture coverage are calculated. If the overlap rate or full aperture coverage is lower than a preset threshold, return to step S3 to optimize the sub-aperture layout.

[0032] The slope calculated in the world coordinate system The sub-aperture contribution in the mirror body coordinate system is obtained by using the inverse rotation matrix to transform back to the mirror body coordinate system.

[0033] After all sub-aperture data are acquired, the full-aperture data fusion stage begins. A unified mirror coordinate system mesh is constructed, and the local slope data acquired from each sub-aperture is mapped and projected onto this mirror coordinate system. For overlapping areas between sub-apertures, a slope field weighted fusion strategy based on sampling point position weight allocation is preferred, and the slope data with multiple coverages is normalized and optimized. Through this method, weight factors are assigned according to the relative positions of sampling points in different sub-apertures, achieving a natural transition of slope gradients in overlapping areas, and ultimately synthesizing a continuous and complete full-aperture slope field. .

[0034] Those skilled in the art will understand that the above-described weighted fusion process can also be replaced by conventional algorithms in the field, such as error registration, global consistency optimization, or robust suppression, to adapt to different measurement noise environments.

[0035] To analyze the system's coverage performance, its overlap rate and coverage rate need to be calculated and evaluated. First, the ratio of the number of effective data points within the overlapping area of ​​any two adjacent sub-apertures (e.g., 0° and 60°) to the total data volume of a single sub-aperture is calculated. In the field of sub-aperture splicing detection, it is generally required that adjacent sub-apertures maintain an overlap rate of at least 30% to 40% to ensure that the splicing algorithm can accurately calculate the relative positions between sub-apertures and guarantee the stability of the numerical solution. In accordance with this general principle, this implementation method, through an optimized six-angle rotation layout, increases the average overlap rate of adjacent sub-apertures to 56.42%. This high overlap rate design effectively enhances the constraint on misalignment errors between sub-apertures, ensuring the smooth continuity of the spliced ​​surface. Based on this, further coverage analysis shows that this scheme achieves 100.00% full-aperture coverage, ensuring the complete detection of the entire large-aperture optical surface shape information.

[0036] S6: A system of overdetermined linear least square equations is constructed using normalized Zernike polynomials. The coefficient vector is solved by combining the full-aperture slope field, and the full-aperture reconstructed surface shape is synthesized by weighting. The full-aperture reconstructed surface shape is aligned with the pose of the theoretical surface shape, and the peak-valley values ​​and root mean square error of the residual surface are calculated.

[0037] Zernike polynomials in normalized coordinates are used as the basis function set to characterize the mirror surface shape. Since the data acquired by PMD is wavefront slope (gradient), its global integral result reflects the relative surface shape change. Considering that the global translation term (Piston) does not contain surface shape distortion information, it is not considered in the reconstruction model. The selection of the basis function truncation order is based on the spatial frequency characteristics and edge gradient change characteristics of the mirror under test. For the surface shape characteristics of large-aperture optical elements, this scheme selects a combination of terms with sufficient spatial bandwidth to ensure that the basis functions can not only cover basic aberrations such as defocus, astigmatism, and coma, but also effectively characterize the higher-order aberration components unique to spherical or complex curved surfaces, thereby minimizing the model truncation error and achieving high-precision surface shape reconstruction.

[0038] Establish an overdetermined linear least squares equation system containing full aperture gradient information. Among them, matrix A Each column is represented by the partial derivative of a certain Zernike polynomial at the sampling point. Composition; Vector b For the slope field of the whole aperture Cascaded together; c Let be the Zernike coefficient vector to be determined. This overdetermined least squares problem is solved using numerically stable methods (such as QR decomposition) to obtain the optimal coefficient solution. Using the obtained coefficients, the full-aperture reconstructed surface shape is synthesized. The full-aperture surface shape will then be reconstructed. With theoretical surface shape Pose alignment is performed to eliminate rigid body displacement errors and to obtain the residual surface. Finally, the peak-to-valley (PV) value and root mean square (RMS) error of the residual surface were calculated. Simulation results show that the PV value of the reconstructed residual is 8.65 × 10⁻⁶. -6 nm, RMS value is 1.26 × 10 -6 The result, nm, is at the relative precision limit of computer floating-point operations, verifying the theoretical correctness of the core algorithm of this scheme. Figures 8 to 10 As shown, Figure 8 For the ideal face shape, Figure 9 To reconstruct the surface shape, Figure 10The residual distribution diagram compares the ideal surface shape with the reconstructed surface shape calculated from the full-aperture slope field, intuitively quantifying the difference in three-dimensional morphology between the two.

[0039] In this embodiment, the complete process of steps S1 to S6 was integrated and simulated using numerical simulation software, and the corresponding visualized data results were output. The system optical path layout diagram, sub-aperture coverage area diagram, full aperture slope distribution diagram, surface shape comparison diagram and residual distribution diagram involved are given in each step, which verifies the feasibility of the detection method.

[0040] For the aforementioned 300mm diameter convex spherical mirror, this embodiment utilizes a compact spatial geometry layout combined with high-coverage rotation path planning, requiring only six sub-apertures to achieve full-aperture inspection of the mirror surface under test. This layout, while ensuring inspection integrity, greatly simplifies the mechanical scanning path and reduces data acquisition, significantly improving the overall inspection efficiency of the system.

[0041] Simulation results show that the sub-aperture splicing detection method for large-aperture optical elements proposed in this invention effectively suppresses the cumulative errors commonly found in traditional splicing methods. Figure 10 As shown in the figure, the residual distribution under ideal conditions reveals that the reconstruction error has an extremely low amplitude across the entire aperture range, exhibiting a smooth and continuous distribution. No step effects or periodic splicing ripples related to the sub-aperture arrangement are observed in the figure, verifying that the algorithm achieves a seamless and smooth transition between sub-aperture data. Quantitative analysis shows that the RMS value of the final reconstructed surface shape residual reaches the numerical calculation accuracy limit of 10. -6 nm indicates that under ideal conditions without systematic errors, it has the theoretical potential to achieve high-precision detection.

[0042] The coverage and overlap rate modules integrated in the simulation of the detection method in this embodiment can effectively evaluate the rationality of the scanning path and improve the reliability of the detection process. The detection device corresponding to the detection method in this embodiment adopts a single-axis rotational scanning mechanism and a single camera for data acquisition, which greatly simplifies the mechanical control difficulty and improves the ease of operation.

[0043] It should be noted that the specific large-aperture optical element to be tested is not limited to the convex spherical mirror shown in the embodiments, but can also be a large-aperture plane mirror, concave spherical mirror, aspherical mirror, or freeform surface mirror. For planar or spherical elements, the system structure layout only needs to be adjusted according to the surface geometry to be directly applied; while for complex surfaces such as aspherical or freeform surfaces, thanks to the large dynamic range characteristics of PMD, this detection method does not require the use of dedicated zero-position compensation optical elements. It only requires adjusting the system structure layout and further introducing the corresponding surface equation constraints in the reverse ray tracing model, and then using the same rotation and splicing process to achieve universal detection of various large-aperture reflective optical surfaces.

[0044] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0045] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for detecting the sub-aperture splicing of large-aperture optical elements, characterized in that, Includes the following steps: S1: Set up the testing system, fix the large-aperture optical element to be tested on the electronically controlled rotating stage, with the rotation axis coinciding with the normal axis of the center of the mirror to be tested, and place the display screen and camera in a preset space above the mirror to be tested, so that the display screen, camera and the center of the mirror to be tested form an asymmetrical triangular geometric layout. S2: Establish a mirror coordinate system with the center of the mirror to be tested as the origin, define the parameters of the mirror to be tested, and obtain the theoretical surface shape of the mirror to be tested; S3: Rotate the mirror to be tested to different preset angles, and use the rotation matrix to transform the mirror coordinates and their theoretical normal vectors collected by the cameras under each sub-aperture to the world coordinate system fixed in space; S4: Use the fringe reflection method to perform ray tracing on the sampling points in each sub-aperture, calculate the coordinates of the intersection point reflected from the camera position through the mirror under test to the display screen, and then calculate the local slope data of the sampling point; S5: Transform the local slope data back to the mirror coordinate system through the inverse rotation matrix, and solve and stitch the slope data of the overlapping area of ​​each sub-aperture to obtain the full aperture slope field; calculate the overlap rate between adjacent sub-apertures and the full aperture coverage. If the overlap rate or full aperture coverage is lower than the preset threshold, return to step S3 to optimize the sub-aperture layout. S6: A system of overdetermined linear least square equations is constructed using normalized Zernike polynomials. The coefficient vector is solved by combining the full-aperture slope field, and the full-aperture reconstructed surface shape is synthesized by weighting. The full-aperture reconstructed surface shape is aligned with the pose of the theoretical surface shape, and the peak-valley values ​​and root mean square error of the residual surface are calculated.

2. The method for detecting sub-aperture splicing of large-aperture optical elements according to claim 1, characterized in that, The large-aperture optical element to be tested includes planar, spherical, aspherical, or freeform reflective optical elements; the mirror parameters to be tested in step S2 include radius of curvature and aperture.

3. The method for detecting sub-aperture splicing of large-aperture optical elements according to claim 1, characterized in that, The ray tracing method in step S4 is as follows: based on the principle of reversibility of light path, the incident light vector is calculated starting from the camera position, the direction of reflected light is calculated according to the law of reflection and the normal vector of the current sampling point, and the coordinates of the intersection point of the reflected light and the display screen plane are solved by analytical geometry.

4. The method for detecting sub-aperture splicing of large-aperture optical elements according to claim 1, characterized in that, The overdetermined linear least squares equation system in step S6 is: , where the matrix A Each column is composed of the partial derivatives of the Zernike polynomial at the sampling points, and the vector... b The Zernike coefficient vector is obtained by cascading slope fields across the entire aperture. c The Zernike coefficient corresponding to the translation term is not considered in the full-caliber reconstruction model.

5. A sub-aperture splicing detection device for a large-aperture optical element, used to implement the sub-aperture splicing detection method for a large-aperture optical element as described in any one of claims 1 to 4, characterized in that, include: An electrically controlled rotary stage is used to fix the large-aperture optical element to be tested and drive it to rotate around the rotation axis to different preset angles, with the rotation axis coinciding with the center normal axis of the mirror surface to be tested. The display screen serves as a structured light illumination source for projecting modulated patterns onto the mirror under test. At least one camera is used to capture the modulation pattern after reflection from the mirror under test; The display screen and camera are placed in a preset space above the mirror to be tested, so that the display screen, camera and the center of the mirror to be tested form an asymmetrical triangular geometric layout. The theoretical surface shape construction module is used to establish a mirror coordinate system with the center of the mirror to be tested as the origin, define the parameters of the mirror to be tested, and obtain the theoretical surface shape of the mirror to be tested. The coordinate system transformation module is used to transform the mirror coordinates and their theoretical normal vectors obtained in the mirror coordinate system to the world coordinate system fixed in space through a rotation matrix; and to transform the slope data in the world coordinate system back to the mirror coordinate system through an inverse rotation matrix. The local slope calculation module for the mirror is used to perform ray tracing on the sampling points within each sub-aperture using the fringe reflection method in the world coordinate system, calculate the coordinates of the intersection point reflected from the camera position through the mirror under test to the display screen, and then calculate the local slope data of the sampling point. The slope data fusion processing module is used to solve and stitch together the slope data of the overlapping areas of each sub-aperture to obtain the full-aperture slope field; after generating the measurement counting map, it calculates the overlap rate between adjacent sub-apertures and the full-aperture coverage rate. If the overlap rate or full-aperture coverage rate is lower than the preset threshold, a warning is issued. The full-aperture surface reconstruction module uses normalized Zernike polynomials to construct an overdetermined linear least squares equation system, combines it with the full-aperture slope field to solve for the coefficient vector, and then weights and synthesizes the full-aperture reconstructed surface. The full-aperture reconstructed surface is then aligned with the pose of the theoretical surface, and the peak-valley values ​​and root mean square error of the residual surface are calculated.

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