Complex surface detection methods

Abstract

This invention belongs to the field of optical inspection technology, and particularly relates to a method for inspecting complex curved surfaces. The invention generally consists of three main steps: First, planning the sampling trajectory data of sub-apertures to generate a stitching measurement scheme. Second, using a combination of a high-precision scanning galvanometer with high trajectory following accuracy and a high-precision displacement stage to accurately obtain the position of each individual sub-aperture, and then using a phase retrieval algorithm to obtain the wavefront of each individual sub-aperture. Finally, after the measurement of each sub-aperture is completed, the data is stitched together to obtain the final stitched surface shape result, achieving high-precision and low-cost inspection of the entire complex curved surface. This invention reduces measurement costs and improves measurement efficiency while ensuring the measurement accuracy of large-size, complex curved surfaces, and can provide a feasible method for solving the inspection problem urgently needed in the current field of high-performance optical component processing.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, and in particular relates to a method for detecting complex curved surfaces. Background Technology

[0002] With the continuous development of optical manufacturing technology, the precision requirements for optical components and systems are becoming increasingly stringent, and the application of complex curved surface optical components is becoming more and more widespread. However, traditional optical inspection methods often struggle to achieve high-precision inspection of complex curved surface optical components, especially large-sized ones. Traditional methods typically require standard surface shapes of the same or larger size as the component being measured, which is not only costly but also difficult to manufacture, thus failing to meet the requirements of modern optical systems for high performance, lightweight design, and miniaturization. Therefore, how to reduce inspection costs and difficulties while improving measurement efficiency, while ensuring the measurement accuracy of large-sized complex curved surfaces, is a pressing issue in the field of high-performance optical component inspection. In the field of optical inspection, lateral translation difference phase retrieval technology uses small-aperture inspection equipment to inspect a portion of the aperture of complex optical components or systems, and finally restores the full aperture surface shape through a stitching algorithm. As a flexible, efficient, and high-precision inspection method, it will play an increasingly important role. However, traditional optical inspection methods are still insufficient for high-precision inspection of large-sized complex curved surface optical components, failing to meet the requirements of modern optical systems for high performance, lightweight design, and miniaturization. Existing sub-aperture stitching interferometric testing methods require altering the relative spatial position of the interferometer and the mirror under test, leading to numerous sources of adjustment error (such as fitting errors in the stitching angle). This necessitates highly complex error compensation algorithms, and the resulting apparatus structures are often quite complex. Current sub-aperture stitching testing technologies still suffer from shortcomings in the matching accuracy and efficiency of the SURF algorithm, impacting both the precision and efficiency of the testing. During the stitching measurement process of sub-apertures, the detection results in the edge regions are prone to deviation, and surface shape errors within a single sub-aperture can lead to the accumulation of errors across the entire stitched surface, affecting the surface quality after stitching. Summary of the Invention

[0003] In view of this, the present invention aims to provide a method for detecting complex curved surfaces, to solve the problems of low detection accuracy, high detection cost, high detection difficulty, and error accumulation during the sub-aperture stitching process in existing technologies for large-size and complex curved surface optical elements. To address the above problems, as well as issues such as edge region detection deviation, error accumulation, and complex adjustment, the present invention provides a method for measuring complex curved surfaces based on lateral translational differential phase recovery, employing a combination of a high-precision galvanometer and a high-precision displacement stage to achieve precise sub-aperture positioning.

[0004] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A method for detecting complex curved surfaces includes the following steps: S1: Acquire the sub-aperture sampling trajectory data of the optical element under test. The sub-aperture sampling trajectory data includes the measurement sequence of each sub-aperture, the displacement of the stage corresponding to each sub-aperture, and the deflection angle of each scanning lens corresponding to each sub-aperture. S2: Set up a measurement system. The measurement system includes the optical element to be measured, a displacement stage, and an adjustable aperture, camera, light source and scanning galvanometer fixed on the displacement stage. The parallel beam emitted from the light source is passed through the adjustable aperture and the scanning galvanometer and then sequentially illuminated to each sub-aperture in the measurement order of each sub-aperture. The wavefront of each sub-aperture is recovered by using the camera to collect the results. S3: Perform data preprocessing on the wavefronts of each sub-aperture, and then stitch and fit the preprocessed wavefronts of each sub-aperture to obtain the full-aperture stitched surface shape of the optical element under test, thus completing the complex surface detection of the optical element under test.

[0005] Furthermore, in step S2, the measurement system also includes a beam splitter and a converging lens, both of which are fixed on the displacement stage; Adjusting the displacement stage and the deflection angle of each scanning lens in the scanning galvanometer causes the parallel beam emitted from the light source to be shaped into a target aperture beam by an adjustable aperture. The target aperture beam is reflected by a beam splitter to the scanning galvanometer, which then reflects the target aperture beam to a designated sub-aperture position on the surface of the optical element under test. The beam reflected from the designated sub-aperture position is reflected by the scanning galvanometer, passes through a beam splitter, and is focused by a converging lens, and finally captured by the camera.

[0006] Furthermore, the scanning galvanometer includes an X-axis scanning lens and a Y-axis scanning lens.

[0007] Furthermore, in step S3, data preprocessing includes high-pass filtering and low-pass filtering.

[0008] Furthermore, step S3 also includes: correcting the registration error of the overlapping portion of each sub-aperture wavefront after preprocessing to obtain the effective overlapping area of ​​each sub-aperture. ; in, i and j For adjacent sub-aperture indices with overlapping regions, N The number of sub-aperture pairs participating in the splicing. For the first i The number of pixels in the effective overlapping area of ​​each aperture ( x , y The original measured surface shape data at () No. j The number of pixels in the effective overlapping area of ​​each aperture ( x , yThe original measured surface shape data at ( ) x , y () represents the spatial coordinates within the effective overlapping area. For the first i Each aperture corresponds to the first k Correction coefficients for each error, For the first j Each aperture corresponds to the first k Correction coefficients for each error, For the first k The basis functions of the error, L The number of error types. For the first i Wavefront data after registration error correction for individual apertures; For the first j Wavefront data after registration error correction for each aperture.

[0009] Furthermore, the specific process of stitching and fitting the preprocessed sub-aperture wavefronts to obtain the full-aperture stitched surface shape of the optical element under test is as follows: S31; Construct the least squares objective function: ; in, D i ( x , y ) is the first i The aperture at the pixel ( x , y Measurement surface shape data at ( ); W ( x , y ) represents the wavefront of the sub-aperture to be solved; Δ x i Δ y i The first i Aperture x Directional translation parameters and y Directional translation parameter; Δ Z i For the first i Piston error per orifice; θ xi θ yi The first i Aperture around x , y Shaft tilt error coefficient; ij For the first i Individual aperture and the first j The residual between individual apertures i and jFor adjacent sub-aperture indices with overlapping regions, Ω i For the first i Effective overlap area of ​​individual apertures M The total number of sub-apertures participating in the splicing. The objective function is the least squares function. S32: The first i The first sub-aperture is used as the sub-aperture to be solved, and the second sub-aperture is established. i Mathematical model of individual aperture: D i ( x , y )= W ( x +Δ x i , y +Δ y i )+Δ Z i +θ xi · y +θ yi · x + ij ; ; in, For the first i The attitude parameter vector of each aperture; S33: Constructing a linear least squares model based on the least squares objective function: ; ; in, A i For the first i Aperture N dimensional coefficient matrix, b i For the first i Aperture N A constant vector of dimension, N For the first i The total number of pixels within the effective overlapping area of ​​each aperture. For the first i The spatial position of the first pixel within the effective overlap area of ​​each aperture. For the first i The spatial position of the second pixel within the effective overlap area of ​​the sub-apertures. For the first i Within the effective overlap region of each sub-aperture, the first N The spatial location of each pixel; S34: Based on the linear least squares model, construct the least squares normal equation and solve the . i The attitude parameters of the individual aperture, and the least squares normal equations are: ; S35: Using the first i Sub-aperture replacement i Add 1 sub-aperture, repeat steps S32-S34 until the attitude parameters of all sub-apertures are obtained; S36: Substitute the calculation result of step S35 into the least squares objective function and determine whether the least squares objective function has converged. If it has, obtain the full-aperture splicing surface shape of the optical element under test based on the calculation result of step S35. Otherwise, repeat steps S32-S35 until the least squares objective function converges.

[0010] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The complex surface detection method described in this invention realizes high-precision detection of large-size and complex surface optical components, overcomes the shortcomings of traditional optical detection methods that are difficult to perform high-precision detection of large-size and complex surface optical components, and meets the requirements of modern optical systems for high performance, lightweight and miniaturization.

[0011] (2) The complex surface detection method described in this invention achieves a reasonable layout of sub-apertures by precisely controlling the overlap coefficient and sub-aperture size, effectively reducing detection costs and difficulties, while improving measurement efficiency and measurement accuracy of large-size complex surface optical elements.

[0012] (3) The complex surface detection method described in this invention uses a combination of a high-precision scanning galvanometer and a high-precision displacement stage to achieve precise sub-aperture positioning without changing the relative spatial position of the optical element being measured. This simplifies the measurement system structure, reduces the sources of adjustment error, avoids the use of complex error compensation algorithms, reduces the complexity of the detection system, and lowers the cost.

[0013] (4) The complex surface detection method described in this invention uses a splicing fitting algorithm that is different from ordinary global fitting. The core is that it solves the surface shape distribution of the entire aperture and the relative position and attitude between each sub-aperture based on local error + splicing error (rigid body motion), which effectively reduces the error, avoids the use of complex error compensation algorithms, and improves the measurement accuracy.

[0014] (5) The complex surface detection method described in this invention is a complex surface measurement method based on the phase recovery of lateral translation difference. It can effectively improve the measurement efficiency, ensure the high-precision measurement effect of large-size complex surface components, and has strong practicality, that is, it has important promotion and application value. Attached Figure Description

[0015] 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 complex surface detection method described in the embodiments of the present invention; Figure 2 A schematic diagram of adjacent sub-apertures with overlapping regions as described in an embodiment of the present invention; Figure 2 (a) A schematic diagram of the structure of the optical element under test according to an embodiment of the present invention; Figure 2 (b) A schematic diagram of the structure of the light beam hitting one of the sub-apertures of the optical element under test according to an embodiment of the present invention; Figure 2 (c) A sub-aperture arrangement diagram of the optical element under test as described in the embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the positional relationship and arrangement of the sub-apertures as described in the embodiments of the present invention; Figure 3 (a) A schematic diagram illustrating the positional relationship between adjacent sub-apertures as described in an embodiment of the present invention; Figure 3 (b) A schematic diagram of the sub-aperture arrangement of the concentric pattern described in the embodiment of the present invention; Figure 4 A schematic diagram of the recovered wavefront of the 10th sub-aperture as described in an embodiment of the present invention; Figure 5 The image shows the spliced ​​surface shape result as described in the embodiment of the present invention. 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] like Figure 1 As shown, the present invention provides a method for detecting complex curved surfaces, which specifically includes the following steps: S1: Acquire the sub-aperture sampling trajectory data of the optical element under test. The sub-aperture sampling trajectory data includes the measurement sequence of each sub-aperture, the displacement of the stage corresponding to each sub-aperture (the displacement of the stage in the X-axis and Z-axis), and the deflection angle of each scanning lens (specifically the X-axis scanning lens and the Y-axis scanning lens) corresponding to each sub-aperture. S2: Set up a measurement system. The measurement system includes the optical element to be measured, a displacement stage, and an adjustable aperture, camera, light source and scanning galvanometer fixed on the displacement stage. The parallel beam emitted from the light source is passed through the adjustable aperture and the scanning galvanometer and then sequentially illuminated to each sub-aperture in the measurement order of each sub-aperture. The wavefront of each sub-aperture is recovered by using the camera to collect the results. S3: Perform data preprocessing on the wavefronts of each sub-aperture, and then stitch and fit the preprocessed wavefronts of each sub-aperture to obtain the full-aperture stitched surface shape of the optical element under test, thus completing the complex surface detection of the optical element under test.

[0022] It should be noted that this invention relates to a method for detecting complex curved surfaces based on lateral translation differential phase retrieval technology. This technology requires, after rationally arranging the sampling sequence and motion path of the sub-apertures, to guide the emitted light from the measurement system onto the optical element under test according to the planned sub-aperture data sampling trajectory. The camera acquires images, and the wavefront of each sub-aperture is recovered using a phase retrieval algorithm. After measuring all sub-apertures, the images are stitched together to complete the detection of the complex curved surface. This invention enables high-precision, low-cost detection of large-size, complex curved surface optical elements.

[0023] This invention generally consists of three main steps: First, planning the sampling trajectory data of each sub-aperture to generate a stitching measurement scheme. Second, using a combination of a high-precision scanning galvanometer and a high-precision displacement stage to accurately obtain the position of each individual sub-aperture, and then using a phase retrieval algorithm to obtain the wavefront of each individual sub-aperture. Finally, after the measurement of each sub-aperture is completed, the data is stitched together to obtain the final stitched surface shape result, achieving high-precision and low-cost inspection of the entire complex curved surface. This invention reduces measurement costs and improves measurement efficiency while ensuring the measurement accuracy of large-size and complex curved surfaces, providing a feasible method for solving the inspection problem that urgently needs to be addressed in the current field of high-performance optical component processing.

[0024] In some embodiments, various methods can be used to obtain sub-aperture sampling trajectory data of the optical element under test. The following is a detailed method for constructing sub-aperture sampling trajectory data of the optical element under test: Based on the design parameters and surface features of the optical element under test, an optical system model is established using optical path simulation analysis software. The optical system model includes the optical element under test, a displacement stage, and a light source, camera, adjustable aperture and scanning galvanometer fixed on the displacement stage. The scanning galvanometer consists of two scanning lenses of the same size. The light spot formed on the optical element under test by the parallel beam emitted from the light source after passing through the adjustable aperture and scanning galvanometer is used as the sub-aperture. The specifications of each sub-aperture at different positions of the optical element under test are set according to the complexity of the surface shape. If the surface shape is more complex, the radius of the sub-aperture is smaller, and vice versa, in order to ensure the detection efficiency and accuracy of the surface shape. The overlap coefficient of adjacent sub-apertures (both adjacent sub-apertures are complete circles) at different positions of the optical element under test is the same. The size of the sub-aperture radius is adjusted by adjusting the adjustable aperture.

[0025] The sub-aperture arrangement, sub-aperture size, and center-to-center distance between adjacent sub-apertures are determined based on the optical system model. The optical system model also includes a beam splitter and a converging lens, both of which are fixed on the displacement stage; Adjusting the displacement stage and the deflection angle of each scanning lens in the scanning galvanometer causes the parallel beam emitted from the light source to be shaped into a target aperture beam by an adjustable aperture. The target aperture beam is reflected by a beam splitter to the scanning galvanometer, which then reflects the target aperture beam to a designated sub-aperture position on the surface of the optical element under test. The beam reflected from the designated sub-aperture position is reflected by the scanning galvanometer, passes through a beam splitter, and is focused by a converging lens, and finally captured by the camera.

[0026] The optical element under test and its sub-apertures are visualized and modeled using 3D modeling software to obtain a model of the optical element under test. Extract the two-dimensional coordinates of the center of each sub-aperture of the optical element model under test, and substitute the two-dimensional coordinates of the center of each sub-aperture into the optical system model for optimization calculation to obtain the deflection angle of each scanning lens and the displacement of the stage corresponding to each sub-aperture. The sorting result determined by the orderly sorting of each sub-aperture is used as the measurement order. Combined with the deflection angle of each scanning lens and the movement of the displacement stage corresponding to each sub-aperture, the data sampling path planning is completed.

[0027] The optical path simulation analysis software used is Zemax. The design parameter information of the optical element under test includes the geometric dimensions of the optical element under test, the material parameters of the optical element under test, and the optical performance indicators of the optical element under test.

[0028] Next, the sub-aperture arrangement is determined based on the geometry of the optical element under test: For an optical element with a circular profile, the sub-aperture at the center of the optical element is used as a reference, and annular layers are arranged from the inside to the outside, with the sub-apertures of each annular layer arranged in a regular hexagon. For the optical element under test with a square profile, the sub-apertures are arranged in a serpentine pattern from top to bottom; For the optical element under test with a rectangular profile, the sub-apertures are arranged in a serpentine pattern along the long side.

[0029] It should be noted that in sub-aperture stitching measurements, the sub-aperture size is closely related to the spatial sampling capability of the measurement system. To ensure the accuracy of the phase recovery results, spatial sampling conditions must be met to avoid aliasing.

[0030] Camera spatial sampling frequency for: ;in, This refers to the camera's pixel dimensions.

[0031] Cutoff frequency of optical system for: ;in, The effective aperture diameter of the optical system. The focal length of the optical system. The wavelength of the light source is denoted as .

[0032] According to the Nyquist sampling criterion, the following should be satisfied: ; The maximum allowable diameter of the sub-aperture is: ; After meeting the above requirements, ensure that the diameter of the largest inscribed circle of each scanning lens in the measurement system is less than or equal to the maximum allowable diameter of the sub-aperture. Next, attempt to assign values ​​to the entrance pupil diameter (referring to the sub-aperture size) from largest to smallest, with the maximum value being the same as the radius of the sub-aperture and the radius of the largest inscribed circle of the scanning lens, as detailed below: The specific steps for determining the sub-aperture size include: A1: Assume that the radius of the sub-aperture is the same as the radius of the maximum inscribed circle of the scanning lens, so that the main ray of the outgoing beam emitted from the scanning galvanometer is perpendicularly incident on the eight edge positions of the optical element under test. The eight edge positions are the top edge, bottom edge, left edge, right edge, top left diagonal end, top right diagonal end, bottom left diagonal end, and bottom right diagonal end of the optical element under test. A2: Determine whether the spot size of the light beam reflected from each edge position on each scanning lens is smaller than the light transmission aperture of the corresponding scanning lens. If so, determine the final sub-aperture size based on the radius of the current sub-aperture. Otherwise, decrease the radius of the sub-aperture by a preset step size to obtain the radius of the next sub-aperture. Replace the radius of the current sub-aperture with the radius of the next sub-aperture and repeat step A1 until the spot size of the light beam reflected from each edge position on each scanning lens is smaller than the light transmission aperture of the corresponding scanning lens, and determine the final sub-aperture size.

[0033] Next, set the target overlap coefficient and calculate the center distance between adjacent sub-apertures using the following formula: ≤m; in, r For the sub-aperture radius, d is the center distance between adjacent sub-apertures, and m is the target overlap coefficient of each sub-aperture.

[0034] Furthermore, the target overlap coefficient is between 20% and 75%.

[0035] Furthermore, the above steps also include removing incomplete sub-apertures on the optical element under test. The removal process specifically includes: B1: Select any sub-aperture from all sub-apertures, calculate the overlap area of ​​the current sub-aperture and the sub-apertures adjacent to the current sub-aperture in turn, and calculate the ratio of the overlap area of ​​the current sub-aperture and the sub-apertures adjacent to the current sub-aperture to the total area of ​​the current sub-aperture to obtain the overlap coefficient set corresponding to the current sub-aperture. B2: Replace the current sub-aperture with the next sub-aperture, and repeat step B1 until the set of overlap coefficients corresponding to each sub-aperture is calculated. B3: Compare the overlap coefficients in the overlap coefficient set corresponding to each sub-aperture with the target overlap coefficient, and remove sub-apertures whose overlap coefficients are greater than the target overlap coefficient.

[0036] Furthermore, a two-dimensional coordinate system is established with the center of the sub-aperture circle corresponding to the center of the optical element under test as the origin, the two-dimensional coordinates of each sub-aperture circle center are extracted, and the two-dimensional coordinates of each sub-aperture circle center are recorded in an Excel spreadsheet.

[0037] For ease of understanding, this invention also provides a sub-aperture stitching trajectory path planning method based on a combination of Zemax optical path simulation analysis and SOLIDWORKS 3D modeling software. The specific implementation steps are as follows: Step 1: Based on the design parameters of the optical component under test, establish an optical system model, such as... Figure 3 As shown; Step 101: Based on the design parameters of the optical element under test, establish an optical system model using Zemax optical path simulation analysis software. The design parameters of the optical element under test include: the geometric dimensions of the optical element under test are 48mm × 48mm, the thickness at the center of the optical element is 6mm, the center deviation is 35mm, and the optical performance index of the optical element under test is an off-axis parabolic mirror with a wavelength range of 0.6μm~1.7μm (average reflectivity ≥97%). The off-axis parabolic mirror represents the surface characteristics of the optical element under test, such as... Figure 3 As shown in (a); Step 102: The optical element under test has a circular outline. The sub-aperture at the center of the optical element under test is the first ring of apertures. The sub-apertures in each ring are arranged in a regular hexagon. Finally, at the edge of the optical element under test, some sub-apertures are added or removed according to the overlap coefficient requirements. That is, sub-apertures with an overlap coefficient greater than m are removed.

[0038] Step 2: Determine the sub-aperture radius r and the center distance of adjacent sub-apertures d Generate sub-aperture layout schemes.

[0039] Step 201: In the optical system model, under the premise of satisfying the maximum allowable diameter of the sub-aperture, try to assign values ​​to the entrance pupil diameter (referring to the size of the sub-aperture) from large to small, with the maximum value being that the radius of the sub-aperture is the same as the radius of the largest inscribed circle of the scanning lens. Adjust from large to small according to a preset step size, specifically 0.1mm. Ensure that the principal ray of the incident beam hits the eight edges of the optical element under test perpendicularly: directly above, directly below, directly left, directly right, 45-degree upper right, 45-degree lower right, 45-degree upper left, and 45-degree lower left. Figure 3As shown in (b). The radius of the sub-aperture is finally determined by checking whether the spot size of the light beam reflected from these 8 points on both scanning lenses is smaller than the aperture of the corresponding scanning lens. r It is 7mm; Step 202: Based on the overlap coefficient calculation formula and the optimized sub-aperture overlap coefficient (overlap coefficient between 20% and 75%), considering splicing efficiency and splicing accuracy, this embodiment sets the target overlap coefficient to 27.75%, and determines the center-to-center distance d between adjacent sub-apertures to be 8.5mm, which can cover a 48mm off-axis parabolic surface. ≤27.75%; like Figure 4 As shown, r For the sub-aperture radius, d α is the distance between the centers of adjacent sub-apertures, and α is the angle between the two intersection points of adjacent sub-apertures relative to the center of one of the sub-apertures; D is the diameter of the optical element to be measured. It is the area of ​​the sector; It is the area of ​​the triangle; It represents the shaded area, i.e., the area of ​​the overlapping region.

[0040] Step 203: Based on the determined sub-aperture arrangement, sub-aperture radius, and center distance between adjacent sub-apertures, use SOLIDWORKS 3D modeling software to perform 3D visualization modeling of the optical element under test and each sub-aperture to generate a sub-aperture layout scheme.

[0041] Step 3: Plan the sub-aperture trajectory path and generate a splicing measurement scheme.

[0042] Step 301: Based on the above operations, a total of 19 sub-apertures are obtained. Taking the 10th sub-aperture as point (0, 0), their coordinates are (-8.5, 14.72243186), (0, 14.72243186), (8.5, 14.72243186), (12.75, 7.36121593), (4.25, 7.36121593), (-4.25, 7.36121593), (-12.75, 7.36121593). (-17, 0), (-8.5, 0), (0, 0), (8.5, 0), (17, 0), (12.75, -7.36121593), (4.25, -7.36121593), (-4.25, -7.36121593), (-12.75, -7.36121593), (-8.5, -14.72243186), (0, -14.72243186), and (8.5, -14.72243186). Record the coordinates of the center of each sub-aperture in SOLIDWORKS using an Excel spreadsheet. Step 302: For each sub-aperture, the principal ray of the incident beam must hit the center of the corresponding sub-aperture and return along the original path, i.e., the principal ray must be perpendicularly incident on the surface of the optical element under test. This needs to be achieved by adjusting the angles of the X-axis scanning lens, the Y-axis scanning lens, and the position of the displacement stage relative to the optical element under test for different sub-apertures. This means that for different sub-apertures, the variables set in the optical system model established in the Zemax software need to be optimized each time to give the deflection angle of each scanning lens and the movement of the displacement stage in the X and Z axes. The two-dimensional coordinates of the centers of the 19 sub-apertures in Step 301 are sequentially input into the optical system model established in the Zemax software to optimize the corresponding X and Z directions of the displacement stage and the deflection angles of each scanning lens, which constitute the sub-aperture trajectory path. Step 303, as follows Figure 3 As shown in (c), all sub-apertures are numbered and sorted so that adjacent sub-apertures are also adjacent in actual position. The numbers are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19, which is to generate the splicing measurement scheme and complete the planning of the sub-aperture sampling path. During the detection process, the data of each sub-aperture is sampled in sequence to guide the data processing during splicing.

[0043] In some embodiments, in step S2, the measurement system further includes a beam splitter and a converging lens, both of which are fixed on the displacement stage; Adjusting the displacement stage and the deflection angle of each scanning lens in the scanning galvanometer causes the parallel beam emitted from the light source to be shaped into a target aperture beam by an adjustable aperture. The target aperture beam is reflected by a beam splitter to the scanning galvanometer, which then reflects the target aperture beam to a designated sub-aperture position on the surface of the optical element under test. The beam reflected from the designated sub-aperture position is reflected by the scanning galvanometer, passes through a beam splitter, and is focused by a converging lens, and finally captured by the camera.

[0044] like Figure 3 As shown in (a), the shaded area is the overlapping area of ​​the two sub-apertures, which is the core area for subsequent data fusion and registration error correction: Only by comparing the common measurement data of the overlapping area can the attitude errors such as translation and tilt between the sub-apertures be calculated, providing constraints for subsequent stitching.

[0045] like Figure 3 As shown in (b), D The diameter of the full aperture of the optical element under test. r The radius of a single sub-aperture. a The angle subtended by the two intersection points of adjacent sub-apertures relative to the center of one of the sub-apertures. dThe distance between the centers of adjacent sub-apertures reflects the distribution characteristics of sub-apertures in the concentric mode. By arranging multiple layers of sub-apertures in a concentric circle, complete coverage of the entire aperture is ensured, and the dense constraint of the central overlap area effectively reduces the accumulation of splicing errors, enabling surface shape detection of large-aperture optical elements.

[0046] In some embodiments, the method for recovering the wavefront of each sub-aperture in step S2 is prior art, and has been recorded in the following journals: (1) Ma Xinxue, Wang Jianli, Wang Bin. Research on phase retrieval technology algorithm [J]. Laser & Infrared, 2012, 42(2):217-221; (2) Ma Xinxue, Wang Jianli, Wang Bin, Wang Zongyang. Quantitative analysis of measurement accuracy of phase retrieval wavefront sensor [J]. Acta Optica Sinica, 2013, 33(10):10280011; (3) Ma Xinxue, Wang Jianli, Wang Bin. Detection of spherical mirror shape using phase retrieval wavefront sensing technology [J]. Infrared & Laser Engineering, 2014, 43(10):3428-3433.

[0047] It should be noted that after installing the optical element under test, adjusting its position so that the light spot emitted by the galvanometer hits the center of the optical element under test when it is initially powered on, the optical system and data acquisition system are started; the measurement system is moved so that the light source hits the optical element under test one by one according to the planned sub-aperture measurement sequence; the camera sequentially acquires the corresponding image of each sub-aperture, and the phase retrieval algorithm is used to recover the wavefront of each single sub-aperture.

[0048] like Figure 4 As shown, this is the recovered wavefront of the 10th sub-aperture.

[0049] In some embodiments, in step S3, data preprocessing includes high-pass filtering and low-pass filtering.

[0050] In some embodiments, step S3 further includes: correcting the registration error of the overlapping portion of each sub-aperture wavefront after preprocessing to obtain the effective overlapping region of each sub-aperture. ; in, i and j For adjacent sub-aperture indices with overlapping regions, N The number of sub-aperture pairs participating in the splicing. For the first i The number of pixels in the effective overlapping area of ​​each aperture ( x , y The original measured surface shape data at () No. j The number of pixels in the effective overlapping area of ​​each aperture ( x , yThe original measured surface shape data at ( ) x , y () represents the spatial coordinates within the effective overlapping area. For the first i Each aperture corresponds to the first k Correction coefficients for each error, For the first j Each aperture corresponds to the first k Correction coefficients for each error, For the first k The basis functions of the error, L The number of error types. For the first i Wavefront data after registration error correction for individual apertures; For the first j Wavefront data after registration error correction for each aperture.

[0051] It should be noted that registration error correction is used to solve the problem of "misalignment": when stitching sub-aperture wavefronts, if the wavefront data of adjacent sub-apertures in the overlapping area are used directly, mismatch will occur due to various errors. These errors specifically include: 1) Rigid body error: caused by translation, rotation, and tilt between sub-apertures (such as minute displacement of the measuring platform or lens installation error); 2) Low-order aberration errors: caused by defocus, astigmatism, etc. (due to temperature drift and vibration during measurement); 3) Systematic error: Inconsistent reference between different sub-apertures.

[0052] Using methods such as least squares, the correction coefficients for each sub-aperture are solved by utilizing common data from the overlapping regions. F k ， Registration error correction is achieved; these coefficients are used to correct the wavefront of each sub-aperture; after correction, the data differences between all adjacent sub-apertures in the overlapping area are minimized, achieving "seamless alignment". Without this step, direct stitching will result in steps and abrupt changes in the overlapping area, making it impossible to obtain a continuous and smooth overall wavefront.

[0053] Once all sub-apertures have completed registration error correction, the stitching and fitting stage can begin, where the corrected sub-aperture wavefronts are fused into a complete large-aperture wavefront. For non-overlapping regions, the corrected sub-aperture data can be directly retained. For overlapping regions, a weighted average fusion is used. Finally, a continuous and smooth overall wavefront (i.e., the wavefront of the optical element under test) covering the entire aperture is obtained.

[0054] In summary, registration error correction is to "calibrate" all sub-apertures to the same coordinate system, eliminating misalignment and deviation between them; stitching fitting is to "seamlessly stitch" the calibrated sub-apertures into a complete wavefront according to rules.

[0055] In some embodiments, the specific process of stitching and fitting the preprocessed sub-aperture wavefronts to obtain the full-aperture stitched surface shape of the optical element under test is as follows: S31; Construct the least squares objective function: ; in, D i ( x , y ) is the first i The aperture at the pixel ( x , y Measurement surface shape data at ( ); W ( x , y ) represents the wavefront of the sub-aperture to be solved; Δ x i Δ y i The first i Aperture x Directional translation parameters and y Directional translation parameter; Δ Z i For the first i Piston error per orifice; θ xi θ yi The first i Aperture around x , y Shaft tilt error coefficient; ij For the first i Individual aperture and the first j The residual between individual apertures i and j For adjacent sub-aperture indices with overlapping regions, Ω i For the first i Effective overlap area of ​​individual apertures M The total number of sub-apertures participating in the splicing. The objective function is the least squares function. S32: The first i The first sub-aperture is used as the sub-aperture to be solved, and the second sub-aperture is established. i Mathematical model of individual aperture: D i ( x , y )= W( x +Δ x i , y +Δ y i )+Δ Z i +θ xi · y +θ yi · x + ij ; ; in, For the first i The attitude parameter vector of each aperture; S33: Constructing a linear least squares model based on the least squares objective function: ; ; in, A i For the first i The N-dimensional coefficient matrix of each aperture b i For the first i Aperture N A constant vector of dimension, N For the first i The total number of pixels within the effective overlapping area of ​​each aperture. For the first i The spatial position of the first pixel within the effective overlap area of ​​each aperture. For the first i The spatial position of the second pixel within the effective overlap area of ​​the sub-apertures. For the first i Within the effective overlap region of each sub-aperture, the first N The spatial location of each pixel; S34: Based on the linear least squares model, construct the least squares normal equation and solve the . i The attitude parameters of the individual aperture, and the least squares normal equations are: ; S35: Using the first i Sub-aperture replacement i Add 1 sub-aperture, repeat steps S32-S34 until the attitude parameters of all sub-apertures are obtained; S36: Substitute the calculation result of step S35 into the least squares objective function and determine whether the least squares objective function has converged. If it has, obtain the full-aperture splicing surface shape of the optical element under test based on the calculation result of step S35. Otherwise, repeat steps S32-S35 until the least squares objective function converges.

[0056] It should be noted that the measurement data preprocessing includes noise filtering and data calibration. High-pass and low-pass filters are used for noise filtering, and data calibration is performed. A weighted average data fusion method is used to process the data in overlapping areas, and registration error correction is applied to all adjacent sub-apertures with overlapping areas to minimize differences. The least squares fitting method is used to calculate the relative stitching coefficients between sub-apertures, and the stitching measurement results are corrected based on the stitching coefficients to obtain the final stitched surface shape result, such as... Figure 5 As shown.

[0057] The specific process is as follows: 1. Initialization: Roughly align all sub-apertures to their initial positions.

[0058] 2. Global Fitting: With fixed attitude parameters, the current global surface shape is fitted using least squares.

[0059] 3. Local registration: With the global surface shape fixed, solve the above least squares problem separately for each sub-aperture and update its attitude parameters.

[0060] 4. Iteration: Repeat steps 2 and 3 until the residuals converge.

[0061] 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.

[0062] 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 complex curved surfaces, characterized in that: Specifically, the steps include the following: S1: Acquire the sub-aperture sampling trajectory data of the optical element under test. The sub-aperture sampling trajectory data includes the measurement sequence of each sub-aperture, the displacement of the stage corresponding to each sub-aperture, and the deflection angle of each scanning lens corresponding to each sub-aperture. S2: Set up a measurement system. The measurement system includes the optical element to be measured, a displacement stage, and an adjustable aperture, camera, light source and scanning galvanometer fixed on the displacement stage. The parallel beam emitted from the light source is passed through the adjustable aperture and the scanning galvanometer and then sequentially illuminated to each sub-aperture in the measurement order of each sub-aperture. The wavefront of each sub-aperture is recovered by using the camera to collect the results. S3: Perform data preprocessing on the wavefronts of each sub-aperture, and then stitch and fit the preprocessed wavefronts of each sub-aperture to obtain the full-aperture stitched surface shape of the optical element under test, thus completing the complex surface detection of the optical element under test.

2. The method for detecting complex curved surfaces according to claim 1, characterized in that: In step S2, the measurement system also includes a beam splitter and a converging lens, both of which are fixed on the displacement stage; Adjusting the displacement stage and the deflection angle of each scanning lens in the scanning galvanometer causes the parallel beam emitted from the light source to be shaped into a target aperture beam by an adjustable aperture. The target aperture beam is reflected by a beam splitter to the scanning galvanometer, which then reflects the target aperture beam to a designated sub-aperture position on the surface of the optical element under test. The beam reflected from the designated sub-aperture position is reflected by the scanning galvanometer, passes through a beam splitter, and is focused by a converging lens, and finally captured by the camera.

3. The method for detecting complex curved surfaces according to claim 1, characterized in that: The scanning galvanometer includes an X-axis scanning lens and a Y-axis scanning lens.

4. The method for detecting complex curved surfaces according to claim 1, characterized in that: In step S3, data preprocessing includes high-pass filtering and low-pass filtering.

5. The method for detecting complex curved surfaces according to claim 1, characterized in that: Step S3 further includes: correcting the registration error of the overlapping portion of each sub-aperture wavefront after preprocessing to obtain the effective overlapping area of ​​each sub-aperture. ； in, i and j For adjacent sub-aperture indices with overlapping regions, N The number of sub-aperture pairs participating in the splicing. For the first i The number of pixels in the effective overlapping area of ​​each aperture ( x , y The original measured surface shape data at () No. j The number of pixels in the effective overlapping area of ​​each aperture ( x , y The original measured surface shape data at ( ) x , y () represents the spatial coordinates within the effective overlapping area. For the first i Each aperture corresponds to the first k Correction coefficients for each error, For the first j Each aperture corresponds to the first k Correction coefficients for each error, For the first k The basis functions of the error, L The number of error types. For the first i Wavefront data after registration error correction for individual apertures; For the first j Wavefront data after registration error correction for each aperture.

6. The method for detecting complex curved surfaces according to claim 5, characterized in that: The specific process of stitching and fitting the pre-processed sub-aperture wavefronts to obtain the full-aperture stitched surface shape of the optical element under test is as follows: S31; Construct the least squares objective function: ； in, D i ( x , y ) is the first i The aperture at the pixel ( x , y Measurement surface shape data at ( ); W ( x , y ) represents the wavefront of the sub-aperture to be solved; Δ x i Δ y i The first i Aperture x Directional translation parameters and y Directional translation parameter; Δ Z i For the first i Piston error per orifice; θ xi θ yi The first i Aperture x , y Shaft tilt error coefficient; ij For the first i Individual aperture and the first j The residual between individual apertures i and j For adjacent sub-aperture indices with overlapping regions, Ω i For the first i Effective overlap area of ​​individual apertures M The total number of sub-apertures participating in the splicing. The objective function is the least squares function. S32: The first i The first sub-aperture is used as the sub-aperture to be solved, and the second sub-aperture is established. i Mathematical model of individual aperture: D i ( x , y )= W ( x +D x i , y +D y i )+D Z i +θ xi · y +θ yi · x + ij ; ； in, For the first i The attitude parameter vector of each aperture; S33: Constructing a linear least squares model based on the least squares objective function: ； ； in, A i For the first i Aperture N dimensional coefficient matrix, b i For the first i An N-dimensional constant vector of individual apertures N For the first i The total number of pixels within the effective overlapping area of ​​each aperture. For the first i The spatial position of the first pixel within the effective overlap area of ​​each aperture. For the first i The spatial position of the second pixel within the effective overlap area of ​​the sub-apertures. For the first i Within the effective overlap region of each sub-aperture, the first N The spatial location of each pixel; S34: Based on the linear least squares model, construct the least squares normal equation and solve the . i The attitude parameters of the individual aperture, and the least squares normal equations are: ； S35: Using the first i Sub-aperture replacement i Add 1 sub-aperture, repeat steps S32-S34 until the attitude parameters of all sub-apertures are obtained; S36: Substitute the calculation result of step S35 into the least squares objective function and determine whether the least squares objective function has converged. If it has, obtain the full-aperture splicing surface shape of the optical element under test based on the calculation result of step S35. Otherwise, repeat steps S32-S35 until the least squares objective function converges.

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