High-precision lens diopter measuring system and method based on microlens array

Abstract

The invention belongs to the technical field of lens diopter measurement, and particularly relates to a high-precision lens diopter measurement system and method based on a microlens array, and the system comprises a green light LED light source, a beam expander, a collimating lens, a to-be-measured lens, the microlens array, ground glass and an area-array camera, the beam expander is arranged in the light path direction of the green light LED light source, and the collimating lens is arranged in the light path direction of the to-be-measured lens. The collimating lens is arranged in the light path direction of the collimating lens, the to-be-measured lens is arranged in the light path direction of the collimating lens, the micro-lens array is arranged in the light path direction of the to-be-measured lens, the ground glass is arranged in the light path direction of the micro-lens array, and the area-array camera is arranged in the light path direction of the ground glass. According to the invention, the green LED light source is adopted, the diopter of the to-be-measured lens is measured through the micro-lens array by collecting the light spot images before and after the to-be-measured lens is placed, and the whole system is simple in structure, high in precision and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of lens diopter measurement, and particularly relates to a high-precision lens diopter measurement system and method based on a microlens array. Background Art

[0002] In the field of optics, free-form lenses, with their unique surface shape design, can achieve optical performances that are difficult to achieve with traditional spherical and aspherical lenses, such as more accurate aberration correction, more compact optical system layout, etc., and are increasingly widely used in high-end optical instruments, virtual reality devices, vehicle-mounted optics and other fields. However, the surface shapes of free-form lenses are complex and diverse, with characteristics such as non-rotation symmetry and high-order asphericity, which pose severe challenges to the existing sampling point measurement method of automatic lensometers.

[0003] Existing automatic lensometers are mainly designed for traditional regular-shaped lenses. By selecting a limited number of sampling points on the lens surface for measurement, the diopter and other parameters of the entire lens are then inferred. This method can, to a certain extent, meet the measurement requirements for traditional lenses with relatively simple and regular surface shapes. However, the surface topography of free-form lenses is extremely complex, and the parameters such as curvature and tilt at each point change violently and without a fixed pattern. Sampling points cannot comprehensively and accurately reflect the optical characteristics of the entire lens surface. For example, in the edge region of a free-form lens or in a region with a large curvature change, there may be significant optical performance differences in the unmeasured regions between sampling points, resulting in the measurement results not being able to truly reflect the overall quality of the lens and being unable to fully measure and evaluate it. With the continuous expansion of the application of free-form lenses in high-precision optical systems, the need for higher-precision detection of their surface topography is becoming increasingly urgent. The traditional sampling point measurement method has become difficult to meet the requirements of industry development, and new measurement methods are urgently needed to solve this problem.

[0004] The Hartmann diaphragm method is one of the commonly used methods for measuring the diopter of lenses. Its basic principle is to modulate the incident light through the small hole array on the diaphragm, and calculate the diopter and other parameters of the lens by detecting the position deviation of the light passing through the small holes on the image plane. This method has the advantages of relatively simple principle and the ability to achieve a certain degree of automated measurement, and has been widely used in the field of lens diopter measurement.

[0005] However, the traditional Hartmann diaphragm method has a significant technical defect, that is, the small holes cause serious light energy loss. Since there are a large number of small holes distributed on the diaphragm, and the areas between the small holes are blocked, only a very small part of the light can pass through the diaphragm to participate in the measurement, and the light energy loss exceeds 90%. This problem brings a series of negative impacts: on the one hand, the large loss of light energy results in an extremely weak signal intensity reaching the detector, a decrease in the signal-to-noise ratio, and the measurement signal is easily submerged by noise, thus affecting the measurement accuracy; on the other hand, in order to increase the signal intensity, it is necessary to extend the measurement time to accumulate more optical signals, which greatly reduces the measurement speed and is difficult to meet the requirements of rapid lens detection on modern high-efficiency production lines.

[0006] In order to overcome the deficiencies of the traditional Hartmann diaphragm method, the prior art (CN202411321872.8) attempts to introduce a Shack-Hartmann wavefront sensor for wavefront information measurement. The Shack-Hartmann wavefront sensor divides the incident wavefront into multiple sub-wavefronts through a microlens array. Each sub-wavefront is focused by the corresponding microlens, and the wavefront information is obtained by detecting the deviation of the focal position, and then parameters such as the diopter of the lens are calculated. This method improves the accuracy and efficiency of wavefront measurement to a certain extent and can better meet the measurement requirements of the complex surface shape of free-form lenses. However, at the same time, this technology also has obvious limitations: firstly, the manufacturing process of the Shack-Hartmann wavefront sensor is complex, and the processing accuracy requirements for the microlens array are extremely high, resulting in high costs; secondly, its system structure is complex, requiring precise optical elements and complex signal processing circuits, increasing the volume and weight of the equipment, and being subject to certain limitations in practical applications, such as being difficult to integrate into existing medium and small-sized optical detection equipment and having a high maintenance cost. Summary of the Invention

[0007] Aiming at the technical problems that the traditional Hartmann diaphragm method causes light energy loss > 90% due to small hole occlusion, which limits the signal-to-noise ratio and measurement speed and has insufficient high-order aberration analysis, the present invention provides a high-precision lens diopter measurement system and method based on a microlens array. By means of an innovative three-stage calibration method and a coupling term compensation model, the microlens array (MLA) is used for wavefront sensing, which can achieve precise measurement and reduce costs.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A high-precision lens diopter measurement system based on a microlens array, comprising a green LED light source, a beam expander, a collimating lens, a lens to be measured, a microlens array, a ground glass, and a area array camera. The beam expander is arranged in the optical path direction of the green LED light source. The collimating lens is arranged in the optical path direction of the collimating lens. The lens to be measured is arranged in the optical path direction of the collimating lens. The microlens array is arranged in the optical path direction of the lens to be measured. The ground glass is arranged in the optical path direction of the microlens array. The area array camera is arranged in the optical path direction of the ground glass.

[0010] The central wavelength λ of the green LED light source 绿 ranges from 500 nm to 560 nm, and the spectral width of the green LED light source is less than 60 nm.

[0011] The aperture range of the microlens array is from 100 μm to 300 μm, the focal length range of the microlens array is from 2 mm to 10 mm, the arrangement is a hexagonal close packing, and the hexagonal filling factor > 90%.

[0012] A high-precision lens diopter measurement method based on a microlens array, comprising the following steps: S1, calibration of the reference wavefront of the microlens array; S2, measurement of the wavefront of the combined system; S3, analysis of the diopter of the lens to be measured.

[0013] The method for calibrating the reference wavefront of the microlens array in S1 is as follows:

[0014] S1.1. After turning on the green LED light source and without placing the lens to be measured first, perform initialization:

[0015] The green LED light source passes through the collimating lens, then through the microlens array, a spot image is obtained on the ground glass, and the area array camera collects the spot image I at this time ref ;

[0016] Perform sub-pixel Gaussian fitting on the spots of each microlens to obtain the actual spot center (x i , y i ) of each microlens:

[0017]

[0018] Where: I(u, v) represents the gray value of the pixel point with coordinates (u, v) in the spot image collected by the area array camera, A represents the maximum gray value of the spot center, μ x , μ y represent the sub-pixel level center coordinates of the spot to be solved, σ represents the standard deviation of the Gaussian function, and argmin represents finding the parameter that minimizes the sum of squared errors;

[0019] S1.2. Wavefront slope calculation: Generate the theoretical positions (x 0i , y 0i ) of an ideal periodic arrangement, thereby obtaining the wavefront slope of the microlens array;

[0020] S1.3. Zernike polynomial fitting, and solve the aberration coefficients through matrix operations.

[0021] The method for obtaining the wavefront slope of the microlens array in S1.2 is as follows:

[0022]

[0023] Where: p size represents the physical pixel size, f MLA represents the focal length of the microlens array, represents the wavefront slope in the x direction, represents the wavefront slope in the y direction.

[0024] The method for solving the aberration coefficients through matrix operations in S1.3 is as follows:

[0025]

[0026] Where: represents the wavefront slope in the x direction; represents the wavefront slope in the y direction; Z J represents the standard Zernike polynomial, J = 0, 1, 2,...; a J represents the coefficient vector of the Zernike polynomial, J = 0, 1, 2,...

[0027] The method for wavefront measurement of the combined system in S2 is as follows:

[0028] After turning on the green LED light source, place the lens to be measured between the collimating lens and the microlens array. With a fixed spacing d:

[0029] The green LED light source passes through the collimating lens, then through the lens to be measured, and then through the microlens array. A spot image is obtained on the ground glass, and the area array camera captures the spot image I test ;

[0030] Based on sub-pixel Gaussian fitting, obtain the actual spot center (x i , y i ) of each microlens, and obtain the wavefront slope of the microlens array:

[0031]

[0032] Where: represents the wavefront slope of the microlens array; x i′ , yi′ represents the actual measured coordinates of the center of the light spot corresponding to the i-th microlens in the camera pixel coordinate system after placing the lens to be measured; p size represents the physical pixel size; f MLA represents the focal length of the microlens array.

[0033] The method for analyzing the diopter of the lens to be measured in S3 is as follows:

[0034] S3.1. Separate the wavefront slope contributed by the lens to be measured:

[0035]

[0036] where: f MLA represents the focal length of the microlens array, represents separating the wavefront slope contributed by the lens to be measured, represents the wavefront slope of the microlens array, represents the wavefront slope of the microlens array;

[0037] Coupled wavefront slope is caused by the distance d between the lens to be measured and the microlens array:

[0038]

[0039] where: represents the two-dimensional coordinates of the microlens on the microlens array plane;

[0040] S3.2. Diopter calculation:

[0041] Spherical lens power:

[0042]

[0043] where: represents the aberration coefficient of the second-order radial order 0 in the Zernike polynomial; r represents the normalized radius of the microlens array;

[0044] Cylindrical lens power and axis position:

[0045]

[0046] where: C represents the cylindrical lens power of the lens to be measured, r represents the normalized radius of the microlens array, represents the aberration coefficient of the second-order radial order +2 in the Zernike polynomial, represents the aberration coefficient of the second-order radial order -2 in the Zernike polynomial, and θ represents the axis position of the cylindrical lens.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] The present invention adopts a green LED light source, and through a microlens array (MLA), by collecting the spot images before and after placing the lens to be measured, it realizes the measurement of the diopter of the measured lens. The whole system has a simple structure, high precision and low cost; the present invention adopts a high-light-efficiency MLA structure, and the light energy utilization rate is >90%. The present invention is based on a 15th-order aberration decomposition model of Zernike polynomials, which can analyze high-order terms such as coma and spherical aberration. The present invention proposes a mathematical compensation formula for the distance d between the lens and the microlens array to eliminate systematic deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained based on the provided drawings.

[0050] The structures, ratios, sizes, etc. illustrated in this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limited conditions under which the present invention can be implemented. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0051] Figure 1 It is a schematic structural diagram of the present invention.

[0052] Among them: 1 is a green light LED light source, 2 is a beam expander, 3 is a collimating lens, 4 is the lens to be measured, 5 is a microlens array, 6 is a ground glass, and 7 is a area array camera. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] To make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. These descriptions are only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention; based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present application.

[0054] The following will further describe in detail the specific implementation manners of the present invention in conjunction with the drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0055] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "linkage" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0056] A high-precision lens diopter measurement system based on a microlens array, as Figure 1 shown, includes a green LED light source 1, a beam expander 2, a collimating lens 3, a lens to be measured 4, a microlens array 5, a ground glass 6, and an area array camera 7. The beam expander 2 is arranged in the optical path direction of the green LED light source 1, the collimating lens 3 is arranged in the optical path direction of the collimating lens 2, the lens to be measured 4 is arranged in the optical path direction of the collimating lens 3, the microlens array 5 is arranged in the optical path direction of the lens to be measured 4, the ground glass 6 is arranged in the optical path direction of the microlens array 5, and the area array camera 7 is arranged in the optical path direction of the ground glass 6.

[0057] Further, preferably, the central wavelength λ 绿 of the green LED light source 1 ranges from 500 nm to 560 nm, and the spectral width of the green LED light source 1 is less than 60 nm.

[0058] Further, preferably, the aperture range of the microlens array 5 is from 100 μm to 300 μm, the focal length range of the microlens array 5 is from 2 mm to 10 mm, the arrangement pattern is a hexagonal close packing, and the hexagonal filling factor > 90%.

[0059] A high-precision lens diopter measurement method based on a microlens array includes the following steps:

[0060] Step 1. Calibration of the reference wavefront of the microlens array 5.

[0061] Step 1.1. After turning on the green LED light source 1 and without placing the lens to be measured 4 first, perform initialization:

[0062] The green LED light source 1 passes through the collimating lens 3, and then through the microlens array 5, and a spot image is obtained on the ground glass 6. The area array camera 7 collects the spot image I ref ;

[0063] Perform sub-pixel Gaussian fitting on the spots of each microlens to obtain the actual spot center (x i , y i ) of each microlens:

[0064]

[0065] Where: I(u, v) represents the gray value of the pixel at coordinates (u, v) in the spot image collected by the area array camera, A represents the maximum gray value of the spot center, and μ x , μ y represents the sub-pixel level center coordinates of the spot to be solved, σ represents the standard deviation of the Gaussian function, and argmin represents finding the parameter that minimizes the sum of squared errors;

[0066] Step 1.2, Wavefront slope calculation: Generate the theoretical positions (x 0i , y 0i ) of the ideal periodic arrangement, so as to obtain the wavefront slope of the microlens array 5:

[0067]

[0068] Where: p size represents the physical pixel size, f MLA represents the focal length of the microlens array 5, represents the wavefront slope in the x direction, represents the wavefront slope in the y direction.

[0069] Step 1.3, Zernike polynomial fitting, solve the aberration coefficients through matrix operations:

[0070]

[0071] Where: represents the wavefront slope in the x direction; represents the wavefront slope in the y direction; Z J represents the standard Zernike polynomial, J = 0, 1, 2, …; a J represents the coefficient vector of the Zernike polynomial, J = 0, 1, 2, …, J takes 15 orders.

[0072] Step 2, Wavefront measurement of the combined system:

[0073] After turning on the green LED light source 1, place the lens 4 to be measured between the collimating lens 3 and the microlens array 5. Under the condition of a fixed spacing d:

[0074] The green LED light source 1 passes through the collimating lens 3, then passes through the lens 4 to be measured, passes through the microlens array 5, and a spot image is obtained on the ground glass 6. The area array camera 7 collects the spot image I test ;

[0075] Based on sub-pixel Gaussian fitting, obtain the actual spot center (x i , y i ) of each microlens, and obtain the wavefront slope of the microlens array 5:

[0076]

[0077] Wherein: represents the wavefront slope of the microlens array 5; x i′ , y i′ represent the actual measured coordinates of the center of the light spot corresponding to the i-th microlens in the camera pixel coordinate system after placing the lens to be measured; p size represents the physical pixel size; f MLA represents the focal length of the microlens array 5.

[0078] Step 3, Diopter analysis of the lens to be measured 4:

[0079] Step 3.1, Separating the wavefront slope contributed by the lens to be measured 4:

[0080]

[0081] Wherein: f MLA represents the focal length of the microlens array 5, represents separating the wavefront slope contributed by the lens to be measured 4, represents the wavefront slope of the microlens array 5, represents the wavefront slope of the microlens array 5;

[0082] Coupled wavefront slope is caused by the distance d between the lens to be measured 4 and the microlens array 5:

[0083]

[0084] Wherein: represents the two-dimensional coordinates of the microlens on the plane of the microlens array 5;

[0085] Step 3.2, Diopter calculation:

[0086] Spherical lens power:

[0087]

[0088] Wherein: represents the aberration coefficient of the second-order radial order 0 in the Zernike polynomial; r represents the normalized radius of the microlens array;

[0089] Cylindrical lens power and axis position:

[0090]

[0091] Wherein: C represents the cylindrical lens power of the lens to be measured 4, r represents the normalized radius of the microlens array,

[0092] Indicates the aberration coefficient of the second-order radial order +2 in the Zernike polynomial, Indicates the aberration coefficient of the second-order radial order -2 in the Zernike polynomial, and θ represents the axis position of the cylindrical lens.

[0093] Only the preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A high-precision lens diopter measurement system based on a microlens array, characterized in that: It includes a green light LED light source (1), a beam expander (2), a collimating lens (3), a lens to be measured (4), a microlens array (5), a ground glass (6) and an area array camera (7). The beam expander (2) is arranged in the optical path direction of the green light LED light source (1), the collimating lens (3) is arranged in the optical path direction of the collimating lens (2), the lens to be measured (4) is arranged in the optical path direction of the collimating lens (3), the microlens array (5) is arranged in the optical path direction of the lens to be measured (4), the ground glass (6) is arranged in the optical path direction of the microlens array (5), and the area array camera (7) is arranged in the optical path direction of the ground glass (6).

2. The high-precision lens diopter measurement system based on a microlens array according to claim 1, characterized in that: The central wavelength λ of the green LED light source (1) 绿 ranges from 500 nm to 560 nm, and the spectral width of the green LED light source (1) is less than 60 nm.

3. A high-precision lens diopter measurement system based on a microlens array according to claim 1, characterized in that: The aperture range of the microlens array (5) is 100μm - 300μm, the focal length range of the microlens array (5) is 2mm - 10mm, the arrangement mode is hexagonal close packing, and the hexagonal filling factor > 90%.

4. A high-precision lens diopter measurement method based on a microlens array, characterized in that: It includes the following steps: S1. Calibration of the reference wavefront of the microlens array (5); S2. Measurement of the wavefront of the combined system; S3. Resolution of the diopter of the lens to be measured (4).

5. A high-precision lens diopter measurement method based on a microlens array according to claim 4, characterized in that The method for calibrating the reference wavefront of the microlens array in S1 is as follows: S1.

1. After turning on the green light LED light source (1), without placing the lens to be measured (4) first, perform initialization: The green LED light source (1) passes through the collimating lens (3), and then through the microlens array (5), and a spot image is obtained on the ground glass (6). The area array camera (7) acquires the spot image I at this time ref ; Perform sub-pixel Gaussian fitting on the light spot of each microlens to obtain the actual light spot center (x i , y i ) of each microlens: Where: I(u, v) represents the gray value of the pixel point with coordinates (u, v) in the spot image collected by the area array camera, A represents the maximum gray value of the spot center, μ x , μ y represents the sub-pixel center coordinates of the spot to be solved, σ represents the standard deviation of the Gaussian function, and argmin represents the parameter that minimizes the sum of squared errors; S1.

2. Wavefront slope calculation: Generate the theoretical positions (x 0i , y 0i ) of an ideal periodic arrangement, thereby obtaining the wavefront slope of the microlens array (5); S1.

3. Zernike polynomial fitting, and solve the aberration coefficients through matrix operations.

6. The high-precision lens diopter measurement method based on a microlens array according to claim 5, characterized in that, The method for obtaining the wavefront slope of the microlens array (5) in S1.2 is as follows: Where: p size represents the physical size of the pixel, f MLA represents the focal length of the microlens array (5), represents the wavefront slope in the x direction, represents the wavefront slope in the y direction.

7. A high-precision lens diopter measurement method based on a microlens array according to claim 5, characterized in that, The method for solving the aberration coefficients through matrix operations in S1.3 is as follows: Wherein: represents the wavefront slope in the x direction; represents the wavefront slope in the y direction; Z J represents the standard Zernike polynomial, J = 0, 1, 2, …; a J represents the coefficient vector of the Zernike polynomial, J = 0, 1, 2, … 8. A high-precision lens diopter measurement method based on a microlens array according to claim 4, characterized in that, The method for measuring the wavefront of the combined system in S2 is as follows: After turning on the green light LED light source (1), place the lens to be measured (4) between the collimating lens (3) and the microlens array (5). Under the condition of a fixed spacing d: The green LED light source (1) passes through the collimating lens (3), then through the lens under test (4), and through the microlens array (5), and a spot image is obtained on the ground glass (6). The area array camera (7) acquires the spot image I at this time test ; Based on sub-pixel Gaussian fitting, the actual spot center (x i , y i ) of each microlens is obtained, and the wavefront slope of the microlens array (5) is obtained: Wherein: represents the wavefront slope of the microlens array (5); x i ′, y i ′ represent the actually measured coordinates of the center of the light spot corresponding to the i-th microlens in the camera pixel coordinate system after placing the lens to be measured; p size represents the physical pixel size; f MLA represents the focal length of the microlens array (5).

9. A high-precision lens diopter measurement method based on a microlens array according to claim 4, characterized in that The method for resolving the diopter of the lens to be measured (4) in S3 is as follows: S3.

1. Separate the wavefront slope contributed by the lens to be measured (4): where: f MLA represents the focal length of the microlens array (5), represents the separated wavefront slope contributed by the lens under test (4), represents the wavefront slope of the microlens array (5), represents the wavefront slope of the microlens array (5); Coupled wavefront slope Caused by the distance d between the lens under test (4) and the microlens array (5): Wherein: represents the two-dimensional coordinates of the microlens on the plane of the microlens array (5); S3.

2. Diopter calculation: Spherical lens degree: Wherein: represents the aberration coefficient of the second-order radial order 0 in the Zernike polynomial; r represents the normalized radius of the microlens array; Cylindrical lens degree and axis position: Where: C represents the cylindrical lens power of the lens to be measured (4), r represents the normalized radius of the microlens array, represents the aberration coefficient with the second-order radial order +2 in the Zernike polynomial, represents the aberration coefficient with the second-order radial order -2 in the Zernike polynomial, and θ represents the axis position of the cylindrical lens.

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