A method for analyzing stress within an optical effective diameter of a lens

Abstract

The present application relates to lens detection technical field, specifically to a kind of lens optical effective diameter inner stress analysis method, comprising the following steps: the actual outer diameter of lens and the actual optical effective diameter size of lens are measured;The inner stress of lens is measured by stress meter, and the measurement area image covering actual lens is obtained;All boundary points of boundary stress value are found to obtain boundary point set;The outer diameter of lens in measurement area image is obtained;The effective diameter of lens in measurement area image is obtained, to carry out data analysis to the inner stress in lens effective diameter.The present application places lens on stress meter stage, detects stress, saves the pixel point data of measurement area image;The data in image is least square method fitting circle, and the outer diameter of lens under image coordinate system is obtained, then the optical effective diameter size under image coordinate system can be deduced, and the present application carries out region identification according to the structure data of lens, and carries out inner stress data analysis in optical effective diameter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lens detection, and particularly to a lens optical effective diameter inner stress analysis method. BACKGROUND

[0002] Optical lenses are one of the key components of precision optical instruments. During installation, optical lenses are often installed and fixed using glue or screws in the radial direction of the lens. Assembly forces such as glue joint force and screw pre-tightening force will form radial loads on the lens and cause unevenly distributed stresses in the lens, thereby affecting the imaging accuracy of the optical system.

[0003] For example, the application No. CN202110016131.9 provides a radial loading device for optical lens stress testing, which can perform radial quantitative loading test on optical lenses with different load sizes and quantities. The device includes a base plate, a lens support platform, a force application system, and a force measurement system. The lens support platform and the force application system are fixed on the base plate through a connecting piece, and the force measurement system is connected to the base plate through a movable connecting piece. The movable connecting piece can move along the radial direction of the lens. The force application system generates force by compressing the spring with a screw, and the sensor of the measurement system measures the force size, thereby achieving accurate control of the radial load size and direction. The present application realizes the radial quantitative loading of optical lenses, has high loading direction accuracy, and has a large adjustment range of load quantity and size, which can be applied to the radial loading of optical lenses of various sizes. The present application can be widely applied to the study of stress distribution state of high-precision optical elements and quantitative mapping relationship between assembly force and internal stress state of optical elements.

[0004] The above-mentioned patent can detect the stress distribution state of the lens. However, the current stress meter can detect the internal stress size of the lens and output the maximum value, average value, and minimum value of the internal stress in a specific range. However, the limitation is that the specific range selected is subjective and cannot accurately output the maximum value, average value, and minimum value of the internal stress in the optical effective diameter of the lens when analyzing the stress size and distribution in the optical effective diameter of the lens. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the prior art, and provides a lens optical effective diameter inner stress analysis method.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a lens optical effective diameter inner stress analysis method, comprising the following steps:

[0007] Step 1, measuring the actual outer diameter of the lens and the actual optical effective diameter of the lens;

[0008] Step 2, measure the internal stress of the lens by the stress meter, obtain a measurement area image covering the actual lens, the measurement area image is in a size scaling relationship with the actual lens, save the pixel data of the measurement area image, one pixel point corresponds to one stress value;

[0009] Step 3, set a boundary stress value for distinguishing the lens and the measurement background according to the experimental situation, find all boundary points of the boundary stress value in the measurement area image to obtain a boundary point set;

[0010] Step 4, fit a circle to the boundary point set by the least square method to obtain the outer diameter of the lens in the measurement area image;

[0011] Step 5, according to the size scaling relationship between the lens image in the measurement area image and the actual lens, there is a formula: actual outer diameter of the lens / image outer diameter of the lens=actual optical effective diameter of the lens / image effective diameter of the lens, obtain the effective diameter of the lens in the measurement area image to analyze the internal stress in the effective diameter of the lens.

[0012] Further, the stress meter adopts a birefringence stress meter, and the stress is represented by an optical path difference.

[0013] Further, before measuring the internal stress of the lens by the stress meter, the stress meter stage is cleaned with an organic solvent.

[0014] Further, the boundary stress value is greater than 4nm.

[0015] Further, in step 3, the measurement area image is divided into left and right halves, and the boundary points of the left and right halves of the measurement area image are obtained respectively.

[0016] Further, the step 4 specifically includes:

[0017] According to the center (A, B) and the radius R, a circle on the plane can be determined, and the general formula of the circle equation on the plane is x 2 +y 2 +ax+by+c=0, which is a linear equation about a, b and c;

[0018] The center (A, B) and the radius R have the following equation set (1):

[0019]

[0020] A mathematical model of circle fitting is created by using the least square method to obtain the values of parameters a, b and c, and then the actual parameters A, B and R of the circle are obtained according to the equation set;

[0021] The mathematical model of circle fitting is created by using the least square method as follows:

[0022] N (N≥3) groups of data (x i , y i ), (i=1, 2, 3, …, N) of the boundary point set are obtained, according to the general formula and the least square principle, the minimum value of the objective function is required, the partial derivatives of F (a, b, c) with respect to a, b, and c are taken, and the partial derivatives are set to zero to obtain extreme points, as follows: let That is:

[0023]

[0024] Let:

[0025]

[0026]

[0027] Then:

[0028]

[0029] Solving the above equations can obtain a, b, and c:

[0030]

[0031] Wherein:

[0032]

[0033] The center and radius of the circle of the outer diameter of the lens in the image can be obtained from the equation set (1).

[0034] Further, after fitting the circle to the boundary point set by the least square method, the median filtering is performed on the full lens region in the image.

[0035] Further, the median filtering detailed process is as follows:

[0036] Suppose that the measurement region image has m rows and k columns of pixel points, and the following operations are performed on the pixel point data: taking the ith row and jth column as an example (2<=i<=m-1, 2<=j<=k-1), taking a 3x3 neighborhood thereof, and sorting the 9 data in the neighborhood from small to large, and taking the median of the 9 numbers to represent the data of the ith row and jth column.

[0037] The beneficial effects of the present application: from the above description of the present application, compared with the prior art, the lens optical effective diameter stress analysis method of the present application includes placing the lens on the alcohol decontamination stress instrument stage, detecting the stress, saving the pixel point data of the measurement area image; the row and column of the region pixel point data in the image are regarded as the abscissa and ordinate of the coordinate system, so that the least square method fitting circle of the data in the image can be obtained, the outer diameter of the lens in the image coordinate system is obtained, then the size of the optical effective diameter in the image coordinate system can be deduced, and the median filter processing is carried out, the maximum value, the average value and the minimum value of the stress in the optical effective diameter of the lens are analyzed, the present application carries out the internal stress data analysis in the optical effective diameter according to the structure data of the lens, and avoids the human measurement error caused by the human selection of the region; at the same time, the median filter process is introduced, and the influence of dirt on the maximum value of internal stress is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The step flow chart of the lens optical effective diameter stress analysis method in the preferred embodiment of the present application is shown in the figure.

[0039] Figure 2 The structure diagram of the measurement area image in the preferred embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0040] The technical solutions in the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0041] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] Referring to Figure 1 The preferred embodiment of the present application, a lens optical effective diameter stress analysis method, includes the following steps:

[0043] Step 1, the actual outer diameter of the lens and the actual optical effective diameter of the lens are measured;

[0044] Step 2, measure the internal stress of the lens by the stress instrument, obtain the measurement area image covering the actual lens, the measurement area image is in a size scaling relationship with the actual lens, save the pixel point data of the measurement area image, one pixel point corresponds to one stress value;

[0045] Step 3, according to the experimental situation, set the boundary stress value for distinguishing the lens and the measuring background, in the measuring area image, find all the boundary points of the boundary stress value to obtain a boundary point set;

[0046] Step 4, fit a circle to the boundary point set by the least square method, and obtain the outer diameter of the lens in the measuring area image;

[0047] Step 5, according to the size scaling relationship between the lens image in the measuring area image and the actual lens, there is a formula: the actual outer diameter of the lens / image outer diameter of the lens = the actual optical effective diameter of the lens / image effective diameter of the lens, the effective diameter of the lens in the measuring area image is obtained, and the internal stress in the effective diameter of the lens is analyzed.

[0048] Referring to Figure 2 As shown in the figure, the lens is placed on the measuring background, the measuring area image is a square image, each pixel point corresponds to a stress value, the lens in the image includes a lens optical effective area and a lens non-optical effective area, the outer diameter of the lens optical effective area is the effective diameter of the lens in the image, the outer diameter of the lens non-optical effective area is the outer diameter of the lens in the image, and the boundary point set is the junction of the measuring background and the lens non-optical effective area.

[0049] The lens optical effective diameter internal stress analysis method of the application includes placing the lens on the stress instrument platform cleaned by alcohol, detecting the stress, and saving the pixel point data of the measuring area image; regarding the row and column of the region pixel point data in the image as the horizontal coordinate and the vertical coordinate of the coordinate system, so that the least square method can be used to fit a circle to the data in the image, the outer diameter of the lens in the image coordinate system is obtained, then the size of the optical effective diameter in the image coordinate system can be deduced, and then the maximum value, the average value and the minimum value of the internal stress in the optical effective diameter of the lens are analyzed through median filtering processing. The application performs region recognition according to the structure data of the lens, and performs internal stress data analysis in the optical effective diameter, so that the human measurement error caused by manual selection of the region is avoided; and the median filtering process is introduced, so that the influence of dirt on the maximum value of the internal stress is reduced.

[0050] As a preferred embodiment of the application, it can also have the following additional technical features:

[0051] In this embodiment, the stress instrument is a birefringence stress instrument, and the stress is represented by the optical path difference. Specifically, the stress instrument is a stress birefringence instrument of Shanghai Zaoqing Photonic brand, model WPA-200, and the unit of stress is nm.

[0052] In this embodiment, before measuring the internal stress of the lens by the stress instrument, the stress instrument platform is cleaned and decontaminated by using an organic solvent. The cleaning and decontamination treatment is performed before measurement, so as to avoid the influence of dirt on the measurement result, and the organic solvent can be alcohol.

[0053] In the embodiment, the boundary stress value is greater than 4 nm. Experimental verification shows that the stress value of the measurement background is between 0-3 nm, and the stress value of the lens is greater than 4 nm, so the boundary stress value for distinguishing the lens and the measurement background is greater than 4 nm.

[0054] In the embodiment, in step 3, the measurement area image is divided into left and right halves, and the boundary points of the left and right halves of the measurement area image are found respectively. The measurement area image is divided into left and right halves, and the first point with a stress value greater than 4 nmd on the left and right sides is found as the boundary point on the left and right sides by searching from the left and right sides to the middle, and finally all the boundary points on the left and right sides form a boundary point set.

[0055] In the embodiment, step 4 specifically includes:

[0056] According to the center (A, B) and the radius R, a circle on the plane can be determined, and the general formula of the circle equation on the plane is x 2 +y 2 +ax+by+c=0, which is a linear equation about a, b and c;

[0057] The center (A, B) and the radius R of the circle have the following equation set (1):

[0058]

[0059] A mathematical model of circle fitting is created by using the least square method to obtain the values of parameters a, b and c, and then the actual parameters A, B and R of the circle are obtained according to the equation set;

[0060] Next, a mathematical model of circle fitting is created by using the least square method:

[0061] In the obtained N (N≥3) groups of data (x i , y i ), (i=1, 2, 3, …, N), according to the general formula and the least square method principle, the minimum value of the objective function is required, the partial derivatives of F(a, b, c) with respect to a, b and c are taken, and the partial derivatives are set to zero to obtain the extreme point, which is as follows: let that is:

[0062]

[0063] Let:

[0064]

[0065]

[0066] Then:

[0067]

[0068] Solving the above equation can obtain a, b, c:

[0069]

[0070] Wherein:

[0071]

[0072] Again, the equation set (1) can be obtained from the center and radius of the lens in the image.

[0073] In this embodiment, after fitting the circle to the boundary point set by the least square method, the full lens region in the image is median filtered, and the detailed process of the median filtering is as follows:

[0074] Suppose that the measurement region image has m rows and k columns of pixel points, and the pixel point data is operated as follows: taking the ith row and jth column as an example (2 <= i <= m-1, 2 <= j <= k-1), taking its 3x3 neighborhood, sorting the 9 data in it from small to large, and taking the median of the 9 numbers to represent the data of the ith row and jth column. Through the median filtering, the effect of removing low-frequency noise can be achieved, while the authenticity of the data is preserved, and the influence of dirt on the maximum internal stress is reduced.

[0075] Without conflict, the person skilled in the art can freely combine and superimpose the above additional technical features.

[0076] It can be understood that the present application is described by some embodiments, and the person skilled in the art knows that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, these features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of the present application.

Claims

1. A method for analyzing the internal stress of a lens's effective optical diameter, characterized in that, Includes the following steps: Step 1: Measure the actual outer diameter and the actual effective optical diameter of the lens; Step 2: Measure the internal stress of the lens using a stress meter to obtain an image of the measurement area covering the actual lens. The measurement area image is scaled relative to the actual lens. Save the pixel data of the measurement area image, with each pixel corresponding to a stress value. Step 3: Based on the experimental conditions, set the boundary stress value to distinguish between the lens and the measurement background. The boundary stress value is greater than 4nm, and the stress value of the measurement background is between 0-3nm. Divide the measurement area image into the left half and the right half, and find the boundary points for the left half and the right half of the measurement area image respectively. In the measurement area image, find all the boundary points of the boundary stress value to obtain the boundary point set. Step 4: Fit a circle to the set of boundary points using the least squares method to obtain the outer diameter of the lens in the image of the measurement area; Step 4 specifically includes: Based on the center (A, B) and radius R, a circle on the plane can be identified. The general formula for the equation of a circle on the plane is: , is a linear equation in terms of a, b, and c; Its center (A,B) and radius R are given by the following system of equations (1): A mathematical model for circle fitting is created using the least squares method to obtain the values ​​of parameters a, b, and c. Then, the actual parameters A, B, and R of the circle are obtained based on the system of equations. The following uses the least squares method to create a mathematical model for circle fitting: In obtaining N sets of data for the boundary point set ( , In the expression, i takes values ​​of 1, 2, 3, ..., N, and N ≥ 3. Based on the general formula and the principle of least squares, we need to find the objective function. To find the minimum value, take the partial derivative of F(a,b,c) with respect to a,b,c, and set the partial derivative to zero. This will give you the extreme point, as follows: Let ,Right now: set up: ， ， ， ， ， , ， ， but: Solving the above equation yields a, b, and c: in: Then, the center and radius of the outer diameter of the lens in the image can be obtained from the system of equations (1); Step 5: Based on the scaling relationship between the lens image in the measurement area image and the actual lens, the formula is: Actual outer diameter of the lens / Outer diameter of the lens in the image = Actual effective optical diameter of the lens / Effective diameter of the lens in the image. The effective diameter of the lens in the measurement area image is then calculated to perform data analysis on the internal stress within the effective diameter of the lens.

2. The method for analyzing the internal stress of the effective optical diameter of a lens according to claim 1, characterized in that, The stress meter is a birefringent stress meter, and the stress is represented by optical path difference.

3. The method for analyzing the internal stress of the effective optical diameter of a lens according to claim 1, characterized in that, Before measuring the internal stress of the lens using a stress meter, the stress meter stage is cleaned and decontaminated using an organic solvent.

4. The method for analyzing the internal stress of the effective optical diameter of a lens according to claim 1, characterized in that, After fitting a circle to the set of boundary points using the least squares method, median filtering is applied to the entire lens region in the image.

5. The method for analyzing the internal stress of the effective optical diameter of a lens according to claim 4, characterized in that, The detailed process of median filtering is as follows: Suppose the measurement area image has m rows and k columns of pixels. Perform the following operation on the pixel data: Taking the i-th row and j-th column as an example, where 2≤i≤m-1, 2≤j≤k-1, take its 3x3 neighborhood, sort the 9 data within it from smallest to largest, and take the median of these 9 numbers to represent the data in the i-th row and j-th column.

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