Optical element desensitization method based on thermal stability of optical axis of space optical camera

Abstract

The invention relates to an optical element desensitization method based on thermal stability of a visual axis of a space optical camera, and relates to the technical field of space optical cameras, and the method comprises the following steps: establishing a visual axis stability optical sensitivity matrix; key optical elements are positioned and optimized; analyzing the surface performance of the optical element; and the visual axis error is calculated through complete machine thermal load simulation analysis. According to the optical element desensitization method based on the thermal stability of the optical axis of the space optical camera, the key optical element influencing the stability of the optical axis of the space optical camera is accurately positioned by establishing the linear optical model, targeted optimization is performed, and the efficiency is improved; an optical element influencing the stability of the visual axis is directly subjected to structural optimization, rigid body displacement constraints are integrated in an optimization model, the sensitivity of the optical element to thermal loads is reduced, and the stability of the visual axis of the whole machine is more effectively guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of space optical camera, in particular to a method for reducing sensitivity of optical elements based on thermal stability of line-of-sight of space optical camera. BACKGROUND

[0002] With the development of space science and technology, space optical cameras have great application potential in aviation, aerospace, navigation and other fields, and there is an urgent need for high-quality image acquisition. Due to the influence of multiple physical fields, the low-frequency and high-frequency errors in pointing measurement are difficult to eliminate, especially the temperature factor (external heat flux such as solar radiation, deep space background radiation, camera internal heat consumption, satellite thermal radiation, etc.), which affects the alignment relationship between the optical system and the image plane, causing the line-of-sight (LOS) drift of the space optical camera, also known as thermal drift or temperature drift, so that the image of a stationary object moves laterally on the image plane, the image becomes blurred or smeared, and the image quality and optical performance are lost, which has a non-negligible impact on the measurement accuracy.

[0003] The line-of-sight error is mainly caused by the rigid body displacement of the optical element. In practical applications, the rigid body displacement of the optical element caused by thermal load is usually indirectly reduced by optimizing the camera light machine structure and thermal control design, so as to reduce the line-of-sight error. For example, low linear expansion coefficient materials, symmetrical structure design, and heat insulation design between the light shield and the mounting flange are selected.

[0004] Most of the existing technologies are to optimize mechanical structural parts to indirectly reduce the rigid body displacement of the optical element, but there is no direct structure optimization of the optical element that affects the line-of-sight stability to reduce its sensitivity to thermal load. Although the optimization method in the prior art indirectly reduces the rigid body displacement of the optical element, it lacks pertinence, especially for complex optical systems, which is low in efficiency. SUMMARY

[0005] The present application solves the technical problems of low efficiency and low pertinence in optimizing the light machine structure in the prior art, and provides a method for reducing the sensitivity of optical elements based on the thermal stability of the line-of-sight of space optical camera.

[0006] In order to solve the above technical problems, the technical scheme of the present application is as follows:

[0007] A method for reducing the sensitivity of optical elements based on the thermal stability of the line-of-sight of space optical camera, comprising the following steps:

[0008] Step 1: Establishing an optical sensitivity matrix for line-of-sight stability;

[0009] Step 2: Positioning key optical elements and optimizing;

[0010] Step 3: Surface performance analysis of optical elements;

[0011] Step four: whole machine thermal load simulation analysis and calculation of visual axis error.

[0012] In the above technical scheme, step one is specifically:

[0013] According to the known optical system model, the visual axis error under the disturbance of a single rigid body displacement term is analyzed by using the ray tracing model; the analysis is repeatedly performed on the surface of each optical element and each rigid body displacement term to obtain a visual axis stability optical sensitivity matrix, and the structural displacement caused by the load is mapped to the visual axis error value at the exit pupil of the space optical camera.

[0014] In the above technical scheme, step two is specifically:

[0015] According to the visual axis stability optical sensitivity matrix obtained in step one, the key optical element having the greatest influence on the visual axis stability is determined, and topology optimization and parameter optimization are performed on the key optical element, and the visual axis stability is integrated in the optimization model.

[0016] In the above technical scheme, step two is specifically:

[0017] According to the design parameters, a finite element model of the non-lightweight design is established, and the mirror body is set as a designable area according to whether the lightweight design can be performed, and the optimal material distribution form is solved in the area; the rest is set as a non-designable area; under the thermal load working condition, the minimum compliance is set as the objective function, and the volume fraction, mirror surface accuracy and rigid body displacement are set as the constraint conditions, and the mathematical expression of the optimization model is:

[0018] Find:X(x1,x2,x3…x N )

[0019] Min:C(x)=F T U=U T KU

[0020]

[0021] Wherein, X is a design variable, representing the relative density of a small element, the value range is [x min ,1], N is the total number of nodes of the mirror finite element model; C(x) is the objective function, F is the external load vector, U is the node displacement matrix, K is the stiffness matrix, the minimum compliance is achieved to realize the maximum stiffness; a* is the volume fraction of the structure, representing the remaining volume ratio; n is the total number of mirror nodes, U n is the mirror node displacement; [T x ,T y ,T z ,R x ,R y ,R zThe rigid displacement of the mirror surface includes three directions of translation and rotation; and the three constraint conditions respectively represent that the volume of the main mirror after optimization meets the lightweight requirement, the surface shape precision error RMS value is better than λ / 50, and the rigid displacement of the mirror surface is within the design range.

[0022] According to the topological optimization result, an initial structure is obtained; a middle surface shell element is established, design sizes are grouped, and the contribution degrees of different groups of size parameters to weight, surface shape precision and visual axis stability are obtained through design sensitivity analysis; the value range of the key size is determined, the key size is determined through parameter optimization, and the final structure is obtained.

[0023] In the above technical solution, step three is specifically:

[0024] The finite element modeling of the key optical element structure obtained in step two is performed by using a finite element analysis software, and the surface performance is analyzed under the conditions of uniform temperature rise, axial temperature gradient and radial temperature gradient;

[0025] The optical surface displacement is obtained through simulation calculation, and the least square method is used to fit the rigid displacement of the optical surface when the axial or offset rigid displacement is calculated under the condition of thermal load.

[0026] In the above technical solution, step four is specifically:

[0027] The finite element model of the whole machine is established, the thermal load is set, the displacement of each optical surface of the space optical camera is simulated and calculated, and the least square method is used to fit the rigid displacement;

[0028] The rigid displacement of the optical surface is independently applied by defining the tilt or eccentricity of the local coordinate system of the optical surface, the visual axis error is calculated, and the imaging quality of the space optical camera is judged.

[0029] The present application has the following advantages:

[0030] The optical element sensitivity reduction method based on the visual axis thermal stability of the space optical camera of the present application can accurately locate the key optical element affecting the visual axis stability of the space optical camera by establishing a linear optical model, and can improve the efficiency by targeted optimization.

[0031] The optical element sensitivity reduction method based on the visual axis thermal stability of the space optical camera of the present application directly optimizes the optical element affecting the visual axis stability, integrates the rigid displacement constraint in the optimization model, reduces the sensitivity to thermal load, and more effectively ensures the visual axis stability of the whole machine.

[0032] The optical element sensitivity reduction method based on the visual axis thermal stability of the space optical camera of the present application has reference significance for the structure optimization and sensitivity reduction design of the space optical camera. BRIEF DESCRIPTION OF DRAWINGS

[0033] The application will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

[0034] Figure 1 A flowchart of the optical element desensitization method based on the thermal stability of the viewing axis of a space optical camera according to the application.

[0035] Figure 2 A diagram of the rigid body displacement of the optical element mentioned in the optical element desensitization method based on the thermal stability of the viewing axis of a space optical camera according to the application.

[0036] Figure 3 A diagram of the viewing axis error under the disturbance of the single rigid body displacement term mentioned in the optical element desensitization method based on the thermal stability of the viewing axis of a space optical camera according to the application. DETAILED DESCRIPTION

[0037] The application will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

[0038] The optical element desensitization method based on the thermal stability of the viewing axis of a space optical camera according to the application, as shown in Figure 1 , includes the following steps:

[0039] Step 1: Establish the viewing axis stability optical sensitivity matrix;

[0040] The load acting on the optical system will change the position of the optical surface, causing the optical element to be out of adjustment. The optical surface position error or rigid body error includes the translation and rotation of a surface along 6 degrees of freedom, as shown in Figure 2 , which is called rigid body displacement. According to the known optical system model, the viewing axis error under the disturbance of a single rigid body displacement term is analyzed using a ray tracing model, as shown in Figure 3 , with a coaxial two-mirror optical system as an example. Repeating the analysis on each optical element surface and each rigid body displacement term, the viewing axis stability optical sensitivity matrix can be obtained, which maps the structural displacement caused by the load to the viewing axis error value at the exit pupil of the space optical camera.

[0041] Step 2: Position the key optical elements and optimize;

[0042] According to the viewing axis stability optical sensitivity matrix obtained in Step 1, the key optical elements that have the greatest impact on the viewing axis stability can be determined. Topological optimization and parameter optimization are performed on the key optical elements, and the viewing axis stability is integrated into the optimization model. The optimization goal is to obtain the optimal configuration of optical and mechanical performance under the condition that the optical elements maintain good surface accuracy and rigid body displacement stability, and the degree of lightweight is high.

[0043] According to the design parameters, a finite element model of the non-lightweight design is established, and the mirror body is set as a designable area according to whether the lightweight design can be performed, and the optimal material distribution form is solved in the area; the rest (mirror surface and back support hole) is set as a non-designable area. Under the thermal load condition, the minimum compliance (i.e. the maximum stiffness) is set as the objective function, and the volume fraction, the mirror surface accuracy, and the rigid body displacement (i.e. the stability of the visual axis) are set as the constraint conditions, and the mathematical expression of the optimization model is:

[0044]

[0045] wherein X is a design variable, representing the relative density of the small element, and the value range is [x min ,1], N is the total number of nodes of the mirror finite element model; C(x) is the objective function, F is the external load vector, U is the node displacement matrix, K is the stiffness matrix, and the minimum compliance is achieved to realize the maximum stiffness; a* is the volume fraction of the structure, representing the remaining volume ratio; n is the total number of mirror nodes, U n is the mirror node displacement; [T x , T y , T z , R x , R y , R z ] is the rigid body displacement of the mirror, including three directions of translation and rotation; the three constraint conditions respectively represent: the volume of the primary mirror after optimization meets the lightweight requirement, the RMS value of the surface accuracy error is better than λ / 50, and the rigid body displacement of the mirror is within the design range.

[0046] According to the topological optimization result, the initial structure is obtained while considering the requirements of the manufacturing process. The middle surface shell element is established, the design size is grouped, the size parameters of different groups are obtained through the design sensitivity analysis (DSA), and the contribution degrees of the weight, the surface accuracy, and the visual axis stability are obtained. The sensitivity analysis result, the related research at home and abroad, and the actual engineering application are combined to determine the value range of the key size, the key size is determined through the parameter optimization of HyperStudy, and the final structure is obtained.

[0047] Step three: surface performance analysis of the optical element;

[0048] The finite element analysis software is used for carrying out finite element modeling to the key optical element structure obtained in step two, three working conditions of uniform temperature rise, axial temperature gradient and radial temperature gradient are established respectively, and the surface performance is analyzed. The optical surface displacement is obtained through simulation calculation, in the case of thermal load, in order to fully consider the radial motion of the node, the least square method is used to fit the rigid body displacement of the optical surface. The results show that the uniform temperature rise has obvious influence on the rigid body displacement of the optical element surface, the axial and radial temperature difference has obvious influence on the curvature radius and surface shape precision. Considering that the boresight error is mainly caused by the rigid body displacement, the worst thermal working condition affecting the boresight stability is determined, and the influence of uniform temperature rise should be mainly considered when studying the boresight thermal stability.

[0049] Step four: whole machine thermal load simulation analysis and calculation of boresight error;

[0050] The finite element model of the whole machine is established, the thermal load is set, the displacement of each optical surface of the space optical camera is simulated and calculated, and the least square method is used to fit the rigid body displacement. The boresight error is calculated by defining the local coordinate system of the optical surface to tilt or centrifugal independently to apply the rigid body displacement of the optical surface, so as to judge the imaging quality of the space optical camera.

[0051] The optical element desensitization method based on the boresight thermal stability of the space optical camera of the application can accurately locate the key optical element affecting the boresight stability of the space optical camera by establishing a linear optical model, and can be optimized and improved in efficiency.

[0052] The optical element desensitization method based on the boresight thermal stability of the space optical camera of the application directly optimizes the optical element affecting the boresight stability, integrates the rigid body displacement constraint in the optimization model, reduces the sensitivity to thermal load, and more effectively ensures the boresight stability of the whole machine.

[0053] The optical element desensitization method based on the boresight thermal stability of the space optical camera of the application has reference significance for the structure optimization and desensitization design of the space optical camera.

[0054] Obviously, the above embodiments are only examples for clearly illustrating, and not limiting the embodiments. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments need not and cannot be exhausted. The obvious changes or variations derived therefrom are still within the protection scope of the application.

Claims

1. A method for desensitizing optical elements based on the thermal stability of the visual axis of a space optical camera, characterized in that: The following steps are involved: Step 1: Establish the optical sensitivity matrix for visual axis stability; Step 2: Locate and optimize key optical components; Step 3: Surface performance analysis of optical components; Step 4: Calculate the boresight error through thermal load simulation analysis of the entire machine.

2. The optical element desensitization method based on the thermal stability of the visual axis of a space optical camera according to claim 1, characterized in that: Step 1 is as follows: Based on the known optical system model, the ray tracing model is used to analyze the line of sight error under the disturbance of a single rigid body displacement term. The analysis is repeated on the surface of each optical element and each rigid body displacement term to obtain the line of sight stability optical sensitivity matrix, which maps the structural displacement caused by the load into the line of sight error value at the exit pupil of the space optical camera.

3. The optical element desensitization method based on the thermal stability of the visual axis of a space optical camera according to claim 1, characterized in that: Step 2 is as follows: Based on the optical sensitivity matrix of the line of sight stability obtained in step 1, the key optical components that have the greatest impact on the line of sight stability are determined, and topological optimization and parameter optimization are performed on them, and the line of sight stability is integrated into the optimization model.

4. The optical element desensitization method based on the thermal stability of the visual axis of a space optical camera according to claim 3, characterized in that: Step 2 is as follows: Based on the design parameters, a finite element model without lightweight design is established. The mirror body is set as a designable area based on whether lightweighting is possible, and the optimal material distribution form is solved within this area. The rest are set as undesignable areas. Under the thermal load condition, the minimum compliance is set as the objective function, and the volume fraction, mirror surface accuracy, and rigid body displacement are set as constraints. The mathematical expression of the optimization model is: Among them, X is the design variable, representing the relative density of the small unit, and its value range is [x min ,1], N is the total number of nodes in the finite element model of the reflector; C(x) is the objective function, F is the external load vector, U is the node displacement matrix, K is the stiffness matrix, and the goal of maximizing stiffness is achieved by minimizing flexibility; a* is the volume fraction of the structure, indicating the proportion of the remaining volume; n is the total number of mirror nodes, U n is the mirror node displacement; [T x ,T y ,T z ,R x ,R y ,R z ] is the rigid body displacement of the mirror, including translation and rotation in three directions; the three constraints represent: the volume of the optimized primary mirror meets the lightweight requirements, the RMS value of the surface accuracy error is better than λ / 50, and the rigid body displacement of the mirror is within the design range; Based on the topology optimization results, the initial structure is obtained; the mid-surface shell unit is established, the design dimensions are grouped, and the contribution of the dimensional parameters of different groups to weight, surface accuracy, and axis stability is obtained through design sensitivity analysis; the value range of the key dimensions is determined, and the key dimensions are determined through parameter optimization to obtain the final structure.

5. The optical element desensitization method based on the thermal stability of the visual axis of a space optical camera according to claim 1, characterized in that: Step three is as follows: Finite element analysis software is used to perform finite element modeling on the key optical element structure obtained in step 2. Uniform temperature rise, axial temperature gradient, and radial temperature gradient working conditions are established, and their surface performance is analyzed. The optical surface displacement is obtained by simulation calculation. When calculating the axial or offset rigid body displacement under thermal load, the least squares method is used to fit the rigid body displacement of the optical surface.

6. The optical element desensitization method based on the thermal stability of the visual axis of a space optical camera according to claim 1, characterized in that: Step 4 is as follows: Establish a finite element model of the entire machine, set the thermal load, simulate and calculate the displacement of each optical surface of the space optical camera, and use the least squares method to fit the rigid body displacement; By defining the local coordinate system of the optical surface to tilt or centrifuge and independently applying the rigid body displacement of the optical surface, the line of sight error is calculated to judge the imaging quality of the space optical camera.

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