Optical-mechanical heat integration analysis method for space low-temperature infrared camera

Abstract

The invention discloses an optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera, which belongs to the technical field of space optical remote sensing and comprises the following steps of: when a low-temperature infrared optical system is designed, firstly, performing structural modeling on parameters of the infrared low-temperature optical system in a normal-temperature state, and establishing a corresponding structural and thermal control analysis finite element model based on a structural model; a thermal control analysis temperature field is used as structural finite element analysis input, and structural simulation analysis is performed on changes of the mirror surface precision and the mirror surface position of the optical system; processing the precision and position change data into a format which can be identified by low-temperature optical system design software, and importing the data into the optical design software; the optical performance of the low-temperature optical system at low temperature is evaluated through optical design software, the stability of interior orientation elements is evaluated, and the reliability of the low-temperature optical system is improved; the low-temperature optical system provides guidance from normal-temperature adjustment test to low-temperature use; the problem that the performance of a low-temperature infrared optical system is difficult to evaluate and predict under large thermal deformation is solved.

Description

Technical Field

[0001] The present invention relates to the field of space optical remote sensing technology, and in particular to an optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera. Background Art

[0002] With the widespread application of infrared optical remote sensing technology in fields such as agricultural and forestry monitoring, meteorological observation, astronomical observation, and space military target detection, the requirements for the detection sensitivity of infrared optical systems are becoming increasingly higher. Cryogenic optics are needed to reduce the system background. In low-temperature environments, the camera structure will undergo significant deformation. If the optomechanical structure is not designed properly, the optical surface accuracy will deteriorate and the relative position of the mirror will change, resulting in degradation of the camera's optical performance. The low-temperature infrared optical optomechanical thermal integration analysis method can evaluate the optical performance and internal element stability of the low-temperature optical system at low temperatures, thereby improving the reliability of the low-temperature optical system. It provides guidance for low-temperature optical systems from room-temperature assembly and testing to low-temperature use. It solves the problem of difficult system performance evaluation and prediction under large thermal deformation of low-temperature infrared optical systems.

[0003] Currently, the Chinese invention patent application disclosure (publication number: CN110245367B) discloses a method for processing surface shape errors through optical-mechanical integration analysis. This method involves extracting the rigid body displacement, spherical aberration, and flexible error of the mirror from the results of a mirror finite element analysis. The rigid body displacement and spherical aberration of the mirror are subtracted when calculating the mirror surface shape error. The rigid body displacement of the mirror is compensated during the assembly process, and the spherical aberration is compensated by focusing. This patent is only used to extract and process the rigid body displacement and spherical aberration of the mirror from the finite element calculation results of the mirror. No deformation is omitted. The Chinese invention patent application disclosure (publication number: CN101114309A) discloses an optical-mechanical integration analysis method based on an int file. This includes coordinate transformation processing of finite element analysis results of optical mirrors of arbitrary shapes, and an optical-mechanical data interface based on an int file. This patent provides an optical-mechanical integration analysis method based on an int file for processing the data interface of finite element analysis results of optical mirrors of arbitrary shapes. This improves surface shape adaptability and reduces the data fitting process. The disclosure specification of the Chinese invention patent application (publication number: CN106649922B) discloses an optical-mechanical integration analysis method and a mirror surface optimization method of a pre-processing interface program. It solves the problem of large amount of calculation and fitting failure caused by a large amount of fitting data in the post-processing method of the optical-mechanical program. It is only a pre-processing method for optical-mechanical integration analysis. The disclosure specification of the Chinese invention patent application (publication number: CN101504685A) discloses an optical-mechanical thermal integration analysis method based on FringeZernike polynomials. This patent can arbitrarily set the number of terms of the FringeZernike polynomial, and can calculate the optical-mechanical thermal integration analysis method of its expression, and use the dat file to transfer the Zernike fitting coefficient to the Guangxu analysis software. It only discloses a method for applying FringeZernike polynomials in integrated analysis.

[0004] The above invention patents: None of them propose specific technical methods for low-temperature infrared optics. Summary of the Invention

[0005] The present invention aims to provide a method for optical-mechanical-thermal integration analysis of a space low-temperature infrared camera to solve the problems raised in the above background technology.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for analyzing optical-mechanical-thermal integration of a space-based low-temperature infrared camera comprises the following steps:

[0008] S1. Establish a common coordinate system for the model: The coordinate system of the light from the cryogenic optical system entering the first mirror vertex is used as the coordinate system for the optical, mechanical, and thermal disciplines. This coordinate system also serves as the common coordinate system for data transmission between the optical, mechanical, and thermal disciplines.

[0009] S2. Export the required files for the finite element model using the optical design software: Use the optical design software to export the room-temperature optical system corresponding to the low-temperature infrared optical system into a STEP or igs format file. The exported model includes the mirror surface information of the reflectors and lenses in the optical system, light rays of various fields of view and wavelengths, and the coordinates of the mirror vertex.

[0010] S3. Build a 3D camera model: Import the STEP or igs file exported from the optical design software into the structural design software. Build a model of the reflector or lens, as well as a 3D model of the lens or camera, based on the coordinate system position of the cryogenic optical system.

[0011] S4. Establishing Static and Thermal Analysis Finite Element Models: Based on the 3D model of the lens or camera established in the previous step, import it into mechanical finite element analysis software and thermal analysis finite element analysis software through the corresponding software interfaces to establish the mechanical analysis model and thermal analysis model of the lens or camera, respectively.

[0012] S5. Establishing a node temperature field based on temperature data: Based on input parameters such as lens or camera trajectory, external heat flux, and temperature control requirements, perform thermal analysis on the camera and export the analyzed temperature field distribution results in tabular form.

[0013] S6: Map the temperature field to the finite element model: The temperature field derived in the previous step is mapped and used as a load input into the mechanical analysis model. The temperature field distribution of the mechanical analysis model and the thermal analysis model are compared to ensure consistency. A mechanical simulation analysis under the influence of the temperature field is performed to obtain the deformation of the lens or camera mirror.

[0014] S7. Extract mirror displacement data and import it into sigfit software to calculate the mirror surface shape: Use data processing and analysis software or professional optical-mechanical-thermal interface data processing software to analyze and process the mirror deformation data output by the mechanical analysis; obtain the deformation values and rigid body displacement values of each mirror in the low-temperature optical system, and form these data into an interface file that can be input into the optical design software;

[0015] S8. Import the optical zpl file into Zemax software for optical performance evaluation: Integrate the file generated by data processing and analysis with the low-temperature optical design file through the optical design software interface. Use the optical analysis software to evaluate changes in optical performance such as the lens or lens transfer function, energy concentration, and diffuse speckle under the influence of temperature fields.

[0016] S9. Simulate the change of the lens's visual axis under the influence of temperature: Based on the previous step, further use optical software to analyze the data and calculate the change of the lens or camera's visual axis under the influence of temperature field.

[0017] Preferably, the cryogenic optical system is any one of the following three types: a total reflection optical system, a total projection system, and a reflector + transmission system;

[0018] The low-temperature optical system may include or not include any one of room-temperature optical calibration and testing compensation mirrors.

[0019] Preferably, the cryogenic optical system coordinate system is located at the first mirror vertex position where light from the cryogenic optical system enters.

[0020] Preferably, the mirror surface model of the lens or camera is established directly on the basis of the optical import model, and the lens model directly adopts the optical import model; the structural finite element model analysis model of the lens or camera is small in size, large in number, and focuses on key force-bearing and high-precision parts, reflecting the details of the structural parts; the thermal analysis finite element model analysis model unit is large in size, small in number, and reflects the shape of the parts.

[0021] Preferably, the thermal analysis of the lens or camera exports a temperature field in tabular form, and the temperature field includes finite element node coordinates and node temperature information; in the thermal analysis finite element model, low-temperature components are grouped separately according to the temperature requirements of each component, and parts with large temperature differences may exist within the group; the parts contained in the mechanical analysis model component and the thermal analysis model component remain consistent.

[0022] Preferably, the integrated analysis of the cryogenic optical system includes conducting a performance analysis of the cryogenic optical system under the action of cryogenic temperature loads and an optical performance analysis under other loads directly applied in the structural finite element analysis software.

[0023] Preferably, the analysis of the reflector surface deformation data adopts a method of solving Zernike polynomial coefficients to perform re-fitting of the optical mirror after deformation.

[0024] Preferably, the simulation of the change in the direction of the visual axis is performed by inserting two virtual surfaces with a known distance at the front end of the cryogenic optical system, and calculating the change in the visual axis by respectively calculating the coordinate deviation of the center points of the light spots on the two virtual surfaces before and after applying the external load.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The working environment of the cryogenic infrared optical system is low, and there are large temperature differences among the components of the optical and mechanical structure, resulting in large thermal deformation. Unifying the modeling coordinate systems of optics, structure, and thermal control in the modeling of cryogenic optical systems is conducive to improving the consistency of the model and making full use of the software interface;

[0027] 2. Modeling is done using models derived from optical software to improve the modeling accuracy of the reflector surface, especially the aspherical mirror surface;

[0028] 3. When modeling the thermal analysis model, ensuring the shape of each part can improve the accuracy of the temperature field from the thermal analysis model to the structural analysis model;

[0029] 5. Using the mapping method, the temperature is transferred from the thermal analysis model to the structural analysis model, solving the problem of different unit sizes, unit numbers, and unit node positions in the finite element models of thermal analysis and mechanical analysis;

[0030] 6. Grouping the parts in the thermal analysis model and the mechanical analysis model based on the temperature distribution of the lens or camera can reduce the error in the temperature field from the thermal analysis model to the structural analysis model caused by the temperature difference of the camera;

[0031] 7. This method can not only obtain the changes in low-temperature infrared optical properties, but also the changes in the direction of the optical axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of an optical-mechanical-thermal integration analysis method for a low-temperature infrared optical system;

[0033] Figure 2 Convert optical files into 3D models;

[0034] Figure 3 Schematic diagram of the temperature field result table corresponding to each node

[0035] Figure 4 Mapping the temperature field to the mechanical analysis model diagram;

[0036] Figure 5 Field of view setting diagram for boresight calculation;

[0037] Figure 6 This is the coordinate information diagram of the center point of the central field of view spot coverage area when calculating the visual axis. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0039] The specific implementation process is as follows:

[0040] like Figure 1 As shown, a method for optical-mechanical-thermal integration analysis of a low-temperature infrared optical system, a lens, and a camera, the method comprising the following steps:

[0041] Step 1: Use the coordinate system of the first mirror vertex where light enters the cryogenic optical system as the unified coordinate system for the entire simulation process. This coordinate system will be shared between the three disciplines of optics, mechanics, and thermal engineering to ensure that all data can be seamlessly transferred between different software and disciplines. Set up a global coordinate system in Zemax optical design software, using this vertex as the origin, to ensure that subsequent exported and imported models are in the same coordinate base.

[0042] Step 2: After completing the design of the low-temperature infrared optical system in Zemax optical design software, use the software's export function to export the optical system file to STEP format. The exported file should include information on all key optical components, such as the mirror shapes of the reflectors and lenses, light data for each field of view and wavelength, and the coordinates of the mirror vertices. Pay special attention to ensuring that the exported model coordinate system uses the first mirror vertex as the origin to ensure consistency with subsequent structural and thermal analysis.

[0043] Step 3: Import the STEP file exported from Zemax into UG structural design software. During the import process, ensure that the position and size of the optical components remain consistent and use the unified coordinate system of the optical system as the reference. Build a complete 3D structural model of the reflector, lens and other key components to facilitate mechanical and thermal analysis in subsequent steps. Figure 2 As shown, a few of the lenses and lens structures are briefly listed;

[0044] Step 4: Based on the three-dimensional model established by UG structural design software, establish mechanical and thermal analysis models. For the thermal analysis model, it is necessary to set boundary conditions, such as heat flow outside the track, radiation heat transfer, and temperature control parameters. Ensure the accuracy of the thermal analysis results by finely meshing the optical components. At the same time, establish a mechanical analysis model and impose appropriate constraints, taking into account the support method of the reflector and the load conditions under actual working conditions, including the effects of gravity and temperature fields;

[0045] Step 5: Based on the temperature field distribution of lens components, group and name the components. According to the input parameters such as lens track, external heat flow, temperature control requirements, etc., conduct thermal analysis on the camera and export the temperature field distribution results in table form, such as Figure 3 As shown;

[0046] Step 6: In the mechanical analysis model, first group the structural model according to the grouping method of the thermal analysis model to ensure that the two are consistent in the common optical, mechanical and thermal coordinate system. When importing temperature field data, enter the node information through a table file, where the dependent variable is the temperature value, the independent variable is set to the node coordinate in the Cartesian coordinate system, and the group name is used to name the established temperature field data set. Then, in the UG software, select the component to which the temperature field needs to be applied, and use the "Select Existing Field" function to map the corresponding temperature field to the specified component, such as Figure 4 Finally, a mechanical simulation under the action of the temperature field is run to simulate the structural response of the lens under temperature load, thereby obtaining the deformation displacement data file of the lens surface, providing accurate input for subsequent optical performance analysis.

[0047] Step 7: Use SigFit, a professional optical-mechanical-thermal interface data processing software, to parse the mirror deformation displacement file output by the mechanical analysis. First, define the geometric characteristics of the optical mirror in SigFit and clarify the relationship between the mirror and the displacement file. The deformation data of the finite element nodes is converted to the optical coordinate system, and the displacement field is projected onto the mirror surface. Subsequently, a surface shape fitting is performed on the mirror deformation data, typically using the standard Zernike polynomial fitting method to accurately describe the mirror surface error. The fitting results can calculate key parameters such as RMS (root mean square) error and PV (peak-to-valley) error. This data is further used to evaluate the impact of mirror surface shape changes on optical system performance, generating analysis results for optical performance parameters such as wavefront error, point spread function (PSF), and modulation transfer function (MTF). Finally, the processed data is output as a ZPL macro file that can be recognized by Zemax optical design software for further performance evaluation and optimization within the optical design software.

[0048] Step 8: For optical performance evaluation, the ZPL macro file generated after data processing and analysis is imported into Zemax optical design software and integrated with the previously created low-temperature optical design file. Zemax software applies the mirror deformation information in the ZPL macro file to the optical system model, simulating the performance changes of the optical system under the influence of temperature fields.

[0049] Optical analysis functions can be used to evaluate changes in the system's optical performance under temperature loads, specifically changes in the lens's medium transfer function (MTF), energy concentration, and diffuse speckle (PSF). Zemax outputs corresponding graphical results, including transfer function plots, energy concentration plots, and diffuse speckle plots, to further verify and optimize the performance of the optical design.

[0050] Step 9: Based on the previous step, you can further simulate the change of the lens or camera's axis direction under the influence of the temperature field. Open the field of view setting in Zemax optical design software, select "real image height", and set the image height to 0, 0, such as Figure 5 As shown (to calculate the change of the visual axis, you can only set the central field of view); insert two virtual surfaces (tentatively named S2 and S3) at the front end of the optical system, with a spacing of d = 100mm (the spacing can be set by yourself). Open the light trace diagram and view the X and Y coordinates of the center point of the center field of view spot coverage area of the two surfaces S2 and S3 respectively; click "Text" above the light trace diagram window to view the results directly in the opened window, as shown in the following figure: Figure 6 As shown; assuming that the center coordinates of the light spot on the S2 surface are (X2, Y2), and the center coordinates of the light spot on the S3 surface are (X3, Y3), the calculation method of the visual axis deviation is as follows:

[0051]

[0052] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for optical-mechanical-thermal integration analysis of a space low-temperature infrared camera, characterized in that: The following steps are involved: S1. Establish a common coordinate system for the model: The coordinate system of the light from the cryogenic optical system entering the first mirror vertex is used as the coordinate system for the optical, mechanical, and thermal disciplines. This coordinate system also serves as the common coordinate system for data transmission between the optical, mechanical, and thermal disciplines. S2. Export the required files for the finite element model using the optical design software: Use the optical design software to export the room-temperature optical system corresponding to the low-temperature infrared optical system into a STEP or igs format file. The exported model includes the mirror information of the reflector and lens optical elements in the optical system, the light of each field of view and each wavelength, and the coordinate information of the mirror vertex; S3. Build a 3D camera model: Import the STEP or igs file exported from the optical design software into the structural design software. Build a model of the reflector or lens, as well as a 3D model of the lens or camera, based on the coordinate system position of the cryogenic optical system. S4. Establishing Static and Thermal Analysis Finite Element Models: Based on the 3D model of the lens or camera established in the previous step, import it into mechanical finite element analysis software and thermal analysis finite element analysis software through the corresponding software interfaces to establish the mechanical analysis model and thermal analysis model of the lens or camera, respectively. S5. Establishing a node temperature field based on temperature data: Based on input parameters such as lens or camera trajectory, external heat flux, and temperature control requirements, perform thermal analysis on the camera and export the analyzed temperature field distribution results in tabular form. S6: Map the temperature field to the finite element model: The temperature field derived in the previous step is input into the mechanical analysis model as a load through mapping, and the temperature field distribution of the mechanical analysis model is compared with that of the thermal analysis model to see if they are consistent. Conduct mechanical simulation analysis under the action of temperature field to obtain the deformation of the lens or camera mirror; S7. Extract mirror displacement data and import it into sigfit software to calculate the mirror surface shape: Use data processing and analysis software or professional optical-mechanical-thermal interface data processing software to analyze and process the mirror deformation data output by the mechanical analysis; obtain the deformation values and rigid body displacement values of each mirror in the low-temperature optical system, and form these data into an interface file that can be input into the optical design software; S8. Import the optical zpl file into Zemax software for optical performance evaluation: Integrate the file generated by data processing and analysis with the low-temperature optical design file through the optical design software interface. Use the optical analysis software to evaluate changes in optical performance such as the lens or lens transfer function, energy concentration, and diffuse speckle under the influence of temperature fields. S9. Simulate the change of the lens's visual axis under the influence of temperature: Based on the previous step, further use optical software to analyze the data and calculate the change of the lens or camera's visual axis under the influence of temperature field.

2. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The cryogenic optical system is any one of the following: a total reflection optical system, a total projection system, and a reflector + transmission system; The low-temperature optical system may include or not include any one of room-temperature optical calibration and testing compensation mirrors.

3. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The cryogenic optical system coordinate system is located at the first mirror vertex position where light from the cryogenic optical system enters.

4. The optical-mechanical-thermal integration analysis method for a space-based low-temperature infrared camera according to claim 1, characterized in that: The mirror surface model of the lens or camera is established directly on the basis of the optical import model, and the lens model directly adopts the optical import model; the structural finite element model analysis model of the lens or camera is small in size and large in number, and focuses on key force-bearing and high-precision parts, reflecting the details of the structural parts; the thermal analysis finite element model analysis model unit is large in size and small in number, reflecting the shape of the parts.

5. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The temperature field derived from the thermal analysis of the lens or camera in a tabular form, the temperature field including finite element node coordinates and node temperature information; In the thermal analysis finite element model, low-temperature components are grouped separately according to the temperature requirements of each component, and parts with large temperature differences may exist within the group; the parts included in the mechanical analysis model components and the thermal analysis model components remain consistent.

6. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The cryogenic optical system integrated analysis includes the analysis of the performance of the cryogenic optical system under the action of cryogenic temperature loads and the analysis of the optical performance under other loads directly applied in the structural finite element analysis software.

7. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The analysis of the reflector surface deformation data adopts a method of solving Zernike polynomial coefficients to perform re-fitting after the optical mirror surface is deformed.

8. The optical-mechanical-thermal integration analysis method for a space low-temperature infrared camera according to claim 1, characterized in that: The simulated visual axis pointing change is performed by inserting two virtual surfaces with a known distance at the front end of the cryogenic optical system, and calculating the visual axis change by respectively calculating the coordinate deviation of the center points of the two virtual surface spots before and after the application of the external load.

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