Disclosure of Invention
The invention provides a thermal stability calibration method for a reflector of a space optical remote sensing camera, aiming at solving the problems that the thermal stability of the reflector is not completely calibrated and is not accurate enough due to the defect that the influence factors of the thermal stability of the reflector are not considered sufficiently in the prior art.
The technical scheme adopted by the invention for solving the technical problem is as follows:
a thermal stability calibration method for a reflector of a space optical remote sensing camera comprises the following steps:
step one, establishing a finite element model of a reflector structure of the space optical remote sensing camera, dividing a grid for the reflector of the space optical remote sensing camera in the finite element model, carrying out convergence inspection on the grid, and determining the grid density of the finite element model through the convergence inspection of the grid;
step two, adopting Zernike polynomials to represent the thermal expansion coefficient distribution and the temperature field distribution, and obtaining the corresponding thermal expansion coefficient distribution and the temperature field distribution by fitting different Zernike coefficients;
thirdly, performing thermo-mechanical coupling finite element analysis on the reflector structure of the space optical remote sensing camera by taking the temperature field distribution obtained in the second step as a load to obtain displacement information of the optical surface of the reflector of the space optical remote sensing camera, compiling an optical machine data interface, and inputting the displacement information into the optical machine data interface to obtain Zernike aberration, surface shape RMS and PV of the reflector of the space optical remote sensing camera under the action of the thermal load;
obtaining a theoretical result or a test result through theoretical calculation, wherein the theoretical result or the test result is used as a verification parameter, comparing Zernike aberration, surface shape RMS and PV of the reflector of the space optical remote sensing camera under the action of thermal load through the verification parameter, and modifying finite element model parameters, wherein the verification parameter comprises the surface shape RMS and PV under the combined action of temperature gradient, temperature level and thermal expansion coefficient distribution;
and step five, substituting the parameters of the modified finite element model obtained in the step four into the finite element model obtained in the step one to obtain the modified finite element model, and analyzing and calculating the surface shape RMS sensitivity, the PV sensitivity and the Zernike aberration sensitivity of the reflector of the space optical remote sensing camera under different temperature field distributions by adopting the modified finite element model.
The invention has the beneficial effects that:
the thermal stability calibration method of the reflector of the space optical remote sensing camera comprehensively considers the influence of factors such as the structural form of the reflector body of the space optical remote sensing camera, the distribution of the thermal expansion coefficient, the distribution of the temperature field and the like on the thermal stability of the reflector, considers the influence of the convergence of a grid and the like, is more comprehensive and accurate compared with the traditional method, and can better guide the structure and the thermal control design. The result obtained by the invention can be used as a data basis of a predictable thermal control method and can be used for scheme optimization of the predictable thermal control. The result obtained by the invention can guide the structural design and provide a basis for selecting a scheme of the light weight form of the light weight reflector.
Drawings
FIG. 1 is a flow chart of a thermal stability calibration method for a reflector of a space optical remote sensing camera according to the present invention.
FIG. 2 is a front view of a finite element model of a lightweight mirror.
Fig. 3 is a structural view of the inner circumferential support of the broken line in fig. 2.
FIG. 4 is a side view of a finite element model of a lightweight mirror.
Fig. 5 is a block diagram of the back support in phantom in fig. 3.
Figure 6 is a temperature field distribution characterized by a Zernike polynomial.
FIG. 7 is a simulation result of the spatial optical remote sensing camera reflector under the action of thermal load.
FIG. 8 shows the results of thermo-optic tests.
FIG. 9 is the thermal stability sensitivity of a uniform chamfered reflector.
FIG. 10 is the sensitivity of the thermal stability of a hexagonal chamfered mirror.
FIG. 11 is the sensitivity of thermal stability of a three-leaf chamfered mirror.
Wherein:
m1 is the mirror body, M2 is circumferential support, M3 is back support, M4 is the mirror chamber, M5 is flexible section, M6 is A frame, M7 is the tangential pull rod.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
A thermal stability calibration method for a reflector of a space optical remote sensing camera, as shown in FIG. 1, comprises the following steps:
step one, establishing a finite element model of the reflector of the space optical remote sensing camera according to the structure model of the reflector of the space optical remote sensing camera, dividing a grid for the whole reflector of the space optical remote sensing camera in the finite element model, carrying out convergence inspection on the grid, and determining the grid density of the finite element model through the convergence inspection of the grid.
According to the structure model of the reflector of the space optical remote sensing camera, a high-precision finite element model of the reflector of the space optical remote sensing camera is established in a hypermesh (high-performance finite element processor), as shown in figures 2-5. The hexahedral cells or the shell cells are preferably selected when the grid is divided. The method determines the grid convergence density through the grid convergence test, improves the model calculation precision and ensures the simulation precision.
Fig. 2 and 4 are referred to as a mirror assembly, namely a space optical remote sensing camera mirror of the invention, wherein M1 is referred to as a mirror body, namely a mirror body.
And secondly, adopting Zernike polynomials to represent the thermal expansion coefficient distribution and the temperature field distribution, and obtaining the corresponding thermal expansion coefficient distribution and the corresponding temperature field distribution by fitting different Zernike coefficients.
The thermal expansion coefficient distribution and the temperature field distribution are both characterized by a Fringe Zernike polynomial:
wherein alpha isx,yDenotes the distribution of thermal expansion coefficient, Tx,yRepresenting the temperature field distribution, Cn,mDenotes the Zernike coefficient, Un,mAre Zernike terms. For the above polynomials by fitting different Zernike coefficients Cn,mCorresponding different thermal expansion coefficient distributions alpha can be obtainedx,yAnd corresponding different temperature field distributions Tx,yA temperature field distribution characterized by a Zernike polynomial as shown in figure 6.
And thirdly, taking the temperature field distribution obtained in the second step as a load, carrying out thermo-mechanical coupling analysis on the reflector structure of the space optical remote sensing camera to obtain displacement information of the optical surface of the reflector of the space optical remote sensing camera, compiling a data interface of a light machine, and inputting the displacement information into the data interface of the light machine to obtain a simulation result of the reflector of the space optical remote sensing camera under the action of the thermal load. The simulation results include parameters of surface shape RMS and PV, Zernike aberration, and the like.
And (3) taking the temperature field distribution generated in the second step as a load by a computer, carrying out thermo-mechanical coupling finite element analysis on the reflector structure in MSC Nastran software (finite element analysis solver) to obtain displacement information of the optical surface of the reflector, compiling a light machine data interface by utilizing Matlab, manually counting surface shape RMS and surface shape PV of the space optical remote sensing camera reflected under the action of the thermal load through the light machine data interface, and fitting parameters such as Zernike aberration of the reflector of the space optical remote sensing camera under the action of the thermal load by the light machine data interface to obtain a simulation result.
And step four, obtaining a theoretical result or obtaining a test result through theoretical calculation, taking the theoretical result or the test result as a verification parameter, and modifying the parameters of the finite element model according to the verification parameter and the simulation result by combining the simulation result obtained in the step three. Validation parameters include RMS and PV of the surface profile at temperature gradient, at temperature level, under the combined effect of the coefficient of thermal expansion distribution;
in order to calibrate the finite element model and improve the simulation accuracy, the mirror thermo-optical test is implemented for calibration to obtain the test result. The method specifically comprises the following steps: the method comprises the steps of placing a reflector of a space optical remote sensing camera on a shock insulation platform according to the horizontal direction of an optical axis, wherein the direction perpendicular to the paper surface is shown in figure 2, arranging a heating sheet and a temperature sensor on the back surface of a reflector body (namely M1), heating the reflector body by using different temperatures through the heating sheet, feeding back temperature data of the reflector body through the temperature sensor, and calibrating the temperature field distribution of a finite element model of the reflector body according to the fed back temperature data of the reflector body. Next, profile changes (i.e., profiles RMS and PV) of the mirror assembly at temperature gradients (e.g., radial temperature gradients), at temperature levels, and under the combined effect of the thermal expansion coefficient profiles were measured using a 4D interferometer, and the profile changes (profiles RMS and PV) measured using the 4D interferometer were compared to the simulation results, as shown in fig. 7 and 8. And modifying parameters of the finite element model according to the comparison between the thermo-optical test result and the simulation result.
The finite element model is calibrated through a computer, and the calculation precision of the finite element model and the accuracy of the optical-mechanical data interface are improved.
And step five, calculating and counting the sensitivity of various temperature field distributions.
And (4) utilizing the modified finite element model parameters obtained in the fourth step to replace the finite element model obtained in the first step to obtain a modified finite element model, and adopting the modified finite element model to respectively analyze and calculate the surface shape RMS sensitivity, the PV sensitivity and the Zernike aberration sensitivity of the reflector of the space optical remote sensing camera under different temperature field distributions.
In the present embodiment, the sensitivities of the surface RMS in different structural forms to different temperature field distributions are obtained through parameters such as surface RMS, surface PV, and Zernike aberration of the mirrors in different lightweight structural forms in 36 temperature field distribution forms, as shown in fig. 9 to 11, the sensitivities are respectively the thermal stability sensitivity of a uniform chamfered mirror, the thermal stability sensitivity of a hexagonal chamfered mirror, and the thermal stability sensitivity of a three-leaf chamfered mirror, where in fig. 9 to 11, each circle represents the sensitivity of the surface RMS to the temperature field distribution, and the high and low sensitivities are represented by the depth, i.e., the larger the corresponding numerical value is, the higher the sensitivity is, the larger the size of the circle also represents the sensitivity as the same depth, and the larger the circle is, the higher the sensitivity is; in fig. 9, the arrows indicate the sensitivities of the second-order astigmatic temperature distributions, n-4 and m-2, m-6 and m-2, respectively, in fig. 10, and the third-order astigmatic temperature distributions, and n-2 and m-0, respectively, in fig. 11.
The method comprehensively considers the influence of factors such as temperature level, temperature gradient, mirror body structure form and thermal expansion coefficient distribution on the thermal stability of the reflector, considers the influence of grid convergence and the like, and is more comprehensive and accurate compared with the prior method. The result obtained by the invention can be used as a data basis of a predictable thermal control method and can be used for scheme optimization of the predictable thermal control. The result obtained by the invention can guide the structural design and provide a basis for selecting a scheme of the light weight form of the light weight reflector.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.