An experimental test alignment system and focal plane preset method for a space camera

Abstract

The application discloses an experimental test adjustment system and a focal plane presetting method for a space camera, and relates to the technical field of space cameras. The test adjustment system comprises a collimator assembly, a to-be-tested camera adjustment platform and a vacuum tank. The collimator assembly comprises a scattering light source, frosted glass, a scale plate, a light source lens, a reflecting screen and a discrimination rate plate. The to-be-tested camera comprises a to-be-tested camera lens and a plane array photoelectric detector. The focal plane presetting method comprises the following steps: adjusting the collimator assembly according to experimental test conditions; then, building the to-be-tested camera adjustment platform according to experimental test conditions; simulating an on-orbit environment to preset a central field of view; and adjusting according to multiple typical field angles in different environments. The application presets the focal plane of the space camera on the ground, guarantees clear imaging of the camera after entering the orbit, and solves the problems of complex structure, tedious steps, long time consumption and high cost in the prior art.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to an experimental testing and adjustment system and focal plane preset method for a space camera. Background Technology

[0002] Space optical remote sensing cameras are one of the important means of obtaining ground remote sensing images and are widely used in meteorology, geological exploration, agriculture and forestry, oceanography, environment, disaster relief and other fields, bringing enormous economic benefits. As the field of remote sensing information continues to expand and remote sensing technology continues to develop, the temporal and spatial resolution of remote sensing satellites is constantly improving, leading to increasingly broad application prospects.

[0003] When a space camera is installed and adjusted in a ground-based laboratory environment (normal temperature and pressure), changes in environmental conditions (such as temperature and pressure) during its operation in orbit can alter the position and shape of the optical mirrors in the camera system, change the refractive index of the optical elements, and consequently change the focal length of the optical system to some extent. This causes a shift in the focal plane position of the optical system, resulting in a deterioration in image quality. Therefore, in order to obtain clear images, it is necessary to change the focal plane position of the space camera to compensate for the shift in the focal plane position.

[0004] Existing methods for compensating for focal plane position offset include the "on-track adjustment method" and the "focal plane position preset method".

[0005] "On-orbit adjustment" involves adding a focusing mechanism to the instruments of a space camera. Focusing refers to changing the position of the object plane (or lens) along the optical axis to ensure the object-image relationship satisfies the Gaussian formula, thus obtaining a clear image. Existing focusing technologies can be divided into automatic focusing and manual focus. Automatic focusing refers to the focusing mechanism automatically judging image quality and placing the photosensitive element in the optimal position based on a certain optical evaluation criterion. Manual focus refers to technicians determining the position of the focal plane of the optical system based on the quality of the optical image and then sending a command to achieve focusing. The optical systems of space cameras vary, and their focusing mechanisms often employ different focusing methods. Three common focusing methods are: focal plane focusing, lens group focusing, and mirror focusing. These are achieved by adjusting the position of the photosensitive element, adding a lens group in front of the focal plane and moving the lens group to achieve focusing, and moving a folding mirror in the optical system to change the optical path of light, respectively. However, in general, the "on-orbit adjustment method" is technically complex and usually requires structural changes to the internal components of the space camera, which increases its mass and reduces its reliability, making it unsuitable for small space optical cameras.

[0006] The "focal plane pre-setting method" involves adjusting the focal plane of the space camera lens to the position of the vacuum focal plane before launch. For space cameras without a focusing mechanism, the photosensitive surface of the photodetector is mounted on the pre-set vacuum focal plane during laboratory assembly and adjustment. Current focal plane pre-setting methods require placing the camera under test into a vacuum chamber, determining image quality using optical transfer function or speckle method, calculating the trimming amount of the focal plane shim based on test parameters, then opening the chamber to replace or trim the focal plane shim, re-vacuuming, and testing. This process is repeated until the image quality in a vacuum environment meets the requirements. Therefore, this method requires repeated adjustments to the probe camera, resulting in repeated chamber insertions. While this has the advantage of eliminating the need for on-orbit adjustments after launch, the experimental phase requires actual measurements of the light source focal length and the camera, along with multiple chamber insertions, leading to high costs, long testing times, and overall high testing costs. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology. To achieve the above objective, an experimental testing and adjustment system and focal plane preset method for a space camera are adopted to solve the problems mentioned in the background technology.

[0008] An experimental test and adjustment system for a space camera, the test and adjustment system comprising a collimator assembly, a camera under test assembly and adjustment platform, and a vacuum chamber;

[0009] The collimator assembly includes a diffused light source, frosted glass, a reticle, a light source lens, a reflective screen, and a resolution plate.

[0010] The camera under test includes a camera lens and an area array photodetector;

[0011] The focal plane preset method includes the following steps:

[0012] Step S1: Assemble and adjust the collimator assembly according to the experimental test results;

[0013] Step S2: Then, build the camera assembly and adjustment platform based on the experimental test results;

[0014] Step S3: Simulate the on-orbit environment to preset the focal plane of the center field of view;

[0015] Step S4: Adjust the device according to various typical field of view angles under different environments.

[0016] As a further aspect of the present invention, the specific steps in step S1 include:

[0017] Step S11: A frosted glass is placed in front of the diffused light source and on a plane perpendicular to the maximum transmission direction of the diffused light source;

[0018] Step S12: Next, set a reticle on the vertical surface in front of the optical axis of the frosted glass;

[0019] Step S13: Arrange the diffused light source, frosted glass, reticle, light source lens, and reflector screen coaxially in sequence; the light emitted by the diffused light source passes through the frosted glass for light source expansion, then passes through the reticle and light source lens in sequence, and is reflected by the reflector screen. After passing through the light source lens, it forms a reticle line image on the reticle to form a light path.

[0020] Step S14: Move the position and angle of the light source lens until the image of the reticle line formed on the reticle coincides with the reticle line. Observe the reticle line and the reticle line image on the reticle with the eyepiece. At the same time, adjust the position of the reticle relative to the light source lens until the reticle line and the reticle line image on the reticle are clearly presented. Then the collimator assembly is assembled and adjusted.

[0021] As a further aspect of the present invention, the specific steps in step S2 include:

[0022] Step S21: Replace the reticle in the collimator assembly with a resolution plate in its original position;

[0023] Step S22: Install the collimator assembly described in step S1 in the vacuum chamber, so that its beam exits from the window of the vacuum chamber;

[0024] Step S23: Outside the vacuum chamber, arrange the camera lens and the area array photodetector sequentially along the optical axis of the collimator assembly; the light emitted from the resolution plate passes through the light source lens and the camera lens under test, and is imaged in the middle of the area array photodetector to form an optical path.

[0025] As a further aspect of the present invention, the specific steps in step S3 include:

[0026] Step S31: Close the vacuum tank door, evacuate the vacuum tank, and adjust the temperature inside the tank to the on-orbit temperature. Under the simulated on-orbit vacuum and temperature environment, the light source lens defocuses, and the stripe group image of the resolution plate obtained by the area array photodetector changes.

[0027] Step S32: Observe the resolution plate image acquired by the area array photodetector, and at the same time, change the position of the area array photodetector relative to the lens of the test camera by adjusting the mechanism or replacing the shims, until the number of the stripe group that can be clearly observed in the image reaches the highest level.

[0028] Step S33: Measure and record the adjustment amount of the adjustment mechanism or the thickness of the shim as the assembly result of the defocus amount and center field of view of the camera under test.

[0029] Step S34: The defocus amount of the camera under test obtained by this method is exactly equal to the defocus amount of the light source lens under given environmental conditions.

[0030] As a further aspect of the present invention, the specific steps in step S4 include:

[0031] Step S41: Change the orientation of the camera lens under test so that the outgoing beam of the collimator assembly is incident from other field angles of view of the camera lens under test.

[0032] Step S42: Repeat step S3 and record the setup and adjustment results of the camera under test at this field of view.

[0033] Step S43: Perform adjustments under several typical field of view angles, comprehensively evaluate the image quality under each field of view angle, and select the optimal focal plane position.

[0034] Compared with the prior art, the present invention has the following technical advantages:

[0035] By employing the above technical solution, the vacuum focal plane position of the camera under test is preset by aligning and measuring the collimator and the camera under test. This reduces the number of transmission links and simplifies the operation, thus effectively improving the operability of focal plane preset. Utilizing the light source lens eliminates the need for actual measurement of the lens's focal length, meaning its absolute value is irrelevant, simplifying the focal plane preset process. This characteristic, based on theoretical calculations using Gaussian optics formulas, facilitates experimentation and is easy to operate.

[0036] Instead of placing the camera under test directly in the vacuum chamber, the collimator is placed in the vacuum chamber. The focal plane of the camera under test is adjusted using the theory of Gaussian optics formula, thereby obtaining the changes in the camera in the vacuum and thus achieving focal plane preset.

[0037] Parallel optical tubes only require one vacuum cryogenic measurement, eliminating the need for repeated tank filling and vacuuming, which greatly saves testing costs and improves testing efficiency. Attached Figure Description

[0038] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings:

[0039] Figure 1 This is a flowchart of a focal plane presetting method according to an embodiment of this application;

[0040] Figure 2 This is a schematic diagram of the installation principle of the collimator according to an embodiment of this application;

[0041] Figure 3 This is a schematic diagram of the experimental testing and assembly system according to an embodiment of this application.

[0042] In the diagram: 1. Scattered light source; 2. Frosted glass; 3. Reticle; 4. Light source lens; 5. Reflecting screen; 6. Camera lens under test; 7. Area array photodetector; 8. Vacuum chamber; 9. Resolution plate; 10. Vacuum chamber window glass. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please refer to Figure 1 and Figure 2 In this embodiment of the invention, an experimental testing and adjustment system and a focal plane preset method for a space camera are provided. The testing and adjustment system includes a collimator assembly, a camera under test adjustment platform, and a vacuum tank 8.

[0045] The collimator assembly includes a diffused light source 1, a frosted glass 2, a reticle 3, a light source lens 4, a reflective screen 5, a resolution plate 9, and a vacuum tank window glass 10, wherein the vacuum tank 8 and the vacuum tank window glass 10 are used to adjust the environment to the on-orbit state.

[0046] The camera under test includes a camera lens 6 and an area array photodetector 7.

[0047] The focal plane preset method includes the following steps:

[0048] Step S1: Assemble and adjust the collimator assembly based on the experimental test results. Specific steps include:

[0049] Step S11: A frosted glass 2 is placed in front of the diffuse light source 1 and on a plane perpendicular to the maximum transmission direction of the diffuse light source 1;

[0050] In the specific implementation steps, the purpose of the frosted glass 2 is to attenuate or scatter the strong light, destroy the spatial coherence between the interference light and the stray light in the system, and avoid the fringes introduced by the stray light in the interference pattern.

[0051] In this embodiment, frosted glass 2 is placed on the vertical plane of the maximum transmission direction of the scattering light source 11, which can protect the high-sensitivity measurement of the system or prevent interference imaging of the reticle 3.

[0052] Step S12: Next, set the reticle 3 on the vertical surface in front of the optical axis of the frosted glass 2;

[0053] Step S13: Arrange the diffuse light source 1, frosted glass 2, reticle 3, light source lens 4, and reflective screen 5 in sequence on the same axis; the light emitted by the diffuse light source 1 passes through the frosted glass 2 for light source expansion, then passes through the reticle 3 and light source lens 4 in sequence, and is reflected by the reflective screen 5. After passing through the light source lens 4, it forms the reticle 3 mark image on the reticle 3 to form a light path.

[0054] In this embodiment, as Figure 2 As shown in the figure, the diffused light source 1 is an incandescent lamp source, or a frosted glass 2 is added to the light outlet of the incandescent lamp source to minimize the interference of the emitted light from the diffused light source 1 on the system. In this embodiment, an incandescent lamp source is used.

[0055] The function of the light source lens 4 is to convert light into parallel light;

[0056] Step S14: Move the position and angle of the light source lens 4 until the reticle 3 image formed on the reticle 3 coincides with the reticle. Observe the reticle and reticle image on the reticle 3 with the eyepiece, and at the same time adjust the position of the reticle 3 relative to the light source lens 4 until the reticle and reticle image on the reticle are clearly presented. Then the collimator assembly is assembled and adjusted.

[0057] The function of the reticle 33 is to receive reflected light and form the image line of the reticle 3, which is used to observe whether the image lines coincide and to determine whether the optical path of the collimator is parallel.

[0058] The function of the reflective screen 5 is to reflect the light path so that the light path can be reflected on the reticle 33.

[0059] Step S2: Based on the experimental test results, build the setup and adjustment platform for the camera under test. Specific steps include:

[0060] Using the camera lens 6, which has the same focal length as the light source lens 4, and an area array photodetector 7, the device is properly adjusted and positioned.

[0061] Step S21: Replace the reticle 3 in the collimator assembly with the resolution plate 9 in the original position;

[0062] In this embodiment, the function of the resolution plate 9 is to form a discernible image on the area array photodetector 7 of the detection camera. Because the crosshairs of the reticle 3 are too fine to be easily distinguished by the photodetector, the resolution plate 9 facilitates the detection camera's adjustment to preset the focal plane.

[0063] Step S22: Install the collimator assembly described in step S1 in the vacuum tank 8 so that its beam exits from the window of the vacuum tank;

[0064] Step S23: Outside the vacuum chamber 8, arrange the camera lens 6 and the area array photodetector 7 sequentially along the optical axis of the collimator assembly; the light emitted from the resolution plate 9 passes through the light source lens 4 and the camera lens 6, and is imaged on the center of the area array photodetector 7, forming an optical path, as shown below. Figure 3 As shown in the figure, it is a schematic diagram of the experimental test assembly system.

[0065] The function of the camera lens 6 under test is to converge light onto the area array photodetector 7. The function of the area array photodetector 7 is to receive light to form the image lines of the reticle 3, which is used to observe whether the image lines coincide and to determine whether the focal plane is at the focal point.

[0066] Step S3: Simulate the on-orbit environment to preset the focal plane of the central field of view. Specific steps include:

[0067] Step S31: Close the door of vacuum tank 8, evacuate the vacuum, and adjust the temperature inside the tank to the on-orbit temperature. Under the simulated on-orbit vacuum and temperature environment, the light source lens 4 defocuses, and the stripe group image of the resolution plate 9 obtained by the area array photodetector 7 changes.

[0068] Step S32: Observe the image of the resolution plate 9 acquired by the area array photodetector 7, and at the same time, change the position of the area array photodetector 7 relative to the lens 6 of the test camera by adjusting the mechanism or replacing the shims, until the number of the stripe group that can be clearly observed in the image reaches the highest level.

[0069] Step S33: Measure and record the adjustment amount of the adjustment mechanism or the thickness of the shim as the assembly result of the defocus amount and center field of view of the camera under test.

[0070] Step S34: The defocus amount of the camera under test obtained by this method is exactly equal to the defocus amount of the light source lens 4 under given environmental conditions.

[0071] Step S4: Perform assembly and adjustment according to various typical field of view angles under different environments. Specific steps include:

[0072] Step S41: Change the orientation of the camera lens 6 under test so that the outgoing beam of the collimator assembly is incident from other field of view angles of the camera lens 6 under test.

[0073] Step S42: Repeat step S3 and record the setup and adjustment results of the camera under test at this field of view.

[0074] Step S43: Perform adjustments under several typical field of view angles, comprehensively evaluate the image quality under each field of view angle, and select the optimal focal plane position.

[0075] By evaluating the setup under multiple fields of view, the accuracy of the setup presets can be maximized, errors can be reduced, and feasibility can be guaranteed.

[0076] Step S5: Error estimation;

[0077] Step S51, denoted as the focal length of the collimator. The focal length of the camera under test. This refers to the focus shift amount of the collimator. The focus shift amount of the camera under test. For the object distance of the collimator, The object distance of the camera to be measured is... The image distance of the collimator. The image distance of the camera to be measured is... Let be the distance between the principal surfaces of the camera lens 6 and the light source lens 4. For a collimator, we have:

[0078] In this embodiment, , ;

[0079] ;

[0080] In this embodiment, .

[0081] Step S52: Measure and record the defocus amount. The required preset distance for the camera's focal plane is calculated.

[0082] According to Gauss's optical formula, the camera under test has...

[0083] In this embodiment, take ;

[0084] ;

[0085] ;

[0086] In this embodiment, , , .

[0087] Step S53: Compare the defocus error based on the calculated defocus amount;

[0088] .

[0089] In this embodiment, .

[0090] In summary, this method utilizes the Gaussian optical formula transformation of two identical lenses, transforming the complex, multi-step measurement method originally applied to the camera under test into an adjustment method for the light source lens, thereby calculating the defocus amount of the camera under test. Compared to existing methods, this invention only uses two systems: a collimator and the camera under test, reducing the number of steps and increasing operability. This method utilizes light source lenses with the same focal length, eliminating the need for actual measurement of the lens's focal length and simplifying the focal plane preset process by not concerning itself with its absolute value. Furthermore, this invention places the collimator in the vacuum chamber 8 instead of directly placing the camera under test in the vacuum chamber 8, using Gaussian formula theory to adjust the focal plane of the camera under test to obtain the preset focal plane distance. The collimator only needs to be placed in the chamber once, eliminating the need for repeated placement, significantly reducing testing costs and improving testing efficiency.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents, all of which should be included within the scope of protection of the invention.

Claims

1. An experimental testing and assembly system for a space camera, characterized in that, The test assembly and adjustment system includes a collimator assembly, a camera under test assembly and adjustment platform, and a vacuum chamber; The collimator assembly includes a diffused light source, frosted glass, a reticle, a light source lens, a reflective screen, and a resolution plate. The camera under test assembly platform includes the camera lens under test and an area array photodetector; The light source lens and the camera lens under test are the same lens, and the light source lens is located inside the vacuum tank. The collimator assembly is fixed inside the vacuum tank, and the camera under test assembly platform is located outside the vacuum tank.

2. A focal plane preset method using the experimental test setup and adjustment system for a space camera as described in claim 1, characterized in that, The focal plane preset method includes the following steps: Step S1: Assemble and adjust the collimator assembly according to the experimental test results; Step S2: Then, build the camera assembly and adjustment platform based on the experimental test results; Step S3: Simulate the on-orbit environment to preset the focal plane of the center field of view; Step S4: Adjust the device according to various typical field of view angles under different environments.

3. The focal plane preset method for an experimental testing and adjustment system for a space camera according to claim 2, characterized in that, The specific steps in step S1 include: Step S11: A frosted glass is placed in front of the diffused light source and on a plane perpendicular to the maximum transmission direction of the diffused light source; Step S12: Next, set a reticle on the vertical surface in front of the optical axis of the frosted glass; Step S13: Arrange the diffused light source, frosted glass, reticle, light source lens, and reflector screen coaxially in sequence; the light emitted by the diffused light source passes through the frosted glass for light source expansion, then passes through the reticle and light source lens in sequence, and is reflected by the reflector screen. After passing through the light source lens, it forms a reticle line image on the reticle to form a light path. Step S14: Move the position and angle of the light source lens until the image of the reticle line formed on the reticle coincides with the reticle line. Observe the reticle line and the reticle line image on the reticle with the eyepiece. At the same time, adjust the position of the reticle relative to the light source lens until the reticle line and the reticle line image on the reticle are clearly presented. Then the collimator assembly is assembled and adjusted.

4. The focal plane preset method for an experimental testing and adjustment system for a space camera according to claim 2, characterized in that, The specific steps in step S2 include: Step S21: Replace the reticle in the collimator assembly with a resolution plate at the reticle position; Step S22: Install the collimator assembly described in step S1 in the vacuum chamber, so that its beam exits from the window of the vacuum chamber; Step S23: Outside the vacuum chamber, arrange the camera lens and the area array photodetector sequentially along the optical axis of the collimator assembly; the light emitted from the resolution plate passes through the light source lens and the camera lens under test, and is imaged in the middle of the area array photodetector to form an optical path.

5. The focal plane preset method for an experimental testing and adjustment system for a space camera according to claim 2, characterized in that, The specific steps in step S3 include: Step S31: Close the vacuum tank door, evacuate the vacuum tank, and adjust the temperature inside the tank to the on-orbit temperature. Under the simulated on-orbit vacuum and temperature environment, the light source lens defocuses, and the stripe group image of the resolution plate obtained by the area array photodetector changes. Step S32: Observe the resolution plate image acquired by the area array photodetector, and at the same time, change the position of the area array photodetector relative to the lens of the test camera by adjusting the mechanism or replacing the shims, until the number of the stripe group that can be clearly observed in the image reaches the highest level. Step S33: Measure and record the adjustment amount of the adjustment mechanism or the thickness of the shim as the assembly result of the defocus amount and center field of view of the camera under test. Step S34: The defocus amount of the camera under test obtained by this method is exactly equal to the defocus amount of the light source lens under given environmental conditions.

6. The focal plane preset method for an experimental testing and adjustment system for a space camera according to claim 2, characterized in that, The specific steps in step S4 include: Step S41: Change the orientation of the camera lens under test so that the outgoing beam of the collimator assembly is incident from other field angles of view of the camera lens under test. Step S42: Repeat step S3 and record the setup and adjustment results of the camera under test at this field of view. Step S43: Perform adjustments under several typical field of view angles, comprehensively evaluate the image quality under each field of view angle, and select the optimal focal plane position.

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