Alignment Method of Off-Axis Three-Mirror Mapping Camera with Double-Sided Array

Abstract

The present invention provides an alignment method for a two-sided array off-axis three-mirror mapping camera. The two-sided array off-axis three-mirror mapping camera is composed of a forward-looking camera and a rear-looking camera. The two cameras share a set of compensators, namely the primary mirror compensator and the tertiary mirror compensator. Taking the optical axes of the primary mirror compensator and the tertiary mirror compensator as the camera optical axes, first align the forward-looking camera. Use a high-precision adjustment frame to translate the above two compensators, and the moving distance is the same as the optical axis interval between the two cameras. Use two theodolites to aim at each other, and adjust the primary mirror compensator and the tertiary mirror compensator to be parallel to before moving. Align the rear-looking camera with the two compensators after moving as the reference. After the two cameras are aligned, install the camera frame on a high-precision two-dimensional turntable and install their respective focal plane assemblies. The present invention can achieve the parallelism of the image planes of the two lenses, improve the mapping accuracy, and achieve the high-precision alignment of the two lenses with a common frame.

Description

Technical Field

[0001] The present invention relates to the technical field of space optical remote sensing mapping, and particularly relates to an alignment method for a dual-sided array off-axis three-mirror mapping camera. Background Art

[0002] Space mapping cameras can obtain three-dimensional stereo information of the earth's surface topography and generate map products with geographical information at different scales, which is of great significance in the military and civilian fields. The off-axis three-mirror system can achieve a larger field of view under the same conditions. When used in a mapping camera, it can greatly improve the data acquisition efficiency and reduce the mapping cost. However, the alignment of the off-axis three-mirror system is more complex than that of the coaxial system, and the number of adjustment degrees of freedom is much higher. Therefore, it is difficult to accurately align the internal elements of the off-axis three-mirror camera to the designed values. According to the traditional alignment method of the off-axis three-mirror camera, it is difficult to achieve the parallelism of the image planes of the two cameras in sequence, and it is impossible to form an accurate equivalent frame photo, thus affecting the mapping accuracy. Summary of the Invention

[0003] The purpose of the present invention is to overcome the technical defect that it is difficult to achieve the parallelism of the image planes of the two cameras and it is impossible to form an accurate equivalent frame photo by using the traditional alignment method of the off-axis three-mirror camera, and to propose an alignment method for a dual-sided array off-axis three-mirror mapping camera, which can achieve the parallelism of the image planes of the two cameras, and the photographic images can form an equivalent frame photo.

[0004] To achieve the above purpose, the present invention adopts the following specific technical solutions:

[0005] An alignment method for a dual-sided array off-axis three-mirror mapping camera provided by the present invention completes the alignment of the dual-sided array off-axis three-mirror mapping camera with the aid of alignment auxiliary equipment. The dual-sided array off-axis three-mirror mapping camera includes a front-view camera, a rear-view camera, and a mapping camera frame. The front-view camera includes a front-view camera primary mirror assembly, a front-view camera secondary mirror assembly, a front-view camera tertiary mirror assembly, and a front-view camera reference cube mirror assembly. The rear-view camera includes a rear-view camera primary mirror assembly, a rear-view camera secondary mirror assembly, a rear-view camera tertiary mirror assembly, and a rear-view camera reference cube mirror assembly. The alignment auxiliary equipment includes a primary mirror compensator, a tertiary mirror compensator, a first theodolite, a second theodolite, a six-axis adjustment frame, an interferometer, a detector, and a collimator. The alignment method includes the following steps:

[0006] S1. Place the primary mirror compensator and the tertiary mirror compensator according to the positions of the camera center height, the primary mirror curvature radius of the front-view camera, and the tertiary mirror curvature radius of the front-view camera. Use a mobile three-coordinate measuring machine as an auxiliary to adjust the coaxiality of the primary mirror compensator and the tertiary mirror compensator, and monitor with the first theodolite;

[0007] S2. Use a six-axis adjustment frame to adjust the front-view camera primary mirror assembly corresponding to the primary mirror compensator, and adjust the front-view camera tertiary mirror assembly corresponding to the tertiary mirror compensator, so that the interference detection results obtained by the front-view camera primary mirror assembly and the front-view camera tertiary mirror assembly after passing through the primary mirror compensator, the tertiary mirror compensator, and the interferometer are consistent with the design values;

[0008] S3. Install the mapping camera frame on the six-axis adjustment frame, adjust the height and attitude angle of the six-axis adjustment frame, so that the front-view camera primary mirror assembly and the front-view camera tertiary mirror assembly correspond to the mounting interfaces on the mapping camera frame, and grind the adjustment pads of the front-view camera primary mirror assembly and the front-view camera tertiary mirror assembly, so that the front-view camera primary mirror assembly and the front-view camera tertiary mirror assembly are installed on the mapping camera frame without stress;

[0009] S4. Keep the position of the mapping camera frame unchanged, adjust the height and attitude angle of the six-axis adjustment mechanism, so that the front-view camera secondary mirror assembly corresponds to the mounting interface of the mapping camera frame, use a small 4D interferometer detection system to detect the wavefront aberration of a total of 5 fields of view of 0, ±0.5, and ±1, making it better than 1 / 14λ (λ = 632.8 nm), and grind the adjustment pads of the front-view camera secondary mirror assembly, so that the front-view camera secondary mirror assembly is installed on the mapping camera frame without stress;

[0010] S5. Install the front-view camera reference cube mirror assembly with the optical axis of the primary mirror compensator of the front-view camera as the reference, so that the normal line of the top surface of the front-view camera reference cube mirror assembly is parallel to the optical axis of the primary mirror compensator, and the normal line of the side surface is horizontal;

[0011] S6. Translate the primary mirror compensator and the tertiary mirror compensator, and the moving distance is the same as the interval between the optical axes of the front-view camera and the rear-view camera. Use the second theodolite to aim at the first theodolite, adjust the primary mirror compensator and the tertiary mirror compensator of the front-view camera to be parallel to before moving, repeat the operation process of S1 - S4, and complete the installation of the rear-view camera primary mirror assembly, the rear-view camera secondary mirror assembly, the rear-view camera tertiary mirror assembly, and the rear-view camera reference cube mirror assembly to complete the alignment and adjustment of the mapping camera lens;

[0012] S7. Install the mapping camera lens on a high-precision two-dimensional turntable, adjust the optical axis of the front-view camera to be parallel to the optical axis of the collimator, the normal line of the side surface of the reference cube mirror of the front-view camera is horizontal, use a six-axis adjustment frame to install the focal plane assembly of the front-view camera, so that the photosensitive surface of the detector is perpendicular to the optical axis of the front-view camera, and the center of the photosensitive surface of the detector coincides with the principal point of the front-view camera, the length direction of the detector is horizontal, power on the imaging electronics, and use the collimator to detect the MTF of each field of view of the front-view camera;

[0013] S8. Repeat S7, install the focal plane assembly of the rear-view camera, and complete the alignment and adjustment of the dual-sided array off-axis three-mirror mapping camera.

[0014] Preferably, the angular resolution of the six-axis adjustment mount is better than 1″, and the linear displacement resolution is better than 0.002 mm.

[0015] Preferably, the theodolite meets the measurement accuracy of 0.5″.

[0016] Preferably, the accuracy of the two-axis turntable is 0.5″.

[0017] The present invention can achieve the following technical effects:

[0018] 1. Compared with the alignment process of a general off-axis three-mirror camera (two units), the alignment method proposed by the present invention adds very little workload and can well control the development cycle of the mapping camera;

[0019] 2. Indirectly realize the alignment of the co-reference (compensator) for the dual-lens, making the parallelism of the focal planes of the two cameras extremely good, which is beneficial to improving the adjustment accuracy of the EFP beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of a dual-array off-axis three-mirror mapping camera according to an embodiment of the present invention.

[0021] Figure 2 is a schematic structural diagram of a primary mirror compensator according to an embodiment of the present invention

[0022] Figure 3 is a schematic diagram of the alignment method of the mapping camera according to an embodiment of the present invention.

[0023] Figure 4 is a schematic structural diagram of a reference cube mirror assembly according to an embodiment of the present invention.

[0024] Figure 5 is a schematic diagram of the principle of mutual aiming of theodolites according to an embodiment of the present invention.

[0025] Figure 6 is a schematic diagram of the alignment method of the focal plane assembly according to an embodiment of the present invention.

[0026] Figure 7 is a flowchart of the alignment method of the dual-array off-axis three-mirror mapping camera according to an embodiment of the present invention.

[0027] The reference numerals therein include: front-view camera 1, rear-view camera 2, interferometer 3, primary mirror compensator 4, standard plane mirror 5, three-mirror compensator 6, front-view camera secondary mirror assembly 7, mapping camera frame 8, front-view camera three-mirror assembly 9, front-view camera primary mirror assembly 10, six-axis adjustment mount 11, compensator reference plane mirror 12. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0030] Figure 1 The structure of a two-sided array off-axis three-mirror mapping camera according to an embodiment of the present invention is shown. Figure 2 The structure of a primary mirror compensator according to an embodiment of the present invention is shown. Figure 3 The alignment method of the mapping camera according to an embodiment of the present invention is shown.

[0031] As Figures 1 - 3 shown, the two-sided array off-axis three-mirror mapping camera consists of three parts: a front-view camera 1, a rear-view camera 2, and a mapping camera frame 8. Among them, the front-view camera includes a front-view camera primary mirror assembly 10, a front-view camera secondary mirror assembly 7, a front-view camera tertiary mirror assembly 9, and a reference cube mirror assembly of the front-view camera. The rear-view camera includes a rear-view camera primary mirror assembly, a rear-view camera secondary mirror assembly, a rear-view camera tertiary mirror assembly, and a reference cube mirror assembly of the rear-view camera. Figures 1 - 3 Some alignment auxiliary equipment is also introduced. The complete alignment auxiliary equipment includes a primary mirror compensator 4, a tertiary mirror compensator 6, a six-axis adjustment frame 11, an interferometer 3, a first theodolite, a second theodolite, a detector, and a collimator.

[0032] Figure 7 The overall process of the alignment method of the two-sided array off-axis three-mirror mapping camera according to an embodiment of the present invention is shown.

[0033] As Figure 7 shown, the specific steps of the alignment method of the two-sided array off-axis three-mirror mapping camera provided by the embodiment of the present invention are as follows:

[0034] S1. Place the primary mirror compensator 4 and the tertiary mirror compensator 6 according to the positions of the camera center height, the primary mirror curvature radius of the front-view camera 1, and the tertiary mirror curvature radius of the front-view camera 1. Both the primary mirror compensator 4 and the tertiary mirror compensator 6 are equipped with a reference flat mirror 12. The reference flat mirror 12 is strictly perpendicular to the corresponding compensator optical axis, and the inner circle axis of the reference flat mirror 12 is coaxial with the compensator optical axis. Using a mobile coordinate measuring machine as an aid, adjust the primary mirror compensator 4 and the tertiary mirror compensator 6 to be coaxial, and monitor them using a first theodolite that meets the measurement accuracy of 0.5″. And use this first theodolite as a reference during the subsequent alignment process to ensure that its position and accuracy remain unchanged.

[0035] S2. Use a six-axis adjustment mount 11 to align and adjust the front-view camera primary mirror assembly 10 and the front-view camera tertiary mirror assembly 9 with the primary mirror compensator 4 and the tertiary mirror compensator 6, so that the interference detection results (surface shape, residual aberration) obtained by the front-view camera primary mirror assembly 10 and the front-view camera tertiary mirror assembly 9 after passing through the primary mirror compensator 4, the tertiary mirror compensator 6, and the interferometer 3 are consistent with the design values. The angular resolution of the six-axis adjustment mount 11 mentioned in the present invention is better than 1″, and the linear displacement resolution is better than 0.002 mm.

[0036] S3. Install the mapping camera frame 8 on the six-axis adjustment mount 11, adjust the height and attitude angle of the six-axis adjustment mount 11, so that the front-view camera primary mirror assembly 10 and the front-view camera tertiary mirror assembly 9 correspond to the mounting interfaces on the mapping camera frame 8. Grind the adjustment pads of the front-view camera primary mirror assembly 10 and the front-view camera tertiary mirror assembly 9, and use a feeler gauge to measure the thickness (actually the air gap) and inclination angle of the adjustment pads. Improve the grinding accuracy of the adjustment pads by gradually approaching through rough grinding and fine grinding, so that the front-view camera primary mirror assembly 10 and the front-view camera tertiary mirror assembly 9 are installed on the mapping camera frame 8 without stress.

[0037] S4. Keep the position of the mapping camera frame 8 unchanged, adjust the height and attitude angle of the six-axis adjustment mechanism 11, so that the front-view camera secondary mirror assembly 7 corresponds to the mounting interface of the mapping camera frame 8. Due to space limitations, use a small 4D interferometer detection system to detect the wavefront aberration of 5 fields of view of 0, ±0.5, and ±1, so that it is better than 1 / 14λ (λ = 632.8 nm). Grind the adjustment pads of the front-view camera secondary mirror assembly 7, so that the front-view camera secondary mirror assembly 7 is installed on the camera frame without stress.

[0038] S5. Install the reference cube mirror assembly of the front-view camera 1 with the optical axis of the primary mirror compensator 4 of the front-view camera 1 as the reference. As Figure 4 shown, the spatial rectangular coordinate system of the reference cube mirror assembly follows the right-hand rule. OX is parallel to the length direction of the detector, OY is the side normal, corresponding to the on-orbit flight direction of the mapping camera, and OZ is the top normal of the cube mirror, corresponding to the optical axis direction of the mapping camera. Adjust so that the normal of the top surface of the reference cube mirror assembly is parallel to the optical axis of the primary mirror compensator 4, and the side normal is horizontal. Here, the parallelism and horizontality should minimize the deviation as much as possible within the allowable period. In this embodiment, it is required to be better than 2″, and record the measured deviation value and direction as the derived error.

[0039] S6. Translate the primary mirror compensator 4 and the tertiary mirror compensator 6. The moving distance is the same as the interval between the optical axes of the forward-looking camera 1 and the rear-looking camera 2. A mobile three-coordinate measuring machine is used to measure and adjust the moving distance. Use the second theodolite to aim at the first theodolite, and adjust the primary mirror compensator 4 and the tertiary mirror compensator 6 to be parallel to the state before movement. Repeat the operation process of S1 - S4 to complete the installation of the rear-looking camera primary mirror assembly, the rear-looking camera secondary mirror assembly, and the rear-looking camera tertiary mirror assembly of the rear-looking camera 6, and complete the alignment and adjustment of the mapping camera lens.

[0040] To understand the principle of theodolite aiming at each other, Figure 5 The principle of theodolite aiming at each other is shown. As Figure 5 shown: O1P1 is the optical axis after autocollimation of the first theodolite, and O2P2 is the optical axis after autocollimation of the second theodolite. The autocollimation targets are both the compensator reference plane mirrors. The included angle between the two optical axes is determined by the following formula:

[0041] δ = ζ + η - 180° (1),

[0042] Adjust δ = 0, which means that the optical axes are parallel before and after the compensator moves. In this embodiment, it is required that the adjustment deviation is less than 2″.

[0043] S7. Figure 6 The alignment and adjustment method of the focal plane assembly provided by the embodiment of the present invention is shown. As Figure 6 shown, install the mapping camera lens on a 0.5″ high-precision two-dimensional turntable. In order to make the image plane of the optical system of the forward-looking camera 1 perpendicular to the collimator and horizontal with the ground, adjust the optical axis of the forward-looking camera 1 to be parallel to the optical axis of the collimator, and the normal line OX of the side of the reference cube mirror is horizontal. In order to make the photosensitive surface of the detector coincide with the image plane of the optical system, use a six-dimensional adjustment frame 11 to install the focal plane assembly of the forward-looking camera, so that the photosensitive surface of the detector is perpendicular to the optical axis of the forward-looking camera, and the center of the photosensitive surface of the detector coincides with the principal point of the forward-looking camera. The length direction of the detector is horizontal, power on the imaging electronics, and use the collimator to detect the MTF of each field of view of the forward-looking camera.

[0044] S8. Repeat S7 to install the focal plane assembly of the rear-looking camera and complete the alignment and adjustment of the dual-sided array off-axis three-mirror mapping camera.

[0045] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0046] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0047] The above specific implementation manners of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An alignment method for a dual-sided array off-axis three-mirror mapping camera, which completes the alignment of the dual-sided array off-axis three-mirror mapping camera with the aid of alignment auxiliary equipment. The dual-sided array off-axis three-mirror mapping camera includes a forward-looking camera, a rear-looking camera, and a mapping camera frame. The forward-looking camera includes a forward-looking camera primary mirror assembly, a forward-looking camera secondary mirror assembly, a forward-looking camera tertiary mirror assembly, and a forward-looking camera reference cube mirror assembly. The rear-looking camera includes a rear-looking camera primary mirror assembly, a rear-looking camera secondary mirror assembly, a rear-looking camera tertiary mirror assembly, and a rear-looking camera reference cube mirror assembly. The alignment auxiliary equipment includes a primary mirror compensator, a tertiary mirror compensator, a first theodolite, a second theodolite, a six-axis adjustment stand, an interferometer, a detector, and a collimator, and is characterized in that, The alignment and adjustment method includes the following steps: S1. Place the primary mirror compensator and the tertiary mirror compensator according to the position of the camera center height, the primary mirror curvature radius of the front view camera, and the tertiary mirror curvature radius of the front view camera. Use a mobile coordinate measuring machine as an aid to adjust the coaxiality of the primary mirror compensator and the tertiary mirror compensator, and use the first theodolite for monitoring; S2. Use the six-axis adjustment frame to adjust the front view camera primary mirror assembly corresponding to the primary mirror compensator, and adjust the front view camera tertiary mirror assembly corresponding to the tertiary mirror compensator, so that the interference detection results obtained by the front view camera primary mirror assembly and the front view camera tertiary mirror assembly through the primary mirror compensator, the tertiary mirror compensator, and the interferometer are consistent with the design values; S3. Install the mapping camera frame on the six-axis adjustment frame, adjust the height and attitude angle of the six-axis adjustment frame, so that the front view camera primary mirror assembly and the front view camera tertiary mirror assembly correspond to the mounting interfaces on the mapping camera frame, and grind the adjustment pads of the front view camera primary mirror assembly and the front view camera tertiary mirror assembly, so that the front view camera primary mirror assembly and the front view camera tertiary mirror assembly are installed on the mapping camera frame without stress; S4. Keep the position of the mapping camera frame unchanged, adjust the height and attitude angle of the six-axis adjustment mechanism, so that the front view camera secondary mirror assembly corresponds to the mounting interface of the mapping camera frame, and use a small 4D interferometer detection system to detect the wavefront aberration of 5 fields of view of 0, ±0.5, and ±1, making it better than 1 / 14λ, λ = 632.8nm, and grind the adjustment pads of the front view camera secondary mirror assembly, so that the front view camera secondary mirror assembly is installed on the mapping camera frame without stress; S5. Install the front view camera reference cube mirror assembly based on the optical axis of the primary mirror compensator of the front view camera, so that the normal line of the top surface of the front view camera reference cube mirror assembly is parallel to the optical axis of the primary mirror compensator, and the normal line of the side surface is horizontal; S6. Translate the primary mirror compensator and the tertiary mirror compensator, and the moving distance is the same as the interval between the optical axes of the front view camera and the rear view camera. Use the second theodolite to aim at the first theodolite, adjust the primary mirror compensator and the tertiary mirror compensator of the front view camera to be parallel to the position before moving, repeat the operation process of S1 - S4, and complete the installation of the rear view camera primary mirror assembly, the rear view camera secondary mirror assembly, the rear view camera tertiary mirror assembly, and the rear view camera reference cube mirror assembly, and complete the alignment and adjustment of the mapping camera lens; S7. Install the mapping camera lens on a high-precision two-dimensional turntable, adjust the optical axis of the front view camera to be parallel to the optical axis of the collimator, the normal line of the side surface of the reference cube mirror of the front view camera is horizontal, use the six-axis adjustment frame to install the focal plane assembly of the front view camera, so that the photosensitive surface of the detector is perpendicular to the optical axis of the front view camera, and the center of the photosensitive surface of the detector coincides with the principal point of the front view camera, the length direction of the detector is horizontal, power on the imaging electronics, and use the collimator to detect the MTF of each field of view of the front view camera; S8. Repeat S7 to install the focal plane assembly of the rear view camera, and complete the alignment and adjustment of the double-sided array off-axis three-mirror mapping camera.

2. The alignment method of the dual-sided array off-axis three-mirror mapping camera according to claim 1, characterized in that, The angular resolution of the six-axis adjustment mount is better than 1″, and the linear displacement resolution is better than 0.002 mm.

3. The alignment method of the two-sided array off-axis three-mirror mapping camera according to claim 1, characterized in that, The theodolite meets the measurement accuracy of 0.5″.

4. The alignment method of the double-sided array off-axis three-mirror mapping camera according to claim 1, characterized in that, The accuracy of the two-axis turntable is 0.5″.

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