CGH-based free-form surface off-axis system common-reference installation and adjustment method

Abstract

The invention relates to an installation and adjustment method, in particular to a free-form surface off-axis system common-reference installation and adjustment method based on a CGH. The method comprises the following steps: 1, selecting three planes on a structural box body as reference planes; 2, using a photoelectric theodolite to collimate the CGH; 3, placing a first target ball on the target ball placing table, adjusting the position of the point source microscope to enable the point source microscope to form an auto-collimation image on the first target ball, and fixing the point source microscope; 4, replacing the first target ball with a second target ball, adjusting the position of the second target ball, enabling the point source microscope to form an auto-collimation image on the second target ball, and determining the position of the second target ball; forming an interferogram on the second target ball by using the dynamic interferometer, and determining the position of the dynamic interferometer; 5, adjusting the position of the CGH to enable the CGH auto-collimation region to present interference fringes meeting the set definition on the dynamic interferometer, and determining the position of the CGH; and 6, aligning the primary mirror with the first primary hologram of the CGH, aligning the secondary mirror with the third mirror with the second primary hologram of the CGH, and assembling and adjusting the primary mirror and the third mirror.

Description

Technical Field

[0001] The present invention relates to an alignment method for an optical instrument, and more particularly to a co - reference alignment method for an off - axis free - form surface system based on CGH (Computer - Generated Holograms). Background Art

[0002] Spaceborne cameras have continuously improved their application scenarios and technical requirements. For imaging systems with wide swaths and high spatial resolutions, their application fields are becoming increasingly extensive, and the performance requirements for imaging systems are getting higher and higher. After the introduction of free - form surfaces in spectrometers in the Offner form, good imaging quality can be achieved while ensuring the volume and weight of the imaging spectrometer.

[0003] Subsequently, the precise alignment of off - axis free - form surface spectrometers and ensuring the implementation of the design have become difficult points; the existing alignment methods for aspherical compensating mirrors cannot achieve the alignment of non - rotationally symmetric free - form surfaces. With the continuous development of technology, off - axis free - form mirrors usually use CGH (Computer - Generated Holograms) to achieve high - precision detection and can also assist in the alignment of optical systems.

[0004] Chinese Patent CN118915294A discloses an alignment method for an off - axis free - form surface space camera using a CGH compensator, but this method does not consider the constraints of the structural frame on the optical system, and the engineering feasibility is insufficient. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems that the existing alignment methods do not consider the constraints of the structural frame on the optical system and the engineering feasibility is insufficient, and to provide a co - reference alignment method for an off - axis free - form surface system based on CGH.

[0006] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0007] A co - reference alignment method for an off - axis free - form surface system based on CGH, characterized by including the following steps:

[0008] Step 1: Taking the laser tracker as a reference, select three planes on the structural box of the off - axis free - form surface system to be aligned, whose flatness errors are within the set error range and are orthogonal to each other pairwise as the reference planes;

[0009] Step 2: Based on any one of the reference planes, use an optoelectronic theodolite to collimate the CGH to determine the pitch direction and yaw direction of the CGH;

[0010] Step 3: Place the first target ball on the target ball placement table according to the focal point position determined by the laser tracker, and adjust the position of the point source microscope so that the point source microscope forms an autocollimation image of the center point of the first target ball, and then fix the point source microscope;

[0011] Step 4: Replace the first target ball with the second target ball. The radius of the second target ball is smaller than the back intercept of the lens of the dynamic interferometer, and adjust the position of the second target ball so that the point source microscope forms an autocollimation image of the center point of the second target ball to determine the position of the second target ball; Use the dynamic interferometer to form an interference pattern of the center point of the second target ball to determine the position of the dynamic interferometer; The interference pattern meets the condition: the number of fringes is a single digit;

[0012] Step 5: Adjust the position of the CGH so that the interference fringes with clarity meeting the set clarity requirements appear in the autocollimation area of the CGH on the dynamic interferometer, and determine the position of the CGH;

[0013] Step 6: Taking the first main hologram of the CGH for the primary mirror and the second main hologram of the CGH for the tertiary mirror as references, adjust the primary mirror and the tertiary mirror so that the interference fringes under the full aperture appear in the dynamic interferometer, and the number of interference fringes is within the set range, completing the adjustment of the primary mirror and the tertiary mirror, that is, realizing the common reference adjustment of the free-form off-axis system.

[0014] Further, in step 1, select the upper surface of the structural box of the free-form off-axis system to be adjusted as the first reference plane; select the side surface of the structural box of the free-form off-axis system to be adjusted close to the laser tracker as the second reference plane, and the side surface far from the laser tracker as the third reference plane.

[0015] Further, in step 1, the set error range is: less than or equal to 0.02 mm.

[0016] Further, in step 6, the set range is: 0 to 5.

[0017] Further, in step 4, the interference pattern meets the condition: the number of fringes is 1.

[0018] Further, in step 3, the first target ball is a corner cube prism.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention can reduce the conversion error between the theoretical position and the actual position in engineering practical applications, and ensure the realization of the design in a high-precision optical manner;

[0021] 2. When imaging with a large aperture, the relative aperture of the lens of the dynamic interferometer is large, and there is a problem that it is impossible to find the image of the center of the target ball, an accessory of the laser tracker. However, the present invention adopts a point source microscope, thus ensuring that the spatial position of the reference is not lost;

[0022] 3. When the structural box is a truss structure, there are many restrictions on the optical elements, such as envelopment and position. The alignment method of the present invention reduces the adjustment amount of the primary mirror and the tertiary mirror, and the process can be quantitatively controlled, providing a complete link guarantee for subsequent alignment and problem troubleshooting. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the implementation principle of a common reference alignment method for a free-form off-axis system based on CGH of the present invention. The dotted lines in the figure represent light rays.

[0024] In the figure: 1 - Laser tracker, 2 - Point source microscope, 3 - Dynamic interferometer, 4 - Target ball, 5 - CGH, 51 - CGH auto - collimation area, 52 - CGH first main hologram, 53 - CGH second main hologram, 6 - Structural box, 61 - First reference plane, 62 - Second reference plane, 63 - Third reference plane, 7 - Primary mirror, 8 - Tertiary mirror, 9 - Photo - electronic theodolite. Detailed Embodiment

[0025] To make the objectives, advantages and features of the present invention clearer, the following further details a common reference alignment method for a free - form off - axis system based on CGH proposed by the present invention in conjunction with the drawings and specific embodiments. According to the following detailed embodiments, the advantages and features of the present invention will be clearer.

[0026] Refer to Figure 1 , in this embodiment, a common reference alignment method for a free - form off - axis system based on CGH mainly uses instruments and equipment including a laser tracking device, a point source microscope 2, a photo - electronic theodolite 9, a dynamic interferometer 3 and a CGH 5.

[0027] Among them, the CGH 5 is provided with a CGH auto - collimation area 51, a CGH first main hologram 52 and a CGH second main hologram 53; the laser tracking device includes a laser tracker 1 and its accessory target ball 4. The target ball 4 includes a first target ball and a second target ball. Among them, the radius of the second target ball is less than the back focal length of the lens of the dynamic interferometer 3.

[0028] The first target ball uses a corner - cube prism, and the second target ball may not use a corner - cube prism and an ordinary prism can be used.

[0029] Based on the above devices, this embodiment specifically adopts the following steps to implement:

[0030] Step 1: Taking the laser tracker 1 as a reference, select three planes on the structural box 6 of the free - form off - axis system to be aligned, the flatness error of which is within a set error range. Specifically, the error range is less than or equal to 0.02 mm, and the two - by - two orthogonal planes are used as reference planes.

[0031] Based on the above-mentioned reference plane selection principle, for reference, in this embodiment, the upper surface of the structural box body 6 is selected as the first reference plane 61; the side surface of the structural box body 6 close to the laser tracker 1 is selected as the second reference plane 62, and the side surface away from the laser tracker 1 is selected as the third reference plane 63. In other embodiments of the present invention, those skilled in the art can also select other surfaces on the structural box body 6 as reference planes according to the aforementioned reference plane selection principle, which will not be listed one by one in this embodiment.

[0032] Step 2: Based on any one of the reference planes, use the photoelectric theodolite 9 to collimate the CGH 5 to determine the pitching direction and yaw direction of the CGH 5.

[0033] For reference, if the selected reference plane is the second reference plane 62 or the third reference plane 63, then make the CGH self-collimation area 51 perpendicular to the third reference plane 63; if the selected reference plane is the first reference plane 61, then make the CGH self-collimation area 51 parallel to the first reference plane 61.

[0034] Step 3: According to the focal position determined by the laser tracker 1, place the first target ball on the target ball placement table, and adjust the position of the point source microscope 2 so that the point source microscope 2 forms a self-collimation image of the center point of the first target ball, and fix the point source microscope 2.

[0035] Step 4: Replace the first target ball with the second target ball, adjust the position of the second target ball so that the point source microscope 2 forms a self-collimation image of the center point of the second target ball, and determine the position of the second target ball; use the dynamic interferometer 3 to form an interference pattern of the center point of the second target ball 4 to determine the position of the dynamic interferometer 3; the interference pattern meets the condition: the number of fringes is a single digit, preferably 1.

[0036] Step 5: Adjust the position of the CGH 5 so that the CGH self-collimation area 51 presents interference fringes on the dynamic interferometer 3 with a clarity meeting the set clarity requirement, and determine the position of the CGH 5.

[0037] Step 6: Taking the CGH first main hologram 52 for the primary mirror 7 and the CGH second main hologram 53 for the tertiary mirror 8 as references, respectively adjust the postures of the primary mirror 7 and the tertiary mirror 8 so that the primary mirror 7 and the tertiary mirror 8 respectively present interference fringes under the full aperture in the dynamic interferometer 3, and the number of interference fringes is within the set range. Specifically, the aforementioned set range is from 0 to 5, and the adjustment of the primary mirror 7 and the tertiary mirror 8 is completed, that is, the common reference adjustment of the free-form off-axis system is realized.

Claims

1. A common reference adjustment method for a free-form surface off-axis system based on CGH, characterized in that: The following steps are involved: Step 1, using the laser tracker (1) as a reference, select three planes on the structural box (6) in the free-form surface off-axis system to be assembled and adjusted, the planes having flatness errors within a set error range and being orthogonal to each other as reference planes; Step 2: Based on any reference plane, use a photoelectric theodolite (9) to align the CGH (5) to determine the pitch direction and yaw direction of the CGH (5); Step 3, placing a first target ball on the target ball placement table according to the focal position of the laser tracker (1), adjusting the position of the point source microscope (2) so that the point source microscope (2) forms a self-collimated image with respect to the center point of the first target ball, and fixing the point source microscope (2); Step 4, replacing the first target ball with a second target ball, wherein the radius of the second target ball is smaller than the back intercept of the lens of the dynamic interferometer (3), and adjusting the position of the second target ball so that the point source microscope (2) forms a self-collimation image with the center point of the second target ball, and the position of the second target ball is determined; using the dynamic interferometer (3) to form an interference pattern with the center point of the second target ball, the position of the dynamic interferometer (3) is determined; the interference pattern satisfies the condition that the number of fringes is in the single digit; Step 5, adjusting the position of the CGH (5) so that the CGH self-alignment area (51) presents interference fringes on the dynamic interferometer (3) with a clarity that meets the set clarity requirement, and determining the position of the CGH (5); Step 6: Using the CGH first master hologram (52) for the main mirror (7) and the CGH second master hologram (53) for the third mirror (8) as references, the positions of the main mirror (7) and the third mirror (8) are adjusted respectively, so that the main mirror (7) and the third mirror (8) respectively present interference fringes at full aperture in the dynamic interferometer (3), and the number of interference fringes is within a set range, and the adjustment of the main mirror (7) and the third mirror (8) is completed, that is, the common reference adjustment of the free-form surface off-axis system is achieved.

2. The method for common reference adjustment of free-form surface off-axis system based on CGH according to claim 1, characterized in that: In step 1, three planes on the structural box (6) in the free-form surface off-axis system to be installed are selected specifically as follows: the upper surface of the structural box (6) in the free-form surface off-axis system to be installed is selected as the first reference plane (61); the side of the structural box (6) in the free-form surface off-axis system to be installed is close to the laser tracker (1) as the second reference plane (62), and the side away from the laser tracker (1) is selected as the third reference plane (63).

3. A common reference adjustment method for a free-form surface off-axis system based on CGH according to claim 1 or 2, characterized in that: In step 1, the setting error range is: less than or equal to 0.02mm.

4. The method for common reference adjustment of free-form surface off-axis system based on CGH according to claim 3, characterized in that: In step 6, the setting range is: 0 to 5.

5. The method for common reference adjustment of free-form surface off-axis system based on CGH according to claim 4, characterized in that: In step 4, the interference pattern satisfies the condition that the number of fringes is 1.

6. The method for common reference adjustment of free-form surface off-axis system based on CGH according to claim 5, characterized in that: In step 3, the first target sphere is a corner cube prism.

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