A Common Reference Assembly and Adjustment Method for Off-Axis Freeform Surface Systems Based on CGH
By selecting the reference surface of the structural box in the freeform off-axis system, and combining it with a photoelectric theodolite and a point source microscope, the common reference assembly and adjustment of the optical system was realized, which solved the problem of insufficient engineering feasibility in the existing technology and improved the assembly and adjustment accuracy and quantitative control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAN INST OF OPTICS & PRECISION MECHANICS CHINESE ACAD OF SCI
- Filing Date
- 2025-03-19
- Publication Date
- 2026-07-17
AI Technical Summary
Existing assembly and adjustment methods do not take into account the constraints of the structural frame on the optical system, resulting in insufficient engineering feasibility and making it difficult to achieve precise assembly and adjustment of freeform off-axis reflective spectrometers.
A laser tracker was used to select three planes of the structural box with a flatness error within 0.02 mm as reference planes. A photoelectric theodolite was used to collimate the CGH. Combined with a point source microscope and a dynamic interferometer, the position of the CGH and optical components was determined by adjusting the target ball to achieve common reference assembly.
It improves the assembly and adjustment accuracy, reduces the conversion error between theoretical and actual positions, reduces the adjustment amount of the primary mirror and the three mirrors, provides a quantitatively controlled assembly and adjustment process, and ensures the high-precision realization of the optical system.
Smart Images
Figure CN120122346B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an assembly and adjustment method for optical instruments, specifically to a common reference assembly and adjustment method for a freeform surface off-axis system based on CGH. Background Technology
[0002] Spaceborne cameras are constantly improving their application scenarios and technical requirements. Wide-swath, high spatial resolution imaging systems are being used in increasingly wider fields, and the performance requirements for imaging systems are getting higher and higher. After introducing freeform surfaces, the Offner-type spectrometer can achieve good imaging quality while ensuring the size and weight of the imaging spectrometer.
[0003] The precise assembly and adjustment of freeform off-axis reflective spectrometers, ensuring the successful implementation of the design, has become a challenge. Existing assembly and adjustment methods for aspherical compensating mirrors cannot achieve assembly and adjustment of freeform surfaces without rotation. With the continuous development of technology, freeform off-axis reflectors typically use CGH (Computer Generated Holograms) to achieve high-precision detection, while also enabling auxiliary assembly and adjustment of the optical system.
[0004] Chinese patent CN118915294A discloses a method for assembling and adjusting a free-form surface off-axis reflective space camera using a CGH compensator. However, this method does not consider the constraints of the structural frame on the optical system, resulting in insufficient engineering feasibility. Summary of the Invention
[0005] The purpose of this invention is to solve the technical problem that existing assembly and adjustment methods do not consider the constraints of the structural frame on the optical system and have insufficient engineering feasibility, and to provide a common reference assembly and adjustment method for free-form surface off-axis systems based on CGH.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] A common reference assembly and adjustment method for a freeform surface off-axis system based on CGH is characterized by the following steps:
[0008] Step 1: Using the laser tracker as a reference, select three planes on the structural box of the freeform off-axis system to be installed, whose flatness errors are within the set error range and are orthogonal to each other, as reference planes.
[0009] Step 2: Based on any reference plane, use an electro-optical theodolite to collimate the CGH to determine the pitch and yaw directions of the CGH;
[0010] Step 3: Based on the focal position determined by the laser tracker, place the first target ball on the target ball placement stage, 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 fix the point source microscope.
[0011] Step 4: Replace the first target ball with a second target ball. The radius of the second target ball is smaller than the back intercept of the lens of the dynamic interferometer. 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, thus determining the position of the second target ball. Use the dynamic interferometer to form an interferogram of the center point of the second target ball, thus determining the position of the dynamic interferometer. The interferogram must meet the condition that the number of fringes is in the single digits.
[0012] Step 5: Adjust the position of CGH so that the CGH self-collimation area presents interference fringes on the dynamic interferometer with a clarity that meets the set clarity requirements, and determine the position of CGH;
[0013] Step 6: Using the first main holographic pair of the CGH primary mirror and the second main holographic pair of the CGH secondary mirror as references, assemble and adjust the primary mirror and the secondary mirror so that the primary mirror and the secondary mirror present interference fringes at full aperture in the dynamic interferometer, and the number of interference fringes is within the set range. This completes the assembly and adjustment of the primary mirror and the secondary mirror, that is, the common reference assembly and adjustment of the freeform surface off-axis system is realized.
[0014] Furthermore, in step 1, the upper surface of the structural box in the off-axis system to be installed is selected as the first reference surface; the side of the structural box in the off-axis system to be installed is selected as the side closest to the laser tracker as the second reference surface, and the side furthest from the laser tracker as the third reference surface.
[0015] Furthermore, in step 1, the set error range is less than or equal to 0.02 mm.
[0016] Furthermore, in step 6, the set range is 0 to 5.
[0017] Furthermore, in step 4, the interference pattern satisfies the condition that the number of fringes is 1.
[0018] Furthermore, in step 3, the first target sphere is a cornerstone prism.
[0019] The beneficial effects of this invention are:
[0020] 1. This invention can reduce the conversion error between theoretical and actual positions in practical engineering applications, and ensure design realization through high-precision optical methods;
[0021] 2. When imaging with a large aperture, the dynamic interferometer lens has a relatively large aperture, which makes it impossible to find the center image of the target sphere, an accessory of the laser tracker. However, this invention uses a point source microscope, which ensures 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 envelope and position of optical elements. The assembly and adjustment method of the present invention reduces the adjustment amount of the primary mirror and the three mirrors, and the process can be quantitatively controlled, providing a complete link guarantee for subsequent assembly and troubleshooting. Attached Figure Description
[0023] Figure 1 This is a schematic diagram illustrating the implementation principle of a common reference assembly and adjustment method for a freeform surface off-axis system based on CGH according to the present invention. The dashed lines in the diagram represent light rays.
[0024] In the figure: 1-Laser tracker, 2-Point source microscope, 3-Dynamic interferometer, 4-Target sphere, 5-CGH, 51-CGH autocollimation zone, 52-CGH first principal hologram, 53-CGH second principal hologram, 6-Structural box, 61-First reference plane, 62-Second reference plane, 63-Third reference plane, 7-Primary mirror, 8-Three mirrors, 9-Photoelectric theodolite. Detailed Implementation
[0025] To make the objectives, advantages, and features of the present invention clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a method for common reference assembly and adjustment of a freeform surface off-axis system based on CGH. The advantages and features of the present invention will become clearer from the following specific embodiments.
[0026] See Figure 1 This embodiment presents a common reference assembly and adjustment method for a freeform surface off-axis system based on CGH. The main instruments and equipment used include a laser tracking device, a point source microscope 2, an optoelectronic theodolite 9, a dynamic interferometer 3, and a CGH 5.
[0027] The CGH 5 includes a CGH autocollimation zone 51, a first CGH master hologram 52, and a second CGH master hologram 53. The laser tracking device includes a laser tracker 1 and its accessory target sphere 4. The target sphere 4 includes a first target sphere and a second target sphere, wherein the radius of the second target sphere is smaller than the back intercept of the lens of the dynamic interferometer 3.
[0028] The first target ball uses a cornerstone prism, while the second target ball does not need to use a cornerstone prism; a regular prism can be used instead.
[0029] Based on the above-mentioned device, this embodiment is implemented using the following steps:
[0030] Step 1: Using the laser tracker 1 as a reference, select three planes on the structural box 6 of the freeform off-axis system to be installed and whose flatness errors are within the set error range, specifically, the error range is less than or equal to 0.02mm, and which are orthogonal to each other, as the reference planes.
[0031] Based on the aforementioned principles for selecting reference surfaces, and for reference purposes, in this embodiment, the upper surface of the structural housing 6 is selected as the first reference surface 61; the side of the structural housing 6 closest to the laser tracker 1 is selected as the second reference surface 62, and the side furthest from the laser tracker 1 is selected as the third reference surface 63. In other embodiments of the present invention, those skilled in the art may also select other surfaces on the structural housing 6 as reference surfaces according to the aforementioned principles for selecting reference surfaces; these are not listed in this embodiment.
[0032] Step 2: Based on any reference plane, use an optical theodolite 9 to collimate CGH 5 to determine the pitch and yaw directions of CGH 5.
[0033] For reference, if the selected reference plane is the second reference plane 62 or the third reference plane 63, then the CGH self-collision area 51 is perpendicular to the third reference plane 63; if the selected reference plane is the first reference plane 61, then the CGH self-collision area 51 is parallel to the first reference plane 61.
[0034] Step 3: Based on the focal position determined by the laser tracker 1, place the first target ball on the target ball placement stage, adjust the position of the point source microscope 2 so that the point source microscope 2 forms an autocollimation 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 an autocollimation 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 interferogram of the center point of the second target ball 4, and determine the position of the dynamic interferometer 3; the interferogram must meet the following conditions: the number of fringes is a single digit, preferably 1.
[0036] Step 5: Adjust the position of CGH 5 so that the CGH self-collimation zone 51 presents interference fringes on the dynamic interferometer 3 with a clarity that meets the set clarity requirements, and determine the position of CGH 5.
[0037] Step 6: Using the first main hologram 52 of CGH paired with the main mirror 7 and the second main hologram 53 of CGH paired with the three mirrors 8 as references, adjust the poses of the main mirror 7 and the three mirrors 8 respectively, so that the main mirror 7 and the three mirrors 8 present interference fringes at full aperture in the dynamic interferometer 3, and the number of interference fringes is within the set range. Specifically, the aforementioned set range is 0 to 5 fringes. The adjustment of the main mirror 7 and the three mirrors 8 is completed, that is, the common reference adjustment of the freeform surface off-axis system is realized.
Claims
1. A common reference assembly and adjustment method for a freeform surface off-axis system based on CGH, characterized in that, Includes the following steps: Step 1: Using the laser tracker (1) as a reference, select three planes on the structural box (6) of the freeform off-axis system to be installed, whose flatness errors are within the set error range and are orthogonal to each other, as reference planes; Step 2: Based on any reference plane, use an optoelectronic theodolite (9) to collimate the CGH (5) to determine the pitch direction and yaw direction of the CGH (5); the CGH (5) is equipped with a CGH autocollimation zone (51), a CGH first master hologram (52) and a CGH second master hologram (53). Step 3: According to the focal position of the laser tracker (1), place the first target ball on the target ball placement stage, adjust the position of the point source microscope (2) so that the point source microscope (2) forms an autocollimation image of the center point of the first target ball, and fix the point source microscope (2). Step 4: Replace the first target ball with a second target ball. The radius of the second target ball is smaller than the back intercept of the lens of the dynamic interferometer (3). Adjust the position of the second target ball so that the point source microscope (2) forms an autocollimation 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 interferogram of the center point of the second target ball, and determine the position of the dynamic interferometer (3). The interferogram satisfies the condition that the number of fringes is in the single digits. Step 5: Adjust the position of CGH (5) so that the CGH self-collimation zone (51) presents interference fringes on the dynamic interferometer (3) with a clarity that meets the set clarity requirements, and determine the position of CGH (5); Step 6: Using the first master hologram (52) of CGH as a reference for the master mirror (7) and the second master hologram (53) of CGH as a reference for the three mirrors (8), adjust the poses of the master mirror (7) and the three mirrors (8) respectively, so that the master mirror (7) and the three mirrors (8) present interference fringes at full aperture in the dynamic interferometer (3), and the number of interference fringes is within the set range. The adjustment of the master mirror (7) and the three mirrors (8) is completed, that is, the common reference adjustment of the freeform surface off-axis system is realized.
2. The common reference assembly and adjustment method for a freeform surface off-axis system based on CGH according to claim 1, characterized in that: In step 1, the three planes selected on the structural box (6) of the free-form off-axis system to be installed are as follows: the upper surface of the structural box (6) of the free-form off-axis system to be installed is selected as the first reference plane (61); the side of the structural box (6) of the free-form 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 assembly and adjustment method for a freeform surface off-axis system based on CGH according to claim 1 or 2, characterized in that: In step 1, the set error range is less than or equal to 0.02 mm.
4. The common reference assembly and adjustment method for a freeform surface off-axis system based on CGH according to claim 3, characterized in that: In step 6, the set range is 0 to 5.
5. The common reference assembly and adjustment method for a freeform surface off-axis system based on CGH according to claim 4, characterized in that: In step 4, the interferogram satisfies the condition that the number of fringes is 1.
6. The common reference assembly and adjustment method for a freeform surface off-axis system based on CGH according to claim 5, characterized in that: In step 3, the first target ball is a corner cube prism.