Method for assembling and adjusting off-axis free-form surface ray machine structure

Abstract

The invention provides an assembling and adjusting method of an off-axis free-form surface ray machine structure. The off-axis free-form surface ray machine structure comprises a main frame, a primary mirror and a secondary mirror (or a third mirror). The adjustment system comprises a CGH device and an interferometer. When an optical machine structure is designed and processed, a mounting reference surface and a positioning feature mark are processed on a main frame and an optical element in a high-precision processing mode. In the installation and adjustment process, the optical element is connected with the main frame through the installation reference surface, and coarse positioning installation is achieved; fine positioning and adjustment are carried out on the assembly body through the positioning feature marks; and finally, the light emitted by the interferometer sequentially passes through elements in a light path and returns to the interferometer to form interference fringes, and the pose of the secondary mirror (or the third mirror) is adjusted by taking the primary mirror as a reference until zero fringes are displayed on the interferometer. According to the method, corresponding structure reference transmission is considered during design of an optical machine structure, and rapid integrated assembly and adjustment of the off-axis free-form surface optical machine system are realized through positioning feature marking during assembly, so that the assembly and adjustment precision is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of the design and alignment of off-axis free-form optical-mechanical structures, and particularly relates to an alignment method for an off-axis free-form optical-mechanical structure. Background Technique

[0002] An off-axis free-form optical-mechanical system includes multiple optical elements, and each optical element has 6 degrees of freedom. If the positioning of each optical element is inaccurate during design, it will be difficult to implement subsequent alignment. To address this problem, current free-form alignment solutions mainly focus on reducing the degrees of freedom of optical elements and using mechanical cooperation between optical elements and the main frame and other elements to achieve the alignment of the optical-mechanical system.

[0003] Chinese Patent CN202110993945.8, an alignment test method and system for an off-axis three-mirror camera based on a CGH compensator. This patent uses a laser tracker target ball for positioning, adjusts the position of the CGH compensator, and then adjusts the position of the optical element to align the off-axis three-mirror camera. In this patent, the pose of the optical element is mainly adjusted to achieve the corresponding alignment, while the main frame only plays a supporting role and does not participate in the structural positioning process, reducing the alignment efficiency of the off-axis optical-mechanical system.

[0004] Chinese Patent CN202110399019.8, a multi-mirror integrated large field of view long focal length off-axis four-mirror optical system. This patent uses the method of forming an integral body of multiple optical elements on the same substrate, reducing the alignment difficulty of the optical-mechanical system. However, this method is only applicable to optical systems with similar curvatures of multi-curved optical elements and is not suitable for optical systems with large height differences and large curvature differences. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of low alignment efficiency of the existing off-axis free-form optical-mechanical system and its inapplicability to optical-mechanical systems with large curvature differences, and to provide an alignment system and an alignment method for an off-axis free-form optical-mechanical structure. During design, positioning feature marks are designed on the main frame, and high-precision positioning reference planes are designed on the primary mirror and the secondary mirror. During alignment, in the detection optical path setup, the interference standard wavefront forms projection marker points through a computer-generated hologram device (CGH device) and aligns with the positioning feature marks on the main frame and the optical element, making the reference of the optical element and the main frame unified, which is conducive to quickly achieving the alignment of the optical-mechanical system.

[0006] To achieve the above purpose, the technical solution provided by the present invention is:

[0007] An alignment method for an off-axis free-form optical-mechanical structure, wherein the off-axis free-form optical-mechanical structure includes a main frame, a primary mirror and a secondary mirror mounted on the main frame, and the primary mirror and the secondary mirror are located on different planes of the main frame; a plurality of positioning feature marks are provided at corresponding mounting positions on the primary mirror, the secondary mirror and the main frame;

[0008] It further includes an alignment system, and the alignment system includes a standard plane mirror, an interferometer and a computer-generated hologram device;

[0009] The standard plane mirror is arranged on one side of the off-axis free-form optical-mechanical structure and is close to the primary mirror; the computer-generated hologram device and the interferometer are sequentially arranged on the other side of the off-axis free-form optical-mechanical structure and are close to the secondary mirror;

[0010] The alignment method includes the following steps:

[0011] Step 1, according to the design requirements of the optical-mechanical structure, design the shape structure of the main frame; machine positioning and mounting reference planes on the main frame, the primary mirror and the secondary mirror, and set a plurality of positioning feature marks on the positioning reference;

[0012] Step 2, based on the zero-position interference principle, perform coordinate transformation on the positioning feature marks on the main frame, the primary mirror and the secondary mirror in the optical design coordinate system, and design and manufacture a computer-generated hologram device according to the coordinates corresponding to the transformed positioning feature marks;

[0013] Step 3, according to the machined positioning and mounting reference planes, install the primary mirror and the secondary mirror at corresponding positions on the main frame to achieve rough positioning and assembly of the optical elements and the main frame;

[0014] Step 4, set up the alignment system: mount the standard plane mirror on one side of the off-axis free-form optical-mechanical structure and close to the primary mirror; sequentially arrange the computer-generated hologram device and the interferometer on the other side of the off-axis free-form optical-mechanical structure and close to the secondary mirror;

[0015] Step 5, positioning and alignment between the main frame and the computer-generated hologram device: adjust the pose of the computer-generated hologram device so that the standard wavefront of the interferometer passes through the alignment grating area of the computer-generated hologram device to form a positioning alignment grating for positioning the positioning feature marks;

[0016] Adjust the pose of the main frame so that the positioning alignment grating aligns with the positioning feature marks on the main frame;

[0017] Step 6, precise positioning and alignment between the main frame, the primary mirror and the secondary mirror: the light emitted by the interferometer passes through the computer-generated hologram device, the secondary mirror, the primary mirror and the standard plane mirror in sequence, and after being reflected by the standard plane mirror, it returns to the interferometer through the primary mirror, the secondary mirror and the computer-generated hologram device in sequence to form interference fringes, and adjust the pose of the secondary mirror until zero fringes are displayed on the interferometer.

[0018] An alignment method for an off-axis free-form optical-mechanical structure, the off-axis free-form optical-mechanical structure includes a main frame and a primary mirror and a tertiary mirror mounted on the main frame, and the primary mirror and the tertiary mirror are located on the same plane of the main frame, and there are several positioning feature marks at the corresponding mounting positions on the primary mirror, the tertiary mirror and the main frame;

[0019] It also includes an alignment system, and the alignment system includes an interferometer, a first computer-generated hologram device and a second computer-generated hologram device;

[0020] The alignment method includes:

[0021] Step 1, according to the design requirements of the optical-mechanical structure, design the shape structure of the main frame, machine the positioning and installation reference surface, and machine several positioning feature marks on the positioning and installation reference surface;

[0022] Step 2, according to the zero-position interference principle, perform coordinate transformation on the positioning feature marks on the main frame, the primary mirror and the tertiary mirror in the optical design coordinate system, and design and manufacture a computer-generated hologram device according to the coordinates corresponding to the transformed positioning feature marks;

[0023] Step 3, according to the machined positioning and installation reference surface, install the primary mirror at the corresponding position on the main frame to achieve the rough positioning and assembly of the primary mirror, the secondary mirror and the main frame; and sequentially set the interferometer and the first computer-generated hologram device on one side of the main frame;

[0024] Step 4, positioning and alignment between the primary mirror, the main frame and the first computer-generated hologram device: Start the interferometer, the light emitted by the interferometer projects a positioning alignment grating through the first computer-generated hologram device, and adjust the spatial pose of the first computer-generated hologram device so that the positioning alignment grating is simultaneously projected on the positioning feature marks on the primary mirror and the main frame;

[0025] Step 5, positioning and alignment between the primary mirror, the main frame and the second computer-generated hologram device: Replace the first computer-generated hologram device with the second computer-generated hologram device, so that the standard wavefront emitted by the interferometer projects an alignment point through the alignment grating of the second computer-generated hologram device, and adjust the pose of the second computer-generated hologram device so that the projected alignment point coincides with the positioning feature marks of the main frame and the primary mirror;

[0026] Step 6, rough positioning and alignment of the tertiary mirror with the primary mirror and the main frame: Install the tertiary mirror at the corresponding position on the main frame, and adjust the pose of the tertiary mirror so that the light emitted by the interferometer passes through the second computer-generated hologram device and is projected on the positioning feature marks on the tertiary mirror;

[0027] Step 7, precise positioning and alignment of the main frame with the primary mirror and the tertiary mirror: According to the interference fringe state displayed by the interferometer, finely adjust the pose of the tertiary mirror until a zero fringe is displayed on the interferometer, and the alignment is completed.

[0028] Further, in the above alignment method, the computer-generated hologram (CGH) device is mounted on an adjustment mount for adjusting the position and pose of the CGH device by adjusting the adjustment mount.

[0029] Further, in the above alignment method, the positioning feature marks processed on the main frame and the optical element are standard target balls or high-precision cross reticles.

[0030] The advantages of the present invention are as follows:

[0031] When designing the optical system of the present invention, a processing and installation reference for the free-form optical element is established, and positioning feature marks are processed on the installation reference. At the same time, positioning feature marks are designed at the installation positions of the optical elements on the main frame. During the alignment process, an interferometer and a CGH device are used to check the alignment of the main frame and the optical element. The positioning and alignment grating emitted by the interferometer is used to accurately position the optical path. Then, only by slightly adjusting the position and pose of the secondary mirror, the interference fringes formed by the reflection of the optical path are made close to the zero fringe state, ensuring the wavefront aberration requirements of the opto-mechanical system and improving the alignment efficiency of the off-axis curved surface opto-mechanical mechanism. Description of the Drawings

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and easier to understand from the following description of the embodiments in conjunction with the accompanying drawings, where:

[0033] Figure 1 is a schematic diagram of the positional relationship between the optical element and the main frame and the positioning feature marks in the off-axis free-form surface opto-mechanical structure of Embodiment 1 of the present invention;

[0034] Figure 2 is a schematic diagram of the integrated alignment optical path of the off-axis free-form surface opto-mechanical structure of Embodiment 1 of the present invention;

[0035] Figure 3 is a schematic diagram of the positional relationship between the optical element and the main frame and the positioning feature marks in the off-axis free-form surface opto-mechanical structure of Embodiment 2 of the present invention.

[0036] Figure 4 is a schematic diagram of the integrated alignment optical path of the off-axis free-form surface opto-mechanical structure of Embodiment 2 of the present invention.

[0037] Description of the reference numerals: 1 - standard plane mirror, 2 - primary mirror, 3 - secondary mirror, 4 - marked point area on the main frame, 5 - CGH positioning and alignment grating, 6 - CGH device, 7 - CGH self-attitude alignment grating, 8 - interferometer, 801 - standard wavefront of the interferometer, 9 - main frame, 10 - positioning feature mark, 11 - tertiary mirror. Detailed Embodiments

[0038] The following describes the embodiments of the present invention in detail. The described embodiments are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0039] Embodiment 1

[0040] Refer to Figure 1 , in this embodiment, an off-axis freeform optical-mechanical structure is shown, including a primary mirror 2, a secondary mirror 3, and a main frame 9. The primary mirror 2 and the secondary mirror 3 are installed on the main frame 9 and are located on different planes of the main frame.

[0041] Refer to Figure 2 , the following specifically describes the process of integrally aligning and adjusting the off-axis curved optical-mechanical structure based on a standard plane mirror, an interferometer, and a CGH device.

[0042] Step 1: According to the design requirements of the optical-mechanical structure, design the structure of the main frame 9. Machine positioning surfaces or determine positioning references on the primary mirror 2, the secondary mirror 3, and the main frame, and set positioning feature marks 10 on the positioning surfaces or positioning references, and unify the positioning feature marks 10 into the optical design coordinate system to obtain the coordinates corresponding to the positioning feature marks. The set feature marks can be standard target balls, or some easily recognizable features such as crosshair lines, circles, etc.

[0043] Step 2: According to the zero-position interference principle and the coordinates of the positioning feature marks converted to the optical design coordinate system in Step 1, design and manufacture a CGH device 6. The CGH device can project both a CGH self-alignment grating 7 for adjusting its own posture and a CGH positioning feature alignment grating 5 for positioning the positioning feature marks determined in Step 1.

[0044] Step 3: Install the primary mirror 2 and the secondary mirror 3 at the corresponding positions of the main frame 9 according to the machined positioning surfaces or positioning installation references to achieve rough positioning and assembly of the optical elements and the main frame.

[0045] Step 4: Refer to Figure 1 to build an optical path: Place a standard plane mirror 1 in front of the assembly composed of the primary mirror 2, the secondary mirror 3, and the main frame 9 to realize the return of the optical path; Place the CGH device 6 and the interferometer 8 successively behind the assembly, where the CGD device is installed on an adjustment bracket.

[0046] Adjust the posture of the CGH device by adjusting the adjustment bracket for clamping the CGH device, so that the CGH self-alignment grating 7 projected by the CGH device is aligned with the standard wavefront 801 of the interferometer, realizing the positioning of the interferometer and the CGH device.

[0047] Step 5, Alignment and adjustment of the positioning between the main frame 9 and the CGH device 6: The beam emitted by the interferometer 8 forms the CGH positioning alignment grating 5 after passing through the CGH device 6, and the CGH positioning alignment grating 5 is projected onto the marked point area 4 on the main frame. Adjust the position and pose of the main frame 9 to align the CGH positioning alignment grating 5 with the positioning feature marks on the main frame, so as to realize the positioning and adjustment between the CGH device and the main frame. Since the main frame 9 and the primary mirror 2 and the secondary mirror 3 are fitted through the installation reference surface, at this time the opto-mechanical system is basically aligned with the interferometer.

[0048] Step 6, Precise positioning and adjustment of the main frame with the primary mirror and the secondary mirror: The light rays emitted by the interferometer pass through the CGH device 6, the secondary mirror 3, the primary mirror 2 and the standard plane mirror 1 in sequence. After being reflected by the standard plane mirror 1, they pass through the primary mirror 2, the secondary mirror 3, and the CGH device 6 in sequence and return to the interferometer, forming interference fringes. Fine-tune the position and pose of the secondary mirror 3 until the zero fringe state appears on the interferometer, then the alignment and adjustment of each optical element with the main frame 9 are completed.

[0049] Due to the adoption of high-precision reference transfer, only the secondary mirror needs to be fine-tuned in Step 6 to quickly realize the positioning and adjustment between the optical elements and between the optical elements and the main frame.

[0050] Embodiment 2

[0051] Refer to Figure 3 , Embodiment 2 shows another off-axis free-form surface opto-mechanical structure, including a primary mirror 2, a tertiary mirror 11 and a main frame 9. The main frame 9 is a substrate, and the primary mirror 2 and the tertiary mirror 11 are installed on this substrate. Since the off-axis amount of the optical elements in this structure is relatively large and it is impossible to realize the integrated detection of the primary and secondary mirrors through one CGH device, in Embodiment 2, a plurality of positioning feature marks are set on the main frame, the primary mirror and the tertiary mirror, and two CGH devices are used to detect and align the positioning feature marks on the primary mirror and the tertiary mirror in sequence to realize the positioning and adjustment of the free-form surface opto-mechanical structure. The specific alignment and adjustment steps are as follows:

[0052] Step 1, According to the design requirements of the opto-mechanical structure, design the structure of the main frame 9. Process the positioning surfaces or determine the positioning references on the primary mirror 2, the tertiary mirror 11 and the main frame 9, and set positioning feature marks 10 on the positioning surfaces or positioning references, and unify the positioning feature marks 10 into the optical design coordinate system to obtain the coordinates corresponding to the positioning feature marks. The set feature marks can be standard target balls, or some easily recognizable features such as crosshair lines, circles, etc.

[0053] Step 2, According to the zero-position interference principle and the coordinates of the positioning feature marks converted to the optical design coordinate system in Step 1, design and manufacture two CGH devices. The CGH device can project both the CGH device self-pose alignment grating 7 for adjusting its own pose and the CGH positioning feature alignment grating 5 for positioning the positioning feature marks determined in Step 1.

[0054] Step 3, set up the optical path according to Figure 4 : Install the primary mirror 2 at the corresponding position of the main frame 9 according to the machined positioning surface or positioning reference, place the interferometer in front of the main frame, and place the first CGH device between the interferometer and the main frame;

[0055] Step 4, positioning and alignment adjustment among the primary mirror, the main frame and the first CGH device: Start the interferometer 8, and the first CGH device 6 emitted by the interferometer projects the CGH positioning alignment grating. The first CGH device positioning alignment grating is simultaneously projected onto the positioning feature marks on the primary mirror 2 and the main frame 9, realizing the positioning and alignment adjustment of the primary mirror 2 and the main frame 9;

[0056] Step 5, positioning and alignment adjustment among the primary mirror, the main frame and the second CGH device: Replace the CGH device, adjust the spatial pose of the second CGH device 6 according to the method in Step 4, and perform positioning adjustment between the second CGH device and the interferometer, so that the standard wavefront of the interferometer emitted by the interferometer projects the alignment points through the alignment grating of the second CGH device, and make the projected alignment points coincide with the positioning feature marks on the main frame 9 and the positioning feature marks of the primary mirror 2. The pose of the second CGH device relative to the opto-mechanical system is unique. At this time, the alignment adjustment of the opto-mechanical system formed by the second CGH device, the primary mirror 2 and the main frame 9 is completed.

[0057] Step 6, rough positioning and alignment adjustment of the tertiary mirror with the primary mirror and the main frame: Install the tertiary mirror 11 on the main frame 9, and adjust the pose of the tertiary mirror 11 so that the light emitted by the interferometer passes through the second CGH device and projects onto the positioning feature marks of the tertiary mirror 11, realizing the preliminary alignment adjustment of the tertiary mirror 11 with the primary mirror 2 and the main frame 9.

[0058] Step 7, precise positioning and alignment adjustment of the main frame with the primary mirror and the tertiary mirror: According to the fringe state displayed on the interferometer, manually grind the installation surface of the tertiary mirror 11 and finely adjust the pose of the tertiary mirror until zero fringes are displayed on the interferometer for both the primary mirror 2 and the tertiary mirror 11. At this time, the alignment adjustment of the primary mirror 2, the tertiary mirror 11 and the main frame 9 is completed.

[0059] In the second embodiment, by aligning and calibrating the same positioning feature marks through both the first CGH device and the second CGH device, the unity of the detection reference is realized, thereby realizing the integrated alignment adjustment of the primary mirror, the tertiary mirror and the main frame.

[0060] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. An alignment method for an off-axis free-form optical-mechanical structure, characterized in that The off-axis free-form optical-mechanical structure includes a main frame, a primary mirror and a secondary mirror mounted on the main frame, and the primary mirror and the secondary mirror are located on different planes of the main frame; positioning feature marks are provided at corresponding mounting positions on the primary mirror, the secondary mirror and the main frame; It further includes an alignment system, and the alignment system includes a standard flat mirror, an interferometer and a computer-generated hologram device; The standard flat mirror is arranged on one side of the off-axis free-form optical-mechanical structure and close to the primary mirror; the computer-generated hologram device and the interferometer are sequentially arranged on the other side of the off-axis free-form optical-mechanical structure and close to the secondary mirror; The alignment method includes the following steps: Step 1, according to the design requirements of the optical-mechanical structure, design the shape structure of the main frame; process positioning and mounting reference surfaces on the main frame, the primary mirror and the secondary mirror, and set a number of positioning feature marks on the positioning and mounting reference surfaces; Step 2, based on the zero-position interference principle, perform coordinate transformation on the positioning feature marks on the main frame, the primary mirror and the secondary mirror in the optical design coordinate system, and design and manufacture a computer-generated hologram device according to the coordinates corresponding to the transformed positioning feature marks; Step 3, according to the processed positioning and mounting reference surfaces, install the primary mirror and the secondary mirror at the corresponding positions on the main frame to achieve rough positioning and assembly of the primary mirror, the secondary mirror and the main frame; Step 4, set up the alignment system: mount the standard flat mirror on one side of the off-axis free-form optical-mechanical structure and close to the primary mirror; sequentially arrange the computer-generated hologram device and the interferometer on the other side of the off-axis free-form optical-mechanical structure and close to the secondary mirror; Step 5, positioning and alignment between the main frame and the computer-generated hologram device: adjust the pose of the computer-generated hologram device so that the standard wavefront of the interferometer passes through the alignment grating area of the computer-generated hologram device to form a positioning alignment grating for positioning the positioning feature marks; Adjust the pose of the main frame so that the positioning alignment grating aligns with the positioning feature marks on the main frame; Step 6, precise positioning and alignment of the main frame with the primary mirror and the secondary mirror: the light emitted by the interferometer passes through the computer-generated hologram device, the secondary mirror, the primary mirror and the standard flat mirror in sequence, and after being reflected by the standard flat mirror, it returns to the interferometer through the primary mirror, the secondary mirror and the computer-generated hologram device in sequence to form interference fringes, and adjust the pose of the secondary mirror until zero fringes are displayed on the interferometer.

2. The alignment method of an off-axis free-form optical machine structure according to claim 1, characterized in that, In the step 4, the computer-generated hologram device is mounted on an adjustment frame for adjusting the pose of the computer-generated hologram device by adjusting the adjustment frame.

3. The alignment method of an off-axis freeform optical machine structure according to claim 1 or 2, characterized in that, The positioning feature marks processed in the step 1 are standard target balls or high-precision cross reticles.

4. An alignment method for an off-axis free-form optical-mechanical structure, characterized in that, The off-axis free-form optical-mechanical structure includes a main frame, a primary mirror and a tertiary mirror mounted on the main frame, and the primary mirror and the tertiary mirror are located on the same plane of the main frame, and positioning feature marks are provided at corresponding mounting positions on the primary mirror, the tertiary mirror and the main frame; It further includes an alignment system, and the alignment system includes an interferometer, a first computer-generated hologram device and a second computer-generated hologram device; The alignment method includes: Step 1, according to the design requirements of the optical-mechanical structure, design the shape structure of the main frame, process the positioning and mounting reference surfaces, and process a number of positioning feature marks on the positioning and mounting reference surfaces; Step 2: According to the zero-position interference principle, perform coordinate transformation on the positioning feature marks on the main frame, the primary mirror, and the tertiary mirror in the optical design coordinate system, and design and fabricate a computer-generated hologram device based on the coordinates corresponding to the positioning feature marks after transformation. Step 3: Install the primary mirror at the corresponding position on the main frame according to the processed positioning and installation reference surface to achieve rough positioning and assembly of the optical element and the main frame; and sequentially arrange the interferometer and the first computer-generated hologram device on one side of the main frame. Step 4: Positioning and alignment adjustment among the primary mirror, the main frame, and the first computer-generated hologram device: Start the interferometer. The light emitted by the interferometer projects a positioning alignment grating through the first computer-generated hologram device. Adjust the spatial pose of the first computer-generated hologram device so that the positioning alignment grating is simultaneously projected onto the positioning feature marks on the primary mirror and the main frame. Step 5: Positioning and alignment adjustment among the primary mirror, the main frame, and the second computer-generated hologram device: Replace the first computer-generated hologram device with the second computer-generated hologram device, so that the standard wavefront emitted by the interferometer projects alignment points through the alignment grating of the second computer-generated hologram device. Adjust the pose of the second computer-generated hologram device so that the projected alignment points coincide with the positioning feature marks of the main frame and the primary mirror. Step 6: Rough positioning and alignment adjustment of the tertiary mirror with the primary mirror and the main frame: Install the tertiary mirror at the corresponding position on the main frame, and adjust the pose of the tertiary mirror so that the light emitted by the interferometer passes through the second computer-generated hologram device and is projected onto the positioning feature marks on the tertiary mirror. Step 7: Precise positioning and alignment adjustment of the main frame with the primary mirror and the tertiary mirror: According to the interference fringe state displayed by the interferometer, finely adjust the pose of the tertiary mirror until zero fringes are displayed on the interferometer, and the alignment adjustment is completed.

5. The alignment method of an off-axis free-form optical-mechanical structure according to claim 4, characterized in that In Step 3 and Step 5, the first computer-generated hologram device and the second computer-generated hologram device are installed on an adjustment frame, which is used to adjust the poses of the first computer-generated hologram device and the second computer-generated hologram device by adjusting the adjustment frame.

6. The alignment method of an off-axis free-form optical-mechanical structure according to claim 4 or 5, characterized in that The positioning feature marks processed in Step 1 are standard target balls or high-precision cross reticles.

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