Precise assembly method of off-axis three-mirror optical system

Abstract

The present application relates to a kind of optical system assembly method, specifically to a kind of precision assembly method of off-axis three-mirror optical system, solve the existing off-axis three-mirror optical system has non-rotational symmetry and the optical axis of each component is not on the same axis, leading to the existence of asymmetric wave aberration in off-axis three-mirror optical system, cannot realize high-precision assembly technical problem.The precision assembly method of the off-axis three-mirror optical system, comprising the following steps:1】respectively to main mirror component, secondary mirror component and three mirror component rough positioning, until the angle deviation of each mirror group is less than or equal to 10″, eccentricity tolerance is less than or equal to 0.05mm;2】analysis of off-axis three-mirror optical system wave aberration, according to wave aberration screening degree of freedom to carry out image quality correction;3】calculate the misalignment amount M of secondary mirror and three mirrors;4】according to misalignment amount M, the angle of secondary mirror and three mirrors is precisely adjusted, so that the off-axis three-mirror optical system full field wave aberration is less than threshold value, complete the precision assembly of off-axis three-mirror optical system.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system assembly method, in particular to a precise assembly method of an off-axis three-mirror optical system. BACKGROUND

[0002] Reflective optical systems are widely used in modern space-based and air-based large-aperture telescopes. Coaxial reflective optical systems generally adopt the form of primary and secondary mirrors and lenses. In coaxial reflective optical systems, the secondary mirror structure leads to central obstruction, limiting the limited range of the image plane, thereby restricting the field of view size of the coaxial reflective optical system and causing light energy loss. In addition, central obstruction also leads to a decrease in the modulation transfer function of the coaxial reflective optical system at the medium and low frequency parts, affecting the final imaging quality. The applicable wavelength range of coaxial reflective optical systems is small. In order to solve the problems caused by coaxial reflective optical systems, optical designers construct off-axis reflective optical systems through pupil off-axis, field of view off-axis, and tilting or decentering of mirror elements. Such off-axis reflective optical systems not only have the advantages of reflective optical systems, but also meet the imaging requirements of large field of view and full wavelength range, while avoiding edge scattering effects and central obstruction, having higher energy concentration and dynamic range, and being able to meet the needs of high-resolution limit detection.

[0003] Off-axis three-mirror optical systems are typical off-axis reflective optical systems. Due to their advantages of no obstruction, no ghost image, and large field of view, they are widely used in many fields. However, due to their non-rotational symmetry, there are asymmetric wave aberrations in off-axis three-mirror optical systems, and the optical axes of the components are not on the same axis, so the traditional coaxial optical system assembly method cannot be used to achieve high-precision assembly, which brings great challenges to the assembly of off-axis three-mirror optical systems. SUMMARY

[0004] The purpose of the present application is to solve the technical problem that the existing off-axis three-mirror optical system has non-rotational symmetry and the optical axes of the components are not on the same axis, resulting in asymmetric wave aberrations in the off-axis three-mirror optical system and unable to achieve high-precision assembly, and to provide a precise assembly method of an off-axis three-mirror optical system.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A precise assembly method of an off-axis three-mirror optical system, the off-axis three-mirror optical system comprising a primary mirror assembly, a secondary mirror assembly, and a three-mirror assembly; the special feature is that it comprises the following steps:

[0007] 1】Taking the primary mirror assembly as a reference, the primary mirror assembly, the secondary mirror assembly, and the three-mirror assembly are roughly positioned respectively until the angle deviation of each mirror group is less than or equal to 10″ and the eccentricity tolerance is less than or equal to 0.05mm.

[0008] 2】Using Zemax optical design software to analyze the wavefront aberration of off-axis three-mirror optical system, adjusting the rotation freedom of secondary mirror assembly and three-mirror assembly in x-axis and y-axis according to the wavefront aberration to correct the image quality;

[0009] 3】Using Zemax optical design software to analyze the full field Zernike wavefront aberration coefficient matrix ΔZ and sensitivity matrix A, and calculating the misalignment M of secondary mirror (7) and three-mirror (12):

[0010] M=(A T A+ρI) -1 A T ΔZ

[0011] Wherein, A T is the transpose matrix of sensitivity matrix A; ρ is the damping coefficient; I represents the unit matrix;

[0012] 4】According to the misalignment M, the angles of secondary mirror and three-mirror are precisely adjusted, so that the full field wavefront aberration of off-axis three-mirror optical system is less than the threshold value, and the precise assembly of off-axis three-mirror optical system is completed.

[0013] Further, step 1】 is specifically:

[0014] 1.1) Rough positioning of the primary mirror assembly;

[0015] 1.2) Transferring the reference of the reference surface A on the back of the primary mirror in the primary mirror assembly to the three-mirror and the secondary mirror;

[0016] 1.3) Rough positioning of the secondary mirror assembly;

[0017] 1.4) Rough positioning of the three-mirror assembly.

[0018] Further, step 1.1) is specifically:

[0019] 1.1.1, preliminary positioning of the primary mirror assembly: reserving the primary mirror assembly mounting hole on the bottom plate, and the primary mirror assembly is fixedly connected with the bottom plate mounting hole through the threaded hole of the primary mirror base;

[0020] 1.1.2, setting the reference surface;

[0021] Taking the upper surface of the bottom plate in the off-axis three-mirror optical system as the bottom plate reference surface C;

[0022] The protruding side wall surface of the bottom plate close to the primary mirror and parallel to the primary mirror as the bottom plate reference surface D;

[0023] The protruding side wall surface of the bottom plate away from the primary mirror and parallel to the primary mirror as the bottom plate reference surface E;

[0024] The side wall surface of the bottom plate close to the primary mirror and perpendicular to the primary mirror as the bottom plate reference surface B;

[0025] The side wall surface of the base plate away from and perpendicular to the primary mirror as the base plate reference surface F;

[0026] 1.1.3, adjust the angle of the primary mirror;

[0027] The first plane mirror is arranged at the base plate reference surface D, and the reference direction is introduced by using the first theodolite and the first plane mirror self- collimation. Then, the angle between the back reference surface A of the primary mirror and the base plate reference surface D is adjusted according to the reference direction, so that the back reference surface A of the primary mirror is perpendicular to the optical axis of the first theodolite, thereby being parallel to the base plate reference surface D;

[0028] 1.1.4, adjust the eccentricity of the primary mirror;

[0029] The outer cylindrical surface of the primary mirror is measured by using the three-coordinate measuring arm to fit the primary mirror axis. The base plate reference surfaces B, C and D are used as the reference, and the eccentricity of the primary mirror is adjusted according to the distance x between the measured primary mirror axis and the base plate reference surface C, the horizontal distance y between the primary mirror axis and the base plate reference surface B, and the horizontal distance z between the back reference surface A of the primary mirror and the base plate reference surface D.

[0030] 1.1.5, judge whether the angle deviation between the back reference surface A of the primary mirror and the base plate reference surface D is less than or equal to 10", and whether the eccentricity tolerance of the primary mirror is less than or equal to 0.05mm. If yes, step 1.2) is executed, otherwise, return to step 1.1.3.

[0031] Further, step 1.2) is specifically as follows:

[0032] 1.2.1, transfer the reference to the three mirrors;

[0033] The reference direction of the back reference surface A of the primary mirror is represented by using the first theodolite and the back reference surface A of the primary mirror self- collimation. The reference direction of the back reference surface A of the primary mirror is transferred to the second theodolite by rotating the first theodolite counterclockwise by 90° and mutual sighting with the second theodolite. The reference direction of the back reference surface A of the primary mirror is represented by rotating the second theodolite counterclockwise by 90° and using the optical axis thereof.

[0034] 1.2.2, transfer the reference to the secondary mirror;

[0035] The reference direction is calibrated by rotating the first theodolite clockwise by 90° and using the first plane mirror at the base plate reference surface D and the first theodolite self- collimation. Then, the first theodolite is translated to the position corresponding to the three mirrors, and the reference direction is ensured to be unchanged by rotating the first theodolite clockwise by 90° and using the second plane mirror on the optical path of the first theodolite and the first theodolite self- collimation. Then, the first theodolite is rotated counterclockwise by 90° and mutual sighting with the third theodolite close to the base plate reference surface E, so as to transfer the back reference surface A of the primary mirror to the third theodolite.

[0036] Further, step 1.3) is specifically:

[0037] 1.3.1, preliminary positioning of the secondary mirror assembly: reserving the secondary mirror assembly mounting hole on the bottom plate, and the secondary mirror assembly is fixedly connected with the bottom plate mounting hole through the threaded hole of the secondary mirror support seat;

[0038] 1.3.2, adjusting the angle of the secondary mirror;

[0039] According to the theoretical difference M of the angle between the back reference surface of the secondary mirror and the back reference surface A of the primary mirror, the third theodolite is counterclockwise rotated by 0.38°, which is used to determine the back reference direction of the secondary mirror, and the angle between the back reference surface of the secondary mirror and the back reference surface A of the primary mirror is adjusted according to the back reference direction of the secondary mirror and the second theodolite is self- calibrated;

[0040] 1.3.3, adjusting the eccentricity of the secondary mirror;

[0041] The three-coordinate measuring arm is used to measure the secondary mirror outer cylindrical surface to fit the secondary mirror axis, and the bottom plate reference surfaces B, C and E are used as references, and the horizontal distance y1 of the secondary mirror axis from the reference surface B, the distance x1 of the secondary mirror axis from the bottom plate reference surface C, and the horizontal distance z1 of the back reference surface of the secondary mirror from the bottom plate reference surface E are measured to adjust the eccentricity of the secondary mirror;

[0042] 1.3.4, judging whether the angle deviation between the back reference surface of the secondary mirror and the back reference surface A of the primary mirror is less than or equal to 10″, and whether the eccentricity tolerance of the secondary mirror is less than or equal to 0.05mm, if yes, step 1.4) is executed, otherwise, step 1.3.2 is returned.

[0043] Further, step 1.4) is specifically:

[0044] 1.4.1, preliminary positioning of the three-mirror assembly: reserving the three-mirror assembly mounting hole on the bottom plate, and the three-mirror assembly is fixedly connected with the bottom plate mounting hole through the threaded hole of the three-mirror support seat;

[0045] 1.4.2, adjusting the angle of the three-mirror;

[0046] According to the theoretical difference N of the angle between the back reference surface of the three-mirror and the back reference surface A of the primary mirror, the second theodolite is clockwise rotated by 0.2°, which is used to determine the back reference direction of the three-mirror, and the angle between the back reference surface of the three-mirror and the back reference surface A of the primary mirror is adjusted according to the back reference direction of the three-mirror and the second theodolite is self- calibrated;

[0047] 1.4.3, adjusting the eccentricity of the three-mirror;

[0048] The three-coordinate measuring arm is used to measure the three-mirror outer cylindrical surface fitting the three-mirror axis, and the three mirror eccentricity is adjusted according to the horizontal distance x2 of the three-mirror axis to the reference surface C, the horizontal distance z2 of the three-mirror back reference surface to the bottom plate reference surface D, and the horizontal distance y2 of the three-mirror axis to the bottom plate reference surface F.

[0049] 1.4.4, judge whether the included angle deviation between the three-mirror back reference surface and the primary mirror back reference surface A is less than or equal to 10", and whether the three-mirror eccentricity tolerance is less than or equal to 0.05mm, if yes, execute step 2, otherwise return to step 1.4.2.

[0050] Further, step 2 is specifically:

[0051] 2.1) build a wave aberration detection system to obtain the wave aberration of the off-axis three-mirror optical system;

[0052] 2.2) use Zemax optical design software to analyze the wave aberration of the off-axis three-mirror optical system, and screen the tx1 / ty1 of the secondary mirror and the tx2 / ty2 rotation freedom of the three-mirror, wherein tx1 represents the rotation amount of the secondary mirror along x1 axis, ty1 represents the rotation amount of the secondary mirror around y1 axis, tx2 represents the rotation amount of the three-mirror around x2 axis, and ty2 represents the rotation amount of the three-mirror around y2 axis;

[0053] 2.3) adjust the tx1 / ty1 of the secondary mirror and the tx2 / ty2 of the three-mirror to realize image quality correction.

[0054] Further, step 2.1) is specifically:

[0055] 2.1.1, use the first theodolite to autocolimate with the primary mirror back reference surface A to introduce the reference direction;

[0056] 2.1.2, keep the reference direction, move the first theodolite to the side of the primary mirror away from the three-mirror, and rotate the first theodolite clockwise by 9° to represent the normal direction of the third plane mirror arranged on the bottom plate reference surface E side;

[0057] 2.1.3, adjust the third plane mirror and autocolimate with the first theodolite to complete the positioning of the third plane mirror;

[0058] 2.1.4, set a 4D laser interferometer at a position corresponding to the three-mirror, and use the 4D laser interferometer to emit laser and detect the wave aberration of the off-axis three-mirror optical system.

[0059] Further, in step 3, the misalignment amount M of the secondary mirror and the three-mirror is calculated by using the adaptive damping least square method; the sensitivity matrix A is 25x12; and the full field Zernike wave aberration coefficient matrix ΔZ is 25x1.

[0060] Further, in step 4, the threshold is 0.05 lambda @ 632.8 nm.

[0061] Advantages of the present application:

[0062] (1) The off-axis three-mirror optical system assembled by the precise assembly method of the off-axis three-mirror optical system has a focal length of 1800 mm, an off-axis field of view of 9°, and a field of view size of ±1°. Within the full field of view, the wavefront error RMS of the off-axis three-mirror optical system is better than 0.05 lambda @ 632.8 nm, the diffraction spot is smaller than the Airy disk size, and the imaging quality is excellent.

[0063] (2) The mirror group tolerance analysis is performed on the off-axis three-mirror optical system. According to the tolerance analysis result, the angle deviation of the remaining mirror groups can be controlled within 10″, and the eccentricity tolerance can be controlled within 0.05 mm, so as to ensure that the imaging quality meets the requirements.

[0064] (3) Based on the angle deviation and eccentricity tolerance requirements, the three-coordinate measuring arm and multiple self-collimation theodolites are used to perform rough positioning on the optical components (i.e. the primary mirror assembly, the secondary mirror assembly, and the three-mirror assembly), to determine the spatial positions of the optical components in three dimensions, to realize precise measurement and eccentric adjustment, and the precision can reach 0.02 mm.

[0065] (4) The present application analyzes the influence characteristics of the 6 degrees of freedom of each mirror group on the wave aberration of the off-axis three-mirror optical system, and selects appropriate degrees of freedom for the misadjustment correction of the system wave aberration. In the off-axis three-mirror optical system, the mirror groups to be adjusted are the secondary mirror and the three-mirror, and there are 12 degrees of freedom. Since it is costly and difficult to adjust all the degrees of freedom of all the mirror groups, the degrees of freedom sensitive to the wave aberration are determined based on the sensitivity matrix, and the secondary mirror two-dimensional adjustment mechanism and the three-mirror two-dimensional adjustment mechanism are adjusted to avoid blind adjustment. The insensitive degrees of freedom can be guaranteed by structure limiting and coarse adjustment.

[0066] (5) The adaptive damping least square method adopted in the present application selects appropriate damping coefficients through algorithm to accurately solve the misadjustment, so as to realize excellent image quality correction effect, avoid excessive adjustment, and ensure the accuracy and reliability of the correction result.

[0067] (6) The method of the present application can be applied to the precise assembly of off-axis multi-mirror optical systems, and provides an efficient and reliable method for precise adjustment of complex optical systems. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1is a stereogram of an off-axis three-mirror optical system in an embodiment of the present application;

[0069] Figure 2 is a plan view of the off-axis three-mirror optical system of Figure 1

[0070] Figure 3(a) is a schematic diagram of rough positioning of a primary mirror assembly in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0071] Figure 3(b) is a bottom view of Figure 3(a);

[0072] Figure 4 is a schematic diagram of reference transfer from the primary mirror to the tertiary mirror in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0073] Figure 5 is a schematic diagram of reference transfer from the primary mirror to the secondary mirror in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0074] Figure 6(a) is a schematic diagram of rough positioning of a secondary mirror assembly in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0075] Figure 6(b) is a bottom view of Figure 6(a);

[0076] Figure 7(a) is a schematic diagram of rough positioning of a tertiary mirror assembly in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0077] Figure 7(b) is a bottom view of Figure 7(a);

[0078] Figure 8 is a schematic diagram of image quality detection in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application;

[0079] Figure 9 is a full field wavefront aberration result diagram in an embodiment of a precision assembly method of an off-axis three-mirror optical system of the present application.

[0080] BRIEF DESCRIPTION OF THE DRAWINGS

[0081] 1, primary mirror base; 2, primary mirror rib plate; 3, primary mirror support seat; 4, primary mirror seat; 5, primary mirror; 6, secondary mirror diaphragm; 7, secondary mirror; 8, secondary mirror base; 9, secondary mirror two-dimensional adjustment mechanism; 10, secondary mirror two-dimensional adapter; 11, secondary mirror support seat; 12, tertiary mirror; 13, tertiary mirror base; 14, tertiary mirror two-dimensional adapter; 15, tertiary mirror two-dimensional adjustment mechanism; 16, tertiary mirror support seat; 17, bottom plate; 18, first plane mirror; 19, second plane mirror; 20, third plane mirror; 21, 4D laser interferometer; 22, first theodolite; 23, second theodolite; 24, third theodolite. DETAILED DESCRIPTION​

[0082] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0083] like Figure 1 , Figure 2 As shown, an off-axis three-mirror optical system includes a base plate 17, a primary mirror assembly, a secondary mirror assembly, and a three-mirror assembly integrated on the base plate 17. The primary mirror assembly includes a primary mirror base 1, a primary mirror rib 2, a primary mirror support 3, a primary mirror mount 4, and a primary mirror 5. The secondary mirror assembly includes a secondary mirror aperture 6, a secondary mirror 7, a secondary mirror base 8, a secondary mirror two-dimensional adjustment mechanism 9, a secondary mirror two-dimensional adapter 10, and a secondary mirror support 11. The three-mirror assembly includes a three-mirror 12, a three-mirror support 16, a three-mirror two-dimensional adapter 14, a three-mirror two-dimensional adjustment mechanism 15, and a three-mirror support 16. The primary mirror assembly is connected to the base plate 17 via the primary mirror base 1. The secondary mirror assembly is connected to the base plate 17 via the secondary mirror two-dimensional adapter 10, the secondary mirror two-dimensional adjustment mechanism 9, and the secondary mirror support 11. Similarly, the three-mirror assembly is connected to the base plate 17 via the three-mirror two-dimensional adapter 14, the three-mirror two-dimensional adjustment mechanism 15, and the three-mirror support 16. The base plate 17 provides a bottom mounting reference for all structures.

[0084] The back reference surfaces of the primary mirror 5, secondary mirror 7, and third mirror 12 are polished, and the perpendicularity deviation between these polished surfaces and the optical axis of the mirror group is better than 30″, which can be used as the reference direction for the mirror group. After parallel light is incident on the off-axis three-mirror optical system, it passes through the primary mirror 5, secondary mirror 7, and third mirror 12 in sequence, and finally forms an ideal image at the rear focal point. The off-axis three-mirror optical system installed by the method of this invention has a focal length of 1800mm, an off-axis field of view of 9°, and a field of view size of ±1°. Throughout the entire field of view, the wavefront error RMS of the off-axis three-mirror optical system is better than 0.05λ@632.8nm, the spot of confusion is smaller than the Airy disk size, reaching the diffraction limit, and the imaging quality is excellent.

[0085] After tolerance analysis, taking the primary mirror assembly as the benchmark, the angular deviation of the secondary mirror 7 and the tertiary mirror 12 is 10″, and the eccentricity tolerance is 0.05mm. The mechanical positioning accuracy of the existing threaded connection cannot meet this requirement. The precision assembly and image quality adjustment of the off-axis three-mirror optical system involves the degrees of freedom of multiple components such as the secondary mirror 7 and the tertiary mirror 12, and it is difficult to accurately identify and adjust their degrees of freedom and their magnitude through experience, making the assembly more difficult.

[0086] The precision assembly method of the off-axis three-mirror optical system mainly includes three key steps: precise positioning of the primary mirror 5, adjustment of the secondary mirror 7 and the third mirror 12, and solving of the misalignment amount based on a sensitive matrix, and optimization of image quality. In the coarse adjustment stage, the multi-instrument network (i.e., the theodolite and the plane mirror) measurement is used to control the mirror group angle deviation within 10' and the eccentricity tolerance within 0.05 mm, so as to eliminate the large misalignment deviation. In the fine adjustment stage, the misalignment amount of the secondary mirror 7 and the third mirror 12 is accurately calculated through the sensitivity matrix algorithm, and the misalignment amount is accurately implemented by using the two-dimensional adjustment mechanism 9 of the secondary mirror, the two-dimensional adjustment mechanism 15 of the third mirror, and the 4D laser interferometer 21 is used to ensure that the imaging quality of the off-axis three-mirror optical system meets the requirements.

[0087] Firstly, the mirror group tolerance analysis is performed. According to the tolerance analysis result, the angle deviation of the remaining mirror groups should be controlled within 10" and the eccentricity tolerance should be controlled within 0.05 mm with the primary mirror 5 as the reference, so as to ensure that the imaging quality meets the requirements. Based on the angle deviation and the eccentricity tolerance requirements, the network measurement is adopted for the rough positioning of the optical components (i.e., the primary mirror assembly, the secondary mirror assembly and the third mirror assembly). The instruments used in the network measurement include a three-coordinate measuring arm and multiple autocollimation theodolites. The three-coordinate measuring arm has high precision, flexibility and portability. The three-dimensional coordinates of each point on the surface of the optical component are determined by measuring the position of the measuring probe in space, the relationship between the space points, lines and surfaces is obtained, the mirror axis and the outer cylindrical surface are fitted, the spatial position of each optical component in three dimensions is determined, the precise measurement and eccentric adjustment are realized, and the precision can reach 0.02 mm. The autocollimation theodolite adopts the optical autocollimation imaging principle, can be self-accurate with the reference surface reserved for each mirror group, and can accurately control the spatial angle deviation of each mirror group within 10". Through this method, high-precision positioning of the optical component can be realized. However, due to the existence of machining deviation, it is still impossible to completely meet the requirements of optical imaging. Finally, the primary mirror assembly, the secondary mirror assembly and the third mirror assembly need to be precisely adjusted according to the wave aberration measurement result, and this process only eliminates the large deviation.

[0088] Since the quantitative relationship between the wave aberration of the misaligned system and the degrees of freedom cannot be explored by artificial experience for the off-axis three-mirror optical system, the influence characteristics of the six degrees of freedom of each mirror group on the wave aberration of the off-axis three-mirror optical system are analyzed, and the appropriate degrees of freedom are selected for the misalignment correction of the wave aberration. Especially in the off-axis three-mirror optical system, the mirror groups to be adjusted are the secondary mirror 7 and the third mirror 12, and there are 12 degrees of freedom. Adjusting all the degrees of freedom of all the mirror groups is high in cost and difficult to realize, so the degrees of freedom sensitive to the wave aberration are determined based on the sensitivity matrix, and the adjustment mechanism is designed to avoid blind adjustment. The degrees of freedom insensitive to the wave aberration can be ensured through structural limiting and coarse adjustment. Through the quantitative analysis of the sensitivity matrix, the rotation degrees of freedom of the secondary mirror assembly and the third mirror assembly in the x\y axis are most sensitive to the wave aberration of the off-axis three-mirror optical system, so the four degrees of freedom are taken as the misalignment for the adjustment of the image quality correction.

[0089] The present application is based on the precise assembly method of the off-axis three-mirror optical system, and the specific steps are as follows:

[0090] 1. Coarse positioning of the primary mirror assembly. The primary mirror assembly is fixedly connected with the mounting hole of the bottom plate 17 through the threaded hole of the primary mirror base 1, which is used for the preliminary positioning of the primary mirror assembly. The back of the primary mirror 5 is taken as the back reference surface A of the primary mirror 5, the bottom plate 17 is taken as the reference, and the upper surface of the bottom plate 17 in the off-axis three-mirror optical system is taken as the bottom plate reference surface C; the protruding side wall surface of the bottom plate 17 close to the primary mirror 5 and parallel to the primary mirror 5 is taken as the bottom plate reference surface D; the protruding side wall surface of the bottom plate 17 away from the primary mirror 5 and parallel to the primary mirror 5 is taken as the bottom plate reference surface E; the side wall surface of the bottom plate 17 close to the primary mirror 5 and perpendicular to the primary mirror 5 is taken as the bottom plate reference surface B; the side wall surface of the bottom plate 17 away from the primary mirror 5 and perpendicular to the primary mirror 5 is taken as the bottom plate reference surface F; the angle deviation of the primary mirror 5 to each mirror group is adjusted to be less than or equal to 10'', and the eccentricity tolerance is less than or equal to 0.05mm.

[0091] As shown in Fig. 3(a), the angle of the primary mirror 5 is adjusted. The first plane mirror 18 is closely attached to the bottom plate reference surface D, and the first theodolite 22 is self- collimated with the first plane mirror 18 to guide the reference direction. The back of the primary mirror 5 is polished, and the angle between the back reference surface A of the primary mirror 5 and the bottom plate reference surface D is adjusted according to the self-imaging principle of the first theodolite 22, so as to ensure that the back reference surface A of the primary mirror 5 is self-collimated with the first theodolite 22, at this time, the reference direction of the back reference surface A of the primary mirror 5 is perpendicular to the optical axis of the first theodolite 22, thereby being parallel to the bottom plate reference surface D, and the coarse positioning of the angle of the primary mirror 5 is completed.

[0092] As shown in Figure 3(b), the eccentricity of the primary mirror 5 is adjusted. A coordinate measuring machine is used to measure the outer cylindrical surface of the primary mirror 5 to fit its axis. Using the base plate reference surfaces B, C, and D as references, the eccentricity of the primary mirror 5 is adjusted based on the measured distance x from the axis of the primary mirror 5 to the base plate reference surface C, the horizontal distance y from the axis of the primary mirror 5 to the base plate reference surface B, and the horizontal distance z from the back reference surface A of the primary mirror 5 to the base plate reference surface D. This ensures that x = 251 ± 0.05 mm, y = 185 ± 0.05 mm, and z = 576 ± 0.05 mm. This completes the rough adjustment of the eccentricity of the primary mirror 5, and subsequent assembly will be carried out using the primary mirror 5 as a reference.

[0093] Determine whether the angle deviation between the reference surface A on the back of the primary mirror 5 and the reference surface D on the base plate is less than or equal to 10″, and whether the eccentricity tolerance of the primary mirror 5 is less than or equal to 0.05mm. If yes, proceed to step 2; otherwise, readjust the angle and / or eccentricity of the primary mirror 5.

[0094] 2. Transfer the reference plane A on the back of the primary mirror 5. After completing the angle and eccentricity adjustment of the primary mirror 5, the reference plane A on the back of the primary mirror 5 is transferred to the secondary mirror 7 using the first theodolite 22, the second theodolite 23, and the third theodolite 24.

[0095] like Figure 4 As shown, the reference direction of the three mirrors 12 is first transferred. After the first theodolite 22 is self-aligned with the reference plane A on the back of the primary mirror 5, it represents the normal direction (i.e., the reference direction) of the reference plane A on the back of the primary mirror 5. Then, the first theodolite 22 is rotated 90° counterclockwise using a two-dimensional translation platform and then aligned with the second theodolite 23, transferring the reference direction of the reference plane A on the back of the primary mirror 5 to the second theodolite 23. After the second theodolite 23 is rotated 90° counterclockwise using a two-dimensional translation platform, its optical axis represents the normal direction of the reference plane A on the back of the primary mirror 5. Finally, the reference of the three mirrors 12 is adjusted using the second theodolite 23.

[0096] like Figure 5 As shown, the reference direction is transferred to the secondary mirror 7. Using a two-dimensional translation platform, the first theodolite 22 at point A (corresponding to the primary mirror 5) is rotated 90° clockwise, and then self-aligned with the first plane mirror 18 at the base plate reference surface D to calibrate the reference direction. Then, using a two-dimensional translation stage, the first theodolite 22 is moved from point A to point B (corresponding to the third mirror 12). During the translation, the first theodolite 22 experiences a slight angular shift, so it needs to be rotated 90° clockwise at point B and self-aligned with the second plane mirror 19 located on the optical path of the first theodolite 22 to ensure the reference direction remains unchanged. The first theodolite 22 at point B is then rotated 90° counterclockwise and mutually aligned with the third theodolite 24 near the base plate reference surface E, transferring the reference surface A on the back of the primary mirror 5 to the third theodolite 24. Finally, the reference of the secondary mirror 7 is adjusted using the first theodolite 22.

[0097] 3. Roughly positioning the secondary mirror assembly. The secondary mirror assembly is fixed to the bottom plate 17 through the threaded holes of the secondary mirror two-dimensional adjustment mechanism 9, the secondary mirror two-dimensional adapter 10 and the secondary mirror support seat 11, and the mounting holes of the bottom plate 17, for the preliminary positioning of the secondary mirror assembly.

[0098] As shown in Fig. 6(a), the angle of the secondary mirror 7 is adjusted. Theoretically, the angle between the back reference surface A of the primary mirror 5 and the bottom plate reference surface B is 90°, and the angle between the back reference surface of the secondary mirror 7 and the bottom plate reference surface B is 89.62°, so the theoretical difference between the angle of the back reference surface of the secondary mirror 7 and the back reference surface A of the primary mirror 5 is 90-89.62=0.38°. The optical axis of the third theodolite 24 represents the back reference direction of the primary mirror 5, and it is rotated counterclockwise by 0.38° to determine the back reference direction of the secondary mirror 7. The angle between the back reference surface of the secondary mirror 7 and the back reference surface A of the primary mirror 5 is adjusted according to the back reference direction of the secondary mirror 7 and the self-orientation of the third theodolite 24, so that the angle between the back reference surface of the secondary mirror 7 and the back reference surface A of the primary mirror 5 is theoretically 0.38°, and the rough positioning of the angle of the secondary mirror 7 is completed.

[0099] As shown in Fig. 6(b), the eccentricity of the secondary mirror 7 is adjusted. The outer cylindrical surface of the secondary mirror 7 is measured by a three-coordinate measuring arm to fit the axis of the secondary mirror 7. The bottom plate reference surfaces B, C and E are used as references, and the horizontal distance y1 between the axis of the secondary mirror 7 and the reference surface B, the distance x1 between the axis of the secondary mirror 7 and the bottom plate reference surface C, and the horizontal distance z1 between the back reference surface of the secondary mirror 7 and the bottom plate reference surface E are measured to adjust the eccentricity of the secondary mirror 7, so that x1=251±0.05mm, y1=390.03±0.05mm, and z1=507±0.05mm. Thus, the rough adjustment of the eccentricity of the secondary mirror 7 is completed.

[0100] It is determined whether the angle deviation between the back reference surface of the secondary mirror 7 and the back reference surface A of the primary mirror 5 is less than or equal to 10", and whether the eccentricity tolerance of the secondary mirror 7 is less than or equal to 0.05mm. If yes, step 4 is performed, otherwise the angle or / and the eccentricity of the secondary mirror 7 is adjusted again.

[0101] Although the angle deviation has reached the tolerance requirement, since the deviation between each polished reference surface (i.e. the back reference surface A of the primary mirror 5, the back reference surface of the secondary mirror 7 and the back reference surface of the tertiary mirror 12) and its optical axis is 30", the imaging quality of the off-axis three-mirror optical system cannot be guaranteed according to the error of the positioning angle of the polished surface.

[0102] 4. Roughly positioning the tertiary mirror assembly. The tertiary mirror assembly is fixed to the bottom plate 17 through the threaded holes of the tertiary mirror two-dimensional adapter 14, the tertiary mirror two-dimensional adjustment mechanism 15 and the tertiary mirror support seat 16, and the mounting holes of the bottom plate 17.

[0103] As shown in Fig. 7(a), the angle of the tertiary mirror 12 is adjusted. Theoretically, the angle between the back reference surface A of the primary mirror 5 and the back reference surface of the tertiary mirror 12 is 90°, and the angle between the back reference surface F of the tertiary mirror 12 and the back reference surface of the tertiary mirror 12 is 90.2°. Therefore, the theoretical difference between the angle of the back reference surface of the tertiary mirror 12 and the back reference surface A of the primary mirror 5 is 90-90.2=-0.2°. The back reference direction of the tertiary mirror 12 is determined by rotating the optical axis of the second theodolite 23 clockwise by 0.2°, which represents the back reference direction of the primary mirror 5. The angle between the back reference surface A of the primary mirror 5 and the back reference surface of the tertiary mirror 12 is adjusted according to the back reference direction of the tertiary mirror 12 and the self-orientation of the second theodolite 23, so that the angle between the back reference surface A of the primary mirror 5 and the back reference surface of the tertiary mirror 12 is 0.2°, and the angle of the tertiary mirror 12 is positioned.

[0104] As shown in Fig. 7(b), the eccentricity of the tertiary mirror 12 is adjusted. The outer cylindrical surface of the tertiary mirror 12 is measured by a three-coordinate measuring arm, and the axis of the tertiary mirror 12 is fitted. The distance x2 between the axis of the tertiary mirror 12 and the reference surface C, the horizontal distance z2 between the back reference surface of the tertiary mirror 12 and the reference surface D, and the horizontal distance y2 between the axis of the tertiary mirror 12 and the reference surface F are measured, and the eccentricity of the tertiary mirror 12 is adjusted according to the measured distances, so that x2=251±0.05mm, y2=195.68±0.05mm, and z2=370.24±0.05mm. Thus, the eccentricity adjustment of the tertiary mirror 12 is completed.

[0105] The angle and eccentricity of the tertiary mirror 12 are repeatedly adjusted by repeating the above operations, so that the eccentricity tolerance of the tertiary mirror 12 is less than or equal to 0.05mm, and the angle deviation between the back reference surface of the tertiary mirror 12 and the back reference surface A of the primary mirror 5 is less than or equal to 10″.

[0106] It is determined whether the angle deviation between the back reference surface of the tertiary mirror 12 and the back reference surface A of the primary mirror 5 is less than or equal to 10″, and whether the eccentricity tolerance of the tertiary mirror 12 is less than or equal to 0.05mm. If yes, step 2 is performed, otherwise the angle or / and eccentricity of the tertiary mirror 12 is adjusted again.

[0107] Although the angle deviation has reached the tolerance requirement, since the processing deviation of each polishing reference surface (i.e. the back reference surface A of the primary mirror 5, the back reference surface of the secondary mirror 7, and the back reference surface of the tertiary mirror 12) from its optical axis is 30″, the imaging quality of the off-axis three-mirror optical system cannot be guaranteed according to the error of the positioning angle of the polishing surface.

[0108] Finally, the primary mirror assembly, the secondary mirror assembly, and the tertiary mirror assembly need to be precisely adjusted according to the wavefront aberration measurement results. The above process only eliminates the large deviation.

[0109] 5. Adjust the attitude of the mirror assembly and correct the image quality.

[0110] After the coarse positioning of the primary mirror 5, the secondary mirror 7 and the tertiary mirror 12 is completed through the above steps, the angle between the third plane mirror 20 and the reference surface A at the back of the primary mirror 5 is designed as 9° in theory. The positioning method of the third plane mirror 20 is as follows: the first theodolite 22 is collimated with the reference surface A at the back of the primary mirror 5 to guide the reference direction. The first theodolite 22 is moved from A to B (i.e. the side of the primary mirror 5 away from the tertiary mirror 12), and then the first theodolite 22 at B is rotated clockwise by 9° to represent the normal direction of the third plane mirror 20. The third plane mirror 20 is collimated with the first theodolite 22 at B to complete the positioning of the third plane mirror 20. The purpose is to determine the relative position of the third plane mirror 20 and the primary mirror 5, and to detect the wavefront aberration.

[0111] As shown in Figure 8 , the 4D laser interferometer 21 is arranged at the position corresponding to the tertiary mirror 12 to detect the wavefront aberration of the off-axis three-mirror optical system by using the interference principle. The position of the 4D laser interferometer 21 is uniquely determined by the position of the third plane mirror 20. However, when the curvature radius, asphericity coefficient, polishing reference surface and perpendicularity of the optical axis of the primary mirror 5, the secondary mirror 7 and the tertiary mirror 12 have deviations, the imaging quality of the off-axis three-mirror optical system cannot be guaranteed to meet the requirements after the primary mirror 5, the secondary mirror 7 and the tertiary mirror 12 are assembled according to the theoretical positions. The wavefront aberration of the off-axis three-mirror optical system is analyzed by using the Zemax optical design software, and it is found that the angles of the secondary mirror 7 and the tertiary mirror 12 have a great influence on the image quality. Therefore, the wavefront aberration of the off-axis three-mirror optical system is detected by using the 4D laser interferometer 21, and the angles of the secondary mirror 7 and the tertiary mirror 12 are slightly adjusted according to the measurement results to ensure that the off-axis three-mirror optical system has good imaging quality.

[0112] In summary, since the installation of the off-axis three-mirror optical system involves multiple components and multiple degrees of freedom adjustment, the precise misadjustment amount cannot be obtained by experience, and the misadjustment amount needs to be solved by using the sensitivity matrix algorithm.

[0113] In Figure 8 , the attitude of the third plane mirror 20 has a corresponding relationship with the field of view. The attitude of the third plane mirror 20 determined in the above steps corresponds to the f1 field of view measured by the 4D laser interferometer 21. The f1 field of view is the initial state of the third plane mirror 20. The f2 field of view measured by the 4D laser interferometer 21 corresponds to the third plane mirror 20 being rotated clockwise by 1° from the f1 field of view. The f3 field of view measured by the 4D laser interferometer 21 corresponds to the third plane mirror 20 being rotated counterclockwise by 1° from the f1 field of view. The f4 field of view measured by the 4D laser interferometer 21 corresponds to the third plane mirror 20 being raised by 1° from the f1 field of view. The f5 field of view measured by the 4D laser interferometer 21 corresponds to the third plane mirror 20 being lowered by 1° from the f1 field of view.

[0114] The mathematical expression of the relationship between the full-field Zernike wave aberration coefficient and the 12 degrees of freedom of the secondary mirror 7 and the tertiary mirror 12 is as follows:

[0115]

[0116] In formula (1), ΔZ is a full-field Zernike wave aberration coefficient matrix, M is a misalignment degree matrix, and A is a sensitivity matrix. In the misalignment degree matrix M, dx1 / dy1 / dz1 / tx1 / ty1 / tz1 are 6 degrees of freedom of the secondary mirror 7, and dx1 / dy1 / dz1 / tx1 / ty1 / tz1 represent the translation amounts and rotation amounts of the secondary mirror 7 along the x1, y1, and z1 axes, respectively, as shown in FIG. 6. dx2 / dy2 / dz2 / tx2 / ty2 / tz2 are 6 degrees of freedom of the tertiary mirror 12, and dx2 / dy2 / dz2 / tx2 / ty2 / tz2 represent the translation amounts and rotation amounts of the tertiary mirror 12 along the x2, y2, and z2 axes, respectively, as shown in FIG. 7.

[0117] In the full-field Zernike wave aberration coefficient matrix ΔZ, elements Z15-Z19 represent the Zernike coefficients of the f1 field, in which Z15 and Z16 represent the astigmatism of the f1 field, Z17 and Z18 represent the coma of the f1 field, and Z19 represents the spherical aberration of the f1 field. Z25-Z29 represent the Zernike coefficients of the f2 field, in which Z25 and Z26 represent the astigmatism of the f2 field, Z27 and Z28 represent the coma of the f2 field, and Z29 represents the spherical aberration of the f2 field. The same applies to the subsequent fields.

[0118] In the sensitivity matrix A, each element represents the differential of the wave aberration with respect to the degree of freedom in each field. For example, the first element represents the first-order partial derivative of Z15 of the f1 field with respect to the dx1 degree of freedom of the secondary mirror 7, and the value can be calculated by using the Zemax software.

[0119] The sensitivity matrix A has a size of 25×12, and the expression of the relationship between the 12 degrees of freedom of the secondary mirror 7 and the tertiary mirror 12 and the 25 Zernike wave aberration coefficients of the f1-f5 fields is as follows:

[0120]

[0121] According to the analysis by the Zemax optical design software, the tx1 / ty1 degrees of freedom of the secondary mirror 7 and the tx2 / ty2 degrees of freedom of the tertiary mirror 12 are sensitive to the wave aberration. Therefore, these four degrees of freedom are selected for image quality correction.

[0122] 6、Calculate the misalignment amount. The adaptive damping least squares method is a misalignment amount solving algorithm based on the sensitivity matrix. Its basic principle is to dynamically adjust the damping coefficient according to the input measured wavefront data, quickly traverse the damping coefficient range, and find the coefficient that minimizes the deviation. In this way, while avoiding over-adjustment, the accuracy and reliability of the correction result can be ensured. This algorithm is based on the Python module and Zemax optical design software, and real-time communication is used for closed-loop simulation verification. The input is the full-field Zernike wave aberration coefficient matrix ΔZ of the measured off-axis three-mirror optical system. The misalignment amount M is solved by the initial damping coefficient ρ. The Python module and Zemax optical design software are used for joint simulation. The misalignment amount M is brought into the Zemax optical design software to adjust the primary mirror assembly, secondary mirror assembly, and three-mirror assembly to the misalignment state, and the full-field Zernike wave aberration coefficient matrix ΔZ of the simulated off-axis three-mirror optical system is obtained. Using the above algorithm, the damping coefficient ρ is dynamically adjusted and a new misalignment amount is solved. The range of damping coefficients is quickly traversed, and the damping coefficient that minimizes the input and output deviation is selected to complete the calculation.

[0123] As shown in Figure 8 , a 4D laser interferometer 21 is used to build a detection light path of an off-axis three-mirror optical system. According to the full-field Zernike wave aberration coefficient matrix ΔZ, the misalignment amount M of the secondary mirror 7 and the three-mirror 12 is calculated by formula (3):

[0124] M=(A T A+ρI) -1 A T ΔZ (3)

[0125] Wherein, A T represents the sensitivity matrix A transpose matrix; ρ is the damping coefficient; I represents the unit matrix;

[0126] 8、According to the misalignment amount M, the secondary mirror two-dimensional adjustment mechanism 9 and the three-mirror two-dimensional adjustment mechanism 15 are used to precisely adjust the angles of the secondary mirror 7 and the three-mirror 12, and the final assembly of the off-axis three-mirror optical system is completed. The full-field wave aberration experimental results of the off-axis three-mirror optical system are shown in Figure 9 , the wavefront error RMS is better than 0.05λ@632.8nm, and the image quality meets the requirements.

[0127] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A precision assembly method of an off-axis three-mirror optical system, the off-axis three-mirror optical system comprising a primary mirror assembly, a secondary mirror assembly, and a tertiary mirror assembly; the method comprising the following steps: 1】Taking the primary mirror assembly as a reference, respectively roughly positioning the primary mirror assembly, the secondary mirror assembly, and the tertiary mirror assembly until the angle deviation of each mirror assembly is less than or equal to 10″ and the eccentricity tolerance is less than or equal to 0.05 mm; specifically: 1.1) Roughly positioning the primary mirror assembly; specifically: 1.1.1, preliminary positioning of the primary mirror assembly: the primary mirror assembly is fixed on the bottom plate (17) through the threaded holes of the primary mirror base (1) and the mounting holes of the bottom plate (17); 1.1.2, set the reference surface; the upper surface of the bottom plate (17) in the off-axis three-mirror optical system is used as the bottom plate reference surface C; the protruding side wall surface of the bottom plate (17) close to the primary mirror (5) and parallel to the primary mirror (5) is used as the bottom plate reference surface D; the protruding side wall surface of the bottom plate (17) away from the primary mirror (5) and parallel to the primary mirror (5) is used as the bottom plate reference surface E; the side wall surface of the bottom plate (17) close to the primary mirror (5) and perpendicular to the primary mirror (5) is used as the bottom plate reference surface B; the side wall surface of the bottom plate (17) away from the primary mirror (5) and perpendicular to the primary mirror (5) is used as the bottom plate reference surface F; 1.1.3, angle adjustment of the primary mirror (5); the first plane mirror (18) is set at the bottom plate reference surface D, and the first theodolite (22) is used to self-align with the first plane mirror (18) to obtain the reference direction; then the angle between the primary mirror (5) back reference surface A and the bottom plate reference surface D is adjusted according to the reference direction, so that the primary mirror (5) back reference surface A is perpendicular to the optical axis of the first theodolite (22), thereby parallel to the bottom plate reference surface D; 1.1.4, eccentricity adjustment of the primary mirror (5); the outer cylindrical surface of the primary mirror (5) is measured by a three-coordinate measuring arm to fit the primary mirror (5) axis, and the bottom plate reference surfaces B, C and D are used as references to adjust the eccentricity of the primary mirror (5) according to the measured distance x between the primary mirror (5) axis and the bottom plate reference surface C, the horizontal distance y between the primary mirror (5) axis and the bottom plate reference surface B, and the horizontal distance z between the primary mirror (5) back reference surface A and the bottom plate reference surface D; 1.1.5, judge whether the angle deviation between the primary mirror (5) back reference surface A and the bottom plate reference surface D is less than or equal to 10", and whether the eccentricity tolerance of the primary mirror (5) is less than or equal to 0.05mm, if yes, execute step 1.2), otherwise return to step 1.1.3; 1.2) transfer the reference of the primary mirror (5) back reference surface A in the primary mirror assembly to the third mirror (12) and the secondary mirror (7); 1.3) rough positioning of the secondary mirror assembly; 1.4) rough positioning of the third mirror assembly; 2) analyze the wave aberration of the off-axis three-mirror optical system by using Zemax optical design software, and adjust the rotation freedom of the secondary mirror assembly and the third mirror assembly in x and y axes according to the wave aberration to correct the image quality; 3) obtain the full field Zernike wave aberration coefficient matrix ΔZ and the sensitivity matrix A by using Zemax optical design software, and calculate the misalignment M of the secondary mirror (7) and the third mirror (12) by using adaptive damping least squares method: ； where A T is the transpose of the sensitivity matrix A of size 25 x 12; p is the damping coefficient; I represents the unit matrix; the full field Zernike wave aberration coefficient matrix ΔZ is 25×1; 4) precisely adjust the angle of the secondary mirror (7) and the third mirror (12) according to the misalignment M, so that the full field wave aberration of the off-axis three-mirror optical system is less than the threshold value, and the precision assembly of the off-axis three-mirror optical system is completed, wherein the threshold value is 0.05λ@632.8nm.

2. The method of claim 1, wherein the method further comprises: Step 1.2) is specifically: 1.2.1, reference transfer of the third mirror (12); The first theodolite (22) is self-accurate with the back reference surface A of the primary mirror (5) and is used to represent the reference direction of the back reference surface A of the primary mirror (5); the first theodolite (22) is rotated counterclockwise by 90° and is mutual sighting with the second theodolite (23), and the reference direction of the back reference surface A of the primary mirror (5) is transmitted to the second theodolite (23); then the second theodolite (23) is rotated counterclockwise by 90°, and the optical axis of the second theodolite (23) is used to represent the reference direction of the back reference surface A of the primary mirror (5); 1.2.2, reference transmission is performed on the secondary mirror (7); The first theodolite (22) is rotated clockwise by 90°, and the first plane mirror (18) at the bottom plate reference surface D is self-accurate with the first theodolite (22) to calibrate the reference direction; then the first theodolite (22) is translated to a position corresponding to the three-mirror (12), and then the first theodolite (22) is rotated clockwise by 90° and is self-accurate with the second plane mirror (19) located on the optical path of the first theodolite (22) to ensure that the reference direction remains unchanged; then the first theodolite (22) is rotated counterclockwise by 90° and is mutual sighting with the third theodolite (24) close to the bottom plate reference surface E, and the back reference surface A of the primary mirror (5) is transmitted to the third theodolite (24).

3. The method of claim 2, wherein the method further comprises: Step 1.3) is specifically: 1.3.1, preliminary positioning of the secondary mirror assembly: reserving secondary mirror assembly mounting hole positions on the bottom plate (17), and the secondary mirror assembly is fixedly connected to the bottom plate (17) through the threaded holes of the secondary mirror support seat (8) and the mounting holes of the bottom plate (17); 1.3.2, angle adjustment of the secondary mirror (7); According to the theoretical difference M of the included angle between the back reference surface of the secondary mirror (7) and the back reference surface A of the primary mirror (5), the third theodolite (24) is rotated counterclockwise by 0.38° to determine the back reference direction of the secondary mirror (7), and the included angle between the back reference surface of the secondary mirror (7) and the back reference surface A of the primary mirror (5) is adjusted according to the back reference direction of the secondary mirror (7) and is self-accurate with the third theodolite (24); 1.3.3, eccentricity adjustment of the secondary mirror (7); The three-coordinate measuring arm is used to measure the outer cylindrical surface of the secondary mirror (7) to fit the axis of the secondary mirror (7), and the bottom plate reference surfaces B, C and E are used as references, and the horizontal distance y1 of the measured axis of the secondary mirror (7) from the reference surface B, the distance x1 of the axis of the secondary mirror (7) from the bottom plate reference surface C, and the horizontal distance z1 of the back reference surface of the secondary mirror (7) from the bottom plate reference surface E are used to adjust the eccentricity of the secondary mirror (7); 1.3.4, whether the included angle deviation between the back reference surface of the secondary mirror (7) and the back reference surface A of the primary mirror (5) is less than or equal to 10″, and whether the eccentricity tolerance of the secondary mirror (7) is less than or equal to 0.05mm, if yes, step 1.4) is executed, otherwise, step 1.3.2 is returned.

4. The precision assembly method of the off-axis three-mirror optical system according to claim 3, characterized in that, Step 1.4) is specifically: 1.4.1, preliminary positioning of the three-mirror assembly: reserving three-mirror assembly mounting hole positions on the bottom plate (17), and the three-mirror assembly is fixedly connected to the bottom plate (17) through the threaded holes of the three-mirror support seat (16) and the mounting holes of the bottom plate (17); 1.4.2, angle adjustment of the three-mirror (12); According to the theoretical difference N of the angle between the back reference surface of the third mirror (12) and the back reference surface A of the primary mirror (5), the second theodolite (23) is rotated clockwise by 0.2°, which is used to determine the back reference direction of the third mirror (12), and the angle between the back reference surface of the third mirror (12) and the back reference surface A of the primary mirror (5) is adjusted according to the back reference direction of the third mirror (12) and is self-aligned with the second theodolite (23); 1.4.3, adjusting the eccentricity of the third mirror (12); The outer cylindrical surface of the third mirror (12) is measured by a three-coordinate measuring arm to fit the axis of the third mirror (12), and the horizontal distance x2 of the measured axis of the third mirror (12) from the reference surface C, the horizontal distance z2 of the back reference surface of the third mirror (12) from the reference surface D of the bottom plate, and the horizontal distance y2 of the axis of the third mirror (12) from the reference surface F of the bottom plate are used to adjust the eccentricity of the third mirror (12); 1.4.4, judging whether the angle deviation between the back reference surface of the third mirror (12) and the back reference surface A of the primary mirror (5) is less than or equal to 10″, and whether the eccentricity tolerance of the third mirror (12) is less than or equal to 0.05mm, if yes, step 2 is executed, otherwise, return to step 1.4.

2.

5. The method of claim 4, wherein the method further comprises: Step 2 is specifically: 2.1) build a wave aberration detection system to obtain the wave aberration of the off-axis three-mirror optical system; 2.2) analyze the wave aberration of the off-axis three-mirror optical system by using Zemax optical design software, and screen tx1 / ty1 of the secondary mirror (7) and tx2 / ty2 of the third mirror (12), wherein tx1 represents the rotation amount of the secondary mirror (7) along the x1 axis, ty1 represents the rotation amount of the secondary mirror (7) around the y1 axis, tx2 represents the rotation amount of the third mirror (12) around the x2 axis, and ty2 represents the rotation amount of the third mirror (12) around the y2 axis; 2.3) adjust the rotation amounts of tx1 / ty1 of the secondary mirror (7) and tx2 / ty2 of the third mirror (12) to realize image quality correction.

6. The precision assembly method of an off-axis three-mirror optical system according to claim 5, wherein Step 2.1) is specifically: 2.1.1, use the first theodolite (22) to self-align with the back reference surface A of the primary mirror (5) to introduce the reference direction; 2.1.2, keep the reference direction and translate the first theodolite (22) to the side of the primary mirror (5) away from the third mirror (12), and rotate the first theodolite (22) clockwise by 9°, which is used to represent the normal direction of the third plane mirror (20) arranged on the bottom plate reference surface E side; 2.1.3, adjust the third plane mirror (20) and self-align with the first theodolite (22) to complete the positioning of the third plane mirror (20); 2.1.4, set a 4D laser interferometer (21) at a position corresponding to the third mirror (12), and use the 4D laser interferometer (21) to emit laser to the third mirror (12) and detect the wave aberration of the off-axis three-mirror optical system.

Images