A precision assembly method for an off-axis dual-mirror and lens combined optical system

Abstract

The invention discloses a precision assembly method for an off-axis two-mirror and lens combination optical system, which mainly solves the technical problem that the existing off-axis two-mirror and lens combination optical system is a non-rotationally symmetrical structure, the optical axes of each component are not coaxial, and the traditional coaxial system adjustment method cannot be used to achieve high-precision adjustment, which brings great difficulty to the adjustment. It includes: step 1, precise positioning and installation of the primary mirror component and establishment of the reference coordinate system; step 2, calibration of the optical axis of the primary mirror; step 3, precise positioning and installation of the secondary mirror component; step 4, image quality detection of the primary and secondary mirror system; step 5, precise positioning and installation of the lens component; step 6, image quality detection of the optical system. The method greatly improves the initial assembly accuracy of the optical system, simplifies the assembly process, and plays a great auxiliary role in the fine adjustment of the optical structure of the optical system.

Description

Technical Field

[0001] The invention relates to an optical-mechanical assembly method of an optical system, and in particular to a precision assembly method of an off-axis two-mirror and lens combined optical system. Background Art

[0002] Reflective optical systems are a common structural form used in modern space-based and air-based large-aperture telescopes, including coaxial reflective optical systems and off-axis reflective optical systems. Among them, the coaxial reflective optical system has central occlusion, which not only loses light energy, but also reduces the response at medium and low frequencies, limiting the observation performance of the system. Compared with the coaxial reflective optical system, the off-axis reflective optical system does not have mutual occlusion, and can achieve a larger effective aperture under the same volume constraint, and also avoids the edge scattering effect. The system has higher energy concentration and dynamic range, and can better meet the needs of high-resolution extreme detection.

[0003] The off-axis two-mirror and lens combination optical system is a typical off-axis reflective optical system. This optical system has the advantages of an off-axis system and is equipped with a lens component at the rear end of the optical system to expand the effective field of view and imaging quality of the optical system, thereby improving the overall performance of the optical system.

[0004] However, the existing off-axis mirror-lens combined optical system is a non-rotationally symmetrical structure, and the optical axes of the components are not coaxial. It is impossible to use the traditional coaxial system adjustment method to achieve high-precision adjustment, which brings great difficulty to the adjustment. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the existing off-axis two-mirror and lens combination optical system has a non-rotationally symmetrical structure, the optical axes of the components are not coaxial, and the traditional coaxial system assembly method cannot be used to achieve high-precision assembly, which brings great difficulty to the assembly. By providing a precision assembly method for an off-axis two-mirror and lens combination optical system.

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

[0007] A precision assembly method for an off-axis two-mirror and lens combined optical system, the optical system comprising a primary mirror assembly, a secondary mirror assembly, a lens assembly, an aperture, a telescopic assembly and a bottom plate; the method is particularly characterized in that the method is specifically implemented according to the following steps:

[0008] Step 1: preliminarily assemble the primary mirror assembly onto the base plate to construct an installation reference for the primary mirror in the primary mirror assembly; measure and adjust the pitch angle and azimuth angle of the primary mirror according to the installation reference until the measured pitch angle and azimuth angle of the primary mirror are both within the deviation range of the installation reference, thereby completing the final assembly of the primary mirror assembly;

[0009] Establish a reference coordinate system based on the primary mirror;

[0010] Step 2, calibrate the optical axis of the primary mirror;

[0011] Step 3, preliminarily assemble the secondary mirror assembly onto the base plate; taking the primary mirror as a reference, measure and adjust the pitch angle and azimuth angle of the secondary mirror in the secondary mirror assembly; taking the coordinate origin of the reference coordinate system as a reference, measure and adjust the eccentric position of the secondary mirror in the reference coordinate system; repeatedly measure and adjust the pitch angle, azimuth angle, and eccentric position of the secondary mirror until the measured pitch angle, azimuth angle, and eccentric position of the secondary mirror are all within the deviation range of the theoretical position, thereby completing the preliminary assembly of the primary and secondary mirror system consisting of the primary mirror assembly and the secondary mirror assembly;

[0012] Step 4, detect the wave aberration of the primary and secondary mirror systems, adjust the secondary mirror according to the detection results, and repeat the detection and adjustment until the wave aberration of the primary and secondary mirror systems finally detected meets the requirements, completing the final assembly of the primary and secondary mirror systems;

[0013] Step 5, preliminarily assemble the lens assembly onto the base plate; take the primary mirror as a reference, measure and adjust the pitch angle and azimuth angle of the lens holder in the lens assembly; take the coordinate origin of the reference coordinate system as a reference, measure and adjust the eccentric position of the lens holder in the reference coordinate system; repeatedly measure and adjust the pitch angle, azimuth angle, and eccentric position of the lens holder until the pitch angle, azimuth angle, and eccentric position of the lens holder are measured to be within the deviation range of the theoretical position, thereby completing the preliminary assembly of the optical system;

[0014] Step 6: Detect the wave aberration of the preliminary assembled optical system, adjust the lens bracket according to the detection result, and repeat the detection and adjustment until it is detected that the wave aberration of the optical system meets the requirements, thereby completing the final assembly of the optical system.

[0015] Furthermore, the step 1 is specifically implemented according to the following steps:

[0016] Step 1.1, preliminarily assemble the primary mirror assembly onto the base plate, respectively construct reference plane A and reference plane B as the installation reference of the primary mirror; define the side surface of the base plate as reference plane A, the upper surface of the base plate as reference plane B, and the back of the primary mirror as reference plane C; respectively measure the angles between reference plane C and reference plane A and reference plane B;

[0017] Step 1.2, according to the measurement result of the angle between reference plane C and reference plane B, adjust the pitch angle of the primary mirror until the actual measured angle between reference plane C and reference plane B is within the deviation range compared with the theoretical angle between reference plane C and reference plane B; according to the measurement result of the angle between reference plane C and reference plane A, adjust the azimuth angle of the primary mirror until the actual measured angle between reference plane C and reference plane A is within the deviation range compared with the theoretical angle between reference plane C and reference plane A;

[0018] Step 1.3, measure the intersection O between the reference plane C and the outer axis of the primary mirror, take the intersection O as the origin, the normal of the reference plane B as the Z-axis direction of the coordinate system, the normal of the reference plane A as the X-axis direction of the coordinate system, and determine the Y-axis direction of the coordinate system according to the X-axis and Z-axis directions according to the right-hand rule to establish the reference coordinate system O{XYZ}.

[0019] Furthermore, the step 2 is specifically implemented according to the following steps:

[0020] Step 2.1, using the primary mirror as a reference, use an interferometer and a standard plane reflector to build a primary mirror surface interferometry detection optical path;

[0021] Step 2.2, detect the main mirror surface shape data, and adjust the angle of the standard plane reflector and translate the interferometer based on the main mirror surface shape data to adjust the normal of the standard plane reflector to a position parallel to the optical axis of the main mirror;

[0022] Step 2.3: Complete the calibration of the primary mirror optical axis.

[0023] Furthermore, step 3 is specifically implemented according to the following steps:

[0024] Step 3.1, preliminarily assemble the secondary mirror assembly onto the base plate;

[0025] Step 3.2, define the back side of the secondary mirror as reference plane D, and measure the angles between reference plane D and reference plane B and reference plane C respectively; adjust the pitch angle of the secondary mirror according to the measurement result of the angle between reference plane D and reference plane B, until the actual measured angle between reference plane D and reference plane B is within the deviation range compared with the theoretical angle between reference plane D and reference plane B; adjust the azimuth angle of the secondary mirror according to the measurement result of the angle between reference plane D and reference plane C, until the actual measured angle between reference plane D and reference plane C is within the deviation range compared with the theoretical angle between reference plane D and reference plane C;

[0026] Step 3.3: Measure the reference plane D and the outer axis of the secondary mirror to obtain the intersection point O 1 , taking the origin O of the reference coordinate system as the reference, according to the intersection O 1 The theoretical deviation from the coordinate origin O adjusts the position of the secondary mirror in the reference coordinate system to ensure that the adjusted intersection point O 1 The actual deviation from the coordinate origin O is within the theoretical deviation;

[0027] Step 3.4, determine whether the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 3.2 until the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the primary and secondary mirror system is completed.

[0028] Furthermore, the step 5 is specifically implemented according to the following steps:

[0029] Step 5.1, preliminarily assemble the lens assembly onto the base plate;

[0030] Step 5.2, define the mounting end surface of the lens holder as reference plane E, measure the angles between reference plane E and reference plane B and reference plane C respectively, and adjust the pitch angle of the lens holder according to the measurement result of the angle between reference plane E and reference plane B, until the actual measured angle between reference plane E and reference plane B is within the deviation range compared with the theoretical angle between reference plane E and reference plane B; adjust the azimuth angle of the lens holder according to the measurement result of the angle between reference plane E and reference plane C, until the actual measured angle between reference plane E and reference plane C is within the deviation range compared with the theoretical angle between reference plane E and reference plane C;

[0031] Step 5.3: Measure the reference plane E and the outer axis of the lens holder to obtain the intersection point O 2 , taking the origin O of the reference coordinate system as the reference, according to the intersection O 2 The theoretical deviation from the coordinate origin O adjusts the position of the lens holder in the reference coordinate system to ensure that the adjusted intersection O 2 The actual deviation from the coordinate origin O is within the theoretical deviation;

[0032] Step 5.4, determine whether the pitch angle and azimuth angle of the lens holder are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 5.2 until the pitch angle and azimuth angle of the lens holder are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the optical system is completed.

[0033] Further, in step 4, an interferometer and a standard plane reflector are used to build an optical path for image quality detection of the primary and secondary mirror systems, and the wave aberration of the primary and secondary mirror systems is detected by the interferometer;

[0034] In step 6, an interferometer and a standard plane mirror are used to build an optical path for image quality detection of the optical system, and the wave aberration of the optical system is detected by the interferometer.

[0035] Further, in step 4, the detection result output by the interferometer is defined as α 1 , the adjustment amount of the secondary mirror is L 1 , then α 1 and L 1 The following formula is satisfied

[0036] L 1 =(M T M) -1 M T α 1 ;

[0037] Where: M is the secondary mirror sensitivity matrix; M T is the matrix transpose of M;

[0038] In step 6, the detection result of the interferometer output is defined as α 2 , the adjustment amount of the lens holder is L 2 , then α 2 and L 2 The following formula is satisfied:

[0039] L 2 =(N T N) -1 N T α 2 ;

[0040] Where: N is the sensitivity matrix of the lens holder; N T Transpose of the matrix N.

[0041] Furthermore, before step 1, there is also:

[0042] Step 01. Install the external flexible joint arm measuring instrument on the base plate for angle measurement, eccentric position measurement, installation reference, intersection determination and reference coordinate system construction.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The present invention first establishes a reference coordinate system based on a theoretical model, then performs preliminary assembly based on the theoretical positions of the features (points, lines, and surfaces) of the parts to be assembled in the reference coordinate system, and performs fine adjustments according to the spatial positions of the features of the parts to be assembled until the parts are adjusted to their theoretical positions, thereby completing high-precision assembly of the parts; finally, the image quality is detected and adjusted to complete the final assembly of the system; this method greatly improves the assembly accuracy of the system and simplifies the assembly process.

[0045] 2. The present invention can obtain the adjustment amount of the sensitive degree of freedom of the element to be adjusted by inputting the image quality measurement results. Adjustment based on the calculated results can ensure that the imaging quality of the optical system meets the requirements, avoid blind adjustment, and greatly improve the assembly efficiency and scientificity of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the structure of an off-axis two-mirror and lens combined optical system;

[0047] Figure 2 is a schematic diagram of the installation reference and reference coordinate system of the primary mirror in an embodiment of the present invention;

[0048] Figure 3 Schematic diagram of the calibration principle of the primary mirror optical axis in an embodiment of the present invention;

[0049] Figure 4 is a schematic diagram of the secondary mirror installation reference in an embodiment of the present invention;

[0050] Figure 5 is a schematic diagram of the image quality detection optical path of the primary and secondary mirror systems in an embodiment of the present invention;

[0051] Figure 6 is a schematic diagram of the lens bracket installation reference in an embodiment of the present invention;

[0052] Figure 7 It is a principle diagram of the optical path for image quality detection of the optical system in an embodiment of the present invention.

[0053] In the figure:

[0054] 01-interferometer, 02-standard plane mirror;

[0055] 1-primary mirror assembly, 2-secondary mirror assembly, 3-lens assembly, 4-aperture, 5-telescopic assembly, 6-base plate. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] like Figure 1 As shown, an off-axis two-mirror and lens combined optical system comprises a primary mirror assembly 1, a secondary mirror assembly 2, a lens assembly 3, an aperture 4, an Invar de-telescoping assembly 5 and a base plate 6; the primary mirror assembly 1 is connected to the base plate 6 via the Invar de-telescoping assembly 5, and the primary mirror is assembled in a primary mirror frame in the primary mirror assembly 1; the secondary mirror assembly 2 is connected to the base plate 6 via the Invar de-telescoping assembly 5, and the secondary mirror is assembled in a secondary mirror frame in the secondary mirror assembly 2; a lens holder is mounted on the lens holder, and a lens optical lens group is mounted inside the lens holder; and the base plate 6 provides a bottom mounting reference for all structures.

[0058] Parallel light enters the optical system through the aperture 4, and passes through the primary mirror assembly 1, the secondary mirror assembly 2, and the lens assembly 3 in sequence to form a perfect image at the rear end focus. The assembly of the optical system must ensure that the image quality at the focus meets the central field of view RMS better than 0.085λ@632.8nm, and the ±1° field of view RMS better than 0.014λ@632.8nm. According to the optical tolerance analysis, in order to ensure that the optical indicators of the optical system meet the requirements, the position error of each component must be better than 0.05mm, and the angle error must be better than 1′, otherwise the optical system will have serious aberrations and cannot be used. Traditional mechanical assembly has low precision and cannot meet the assembly requirements of this type of system; for the existing off-axis two-mirror and lens combined optical system, the present invention proposes a precision assembly method, using a flexible joint arm measuring instrument to ensure that the position error and angle error meet the requirements, and finally using the interference detection principle to fine-tune the sensitive element to ensure the imaging quality of the optical system.

[0059] Based on the above optical system structure, the present invention provides a precision assembly method for an off-axis two-mirror and lens combined optical system. First, an external flexible joint arm measuring instrument is installed on the bottom plate 6 so that the entire optical system to be assembled is within its detection range. The spatial positioning accuracy of the measuring instrument is 0.02mm, which meets the accuracy requirement of 0.05mm for optical system assembly. It is used for angle measurement, eccentric position measurement, construction of installation reference, determination of intersection and construction of reference coordinate system.

[0060] Then follow the steps below to implement it;

[0061] Step 1: Precision positioning and installation of the primary mirror assembly 1 and establishment of a reference coordinate system;

[0062] Step 1.1, preliminarily assemble the primary mirror assembly 1 onto the bottom plate 6 through the threaded holes provided on the bottom plate 6. The primary mirror is an off-axis parabolic mirror, and high and low point engraved lines are reserved during optical processing. Ensure that the high and low point engraved lines are consistent during assembly; spin the primary mirror around its bracket, and use a height gauge to measure the high and low point marking lines to ensure that the two engraved lines are at the same height, and the deviation is controlled within 0.05mm;

[0063] like Figure 2 As shown, a flexible joint mechanical arm measuring instrument is used to construct reference plane A and reference plane B as the installation reference of the primary mirror; the side surface of the base plate is defined as reference plane A, the upper surface of the base plate is defined as reference plane B, and the back surface of the primary mirror is defined as reference plane C, and the angles between reference plane C and reference plane A and reference plane B are measured respectively;

[0064] Step 1.2, according to the measurement result of the angle between the reference plane C and the reference plane B, the pitch angle of the primary mirror is adjusted until the actual measured angle between the reference plane C and the reference plane B is within the deviation range compared with the theoretical angle between the reference plane C and the reference plane B. In this embodiment, the angle between the reference plane C and the reference plane B is ensured to be 90°±1′; according to the measurement result of the angle between the reference plane C and the reference plane A, the azimuth angle of the primary mirror is adjusted until the actual measured angle between the reference plane C and the reference plane A is within the deviation range compared with the theoretical angle between the reference plane C and the reference plane A. In this embodiment, the angle between the primary reference plane C and the reference plane A is ensured to be 17.39°±1′, and the final assembly of the primary mirror assembly 1 is completed;

[0065] Step 1.3, the above steps ensure the spatial angle between the main mirror assembly 1 and the base plate 6. The subsequent other components will be based on the main mirror, and the position deviation will be precisely controlled to be better than 0.05mm and the angle deviation will be less than 1'. Therefore, after the main mirror assembly 1 is positioned, it is necessary to establish a coordinate system on the main mirror as the assembly reference for subsequent components.

[0066] Use a flexible joint arm measuring instrument to measure the reference plane C and the outer axis of the primary mirror to obtain the intersection O. Take the intersection O on the primary mirror as the coordinate origin, the normal of the reference plane B as the Z-axis direction of the coordinate system, the normal of the reference plane A as the X-axis direction of the coordinate system, and determine the Y-axis direction of the coordinate system according to the X-axis and Z-axis directions according to the right-hand rule to establish the reference coordinate system O{XYZ}.

[0067] Step 2: Calibrate the optical axis of the primary mirror. Please follow the steps below:

[0068] Step 2.1, using the primary mirror as a reference, use the 4D interferometer 01 and the standard plane reflector 02 to build the primary mirror surface interferometry detection optical path, such as Figure 3 As shown; the standard plane reflector 02 is used for the most important image quality measurement of the optical system, and its normal must be precisely parallel to the optical axis of the primary mirror; the mirror surface of the standard plane reflector 02 is measured using a flexible joint mechanical arm measuring instrument to ensure that the parallel error with the reference surface A is better than 1′, and the angle posture of the standard plane reflector 02 is preliminarily located;

[0069] Step 2.2, detect the main mirror shape by a flexible joint mechanical arm measuring instrument, and output the main mirror shape detection data. Based on the main mirror shape detection data, adjust the angle of the standard plane reflector 02 and translate the interferometer 01 to ensure that the astigmatism coefficient in the X and Y directions is minimized and the surface shape RMS is better than 1 / 60λ@632.8nm, and adjust the normal of the standard plane reflector 02 to a position parallel to the optical axis of the main mirror;

[0070] Step 2.3: Complete the calibration of the primary mirror optical axis.

[0071] Step 3: Precision positioning and installation of the secondary mirror assembly 2, specifically implemented in the following steps:

[0072] Step 3.1, preliminarily assemble the secondary mirror assembly 2 onto the bottom plate 6 through the threaded holes on the bottom plate 6. The secondary mirror is an off-axis hyperboloid. The high and low point marking standards are reserved during optical processing. During assembly, the high and low point markings must be consistent. Spin the secondary mirror around its bracket and use a height gauge to measure the high and low point marking lines to ensure that the two marking lines are at the same height. The deviation can be controlled within 0.05mm.

[0073] Step 3.2: Define the back side of the secondary mirror as reference plane D, and use the flexible joint robot arm measuring instrument to measure the angles between reference plane D and reference plane B and reference plane C, as shown in Figure 4As shown; the pitch angle of the secondary mirror is adjusted according to the measurement result of the angle between the reference plane D and the reference plane B, until the actual measured angle between the reference plane D and the reference plane B is within the deviation range compared with the theoretical angle between the reference plane D and the reference plane B. In this embodiment, the angle between the reference plane D and the reference plane B is ensured to be 90°±1′; the azimuth angle of the secondary mirror is adjusted according to the measurement result of the angle between the reference plane D and the reference plane C, until the actual measured angle between the reference plane D and the reference plane C is within the deviation range compared with the theoretical angle between the reference plane D and the reference plane C. In this embodiment, the angle between the reference plane D and the reference plane C on the back of the primary mirror is ensured to be 34.46°±1′;

[0074] Step 3.3: Use the flexible joint robot arm measuring instrument to measure the reference surface D and the outer axis of the secondary mirror to obtain the intersection point O. 1 (x 1 ,y 1 ,z 1 ), in the primary mirror reference coordinate system O{XYZ}, taking the coordinate origin O of the reference coordinate system as the reference, according to the intersection point O 1 The theoretical deviation from the coordinate origin O is achieved by adjusting the position of the secondary mirror on the reference coordinate system through the translation adjustment frame mechanism on the secondary mirror assembly 2 to ensure that the adjusted intersection O 1 The actual deviation from the coordinate origin O is within the theoretical deviation. In this embodiment, it is ensured that x 1 =383.56±0.05mm, y 1 =266.60±0.05mm, z 1 = ±0.05mm;

[0075] Step 3.4: Since the eccentric adjustment will affect the pitch angle and azimuth angle of the secondary mirror, it is necessary to determine whether the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 3.2 until the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the primary and secondary mirror system is completed.

[0076] Step 4: When there are deviations in the radius of curvature, aspheric coefficient, etc. of the optical element, simply assembling the optical components according to the theoretical position may not necessarily guarantee that the imaging quality of the optical system meets the requirements. According to the aberration characteristic analysis, the angle of the secondary mirror assembly 2 is very sensitive to the image quality. Therefore, the interferometer 01 must be used to detect the primary and secondary mirror wave aberrations, and the position of the secondary mirror must be slightly adjusted according to the measurement results to ensure that the primary and secondary systems have good imaging quality.

[0077] Formula (1) is the degree of freedom of the secondary mirror and the aberration coefficient Z of the primary and secondary mirror system 5 ~Z 9 The mathematical relationship between the terms, the degree of freedom of the secondary mirror is Figure 6 The coordinate system O 1 {X1 Y 1 Z 1} as the benchmark, d x d y d z Indicates that along X 1 , Y 1 , Z 1 Translation, t x ,t y Indicates around X 1 , Y 1 From the analysis, we can know that the azimuth and elevation angles of the secondary mirror are x ,t y The most sensitive, has the greatest impact on image quality, and has little impact on other degrees of freedom.

[0078]

[0079] Use 4D interferometer 01 and standard plane mirror 02 to build primary and secondary mirror system to detect the optical path, such as Figure 5 As shown in the figure, the normal of the plane reflector is the direction of the optical axis of the main mirror, which has been calibrated in step 2. According to the image quality measurement coefficient α 1 , use formula (2) to calculate the adjustment amount L of the secondary mirror 1 , according to L 1 Use a flexible joint arm measuring instrument to measure and precisely adjust the secondary mirror. From the analysis, it can be seen that the wavefront Zernike coefficient term Z of the primary and secondary mirror system 5 , Z 6 is the main aberration, the secondary mirror azimuth angle t x Impact Z 5 Term coefficient, pitch angle t y Impact Z 6 The other degrees of freedom have little effect on the image quality. Therefore, the pitch angle and azimuth angle of the secondary mirror are adjusted so that Z 5 , Z 6 The coefficient is the smallest, and ultimately the RMS of the primary and secondary mirror system can be guaranteed to be better than 0.065λ@632.8nm. After the image quality meets the requirements, the final assembly of the secondary mirror assembly and the primary and secondary mirror system is completed.

[0080] L 1 =(M T M) -1 M T α 1 ; (2)

[0081] Where: M is the secondary mirror sensitivity matrix; M T is the matrix transpose of M;

[0082] Step 5: Precision positioning and installation of lens assembly 3, specifically implemented according to the following steps:

[0083] Step 5.1, preliminarily assemble the lens assembly 3 onto the bottom plate 6 through the threaded holes on the bottom plate 6;

[0084] Step 5.2: Define the mounting end surface of the lens holder as reference plane E, and use the flexible joint measuring instrument to measure the angles between reference plane E and reference plane B and reference plane C, as shown in the figure below: Figure 6 As shown; according to the measurement result of the angle between the reference plane E and the reference plane B, the pitch angle of the lens bracket is adjusted until the actual measured angle between the reference plane E and the reference plane B is within the deviation range compared with the theoretical angle between the reference plane E and the reference plane B. In this embodiment, the angle between the reference plane E and the reference plane B is ensured to be 90°±1′; according to the measurement result of the angle between the reference plane E and the reference plane C, the azimuth angle of the lens bracket is adjusted until the actual measured angle between the reference plane E and the reference plane C is within the deviation range compared with the theoretical angle between the reference plane E and the reference plane C. In this embodiment, the angle between the reference plane E and the reference plane C on the back of the primary mirror is ensured to be 51.50°±1′;

[0085] Step 5.3: Use the flexible joint arm measuring instrument to measure the reference surface E and the outer axis of the lens holder to obtain the intersection point O. 2 (x 2 ,y 2 ,z 2 ), in the primary mirror reference coordinate system O{XYZ}, according to the intersection point O 2 The position of the lens holder on the reference coordinate system is adjusted by the translation adjustment mechanism in the lens assembly 3 to ensure that the intersection point O after adjustment is 2 The actual deviation from the coordinate origin O is within the theoretical deviation. In this embodiment, it is ensured that x 2 =-351±0.05mm, y 2 =132.23±0.05mm, z 2 = ±0.05mm, complete the eccentric adjustment of the lens holder; since the inner hole of the lens holder and the outer circle of the lens barrel are precision hole-shaft matched, the diameter gap is better than 0.02mm, therefore, after the lens holder is installed, it is only necessary to install the lens barrel on the lens holder;

[0086] Step 5.4: Since the eccentric adjustment will affect the pitch angle and azimuth angle of the lens holder, it is necessary to determine whether the pitch angle and azimuth angle of the lens holder are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 5.2 until the pitch angle and azimuth angle of the lens holder are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the optical system is completed.

[0087] Step 6. At this point, the full process assembly of the primary mirror assembly 1, the secondary mirror assembly 2 and the lens assembly 3 is completed; however, when there are deviations in the radius of curvature, thickness, refractive index, etc. of each optical element of the lens assembly 3, simply assembling each optical component according to the theoretical position may not necessarily guarantee that the imaging quality of the optical system meets the requirements. Therefore, the 4D interferometer 01 must be used to detect the final wave aberration of the optical system, and the position of the lens assembly 3 is slightly adjusted according to the measurement results to ensure that the optical system has good imaging quality.

[0088] Formula (3) is the relationship between the 3 degrees of freedom of the lens assembly and the system aberration coefficient Z 5 ~Z 9 The mathematical relationship between the terms, the degree of freedom of the lens assembly 3 is Figure 7 The coordinate system O 2 {X 2 Y 2 Z 2} as the benchmark, d x d y d z Indicates that along X 1 , Y 1 , Z 1 Translation, t x ,t y Indicates around X 1 , Y 1 The analysis shows that the azimuth angle of the lens is y and pitch angle t x It is the most sensitive and has the greatest impact on the image quality of the system, while other degrees of freedom have little impact.

[0089]

[0090] L 2 =(N T N) -1 N T α 2 ; (4)

[0091] Where: N is the sensitivity matrix of the lens holder; N T Transpose of the matrix N.

[0092] Use 4D interferometer 01 and standard plane mirror 02 to build the optical system image quality detection optical path, such as Figure 7 As shown in the figure, the normal phase of the standard plane reflector 02 is the direction of the optical axis of the main mirror, which has been calibrated in step 2. 2 , use formula (4) to calculate the lens adjustment amount L 2 , according to L 2 Use a flexible joint arm measuring instrument to measure and precisely adjust the lens. From the analysis, we can see that the optical system wavefront Zernike coefficient term Z5 , Z 6 The main aberration is the lens position angle, which affects Z 5 Term coefficient, pitch angle affects Z 6 The other degrees of freedom have little effect on the image quality. Therefore, it is only necessary to adjust the pitch t x and azimuth t y , so that Z 5 , Z 6 The coefficient is the smallest, which can ultimately ensure that the on-axis RMS of the optical system is better than 0.085λ@632.8nm and the off-axis 1° field RMS is better than 0.14λ@632.8nm. After the image quality meets the requirements, the final assembly of the optical system is completed.

Claims

1. A precision assembly method for an off-axis two-mirror and lens combined optical system, the optical system comprising a primary mirror assembly (1), a secondary mirror assembly (2), a lens assembly (3), an aperture (4), a telescopic assembly (5) and a base plate (6); It is characterized in that Follow the steps below to implement it: Step 1, preliminarily assembling the main mirror assembly (1) onto the base plate (6), constructing an installation reference of the main mirror in the main mirror assembly (1); measuring and adjusting the pitch angle and azimuth angle of the main mirror according to the installation reference, until the measured pitch angle and azimuth angle of the main mirror are both within the deviation range of the installation reference, completing the final assembly of the main mirror assembly (1); establishing a reference coordinate system with the main mirror as the reference; Step 2, calibrate the optical axis of the primary mirror; Step 3, preliminarily assembling the secondary mirror assembly (2) onto the base plate (6); taking the primary mirror as a reference, measuring and adjusting the pitch angle and azimuth angle of the secondary mirror in the secondary mirror assembly (2); taking the coordinate origin of the reference coordinate system as a reference, measuring and adjusting the eccentric position of the secondary mirror in the reference coordinate system; repeatedly measuring and adjusting the pitch angle, azimuth angle, and eccentric position of the secondary mirror until the measured pitch angle, azimuth angle, and eccentric position of the secondary mirror are all within the deviation range of the theoretical position, thereby completing the preliminary assembly of the primary and secondary mirror system composed of the primary mirror assembly (1) and the secondary mirror assembly (2); Step 4: Detect the wavefront aberration of the primary and secondary mirror systems, adjust the secondary mirror according to the detection results, and repeat the detection and adjustment until the wavefront aberration of the primary and secondary mirror systems detected finally meets the requirements, thus completing the final assembly of the primary and secondary mirror systems; Step 5, preliminarily assembling the lens assembly (3) onto the base plate (6); taking the primary mirror as a reference, measuring and adjusting the pitch angle and azimuth angle of the lens bracket in the lens assembly (3); Taking the coordinate origin of the reference coordinate system as a reference, measure and adjust the eccentric position of the lens holder in the reference coordinate system; repeatedly measure and adjust the pitch angle, azimuth angle, and eccentric position of the lens holder until the pitch angle, azimuth angle, and eccentric position of the lens holder are measured to be within the deviation range of the theoretical position, thereby completing the preliminary assembly of the optical system; Step 6, detecting the wave aberration of the preliminary assembled optical system, adjusting the lens bracket according to the detection result, and repeating the detection and adjustment until the wave aberration of the optical system is detected to meet the requirements; Complete the final assembly of the optical system.

2. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 1, characterized in that: The step 1 is specifically implemented according to the following steps: Step 1.1, preliminarily assemble the primary mirror assembly (1) onto the base plate (6), respectively construct reference plane A and reference plane B as the installation reference of the primary mirror; define the side surface of the base plate as reference plane A, the upper surface of the base plate as reference plane B, and the back surface of the primary mirror as reference plane C; respectively measure the angles between reference plane C and reference plane A and reference plane B; Step 1.2, according to the measurement result of the angle between reference plane C and reference plane B, adjust the pitch angle of the primary mirror until the actual measured angle between reference plane C and reference plane B is within the deviation range compared with the theoretical angle between reference plane C and reference plane B; according to the measurement result of the angle between reference plane C and reference plane A, adjust the azimuth angle of the primary mirror until the actual measured angle between reference plane C and reference plane A is within the deviation range compared with the theoretical angle between reference plane C and reference plane A; Step 1.3, measure the intersection O between the reference plane C and the outer axis of the primary mirror, take the intersection O as the origin, the normal of the reference plane B as the Z-axis direction of the coordinate system, the normal of the reference plane A as the X-axis direction of the coordinate system, and determine the Y-axis direction of the coordinate system according to the X-axis and Z-axis directions according to the right-hand rule to establish the reference coordinate system O{XYZ}.

3. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 2, characterized in that: The step 2 is specifically implemented according to the following steps: Step 2.1, using the primary mirror as a reference, using an interferometer (01) and a standard plane reflector (02) to build a primary mirror surface interferometry detection optical path; Step 2.2, detecting the primary mirror surface shape data, and adjusting the angle of the standard plane reflector (02) and translating the interferometer (01) based on the primary mirror surface shape data, so as to adjust the normal line of the standard plane reflector (02) to a position parallel to the optical axis of the primary mirror; Step 2.3: Complete the calibration of the primary mirror optical axis.

4. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 3, characterized in that: The step 3 is specifically implemented according to the following steps: Step 3.1, preliminarily assembling the secondary mirror assembly (2) onto the base plate (6); Step 3.2, define the back side of the secondary mirror as reference plane D, and measure the angles between reference plane D and reference plane B and reference plane C respectively; adjust the pitch angle of the secondary mirror according to the measurement result of the angle between reference plane D and reference plane B, until the actual measured angle between reference plane D and reference plane B is within the deviation range compared with the theoretical angle between reference plane D and reference plane B; adjust the azimuth angle of the secondary mirror according to the measurement result of the angle between reference plane D and reference plane C, until the actual measured angle between reference plane D and reference plane C is within the deviation range compared with the theoretical angle between reference plane D and reference plane C; Step 3.3, measure the reference surface D and the outer axis of the secondary mirror to obtain the intersection O1, take the coordinate origin O of the reference coordinate system as the reference, and adjust the position of the secondary mirror on the reference coordinate system according to the theoretical deviation between the intersection O1 and the coordinate origin O, to ensure that the actual deviation between the adjusted intersection O1 and the coordinate origin O is within the theoretical deviation; Step 3.4, determine whether the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 3.2 until the azimuth angle and pitch angle of the secondary mirror are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the primary and secondary mirror system is completed.

5. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 4, characterized in that: The step 5 is specifically implemented according to the following steps: Step 5.1, preliminarily assembling the lens assembly (3) onto the base plate (6); Step 5.2, define the mounting end surface of the lens holder as reference plane E, measure the angles between reference plane E and reference plane B and reference plane C respectively, and adjust the pitch angle of the lens holder according to the measurement result of the angle between reference plane E and reference plane B, until the actual measured angle between reference plane E and reference plane B is within the deviation range compared with the theoretical angle between reference plane E and reference plane B; adjust the azimuth angle of the lens holder according to the measurement result of the angle between reference plane E and reference plane C, until the actual measured angle between reference plane E and reference plane C is within the deviation range compared with the theoretical angle between reference plane E and reference plane C; Step 5.3, measure the reference surface E and the outer axis of the lens holder to obtain the intersection O2, take the coordinate origin O of the reference coordinate system as the reference, and adjust the position of the lens holder on the reference coordinate system according to the theoretical deviation between the intersection O2 and the coordinate origin O, so as to ensure that the actual deviation between the adjusted intersection O2 and the coordinate origin O is within the theoretical deviation; Step 5.4, determine whether the pitch angle and azimuth angle of the lens holder are within the deviation range, and whether the eccentric position is within the theoretical deviation; if not, return to step 5.2 until the pitch angle and azimuth angle of the lens holder are within the deviation range, and the eccentric position is within the theoretical deviation; if so, the preliminary assembly of the optical system is completed.

6. A precision assembly method for an off-axis two-mirror and lens combined optical system according to any one of claims 1 to 5, characterized in that: In step 4, an interferometer (01) and a standard plane reflector (02) are used to construct an optical path for detecting image quality of the primary and secondary mirror systems, and the wave aberration of the primary and secondary mirror systems is detected by the interferometer (01); In step 6, an interferometer (01) and a standard plane reflector (02) are used to construct an optical path for image quality detection of the optical system, and the wave aberration of the optical system is detected by the interferometer (01).

7. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 6, characterized in that: In step 4, the detection result output by the interferometer (01) is defined as α1, and the adjustment amount of the secondary mirror is defined as L1. Then, the following formula is satisfied between α1 and L1: L1=(M T M) -1 M T α1; Where: M is the secondary mirror sensitivity matrix; M T is the matrix transpose of M; In step 6, the detection result output by the interferometer (01) is defined as α2, and the adjustment amount of the lens holder is defined as L2. Then, the following formula is satisfied between α2 and L2: L2=(N T N) -1 N T α2; Where: N is the sensitivity matrix of the lens holder; N T Transpose of the matrix N.

8. The precision assembly method of an off-axis mirror-lens combined optical system according to claim 7, characterized in that: Before step 1, you also have: Step 01: Install the external flexible joint arm measuring instrument on the base plate (6) for angle measurement, eccentric position measurement, installation reference, intersection determination and reference coordinate system construction.

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