Geometric parameter testing method for large-aperture aspheric mirror based on gravity unloading

Abstract

The application provides a large-aperture aspheric mirror geometric parameter testing method based on gravity unloading, which comprises the following steps: establishing a theoretical testing optical path model, and obtaining optical compensator parameters; building an actual testing optical path according to the optical compensator and the theoretical testing optical path model; adjusting the pose of the optical compensator and a laser interferometer so that the aberration of the actual testing optical path is 0, and measuring the long-axis distance and the short-axis distance of the actual testing optical path; setting up a gravity unloading device on the back of the measured mirror to eliminate the influence of the gravity of the aspheric mirror on the aberration of the actual testing optical path; measuring the long-axis distance and the short-axis distance of the actual testing optical path when the aberration of the actual testing optical path after gravity unloading is 0; and bringing the long-axis distance and the short-axis distance of the actual testing optical path before and after gravity unloading into the theoretical testing optical path model for simulation calculation to obtain the actual value of the aspheric coefficient of the aspheric mirror. The application effectively solves the problem of low testing precision of the geometric parameters of a large-aperture aspheric mirror supported discretely.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, and specifically relates to a method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading. Background Technology

[0002] With the increasing demands for resolution in space optical remote sensors, large-aperture reflective optical systems are frequently used in remote sensor design. During the assembly and testing of such systems, the geometric parameters of each mirror are critical parameters, directly affecting the on-orbit imaging quality of the optical remote sensor. Typically, large-aperture mirrors are assembled and adjusted using a discrete support vertical method. This support method causes deformation of the mirrors under gravity. These deformations, combined with the surface mass of the mirrors, affect the measurement of the aspheric coefficient K of aspherical mirrors, thus impacting the accuracy of ground-based assembly and adjustment, and directly affecting the on-orbit quality of the remote sensor.

[0003] The geometric parameters of traditional large-aperture mirrors are obtained by contour scanning and fitting using methods such as coordinate measuring machines. However, this method has the following drawbacks: the accuracy of coordinate measurement decreases as the diameter of the mirror increases, resulting in low fitting accuracy of the mirror's aspherical coefficient K value. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method for testing the geometric parameters of large-aperture aspherical mirrors based on gravity unloading, which effectively solves the problem of low testing accuracy of geometric parameters of large-aperture mirrors with discrete support design and vertical optical axis.

[0005] The technical solution of this invention is:

[0006] A method for testing the geometric parameters of large-aperture aspherical mirrors based on gravity unloading includes the following steps:

[0007] 1) Establish a simulation model of the test optical path, which includes a laser interferometer, an optical compensator, and an aspherical mirror arranged sequentially along the optical axis. The laser interferometer emits a spherical wave, which is compensated into an aspherical wavefront by the optical compensator. The wavefront is then incident on the aspherical mirror, reflected, and compensated back into a spherical wavefront by the optical compensator. The wavefront is then reflected back to the laser interferometer and interferes with the emitted spherical wave to form interference fringes. In the simulation model, the aspherical mirror is not subject to gravity, and the aspherical coefficient of the aspherical mirror is set to its theoretical value.

[0008] Obtain the optical compensator parameters and the short and long axis distances of the test optical path when the aberration of the test optical path is 0 in the simulation model; the short axis distance is the distance between the center of the spherical wave emitted by the laser interferometer and the first vertex of the optical compensator, and the long axis distance is the distance between the second vertex of the optical compensator and the vertex of the aspherical mirror; the first vertex is the vertex of the optical compensator facing the laser interferometer, and the second vertex is the vertex of the optical compensator facing the aspherical mirror.

[0009] 2) Construct an optical compensator based on the optical compensator parameters obtained in step 1), and build the actual test optical path by combining the short axis and long axis of the obtained test optical path.

[0010] 3) Calculate the aberration of the actual test optical path based on the interference fringes of the laser interferometer, and adjust the pose of the optical compensator and the laser interferometer to make the aberration of the actual test optical path zero, and obtain the long axis and short axis of the actual test optical path before gravity unloading.

[0011] 4) Install a gravity unloading device on the back of the aspherical mirror to eliminate the influence of the aspherical mirror's own gravity on the aberrations of the actual test optical path.

[0012] 5) Calculate the aberration of the actual test optical path based on the interference fringes of the laser interferometer. Adjust the pose of the optical compensator and the laser interferometer to make the aberration of the actual test optical path after gravity unloading zero, and obtain the major axis and minor axis of the actual test optical path after gravity unloading.

[0013] 6) Input the long axis and short axis of the actual test optical path before gravity unloading and the long axis and short axis of the actual test optical path after gravity unloading into the simulation model of the test optical path, perform simulation calculations, and obtain the actual value of the aspherical coefficient of the aspherical mirror.

[0014] Preferably, in step 3), measuring the major and minor axis distances of the actual test optical path specifically includes the following steps:

[0015] 31) Place the target ball 1 at the laser interferometer exit point, adjust the position of the target ball 1 so that its center is aligned with the center of the emitted spherical wave and its interference fringes are 0 fringes, and use the laser tracker to measure the coordinates of the center of the target ball 1.

[0016] 32) Place the target ball 2 at the first vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 2;

[0017] 33) Place the target ball 3 at the second vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 3;

[0018] 34) Place the target ball 4 at the vertex of the aspherical mirror and use a laser tracker to measure the coordinates of the center of the target ball 4;

[0019] 35) Calculate the short axis distance of the actual test optical path based on the center coordinates of target ball 1 and target ball 2, and calculate the long axis distance of the actual test optical path based on the center coordinates of target ball 3 and target ball 4.

[0020] Preferably, step 35) calculates the minor axis distance of the test optical path based on the center coordinates of target sphere 1 and target sphere 2, and calculates the major axis distance of the test optical path based on the center coordinates of target sphere 3 and target sphere 4, specifically as follows:

[0021] The short axis of the actual test optical path is the sum of the distance between the centers of target sphere 1 and target sphere 2 and the radius of target sphere 2; the long axis of the actual test optical path is the sum of the distance between the centers of target sphere 3 and target sphere 4 and the radii of target sphere 3 and target sphere 4.

[0022] Preferably, in step 6), the major and minor axis distances of the actual test optical path before gravity unloading and after gravity unloading are input into the simulation model of the test optical path for simulation calculation to obtain the actual value of the aspheric coefficient of the aspheric mirror, specifically:

[0023] Adjust the aspheric coefficient of the aspherical mirror in the simulation model so that when the major and minor axes of the test optical path in the simulation model are the same as the major and minor axes of the actual test optical path before gravity unloading, the aberration of the test optical path in the simulation model is equal to the aberration caused by the gravity of the aspherical mirror itself. When the major and minor axes of the test optical path in the simulation model are the same as the major and minor axes of the actual test optical path after gravity unloading, the aberration of the test optical path in the simulation model is equal to 0. At this time, the aspheric coefficient of the aspherical mirror in the simulation model is the actual value of the aspheric coefficient of the aspherical mirror.

[0024] Preferably, step 3) further includes:

[0025] The aspherical mirror is rotated N times around the optical axis, with each rotation angle being _____. After each rotation, the poses of the optical compensator and laser interferometer are adjusted to ensure that the aberration of the actual test optical path is zero. The major and minor axis distances of the actual test optical path under different rotation angles of the aspherical mirror are obtained. The average major axis distance of the actual test optical path under different rotation angles of the aspherical mirror is calculated. and average short wheelbase Will As the long axis of the actual test optical path before gravity unloading, The short axis of the actual test optical path before gravity unloading.

[0026] Preferably, step 5) further includes:

[0027] The aspherical mirror is rotated N times around the optical axis, with each rotation angle being _____. After each rotation, the poses of the optical compensator and laser interferometer are adjusted to ensure that the aberration of the actual test optical path is zero. The major and minor axis distances of the actual test optical path under different rotation angles of the aspherical mirror after gravity unloading are then obtained. The average major axis distance of the actual test optical path under different rotation angles of the aspherical mirror after gravity unloading is calculated. and average short wheelbase Will As the long axis of the actual test optical path after gravity unloading, This serves as the short axis of the actual test optical path after gravity unloading.

[0028] Preferably, in step 4), N is 2.

[0029] Preferably, in step 4), N is 5.

[0030] Preferably, in step 5), the design parameters of the gravity unloading device are obtained through finite element calculation.

[0031] Preferably, the simulation model of the test optical path is established using Code V optical design software.

[0032] The advantages of this invention compared to the prior art are:

[0033] (1) This invention establishes a test optical path theoretical model, obtains optical path theoretical parameters to build an actual test optical path, measures the changes in the path length and short axis distance of the actual test optical path before and after gravity unloading when the optical path aberration is 0, and then substitutes them into the test optical path theoretical model for optimization calculation, thereby obtaining the aspherical coefficient of the large-aperture aspherical mirror. The combination of testing and simulation has strong versatility and improves the test accuracy.

[0034] (2) In the testing process, the present invention distinguishes the aberrations of the test optical path and the aberrations of the aspherical mirror itself by rotating the aspherical mirror multiple times, thereby eliminating optical path aberrations and improving test accuracy. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the actual test optical path of the present invention. Detailed Implementation

[0036] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0037] A method for testing the geometric parameters of large-aperture aspherical mirrors based on gravity unloading includes the following steps:

[0038] S1: Establish a theoretical model of the test optical path, including a large-aperture aspherical mirror, an optical compensator, and a laser interferometer arranged sequentially along the optical axis. The laser interferometer emits a standard spherical wave, which, after compensation by the optical compensator, is incident on the large-aperture aspherical mirror. After reflection, the optical path returns to the laser interferometer. The aspheric coefficient of the large-aperture aspherical mirror is set to the design value K of the aspheric coefficient of the large-aperture aspherical mirror under test. d By designing the optical compensator parameters, the optical compensator compensates the spherical wavefront of the laser interferometer's spherical wave to the corresponding aspherical wavefront of the reflecting mirror, eliminating aberrations in the test optical path. The optical compensator design parameters and the theoretical axial distance of the test optical path are then obtained. The theoretical axial distance of the test optical path includes the theoretical short axial distance L. s and theoretical long wheelbase L l The short axis distance is the distance between the center of the spherical wave and the first vertex of the optical compensator, and the long axis distance is the distance between the second vertex of the optical compensator and the vertex of the large-aperture aspherical mirror. The first vertex is the vertex of the optical compensator facing the laser interferometer, and the second vertex is the vertex of the optical compensator facing the large-aperture aspherical mirror. In the theoretical model, the large-aperture aspherical mirror is not affected by gravity.

[0039] Specifically, the theoretical model of the test optical path can be established using Code V optical design software.

[0040] S2: Construct the actual test optical path based on the theoretical model of the test optical path, such as... Figure 1 As shown.

[0041] Specifically, an optical compensator is constructed based on the optical compensator design parameters in step S1, and the axial distance of the actual test optical path is initially set based on the theoretical axial distance of the test optical path.

[0042] S3: A standard spherical wave is emitted by a laser interferometer. After compensation by an optical compensator, it is incident on a large-aperture aspherical mirror. After reflection, the light returns to the laser interferometer, forming interference fringes. By calculating the interference fringes, the aberrations of the measured optical path are obtained. The positions of the interferometer and compensator are adjusted to make the aberrations of the measured optical path zero. The long axis distance L is tested under these conditions. a1 Short wheelbase L b1 .

[0043] Specifically, it includes the following steps:

[0044] S31: Place the target ball 1 at the laser output of the laser interferometer, adjust the position of the target ball 1 so that its center is aligned with the output standard spherical wave and its interference fringes are 0 fringes, and use the laser tracker to measure the coordinates of the center of the target ball 1.

[0045] S32: Place the target ball 2 at the first vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 2;

[0046] S33: Place the target ball 3 at the second vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 3;

[0047] S34: Place the target ball 4 at the vertex of the large-aperture aspherical mirror and use a laser tracker to measure the coordinates of the center of the target ball 4;

[0048] S35: Calculate the minor wheelbase L based on the coordinates of the sphere centers of points 1, 2, 3, and 4. a1 and long wheelbase L b1 Specifically, short wheelbase L a1 The distance between the centers of target ball 1 and target ball 2 is the sum of the radius of the target ball; the major axis distance L b1 It is the sum of the distance between the centers of target ball 3 and target ball 4 and the diameter of the target ball.

[0049] S4: Rotate the large-aperture aspherical mirror N times around the optical axis, with each rotation angle being 360° / (N+1), where N is typically 2 or 5. Repeat step S3 after each rotation to obtain the short axis distance L of the test optical path under different rotation angles of the mirror. ai and long wheelbase L bi Where i = 1, 2, ..., N+1. By rotating the reflector, the aberrations of the optical path and the aberrations of the reflector itself can be distinguished, thus eliminating optical path aberrations and improving test accuracy.

[0050] S5: Install a gravity unloading device on the back of the large-aperture aspherical mirror to eliminate the influence of the large-aperture aspherical mirror's own weight on the test optical path.

[0051] Specifically, the design parameters of the gravity unloading device are obtained through finite element calculation.

[0052] S6: Repeat steps S3 and S4; obtain the short axis distance L of the test optical path under different rotation angles of the reflector after gravity unloading. ci and long wheelbase L di .

[0053] S7: Data processing: Obtain the average long wheelbase measurement value L before unloading based on the short wheelbase measurement values ​​of the test optical path at various rotation angles before unloading. a ;

[0054] The average value L of the short wheelbase measurement before unloading was obtained based on the long wheelbase measurement values ​​of the test optical path at various rotation angles before unloading. b ;

[0055] The mean value L of the long wheelbase measurement after unloading was obtained based on the short wheelbase measurement values ​​of the test optical path at various rotation angles after unloading. c ;

[0056] The mean value L of the short wheelbase measurement after unloading was obtained based on the long wheelbase measurement values ​​of the test optical path at various rotation angles after unloading. d .

[0057] S8: Calculate L in step S7 a L b L c L d The actual value of the aspheric coefficient of the aspheric mirror is obtained by substituting the theoretical test optical path model into the simulation calculation.

[0058] Specifically, the aspherical coefficient of the large-aperture aspherical mirror is adjusted so that the major axis distance and minor axis distance of the theoretical model are L... a L b At that time, the aberration of the test optical path is equal to the aberration caused by the gravity of the aspherical mirror to the test optical path;

[0059] Furthermore, the major and minor wheelbases of the theoretical model are L... c L d At that time, the aberration of the test optical path is equal to 0.

[0060] The aspheric coefficient at this point is the actual value of the large-aperture aspheric reflector being measured.

[0061] In one specific embodiment, the aspheric coefficient of an aspherical mirror with a diameter of φ1300mm is tested using the method of the present invention.

[0062] The theoretical aspheric coefficient of the mirror is -0.9833, the theoretical optical path major axis distance is 3600.615 mm, the minor axis distance is 164.28 mm, and the gravity unloading device compensates for spherical aberration of -0.06λ (@632.8 nm).

[0063] Without gravity unloading, the average long axis distance of the actual measured optical path at different rotation angles was 3600.69 mm, and the average short axis distance was 164.51 mm.

[0064] Under gravity unloading conditions, the average long axis distance of the actual measured optical path at different rotation angles was 3600.82 mm, and the average short axis distance was 164.37 mm.

[0065] By substituting the measured value into the theoretical test optical path model for simulation calculation, the actual value of the aspherical coefficient of the aspherical mirror is -0.9836.

[0066] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading, characterized in that, Includes the following steps: 1) Establish a simulation model of the test optical path, which includes a laser interferometer, an optical compensator, and an aspherical mirror arranged sequentially along the optical axis. The laser interferometer emits a spherical wave, which is compensated into an aspherical wavefront by the optical compensator. The wavefront is then incident on the aspherical mirror, reflected, and compensated back into a spherical wavefront by the optical compensator. The wavefront is then reflected back to the laser interferometer and interferes with the emitted spherical wave to form interference fringes. In the simulation model, the aspherical mirror is not subject to gravity, and the aspherical coefficient of the aspherical mirror is set to its theoretical value. Obtain the optical compensator parameters and the short and long axis distances of the test optical path when the aberration of the test optical path is 0 in the simulation model; the short axis distance is the distance between the center of the spherical wave emitted by the laser interferometer and the first vertex of the optical compensator, and the long axis distance is the distance between the second vertex of the optical compensator and the vertex of the aspherical mirror; the first vertex is the vertex of the optical compensator facing the laser interferometer, and the second vertex is the vertex of the optical compensator facing the aspherical mirror. 2) Construct an optical compensator based on the optical compensator parameters obtained in step 1), and build the actual test optical path by combining the short axis and long axis of the obtained test optical path. 3) Calculate the aberration of the actual test optical path based on the interference fringes of the laser interferometer, and adjust the pose of the optical compensator and the laser interferometer to make the aberration of the actual test optical path zero, and obtain the long axis and short axis of the actual test optical path before gravity unloading. 4) Install a gravity unloading device on the back of the aspherical mirror to eliminate the influence of the aspherical mirror's own gravity on the aberrations of the actual test optical path. 5) Calculate the aberration of the actual test optical path based on the interference fringes of the laser interferometer. Adjust the pose of the optical compensator and the laser interferometer to make the aberration of the actual test optical path after gravity unloading zero, and obtain the major axis and minor axis of the actual test optical path after gravity unloading. 6) Input the long axis and short axis of the actual test optical path before gravity unloading and the long axis and short axis of the actual test optical path after gravity unloading into the simulation model of the test optical path, perform simulation calculations, and obtain the actual value of the aspherical coefficient of the aspherical mirror.

2. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 1, characterized in that, In step 3), the long axis and short axis of the actual test optical path are measured, which specifically includes the following steps: 31) Place the target ball 1 at the laser interferometer exit point, adjust the position of the target ball 1 so that its center is aligned with the center of the emitted spherical wave and its interference fringes are 0 fringes, and use the laser tracker to measure the coordinates of the center of the target ball 1. 32) Place the target ball 2 at the first vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 2; 33) Place the target ball 3 at the second vertex of the optical compensator and use a laser tracker to measure the coordinates of the center of the target ball 3; 34) Place the target ball 4 at the vertex of the aspherical mirror and use a laser tracker to measure the coordinates of the center of the target ball 4; 35) Calculate the short axis distance of the actual test optical path based on the center coordinates of target ball 1 and target ball 2, and calculate the long axis distance of the actual test optical path based on the center coordinates of target ball 3 and target ball 4.

3. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 2, characterized in that, Step 35) calculates the minor axis distance of the test optical path based on the center coordinates of target sphere 1 and target sphere 2, and calculates the major axis distance of the test optical path based on the center coordinates of target sphere 3 and target sphere 4, specifically as follows: The short axis of the actual test optical path is the sum of the distance between the centers of target sphere 1 and target sphere 2 and the radius of target sphere 2; the long axis of the actual test optical path is the sum of the distance between the centers of target sphere 3 and target sphere 4 and the radii of target sphere 3 and target sphere 4.

4. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 3, characterized in that, In step 6), the long axis and short axis of the actual test optical path before gravity unloading, and the long axis and short axis of the actual test optical path after gravity unloading, are substituted into the simulation model of the test optical path for simulation calculation to obtain the actual value of the aspherical coefficient of the aspherical mirror, specifically: Adjust the aspheric coefficient of the aspherical mirror in the simulation model so that when the major and minor axes of the test optical path in the simulation model are the same as the major and minor axes of the actual test optical path before gravity unloading, the aberration of the test optical path in the simulation model is equal to the aberration caused by the gravity of the aspherical mirror itself. When the major and minor axes of the test optical path in the simulation model are the same as the major and minor axes of the actual test optical path after gravity unloading, the aberration of the test optical path in the simulation model is equal to 0. At this time, the aspheric coefficient of the aspherical mirror in the simulation model is the actual value of the aspheric coefficient of the aspherical mirror.

5. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 4, characterized in that, Step 3) further includes: The aspherical mirror is rotated N times around the optical axis, with each rotation angle being _____. After each rotation, the poses of the optical compensator and laser interferometer are adjusted to ensure that the aberration of the actual test optical path is zero. The major and minor axis distances of the actual test optical path under different rotation angles of the aspherical mirror are obtained. The average major axis distance L of the actual test optical path under different rotation angles of the aspherical mirror is calculated. a and the average short wheelbase L b , will L a As the long axis of the actual test optical path before gravity unloading, L b The short axis of the actual test optical path before gravity unloading.

6. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 5, characterized in that, Step 5) further includes: The aspherical mirror is rotated N times around the optical axis, with each rotation angle being _____. After each rotation, the poses of the optical compensator and laser interferometer are adjusted to ensure that the aberration of the actual test optical path is zero. The major and minor axis distances of the actual test optical path under different rotation angles of the aspherical mirror after gravity unloading are then obtained. The average major axis distance of the actual test optical path under different rotation angles of the aspherical mirror after gravity unloading is calculated. and average short wheelbase Will As the long axis of the actual test optical path after gravity unloading, This serves as the short axis of the actual test optical path after gravity unloading.

7. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 6, characterized in that, In step 4), N is 2.

8. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to claim 6, characterized in that, In step 4), N is 5.

9. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to any one of claims 1 to 8, characterized in that, In step 5), the design parameters of the gravity unloading device are obtained through finite element calculation.

10. The method for testing the geometric parameters of a large-aperture aspherical mirror based on gravity unloading according to any one of claims 1 to 8, characterized in that, The simulation model of the test optical path was established using Code V optical design software.

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