An alignment method for a coaxial afocal all-reflective optical system

Abstract

The present invention belongs to the field of precision optical and mechanical alignment, and specifically relates to an alignment method for a coaxial afocal all-reflective optical system, realizing the precise and rapid alignment of a coaxial double-parabolic afocal all-reflective optical system with an intermediate image plane. The present invention designs an intermediate image plane folding and compensating mirror, which can assist in collimation with the original optical path intermediate image plane folding mirror. At the same time, a method for calibrating the folding and compensating mirror with a self-collimating light tube and a standard plane mirror is proposed to complete the precise adjustment and fixation of the folding and compensating mirror. A laser interferometer and a standard sphere are used to establish the alignment reference of the primary mirror. The precise assembly of the intermediate image plane folding mirror is completed through the calibrated folding and compensating mirror above. Finally, the alignment of the secondary mirror is completed through a standard plane mirror. The present invention effectively simplifies and separates the multiple adjustment dimensions of the intermediate image plane folding mirror and the secondary mirror, and gradually completes the alignment of the entire optical system. The method and device of the present invention are simple, flexible in operation, and have high precision, which can greatly improve the alignment efficiency of the optical system.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision optical and mechanical alignment for airborne optoelectronic aiming systems, and particularly relates to an alignment method for a coaxial afocal all-reflective optical system. Background Art

[0002] With the development of airborne weapons in recent years, higher requirements have been put forward for airborne optoelectronic detection equipment, and airborne optoelectronic products have been continuously developing in the direction of high sensitivity, high resolution, and long-distance detection. To meet the combat mission requirements of the new generation of fighter jets in our country, reflective optical systems with large apertures, long detection distances, long focal lengths, high resolutions, and achromatism are mostly adopted in airborne optical systems. This system has a compact structure and can effectively shorten the optical barrel length, and is currently a research hotspot in the international and domestic airborne aviation fields.

[0003] For example, a dual-paraboloid coaxial afocal all-reflective telescopic optical system with an intermediate image plane. This optical system mainly consists of a primary mirror component 1, a secondary mirror component, a folding mirror 3, and a telescope chamber 4. The optical path schematic diagram is shown in the appendix Figure 1 as shown. The primary and secondary mirror components are assembled on both sides of the telescope chamber 4, and the folding mirror 3 is assembled in the middle of the mirror chamber through a connecting rod. Parallel light is incident on the primary mirror component and converges at the focus of the paraboloid. The focus is near the reflecting surface of the folding mirror, and the foci of the two paraboloids coincide. The light beam is deflected by 90° by the folding mirror and incident on the secondary mirror component, and the converging light beam is converted into parallel light and exits by the reflecting surface of the secondary mirror. After the light beam passes through this telescopic afocal system, the aperture is reduced to two-thirds of the original, effectively reducing the size of the subsequent optical elements. This system uses the laser interference wavefront aberration method for alignment. This method can be measured and adjusted, and the evaluation is objective, and it is a relatively mainstream alignment method for reflective systems. The alignment is based on the primary mirror component, and the spatial postures of the folding mirror and the secondary mirror need to be adjusted simultaneously to ensure that the wavefront aberration of the system reaches the theoretical design index. Due to the coupling of the adjustment dimensions of the folding mirror and the secondary mirror, there are more adjustment dimensions and the alignment efficiency is low.

[0004] Therefore, it is necessary to design an alignment method for a coaxial afocal all-reflective optical system. Summary of the Invention

[0005] The technical problem to be solved by the present invention:

[0006] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a compensating mirror assembly, a calibration method, and an alignment method applied to a coaxial afocal all-reflective optical system.

[0007] A technical solution provided by the present invention is:

[0008] An intermediate image plane folding compensating mirror, wherein the structure of the folding compensating mirror is the same as that of the folding mirror to be aligned, and the size is the same as that of the folding mirror to be aligned.

[0009] Another technical solution provided by the present invention is:

[0010] A compensation mirror assembly includes the intermediate image plane folding compensation mirror and the folding mirror. The intermediate image plane folding compensation mirror includes a first surface, and the folding mirror includes a second surface. Both the first surface and the second surface are coated reflective surfaces. After the intermediate image plane folding compensation mirror and the folding mirror are bonded and cured, the first surface and the second surface are in a parallel relationship.

[0011] Another technical solution provided by the present invention is:

[0012] A method for precisely adjusting the compensation mirror assembly, the specific steps are as follows:

[0013] Step 1: Erect a first standard plane mirror in front of the axis of the first photoelectric autocollimator, and adjust its angle to make it collimated with the first photoelectric autocollimator;

[0014] Step 2: After erecting a pentaprism at the middle position between the first photoelectric autocollimator and the first standard plane mirror, place a second standard plane mirror along the direction perpendicular to the axis of the first photoelectric autocollimator, and adjust its angle to make it collimated with the first photoelectric autocollimator after 90° folding through the pentaprism, and then remove the pentaprism;

[0015] Step 3: Erect a second photoelectric autocollimator in front of the axis of the second standard plane mirror, and adjust its angle to make it collimated with the second standard plane mirror;

[0016] Step 4: Put the pre-connected compensation mirror assembly into the optical path, adjust the folding mirror to make it collimated with the first standard plane mirror and the second photoelectric autocollimator respectively, and then fix the position of the folding mirror;

[0017] Step 5: Fine-tune the corresponding angle between the intermediate image plane folding compensation mirror and the folding mirror to make it collimated with the second standard plane mirror and the first photoelectric autocollimator, and fix the positions of the intermediate image plane folding compensation mirror and the folding mirror with photosensitive glue to complete the adjustment.

[0018] A further technical solution of the present invention is: The pre-connected compensation mirror assembly in Step 4 is preliminarily fastened with an elastomer.

[0019] A further technical solution of the present invention is: The fine adjustment in Step 5 is achieved by adding or subtracting gaskets on the contact surface between the intermediate image plane folding compensation mirror and the folding mirror to finely adjust the angle.

[0020] Another technical solution provided by the present invention is:

[0021] An alignment method for a coaxial afocal all-reflective optical system, the specific steps are as follows:

[0022] Step 1: After assembling the main mirror component on the telescope chamber, the whole is mounted on the adjustment rack. The adjustment rack is placed in front of the large-aperture laser interferometer. Adjust the adjustment rack to make the main mirror component enter the light passing envelope of the laser interferometer. Place a standard sphere at the focal position of the main mirror component. The standard sphere is placed on a three-dimensional adjustment rack;

[0023] Step 2: Adjust the position of the standard sphere and the angle of the main mirror component. After reaching the preset conditions, determine the position of the main mirror component as the assembly reference of the optical system;

[0024] Step 3: Set up a theodolite between the large-aperture laser interferometer and the main mirror component. Adjust the collimation of the main mirror component and the theodolite, and then rotate the theodolite 90° clockwise and fix it; Set up a third standard plane mirror in front of it. Adjust its azimuth and pitch angles to make it collimated with the theodolite, and fix the position of the third standard plane mirror. The position of this plane mirror is determined as the assembly reference of the entire telescopic system;

[0025] Step 4: Assemble the compensated mirror component calibrated by the above precise calibration method to the telescope chamber with a connecting rod. Use the laser interferometer to observe the third standard plane mirror through the intermediate image plane folding compensated mirror. After reaching the preset conditions, the collimation of the intermediate image plane folding compensated mirror and the third standard plane mirror is completed, and the spatial position of the folding mirror is fixed;

[0026] Step 5: Disassemble the intermediate image plane folding compensated mirror, assemble the secondary mirror component to the corresponding position of the telescope chamber. After the spatial positions of the laser interferometer, the main mirror component, the folding mirror and the third standard plane mirror have been determined, adjust the angle and translation of the secondary mirror component to meet the preset system indicators, and fix the position of the secondary mirror component to complete the precise alignment and adjustment of the entire optical system.

[0027] A further technical solution of the present invention is that the preset condition in Step 2 is that the coma term of the wavefront Zernike coefficient of the main mirror component is close to 0.

[0028] A further technical solution of the present invention is that the preset condition in Step 4 is that the least number of interference fringes is observed.

[0029] A further technical solution of the present invention is that the method of disassembling the intermediate image plane folding compensated mirror in Step 5 is to disassemble it through the water solubility of the photosensitive glue.

[0030] A further technical solution of the present invention is that the preset system indicators in Step 5 are: the image point of the telescopic system is located at the center of the interferometer, the astigmatism, coma and spherical aberration of the Zernike coefficient of the secondary mirror component tend to zero, and the RMS value of the wavefront aberration of the telescopic optical system is adjusted to the minimum.

[0031] Beneficial effects

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. A compensating mirror assembly according to the present invention, wherein the intermediate image plane folding compensating mirror has the same structural dimensions as the folding mirror and is detachably connected. Gaskets are added or removed on the contact surface between the intermediate image plane folding compensating mirror and the folding mirror for fine angle adjustment, and then bonded and cured with photosensitive glue. The photosensitive glue is a water-soluble glue, which can be disassembled without stress in water and does not affect the actual assembly of the product. After the first surface A and the second surface B are arranged in a parallel relationship, it is convenient for the installation and adjustment of the folding mirror.

[0034] 2. A calibration method according to the present invention uses an optical path composed of a first standard plane mirror, a second standard plane mirror, a first photoelectric autocollimator, and a second photoelectric autocollimator to achieve precise calibration of the designed compensating mirror assembly, thereby providing an accuracy basis for the installation and adjustment of the entire optical system.

[0035] 3. The present invention designs an installation and adjustment method for a coaxial afocal all-reflective optical system, which can effectively split the adjustment links of the folding mirror and the secondary mirror and adopt a step-by-step installation and adjustment method to achieve the installation and adjustment of the interferometer, the main mirror component, the folding mirror, the standard plane mirror, and the secondary mirror component. The installation and adjustment method has simple steps, clear principles, and high precision, and can greatly improve the installation and adjustment precision and efficiency of the optical system. Description of the Drawings

[0036] Attached Figure 1 is a schematic diagram of the optical path of a coaxial afocal reflection system.

[0037] Attached Figure 2 is a schematic diagram of the structure of the folding mirror and the folding compensating mirror.

[0038] Attached Figure 3 is a schematic diagram of the precise calibration principle of the folding compensating mirror.

[0039] Attached Figure 4 is a schematic diagram of the principle of establishing an installation and adjustment reference for the main mirror component.

[0040] Attached Figure 5 is a schematic diagram of the principle of establishing an installation and adjustment reference for the plane mirror.

[0041] Attached Figure 6 is a schematic diagram of the installation and adjustment principle of the telescopic optical system.

[0042] In the figure: 1 - main mirror component, 2 - secondary mirror component, 3 - folding mirror, 4 - telescope chamber; 21 - folding compensating mirror, 22 - connecting rod; 33 - first standard plane mirror, 34 - second standard plane mirror, 35 - first photoelectric autocollimator, 36 - second photoelectric autocollimator; 41 - laser interferometer, 42 - standard sphere; 52 - theodolite, 53 - third standard plane mirror. Detailed Embodiments

[0043] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0044] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

[0045] Embodiment 1

[0046] An intermediate image plane folding compensation mirror 21, the structure of the folding compensation mirror 21 is the same as that of the folding mirror 3 to be adjusted, and the size is the same as that of the folding mirror 3 to be adjusted.

[0047] Embodiment 2

[0048] A compensation mirror assembly includes the intermediate image plane folding compensation mirror 21 and the folding mirror 3 described in Embodiment 1. The intermediate image plane folding compensation mirror 21 includes a first surface, and the folding mirror 3 includes a second surface. Both the first surface and the second surface are coated reflective surfaces. After the intermediate image plane folding compensation mirror 21 and the folding mirror 3 are bonded and cured, it is satisfied that the A surface of the first surface and the B surface of the second surface are parallel.

[0049] Bonding and curing are carried out through a photosensitive adhesive. This photosensitive adhesive is a water-soluble adhesive, which can be disassembled without stress in water and does not affect the actual assembly of the product. The intermediate image plane folding compensation mirror 21 and the folding mirror 3 are connected to the telescope chamber 4 through a connecting rod 22.

[0050] Embodiment 3

[0051] A precise adjustment method for the above compensation mirror assembly, as Figure 3 shown, the specific method steps are as follows:

[0052] Step 1: A first standard flat mirror 33 is erected in front of the axis of the first photoelectric autocollimator 35, and its angle is adjusted to make it collinear with the first photoelectric autocollimator 35;

[0053] Step 2: A pentaprism is erected at the intermediate position between the first photoelectric autocollimator 35 and the first standard flat mirror 33. Then, a second standard flat mirror 34 is placed along the direction perpendicular to the axis of the first photoelectric autocollimator 35, and its angle is adjusted to make it collinear with the first photoelectric autocollimator 35 after 90° folding through the pentaprism, and then the pentaprism is removed;

[0054] Step 3: Install a second optoelectronic autocollimator 36 in front of the axis of the second standard plane mirror 34, and adjust its angle to collimate it with the second standard plane mirror 34;

[0055] Step 4: Place the pre-connected compensating mirror assembly into the optical path. After adjusting the folding mirror 3 to be collimated with the first standard plane mirror 33 and the second optoelectronic autocollimator 36 respectively, fix the position of the folding mirror 3; in this step, the collimation is based on the crosshair of the second optoelectronic autocollimator 36 being at the center position.

[0056] The pre-connected compensating mirror assembly is initially fastened using an elastomer, and the elastomer can be a simple rubber band, etc. A simple initial pre-connection is sufficient.

[0057] Step 5: Fine-tune the corresponding angle between the intermediate image plane folding compensating mirror 21 and the folding mirror 3 to collimate it with the second standard plane mirror 34 and the first optoelectronic autocollimator 35. The collimation is based on the crosshair of the first optoelectronic autocollimator 35 being at the center position. Fix the positions of the intermediate image plane folding compensating mirror 21 and the folding mirror 3 using photosensitive glue to complete the calibration.

[0058] The fine-tuning is achieved by adding or removing shims on the contact surface between the intermediate image plane folding compensating mirror 21 and the folding mirror 3 to finely adjust the angle.

[0059] Embodiment 4

[0060] After the calibration of the intermediate image plane folding compensating mirror 21, the above compensating mirror assembly is used for the alignment of the optical system as a whole. As shown in the appendix Figures 4 - 6 The specific steps of the coaxial afocal all-reflective optical system alignment method are as follows:

[0061] After assembling the main mirror component 1 on the telescope chamber 4, the whole is mounted on an adjustment stand. The adjustment stand can be a five-dimensional adjustment stand. The adjustment stand is placed in front of a large-aperture laser interferometer 41. Adjust the adjustment stand so that the main mirror component 1 enters the light passing envelope of the laser interferometer 41. Place a standard sphere 42 at the focal position of the main mirror component 1. The standard sphere 42 is placed on a three-dimensional adjustment stand, as shown in the appendix Figure 4 as shown.

[0062] Adjust the vertical, horizontal, left, and right translation of the standard sphere 42, and adjust the azimuth and pitch angles of the main mirror component 1 to make the coma term of its wavefront Zernike coefficient close to 0. At this time, the position of the main mirror is the assembly reference for the entire optical system.

[0063] Set up a theodolite 52 between the large-aperture laser interferometer 41 and the primary mirror assembly 1. Adjust the collimation between the primary mirror assembly 1 and the theodolite 52, and then rotate the theodolite 52 90° clockwise and fix it. Set up the third reference flat mirror 53 in front of it, adjust its azimuth and elevation angles to make it collimated with the theodolite 52, and fix the position of the third reference flat mirror 53. The position of this flat mirror is determined as the assembly reference for the entire telescopic system, as shown in the appendix Figure 5 as shown

[0064] Assemble the compensator mirror assembly adjusted by the above precise calibration method to the telescope chamber 4 with the connecting rod 22. Use the laser interferometer 41 to observe the least number of interference fringes of the third reference flat mirror 53 through the intermediate image plane folding compensator mirror 21, that is, complete the collimation between the intermediate image plane folding compensator mirror 21 and the third reference flat mirror 53, and complete the fixing of the spatial position of the folding mirror 3, as shown in the appendix Figure 6 as shown

[0065] Disassemble the intermediate image plane folding compensator mirror 21, and assemble the secondary mirror assembly 2 to the corresponding position in the telescope chamber 4. After the spatial positions of the laser interferometer 41, the primary mirror assembly 1, the folding mirror 3, and the third reference flat mirror 53 have been determined, adjust the angle and translation of the secondary mirror assembly 2 so that the image point of the telescopic system is located at the center of the interferometer. Fine-tune it so that the Zernike coefficients astigmatism, coma, and spherical aberration all tend to zero, that is, adjust the wavefront aberration RMS value of the telescopic optical system to the minimum until the design index is met, and fix the position of the secondary mirror assembly 2 to complete the precise alignment of the optical system

[0066] An alignment method for a coaxial afocal all-reflective optical system provided by the present invention can effectively split the adjustment links of the folding mirror 3 and the secondary mirror, and is carried out by a step-by-step alignment method, realizing the alignment of the interferometer, the primary mirror assembly 1, the folding mirror 3, the reference flat mirror, and the secondary mirror assembly 2. This alignment method has simple steps, clear principles, and high precision, and can greatly improve the alignment precision and efficiency of this optical system

[0067] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention

Claims

1. A method for precisely adjusting a compensation mirror assembly, characterized in that: The compensation mirror assembly includes an intermediate image plane folding compensation mirror and a folding mirror. The structure of the folding compensation mirror is the same as that of the folding mirror to be adjusted, and the size is the same as that of the folding mirror to be adjusted. The intermediate image plane folding compensation mirror includes a first surface, and the folding mirror includes a second surface. Both the first surface and the second surface are coated reflective surfaces. After the intermediate image plane folding compensation mirror and the folding mirror are bonded and cured, the first surface and the second surface are parallel; The steps of the precise adjustment method are as follows: S1.1: Install a first standard plane mirror in front of the axis of the first optoelectronic autocollimator, and adjust its angle to make it collimated with the first optoelectronic autocollimator; S1.2: Install a pentaprism at the middle position between the first optoelectronic autocollimator and the first standard plane mirror. Then, place a second standard plane mirror along the direction perpendicular to the axis of the first optoelectronic autocollimator, and adjust its angle to make it collimated with the first optoelectronic autocollimator after a 90° folding through the pentaprism. Then remove the pentaprism; S1.3: Install a second optoelectronic autocollimator in front of the axis of the second standard plane mirror, and adjust its angle to make it collimated with the second standard plane mirror; S1.4: Put the pre-connected compensation mirror assembly into the optical path, adjust the folding mirror to make it collimated with the first standard plane mirror and the second optoelectronic autocollimator respectively, and then fix the position of the folding mirror; S1.5: Fine-tune the corresponding angle between the intermediate image plane folding compensation mirror and the folding mirror to make it collimated with the second standard plane mirror and the first optoelectronic autocollimator, and fix the positions of the intermediate image plane folding compensation mirror and the folding mirror with photosensitive glue to complete the adjustment.

2. The method for precisely adjusting a compensation mirror assembly according to claim 1, wherein: In S1.4, the pre-connected compensation mirror assembly is preliminarily fastened with an elastomer.

3. A method for precisely adjusting a compensation mirror assembly according to claim 1, characterized in that: In S1.5, the angle is finely adjusted by adding or removing shims on the contact surface between the intermediate image plane folding compensation mirror and the folding mirror.

4. An alignment method for a coaxial afocal all-reflective optical system, characterized in that: The steps of the adjustment method are as follows: S4.1: Assemble the main mirror component on the telescope chamber and then mount it on the adjustment stand as a whole. The adjustment stand is placed in front of a large-aperture laser interferometer. Adjust the adjustment stand to make the main mirror component enter the light passing envelope of the laser interferometer. Place a standard sphere at the focal position of the main mirror component. The standard sphere is placed on a three-dimensional adjustment stand; S4.2: Adjust the position of the standard sphere and the angle of the main mirror component. After reaching the preset conditions, determine the position of the main mirror component as the assembly reference of the optical system; S4.3: Set up a theodolite between the large-aperture laser interferometer and the main mirror component, adjust the main mirror component to be collimated with the theodolite, and then fix the theodolite by rotating it 90° clockwise; Install a third standard plane mirror in front of it, adjust its azimuth and elevation angles to make it collimated with the theodolite, and fix the position of the third standard plane mirror. The position of this plane mirror is determined as the assembly reference of the entire telescopic system; S4.4: Assemble the compensation mirror assembly adjusted by the precise adjustment method described in claim 1 to the telescope chamber with a connecting rod. Use the laser interferometer to observe the third standard plane mirror through the intermediate image plane folding compensation mirror. After reaching the preset conditions, the collimation between the intermediate image plane folding compensation mirror and the third standard plane mirror is completed, and the spatial position of the folding mirror is fixed; S4.5: Dismantle the intermediate image plane folding compensating mirror, assemble the secondary mirror component to the corresponding position in the telescope chamber. After the spatial positions of the laser interferometer, the primary mirror component, the folding mirror and the third standard flat mirror have been determined, adjust the angle and translation of the secondary mirror component to meet the preset system indicators, fix the position of the secondary mirror component, and complete the precise alignment of the entire optical system.

5. A method for aligning a coaxial afocal all-reflective optical system according to claim 4, characterized in that: In S4.2, the preset condition is that the coma term of the wavefront Zernike coefficient of the primary mirror component is close to 0.

6. A coaxial afocal all-reflective optical system alignment method according to claim 4, characterized in that: In S4.4, the preset condition is that when observing the third standard flat mirror through the intermediate image plane folding compensating mirror using the laser interferometer, the least number of interference fringes is observed.

7. A method for aligning a coaxial afocal all-reflective optical system according to claim 4, characterized in that: In S4.5, the intermediate image plane folding compensating mirror is dismantled by taking advantage of the water solubility of the photosensitive adhesive.

8. A method for aligning a coaxial afocal all-reflective optical system according to claim 4, characterized in that: In S4.5, the preset system indicators are as follows: the image point of the telescopic system is located at the center of the interferometer, the astigmatism, coma and spherical aberration of the Zernike coefficient of the secondary mirror component all tend to zero, and the RMS value of the wavefront aberration of the telescopic optical system is adjusted to the minimum.

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