High-lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing

Abstract

The invention discloses a high-lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing. The high-lightweight double-sided integrated mirror system comprises a high-lightweight double-sided integrated mirror structure and a low-temperature supporting device of an integrated mirror, the high-lightweight double-sided integrated mirror structure comprises an integrated mirror, an outer ring, an inner ring and radial reinforcing ribs, the integrated mirror is made of silicon carbide, a mirror face A and a mirror face B are arranged on the two sides of the integrated mirror, the two mirror faces are coaxial, and the mirror face A and the mirror face B are connected together through the inner ring, the outer ring and the radial reinforcing ribs. The integrated mirror low-temperature supporting structure comprises a PAD piece, an unloading piece, a gasket and a mirror frame. The PAD sheet is made of an expansion alloy with a thermal expansion coefficient close to that of silicon carbide, and is adhered and fixed on the outer ring of the integrated mirror through low-temperature epoxy glue; the unloading sheet is a titanium alloy sheet, one side is connected with the PAD sheet through a screw and a gasket, and the other side is connected with the mirror frame through a screw and a gasket.

Description

Technical Field

[0001] The invention relates to a highly lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing, belonging to the technical field of space optical remote sensor reflector mirrors. Background Art

[0002] Cryogenic optical systems are widely used in the fields of space target monitoring, near-Earth asteroid monitoring and early warning, space infrared astronomical observation, etc. Cryogenic optical systems require that the optical lens has good temperature adaptability, the reflector has high surface accuracy at low temperatures, and the lens achieves high imaging quality at low temperatures. Due to the characteristics of low-temperature operation, the lens is required to have a compact structure, light weight, high thermal conductivity, and good mechanical resistance to meet the size and weight requirements of aerospace products.

[0003] The off-axis optical system is asymmetric, and thermal deformation at low temperatures can easily cause lens misalignment, which is not conducive to low-temperature operation. The coaxial four-mirror optical system has a stronger ability to correct aberrations than the coaxial two-mirror and coaxial three-mirror optical systems. At the same time, the main mirror and the four mirrors can be designed as an integrated mirror, with a compact structure and good system symmetry, which is more suitable for low-temperature applications. Chinese patent CN102385143A "A microcrystalline low-temperature lens and its camera" proposes a coaxial four-mirror low-temperature lens designed with all-microcrystalline materials. The main mirror and the four mirrors are integrated mirrors. The microcrystalline material has low strength and low thermal conductivity. Chinese patent CN102338922A "An all-aluminum low-temperature reflective lens" proposes a coaxial four-mirror low-temperature lens designed with aluminum alloy materials. The main mirror and the four mirrors are integrated mirrors. The aluminum alloy material has high thermal conductivity and good processing performance, but the material has low specific stiffness. It is difficult to achieve a high lightweight design for the lens. At the same time, it is limited by the optical aluminum material forming process. It is currently difficult to develop large-diameter aluminum mirrors. Chinese patent CN115826168A "Two-reflecting-surface integrated reflector and coaxial four-mirror optical system using the reflector" proposes a support device for the main four-in-one mirror of a coaxial four-mirror optical system, which is fixed at three points on the back. The reflector adopts a traditional back-open lightweight structure. At the same time, the main mirror and the four mirrors are solid structures, and the integrated mirror has a low degree of lightweight. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and solve the problems of high lightweight design of a double-sided integrated mirror and high and low temperature surface precision support design in a space infrared low temperature coaxial four-mirror lens.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A highly lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing, comprising a highly lightweight double-sided integrated mirror structure and a cryogenic support device for the integrated mirror;

[0007] The highly lightweight double-sided integrated mirror structure includes an integrated mirror, an outer ring, an inner ring, and radial reinforcement ribs; the two sides of the integrated mirror are mirror surface A and mirror surface B, the two mirror surfaces are coaxial, and mirror surface A and mirror surface B are connected together through the inner ring, outer ring, and radial reinforcement ribs;

[0008] The low-temperature support structure of the integrated mirror includes a PAD sheet, an unloading sheet, a gasket, and a mirror frame; the PAD sheet material is an expansion alloy with a thermal expansion coefficient close to that of silicon carbide, and is fixed to the outer ring of the integrated mirror by low-temperature epoxy adhesive; the unloading sheet is a titanium alloy thin plate, one side of which is connected to the PAD sheet by screws and gaskets, and the other side is connected to the mirror frame by screws and gaskets.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] (1) The double-sided integrated mirror of the present invention is made of silicon carbide, which has higher rigidity, higher thermal conductivity at low temperatures, smaller thermal expansion coefficient, and better overall performance than the traditional double-sided integrated aluminum mirror.

[0011] (2) The double-sided integrated mirror of the present invention adopts a silicon carbide additive manufacturing process to achieve a semi-enclosed structure. The traditional mirror blank forming process can only realize a solid double-sided mirror and a back open reflector. The semi-enclosed structure adopted by the present invention can achieve a higher degree of lightweight.

[0012] (3) The present invention utilizes the high rigidity of silicon carbide. Compared with the double-sided integrated aluminum mirror, it can reduce the distance between the vertices of the two sides of the integrated mirror, compress the thickness of the integrated mirror, and thus compress the size of the optical system in the optical axis direction.

[0013] (4) The one-piece mirror in the present invention is designed with a mushroom head structure, which reduces the size of the one-piece mirror support structure and realizes miniaturization of the overall structure.

[0014] (5) The one-piece mirror in the present invention is fixed by low-temperature epoxy adhesive, which has higher tensile strength and shear strength than traditional silicone rubber, a more solid bonding structure, and can work at a lower temperature.

[0015] (6) The integrated mirror support structure of the present invention has high rigidity, which meets the support frequency requirements of aerospace products for optical components and is conducive to passing the mechanical vibration test of the launch stage.

[0016] (7) The integrated mirror support structure of the present invention has a strong radial unloading capability and can operate within a wide temperature range, even at low temperatures of 100K, while ensuring surface accuracy.

[0017] (8) In the present invention, radial unloading of the integrated mirror is achieved by six groups of titanium alloy thin plates evenly distributed around the circumference. Titanium alloy has high strength and its fracture toughness does not change much from room temperature to low temperature, so it is suitable for low temperature applications.

[0018] (9) The integrated mirror assembly in the present invention is connected to the other structures of the lens through a titanium alloy frame, and the external interface is designed with a radial unloading structure, which can reduce the influence of thermal deformation of other structures of the lens on the integrated mirror.

[0019] (10) The integrated lens assembly of the present invention has a compact structure and can effectively reduce the size of the lens and reduce the weight of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A three-dimensional diagram of a semi-enclosed double-sided integrated mirror of the present invention;

[0021] Figure 2 It is a cross-sectional view of a semi-enclosed double-sided integrated mirror of the present invention;

[0022] Figure 3 It is a three-dimensional diagram of the double-sided integrated mirror low-temperature support device of the present invention;

[0023] Figure 4 A three-dimensional diagram of the low-temperature flexible unloading structure of the double-sided integrated mirror of the present invention;

[0024] Figure 5 It is the simulation result of gravity deformation and gravity surface shape of double-sided integrated mirror and supporting device;

[0025] Figure 6 These are the low-temperature 100K deformation and low-temperature surface simulation results of a double-sided integrated mirror and supporting device. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] A highly lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing, which adopts silicon carbide additive manufacturing technology to complete the development of mirror blanks. Silicon carbide material has high strength, high elastic modulus, and high thermal conductivity. Combined with the semi-closed high-rigidity form, a highly lightweight design of the reflector is achieved. At the same time, the integrated mirror adopts a radial six-point flexible unloading support structure to ensure the shape accuracy under low temperature. The integrated mirror and support structure can be used in the design of space infrared coaxial four-mirror low-temperature lens.

[0028] A highly lightweight double-sided one-piece mirror system based on silicon carbide additive manufacturing comprises a highly lightweight double-sided one-piece mirror structure and a low-temperature support device for the one-piece mirror.

[0029] Highly lightweight double-sided integrated mirror structure Figure 1 , Figure 2 , Figure 3 As shown, it is mainly composed of an integrated mirror, an outer ring, an inner ring, and radial reinforcement ribs.

[0030] 1) The material of the one-piece mirror is silicon carbide, which is formed into a blank by additive manufacturing and then subjected to reaction sintering to form a high-rigidity silicon carbide mirror blank.

[0031] 2) Mirror A and mirror B are located on both sides of the integrated mirror. According to the structure of the optical system, a light hole is designed in the center of the integrated mirror.

[0032] 3) Mirror A and mirror B are coaxial.

[0033] 4) Mirror A and mirror B are connected together through the inner ring, outer ring and radial reinforcement ribs, wherein the inner ring connects the inner holes of mirror A and mirror B, the outer ring connects the outer circles of mirror A and mirror B, and the radial reinforcement ribs are connected to the inner ring, outer ring, mirror A and mirror B respectively.

[0034] 5) The integrated mirror is designed with a mushroom head structure, that is, the outer diameter of the outer ring is smaller than the outer diameter of the mirror surface, which reduces the size of the integrated mirror support structure and realizes the miniaturized design of the integrated mirror assembly.

[0035] 6) The rigidity of the reflector is improved by means of a semi-enclosed structure consisting of internal radial reinforcement ribs and inner and outer rings.

[0036] 7) The radial reinforcement ribs are evenly distributed in a radial pattern, with a total of 12 groups, and the angle between each group is 30°.

[0037] 8) Design square lightening holes on the outer ring to reduce weight.

[0038] 9) Three sets of mounting holes are designed on the inner ring to provide a central stray light elimination structure mounting interface.

[0039] 10) After the cylindrical surface of the outer ring of the mirror blank is processed, the diameter, cylindricity and roughness are guaranteed to meet the installation requirements of the supporting structure.

[0040] 11) According to the characteristics of silicon carbide additive manufacturing and optical processing technology, the thickness of mirror A and mirror B is 4mm, and the thickness of the outer ring, inner ring and radial reinforcement ribs are all 3mm. In order to meet the requirements of optical processing, when designing the mirror blank, a processing allowance of 1mm to 1.5mm is reserved for the thickness of mirror A and mirror B, a processing allowance of 1mm to 2mm is reserved for the outer diameter of the outer ring, and a processing allowance of 1mm is reserved for the diameter of the mounting hole of the inner ring stray light elimination structure.

[0041] The low temperature support structure of the integrated mirror is mainly composed of PAD sheet, unloading sheet, gasket and mirror frame, such as Figure 4 shown.

[0042] 1) The PAD sheets are fixed to the outer ring of the integrated mirror by low-temperature epoxy adhesive. A total of six groups are designed, evenly distributed at 60° intervals.

[0043] 2) The PAD sheet material is an expansion alloy with a thermal expansion coefficient close to that of silicon carbide. The average thermal expansion coefficient of silicon carbide from room temperature to low temperature is 1×10 -6 / ℃~2×10 -6 / ℃, the thermal expansion coefficient of the selected expansion alloy is also within this range, and 4J32 series expansion alloy is usually selected.

[0044] 3) The unloading sheet is a titanium alloy thin plate, one side of which is connected to the PAD sheet by screws and gaskets, and the other side is connected to the mirror frame by screws and gaskets. The unloading sheet is a thin plate structure, which uses the low bending stiffness of the thin plate to achieve low-temperature stress unloading and ensure the low-temperature surface accuracy of the reflector.

[0045] 4) Six groups of unloading plates are evenly distributed around the circumference, and the tensile and compressive stiffness of the thin plate in two directions is high. The six groups are evenly distributed around the circumference to achieve high-rigidity support for the integrated mirror with good mechanical properties.

[0046] 5) By adjusting the thickness, length and width of the unloading sheet, the stiffness and thermal deformation unloading requirements of the integrated mirror assembly can be met. Usually, to achieve the unloading effect, the thickness of the unloading sheet is within the range of 0.5mm to 1.5mm.

[0047] 6) The frame material is titanium alloy TC4, which has good mechanical properties. At the same time, indicators such as fracture toughness do not change much from room temperature to low temperature, making it suitable for low-temperature applications.

[0048] 7) A radial flexible unloading structure is designed for the external mounting position of the titanium alloy frame to reduce the impact of thermal deformation of other lens structures on the integrated mirror shape.

[0049] 8) When assembling the integrated mirror assembly, first complete the bonding of the PAD sheet and the integrated mirror, and install the unloading sheet, gasket and mirror frame after the low-temperature epoxy glue is cured. The specific installation method is as follows: fix the mirror frame, adjust the position of the integrated mirror, achieve a good fit between the unloading sheet, the PAD sheet and the mounting surface of the mirror frame, and then fix the unloading sheet with screws and gaskets.

[0050] In order to verify the correctness and feasibility of the present invention, a finite element modeling analysis is performed on a double-sided integrated mirror and its supporting device. The diameter of the integrated mirror surface A is φ462mm, the diameter of the mirror surface B is φ318mm, the design weight is 5.8kg, and the surface density is 25.2kg / m 2 Compared with the lightweight data of silicon carbide reflectors and aluminum alloy reflectors developed by traditional processes, the one-piece mirror proposed by the present invention has a higher degree of lightweight. Using the support structure of the present invention, the weight of the one-piece mirror assembly is 8.94kg. The first three-order constraint modal frequencies of the one-piece mirror are 185Hz, 245Hz, and 245Hz respectively, and the stiffness is relatively high.

[0051] When the ground optical axis is adjusted horizontally, the maximum translation of the integrated mirror under gravity is 2.4μm, the maximum tilt is 0.8″, the gravity surface shape RMS of mirror A is 0.009λ (λ=0.6328μm, the same below), and the gravity surface shape RMS of mirror B is 0.003λ. The rigid body displacement and gravity surface shape are both small, meeting the test requirements of consistent adjustment between heaven and earth. The deformation cloud map and surface shape cloud map are shown in Figure 5 .

[0052] The thermal deformation analysis of the integrated mirror assembly from room temperature 293K to low temperature 100K was carried out, and then the surface shape analysis of mirror A and mirror B at low temperature was carried out. From 293K to 100K, the RMS change of the surface shape of mirror A was 0.051λ, and the RMS change of the surface shape of mirror B was 0.014λ, both of which met the surface shape requirements of medium- and long-wave infrared optical lenses for reflectors (required to be better than 0.1λ), indicating that the support structure designed by the present invention has good temperature unloading ability. The deformation cloud map and surface shape cloud map are shown in Figure 6 .

[0053] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

[0054] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A highly lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing, characterized in that: It includes a highly lightweight double-sided integrated mirror structure and a cryogenic support device for the integrated mirror; The highly lightweight double-sided integrated mirror structure includes an integrated mirror, an outer ring, an inner ring, and radial reinforcement ribs; the two sides of the integrated mirror are mirror surface A and mirror surface B, the two mirror surfaces are coaxial, and mirror surface A and mirror surface B are connected together through the inner ring, outer ring, and radial reinforcement ribs; The low-temperature support structure of the integrated mirror includes a PAD sheet, an unloading sheet, a gasket, and a mirror frame; the PAD sheet material is an expansion alloy with a thermal expansion coefficient close to that of silicon carbide, and is fixed to the outer ring of the integrated mirror by low-temperature epoxy adhesive; the unloading sheet is a titanium alloy thin plate, one side of which is connected to the PAD sheet by screws and gaskets, and the other side is connected to the mirror frame by screws and gaskets.

2. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: The material of the one-piece mirror is silicon carbide, which is formed into a blank using additive manufacturing and then reaction sintered to form a high-rigidity silicon carbide mirror blank.

3. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: A light-through hole is arranged at the center of the integrated mirror.

4. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: The one-piece mirror is provided with a mushroom head structure, that is, the outer diameter of the outer ring is smaller than the outer diameter of the mirror surface, thereby reducing the size of the one-piece mirror support structure.

5. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: Square lightening holes are provided on the outer ring to reduce weight.

6. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: There are six groups of PAD sheets, evenly distributed along the circumference.

7. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: The thermal expansion coefficient of the PAD sheet material is within the range of the thermal expansion coefficient of silicon carbide that varies with temperature.

8. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: There are six groups of unloading plates, which are evenly distributed along the circumference.

9. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: By adjusting the thickness, length and width of the unloading sheet, the rigidity and thermal deformation unloading requirements of the integrated mirror assembly can be met.

10. The highly lightweight double-sided integrated mirror system according to claim 1, characterized in that: When assembling the integrated mirror assembly, first complete the bonding of the PAD sheet and the integrated mirror, and install the unloading sheet, gasket and mirror frame after the low-temperature epoxy glue is cured. The specific installation method is as follows: fix the mirror frame, adjust the position of the integrated mirror, achieve a good fit between the unloading sheet, the PAD sheet and the mounting surface of the mirror frame, and then fix the unloading sheet with screws and gaskets.

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