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

Abstract

A lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing includes a lightweight double-sided integrated mirror structure and a cryogenic support device for the integrated mirror. The lightweight double-sided integrated mirror structure includes an integrated mirror, an outer ring, an inner ring, and radial reinforcing ribs. The integrated mirror is made of silicon carbide, and its two sides are mirror surface A and mirror surface B, which are coaxial and connected together by the inner ring, outer ring, and radial reinforcing ribs. The cryogenic support structure for the integrated mirror includes a PAD sheet, an unloading plate, 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 bonded to the outer ring of the integrated mirror with a cryogenic epoxy adhesive. The unloading plate is a thin titanium alloy plate, connected to the PAD sheet on one side by screws and gaskets, and connected to the mirror frame on the other side by screws and gaskets.

Description

Technical Field

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

[0002] Cryogenic optical systems are widely used in fields such as space target monitoring, near-Earth asteroid surveillance and early warning, and space infrared astronomical observation. Cryogenic optical systems require optical lenses with good temperature adaptability, mirrors with high surface accuracy at low temperatures, and lenses that achieve high imaging quality at low temperatures. Due to the characteristics of cryogenic operation, the lenses must have a compact structure, light weight, high thermal conductivity, and good mechanical properties to meet the size and weight requirements of aerospace products.

[0003] Off-axis optical systems are asymmetrical, and thermal deformation at low temperatures can easily cause lens misalignment, which is detrimental to low-temperature operation. Coaxial four-mirror optical systems offer stronger aberration correction capabilities compared to coaxial two-mirror and three-mirror systems. Furthermore, the primary and four mirrors can be designed as a single unit, resulting in a compact structure and good system symmetry, making them well-suited for low-temperature applications. Chinese patent CN102385143A, "A Microcrystalline Low-Temperature Lens and Camera Thereof," proposes a coaxial four-mirror low-temperature lens designed entirely with microcrystalline materials, where the primary and four mirrors are integrated. Microcrystalline materials have 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, where the primary and four mirrors are integrated. Aluminum alloys have high thermal conductivity and good processing performance, but their low specific stiffness makes it difficult to achieve a highly lightweight design. Additionally, limitations in the forming process of optical aluminum materials currently hinder the development of large-aperture aluminum lenses. Chinese patent CN115826168A, "Two-reflecting-surface integrated mirror and coaxial four-mirror optical system using the mirror", proposes a support device for a coaxial four-mirror optical system with a main mirror and four mirrors integrated. The mirror is fixed at three points on the back. The mirror adopts a traditional open-back lightweight structure. At the same time, the main mirror and the four mirrors are solid structures. The integrated mirror has a low degree of lightweighting. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and solve the problems of high-lightweight design and high-low temperature surface shape accuracy support design of the double-sided integrated mirror in the space infrared low-temperature coaxial four-reflection lens.

[0005] The objective of this invention is achieved through the following technical solutions:

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

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

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

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

[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 temperature, smaller coefficient of thermal expansion and better overall performance compared with traditional double-sided integrated aluminum mirror.

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

[0012] (3) This invention utilizes the high stiffness of silicon carbide, which, compared with double-sided integrated aluminum mirror, can reduce the distance between the vertices of the two sides of the integrated mirror and compress the thickness of the integrated mirror, thereby compressing the optical axis dimension of the optical system.

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

[0014] (5) In this invention, the integrated mirror is bonded and fixed with low-temperature epoxy adhesive, which has higher tensile strength and shear strength than traditional silicone rubber, and the bonding structure is more solid. It can also work at lower temperatures.

[0015] (6) The integrated mirror support structure in this 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 section.

[0016] (7) The integrated mirror support structure in this invention has strong radial unloading capacity, can work in a wide temperature range, can work at a low temperature of 100K, and at the same time ensures surface accuracy.

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

[0018] (9) In this invention, the integrated lens assembly is connected to other structures of the lens via a titanium alloy frame, and the external interface is designed with a radial unloading structure, which can reduce the impact of thermal deformation of other structures of the lens on the integrated lens.

[0019] (10) The integrated lens assembly in this invention has a compact structure, which can effectively compress the lens size and reduce the lens weight. Attached Figure Description

[0020] Figure 1 This is a perspective view of the semi-enclosed double-sided integrated mirror of the present invention;

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

[0022] Figure 3 This is a perspective view of the low-temperature support device for the double-sided integrated mirror of the present invention;

[0023] Figure 4 This is a perspective view of the low-temperature flexible unloading structure of the double-sided integrated mirror of the present invention;

[0024] Figure 5 The simulation results of gravity deformation and gravity surface shape are presented for an example of a double-sided integrated mirror and its support device.

[0025] Figure 6 The results show the low-temperature deformation and low-temperature surface shape simulation results of a double-sided integrated mirror and its support device at 100K. Detailed Implementation

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

[0027] A lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing is proposed. The mirror blank is prepared by silicon carbide additive manufacturing process. Silicon carbide material has high strength, high elastic modulus and high thermal conductivity. Combined with the semi-enclosed high stiffness form, the mirror achieves a lightweight design. At the same time, the integrated mirror adopts a radial six-point flexible unloading support structure to ensure the shape accuracy at low temperature. This integrated mirror and support structure can be applied to the design of a space infrared coaxial four-reflector low temperature lens.

[0028] A lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing includes a lightweight double-sided integrated mirror structure and a cryogenic support device for the integrated mirror.

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

[0030] 1) The integral mirror material is silicon carbide. The blank is formed by additive manufacturing and then reaction sintering is carried out 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-transmitting 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 by an inner ring, an outer ring, and radial reinforcing ribs. 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 reinforcing ribs are connected to the inner ring, the outer ring, Mirror A, and Mirror B, respectively.

[0034] 5) The integrated mirror design features a mushroom-shaped structure, meaning the outer diameter of the outer ring is smaller than the outer diameter of the mirror surface, reducing the size of the integrated mirror support structure and enabling a miniaturized design of the integrated mirror assembly.

[0035] 6) The stiffness of the reflector is improved by using internal radial stiffeners and a semi-enclosed structure consisting of an inner ring and an outer ring.

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

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

[0038] 9) The inner ring is designed with three sets of mounting holes to provide a central anti-stray light structure mounting interface.

[0039] 10) After machining the outer cylindrical surface of the mirror blank, ensure the diameter, cylindricity and roughness to meet the installation requirements of the support structure.

[0040] 11) Based on 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 reinforcing ribs is 3mm. To meet the requirements of optical processing, a machining allowance of 1mm to 1.5mm is reserved for the thickness of mirror A and mirror B, a machining allowance of 1mm to 2mm is reserved for the outer diameter of the outer ring, and a machining allowance of 1mm is reserved for the diameter of the mounting hole for the anti-stray light structure of the inner ring.

[0041] The integrated cryogenic support structure for the lens mainly consists of a PAD element, a release element, a spacer, and a lens frame. Figure 4 As shown.

[0042] 1) The PAD pieces are bonded and fixed to the outer ring of the integrated mirror with low-temperature epoxy adhesive. There are six sets in total, 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. -6 / ℃~2×10 -6 Between / ℃, the coefficient of thermal expansion of the selected expansion alloy is also within this range, and the 4J32 series expansion alloy is usually selected.

[0044] 3) The unloading plate is a thin titanium alloy plate. One side is connected to the PAD plate by screws and washers, and the other side is connected to the mirror frame by screws and washers. The unloading plate is a thin plate structure. Taking advantage of the low bending stiffness of the thin plate, it can realize low-temperature stress unloading and ensure the low-temperature surface accuracy of the mirror.

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

[0046] 5) By adjusting the thickness, length, and width of the unloading plate, the rigidity and thermal deformation unloading requirements of the integrated mirror assembly can be met. Typically, to achieve the desired unloading effect, the thickness of the unloading plate is in the range of 0.5mm to 1.5mm.

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

[0048] 7) The titanium alloy lens frame is designed with a radial flexible unloading structure at the external mounting position to reduce the impact of thermal deformation of other lens structures on the shape of the integrated lens surface.

[0049] 8) When assembling the integrated mirror assembly, first complete the bonding of the PAD piece and the integrated mirror. After the low-temperature epoxy adhesive has cured, install the unloading plate, gasket, and mirror frame. The specific installation method is as follows: fix the mirror frame, adjust the position of the integrated mirror to achieve good contact between the mounting surfaces of the unloading plate, PAD piece, and mirror frame, and then fix the unloading plate with screws and gaskets.

[0050] To verify the correctness and feasibility of this invention, a finite element modeling analysis was performed on an example of a double-sided integrated mirror and its supporting device. The integrated mirror has a mirror surface A diameter of φ462mm, a mirror surface B diameter of φ318mm, a designed weight of 5.8kg, and a surface density of 25.2kg / m³. 2 Compared with the lightweight data of silicon carbide and aluminum alloy reflectors manufactured using traditional processes, the integrated mirror proposed in this invention achieves a higher degree of lightweighting. Using the support structure of this invention, the integrated mirror assembly weighs 8.94 kg. The first three constraint mode frequencies of the integrated mirror are 185Hz, 245Hz, and 245Hz, respectively, indicating high stiffness.

[0051] During horizontal alignment of the ground optical axis, the integrated mirror exhibited a maximum translation of 2.4 μm and a maximum tilt of 0.8″ under gravity. The RMS of the gravity surface shape of mirror A was 0.009λ (λ = 0.6328 μm, the same below), and the RMS of the gravity surface shape of mirror B was 0.003λ. Both the rigid body displacement and gravity surface shape were relatively small, meeting the requirements for alignment test between ground and surface. Deformation cloud diagrams and surface shape cloud diagrams are shown below. Figure 5 .

[0052] Thermal deformation analysis of the integrated mirror assembly was performed from room temperature (293K) to low temperature (100K). Then, surface shape analysis of mirror surfaces A and B was conducted at low temperature. From 293K to 100K, the RMS change of mirror surface A was 0.051λ, and the RMS change of mirror surface B was 0.014λ, both meeting the surface shape requirements of mid-wavelength and long-wavelength infrared optical lenses (requiring a value better than 0.1λ). This indicates that the support structure designed in this invention has good temperature unloading capability. Deformation and surface shape cloud diagrams are shown below. Figure 6 .

[0053] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0054] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A lightweight double-sided integrated mirror system based on silicon carbide additive manufacturing, characterized in that, Including a lightweight double-sided integrated mirror structure and a cryogenic support device for the integrated mirror; The lightweight double-sided integrated mirror structure includes an integrated mirror, an outer ring, an inner ring, and radial reinforcing ribs; the two sides of the integrated mirror are mirror surface A and mirror surface B, which are coaxial and connected together by the inner ring, outer ring, and radial reinforcing ribs. The integrated lens cryogenic support structure includes a PAD plate, an unloading plate, a gasket, and a lens frame. The PAD plate is made of an expansion alloy with a thermal expansion coefficient close to that of silicon carbide, and is bonded to the outer ring of the integrated lens with low-temperature epoxy adhesive. The unloading plate is a thin titanium alloy plate, which is connected to the PAD plate on one side by screws and gaskets, and to the lens frame on the other side by screws and gaskets. The integrated mirror is made of silicon carbide. The blank is formed by additive manufacturing and then reacted and sintered to form a high-rigidity silicon carbide mirror blank.

2. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, The integrated mirror has a light-transmitting hole in the center.

3. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, The integrated mirror has a mushroom-shaped structure, meaning that 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.

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

5. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, There are six groups of PAD sheets, evenly distributed circumferentially.

6. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, The coefficient of thermal expansion of the PAD sheet material is within the range of the coefficient of thermal expansion of silicon carbide as temperature changes.

7. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, There are six groups of unloading plates, evenly distributed circumferentially.

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

9. The lightweight double-sided integrated mirror system according to claim 1, characterized in that, When assembling the integrated mirror assembly, first bond the PAD and the integrated mirror together. After the low-temperature epoxy adhesive has cured, install the unloading plate, gasket, and mirror frame. The specific installation method is as follows: fix the mirror frame, adjust the position of the integrated mirror to ensure good contact between the mounting surfaces of the unloading plate, PAD, and mirror frame, and then fix the unloading plate with screws and gaskets.

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