A mirror assembly mounting structure and mounting method with a designable coefficient of thermal expansion

Abstract

The application relates to a mirror assembly mounting structure with a designable thermal expansion coefficient and a mounting method, and belongs to the field of mirror mounting structure design; the mounting structure comprises a mirror assembly, a main bearing plate, three mirror mounting structures and three supporting rods; the main bearing plate is horizontally placed; the three mirror mounting structures are horizontally connected in a head-tail mode to form a regular triangle supporting structure; the regular triangle supporting structure is concentrically arranged on the upper surface of the main bearing plate; one supporting rod is vertically arranged at each corner of the regular triangle supporting structure; the mirror assembly is concentrically arranged above the regular triangle supporting structure; the lower surface of the mirror assembly is in contact with the top of the supporting rod; the application realizes the designability of the thermal expansion coefficient between the supporting points of the mirror, thereby realizing the matching with the thermal expansion coefficient of the mirror itself, achieving the non-thermal effect of the whole assembly, keeping the thermal deformation small enough under the action of the external temperature fluctuation environment, and further ensuring the mirror surface shape precision.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of design of mirror mounting structure, in particular to a mirror assembly mounting structure with designed thermal expansion coefficient and a mounting method. BACKGROUND

[0002] In order to keep high precision surface shape and position of mirror assembly on space camera, it is required that the mirror and its support structure have low thermal expansion coefficient to match each other, so as to achieve synchronous expansion or shrink under the action of external temperature field, low stress level in the mirror, and high precision surface shape and position keeping requirements. In order to meet this requirement, the mounting structure of the mirror assembly is usually selected from materials with small thermal expansion coefficient, such as carbon fiber composite materials, etc., but it cannot guarantee the matching of the thermal expansion coefficient with the mirror material. After the satellite is launched into orbit, the mirror assembly and its mounting structure will produce thermal deformation due to temperature change, and the deformation amount is not equal, which will generate force on the mirror, reduce the mirror surface shape and position precision, and affect the imaging quality of the space camera. SUMMARY

[0003] The technical problem solved by the present application is to overcome the shortcomings of the prior art, and to provide a mirror assembly mounting structure with designed thermal expansion coefficient and a mounting method, so as to realize the designability of the thermal expansion coefficient between each support point of the mirror, match the thermal expansion coefficient of the mirror itself, achieve the effect of thermalization of the whole assembly, keep small thermal deformation under the action of external temperature fluctuation environment, and further ensure the mirror surface shape precision.

[0004] The technical solution of the present application is:

[0005] A mirror assembly mounting structure with designed thermal expansion coefficient, comprising a mirror assembly, a main load-bearing plate, three mirror mounting structures and three support rods, wherein the main load-bearing plate is horizontally placed; the three mirror mounting structures are horizontally connected in a head-to-tail manner to form a regular triangle support structure; the regular triangle support structure is concentrically arranged on the upper surface of the main load-bearing plate; one support rod is vertically installed at each corner of the regular triangle support structure; the mirror assembly is concentrically arranged above the regular triangle support structure; and the lower surface of the mirror assembly is in contact with the top of the support rod.

[0006] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the connecting plate is a T-shaped plate structure arranged vertically; the straight section of the connecting plate extends into the gap between the two compensation plates of the corresponding group, and the extending end of the straight section of the connecting plate is flush with the inner side walls of the two compensation plates after extension.

[0007] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the connecting plate is a T-shaped plate structure arranged vertically; the straight section of the connecting plate extends into the gap between the two compensation plates of the corresponding group, and the extending end of the straight section of the connecting plate is flush with the inner side walls of the two compensation plates after extension.

[0008] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the connecting plate is a T-shaped plate structure arranged vertically; the straight section of the connecting plate extends into the gap between the two compensation plates of the corresponding group, and the extending end of the straight section of the connecting plate is flush with the inner side walls of the two compensation plates after extension.

[0009] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the connecting plate is a T-shaped plate structure arranged vertically; the straight section of the connecting plate extends into the gap between the two compensation plates of the corresponding group, and the extending end of the straight section of the connecting plate is flush with the inner side walls of the two compensation plates after extension.

[0010] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the connecting plate is a T-shaped plate structure arranged vertically; the straight section of the connecting plate extends into the gap between the two compensation plates of the corresponding group, and the extending end of the straight section of the connecting plate is flush with the inner side walls of the two compensation plates after extension.

[0011] 2a1L1-2a2L2+a3L3=2a4L4·sin60

[0012] 2L1-2L2+L3=2L4·sin60。

[0013] In the above-mentioned mirror assembly mounting structure with designed thermal expansion coefficient, the side walls of the connecting plate, the compensation plate and the conversion plate are lightened by setting the lightening grooves, and the lightening grooves are filled with damping glue, without affecting the thermal expansion coefficient.

[0014] In the above-mentioned mounting method of the mirror assembly mounting structure with designed thermal expansion coefficient, the method comprises the following steps:

[0015] The main bearing plate is horizontally placed; the three mirror assembly mounting structures are connected in a horizontal manner to form a regular triangle support structure; and the regular triangle support structure is concentrically mounted on the upper surface of the main bearing plate.

[0016] A support rod is vertically mounted at each corner of the regular triangle support structure; and the mirror assembly is concentrically mounted above the regular triangle support structure.

[0017] In the above-mentioned mounting method of the mirror assembly mounting structure with designed thermal expansion coefficient, the mirror assembly mounting structure comprises two connecting plates, four compensation plates and two conversion plates; the compensation plates and the conversion plates are rectangular plate structures; one of the conversion plates is horizontally placed; the four compensation plates are divided into two groups; the two groups of compensation plates are arranged at two ends of the upper surface of the conversion plate; the two compensation plates in each group are oppositely arranged and arranged in parallel with the side edges of the conversion plate; a gap is left between the two compensation plates in each group; the two connecting plates are respectively inserted into the gaps between the two groups of compensation plates from the outer side; and the other conversion plate is horizontally arranged on the top of the two groups of compensation plates.

[0018] In the above-mentioned mounting method of the mirror assembly mounting structure with designed thermal expansion coefficient, the connecting part of the compensation plate and the connecting plate is arranged at the inner end of the compensation plate; the connecting part of the compensation plate and the top conversion plate is arranged at the outer end of the top of the compensation plate; the axial length of the connecting plate from the outer end to the connecting part of the compensation plate and the connecting plate is L1, the length from the outer end of the compensation plate to the connecting part of the compensation plate and the connecting plate is L2, the distance between the two ends of the conversion plate and the connecting part of the compensation plate is L3, and the distance from the axis of the support rod to the axis of the mirror assembly is L4; the thermal expansion coefficient of the connecting plate is a1, the thermal expansion coefficient of the compensation plate is a2, the thermal expansion coefficient of the conversion plate is a3, and the thermal expansion coefficient of the mirror assembly is a4; and the thermal expansion relationship is:

[0019] 2a1L1-2a2L2+a3L3=2a4L4·sin60

[0020] 2L1-2L2+L3=2L4·sin60。

[0021] Compared with the prior art, the present application has the following advantages:

[0022] (1) The mounting structure with designable thermal expansion coefficient can determine reasonable length according to thermal expansion relation, so that the thermal expansion coefficient of the mounting structure matches the thermal expansion characteristics of the mirror and its support structure, expands or shrinks synchronously under the same external temperature field, does not generate thermal stress on the mirror, and ensures the index level during in-orbit imaging.

[0023] (2) The connecting plate, compensation plate and conversion plate of the mounting structure are in the form of plates, are easy to obtain and form, and are connected with each other in a mutually orthogonal spatial relationship, so that the whole mounting structure is in a closed form, high rigidity design is easy to realize, and the requirements of the mirror assembly mounting structure are met.

[0024] (3) The thickness direction design of the connecting plate, compensation plate and conversion plate does not affect the realization of the designable thermal expansion coefficient function, and allows reasonable lightweight design combined with weight constraints.

[0025] (4) The mounting structure is suitable for small and medium-sized mirror assemblies with an aperture of less than 1 m in a 3-point support form. For light and small design, the mounting structure can also be used as the main bearing structure without the need for an external special main bearing plate. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic view of a mirror assembly mounting structure of the present application;

[0027] Figure 2 is a schematic view of a mirror mounting structure of the present application.

[0028] In the drawings:

[0029] 1 - mirror assembly; 2 - main bearing plate; 3 - mirror mounting structure; 4 - support rod;

[0030] 31 - connecting plate; 32 - compensation plate; 33 - conversion plate. DETAILED DESCRIPTION

[0031] The present application will be further described below in conjunction with examples.

[0032] The present application provides a mirror assembly mounting structure with designable thermal expansion coefficient and a mounting method. A structure with designable thermal expansion coefficient is designed, which is used as a mounting structure of a mirror assembly, can match the thermal expansion coefficient of the mirror material, and can keep the mirror in good surface shape and position precision.

[0033] The mirror assembly mounting structure comprises a main bearing plate, a mirror mounting structure and a support rod. Figure 1As shown, it specifically includes a reflector assembly 1, a main load-bearing plate 2, three reflector mounting structures 3, and three support rods 4; wherein, the main load-bearing plate 2 is placed horizontally; the three reflector mounting structures 3 are connected end to end horizontally to form an equilateral triangle support structure; the equilateral triangle support structure is concentrically set on the upper surface of the main load-bearing plate 2; one support rod 4 is vertically installed at each corner of the equilateral triangle support structure; the reflector assembly 1 is concentrically set above the equilateral triangle support structure; the lower surface of the reflector assembly 1 is in contact with the top of the support rod 4.

[0034] The structure is composed of several interconnected metal plates. By coordinating the length and thermal expansion coefficient of each plate, the thermal expansion coefficient can be designed, ensuring thermal matching of the reflector assembly within a certain temperature range and guaranteeing the stability of the on-orbit imaging quality of the space camera.

[0035] like Figure 2 As shown, the reflector mounting structure 3 includes two connecting plates 31, four compensation plates 32, and two conversion plates 33. Both the compensation plates 32 and conversion plates 33 are rectangular plate structures; one conversion plate 33 is placed horizontally; the four compensation plates 32 are divided into two groups of two; the two groups of compensation plates 32 are respectively located at both ends of the upper surface of the conversion plate 33; the two compensation plates 32 in each group are placed opposite each other and parallel to the side of the conversion plate 33; a gap is left between the two compensation plates 32 in each group; two connecting plates 31 extend horizontally from the outside into the gap between the two groups of compensation plates 32; another conversion plate 33 is horizontally positioned on top of the two groups of compensation plates 32. The connecting plate 31 is a vertically placed T-shaped plate structure; the straight section of the connecting plate 31 extends into the gap between the two compensation plates 32 in the corresponding group, and after insertion, the extended end of the straight section of the connecting plate 31 is flush with the inner sidewall of the two compensation plates 32.

[0036] Regarding the design of materials and lightweighting, this invention uses titanium alloy for the connecting plate 31, aluminum alloy for the compensation plate 32, and indium tinplate for the conversion plate 33 to compensate for the coefficient of thermal expansion. The sidewalls of the connecting plate 31, compensation plate 32, and conversion plate 33 are lightweighted by setting light-reducing grooves, which are filled with damping adhesive without affecting the coefficient of thermal expansion.

[0037] The side wall of the straight section of the connecting plate 31 is fixed to the two corresponding compensation plates 32 by screws; the four compensation plates 32 are fixed to the top conversion plate 33 and the bottom conversion plate 33 by screws respectively; the bottom conversion plate 33 is fixed to the main load-bearing plate 2; the screws used to connect the connecting plate 31 and the compensation plate 32 are orthogonal to the screws used to connect the compensation plate 32 and the conversion plate 33; the connection between the compensation plate 32 and the connecting plate 31 is located at the inner end of the compensation plate 32; the connection between the compensation plate 32 and the top conversion plate 33 is located at the outer end of the top of the compensation plate 32.

[0038] The axial length of the connecting plate 31 from the outer end to the connecting position of the connecting plate 31 and the compensation plate 32 is L1, the length of the compensation plate 32 from the outer end to the connecting position of the compensation plate 32 and the connecting plate 31 is L2, the distance between the connecting position of the conversion plate 33 and the compensation plate 32 is L3, and the distance between the axis of the support rod 4 and the axis of the mirror assembly 1 is L4; the thermal expansion coefficient of the connecting plate 31 is a1, the thermal expansion coefficient of the compensation plate 32 is a2, the thermal expansion coefficient of the conversion plate 33 is a3, and the thermal expansion coefficient of the mirror assembly 1 is a4; the thermal expansion relationship is satisfied:

[0039] 2a1L1-2a2L2+a3L3=2a4L4·sin60

[0040] 2L1-2L2+L3=2L4·sin60.

[0041] According to the above formula, the specific dimensions of the three parts are designed, the special design of the connection relationship is used, the thermal deformation amount is compensated, the function of the thermal expansion coefficient of the whole is designed, the matching with the thermal deformation of the mirror is realized, and therefore the stress caused by the thermal deformation of the mounting surface on the mirror is eliminated, and the in-orbit imaging quality of the space camera is ensured.

[0042] The mounting method of the mirror assembly mounting structure specifically includes the following steps:

[0043] The main bearing plate 2 is horizontally placed; the three mirror mounting structures 3 are horizontally connected in series to form a regular triangle support structure; and the regular triangle support structure is concentrically mounted on the upper surface of the main bearing plate 2;

[0044] A support rod 4 is vertically mounted at each corner of the regular triangle support structure; and the mirror assembly 1 is concentrically mounted above the regular triangle support structure.

[0045] The mirror mounting structure 3 includes two connecting plates 31, four compensation plates 32 and two conversion plates 33; the compensation plate 32 and the conversion plate 33 are both rectangular plate structures; one of the conversion plates 33 is horizontally placed; the four compensation plates 32 are divided into two groups; the two groups of compensation plates 32 are respectively arranged at the two ends of the upper surface of the conversion plate 33; the two compensation plates 32 in each group are oppositely arranged and arranged in parallel with the side edges of the conversion plate 33; a gap is left between the two compensation plates 32 in each group; the two connecting plates 31 respectively extend into the gap between the two groups of compensation plates 32 from the horizontal outer side; and the other conversion plate 33 is horizontally arranged on the top of the two groups of compensation plates 32.

[0046] The connecting part of the compensation plate 32 and the connecting plate 31 is arranged at the inner end of the compensation plate 32; the connecting part of the compensation plate 32 and the top conversion plate 33 is arranged at the outer end of the top of the compensation plate 32; the axial length of the connecting plate 31 from the outer end to the connecting part of the connecting plate 31 and the compensation plate 32 is L1, the length of the compensation plate 32 from the outer end to the connecting part of the compensation plate 32 and the connecting plate 31 is L2, the distance between the connecting part of the conversion plate 332 end and the compensation plate 32 is L3, the distance between the axis of the support rod 4 and the axis of the mirror assembly 1 is L4; the thermal expansion coefficient of the connecting plate 31 is a1, the thermal expansion coefficient of the compensation plate 32 is a2, the thermal expansion coefficient of the conversion plate 33 is a3, and the thermal expansion coefficient of the mirror assembly 1 is a4; the thermal expansion relationship is satisfied:

[0047] 2a1L1-2a2L2+a3L3=2a4L4·sin60

[0048] 2L1-2L2+L3=2L4·sin60.

[0049] The length of the connecting plate 31, the length of the compensation plate 32 and the length of the conversion plate 33 can be determined according to the space camera mounting structure stiffness requirement, and the local lightweight design, the filling damping glue in the groove and the like are allowed, and the thermal expansion coefficient can be designed without affecting the function implementation.

[0050] Embodiment

[0051] For a φ400mm aperture mirror, the mirror material is microcrystalline glass, the main force plate is titanium alloy, the connecting plate is titanium alloy, the compensation plate is aluminum alloy, and the conversion plate is indium steel, L4 is obtained according to the mirror assembly support design optimization, and the preferred range is 120mm-140mm according to the empirical formula, and the example takes 121mm. According to the following formula:

[0052] 2a1L1-2a2L2+a3L3=2a4L4·sin60

[0053] 2L1-2L2+L3=2L4·sin60

[0054] L1=75mm, L2=30mm, L3=130mm.

[0055] According to the above results, the mirror surface shape change RMS under the action of temperature fluctuation is 0.01λ in the temperature range of 20℃±5℃. Without the mounting structure of the application, the mirror surface shape change RMS caused by the same temperature change reaches 0.07λ. After applying the application, the mirror surface shape change RMS caused by thermal deformation is reduced by about 7 times.

[0056] The main influencing factor of the performance of the mirror assembly of a space camera in orbit is the thermal environment and the thermal deformation caused thereby. In order to enable the mirror assembly to meet the requirements of the mirror surface shape and position accuracy after the thermal deformation occurs, the support structure of the mirror needs to have high flexibility, to be able to adapt to the thermal deformation of the mismatched structures and not to cause large force to the mirror. However, the increase of the flexibility of the support structure significantly increases the sensitivity of the mirror assembly to the gravity during the ground test and to the dynamic environment during the launch stage, and thus reduces the reliability and safety of the mirror assembly during the ground test and the launch process. The mounting structure with the designable thermal expansion coefficient proposed by the present application can determine the reasonable length according to the formulas 1 and 2, so as to make the thermal expansion coefficient of the mounting structure match the thermal expansion characteristics of the mirror and the support structure thereof, to expand or shrink synchronously under the same external temperature field, not to cause thermal stress to the mirror, and to ensure the index level during the in-orbit imaging.

[0057] The connecting plate 31, the compensation plate 32 and the conversion plate 33 adopt a plate shape, are easy to obtain and form, and the connection between the three parts forms a mutual orthogonal spatial relationship, so that the whole mounting structure is in a closed form, is easy to realize high rigidity design, and meets the requirements of the mounting structure of the mirror assembly. Moreover, the design of the connecting plate 31, the compensation plate 32 and the conversion plate 33 in the thickness direction does not affect the realization of the designable thermal expansion coefficient function, and allows reasonable lightweighting in combination with the weight constraint.

[0058] The present application is suitable for small and medium-sized mirror assemblies with an aperture of less than 1 m in the form of 3-point support. For light and small design, the mounting structure of the present application can also be used as the main force-bearing structure, without the need for an external special main force-bearing plate.

[0059] Although the present application has been disclosed with reference to the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, all belong to the protection scope of the technical solutions of the present application.

Claims

1. A mirror assembly mounting structure with a designable coefficient of thermal expansion, characterized by: The application relates to a mirror assembly, which comprises a main bearing plate (2), three mirror mounting structures (3) and three supporting rods (4); the main bearing plate (2) is horizontally arranged; the three mirror mounting structures (3) are horizontally connected in a head-to-tail mode to form a regular triangle supporting structure; the regular triangle supporting structure is concentrically arranged on the upper surface of the main bearing plate (2); one supporting rod (4) is vertically arranged at each corner of the regular triangle supporting structure; and the mirror assembly (1) is concentrically arranged above the regular triangle supporting structure; the lower surface of the mirror assembly (1) is in contact with the top of the supporting rod (4). The mirror mounting structure (3) comprises two connecting plates (31), four compensation plates (32) and two conversion plates (33); the compensation plates (32) and the conversion plates (33) are all rectangular plate structures; one conversion plate (33) is horizontally arranged; two compensation plates (32) form a group, and the four compensation plates (32) are divided into two groups; the two groups of compensation plates (32) are arranged at the two ends of the upper surface of the conversion plate (33); the two compensation plates (32) in each group are oppositely arranged and are arranged in parallel with the side edges of the conversion plate (33); a gap is formed between the two compensation plates (32) in each group; and the two connecting plates (31) are respectively arranged in the gaps between the two groups of compensation plates (32) from the horizontal outer side.

2. The CTE-engineered mirror assembly mounting structure of claim 1, wherein: The connecting plate (31) is a T-shaped plate structure arranged vertically; the straight plate section of the connecting plate (31) is arranged in the gap between the two compensation plates (32) in the corresponding group, and the straight plate section of the connecting plate (31) is flush with the inner side walls of the two compensation plates (32) after being arranged in the gap.

3. The CTE-engineered mirror assembly mounting structure of claim 2, wherein: The side wall of the straight plate section of the connecting plate (31) is fixedly connected with the two compensation plates (32) in the corresponding group through screws; the four compensation plates (32) are fixedly connected with the conversion plates (33) at the top and the bottom through screws; the bottom conversion plate (33) is fixedly connected with the main bearing plate (2); the screws used for connecting the connecting plate (31) and the compensation plate (32) and the screws used for connecting the compensation plate (32) and the conversion plate (33) are orthogonal to each other; the connecting position of the compensation plate (32) and the connecting plate (31) is arranged at the inner end of the compensation plate (32); and the connecting position of the compensation plate (32) and the conversion plate (33) at the top is arranged at the outer end of the top of the compensation plate (32).

4. The CTE-engineered mirror assembly mounting structure of claim 1, wherein: The connecting plate (31) is made of titanium alloy material; the compensation plate (32) is made of aluminum alloy material; and the conversion plate (33) is made of indium steel material, so that the compensation of the thermal expansion coefficient is realized.

5. The CTE-engineered mirror assembly mounting structure of claim 1, wherein: The axial length of the connecting plate (31) from the outer end to the connecting position of the connecting plate (31) and the compensation plate (32) is L 1. The length of the compensation plate (32) from the outer end to the connecting position of the compensation plate (32) and the connecting plate (31) is L 2. The distance between the connecting positions of the two ends of the conversion plate (33) and the compensation plate (32) is L 3. The distance between the axis of the support rod (4) and the axis of the mirror assembly (1) is L 4. The thermal expansion coefficients of the connecting plate (31), the compensation plate (32), the conversion plate (33), and the mirror assembly (1) are α1, α2, α3, and α4 respectively. The thermal expansion relationship is: 2 α1 L 1 -2 α2 L 2 + α3 L 3 =2 α4 L 4 • sin 60° 2 L 1 -2 L 2 + L 3 =2 L 4 • sin 60°.

6. The CTE-engineered mirror assembly mounting structure of claim 1, wherein: The side walls of the connecting plate (31), the compensation plate (32) and the conversion plate (33) are subjected to lightweight treatment through the arrangement of lightening grooves, and damping glue is filled in the lightening grooves, so that the thermal expansion coefficient is not affected.

7. A mounting method of a mirror assembly mounting structure with a designable coefficient of thermal expansion according to claim 1, characterized by: The application further discloses a mirror assembly installation method, which comprises the following steps: The main bearing plate (2) is horizontally arranged; the three mirror mounting structures (3) are horizontally connected in a head-to-tail mode to form a regular triangle supporting structure; and the regular triangle supporting structure is concentrically arranged on the upper surface of the main bearing plate (2); One supporting rod (4) is vertically arranged at each corner of the regular triangle supporting structure; and the mirror assembly (1) is concentrically arranged above the regular triangle supporting structure.

8. A method of mounting a mirror assembly with a designable coefficient of thermal expansion according to claim 7, wherein: The mirror mounting structure (3) comprises two connecting plates (31), four compensation plates (32) and two conversion plates (33); the compensation plates (32) and the conversion plates (33) are all rectangular plate-shaped structures; one of the conversion plates (33) is horizontally placed; two compensation plates (32) form a group, and the four compensation plates (32) are divided into two groups; the two groups of compensation plates (32) are respectively arranged at two ends of the upper surface of the conversion plate (33); the two compensation plates (32) in each group are oppositely placed and are placed in parallel with the side edges of the conversion plate (33); a gap is left between the two compensation plates (32) in each group; the two connecting plates (31) respectively extend into the gaps between the two groups of compensation plates (32) from the horizontal outer side; the other conversion plate (33) is horizontally arranged at the top of the two groups of compensation plates (32).

9. A method of mounting a mirror assembly with a designable coefficient of thermal expansion according to claim 8, wherein: The connecting part of the compensation plate (32) and the connecting plate (31) is arranged at the inner end of the compensation plate (32); the connecting part of the compensation plate (32) and the top conversion plate (33) is arranged at the outer end of the top of the compensation plate (32); the axial length of the connecting plate (31) from the outer end to the connecting part of the compensation plate (32) is L 1. The length of the compensation plate (32) from the outer end to the connecting part of the compensation plate (32) and the connecting plate (31) is L 2. The distance between the connecting part of the conversion plate (33) and the compensation plate (32) is L 3. The distance between the axis of the supporting rod (4) and the axis of the mirror assembly (1) is L 4. The thermal expansion coefficient of the connecting plate (31) is α1, the thermal expansion coefficient of the compensation plate (32) is α2, the thermal expansion coefficient of the conversion plate (33) is α3, and the thermal expansion coefficient of the mirror assembly (1) is α4; the thermal expansion relationship is satisfied: 2 α1 L 1 -2 α2 L 2 + α3 L 3 =2 α4 L 4 • sin 60° 2 L 1 -2 L 2 + L 3 =2 L 4 • sin 60°.

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