Light and small telescopic unit system based on peripheral flexible support

Abstract

The invention discloses a light and small telescopic unit system based on a peripheral flexible support, relates to the technical field of optical precision instruments, and solves the problems that a conventional telescopic system based on a peripheral support and a back support is insufficient in mirror surface shape precision stability, relatively heavy in weight and relatively long in assembly period. The light and small telescope unit system is composed of a primary mirror assembly, a secondary mirror assembly and a supporting cylinder assembly, the primary mirror assembly comprises a primary mirror and a primary mirror base, and the primary mirror is connected to the interior of the primary mirror base through glue injection; the secondary mirror assembly comprises a secondary mirror, a secondary mirror chamber and a truss, the secondary mirror is connected to the interior of the secondary mirror chamber through glue injection, and the secondary mirror chamber is connected to the truss; the supporting cylinder assembly comprises a supporting cylinder, a first gasket and a second gasket. The two ends of the supporting cylinder assembly are connected with the primary mirror base and the truss respectively. According to the telescopic unit system prepared by the invention, the design of a light, small and peripheral flexible supporting structure is adopted, the stress generated by structural deformation is reduced by utilizing the elastic deformation of the hinge, and the stability of the system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of optical precision instruments, and in particular to a light and small telescope unit system based on peripheral flexible support. Background Art

[0002] In space optical systems, the telescope unit is the core imaging component, and its structural stability directly affects the imaging quality and system performance. In order to ensure that the telescope system can still operate stably under complex environmental conditions (temperature changes, vibrations and external forces), the support structure design of the optical elements inside the telescope unit has become a key technical problem.

[0003] Common support structures mainly include back support, side support and peripheral support. First, back support usually ensures the stability of the system by setting a support structure on the back of the optical element. The three-point support on the back mostly adopts a combination of a cone sleeve, a flexible joint and a back plate. However, due to the bonding process, the back-supported reflector needs to go through the steps of grinding the cone hole on the back of the primary mirror, bonding and positioning the cone sleeve, and grinding the flexible joint end face to be coplanar. The process is cumbersome and the assembly period is long. It is mostly used in large-aperture reflector support cases; secondly, side support is mostly suitable for rectangular reflectors. The structure is fixed by setting support points on the side of the optical element. Compared with the back support, the side support is simpler in structure and lighter in weight, but this design may cause uneven deformation of the system when subjected to gravity or temperature changes, affecting the accuracy and stability of the optical system.

[0004] Peripheral support is suitable for supporting small reflectors. Usually, a support structure is designed around the optical element. Compared with the first two support structures, the peripheral support method is simple in structure and easy to assemble. However, this support method lacks a flexible support structure. When the temperature environment changes, even if a support material with a linear expansion coefficient close to that of the reflector in the optical system is used, thermal stress may still exist, thereby affecting the imaging quality of the system. Summary of the invention

[0005] In order to solve the problems of insufficient stability of mirror surface accuracy, large system mass and long assembly period in the traditional telescope system based on peripheral support and back support, the present invention proposes a lightweight telescope unit system based on peripheral flexible support. The technical solution of the present invention is as follows: A light and small telescope unit system based on peripheral flexible support, consisting of a primary mirror assembly, a secondary mirror assembly and a support tube assembly; The main mirror assembly comprises a main mirror and a main mirror seat, the main mirror seat comprises a main mirror chamber and a base, the main mirror chamber is arranged on the base, the main mirror is connected to the inside of the main mirror chamber by glue injection, and the main mirror chamber adopts a structure form of enclosing and covering the main mirror on all sides to increase the structural rigidity; 16 groups of flexible support structures are symmetrically arranged around the main mirror chamber, each group of flexible support structures is composed of two groups of hinges, and the influence of structural deformation on the surface accuracy of the main mirror is reduced by slotting; the base is provided with a plurality of weight-reducing grooves for reducing the overall weight; the material of the main mirror seat is made of Invar material having the same linear expansion coefficient as the main mirror body; The secondary mirror assembly comprises a secondary mirror, a secondary mirror chamber, a secondary mirror adjustment pad and a truss, wherein the secondary mirror is connected to the interior of the secondary mirror chamber by gluing, and the secondary mirror chamber is connected to the truss; the truss and the secondary mirror chamber are made of Invar material having the same linear expansion coefficient as the secondary mirror body; The support tube assembly includes a support tube, a first gasket and a second gasket, one end of the support tube is connected to one side of the first gasket, and the other side of the first gasket is connected to the base; the other end of the support tube is connected to one side of the second gasket, and the other side of the second gasket is connected to the truss; the support tube is made of carbon fiber; the first gasket and the second gasket are made of Invar material with the same linear expansion coefficient as the support tube body; Furthermore, the bottom surface of the main mirror chamber is provided with a plurality of positioning bosses, the height of the positioning bosses is 0.5 mm, the plurality of positioning bosses are coplanar, forming a positioning surface 1, the flatness of the positioning surface 1 is less than 0.003 mm; the bottom surface of the main mirror is in full contact with the positioning bosses; Furthermore, a circle of annular step structure is left at the outer edge where the base is connected to the main mirror chamber, and the annular step structure is used to connect the support tube assembly to the main mirror seat; Furthermore, a plurality of bonding surfaces are provided at positions corresponding to the peripheral flexible support structure inside the mirror chamber of the main mirror, and a glue injection groove is provided at the bonding surface, and the glue injection groove is arranged along the radial direction of the main mirror, and the main mirror is connected to the inside of the main mirror base by glue injection through the glue injection groove; Furthermore, with the inner side of the main mirror chamber as a reference, the height of the bonding surface is 0.5 mm higher than the height of the inner side of the main mirror chamber, and a gap of 0.2 mm is left between the bonding surface and the main mirror for adhesive filling; Furthermore, a step is provided inside the secondary mirror chamber, and the back of the secondary mirror contacts the step inside the secondary mirror chamber to form axial positioning; three glue injection holes are evenly distributed along the circumference of the radial direction in the secondary mirror chamber; and three flexible nodes are evenly distributed along the circumference of the radial direction in the secondary mirror chamber; Further, the secondary mirror assembly further comprises a secondary mirror adjustment pad, wherein the secondary mirror adjustment pad is installed between the secondary mirror chamber and the truss, and the relative position of the secondary mirror with respect to the primary mirror is adjusted by grinding the adjustment pad; Furthermore, reinforcing ribs are installed inside the support tube, and the reinforcing ribs include a plurality of staggered annular ribs and longitudinal ribs; Furthermore, a step-shaped stop structure 1 is provided on one side where the first gasket is connected to the support tube, a step-shaped stop structure 2 is provided on one side where the second gasket is connected to the support tube, a step-shaped stop structure 3 is provided on one end where the support tube is connected to the first gasket, a step-shaped stop structure 4 is provided on one end where the support tube is connected to the second gasket, the step-shaped stop structure 1 is cooperatively connected with the step-shaped stop structure 3; the step-shaped stop structure 2 is cooperatively connected with the step-shaped stop structure 4; the first gasket and the second gasket are provided with countersunk holes, nuts are pre-embedded as inlays at both ends of the support tube at positions corresponding to the countersunk holes, and the first gasket and the second gasket are fixed to both ends of the support tube by screws; Furthermore, the first gasket is provided with a plurality of bosses one, the height of the bosses one is 0.5 mm, the flatness of the plurality of bosses one is less than 0.003 mm, and the plurality of bosses one are coplanar, serving as positioning surface two; the second gasket is provided with a plurality of bosses two, the height of the bosses two is 0.5 mm, the flatness of the plurality of bosses two is less than 0.003 mm, and the plurality of bosses two are coplanar, serving as positioning surface three; the parallelism of positioning surface three relative to positioning surface two is less than 0.005 mm; the annular step structure is provided with a mounting hole corresponding to the boss two, and the truss is provided with a mounting hole corresponding to the boss one.

[0006] Compared with the prior art, the present invention solves the problems of insufficient stability of mirror surface accuracy, large system mass and long assembly period in telescope systems based on peripheral support and back support. The specific beneficial effects are: 1. Ensure surface shape accuracy: The present invention adopts a peripheral flexible support structure, and uses the elastic deformation of the hinge itself to reduce the stress of the entire structure, so that the maximum stress point is far away from the primary mirror, thereby reducing the influence on the surface shape accuracy of the primary mirror, and effectively avoiding the influence of the external environment on the surface shape accuracy of the primary mirror; at the same time, the primary mirror seat is made of Invar material with the same linear expansion coefficient as the primary mirror; the truss and the secondary mirror chamber are made of Invar material with the same linear expansion coefficient as the secondary mirror, which further alleviates the influence of different temperature environments on the surface shape accuracy of the primary mirror and the secondary mirror, so that the telescope unit system has good thermal stability, and improves the problem that the traditional peripherally supported telescope unit system, when there is no flexible support, when the temperature environment changes, even if a support material with a linear expansion coefficient close to that of the reflector in the optical system is used, thermal stress may still exist, thereby affecting the imaging quality of the system.

[0007] 2. Lightweight and compact design: The main mirror mount of the telescope unit system provided by the present invention is provided with a weight-reducing groove to reduce the weight of the system while ensuring the supporting strength; the present invention adopts a support tube made of carbon fiber material. Since carbon fiber material has the advantages of high strength and low density, and the linear expansion coefficient is close to zero, at the same time, staggered annular ribs and longitudinal ribs are installed inside the support tube, which increases the supporting stiffness of the support tube, minimizes the impact of the telescope unit system on the imaging quality of the system under different temperature environments, and improves the defect of the traditional peripherally supported telescope unit system with a large overall weight.

[0008] 3. Simple structure and easy to assemble: The light and small telescope unit system proposed in the present invention is assembled based on a peripheral flexible support structure. This support method has a simple structure, adopts the form of an integrated mirror chamber and a flexible joint, has few assembly operation procedures, and has a short bonding and curing time. Compared with the traditional central support and back three-point support telescope unit system, it greatly shortens the assembly time and improves the assembly efficiency, and is suitable for large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a structural schematic diagram of a light and small telescope unit system; Figure 2 is a schematic diagram of the structure of the main mirror mount; Figure 3 It is a structural schematic diagram of the weight reduction tank; Figure 4 is a schematic diagram of a flexible support structure; Figure 5 is a schematic structural diagram of a secondary mirror assembly; Figure 6 It is a structural schematic diagram of the support cylinder assembly; Figure 7 is a schematic cross-sectional view of a support cylinder assembly; Among them: 1. main mirror base; 101. hinge; 102. bonding surface; 103. positioning boss; 104. glue injection groove; 105. base; 106. annular step structure; 107. weight reduction groove; 108. main mirror chamber; 2. second gasket; 201. boss two; 3. support tube; 301. reinforcing rib; 4. first gasket; 401. boss one; 5. truss; 6. secondary mirror adjustment pad; 7. secondary mirror chamber; 701. glue injection hole; 702. flexible joint; 8. main mirror; 9. secondary mirror. DETAILED DESCRIPTION

[0010] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as a limitation to the present invention.

[0011] Example 1. The present invention provides a light and small telescope unit system based on peripheral flexible support, which is composed of a primary mirror assembly, a secondary mirror assembly and a support tube assembly. Figure 1-7 As shown, the main mirror assembly includes a main mirror 8 and a main mirror base 1, the main mirror 8 is connected to the inside of the main mirror base 1 by glue injection, and the main mirror base 1 is set in the form of a structure that closes and covers the main mirror 8 on all sides to increase the rigidity of the main mirror base 1; in order to ensure that the surface accuracy of the main mirror 8 of the telescope unit system tends to be stable under different temperature environments, the main mirror base 1 is made of Invar material with the same linear expansion coefficient as the main mirror 8; the main mirror base 1 includes a base 105 and a main mirror chamber 108, and the main mirror chamber 108 is arranged on the base 105; 16 groups of flexible support structures are arranged at positions corresponding to the bonding surface 102 inside the main mirror chamber 108, and each group of flexible support structures is composed of two groups of flexible hinges 101, such as Figure 1 , Figure 2 and Figure 4 As shown, by slotting between the two sets of hinges 101, the stress caused by structural deformation is reduced, and at the same time, the maximum stress point is kept away from the bonding surface 102, thereby reducing the impact on the surface shape of the primary mirror 8; Figure 2 and Figure 3 As shown, the back of the base 105 is provided with a plurality of weight-reducing grooves 107 for reducing the weight of the telescope unit system and ensuring a lightweight and compact design; Figure 1 and Figure 5 As shown, the secondary mirror assembly includes a secondary mirror 9, a secondary mirror chamber 7 and a truss 5. The secondary mirror 9 is connected to the inside of the secondary mirror chamber 7 by gluing, and the secondary mirror chamber 7 is connected to the truss 5. The material of the truss 5 and the secondary mirror chamber 7 is made of invar material with the same linear expansion coefficient as the secondary mirror 9 body. Figure 1-7 As shown, the support tube assembly includes a support tube 3, a first gasket 4 and a second gasket 2, one end of the support tube 3 is connected to one side of the first gasket 4, and the other side of the first gasket 4 is connected to the base 105; the other end of the support tube 3 is connected to one side of the second gasket 2, and the other side of the second gasket 2 is connected to the truss 5; in order to meet the lightweight and miniaturized design of the telescope unit system, the support tube 3 is made of carbon fiber, and the carbon fiber material has the advantages of high strength and low density, and the linear expansion coefficient is close to zero; the material of the first gasket 4 and the second gasket 2 is made of Invar material that is consistent with the linear expansion coefficient of the support tube 3 body.

[0012] Example 2. This embodiment is a further illustration of embodiment 1. Figure 1-4 and Figure 6As shown, the inner bottom surface of the main mirror chamber 108 is provided with a plurality of positioning bosses 103, the height of the positioning bosses 103 is 0.5 mm, and the plurality of positioning bosses 103 are coplanar to form a positioning surface 1, and the flatness of the positioning surface 1 is less than 0.003 mm; the bottom surface of the main mirror 8 is in full contact with the positioning bosses 103; a circle of annular step structures 106 are provided around the outer edge where the base 105 is connected to the main mirror chamber 108, for connecting the support tube 3 to the main mirror base 1; as shown Figure 1-4 As shown, a plurality of bonding surfaces 102 are provided at positions inside the main mirror chamber 108 corresponding to the surrounding flexible support structure, and a glue injection groove 104 is provided at the bonding surface 102, and the glue injection groove 104 is arranged along the radial direction of the main mirror 8, and the main mirror 8 is bonded to the inside of the main mirror chamber 108 by using silicone rubber; with the inside of the main mirror chamber 108 as a reference, the height of the bonding surface 102 is 0.5 mm higher than the inner side of the mirror chamber 108, and a gap of 0.2 mm is left between the bonding surface 102 and the main mirror 8 for filling with adhesive.

[0013] Example 3. This embodiment is a further illustration of embodiment 1. Figure 1 and Figure 5 As shown, a step is provided inside the secondary mirror chamber 7, and the back of the secondary mirror 9 contacts the step inside the secondary mirror chamber 7 to form axial positioning; the secondary mirror chamber 7 is provided with three glue injection holes 701 evenly distributed along the circumference of the radial direction; the secondary mirror chamber 7 is provided with three flexible joints 702 evenly distributed along the circumference of the radial direction; the secondary mirror assembly also includes a secondary mirror adjustment pad 6, which is installed between the secondary mirror chamber 7 and the truss 5, and is used for grinding and adjusting the relative position of the secondary mirror 9 with respect to the primary mirror 8.

[0014] Example 4. This embodiment is a further illustration of embodiment 1. Figure 1 , Figure 2 , Figure 5 , Figure 6 and Figure 7As shown, reinforcing ribs 301 are installed inside the support tube 3, and the reinforcing ribs 301 include a plurality of staggered annular ribs and longitudinal ribs for enhancing the supporting stiffness of the support tube 3; a step-shaped stop structure 1 is provided on the side where the first gasket 4 is connected to the support tube 3, a step-shaped stop structure 2 is provided on the side where the second gasket 2 is connected to the support tube 3, a step-shaped stop structure 3 is provided on the end where the support tube 3 is connected to the first gasket 4, and a step-shaped stop structure 4 is provided on the end where the support tube 3 is connected to the second gasket 2. The mouth structure 1 is connected with the stepped stop structure 3; the stepped stop structure 2 is connected with the stepped stop structure 4, and the stepped stop structure can prevent the shear force of the screw from causing an unstable effect on the structure; the first gasket 4 and the second gasket 2 are provided with countersunk holes, and nuts are pre-embedded as inlays at the two ends of the support tube 3 at the positions corresponding to the countersunk holes, and the first gasket 4 and the second gasket 2 are fixed to the two ends of the support tube 3 by screws; the first gasket 4 is provided with a plurality of bosses 401, and the height of the bosses 401 is 0.5 mm, the flatness of the plurality of bosses 401 is less than 0.003 mm, and the plurality of bosses 401 are coplanar, serving as the second positioning surface; the second gasket 2 is provided with a plurality of bosses 201, the height of the bosses 201 is 0.5 mm, the flatness of the plurality of bosses 201 is less than 0.003 mm, and the plurality of bosses 201 are coplanar, serving as the third positioning surface; the parallelism of the third positioning surface relative to the second positioning surface is less than 0.005 mm; Figure 2 and Figure 5 As shown, the annular step structure 106 is provided with a mounting hole corresponding to the second boss 201 , and the truss 5 is provided with a mounting hole corresponding to the first boss 401 .

[0015] In combination with the lightweight and small telescope unit system provided in the above-mentioned embodiments 1-4, from the perspective of lightweight and miniaturized design, the present invention uses the base 105 to set a weight-reducing groove 107 to reduce the overall mass. At the same time, the support tube 3 adopts a carbon fiber material and a method of installing reinforcing ribs 301, which reduces the mass of the support tube 3 while increasing the support stiffness of the support tube 3; from the perspective of flexible support structure design, the present invention adopts a peripheral flexible support structure design, and uses the elastic deformation of the hinge 101 itself to reduce the stress impact on the overall structure, so that the maximum stress point is away from the primary mirror 8, thereby reducing the impact on the surface accuracy of the primary mirror; at the same time, the primary mirror seat 1 is made of Invar material with the same linear expansion coefficient as the primary mirror 8; the truss 5 and the secondary mirror chamber 7 are made of Invar material with the same linear expansion coefficient as the secondary mirror 9, which further ensures that the lightweight and small telescope unit system reduces the impact of temperature on the surface accuracy of the primary mirror 8 and the secondary mirror 9 under different temperature environments, and effectively increases the thermal stability of the lightweight and small telescope unit system.

[0016] Obviously, the above embodiments are only examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the technical solution. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A light and small telescopic unit system based on peripheral flexible support, characterized in that: It consists of a primary mirror assembly, a secondary mirror assembly and a support tube assembly; The main mirror assembly comprises a main mirror (8) and a main mirror seat (1), the main mirror seat (1) comprising a main mirror chamber (108) and a base (105), the main mirror chamber (108) being arranged on the base (105), the main mirror (8) being connected to the inside of the main mirror chamber (108) by glue injection, the main mirror chamber (108) sealingly covering the main mirror (8) on all sides; 16 groups of flexible support structures are symmetrically arranged around the periphery of the main mirror chamber (108), each group of flexible support structures being composed of two groups of hinges (101); the base (105) being provided with a plurality of weight-reducing grooves (107); the main mirror seat (1) is made of an Invar material having a linear expansion coefficient consistent with that of the main mirror (8) body; The secondary mirror assembly comprises a secondary mirror (9), a secondary mirror chamber (7) and a truss (5); the secondary mirror (9) is connected to the interior of the secondary mirror chamber (7) by gluing, and the secondary mirror chamber (7) is connected to the truss (5); the material of the truss (5) and the secondary mirror chamber (7) is made of Invar material having a linear expansion coefficient consistent with that of the secondary mirror (9) body; The support tube assembly comprises a support tube (3), a first gasket (4) and a second gasket (2); one end of the support tube (3) is connected to one side of the first gasket (4), and the other side of the first gasket (4) is connected to the base (105); the other end of the support tube (3) is connected to one side of the second gasket (2), and the other side of the second gasket (2) is connected to the truss (5); the support tube (3) is made of carbon fiber; the first gasket (4) and the second gasket (2) are made of Invar material having the same linear expansion coefficient as the support tube (3) body.

2. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: The inner bottom surface of the main mirror chamber (108) is provided with a plurality of positioning bosses (103), the height of the positioning bosses (103) is 0.5 mm, the plurality of positioning bosses (103) are coplanar to form a first positioning surface, and the flatness of the first positioning surface is less than 0.003 mm; the bottom surface of the main mirror (8) is in full contact with the positioning bosses (103).

3. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: A circle of annular step structures (106) are provided around the outer edge where the base (105) is connected to the main mirror chamber (108), and the annular step structures (106) are used to connect the support tube (3) to the main mirror seat (1).

4. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: A plurality of bonding surfaces (102) are provided at positions inside the primary mirror chamber (108) corresponding to the peripheral flexible support structure, and a glue injection groove (104) is provided at the bonding surface (102), the glue injection groove (104) is arranged along the radial direction of the primary mirror (8), and the primary mirror (8) is connected to the inside of the primary mirror chamber (108) by glue injection through the glue injection groove (104).

5. The light and small telescopic unit system based on peripheral flexible support according to claim 4 is characterized in that: Taking the inner side surface of the main mirror chamber (108) as a reference, the height of the bonding surface (102) is 0.5 mm higher than the inner side surface of the main mirror chamber (108), and a gap of 0.2 mm is left between the bonding surface (102) and the main mirror (8) for filling with bonding glue.

6. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: The secondary mirror chamber (7) is provided with a step inside, and the back of the secondary mirror (9) contacts the step inside the secondary mirror chamber (7); the secondary mirror chamber (7) is provided with three glue injection holes (701) evenly distributed along the circumference in the radial direction; the secondary mirror chamber (7) is provided with three flexible joints (702) evenly distributed along the circumference in the radial direction, and flexible joints (702) are provided at positions corresponding to the glue injection holes (701).

7. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: The secondary mirror assembly further comprises a secondary mirror adjustment pad (6), wherein the secondary mirror adjustment pad (6) is installed between the secondary mirror chamber (7) and the truss (5) and is used for grinding and adjusting the relative position of the secondary mirror (9) relative to the primary mirror (8).

8. The light and small telescopic unit system based on peripheral flexible support according to claim 1 is characterized in that: The support tube (3) is internally installed with reinforcing ribs (301), and the reinforcing ribs (301) include a plurality of staggeredly arranged annular ribs and longitudinal ribs.

9. The light and small telescopic unit system based on peripheral flexible support according to claim 1, characterized in that: A stepped stop structure 1 is provided on one side of the first gasket (4) connected to the support tube (3), a stepped stop structure 2 is provided on one side of the second gasket (2) connected to the support tube (3), a stepped stop structure 3 is provided on one end of the support tube (3) connected to the first gasket (4), a stepped stop structure 4 is provided on one end of the support tube (3) connected to the second gasket (2), the stepped stop structure 1 is cooperatively connected with the stepped stop structure 3; the stepped stop structure 2 is cooperatively connected with the stepped stop structure 4; the first gasket (4) and the second gasket (2) are provided with countersunk holes, nuts are pre-embedded as inlays at both ends of the support tube (3) at positions corresponding to the countersunk holes, and the first gasket (4) and the second gasket (2) are fixed to the two ends of the support tube (3) by screws.

10. The light and small telescopic unit system based on peripheral flexible support according to claim 3, characterized in that: The first gasket (4) is provided with a plurality of bosses one (401), the height of the bosses one (401) is 0.5 mm, the flatness of the plurality of bosses one (401) is less than 0.003 mm, and the plurality of bosses one (401) are coplanar, serving as positioning surface two; the second gasket (2) is provided with a plurality of bosses two (201), the height of the bosses two (201) is 0.5 mm, the flatness of the plurality of bosses two (201) is less than 0.003 mm, and the plurality of bosses two (201) are coplanar, serving as positioning surface three; the parallelism of positioning surface three relative to positioning surface two is less than 0.005 mm; the annular step structure (106) is provided with a mounting hole corresponding to the boss two (201), and the truss (5) is provided with a mounting hole corresponding to the boss one (401).

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