Fixing device of atomic gas chamber

Abstract

The utility model relates to the technical field of atomic gas chambers, and discloses a fixing device of an atomic gas chamber, which comprises a base, a middle cover and a top cover which are sequentially connected from bottom to top, a first containing cavity is formed in the top of the base, a mounting blind hole is formed in the bottom of the first containing cavity, first semicircular holes are formed in the edges of the top of the first containing cavity, a second containing cavity is formed in the bottom of the middle cover, second semicircular holes are formed in the edges of the bottom of the second containing cavity, and a plurality of wire passing holes are formed in the top of the middle cover. The top cover is provided with a plurality of wire passing channels, and each wire passing channel is used for connecting the wire passing hole and the outside; a plurality of mounting holes are formed in the bottom of the base; according to the modularized fixing device for the atomic gas chamber, an operator can place the atomic gas chamber and a heating device into the mounting cavities in the base and the middle cover, the first semicircular hole of the base and the second semicircular hole of the middle cover are aligned to form a complete light through hole when being closed, and a lead channel is integrated on the fixing device, so that wiring of the operator is facilitated.

Description

Technical Field

[0001] This utility model relates to the field of atomic gas chamber technology, and in particular to a fixing device for an atomic gas chamber. Background Technology

[0002] The atomic gas chamber is a core component in the field of quantum instruments and precision measurement systems. The atomic gas chamber consists of a gas chamber and an outer shell. The gas chamber is usually made of glass or other transparent materials. During the manufacturing process, an inflation port needs to be reserved on one side wall of the gas chamber. Atomic vapor (such as alkali metal atomic vapors such as rubidium and cesium) is filled into the gas chamber through the inflation port. After inflation is completed, the inflation port is sealed, thereby sealing the atomic vapor in the gas chamber. The sealed inflation port protrudes outward to form a process protrusion. The outer shell installed outside the gas chamber forms a protective structure for the gas chamber. Each side wall of the outer shell is provided with light-passing holes.

[0003] In experiments, the process protrusion of the atomic gas chamber is usually placed with the protrusion facing upwards, and a temporary fixing bracket is used to limit the atomic gas chamber. Then, the atomic gas chamber is heated by a heating device. However, fixing the atomic gas chamber with only a temporary bracket has a poor fixing effect, and the existing temporary bracket does not integrate the lead wire channel of the heating device, which makes the wiring and installation of the heating device complicated. Utility Model Content

[0004] The technical problem this invention aims to solve is that atomic gas chambers are installed in instruments such as atomic clocks and atomic magnetometers. Existing technologies require customized brackets for the different shapes of the mounting cavities of different instruments. The parts of customized brackets of different models have poor versatility, poor compatibility, and high maintenance costs. At the same time, the atomic gas chamber needs to be heated by a heating device during the experiment. Existing brackets do not integrate the lead wire channel of the heating device, which makes the installation of the heating device complicated.

[0005] To solve the above-mentioned technical problems, this utility model provides a fixing device for an atomic gas chamber. The atomic gas chamber includes a gas chamber and an outer shell. Each side wall of the outer shell is provided with a light-passing hole. The fixing device for the atomic gas chamber includes a base, a middle cover and a top cover connected in sequence from bottom to top.

[0006] The base has a first receiving cavity at the top, and each edge of the top of the first receiving cavity has a first semi-circular hole, and each first semi-circular hole connects the first receiving cavity to the outside.

[0007] The bottom of the middle cover is provided with a second receiving cavity, and each edge of the bottom of the second receiving cavity is provided with a second semi-circular hole, and each second semi-circular hole is connected to the second receiving cavity and the outside.

[0008] The first and second cavities are flush to form a chamber for containing atomic gas.

[0009] The first and second semicircular holes are aligned to form a light-passing hole;

[0010] The top of the middle cover has several wire holes, and the top cover has several wire channels. Each wire channel is used to connect the wire holes to the outside.

[0011] The base has several mounting holes at its bottom.

[0012] As a preferred embodiment, the bottom of the first receiving cavity is provided with a blind mounting hole.

[0013] As a preferred embodiment, the bottom of the top cover is provided with a third receiving cavity, and each wire passage is located at each edge of the bottom of the third receiving cavity, and each wire passage is connected to the third receiving cavity.

[0014] As a preferred embodiment, the wiring channel includes two symmetrically arranged first wiring channels that extend along the length direction of the top cover, and also includes two symmetrically arranged second wiring channels that extend along the width direction of the top cover.

[0015] As a preferred embodiment, each of the first semicircular holes is provided with a first arc-shaped groove on its outer side, and the radius of the first arc-shaped groove is larger than the radius of the corresponding first semicircular hole.

[0016] Each second semicircular hole has a second arc-shaped groove on its outer side, and the radius of the second arc-shaped groove is larger than the radius of the corresponding second semicircular hole.

[0017] The first and second arc-shaped grooves are aligned.

[0018] As a preferred embodiment, the first arc-shaped groove is concentric with the corresponding first semicircular hole, and the second arc-shaped groove is concentric with the corresponding second semicircular hole.

[0019] As a preferred embodiment, the top of the second receiving cavity is provided with a positioning protrusion, which is fixed to the bottom of the middle cover and is used to position the light-passing hole.

[0020] As a preferred embodiment, the wire hole includes two first elongated holes symmetrically arranged and extending along the length direction of the middle cover, and also includes two second elongated holes symmetrically arranged and extending along the width direction of the middle cover.

[0021] As a preferred embodiment, both the first and second receiving cavities have polygonal cross-sections. Each corner of the first receiving cavity is provided with a first circular groove extending along the height direction, and each corner of the second receiving cavity is provided with a second circular groove extending along the height direction. Each second circular groove is connected to each first circular groove.

[0022] As a preferred embodiment, each corner of the base is provided with a first connecting hole extending along the height, each corner of the middle cover is provided with a second connecting hole extending along the height, and each corner of the top cover is provided with a third connecting hole extending along the height. The first connecting hole, the second connecting hole and the third connecting hole are interconnected, and the first connecting hole is provided with a thread.

[0023] Compared with the prior art, the advantages of the fixing device for the atomic gas chamber in this embodiment of the utility model are as follows:

[0024] A modular mounting device for an atomic gas chamber is provided. The operator can place the atomic gas chamber and heating device into the mounting cavity inside the base and the middle cover. The mounting device can be fixed in the experimental position through the mounting hole at the bottom of the base. The first semicircular hole of the base and the second semicircular hole of the middle cover are aligned when closed to form a complete light-passing hole, ensuring precise matching of the optical axis with the external light source without additional adjustment. Furthermore, the mounting device integrates a lead wire channel. The leads of the temperature sensor in the atomic gas chamber and the leads of the heating device can pass through several wire holes set on the top of the middle cover and then extend out of the mounting device through the wire channel on the top cover, which is convenient for the operator to connect wires. When it is necessary to remove the atomic gas chamber or replace the heating device, only the middle cover needs to be opened, without disassembling the entire mounting device. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the fixing device for assembling the atomic gas chamber according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the atomic gas chamber structure;

[0028] Figure 4 This is a schematic diagram of the base structure of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0029] Figure 5 This is a top view of the base of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0030] Figure 6 This is a side view of the base of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the middle cover structure of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0032] Figure 8 This is a top view of the middle cover of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0033] Figure 9 This is a bottom view of the middle cover of the fixing device for the atomic gas chamber according to an embodiment of this utility model;

[0034] Figure 10 This is a schematic diagram of the middle cover structure of the fixing device for the atomic gas chamber according to an embodiment of the present invention. Figure 2 ;

[0035] Figure 11 This is a side view of the middle cover of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0036] Figure 12 This is a schematic diagram of the top cover structure of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0037] Figure 13 This is a top view of the fixing device for the atomic gas chamber according to an embodiment of the present invention;

[0038] Figure 14 This is a bottom view of the top cover of the fixing device for the atomic gas chamber according to an embodiment of this utility model;

[0039] Figure 15 This is a schematic diagram of the top cover structure of the fixing device for the atomic gas chamber according to an embodiment of the present invention. Figure 2 .

[0040] In the diagram, 1. Base; 2. Middle cover; 3. Top cover; 4. First receiving cavity; 5. Mounting blind hole; 6. First semi-circular hole; 7. Second receiving cavity; 8. Second semi-circular hole; 9. Third receiving cavity; 10. First arc-shaped groove; 11. Second arc-shaped groove; 12. First elongated hole; 13. Second elongated hole; 14. Positioning protrusion; 15. First wire passage; 16. Second wire passage; 17. First circular groove; 18. Second circular groove; 19. Mounting plate; 20. Mounting hole; 21. First connecting hole; 22. Second connecting hole; 23. Third connecting hole; 24. Gas chamber; 25. Process protrusion; 26. Outer shell body; 27. Light passage hole; 28. Outer shell top cover. Detailed Implementation

[0041] The specific embodiments of this utility model will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this utility model, but are not intended to limit its scope.

[0042] In the description of this utility model, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0043] It should be understood that the terms "first," "second," etc., are used in this utility model to describe various information, but this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this utility model, "first" information can also be called "second" information, and similarly, "second" information can also be called "first" information.

[0044] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0045] Atomic gas chambers in existing technologies, such as Figure 3 As shown, the atomic gas chamber includes a gas chamber 24 and an outer shell. Each side wall of the outer shell is provided with a light-passing hole 27. Specifically, the outer shell includes an outer shell body 26 and an outer shell cover 28. Each side wall of the outer shell body 26 is provided with a light-passing hole 27, and the outer shell cover 28 is also provided with a light-passing hole 27. One side wall of the gas chamber 24 has a process protrusion 25. A temperature sensor (not shown in the figure) is provided inside the outer shell body 26.

[0046] like Figures 1 to 15 As shown, a preferred embodiment of the present invention provides a fixing device for an atomic gas chamber, comprising a base 1, a middle cover 2, and a top cover 3 connected sequentially from bottom to top, for fixing the atomic gas chamber.

[0047] Specifically, the base 1 has a first receiving cavity 4 at its top, and each edge of the top of the first receiving cavity 4 has a first semi-circular hole 6, each of which connects the first receiving cavity 4 to the outside; the middle cover 2 has a second receiving cavity 7 at its bottom, and each edge of the bottom of the second receiving cavity 7 has a second semi-circular hole 8, each of which connects the second receiving cavity 7 to the outside; the first receiving cavity 4 and the second receiving cavity 7 are flush to form a chamber for containing atomic gas cells; the first semi-circular hole 6 and the second semi-circular hole 8 are aligned to form a light-transmitting hole; the top of the middle cover 2 has several wire-passing holes, and the top cover 3 has several wire-passing channels, each of which is used to connect the wire-passing holes to the outside; the bottom of the base 1 has several mounting holes 20.

[0048] This application provides a modular fixing device for an atomic gas chamber. The operator can place the atomic gas chamber and the heating device into the mounting cavity inside the base 1 and the middle cover 2. The fixing device can be fixed in the experimental position through the mounting hole 20 at the bottom of the base 1. The first semicircular hole 6 of the base 1 and the second semicircular hole 8 of the middle cover 2 are aligned when closed to form a complete light-transmitting hole. The optical axis can be accurately matched with the external light source without additional adjustment. Furthermore, the fixing device integrates a lead wire channel. The lead wires of the temperature sensor in the atomic gas chamber and the lead wires of the heating device can pass through several wire holes provided on the top of the middle cover 2 and then extend out of the fixing device through the wire channel on the top cover 3, which is convenient for the operator to connect wires. When it is necessary to remove the atomic gas chamber or replace the heating device, only the middle cover 2 needs to be opened, without disassembling the entire fixing device.

[0049] Specifically, the bottom of the first receiving cavity 4 is provided with a blind mounting hole 5. Existing atomic gas chamber fixing structures generally place the process protrusion 25 of the atomic gas chamber facing upwards. When the atomic vapor is heated, it moves towards the top of the atomic gas chamber and accumulates at the process protrusion 25. After temperature changes, the atomic vapor is deposited in the process protrusion 25. After long-term use, the number of effective atoms in the atomic gas chamber gradually decreases, resulting in a significant decrease in the lifespan of the atomic gas chamber. This application provides a blind mounting hole 5 at the bottom of the first receiving cavity 4, so that the operator can place the atomic gas chamber downwards and place the process protrusion 25 into the blind mounting hole 5, thereby avoiding the deposition of atomic vapor in the process protrusion 25 after the atomic gas chamber is heated.

[0050] Specifically, the bottom of the top cover 3 is provided with a third receiving cavity 9, and each wire passage is located at the bottom edge of the third receiving cavity 9, and each wire passage is connected to the third receiving cavity 9. The top cover 3 is provided with a third receiving cavity 9, so that after the lead wire of the heating device or temperature sensor passes out from the middle cover 2, it can be bent in the third receiving cavity 9 and then pass out through the corresponding wire passage. The third receiving cavity 9 forms a bending cavity for the lead wire, realizing the reasonable turning of the lead wire within the limited structure. At the same time, the top cover 3 protects the lead wire and effectively prevents the bent lead wire from being damaged by squeezing, pulling and other damage during assembly and use.

[0051] Specifically, the wire passage includes two symmetrically arranged first wire passages 15, which extend along the length of the top cover 3, and two symmetrically arranged second wire passages 16, which extend along the width of the top cover 3. The first wire passages 15 are lower in height but wider in width, while the second wire passages 16 are higher in height but narrower in width, thus accommodating lead wires of different specifications.

[0052] Specifically, each of the first semicircular holes 6 has a first arc-shaped groove 10 on its outer side, the radius of which is larger than the radius of the corresponding first semicircular hole 6; each of the second semicircular holes 8 has a second arc-shaped groove 11 on its outer side, the radius of which is larger than the radius of the corresponding second semicircular hole 8; the first arc-shaped groove 10 and the second arc-shaped groove 11 are aligned, and the aligned first arc-shaped groove 10 and the second arc-shaped groove 11 form a glass plate mounting cavity. After the atomic gas chamber is installed, the operator can install a glass plate of suitable size in the glass plate mounting cavity. After the glass plate is installed, the glass plate closes the light-transmitting hole, reducing the air flow between the inside and outside of the fixing device and reducing the temperature fluctuation inside the fixing device caused by the air flow.

[0053] Specifically, the first arc-shaped groove 10 is concentric with the corresponding first semi-circular hole 6, and the second arc-shaped groove 11 is concentric with the corresponding second semi-circular hole 8. The concentric design ensures that the glass plate mounting cavity is precisely aligned, effectively improving the sealing performance and thus minimizing temperature fluctuations caused by air flow.

[0054] Specifically, the top of the second receiving cavity 7 is provided with a positioning protrusion 14, which is fixed to the bottom of the middle cover 2. The positioning protrusion 14 is used to position the light-passing hole 27. After the middle cover 2 is installed, the positioning protrusion 14 on the middle cover 2 is inserted into the light-passing hole 27 on the outer shell cover 28 to achieve accurate positioning of the atomic gas chamber and enhance the overall structural stability.

[0055] Specifically, the wire guide hole includes two symmetrically arranged first elongated holes 12, which extend along the length direction of the middle cover 2, and also includes two symmetrically arranged second elongated holes 13, which extend along the width direction of the middle cover 2. The first elongated holes 12 are longer but narrower, while the second elongated holes 13 are shorter but wider, thus accommodating lead wires of different specifications.

[0056] Specifically, the cross-sections of the first receiving cavity 4 and the second receiving cavity 7 are both polygonal. Each corner of the first receiving cavity 4 is provided with a first circular groove 17 extending along the height direction, and each corner of the second receiving cavity 7 is provided with a second circular groove 18 extending along the height direction. Each second circular groove 18 is connected to each first circular groove 17. After the first circular groove 17 and the second circular groove 18 are connected, they form a clearance groove, thereby avoiding each corner of the atomic gas chamber and improving the structural reliability.

[0057] Specifically, each corner of the base 1 is provided with a first connecting hole 21 extending along the height, each corner of the middle cover 2 is provided with a second connecting hole 22 extending along the height, and each corner of the top cover 3 is provided with a third connecting hole 23 extending along the height. The first connecting hole 21, the second connecting hole 22, and the third connecting hole 23 are interconnected. The first connecting hole 21 is provided with a thread. The through-type fastening structure design forms a continuous assembly channel through the vertical through connecting holes of the base 1, the middle cover 2, and the top cover 3. The thread engagement and fixation of the long bolts are achieved with the thread in the first connecting hole 21, which effectively constructs a three-dimensional rigid connection system, significantly improves the assembly coaxiality and structural stability of the multi-layer components, and simplifies the assembly process.

[0058] Specifically, a mounting plate 19 is fixed to the bottom of the base 1. The base 1 and the mounting plate 19 are integrally formed, and each mounting hole 20 is provided on the mounting plate 19.

[0059] In other embodiments, a first magnetic strip is provided at the top of each corner of the base 1, a second magnetic strip is provided at the bottom of each corner of the middle cover 2, a third magnetic strip is provided at the top of each corner of the middle cover 2, and a fourth magnetic strip is provided at the bottom of each corner of the top cover 3. The first and second magnetic strips are magnetically attracted to each other, and the third and fourth magnetic strips are magnetically attracted to each other. Through the magnetic multi-layer docking structure, the magnetic strip array at the corners of the base 1, middle cover 2 and top cover 3 is used to achieve adsorption and positioning, forming a modular assembly that can be quickly assembled and disassembled without tools, which significantly improves assembly efficiency.

[0060] The working process of this utility model is as follows: The operator fixes the base 1 to the position to be measured through the mounting hole 20 on the base 1, and then places the atomic gas chamber and the heating device in the first mounting cavity. The process protrusion 25 on the atomic gas chamber is placed downward in the mounting blind hole 5 in the first mounting cavity. Then, the middle cover 2 is installed on the base 1. The positioning protrusion 14 of the second receiving cavity 7 on the middle cover 2 is inserted into the light-passing hole 27 on the top of the atomic gas chamber to fix the atomic gas chamber. The operator then passes the lead wire of the heating device and the lead wire of the temperature sensor on the atomic gas chamber through the first long hole 12 and the second long hole 13 on the middle cover 2, respectively. Then, the top cover 3 is placed on the top of the middle cover 2. The lead wire is bent in the third mounting cavity and extends out from the first wire passage 15 and the second wire passage 16. Then, the long bolt is inserted through the vertical through-connection hole of the base 1, the middle cover 2 and the top cover 3, and the base 1, the middle cover 2 and the top cover 3 are fixed by the internal thread of the first connecting hole 21.

[0061] In summary, this utility model provides a modular fixing device for an atomic gas chamber. Operators can place the atomic gas chamber and heating device into the mounting cavity inside the base and the middle cover. The fixing device can be fixed in the experimental position through the mounting hole at the bottom of the base. The first semicircular hole of the base and the second semicircular hole of the middle cover are aligned when closed to form a complete light-passing hole, ensuring precise matching of the optical axis with the external light source without additional adjustment. Furthermore, the fixing device integrates a lead wire channel, allowing the leads of the temperature sensor in the atomic gas chamber and the heating device to pass through several wire holes on the top of the middle cover and then extend out of the fixing device through the wire channel on the top cover, facilitating wiring by the operator. When it is necessary to remove the atomic gas chamber or replace the heating device, only the middle cover needs to be opened, without disassembling the entire fixing device.

[0062] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present utility model, and these improvements and substitutions should also be considered within the protection scope of the present utility model.

Claims

1. A fixing device for an atomic gas chamber, the atomic gas chamber comprising a gas chamber (24) and a shell, wherein each side wall of the shell is provided with a light-passing hole (27), characterized in that, The fixing device for the atomic gas chamber includes a base (1), a middle cover (2) and a top cover (3) connected sequentially from bottom to top; The base (1) has a first receiving cavity (4) at the top, and each edge of the top of the first receiving cavity (4) has a first semi-circular hole (6), and each of the first semi-circular holes (6) is connected to the first receiving cavity (4) and the outside. The bottom of the middle cover (2) is provided with a second receiving cavity (7), and each edge of the bottom of the second receiving cavity (7) is provided with a second semi-circular hole (8), and each second semi-circular hole (8) is connected to the second receiving cavity (7) and the outside; The first receiving cavity (4) and the second receiving cavity (7) are flush to form a cavity for receiving the atomic gas chamber; The first semicircular hole (6) and the second semicircular hole (8) are aligned to form a light-transmitting hole; The top of the middle cover (2) is provided with several wire holes, and the top cover (3) is provided with several wire channels, each of which is connected to the wire hole and the outside. The base (1) has several mounting holes (20) at its bottom.

2. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The bottom of the first receiving cavity (4) is provided with a blind hole (5).

3. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The bottom of the top cover (3) is provided with a third receiving cavity (9), and each of the wire passages is provided at each edge of the bottom of the third receiving cavity (9), and each of the wire passages is connected to the third receiving cavity (9).

4. The device for fixing an atomic gas chamber according to claim 3, characterized in that, The wire passage includes two first wire passages (15) arranged symmetrically, which extend along the length direction of the top cover (3), and also includes two second wire passages (16) arranged symmetrically, which extend along the width direction of the top cover (3).

5. The device for fixing an atomic gas chamber according to claim 1, characterized in that, Each of the first semicircular holes (6) is provided with a first arc-shaped groove (10) on its outside, and the radius of the first arc-shaped groove (10) is greater than the radius of the corresponding first semicircular hole (6). Each of the second semicircular holes (8) is provided with a second arc-shaped groove (11) on its outside, and the radius of the second arc-shaped groove (11) is larger than the radius of the corresponding second semicircular hole (8); The first arc-shaped groove (10) and the second arc-shaped groove (11) are aligned.

6. The device for fixing an atomic gas chamber according to claim 5, characterized in that, The first arc groove (10) is concentric with the corresponding first semicircular hole (6), and the second arc groove (11) is concentric with the corresponding second semicircular hole (8).

7. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The top of the second receiving cavity (7) is provided with a positioning protrusion (14), which is fixed to the bottom of the middle cover (2) and is used to position the light-passing hole (27).

8. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The wire hole includes two first elongated holes (12) arranged symmetrically, which extend along the length direction of the middle cover (2), and also includes two second elongated holes (13) arranged symmetrically, which extend along the width direction of the middle cover (2).

9. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The first receiving cavity (4) and the second receiving cavity (7) are both polygonal in cross-section. Each corner of the first receiving cavity (4) is provided with a first circular groove (17) extending along the height direction. Each corner of the second receiving cavity (7) is provided with a second circular groove (18) extending along the height direction. Each second circular groove (18) is connected to each first circular groove (17).

10. The device for fixing an atomic gas chamber according to claim 1, characterized in that, The base (1) has a first connecting hole (21) extending along the height at each corner, the middle cover (2) has a second connecting hole (22) extending along the height at each corner, and the top cover (3) has a third connecting hole (23) extending along the height at each corner. The first connecting hole (21), the second connecting hole (22) and the third connecting hole (23) are interconnected. The first connecting hole (21) is threaded.

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