A socket connection tee suitable for large load unmanned aerial vehicle and an assembling method thereof

Abstract

The application discloses a socket connection tee suitable for a large-load unmanned aerial vehicle and an assembling method thereof, and relates to the technical field of unmanned aerial vehicles. The open socket connection tee comprises a tee body and a rack connecting pipe, the tee body comprises a horizontal interface and two vertical interfaces, the two vertical interfaces are respectively arranged on the upper side and the lower side of the horizontal interface, one end of the rack connecting pipe is detachably nested in the horizontal interface of the tee body, the other end of the rack connecting pipe is connected to the body of the unmanned aerial vehicle, and the vertical interfaces of the tee body are used for installing rotor drive motors of the unmanned aerial vehicle. The application has the characteristics of convenient dismounting and mounting, high assembling precision and reliable connection, and is beneficial to improving the flight stability of the unmanned aerial vehicle.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) technology, and more specifically to a socket-connected tee suitable for heavy-load UAVs and its assembly method. Background Technology

[0002] With the rapid development of drone technology in logistics, engineering operations, and other fields, heavy-duty drones are placing higher demands on structural connection strength and assembly precision. As a key component of the fuselage load-bearing structure, the assembly quality of the open-type socket tee directly affects the drone's payload capacity, flight stability, and service life. The connection of the drone frame structure's rods is a core element in ensuring the overall load-bearing capacity and operational stability. Due to its convenient installation, the open-type socket tee has become a crucial connector between the structure and piping system of heavy-duty drones. This connection structure, through the combination of socket fitting and open design, achieves a balance between lightweight and high strength, making it suitable for multi-rotor heavy-duty drone models.

[0003] The existing open-type socket tee assembly has the following main shortcomings: (1) Uneven torque control and force distribution lead to unstable connection strength. The existing assembly method relies on operators to use a torque wrench to operate according to the "diagonal tightening" process, but there are differences in the tightening sequence and torque application timing judged by the operator. This causes uneven force distribution on the tee flange lugs, local stress concentration, and micro-deformation of the tee body; under long-term heavy load vibration, fatigue cracks are prone to occur at the deformed areas.

[0004] (2) The single reference between the positioning slot and the positioning block leads to deviations in assembly accuracy. Existing assembly methods mostly use the positioning method of "marking on the surface of the main pipe" without setting high-precision tooling positioning pins or positioning slots. The relative position of the tee and the main pipe is prone to shift during pre-assembly and fastening, causing the angle and coaxiality of the branch pipe to exceed the design tolerance. After the UAV frame is assembled, the overall center of gravity shifts, affecting flight stability. Under heavy loads, this deviation will be amplified and may even cause structural resonance.

[0005] (3) The tee fittings are mainly formed by welding, which poses a safety hazard. The existing open socket connection tee fittings of UAVs are mainly used to cope with ultra-heavy load scenarios, and the composite reinforcement scheme of "socket fastening + spot welding" is adopted. However, the high temperature of spot welding will change the metallographic structure of the tee and the pipeline, and a brittle zone will appear at the welded part, which will reduce the fatigue resistance. Under the long-term high-frequency vibration of heavy UAVs, the welded part will become a fracture risk point. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of existing open-type socket connection tees for heavy-load UAVs, such as complex installation, uneven stress leading to unstable structural strength, and poor fatigue resistance. The present invention provides a socket connection tee and its assembly method that are compact, easy to assemble and disassemble, and have high structural stability, suitable for heavy-load UAVs.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A socket-connected tee for heavy-duty UAVs includes a tee body and a frame connecting pipe. The tee body includes a horizontal interface and two vertical direct ports, which are located on the upper and lower sides of the horizontal interface, respectively. One end of the frame connecting pipe is detachably nested in the horizontal interface of the tee body, and the other end of the frame connecting pipe is connected to the body of the UAV. The vertical direct ports of the tee body are used to install the rotor drive motor of the UAV.

[0008] As a further improvement of the present invention, the tee body is an integral structure, one end of the horizontal interface is provided with a first positioning groove, and the end of the frame connecting pipe is provided with a second positioning groove, the first positioning groove and the second positioning groove are corresponding to each other; when the frame connecting pipe is nested in the horizontal interface and the second positioning groove is aligned with the first positioning groove, a positioning block is inserted into the first positioning groove and the second positioning groove, and the positioning block is connected and fixed to the side of the tee body to realize the positioning of the frame connecting pipe in the tee body.

[0009] As a further improvement of the present invention, the other end of the horizontal interface is provided with an opening groove, and both the upper and lower sides of the opening groove are provided with flanges with mounting holes. After the frame connecting pipe is positioned in the tee body, a rubber gasket with a through hole is inserted into the opening groove, and a fastener is screwed into the mounting hole to realize the connection and fixation between the rubber gasket and the flange on the side of the horizontal interface.

[0010] As a further improvement of the present invention, a locking tube is also included. After the frame connecting tube is positioned in the tee body, the locking tube is nested inside the frame connecting tube. The side of the horizontal interface is provided with multiple mounting holes, through which fasteners are inserted and fixed, so as to realize the connection and fixation of the locking tube with the horizontal interface of the frame connecting tube and the tee body.

[0011] As a further improvement of the present invention, the tee body is an integral structure, and expansion rings are provided between the two sides of the horizontal interface and the outer surface of the frame connecting pipe, and expansion bolts are provided at both ends of the horizontal interface to realize the connection and fixation between the frame connecting pipe and the horizontal interface of the tee body.

[0012] As a further improvement of the present invention, the tee body is a two-part split structure, the two split structures are connected by flanges, and a gasket is provided at the flange connection.

[0013] As a general technical concept, the present invention also provides an assembly method for the above-mentioned socket connection tee applicable to heavy-load UAVs, comprising the following steps: Step S1: Insert the rack connecting pipe into the horizontal interface of the tee body, and align the second positioning groove at the end of the rack connecting pipe with the first positioning groove at the end of the horizontal interface. Step S2: Insert positioning blocks into the second positioning groove and the first positioning groove, insert rubber pads into the opening groove at the end of the horizontal interface, and connect and fix the rubber pads to the flange of the tee body. Step S3: First, remove the positioning block, and then insert the locking tube into the frame connecting tube from the end of the horizontal interface; Step S4: Insert the positioning block into the second positioning slot and the first positioning slot, and connect and fix the positioning block to the tee body. Then connect and fix the locking tube, the frame connecting tube and the tee body.

[0014] As a further improvement of the present invention, in step S1, silicone-based grease is applied to the outer wall of the rack connecting tube, and the end of the rack connecting tube is gently tapped with a rubber hammer to assist the rack connecting tube in being inserted into the horizontal interface.

[0015] As a further improvement of the present invention, in step S3, silicone-based grease is applied to the outer wall of the locking tube, and the end of the locking tube is gently tapped with a rubber hammer to assist the locking tube in being inserted into the frame connecting tube.

[0016] As a further improvement of the present invention, after assembly, a cap is placed on the end of the locking tube, and an anti-rust agent is sprayed on the exposed metal surface of the socket connection tee to prevent corrosion.

[0017] Compared with the prior art, the socket connection tee and its assembly method for heavy-load UAVs of the present invention have the following significant advantages: (1) By setting positioning grooves on both the tee body and the frame connecting pipe, the assembly accuracy between the frame connecting pipe and the tee body is improved, eliminating the positioning deviation caused by manual visual judgment and ruler measurement, avoiding the phenomenon of local stress concentration in the open socket connection tee, so that the tee body is evenly stressed, and ensuring the stable flight of the UAV under long-term heavy load vibration.

[0018] (2) An opening groove is provided at the end of the horizontal interface, making the tee body an open clamp structure. The step-by-step fastening method is adopted. First, the frame connecting pipe is inserted into the tee body from one end of the horizontal interface. Then, the rubber gasket is inserted into the opening groove and the rubber gasket is connected and fixed to the flange on the side of the horizontal interface. This realizes the connection and fixation of one end of the frame connecting pipe and the tee body. Then, the locking pipe is inserted into the frame connecting pipe from the other end of the horizontal interface. The locking pipe is connected and fixed to the horizontal interface of the frame connecting pipe and the tee body using fasteners. This further enhances the connection stability between the frame connecting pipe and the tee body, avoids the defect of decreased fatigue resistance of the connection part, and solves the problem of insufficient connection rigidity caused by the weak connection between the tee body and the frame connecting pipe in the existing socket connection tee. Attached Figure Description

[0019] Figure 1 This is an exploded structural diagram of the socket connection tee for heavy-load UAVs in specific embodiment 1 of the present invention; Figure 2 This is an overall structural diagram of the socket connection tee for heavy-load UAVs in specific embodiment 1 of the present invention; Figure 3 This is a front view structural diagram of the socket connection tee applicable to heavy-load UAVs in specific embodiment 1 of the present invention; Figure 4 for Figure 3 Cross-sectional view along the AA direction; Figure 5 This is a top view of the socket connection tee for heavy-load UAVs in specific embodiment 1 of the present invention; Figure 6 for Figure 5 Cross-sectional view of the structure along the BB direction; Figure 7 This is an exploded structural diagram of the socket connection tee for heavy-load UAVs in specific embodiment 2 of the present invention; Figure 8 This is an overall structural diagram of the socket connection tee for heavy-load UAVs in specific embodiment 2 of the present invention; Figure 9 This is a cross-sectional view of the socket connection tee for heavy-load UAVs in specific embodiment 3 of the present invention.

[0020] Legend: 1. Tee body; 101. Horizontal interface; 102. Vertical interface; 103. Flange; 104. Rivet hole; 2. Frame connecting pipe; 3. Locking pipe; 4. Opening groove; 5. Rubber gasket; 6. First positioning groove; 7. Positioning block; 8. Cap; 9. Second positioning groove; 10. Mounting hole; 11. Rivet; 12. Nut; 13. Fastening bolt; 14. Expansion bolt; 15. Expansion ring. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0022] In the description of this invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0024] Example 1 like Figures 1 to 6 As shown, the socket connection tee of the present invention, applicable to heavy-load UAVs, includes a tee body 1 and a frame connecting pipe 2. The tee body 1 is made of metal, and the frame connecting pipe 2 is made of carbon fiber. The tee body 1 includes a horizontal interface 101 and two vertical direct ports 102, which are located on the upper and lower sides of the horizontal interface 101, respectively. One end of the frame connecting pipe 2 is detachably nested in the horizontal interface 101 of the tee body 1, and the other end of the frame connecting pipe 2 is connected to the body of the UAV. The vertical direct ports 102 of the tee body 1 are used to install the rotor drive motor of the UAV, and the output shaft of the drive motor is used to connect the rotor.

[0025] like Figure 1 , Figure 3 and Figure 4As shown, the tee body 1 is a high-strength aluminum alloy integrated structure, which is lightweight, high-strength, and has high dimensional accuracy. The front end of the horizontal interface 101 is provided with a first positioning groove 6, and the front end of the frame connecting pipe 2 is provided with a second positioning groove 9. The first positioning groove 6 and the second positioning groove 9 correspond to each other to mark the frame connecting pipe 2 and the tee body 1 to maintain coaxial assembly and eliminate assembly positioning deviation. When the frame connecting pipe 2 is nested in the horizontal interface 101 and the second positioning groove 9 is aligned with the first positioning groove 6, a positioning block 7 is inserted into the first positioning groove 6 and the second positioning groove 9. The through holes on both sides of the positioning block 7 are corresponding to the threaded mounting holes 10 on the side of the tee body 1. The fastening bolt 13 passes through the through holes of the positioning block 7 and is screwed into the mounting holes 10 of the tee body 1 to realize the fixed connection between the positioning block 7 and the tee body 1, so as to realize the positioning of the frame connecting pipe 2 in the tee body 1.

[0026] like Figure 1 , Figure 3 and Figure 5 As shown, the other end of the horizontal interface 101 is provided with an opening groove 4, and both the upper and lower sides of the opening groove 4 are provided with flanges 103 with mounting holes 10. The tee body becomes an open clamp structure to facilitate the insertion of the frame connecting pipe 2 into the horizontal interface 101, preventing damage to parts from violent impacts. After the frame connecting pipe 2 is positioned in the tee body 1, a rubber gasket 5 with a through hole is inserted into the opening groove 4, and a nut 12 and a fastening bolt 13 are screwed into the mounting hole 10 to connect and fix the rubber gasket 5 to the flange 103 on the side of the horizontal interface 101, thereby locking and fixing the frame connecting pipe 2 and the tee body 1.

[0027] like Figure 1 , Figure 4 and Figure 6 As shown, the open-type socket connection tee also includes an aluminum locking tube 3. After the frame connecting tube 2 is positioned in the tee body 1, the locking tube 3 is nested inside the frame connecting tube 2. After the locking tube 3 is inserted into the frame connecting tube 2, corresponding rivet holes are drilled on the side of the locking tube 3 and the side of the frame connecting tube 2 according to the rivet hole positions 104 preset on the side of the tee body 1, and rivets 11 are driven into the rivet holes to achieve the connection and fixation of the locking tube 3 with the horizontal interface 101 of the frame connecting tube 2 and the tee body 1.

[0028] This embodiment also provides an assembly method for the above-mentioned socket connection tee suitable for heavy-load UAVs, including the following steps: Step S1: Insert the front end of the frame connecting pipe 2 into the horizontal interface 101 from the rear end of the horizontal interface 101, ensuring that the second positioning groove 9 at the end of the frame connecting pipe 2 is aligned with the first positioning groove 6 at the end of the horizontal interface 101, thus ensuring proper insertion. If there is significant resistance during insertion, apply a small amount of silicone-based grease to the outer wall of the frame connecting pipe 2 and gently tap the end of the frame connecting pipe 2 with a rubber mallet to avoid deformation caused by forceful striking, thus assisting in the insertion of the frame connecting pipe 2 into the horizontal interface 101.

[0029] Step S2: Insert positioning blocks 7 into the second positioning groove 9 and the first positioning groove 6. Insert rubber pads 5 into the opening grooves 4 at both ends of the horizontal interface 101, and connect and fix the rubber pads 5 to the flange 103 of the tee body 1 using nuts 12 and fastening bolts 13, so that the rear end of the horizontal interface 101 is locked to the frame connecting pipe 2. During the process of inserting fastening bolts 13 into the mounting holes 10 of the rubber pads 5 and flange 103, the insertion direction of multiple fastening bolts 13 should be consistent, and the fastening bolts 13 should be installed in a symmetrical order to ensure that each fastening bolt 13 is subjected to uniform force. Tighten the fastening bolts 13 symmetrically and alternately, and use a torque wrench to control the torque to avoid deformation of the socket due to unilateral force, and ensure that the tee body 1 and the frame connecting pipe 2 are firmly locked. After the torque reaches the standard, apply anaerobic adhesive to the contact surface between the nut 12 and the tee body 1 to ensure reliable connection under long-term vibration environment.

[0030] Step S3: First, remove the positioning block 7, and then insert the locking tube 3 into the frame connecting tube 2 from the front end of the horizontal interface 101. If there is a lot of resistance during the insertion process, apply silicone-based grease to the outer wall of the locking tube 3 and gently tap the end of the locking tube 3 with a rubber hammer to avoid violent knocking that could deform the parts, thus assisting the locking tube 3 in being inserted into the frame connecting tube 2.

[0031] Step S4: Insert the positioning block 7 into the second positioning groove 9 and the first positioning groove 6, and connect and fix the positioning block 7 to the tee body 1 with the fastening bolt 13. Then, according to the rivet hole positions 104 on the side of the tee body 1, drill rivet holes at the corresponding positions of the frame connecting pipe 2 and the locking pipe 3, and insert and rivet 11 into the rivet holes to connect and fix the locking pipe 3, the frame connecting pipe 2 and the tee body 1. Through the multiple locking connection of bolt fastening and rivet fixing structure, the "pre-tightening-rivet-final tightening" step-by-step tightening improves the connection rigidity and strength.

[0032] like Figure 2 As shown, after assembly, cap 8 is placed on the end of locking tube 3. At the same time, rust inhibitor is sprayed on the exposed metal surface of the socket connection tee to prevent corrosion.

[0033] In this embodiment, before assembly, the inner wall of the tee body 1, the outer wall of the frame connecting pipe 2, and the corresponding sealing groove are cleaned with alcohol or a special cleaning agent to remove oil, dust, and metal shavings, ensuring that the connection surfaces are clean. The assembled open-type socket connection tee is then installed onto the UAV frame for overall assembly. The linkage of each component is tested to ensure that the open-type socket connection tee does not affect other functions of the UAV, such as arm rotation and landing gear retraction.

[0034] Example 2 like Figure 7 and Figure 8 As shown, the socket connection tee for heavy-load UAVs of the present invention has a similar structural configuration and working principle to the socket connection tee for heavy-load UAVs in Embodiment 1. The main difference is that the tee body 1 is a two-piece split structure. A sealing groove and a positioning step can be machined on the inner side of the socket. The frame connecting pipe 2 is inserted into the horizontal interface 101 to the positioning step, and a metal-clad sealing ring or metal spiral wound gasket is embedded to ensure a tight seal. The two split structures are connected by a flange, and a rubber gasket 5 is provided at the flange connection. High-strength nuts 12 and fastening bolts 13 are used for symmetrical ring fastening. The torque increases in stages according to the flange size. Anti-loosening washers and anti-loosening adhesive are added for double anti-loosening. Reinforcing ribs are also welded to the outside of the flange to improve overall rigidity and prevent socket deformation under heavy loads.

[0035] The socket connection tee of this embodiment has a load-bearing capacity that is more than 30% higher than that of the socket connection tee in embodiment 1, and has higher sealing reliability. It does not require special flaring tools for disassembly and assembly, making maintenance convenient. It is suitable for high-pressure / heavy-load scenarios and can be installed on the main load-bearing frame and heavy-duty leg connection parts of heavy-duty drones.

[0036] Example 3 like Figure 9 As shown, the socket connection tee for heavy-load UAVs of the present invention has a similar structural setting and working principle to the socket connection tee for heavy-load UAVs in Embodiment 1. The main difference is that the tee body 1 is an integral structure, and the horizontal interface 101 is provided with mounting grooves on both sides. The mounting grooves are provided with expansion rings 15, that is, expansion rings 15 are provided between the two sides of the horizontal interface 101 and the outer surface of the frame connecting pipe 2. Expansion bolts 14 are provided at both ends of the horizontal interface 101. The radial expansion of the expansion rings 15 achieves an interference fit, so as to realize the connection and fixation between the frame connecting pipe 2 and the horizontal interface 101 of the tee body 1, and improve the connection strength and vibration resistance.

[0037] In this embodiment, after the frame connecting pipe 2 is inserted into the horizontal interface 101, the expansion ring 15 is placed into the mounting groove and locked and pressurized by the expansion bolt 14. The expansion ring 15 expands radially, and at the same time, the opening of the tee body 1 contracts and is tightly clamped to the frame connecting pipe 2, ensuring that the interference fit does not damage the pipe material. Moreover, the connection stress is evenly distributed and there is no local stress concentration. It can be applied to the connection parts of UAVs that require quick installation and unloading and have low torque.

[0038] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A socket-type tee suitable for heavy-load unmanned aerial vehicles, characterized in that, The device includes a three-way body (1) and a frame connecting pipe (2). The three-way body (1) includes a horizontal interface (101) and two vertical direct ports (102), which are located on the upper and lower sides of the horizontal interface (101), respectively. One end of the frame connecting pipe (2) is detachably nested in the horizontal interface (101) of the three-way body (1), and the other end of the frame connecting pipe (2) is connected to the body of the UAV. The vertical direct ports (102) of the three-way body (1) are used to install the rotor drive motor of the UAV.

2. The socket-type tee for heavy-load UAVs according to claim 1, characterized in that, The three-way body (1) is an integral structure. One end of the horizontal interface (101) is provided with a first positioning groove (6), and the end of the frame connecting pipe (2) is provided with a second positioning groove (9). The first positioning groove (6) and the second positioning groove (9) correspond to each other. When the rack connecting pipe (2) is nested in the horizontal interface (101) and the second positioning groove (9) is aligned with the first positioning groove (6), the positioning block (7) is inserted into the first positioning groove (6) and the second positioning groove (9), and the positioning block (7) is connected and fixed to the side of the tee body (1) so as to realize the positioning of the rack connecting pipe (2) in the tee body (1).

3. The socket-type tee for heavy-load UAVs according to claim 2, characterized in that, The other end of the horizontal interface (101) is provided with an opening groove (4), and both the upper and lower sides of the opening groove (4) are provided with flanges (103) with mounting holes (10). After the frame connecting pipe (2) is positioned in the tee body (1), a rubber pad (5) with a through hole is inserted into the opening groove (4), and a fastener is screwed into the mounting hole (10) to achieve connection and fixation between the rubber pad (5) and the flange (103) on the side of the horizontal interface (101).

4. The socket connection tee for heavy-load UAVs according to claim 3, characterized in that, It also includes a locking tube (3). After the frame connecting tube (2) is positioned in the tee body (1), the locking tube (3) is nested into the frame connecting tube (2). The side of the horizontal interface (101) is provided with multiple mounting holes (10). Fasteners are inserted and fixed in the mounting holes (10) to realize the connection and fixation of the locking tube (3) with the horizontal interface (101) of the frame connecting tube (2) and the tee body (1).

5. The socket-connected tee for heavy-load UAVs according to claim 1, characterized in that, The three-way body (1) is an integral structure. Expansion rings (15) are provided between the two sides of the horizontal interface (101) and the outer surface of the frame connecting pipe (2), and expansion bolts (14) are provided at both ends of the horizontal interface (101) to realize the connection and fixation between the frame connecting pipe (2) and the horizontal interface (101) of the three-way body (1).

6. The socket-connected tee for heavy-load UAVs according to claim 1, characterized in that, The three-way body (1) is a two-piece split structure, which is connected by flanges, and a gasket (5) is provided at the flange connection.

7. An assembly method for a socket-connected tee for a heavy-load UAV as described in claim 4, characterized in that, Includes the following steps: Step S1: Insert the rack connecting pipe (2) into the horizontal interface (101) of the tee body (1), and align the second positioning groove (9) at the end of the rack connecting pipe (2) with the first positioning groove (6) at the end of the horizontal interface (101); Step S2: Insert positioning blocks (7) into the second positioning groove (9) and the first positioning groove (6), insert rubber pads (5) into the opening groove (4) at the end of the horizontal interface (101), and connect and fix the rubber pads (5) to the flange (103) of the tee body (1); Step S3: Take out the positioning block (7) and insert the locking tube (3) into the frame connecting tube (2) from the end of the horizontal interface (101); Step S4: Insert the positioning block (7) into the second positioning slot (9) and the first positioning slot (6). First, connect and fix the positioning block (7) to the tee body (1), and then connect and fix the locking tube (3), the frame connecting tube (2) and the tee body (1).

8. The assembly method according to claim 7, characterized in that, In step S1, apply silicone-based grease to the outer wall of the rack connecting tube (2) and gently tap the end of the rack connecting tube (2) with a rubber hammer to help the rack connecting tube (2) be inserted into the horizontal interface (101).

9. The assembly method according to claim 7, characterized in that, In step S3, silicone-based grease is applied to the outer wall of the locking tube (3), and the end of the locking tube (3) is gently tapped with a rubber hammer to assist the locking tube (3) in being inserted into the frame connecting tube (2).

10. The assembly method according to any one of claims 7 to 9, characterized in that, After assembly, cover the end of the locking tube (3) with a cap (8) and spray rust inhibitor on the exposed metal surface of the socket connection tee to prevent corrosion.

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