Lithium battery weight impact test detection device

Abstract

The invention discloses a lithium battery weight impact test detection device which comprises a base, stand columns are installed on the four sides of the top of the base, a top plate is installed on the tops of the stand columns, a transmission mechanism is installed on the top of the top plate and connected with a driving motor, the output ends of the two sides of the transmission mechanism are connected with lead screws, and the lead screws are connected with nut moving seats. A lifting electromagnet is installed between the nut moving seats on the two sides, the lifting electromagnet is connected with a loading plate in a magnetic attraction mode, guide sleeves are installed on the four sides of the loading plate, the guide sleeves are installed on the stand columns in a sliding mode, receding grooves are formed in the positions, corresponding to the lead screws, of the loading plate, the lead screws are arranged in the receding grooves, a counterweight frame is installed at the bottom of the loading plate, and a positioning column is arranged in the center of the counterweight frame. The outer side of the positioning column is sleeved with a plurality of balancing weights, the balancing weights are sequentially and vertically overlapped on the counterweight frame, lock columns are installed on the four sides of the top of the counterweight frame, the tops of the lock columns penetrate through the loading plate and extend to the upper side of the loading plate, lock blocks are installed on the tops of the lock columns, and a hammer head is installed at the bottom of the counterweight frame.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium battery detection, and particularly relates to a lithium battery heavy object impact test detection device. Background Art

[0002] A lithium battery is a type of battery with lithium metal or lithium alloy as the positive / negative electrode material and using a non-aqueous electrolyte solution. Due to the very active chemical properties of lithium metal, the processing, storage, and use of lithium metal have very high environmental requirements. With the development of science and technology, lithium batteries have become the mainstream. The wide application of lithium batteries in various fields such as electronic devices and new energy vehicles makes the use safety of lithium batteries crucial. The heavy object impact test is a safety test item that simulates the situation of a lithium battery being collided by an external heavy object.

[0003] When a traditional heavy object impact test detection device conducts a heavy object impact test, the battery is placed on the ground, the heavy hammer is lifted by a steel wire rope, and then the heavy hammer is released. Since the heavy hammer is only suspended by the steel wire, the swaying of the steel wire causes the heavy hammer to easily deviate from the predetermined direction during free fall, resulting in failure to hit the battery, so that the impact accuracy is not high, and the impact weight is generally a fixed value. It is not only time-consuming but also troublesome to replace, so there is an urgent need for a lithium battery heavy object impact test detection device to solve the above problems. Summary of the Invention

[0004] Aiming at the problems raised in the above background art, the purpose of the present invention is to provide a lithium battery heavy object impact test detection device.

[0005] To achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0006] A lithium battery heavy object impact test detection device includes a base. Columns are installed on the four sides of the top of the base. A top plate is installed on the top of the columns. A transmission mechanism is installed on the top of the top plate. The transmission mechanism is connected to a driving motor. The output ends on both sides of the transmission mechanism are connected to lead screws. The lead screws are rotatably installed vertically between the base and the top plate. The lead screws are connected to nut moving seats. A lifting electromagnet is installed between the two nut moving seats. The lifting electromagnet is magnetically connected to a load plate. Guide sleeves are installed on the four sides of the load plate. The guide sleeves are slidably installed on the columns. The load plate is provided with an avoidance groove corresponding to the lead screw. The lead screw is arranged in the avoidance groove. A counterweight frame is installed at the bottom of the load plate. A positioning column is provided at the center of the counterweight frame. A number of counterweight blocks are sleeved outside the positioning column. The counterweight blocks are stacked on the counterweight frame one above the other in sequence. Locking columns are installed on the four sides of the top of the counterweight frame. The tops of the locking columns penetrate through the load plate and extend to the upper side thereof. Locking blocks are installed at the tops of the locking columns. A hammer head is installed at the bottom of the counterweight frame.

[0007] Further defined, a protective cover is installed on the top of the top plate, the driving motor is installed on the protective cover, the transmission mechanism is installed inside the protective cover, the transmission mechanism includes a first synchronous pulley, the first synchronous pulley is connected with a synchronous belt, the other side of the synchronous belt is connected with a second synchronous pulley, the first synchronous pulley and the second synchronous pulley are respectively connected with the tops of the two side lead screws, and the power output end of the driving motor is connected with the first synchronous pulley. Such a structural design plays a protective effect on the transmission mechanism, and at the same time, the transmission mechanism can stably drive the two side lead screws to move synchronously.

[0008] Further defined, bearing seats are installed on both the upper and lower sides of the lead screw. Among them, the upper bearing seat is installed at the bottom of the top plate, and the lower bearing seat is installed on the base. Such a structural design ensures that the lead screw can perform stable rotational motion.

[0009] Further defined, a lubricating oil groove is formed on the surface of the column, and the lubricating oil groove is arranged in a spiral or annular structure. Such a structural design makes the sliding of the guide sleeve smoother and is not prone to jamming.

[0010] Further defined, a number of mounting holes are provided on the guide sleeve, graphite particles are installed in the mounting holes, and the guide sleeve is made of bronze material. Such a structural design can reduce friction and extend the service life of the guide sleeve.

[0011] Further defined, an assembly groove is provided at the bottom of the counterweight frame, an assembly seat is installed in the assembly groove, the hammer head is installed at the bottom of the assembly seat, the hammer head and the assembly seat are integrally formed, and a sealing block is installed on the outside of the assembly seat in the assembly groove. Such a structural design facilitates the installation and use of the hammer head.

[0012] Further defined, a puncture head can also be installed at the bottom of the assembly seat. Such a structural design can also be used for puncture test detection.

[0013] Further defined, side plates are installed on both sides of the surface of the base, a number of first spring seats are installed on the side plates, springs are installed in the first spring seats, the free ends of the springs are connected with second spring seats, the second spring seats are connected with clamping plates, the clamping plates are locked and connected with the second spring seats by screws, and triangular reinforcing ribs are installed on both sides of the side plates, and the bottoms of the triangular reinforcing ribs are welded and installed on the base. Such a structural design can centeringly clamp the lithium battery to be tested.

[0014] Further defined, a fence plate is installed on the outside of the base by bolt locking, a movable door is hinged and installed on one side of the fence plate, and a transparent observation plate is installed on the movable door. Such a structural design can observe the internal impact test state while playing a protective role.

[0015] Further defined, plug seats are installed on the upper and lower sides of the movable door. Limiting grooves are provided on both sides of the plug seats. An L-shaped plug is slidably installed in the plug seats. One side of the L-shaped plug is placed in one of the limiting grooves, and the other side of the L-shaped plug is connected to a socket, and the socket is installed on the fence board. Such a structural design can achieve the effect of fixedly closing the movable door.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. By energizing and de-energizing the lifting electromagnet of the present invention, magnetic attraction connection is generated with the load plate to move upward or quickly drop downward due to the disappearance of magnetism. Under the sliding fit of the guide sleeve and the column, the hammer head will not shake, and it will not deviate from the predetermined direction when falling, improving the impact accuracy;

[0018] 2. During the detection of the present invention, according to the impact weight to be tested, appropriate counterweight blocks can be sleeved on the positioning posts on the counterweight frame. Only by installing and disassembling the counterweight blocks, the replacement is simple and time-saving, and the operation is convenient;

[0019] 3. The present invention also provides a splint and a spring. When the lithium battery explodes during the detection, the explosion force acts on the splint, and the elastic potential energy of the spring further absorbs the explosion energy, reducing the damage to the detection equipment. After the detection is completed, only the damaged splint needs to be disassembled and a new splint is replaced to conduct the test again, reducing the equipment maintenance cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention can be further illustrated by the non-limiting embodiments given in the drawings;

[0021] Figure 1 is an axonometric structural schematic diagram of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0022] Figure 2 is a transverse sectional structural schematic diagram of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0023] Figure 3 is a vertical sectional structural schematic diagram of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0024] Figure 4 is a sectional structural schematic diagram of a load plate of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0025] Figure 5 is a structural schematic diagram of a fence board of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0026] Figure 6Schematic enlarged structure view of location A of a lithium battery heavy object impact test detection device according to an embodiment of the present invention;

[0027] Main component symbol descriptions are as follows:

[0028] Base 1, column 2, top plate 3, transmission mechanism 4, drive motor 5, lead screw 6, nut moving seat 7, lifting electromagnet 8, load plate 9, guide sleeve 10, clearance groove 11, counterweight frame 12, positioning column 13, counterweight block 14, locking column 15, locking block 16, hammer head 17, protective cover 18, first synchronous pulley 19, synchronous belt 20, second synchronous pulley 21, bearing seat 22, assembly groove 23, assembly seat 24, plugging block 25, side plate 26, first spring seat 27, spring 28, second spring seat 29, clamping plate 30, triangular reinforcing rib 31, fence plate 32, movable door 33, transparent observation plate 34, plug seat 35, limit groove 36, L-shaped plug 37, socket 38. Specific implementation manners

[0029] In order to enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments.

[0030] Embodiment 1, as shown in Figure 1 、 Figure 2 and Figure 3 shown, a lithium battery heavy object impact test detection device, columns 2 are installed on four sides of the top of the base 1, a top plate 3 is installed on the top of the columns 2, a transmission mechanism 4 is installed on the top of the top plate 3, the transmission mechanism 4 is connected to a drive motor 5, output ends on both sides of the transmission mechanism 4 are connected to lead screws 6, the lead screws 6 are rotatably installed vertically between the base 1 and the top plate 3, the lead screws 6 are connected to nut moving seats 7, a lifting electromagnet 8 is installed between the two nut moving seats 7, the lifting electromagnet 8 is magnetically connected to a load plate 9, guide sleeves 10 are installed on four sides of the load plate 9, the guide sleeves 10 are slidably installed on the columns 2, a clearance groove 11 is provided on the load plate 9 corresponding to the lead screws 6, the lead screws 6 are arranged in the clearance groove 11, a counterweight frame 12 is installed at the bottom of the load plate 9, a positioning column 13 is provided at the center of the counterweight frame 12, several counterweight blocks 14 are sleeved outside the positioning column 13, the several counterweight blocks 14 are sequentially stacked up and down on the counterweight frame 12, locking columns 15 are installed on four sides of the top of the counterweight frame 12, the tops of the locking columns 15 penetrate through the load plate 9 and extend to the upper side thereof, locking blocks 16 are installed at the tops of the locking columns 15, and a hammer head 17 is installed at the bottom of the counterweight frame 12.

[0031] In this embodiment, during use, first install the hammer head 17 at the bottom of the counterweight frame 12, and place the hammer head 17 on the base 1 first. Then, according to the impact weight to be tested, place appropriate counterweight blocks 14 on the positioning posts 13 on the counterweight frame 12. After that, drive the motor 5 to drive the transmission mechanism 4. The transmission mechanism 4 drives the two-sided lead screws 6 to rotate, causing the lead screws 6 to drive the nut moving seats 7. The nut moving seats 7 drive the lifting electromagnet 8. The lifting electromagnet 8 drives the load plate 9, and the load plate 9 drives the guide sleeve 10 to slide downward along the column 2 until the load plate 9 is installed on the top of the counterweight frame 12. After the locking post 15 on the counterweight frame 12 passes through the load plate 9, the lifting electromagnet 8 is powered off, causing the magnetism between the lifting electromagnet 8 and the load plate 9 to disappear. At this time, drive the motor 5 to drive the transmission mechanism 4 to reverse, causing the lifting electromagnet 8 to move upward. Then install a locking block 16 on the top of the locking post 15 to install the counterweight frame 12 on the load plate 9. Then control the lifting electromagnet 8 to move downward again, contact with the load plate 9, and make the lifting electromagnet 8 energized to generate magnetic attraction connection with the load plate 9. Then drive the transmission mechanism 4 through the drive motor 5 to drive the two-sided lead screws 6 to rotate, causing the lead screws 6 to drive the nut moving seats 7. The nut moving seats 7 drive the lifting electromagnet 8. The lifting electromagnet 8 drives the load plate 9, and the load plate 9 drives the guide sleeve 10 to move upward along the column 2, thereby causing the load plate 9 to drive the counterweight frame 12, and the counterweight frame 12 to drive the hammer head 17 to move upward. After the hammer head 17 moves upward, place the lithium battery to be tested on the base 1. At this time, a heavy object impact test can be carried out. By powering off the lifting electromagnet 8, the magnetism between the lifting electromagnet 8 and the load plate 9 disappears, and the load plate 9 quickly drops downward under the effect of the gravity of the lower counterweight frame 12, so that the hammer head 17 impacts on the lithium battery to achieve the heavy object impact test detection. During the rapid drop of the load plate 9, the four-sided guide sleeve 10 slides along the column 2, so that the hammer head 17 will not shake and will not deviate from the predetermined direction when falling, improving the impact accuracy.

[0032] Embodiment 2, as Figure 2 shown, on the basis of Embodiment 1, the following structure is added to this embodiment. A protective cover 18 is installed on the top of the top plate 3, the drive motor 5 is installed on the protective cover 18, the transmission mechanism 4 is installed inside the protective cover 18. The transmission mechanism 4 includes a first synchronous pulley 19, the first synchronous pulley 19 is connected with a synchronous belt 20, the other side of the synchronous belt 20 is connected with a second synchronous pulley 21, the first synchronous pulley 19 and the second synchronous pulley 21 are respectively connected with the tops of the two-sided lead screws 6, and the power output end of the drive motor 5 is connected with the first synchronous pulley 19.

[0033] In this embodiment, during use, the driving motor 5 drives the first synchronous pulley 19 to rotate. The first synchronous pulley 19 drives the synchronous belt 20, and the synchronous belt 20 drives the second synchronous pulley 21 to rotate synchronously, causing the first synchronous pulleys 19 and the second synchronous pulleys 21 on both sides to drive the lead screw 6 to rotate synchronously. Furthermore, the nut moving seats 7 on the lead screws 6 on both sides drive the lifting electromagnet 8 to move upward or downward, improving the use effect. At the same time, the protective cover 18 protects the transmission mechanism 4, reducing the situation where the transmission mechanism 4 is affected by the outside world and its service life is shortened.

[0034] Embodiment 3, as Figure 2 and Figure 3 shown, on the basis of Embodiment 1, this embodiment adds the following structure. Bearing seats 22 are installed on both the upper and lower sides of the lead screw 6. The upper bearing seat 22 is installed at the bottom of the top plate 3, and the lower bearing seat 22 is installed on the base 1.

[0035] In this embodiment, when the first synchronous pulleys 19 and the second synchronous pulleys 21 on both sides drive the lead screw 6 to rotate synchronously, the lead screw 6 rotates along the bearing seats 22 on both the upper and lower sides, enabling the lead screw 6 to perform a stable rotational movement. Furthermore, it ensures that the nut moving seat 7 drives the lifting electromagnet 8 to have a stable moving effect when moving upward or downward.

[0036] Embodiment 4, on the basis of Embodiment 1, this embodiment adds the following structure. A lubricating oil groove is formed on the surface of the column 2, and the lubricating oil groove is arranged in a spiral or annular structure.

[0037] In this embodiment, by setting the lubricating oil groove in a spiral or annular structure and filling lubricating oil in the lubricating oil groove, the guide sleeve 10 slides more smoothly along the column 2, is not easily stuck, and meets the impact test detection for the rapid descent of heavy objects.

[0038] Embodiment 5, on the basis of Embodiment 1, this embodiment adds the following structure. The guide sleeve 10 is provided with a number of mounting holes, and graphite particles are installed in the mounting holes. The guide sleeve 10 is made of bronze material.

[0039] In this embodiment, during use, the graphite particles on the guide sleeve 10 can form a protective film during the friction process, reducing the friction damage between the guide sleeve 10 and the column 2, thereby extending the overall service life and saving costs.

[0040] Embodiment 6, as Figure 4 shown, on the basis of Embodiment 1, this embodiment adds the following structure. An assembly groove 23 is provided at the bottom of the counterweight frame 12. An assembly seat 24 is installed in the assembly groove 23. The hammer head 17 is installed at the bottom of the assembly seat 24. The hammer head 17 and the assembly seat 24 are integrally formed. A sealing block 25 is installed outside the assembly seat 24 in the assembly groove 23.

[0041] In this embodiment, during installation, the fitting seat 24 at the bottom of the hammer head 17 is inserted into the fitting groove 23 at the bottom of the counterweight frame 12, and a blocking block 25 is installed outside the fitting seat 24 to limit and fix the installation of the fitting seat 24, ensuring the installation and use of the hammer head 17.

[0042] Embodiment 7. On the basis of Embodiment 1, the following structure is added to this embodiment. A piercing head can also be installed at the bottom of the fitting seat 24.

[0043] In this embodiment, during use, the hammer head 17 can also be replaced with a piercing head to facilitate piercing test detection and improve the use effect.

[0044] Embodiment 8, as Figure 1 and Figure 2 shown, on the basis of Embodiment 1, the following structure is added to this embodiment. Side plates 26 are installed on both sides of the surface of the base 1. A number of first spring seats 27 are installed on the side plates 26. Springs 28 are installed in the first spring seats 27. The free end of the spring 28 is connected to a second spring seat 29. The second spring seat 29 is connected to a clamping plate 30. The clamping plate 30 is locked and connected to the second spring seat 29 by screws. Triangular reinforcing ribs 31 are installed on both sides of the side plates 26. The bottom of the triangular reinforcing ribs 31 is welded and installed on the base 1.

[0045] In this embodiment, after the lithium battery is placed on the base 1, the springs 28 on both sides will push the second spring seat 29, and the second spring seat 29 will push the clamping plate 30 to clamp and fix the lithium battery in the center, facilitating the subsequent impact test detection of the hammer head 17. When the lithium battery expands after being impacted, the expansion force pushes the clamping plate 30, and the clamping plate 30 squeezes the spring 28. The spring 28 plays a buffering role. If the lithium battery explodes, the explosion force acts on the clamping plate 30, and the elastic potential energy of the spring 28 further absorbs the explosion energy, reducing the damage to the detection equipment. After the detection is completed, if the clamping plate 30 is damaged due to the explosion of the lithium battery, only the damaged clamping plate 30 needs to be removed and a new clamping plate is replaced to conduct the test again, reducing the equipment maintenance cost.

[0046] Embodiment 9, as Figure 5 shown, on the basis of Embodiment 1, the following structure is added to this embodiment. A fence plate 32 is installed on the outside of the base 1 by bolt locking. A movable door 33 is hingedly installed on one side of the fence plate 32. A transparent observation plate 34 is installed on the movable door 33.

[0047] In this embodiment, during the use and detection process, the internal impact test state can be observed through the transparent observation plate 34. When the lithium battery explodes, the fence plate 32 can block the explosion force and prevent harm to nearby staff.

[0048] Embodiment 10, as shown in Figure 6 shown, on the basis of Embodiment 1, the following structure is added in this embodiment. Plug seats 35 are installed on the upper and lower sides of the movable door 33. Limiting grooves 36 are provided on both sides of the plug seat 35. An L-shaped plug 37 is slidably installed in the plug seat 35. One side of the L-shaped plug 37 is placed in one of the limiting grooves 36, and the other side of the L-shaped plug 37 is connected to a socket 38, and the socket 38 is installed on the fence panel 32.

[0049] In this embodiment, after the lithium battery is placed on the base 1, the movable door 33 is closed, and the L-shaped plug 37 in the plug seat 35 is pushed to insert into the socket 38 for locking. Then the L-shaped plug 37 is rotated so that one side of the L-shaped plug 37 is caught in the limiting groove 36 to complete the limiting fixation, so that the movable door 33 is closed, and subsequent detection work can be carried out.

[0050] The above embodiments only exemplarily illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A lithium battery heavy object impact test detection device, characterized in that: It includes a base (1), columns (2) are installed on four sides of the top of the base (1), a top plate (3) is installed on the top of the columns (2), a transmission mechanism (4) is installed on the top of the top plate (3), the transmission mechanism (4) is connected to a driving motor (5), output ends on both sides of the transmission mechanism (4) are connected to lead screws (6), the lead screws (6) are rotatably installed vertically between the base (1) and the top plate (3), the lead screws (6) are connected to nut moving seats (7), a lifting electromagnet (8) is installed between the two nut moving seats (7), the lifting electromagnet (8) is magnetically connected to a load plate (9), guide sleeves (10) are installed on four sides of the load plate (9), the guide sleeves (10) are slidably installed on the columns (2), an avoidance groove (11) is provided on the load plate (9) corresponding to the lead screws (6), the lead screws (6) are arranged in the avoidance groove (11), a counterweight frame (12) is installed at the bottom of the load plate (9), a positioning column (13) is provided at the center of the counterweight frame (12), a number of counterweight blocks (14) are sleeved on the outside of the positioning column (13), the number of counterweight blocks (14) are stacked on top of each other on the counterweight frame (12) in sequence, locking columns (15) are installed on four sides of the top of the counterweight frame (12), the tops of the locking columns (15) penetrate through the load plate (9) and extend to its upper side, a locking block (16) is installed at the top of the locking columns (15), and a hammer head (17) is installed at the bottom of the counterweight frame (12).

2. The lithium battery heavy object impact test detection device according to claim 1, wherein: A protective cover (18) is installed on the top of the top plate (3), the driving motor (5) is installed on the protective cover (18), the transmission mechanism (4) is installed inside the protective cover (18), the transmission mechanism (4) includes a first synchronous belt pulley (19), the first synchronous belt pulley (19) is connected to a synchronous belt (20), the other side of the synchronous belt (20) is connected to a second synchronous belt pulley (21), the first synchronous belt pulley (19) and the second synchronous belt pulley (21) are respectively connected to the tops of the lead screws (6) on both sides, and the power output end of the driving motor (5) is connected to the first synchronous belt pulley (19).

3. A lithium battery heavy object impact test detection device according to claim 2, characterized in that: Bearing seats (22) are installed on both the upper and lower sides of the lead screw (6), wherein the upper bearing seat (22) is installed at the bottom of the top plate (3), and the lower bearing seat (22) is installed on the base (1).

4. A lithium battery heavy object impact test detection device according to claim 3, characterized in that: A lubricating oil groove is formed on the surface of the column (2), and the lubricating oil groove is arranged in a spiral or annular structure.

5. The lithium battery heavy object impact test detection device according to claim 4, characterized in that: A number of mounting holes are provided on the guide sleeve (10), graphite particles are installed in the mounting holes, and the guide sleeve (10) is made of bronze material.

6. The lithium battery heavy object impact test detection device according to claim 5, wherein: An assembly groove (23) is provided at the bottom of the counterweight frame (12), an assembly seat (24) is installed in the assembly groove (23), the hammer head (17) is installed at the bottom of the assembly seat (24), the hammer head (17) and the assembly seat (24) are integrally formed, and a sealing block (25) is installed on the outside of the assembly seat (24) in the assembly groove (23).

7. The lithium battery heavy object impact test detection device according to claim 6, characterized in that: A puncture head can also be installed at the bottom of the assembly seat (24).

8. The lithium battery heavy object impact test detection device according to claim 7, wherein: On both sides of the surface of the base (1), side plates (26) are installed. A number of first spring seats (27) are installed on the side plates (26). Springs (28) are installed in the first spring seats (27). The free ends of the springs (28) are connected to second spring seats (29). The second spring seats (29) are connected to clamping plates (30). The clamping plates (30) are tightly connected to the second spring seats (29) by screws. Triangular reinforcing ribs (31) are installed on both sides of the side plates (26). The bottoms of the triangular reinforcing ribs (31) are welded and installed on the base (1).

9. The lithium battery heavy object impact test detection device according to claim 8, wherein: A fence plate (32) is tightly installed on the outside of the base (1) by bolts. A movable door (33) is hingedly installed on one side of the fence plate (32). A transparent observation plate (34) is installed on the movable door (33).

10. A lithium battery heavy object impact test detection device according to claim 9, characterized in that: Plug sockets (35) are installed on the upper and lower sides of the movable door (33). Limiting grooves (36) are provided on both sides of the plug sockets (35). An L-shaped plug (37) is slidably installed in the plug sockets (35). One side of the L-shaped plug (37) is placed in one of the limiting grooves (36). The other side of the L-shaped plug (37) is connected to a socket (38). The socket (38) is installed on the fence plate (32).

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