Tearing force jacking mechanism

Abstract

The invention relates to a tearing force jacking mechanism. The tearing force jacking mechanism relates to the technical field of jacking mechanisms. The tearing force jacking mechanism comprises a servo motor module, a ball screw module and a jacking block module, wherein the servo motor module comprises a servo motor; the ball screw module comprises a ball screw; the top block module comprises a top block; when the servo motor module is started, the ball screw is used for driving the top block to ascend, so that the bottom of the cable is pushed, and material taking and tearing force testing are achieved. Through the structure of the servo motor and the ball screw, the purpose of testing the tearing force of the terminal is achieved in a torsion control mode. According to the requirements of customers and the required tearing force, the output torque of the servo motor is designed, the ejector block is started to push a welded finished product, and if the finished product is not damaged under set data, the welding of the product is qualified. According to the test, the test can be carried out on welded equipment under the condition that the welded equipment is not damaged.

Description

Technical Field

[0001] The invention belongs to the technical field of lifting mechanisms, and in particular relates to a tearing force lifting mechanism. Background Art

[0002] ‌Welding cables and copper sheets together is mainly used to make photovoltaic junction boxes. In photovoltaic systems, photovoltaic junction boxes are key components that connect photovoltaic panels and inverters. Their function is to connect multiple photovoltaic cells in series or in parallel to achieve current collection and distribution. The quality of welding directly affects the current transmission efficiency and the durability of the system.

[0003] In the manufacturing process of photovoltaic junction boxes, automated welding technology is usually used to ensure welding quality. This technology ensures that the connection between the copper wire and the copper sheet is stable and has excellent conductivity by accurately controlling the welding temperature, time and pressure. In addition, by using advanced automated equipment, production efficiency can be improved, manual operation errors can be reduced, and scrap rates can be reduced.

[0004] Reliable welding can not only ensure efficient transmission of current, but also improve the overall durability of the photovoltaic system. Problems such as cold welding and overheating during welding will affect the welding quality, and thus affect the service life of the photovoltaic connector and the stability of the system. Therefore, high-quality welding technology is crucial for the long-term stable operation of the photovoltaic system.

[0005] In the prior art, the material taking mechanism or testing mechanism commonly used when welding cables and copper sheets is driven by a cylinder, which has the following disadvantages: First, the structural space occupancy rate is relatively large.

[0006] Second, the driving torque is not large enough and the value cannot be fed back.

[0007] Third, the workpiece needs to be taken out and tested to see if it meets the requirements.

[0008] Therefore, a tearing force lifting mechanism is proposed to solve the above-mentioned drawbacks. Summary of the invention

[0009] The purpose of the present invention is to provide a tearing force lifting mechanism with simple structure and reasonable design in order to solve the above problems.

[0010] The present invention achieves the above-mentioned purpose through the following technical solutions: The tearing force lifting mechanism comprises a servo motor module, a ball screw module and a lifting block module, wherein the servo motor module comprises a servo motor; The ball screw module includes a ball screw; Among them, the servo motor drives the ball screw to rotate and rise at the same time; The top block module includes a top block; Wherein, the top block is arranged above the ball screw; When the servo motor module is started, the ball screw is used to drive the top block to rise, thereby pushing the bottom of the cable to achieve material removal and tear force testing.

[0011] As a further optimization solution of the present invention, a welding table is also included, and the servo motor module, the ball screw module and the top block module are integrated and arranged above the welding table.

[0012] As a further optimization solution of the present invention, a support frame is fixedly installed on the upper surface of the welding table, and a welding head is installed below the support frame, and the welding head is used for welding cables and copper sheets.

[0013] As a further optimization solution of the present invention, a bottom felt is fixedly provided on the upper surface of the welding table, and the copper sheet is attached to the upper surface of the bottom felt, and the copper sheet is directly opposite to the bottom of the welding head.

[0014] As a further optimization scheme of the present invention, a wire clamping cylinder and a wire clamping block are installed on the upper surface of the welding table. The wire clamping block is arranged in a sliding manner. When the wire clamping cylinder is started, it drives the wire clamping block to achieve relative clamping and relative separation. The cable clamp is fixed on the wire clamping block.

[0015] As a further optimization scheme of the present invention, a column is fixedly installed on the upper surface of the welding table, the ball screw is cooperatively arranged inside the column, a servo motor is arranged below the ball screw, and a top block is arranged above the ball screw.

[0016] As a further optimization solution of the present invention, the top block is located between the copper sheet and the wire clamping block.

[0017] As a further optimization solution of the present invention, a groove is provided on the upper surface of the top block, and a pressure sensor is installed in the groove.

[0018] As a further optimization solution of the present invention, the welding table is provided with a handheld tablet, which is used to display the value of the pressure sensor, and the handheld tablet is connected to the pressure sensor through a controller; When the top block is pushed up and pressed under the cable, the pressure sensor is pressed to test the tearing force of the cable, and the controller controls the value monitored by the pressure sensor to be fed back to the handheld tablet for display.

[0019] As a further optimization scheme of the present invention, the top block is slidably arranged inside the column, an upper sealing plate is fixedly arranged inside the upper end of the column, a circular hole is arranged in the middle of the upper sealing plate, a top rod is fixedly arranged in the middle of the upper surface of the top block, the upper end of the top rod extends out from the upper end of the circular hole, and the diameter of the top rod is smaller than the diameter of the circular hole, and an air cavity is formed between the upper surface of the top block and the lower surface of the upper sealing plate.

[0020] As a further optimization solution of the present invention, the welding head is provided with a motor, and the motor is used to drive the welding head to rotate; The upper and lower sides of the welding head are both corrugated pressing surfaces, and the left and right sides of the welding head are both flat pressing surfaces; A trapezoidal extrusion block is arranged on one side of the welding head away from the motor; An electric heating tube is arranged in the welding head.

[0021] The beneficial effect of the present invention is that the present invention uses a servo motor and a ball screw structure and a torque control mode to achieve the purpose of testing the tearing force of the terminal.

[0022] The present invention is based on the tearing force required by the customer, and the output torque of the servo motor is designed. The top block is started to push the welded finished product. If the finished product is not damaged under the set data, it means that the product welding is qualified. The test can be carried out on the welding equipment without being damaged.

[0023] Traditional testing can only be done by removing the device from the welding machine and then performing destructive testing. Therefore, the testing efficiency of the present invention is high.

[0024] The present invention can also make the cable be lifted up by the lifting block by controlling the ball screw and the servo motor, and complete the material taking when the cable is clamped by the clamping block, and has many functions.

[0025] In the present invention, when the motor drives the welding head to rotate, the corrugated pressing surface or the flat pressing surface can be aligned with the top of the cable, so that the cable end is flattened. After the cable end is flattened, the bonding force between the cable end and the copper sheet is higher.

[0026] In the present invention, if the overall diameter of the cable is relatively thick or there are other situations where it is difficult to press together, the cable can also be pressed together using the corrugated pressing surface, so that the cable has a higher bonding strength with the copper sheet structure after the corrugated surface is formed.

[0027] When the trapezoidal extrusion block in the present invention squeezes the cable end, the cable can be squeezed out of the wire clamping block, which is convenient for material removal. In addition, based on the fact that the trapezoidal extrusion block can squeeze the cable to move, it is also convenient to adjust the cable position, thereby controlling the length of the pressed position of the cable end, which is convenient for use according to actual needs.

[0028] In the present invention, an electric heating tube is also provided inside the welding head. When the electric heating tube is started, it can transfer heat to the cable, thereby heating the cable during the welding process, further improving the welding efficiency and the bonding strength between the structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of the tearing force lifting mechanism of the present invention; Figure 2It is a schematic diagram of the surface structure of the welding table of the present invention; Figure 3 is a top view of the tearing force lifting mechanism of the present invention; Figure 4 is a cross-sectional view of the tearing force lifting mechanism in Example 1 of the present invention; Figure 5 is a cross-sectional view of a tearing force lifting mechanism in Example 2 of the present invention; Figure 6 The present invention Figure 5 A schematic diagram of the structure enlargement in the middle; Figure 7 is a cross-sectional view of a tearing force lifting mechanism in Example 3 of the present invention; Figure 8 It is a schematic diagram of the welding head structure in Example 4 of the present invention.

[0030] In the figure: welding head 1, bottom felt 2, copper sheet 3, cable 4, wire clamping block 5, wire clamping cylinder 6, round hole 7, ball screw 8, servo motor 9, welding table 10, support frame 11, column 12, top block 13, groove 14, pressure sensor 15, push rod 16, upper sealing plate 17, air cavity 18, motor 19, flat pressing surface 20, corrugated pressing surface 21, trapezoidal extrusion block 22, electric heating tube 23. DETAILED DESCRIPTION

[0031] The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0032] In Example 1, Figure 1 , Figure 2 As shown, the tearing force lifting mechanism includes a welding table 10, a support frame 11 is installed above the welding table 10, a welding head 1 is arranged on the support frame 11, and the welding head 1 uses ultrasonic welding to weld and fix the cable 4 on the copper sheet 3, a bottom felt 2 is installed on the upper surface of the welding table 10, the copper sheet 3 is placed on the bottom felt 2, a column 12 is arranged on one side of the bottom felt 2, and a top block 13 is arranged on the top of the column 12 for lifting.

[0033] refer to Figure 3 and Figure 4As shown, a ball screw 8 is arranged inside the column 12, and the lower end of the ball screw 8 is connected to a servo motor 9. A wire clamping block 5 is arranged on the side of the column 12 away from the bottom felt 2. The wire clamping block 5 is controlled by a wire clamping cylinder 6. The specific control method is not described here. It is a common clamping and fixing mechanism. The cable 4 is clamped and fixed on the wire clamping block 5, and the end of the copper sheet 3 away from the wire clamping block 5 is movably fitted on the top block 13 and the upper surface of the copper sheet 3 in turn.

[0034] refer to Figure 4 As shown in the figure, the present invention uses a torque control mode through the structure of a servo motor 9 and a ball screw 8 to achieve the purpose of testing the tearing force of the terminal. Other principles and basic structures that are the same or similar to those of this embodiment are within the protection scope of the present invention.

[0035] Specific implementation ideas: The tearing force lifting mechanism of the present invention is divided into a servo motor module, a ball screw module and a top block module. The servo motor 9 drives the ball screw 8 to realize the up and down movement of the top block 13, thereby achieving the purpose of measuring the tearing force. The top block 13 is rotatably arranged above the ball screw 8.

[0036] The action flow is as follows: Put the copper sheet 3 on the bottom felt 2, and then put the cable 4 to be welded on the copper sheet 3, and start the wire clamping cylinder 6 to clamp and fix the cable 4 on the wire clamping block 5.

[0037] The ultrasonic welding is started to make the welding head 1 vibrate at a high frequency, so as to achieve welding between the cable 4 and the copper sheet 3 .

[0038] It should be noted that ultrasonic welding uses high-frequency vibration waves to be transmitted to the surfaces of two objects to be welded. Under pressure, the surfaces of the two objects rub against each other to form a fusion between the molecular layers.

[0039] Specifically, ultrasonic welding converts 50 / 60 Hz current into 15, 20, 30 or 40KHz electrical energy through an ultrasonic generator. The converted high-frequency electrical energy is converted again into mechanical motion of the same frequency through a transducer, and then the mechanical motion is transmitted to the welding head through a set of amplitude-changing rod devices that can change the amplitude. The welding head transmits the received vibration energy to the joint of the workpiece to be welded. In this area, the vibration energy is converted into heat energy by friction to melt the plastic. Ultrasonic waves can not only be used to weld hard thermoplastics, but also to process fabrics and films.

[0040] The main components of an ultrasonic welding system include an ultrasonic generator, a transducer / amplifier / weld head triplex, a mold and a frame.

[0041] Linear vibration friction welding uses the friction heat energy generated on the contact surface of two workpieces to be welded to melt the plastic. The heat energy comes from the reciprocating movement of one workpiece on another surface with a certain displacement or amplitude under a certain pressure. Once the desired welding degree is reached, the vibration will stop, and at the same time, a certain pressure will still be applied to the two workpieces to cool and solidify the parts just welded, thus forming a tight bond.

[0042] Orbital vibration friction welding is a welding method that uses friction heat. During orbital vibration friction welding, the upper workpiece moves in an orbit at a fixed speed - a circular motion in all directions. The movement can generate heat energy, which can bring the welding parts of the two plastic parts to the melting point. Once the plastic begins to melt, the movement stops, and the welding parts of the two workpieces will solidify and be firmly connected together. The small clamping force will cause minimal deformation of the workpiece. Workpieces with a diameter of less than 10 inches can be welded using orbital vibration friction.

[0043] After welding is completed, how to judge whether the welded product meets the relative tearing force requirements requires testing the welded product.

[0044] According to customer requirements, the tearing force is required, and the output torque of the servo motor 9 is designed. The top block 13 is started to push the welded finished product. If the finished product is not damaged under the set data, it means that the product welding is qualified. This test can be carried out on the welding equipment without being damaged.

[0045] Traditional testing can only be done by removing the device from the welding machine and then performing destructive testing. Therefore, the testing efficiency of the present invention is high.

[0046] The benefits of welding the cable 4 and the copper sheet 3 together in the present invention mainly include the following aspects: ‌Excellent electrical conductivity‌: Copper is a metal material with excellent electrical conductivity. The resistivity of the connection parts after welding is extremely low or close to zero, which has better conductivity and can improve durability‌.

[0047] ‌High density of welding parts‌: The cross-section density of the welding parts of the ultrasonic copper stranded wire welding machine is better, and it is not easy to form voids, thus ensuring the stability and reliability of the welding points‌.

[0048] ‌Not easy to heat up and oxidize‌: The welding point is not easy to heat up, and there will be no heat accumulation, which will cause local temperature rise and form a potential quality risk point of cable 4 burning. In addition, the welding inside is minimally affected by external moisture, dust, oil and gas and other adverse factors, and it is not easy to cause copper wire rust, oxidation and other adverse conditions, thereby maintaining the electrical conductivity and signal transmission performance of the cable 4‌.

[0049] ‌Long-term stability‌: For the centralized ground wire of cable 4, ultrasonic welding technology is used. After long-term use, the conductivity will not decrease due to rust and oxidation of the copper wire inside the welding point, ensuring the stability of the vehicle's electrical functions‌.

[0050] Specifically, refer to Figure 2 As shown in the figure, the wire clamping block 5 is composed of a pair of clamping plates, each set of clamping plates is composed of a plurality of trapezoidal plates, and the plurality of trapezoidal plates are staggered with each other, so that when a pair of clamping plates are engaged with each other, the trapezoidal plates are staggered and engaged with each other, so that the cable 4 can be clamped and fixed in the wire clamping block 5, thereby achieving the purpose of clamping and fixing the cable 4 to adapt to the diameter size.

[0051] It should be noted that the rotating shaft on the wire clamping cylinder 6 is connected to a screw structure, and the wire clamping block 5 achieves the purpose of relative engagement or separation through the screw structure. The screw structure is a common mechanism for controlling the movement of objects and will not be described in detail here.

[0052] Specifically, the ball screw is an ideal product for converting rotary motion into linear motion, or converting linear motion into rotary motion. It is the most commonly used transmission element in tool machinery and precision machinery. Its main function is to convert rotary motion into linear motion, or to convert torque into axial repetitive force. Due to its small friction resistance, the ball screw is widely used in various industrial equipment and precision instruments. There are two common circulation methods: external circulation and internal circulation. The ball screw consists of a screw, a nut, a steel ball, a pre-loaded sheet, a reverser, and a dust collector. It has the characteristics of high precision, reversibility and high efficiency.

[0053] The present invention can also make the cable 4 be lifted up by the lifting block 13 by controlling the ball screw 8 and the servo motor 9, and complete the material removal when the cable 4 is clamped by the clamping block 5, which has many functions.

[0054] In Example 2, reference Figure 5 and Figure 6 As shown in the figure, a groove 14 is provided on the upper surface of the top block 13, and a pressure sensor 15 is provided in the groove 14. The welding table 10 is also equipped with a handheld tablet, and the handheld tablet and the pressure sensor 15 are connected through a controller. When the pressure sensor 15 monitors the value of the jacking cable 4 of the top block 13, the controller can send the value to the handheld tablet through a wireless sending device for display, and can display specific test values, which is better than the existing technology.

[0055] It should be noted that the reference Figure 2As shown in the figure, when the cable 4 is welded on the copper sheet 3, one end of the cable 4 is clamped and fixed by the wire clamping block 5, and the other end of the cable 4 is pressed and fixed on the bottom felt 2 by the welding head 1. Therefore, when the servo motor 9 is started to drive the ball screw 8 to rotate, the ball screw 8 drives the top block 13 to rise, and the top block 13 can push the cable 4 from the bottom position of the cable 4, so that the tearing force of the cable 4 can be tested after welding.

[0056] In Example 3, reference Figure 7 As shown in the figure, an upper sealing plate 17 is fixedly arranged inside the upper part of the column 12, a circular hole 7 is arranged in the middle of the upper sealing plate 17, a top block 13 is slidably arranged inside the column 12, a top rod 16 is fixedly arranged in the middle of the upper surface of the top block 13, the diameter of the top rod 16 is smaller than the diameter of the circular hole 7, the upper end of the top rod 16 extends out from the circular hole 7, and an air cavity 18 is formed between the upper surface of the top block 13 and the bottom of the upper sealing plate 17.

[0057] When the servo motor 9 is started, the ball screw 8 rotates and rises, and the ball screw 8 rotates and rises, while driving the top block 13 and the top rod 16 to rise. The top rod 16 extends from the upper end of the circular hole 7 and presses the lower surface of the cable 4 to achieve the purpose of testing the tearing force and taking the material.

[0058] Furthermore, when the top block 13 rises, the gas in the air cavity 18 is pushed to be discharged from the gap between the circular hole 7 and the top rod 16, and the gas is blown to the bottom of the cable 4, thereby blowing away the dust on the surface of the cable 4, and removing impurities such as welding slag formed by welding between the cable 4 and the copper sheet 3, thereby achieving the purpose of synchronous dust removal.

[0059] In Example 4, reference Figure 8 As shown in the figure, a motor 19 is arranged on the welding head 1, and the motor 19 can drive the welding head 1 to rotate as a whole, and the upper and lower sides of the welding head 1 are both corrugated pressing surfaces 21, and the left and right sides of the welding head 1 are both flat pressing surfaces 20. When the motor 19 drives the welding head 1 to rotate, the corrugated pressing surface 21 or the flat pressing surface 20 can be aligned above the cable 4, so as to flatten the end of the cable 4. After the end of the cable 4 is flattened, the bonding force between the copper sheet 3 is higher.

[0060] Furthermore, if the cable 4 has a relatively large overall diameter or is otherwise difficult to press together, the cable 4 can be pressed together using the corrugated pressing surface 21 , so that the cable 4 forms a corrugated surface and has a higher bonding strength with the copper sheet 3 .

[0061] Furthermore, a trapezoidal extrusion block 22 is provided on the side of the welding head 1 away from the motor 19. When the trapezoidal extrusion block 22 squeezes the end of the cable 4, the cable 4 can be squeezed out of the wire clamping block 5, which is convenient for material removal. Moreover, based on the fact that the trapezoidal extrusion block 22 can squeeze the cable 4 to move, it is also convenient to adjust the position of the cable 4, thereby controlling the length of the pressing position of the end of the cable 4, which is convenient for use according to actual needs.

[0062] The motor 19 is used in combination with the ultrasonic welding horn 1, which can apply ultrasonic welding to a wider range and facilitate adjustment according to the actual welding position or welding needs, replacing the existing technology in which the position needs to be stable and cannot be adjusted due to the high-frequency vibration requirements of the horn 1.

[0063] It should be noted that the motor 19 in the present invention uses some common shock-absorbing mechanisms in the prior art to achieve the purpose of shock absorption, thereby reducing the impact of the vibration of the welding head 1 on the motor 19 .

[0064] In the present invention, an electric heating tube 23 is further provided inside the welding head 1. When the electric heating tube 23 is started, it can transfer heat to the cable 4, thereby heating the cable 4 during the welding process, further improving the welding efficiency and the bonding strength between the structures.

[0065] The outer surface of the electric heating tube 23 is covered with a mesh metal layer, which can reduce the relative friction between the electric heating tube 23 and the external structure without affecting the heat transfer, thereby facilitating the adaptation to the vibration of the welding head 1.

[0066] It should be noted that the device for driving the welding head 1 to rise, fall and move in the present invention is an electric cylinder, etc., which has been shown in the figure and will not be described in detail here.

[0067] In another embodiment, a heating device such as a heating electrode sheet may be installed on the upper portion of the top rod 16 to heat the cable 4 when the top rod 16 is in contact with the cable 4, thereby testing the tear resistance of the cable 4 at different temperatures.

[0068] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. The tearing force lifting mechanism includes a servo motor module, a ball screw module and a lifting block module, characterized in that: The servo motor module comprises a servo motor (9); The ball screw module comprises a ball screw (8); The servo motor (9) drives the ball screw (8) to rotate and rise at the same time; The top block module comprises a top block (13); Wherein, the top block (13) is arranged above the ball screw (8); When the servo motor module is started, the ball screw (8) is used to drive the top block (13) to rise, thereby pushing the bottom of the cable (4) to achieve material removal and tear force testing.

2. The tearing force lifting mechanism according to claim 1, characterized in that: It also comprises a welding table (10), wherein the servo motor module, the ball screw module and the top block module are integrated and arranged above the welding table (10).

3. The tearing force lifting mechanism according to claim 2, characterized in that: A support frame (11) is fixedly mounted on the upper surface of the welding table (10), a welding head (1) is mounted below the support frame (11), and the welding head (1) is used to weld the cable (4) and the copper sheet (3).

4. The tearing force lifting mechanism according to claim 3, characterized in that: A bottom felt (2) is fixedly arranged on the upper surface of the welding table (10), the copper sheet (3) is attached to the upper surface of the bottom felt (2), and the copper sheet (3) is directly opposite to the bottom of the welding head (1).

5. The tearing force lifting mechanism according to claim 4, characterized in that: A wire clamping cylinder (6) and a wire clamping block (5) are mounted on the upper surface of the welding table (10); the wire clamping block (5) is arranged in a sliding manner; when the wire clamping cylinder (6) is started, the wire clamping block (5) is driven to achieve relative clamping and relative separation; and the cable (4) is clamped and fixed on the wire clamping block (5).

6. The tearing force lifting mechanism according to claim 5, characterized in that: A column (12) is fixedly mounted on the upper surface of the welding table (10), the ball screw (8) is cooperatively arranged inside the column (12), a servo motor (9) is arranged below the ball screw (8), and a top block (13) is arranged above the ball screw (8).

7. The tearing force lifting mechanism according to claim 6, characterized in that: The top block (13) is located between the copper sheet (3) and the wire clamping block (5); The upper surface of the top block (13) is provided with a groove (14), and a pressure sensor (15) is installed in the groove (14).

8. The tearing force lifting mechanism according to claim 3, characterized in that: The welding head (1) is provided with a motor (19), and the motor (19) is used to drive the welding head (1) to rotate; The upper and lower sides of the welding head (1) are both corrugated pressing surfaces (21), and the left and right sides of the welding head (1) are both flat pressing surfaces (20); A trapezoidal extrusion block (22) is provided on a side of the welding head (1) away from the motor (19); An electric heating tube (23) is provided in the welding head (1).

9. The tearing force lifting mechanism according to claim 7, characterized in that: The welding table (10) is provided with a handheld tablet, which is used to display the value of the pressure sensor (15), and the handheld tablet is connected to the pressure sensor (15) via a controller; When the top block (13) is pushed up and pressed under the cable (4), the pressure sensor (15) is pressed to test the tearing force of the cable (4), and the controller controls the value monitored by the pressure sensor (15) to be fed back to the handheld tablet display.

10. The tearing force lifting mechanism according to claim 6, characterized in that: The top block (13) is slidably arranged inside the column (12); an upper sealing plate (17) is fixedly arranged inside the upper end of the column (12); a circular hole (7) is arranged in the middle of the upper sealing plate (17); a top rod (16) is fixedly arranged in the middle of the upper surface of the top block (13); the upper end of the top rod (16) extends from the upper end of the circular hole (7); the diameter of the top rod (16) is smaller than the diameter of the circular hole (7); and an air cavity (18) is formed between the upper surface of the top block (13) and the lower surface of the upper sealing plate (17).

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