Vacuum testing mechanism for frequency converter stator testing

Abstract

This utility model relates to the field of variable frequency stator testing technology, specifically a vacuum testing mechanism for variable frequency stator testing. It includes a support frame, a housing on the outside of the support frame, and the support frame is screwed into the housing. A vacuum cover body is located below the connecting plate body. Bakelite boards are screwed onto the surface of the housing, and a high-sealing mechanism is provided between the bakelite boards and the housing surface. The connecting plate body and the vacuum cover body have convenient assembly mechanisms. This utility model not only makes it convenient for users to assemble the vacuum cover body onto the connecting plate body, but also ensures the stability of the vacuum cover body during use. Furthermore, it significantly improves the sealing between the vacuum cover body and the bakelite boards, resulting in more accurate test results when performing vacuum tests on the stator.

Description

Technical Field

[0001] This utility model relates to the field of frequency converter stator testing technology, specifically a vacuum testing mechanism for frequency converter stator testing. Background Technology

[0002] The motor stator is the stationary part of the motor. It consists of three parts: the stator core, the stator windings, and the frame. The main reason for testing the motor stator in a vacuum environment is to improve the sensitivity and accuracy of the test. In a vacuum environment, electrons are more active and easier to ionize, which makes it easier to detect minute problems that are difficult to detect in a normal environment. Existing vacuum testing mechanisms have some shortcomings in use. In order to meet the needs of the market, a vacuum testing mechanism for frequency converter stator testing is needed.

[0003] The poor sealing performance of existing vacuum testing mechanisms can lead to the infiltration of outside air, affecting the accuracy of the tests. This is especially true in the testing of high-voltage motor stator coils after vacuum impregnation, where the stator's ground pressure failure can cause problems. Furthermore, existing vacuum testing mechanisms are inconvenient to assemble and lack sufficient stability, making it difficult for users to assemble the vacuum cover onto the surface of the connecting plate. Additionally, the stability of the vacuum cover during use cannot be guaranteed. Moreover, the sealing performance of existing vacuum testing mechanisms needs further improvement, resulting in less accurate test results when performing vacuum tests on stators. Utility Model Content

[0004] The purpose of this invention is to provide a vacuum testing mechanism for testing frequency converter stators, in order to solve the problems mentioned in the background art, such as inconvenience in assembly, insufficient stability, and the need for further improvement in sealing.

[0005] To achieve the above objectives, this utility model provides the following technical solution: a vacuum testing mechanism for frequency converter stator testing, comprising a mechanism support, a housing provided on the outside of the mechanism support, the mechanism support being installed inside the housing by screws, two sets of mechanism supports, a controller being installed on the surface of the housing, linear guide rails being installed on the surface of each mechanism support by screws, lifting brackets being provided on the surface of each linear guide rail, the lifting brackets slidingly engaging with the surface of the linear guide rails, a connecting plate body being installed on the surface of each lifting bracket by screws, a vacuum cover body being provided below the connecting plate body, bakelite boards being installed on the surface of each housing by screws, a high-sealing mechanism being provided between the bakelite boards and the surface of the housing, and a convenient assembly mechanism being provided on the surface of the connecting plate body and the vacuum cover body.

[0006] Preferably, the surface of the mechanism support is provided with a guide groove, a buffer support is installed on the surface of the mechanism support by screws, a buffer body is installed on the surface of the buffer support, a cylinder body is installed inside the mechanism support by screws, the input end of the cylinder body is electrically connected to the output end of the controller, a cylinder connecting rod is installed on the output end of the cylinder body, one end of the cylinder connecting rod passes through the guide groove and is fixed to the surface of the lifting support, the cylinder connecting rod slides against the inner wall of the guide groove, there are two bakelite boards, the bakelite boards are located directly below the vacuum chamber body, the surface of the bottom position of the vacuum chamber body is in contact with the surface of the bakelite boards, and a test component is installed inside the controller.

[0007] Preferably, the high-sealing mechanism consists of a mounting stud, a clamping ring, a rectangular sealing ring, an O-ring, and a sealing ring. The interior of the chassis is provided with clamping rings for pressing the bakelite board. The inner wall of the clamping ring is in contact with the surface of the bakelite board. The surface of the clamping ring is threaded with a mounting stud. One end of the mounting stud passes through the clamping ring and is threadedly fastened to the surface of the chassis. The surface of the clamping ring is in contact with the surface of the vacuum chamber body.

[0008] Preferably, a rectangular sealing ring is installed on the surface of the bakelite board, and the surface of the rectangular sealing ring is in contact with the surface at the bottom of the vacuum chamber body. An O-ring is installed on the inner wall of the chassis, and the surface of the O-ring is in contact with the surface at the bottom of the bakelite board. A sealing ring is installed on the inner wall of the chassis, and the surface of the sealing ring is in contact with the surface at the bottom of the bakelite board.

[0009] Preferably, the easy assembly mechanism consists of mounting bolts, ball-end screws, hexagonal nuts, fastening bolts, a vacuum cover connecting plate, and a mounting plate. A vacuum cover connecting plate is provided on the surface of the top position of the vacuum cover body. Mounting bolts are threadedly connected to the surface of the vacuum cover connecting plate. One end of each mounting bolt passes through the vacuum cover connecting plate and is threadedly fastened to the surface of the vacuum cover body. A mounting plate is installed on the surface of the connecting plate body. Fastening bolts are threadedly connected to the surface of the vacuum cover connecting plate. One end of each fastening bolt passes through the mounting plate and is threadedly fastened to the surface of the vacuum cover connecting plate.

[0010] Preferably, a ball-head screw is provided on the surface of the top center position of the vacuum hood connecting plate. The ball-head screw is engaged with the surface of the vacuum hood connecting plate. The top end of the ball-head screw penetrates the connecting plate body and extends to the top of the connecting plate body. A hexagonal nut is threaded on the surface of the ball-head screw. The bottom surface of the hexagonal nut is in contact with the surface of the connecting plate body.

[0011] Compared with the prior art, the beneficial effects of this utility model are: the vacuum testing mechanism for frequency converter stator testing not only makes it convenient for users to assemble the vacuum cover body onto the surface of the connecting plate body, but also ensures the stability of the vacuum cover body during use. Furthermore, it greatly improves the sealing between the vacuum cover body and the bakelite board, making the test results of the vacuum testing mechanism more accurate when performing vacuum testing on the stator.

[0012] With a convenient assembly mechanism, the user places the vacuum chamber connecting plate on the top surface of the vacuum chamber body, then tightens the mounting bolts on the surface of the vacuum chamber connecting plate. The user then places the ball-head screw on the surface of the vacuum chamber connecting plate, causing the ball-head screw to drive the mounting plate into the interior of the vacuum chamber connecting plate. The user then tightens the hexagonal nut on the surface of the ball-head screw, and with the thread engagement between the ball-head screw and the hexagonal nut, the ball-head screw is installed on the surface of the connecting plate body. Subsequently, the user tightens the fastening bolts on the surface of the mounting plate, allowing the vacuum chamber body to be stably installed on the bottom surface of the connecting plate body for use. This achieves the function of convenient assembly of the vacuum testing mechanism, making it easy for the user to assemble the vacuum chamber body onto the surface of the connecting plate body during use, while ensuring the stability of the vacuum chamber body during use.

[0013] By incorporating a high-sealing mechanism, a clamping ring is installed inside the chassis using mounting studs. When the bakelite board is installed inside the chassis with screws, its surface contacts the inner wall of the clamping ring, pressing it firmly. As the vacuum chamber moves downwards, it contacts the surface of the rectangular sealing ring. At this point, the surface of the vacuum chamber contacts the inner wall of the clamping ring. The combined action of the clamping ring and the rectangular sealing ring improves the seal between the vacuum chamber and the bakelite board. When the bakelite board is installed inside the chassis, the combined action of the O-ring and the sealing ring further enhances the seal between the bakelite board and the chassis, achieving a high-sealing function for the vacuum testing mechanism. This significantly improves the seal between the vacuum chamber and the bakelite board during use, resulting in more accurate test results when performing vacuum tests on the stator. Attached Figure Description

[0014] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0015] Figure 2 This is a front view cross-sectional structural diagram of the present invention in its usage state;

[0016] Figure 3 This is an enlarged side cross-sectional view of the present invention in its usage state.

[0017] Figure 4 For the present utility model Figure 2 Enlarged structural diagram of a medium-to-high sealing mechanism;

[0018] Figure 5 For the present utility model Figure 3 An enlarged structural diagram of the convenient assembly mechanism.

[0019] In the diagram: 1. Mechanism support; 101. Lifting support; 102. Linear guide rail; 103. Vacuum chamber body; 104. Bakelite board; 105. Controller; 106. Chassis; 107. Buffer support; 108. Buffer body; 109. Guide groove; 110. Cylinder body; 111. Cylinder connecting rod; 112. Connecting plate body; 113. Test assembly; 2. High sealing mechanism; 21. Mounting stud; 22. Compression ring; 23. Rectangular sealing ring; 24. O-ring seal; 25. Sealing ring; 3. Easy assembly mechanism; 31. Mounting bolt; 32. Ball head screw; 33. Hex nut; 34. Fastening bolt; 35. Vacuum chamber connecting plate; 36. Mounting plate. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, not all embodiments. In addition, the terms "first", "second", "third", "upper", "lower", "left", "right", etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance. At the same time, in the description of the present utility model, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present utility model.

[0021] The structure of the vacuum testing mechanism for frequency converter stator testing provided by this utility model is as follows: Figure 1 , Figure 2 and Figure 3As shown, the device includes a mechanism support 1, with a housing 106 mounted on its outer side. The mechanism support 1 is installed inside the housing 106 by screws. There are two sets of mechanism supports 1. A controller 105 is mounted on the surface of the housing 106. The controller 105 can be of the LA series. Linear guide rails 102 are mounted on the surface of each mechanism support 1 by screws. Lifting brackets 101 are mounted on the surface of the linear guide rails 102. The lifting brackets 101 and the surfaces of the linear guide rails 102 slide against each other. A connecting plate body 112 is mounted on the surface of the lifting brackets 101 by screws. A guide groove 109 is formed on the surface of the mechanism support 1. A buffer bracket 107 is mounted on the surface of the mechanism support 1 by screws. A buffer body 108 is mounted on the surface of the buffer bracket 107. The interior of the mechanism support 1 is connected by screws. A cylinder body 110 is installed, and the cylinder body 110 model can be selected from the DNC series. The input end of the cylinder body 110 is electrically connected to the output end of the controller 105. A cylinder connecting rod 111 is installed at the output end of the cylinder body 110. One end of the cylinder connecting rod 111 passes through the guide groove 109 and is fixed to the surface of the lifting bracket 101. The cylinder connecting rod 111 and the inner wall of the guide groove 109 slide against each other. A vacuum cover body 103 is set below the connecting plate body 112. The surface of the chassis 106 is screwed with bakelite boards 104. There are two bakelite boards 104. The bakelite boards 104 are located directly below the vacuum cover body 103. The surface of the bottom position of the vacuum cover body 103 is in contact with the surface of the bakelite board 104. A test component 113 is installed inside the controller 105.

[0022] Furthermore, such as Figure 2 and Figure 4 As shown, the bakelite board 104 and the surface of the chassis 106 are provided with a high-sealing mechanism 2. The high-sealing mechanism 2 consists of a mounting stud 21, a clamping ring 22, a rectangular sealing ring 23, an O-ring sealing ring 24, and a sealing ring 25. The interior of the chassis 106 is provided with clamping rings 22 for pressing the bakelite board 104. The inner wall of the clamping ring 22 is in contact with the surface of the bakelite board 104. The surface of the clamping ring 22 is threaded with mounting studs 21. One end of the mounting stud 21 passes through the clamping ring 22 and is connected to the surface of the chassis 106. The threaded fasteners are tightened, and the surface of the clamping ring 22 contacts the surface of the vacuum chamber body 103. A rectangular sealing ring 23 is installed on the surface of the bakelite board 104, and the surface of the rectangular sealing ring 23 contacts the surface at the bottom of the vacuum chamber body 103. An O-ring 24 is installed on the inner wall of the chassis 106, and the surface of the O-ring 24 contacts the surface at the bottom of the bakelite board 104. A sealing ring 25 is installed on the inner wall of the chassis 106, and the surface of the sealing ring 25 contacts the surface at the bottom of the bakelite board 104.

[0023] During implementation, the user places the clamping ring 22 inside the chassis 106 and then tightens the mounting studs 21 on the surface of the clamping ring 22. The mounting studs 21 then install the clamping ring 22 inside the chassis 106. When the bakelite board 104 is installed inside the chassis 106 by screws, the surface of the bakelite board 104 contacts the inner wall of the clamping ring 22, pressing the bakelite board 104 firmly under the action of the clamping ring 22. When the vacuum chamber body 103 moves downwards, it moves downwards until it is aligned with the rectangular... When the surfaces of the sealing ring 23 are in contact, the surface of the vacuum chamber body 103 is in contact with the inner wall of the clamping ring 22. Under the combined action of the clamping ring 22 and the rectangular sealing ring 23, the sealing performance between the vacuum chamber body 103 and the bakelite board 104 is better. When the bakelite board 104 is installed inside the chassis 106, the sealing effect between the bakelite board 104 and the chassis 106 can be further improved under the combined action of the O-ring 24 and the sealing ring 25, so as to achieve the high sealing performance of the vacuum testing mechanism.

[0024] Furthermore, such as Figure 3 and Figure 5 As shown, the surfaces of the connecting plate body 112 and the vacuum chamber body 103 are provided with a convenient assembly mechanism 3. The convenient assembly mechanism 3 consists of mounting bolts 31, ball head screws 32, hexagonal nuts 33, fastening bolts 34, a vacuum chamber connecting plate 35, and a mounting plate 36. A vacuum chamber connecting plate 35 is provided on the surface of the top position of the vacuum chamber body 103. The surface of the vacuum chamber connecting plate 35 is threaded with mounting bolts 31. One end of the mounting bolt 31 passes through the vacuum chamber connecting plate 35 and is threadedly fastened to the surface of the vacuum chamber body 103. A mounting plate 36 is installed on the surface of the connecting plate body 112. All surfaces of the vacuum cover connecting plate 35 are threaded with fastening bolts 34. One end of the fastening bolt 34 passes through the mounting plate 36 and is threadedly fastened to the surface of the vacuum cover connecting plate 35. A ball head screw 32 is provided on the surface at the top center of the vacuum cover connecting plate 35. The ball head screw 32 is engaged with the surface of the vacuum cover connecting plate 35. The top end of the ball head screw 32 passes through the connecting plate body 112 and extends to the top of the connecting plate body 112. A hexagonal nut 33 is threaded on the surface of the ball head screw 32. The surface at the bottom of the hexagonal nut 33 is in contact with the surface of the connecting plate body 112.

[0025] In practice, the user places the vacuum chamber connecting plate 35 on the surface of the top position of the vacuum chamber body 103, and then tightens the mounting bolts 31 on the surface of the vacuum chamber connecting plate 35. Under the action of the mounting bolts 31, the vacuum chamber connecting plate 35 is installed on the surface of the vacuum chamber body 103. Subsequently, the user places the vacuum chamber body 103 and the vacuum chamber connecting plate 35 under the connecting plate body 112, and places the ball head screw 32 on the surface of the vacuum chamber connecting plate 35, so that the ball head screw 32 drives the mounting plate 36 to lock into the interior of the vacuum chamber connecting plate 35. At this time, the top end of the ball head screw 32 extends... Above the connecting plate body 112, the user tightens the hexagonal nut 33 on the surface of the ball head screw 32. With the threaded engagement of the ball head screw 32 and the hexagonal nut 33, the ball head screw 32 is installed on the surface of the connecting plate body 112. Then, the user tightens the fastening bolts 34 on the surface of the mounting plate 36. Under the action of the fastening bolts 34, the connecting plate body 112 and the vacuum chamber connecting plate 35 are installed and fixed together, so that the vacuum chamber body 103 can be stably installed on the surface at the bottom of the connecting plate body 112 for use, thereby realizing the function of easy assembly of the vacuum testing mechanism.

[0026] Working principle: In use, first place the mechanism bracket 1 in the designated position. The user places the vacuum chamber connecting plate 35 on the surface of the top position of the vacuum chamber body 103, and then tightens the mounting bolts 31 on the surface of the vacuum chamber connecting plate 35. Under the action of the mounting bolts 31, the vacuum chamber connecting plate 35 is installed on the surface of the vacuum chamber body 103. Subsequently, the user places the vacuum chamber body 103 and the vacuum chamber connecting plate 35 under the connecting plate body 112, and places the ball head screw 32 on the surface of the vacuum chamber connecting plate 35, so that the ball head screw 32 drives the mounting plate 36 to lock into the interior of the vacuum chamber connecting plate 35. At this time, the top of the ball head screw 32 extends to the top of the connecting plate body 112. The user then tightens the ball head screw. The hexagonal nut 33 on the surface of the ball head screw 32 is used to install the ball head screw 32 onto the surface of the connecting plate body 112 through the threaded engagement between the ball head screw 32 and the hexagonal nut 33. Then, the user tightens the fastening bolts 34 on the surface of the mounting plate 36. Under the action of the fastening bolts 34, the connecting plate body 112 and the vacuum chamber connecting plate 35 are fixed together, so that the vacuum chamber body 103 can be stably installed on the surface of the bottom position of the connecting plate body 112 for use. This realizes the function of easy assembly of the vacuum testing mechanism, so that the user can easily assemble the vacuum chamber body 103 onto the surface of the connecting plate body 112 when using the vacuum testing mechanism. At the same time, it can ensure the stability of the vacuum chamber body 103 during use.

[0027] Subsequently, the vacuum chamber body 103, under normal conditions, moves away from the surface of the bakelite board 104. During stator testing, the controller 105 controls the cylinder body 110 to operate. Under the action of the cylinder body 110, the cylinder connecting rod 111 moves downward, causing the connecting plate body 112 and the vacuum chamber body 103 to move downward. When the cylinder connecting rod 111 moves, it causes the lifting bracket 101 and the connecting plate body 112 to slide on the surface of the linear guide rail 102, causing the bottom of the vacuum chamber body 103 to move downward until it contacts the surface of the bakelite board 104. The stator placed on the surface of the bakelite board 104 is then tested under vacuum. After the test is completed, the cylinder body 110 drives the lifting bracket 101 to move upward and reset. Under the action of the buffer body 108 on the surface of the buffer bracket 107, the surface of the lifting bracket 101 is buffered.

[0028] Subsequently, the user places the clamping ring 22 inside the chassis 106 and tightens the mounting studs 21 on the surface of the clamping ring 22. Under the action of the mounting studs 21, the clamping ring 22 is installed inside the chassis 106. When the bakelite board 104 is installed inside the chassis 106 by screws, the surface of the bakelite board 104 contacts the inner wall of the clamping ring 22, pressing the bakelite board 104 firmly. When the vacuum chamber body 103 moves downwards, it moves downwards until it contacts the surface of the rectangular sealing ring 23. At this time, the surface of the vacuum chamber body 103 contacts the inner wall of the clamping ring 22. The combined action of O-ring 24 and rectangular sealing ring 25 improves the sealing performance between vacuum chamber body 103 and bakelite board 104. When bakelite board 104 is installed inside chassis 106, the combined action of O-ring 24 and sealing ring 25 further enhances the sealing effect between bakelite board 104 and chassis 106, achieving high sealing performance of vacuum testing mechanism. This greatly improves the sealing performance between vacuum chamber body 103 and bakelite board 104 during vacuum testing, making the test results of vacuum testing mechanism more accurate when performing vacuum tests on stator, and ultimately completing the use of vacuum testing mechanism.

[0029] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A vacuum testing mechanism for testing variable frequency stators, comprising a mechanism support (1), characterized in that: A housing (106) is provided on the outside of the mechanism support (1). The mechanism support (1) is installed inside the housing (106) by screws. There are two sets of mechanism supports (1). A controller (105) is installed on the surface of the housing (106). Linear guide rails (102) are installed on the surface of each mechanism support (1) by screws. A lifting bracket (101) is provided on the surface of the linear guide rail (102). The lifting bracket (101) and the linear guide rail (102) are connected. The surfaces slide against each other. A connecting plate body (112) is mounted on the surface of the lifting bracket (101) by screws. A vacuum cover body (103) is provided below the connecting plate body (112). A bakelite board (104) is mounted on the surface of the chassis (106) by screws. A high-sealing mechanism (2) is provided on the surface of the bakelite board (104) and the surface of the chassis (106). A convenient assembly mechanism (3) is provided on the surface of the connecting plate body (112) and the vacuum cover body (103).

2. The vacuum testing mechanism for frequency converter stator testing according to claim 1, characterized in that: The surface of the mechanism support (1) is provided with a guide groove (109). A buffer support (107) is installed on the surface of the mechanism support (1) by screws. A buffer body (108) is installed on the surface of the buffer support (107). A cylinder body (110) is installed inside the mechanism support (1) by screws. The input end of the cylinder body (110) is electrically connected to the output end of the controller (105). A cylinder connecting rod (111) is installed on the output end of the cylinder body (110). One end of the cylinder connecting rod (111) passes through the guide groove (109) and is fixed to the surface of the lifting bracket (101). The cylinder connecting rod (111) and the inner wall of the guide groove (109) slide against each other. There are two bakelite boards (104). The bakelite boards (104) are located directly below the vacuum chamber body (103). The surface of the bottom of the vacuum chamber body (103) is in contact with the surface of the bakelite boards (104). The test assembly (113) is installed inside the controller (105).

3. The vacuum testing mechanism for frequency converter stator testing according to claim 1, characterized in that: The high-sealing mechanism (2) consists of a mounting stud (21), a clamping ring (22), a rectangular sealing ring (23), an O-ring (24), and a sealing ring (25). The interior of the chassis (106) is provided with clamping rings (22) for clamping the bakelite board (104). The inner wall of the clamping ring (22) is in contact with the surface of the bakelite board (104). The surface of the clamping ring (22) is threaded with mounting studs (21). One end of the mounting stud (21) passes through the clamping ring (22) and is threadedly fastened to the surface of the chassis (106). The surface of the clamping ring (22) is in contact with the surface of the vacuum chamber body (103).

4. The vacuum testing mechanism for frequency converter stator testing according to claim 1, characterized in that: A rectangular sealing ring (23) is installed on the surface of the bakelite board (104), and the surface of the rectangular sealing ring (23) is in contact with the surface at the bottom of the vacuum chamber body (103). An O-ring (24) is installed on the inner wall of the chassis (106), and the surface of the O-ring (24) is in contact with the surface at the bottom of the bakelite board (104). A sealing ring (25) is installed on the inner wall of the chassis (106), and the surface of the sealing ring (25) is in contact with the surface at the bottom of the bakelite board (104).

5. A vacuum testing mechanism for testing frequency converter stators according to claim 1, characterized in that: The easy assembly mechanism (3) consists of mounting bolts (31), ball head screws (32), hexagonal nuts (33), fastening bolts (34), vacuum cover connecting plate (35), and mounting plate (36). The vacuum cover connecting plate (35) is provided on the surface of the top position of the vacuum cover body (103). The surface of the vacuum cover connecting plate (35) is threaded with mounting bolts (31). One end of the mounting bolt (31) passes through the vacuum cover connecting plate (35) and is threadedly fastened to the surface of the vacuum cover body (103). The surface of the connecting plate body (112) is mounted with mounting plate (36). The surface of the vacuum cover connecting plate (35) is threaded with fastening bolts (34). One end of the fastening bolt (34) passes through the mounting plate (36) and is threadedly fastened to the surface of the vacuum cover connecting plate (35).

6. A vacuum testing mechanism for testing frequency converter stators according to claim 5, characterized in that: A ball-head screw (32) is provided on the surface of the top center position of the vacuum cover connecting plate (35). The ball-head screw (32) is engaged with the surface of the vacuum cover connecting plate (35). The top end of the ball-head screw (32) penetrates the connecting plate body (112) and extends to the top of the connecting plate body (112). A hexagonal nut (33) is threaded on the surface of the ball-head screw (32). The surface of the bottom position of the hexagonal nut (33) is in contact with the surface of the connecting plate body (112).

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