Feeding mechanism of sheet metal bending machine

Abstract

The utility model relates to related technical field of plate processing especially, a kind of plate bending machine's feeding mechanism, including rack, the bottom of the rack is equipped with adjustable support leg, the bottom of the adjustable support leg is connected with foot pad, the surface of the rack is equipped with transmission group, the inner side of the rack is connected with conveyor belt, the surface of the rack and conveyor belt is all provided with tensioning mechanism, the top of the rack is provided with anti-offset mechanism.This kind of plate bending machine's feeding mechanism, by the setting of tensioning mechanism, continuously maintain conveyor belt stable tension, avoid the transmission speed fluctuation, length deviation and loss intensification caused by conveyor belt slackening, reduce manual intervention and equipment downtime, reduce operation and maintenance cost, by the setting of anti-offset mechanism, can be according to the width of plate adjust the position of positioning plate and form lateral constraint, prevent plate lateral offset along conveyor belt, avoid bending misplacement and scrap rate rise, adapt high-precision scale automatic bending production demand.

Description

Technical Field

[0001] This utility model relates to the field of sheet metal processing technology, and in particular to a feeding mechanism for a sheet metal bending machine. Background Technology

[0002] A bending machine is an industrial device used to bend and shape metal sheets. Its core principle is to use a hydraulic, mechanical, or servo drive system to drive the upper and lower dies to move relative to each other. The shape of the dies is used to press the sheet into a preset angle or a specific curved shape to meet the processing requirements of various bent structural parts in industrial products. The processing of metal sheets by bending machines requires precise control of the feeding position, speed, and angle of the sheet. Manual feeding is not only inefficient but also difficult to adapt to the automated batch processing requirements of CNC bending machines. Therefore, a feeding mechanism for sheet metal bending machines is particularly needed.

[0003] Chinese Patent CN221754544U, published on September 24, 2024, discloses a feeding mechanism for a sheet metal bending machine. An auxiliary pressure plate installed in the feed trough helps to fix the sheet metal during bending, enhancing its stability within the auxiliary positioning mechanism and on the conveyor belt surface. This prevents positional shifts during bending, making the bending process more precise and stable. However, this feeding mechanism lacks a tensioning function for the conveyor belt and an anti-deviation function above the conveyor belt. This not only leads to fluctuations in sheet metal conveying speed, length deviations, and increased wear due to conveyor belt slack, but also causes bending misalignment and increased scrap rates due to the sheet metal easily shifting laterally along the conveyor belt. Furthermore, it increases the frequency of manual intervention, equipment downtime, and maintenance costs, making it unsuitable for the demands of high-precision, large-scale automated bending production. Utility Model Content

[0004] The purpose of this utility model is to provide a feeding mechanism for a sheet metal bending machine to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, this utility model provides the following technical solution: a feeding mechanism for a sheet metal bending machine, comprising a frame, an adjustable support leg installed at the bottom of the frame, a foot pad connected to the bottom of the adjustable support leg, a transmission assembly installed on the surface of the frame, a conveyor belt connected to the inner side of the frame, a tensioning mechanism provided on the surface of both the frame and the conveyor belt, and an anti-deviation mechanism provided on the top of the frame;

[0006] The tensioning mechanism includes a positioning plate, which is installed on the side of the frame. A shaft is connected through the inside of the positioning plate. A first stop is connected to one end of the shaft. A tensioning wheel is sleeved on the outside of the shaft. A threaded post is provided at the other end of the shaft. A fixed plate is installed on the other side of the frame. A threaded groove is opened on the inner wall of the fixed plate. Positioning holes are opened on the surfaces of both the positioning plate and the fixed plate. A tension spring is connected to the outside of the positioning hole. A pull block is connected to the outer end of the tension spring. A positioning rod is connected to the inner end of the pull block. An elastic ball is connected to the end of the positioning rod away from the pull block. Limit holes are opened inside the frame.

[0007] Preferably, the adjustable support legs are symmetrically arranged at the four corners of the bottom of the frame with respect to the central axis of the frame, and each set of adjustable support legs is connected to a foot pad at the bottom.

[0008] Preferably, a sliding bearing is provided at the through connection between the shaft and the positioning disk. The inner ring of the sliding bearing is interference-fitted with the shaft, and the outer ring of the sliding bearing is interference-fitted with the inner wall of the positioning disk. The shaft is rotatably connected to the positioning disk through the sliding bearing.

[0009] Preferably, the positioning rod slides in conjunction with the positioning holes on the surfaces of the positioning disk and the fixed disk, and the positioning holes are symmetrically distributed on the surfaces of the positioning disk and the fixed disk.

[0010] Preferably, the anti-deviation mechanism includes a fixed plate connected to the top of the frame. A hydraulic cylinder is installed on the middle of the outer side of the fixed plate. A positioning plate is connected to the output end of the hydraulic cylinder. Auxiliary rods are connected to both sides of the positioning plate. One end of the auxiliary rod passes through the fixed plate. A buffer spring is connected to the outer side of the auxiliary rod. A second stop is connected to the end of the auxiliary rod away from the fixed plate.

[0011] Preferably, the auxiliary rods are provided in two identical sets on the surface of the positioning plate, and the two sets of auxiliary rods are symmetrically distributed about the central axis of the positioning plate.

[0012] Preferably, the buffer spring is sleeved on the outside of the auxiliary rod, with one end abutting against the outside of the fixed plate and the other end abutting against the inside of the second stop, the diameter of the second stop being larger than the diameter of the auxiliary rod.

[0013] Compared with the prior art, the beneficial effects of this utility model are:

[0014] 1. The feeding mechanism of this sheet metal bending machine, through the setting of the tensioning mechanism, the tensioning wheel applies a squeezing support force to the conveyor belt, continuously maintains the stable tension of the conveyor belt, avoids the conveying speed fluctuation, length deviation and increased wear caused by the slack of the conveyor belt, reduces manual intervention and equipment downtime, and lowers operation and maintenance costs.

[0015] 2. The feeding mechanism of this sheet metal bending machine, through the setting of the anti-deviation mechanism, can adjust the position of the positioning plate according to the width of the sheet metal and form a lateral constraint to prevent the sheet metal from shifting laterally along the conveyor belt, avoid bending misalignment and increase scrap rate, and adapt to the needs of high-precision large-scale automated bending production. Attached Figure Description

[0016] Figure 1 This is a side view of the structure of the present utility model;

[0017] Figure 2 This is a schematic diagram of the tensioning mechanism of this utility model;

[0018] Figure 3 This is a schematic diagram of the interaction between the shaft and the tension wheel of this utility model;

[0019] Figure 4 This is a schematic diagram of the anti-deviation mechanism of this utility model;

[0020] Figure 5 This utility model Figure 2 Enlarged structural diagram at point A in the middle.

[0021] In the diagram: 1. Frame; 2. Adjustable support leg; 3. Foot pad; 4. Transmission assembly; 5. Conveyor belt; 6. Tensioning mechanism; 601. Positioning plate; 602. Shaft; 603. First stop block; 604. Tensioning wheel; 605. Threaded column; 606. Fixed plate; 607. Threaded groove; 608. Positioning hole; 609. Tension spring; 610. Pull block; 611. Positioning rod; 612. Elastic ball; 613. Limiting hole; 7. Anti-deviation mechanism; 701. Fixed plate; 702. Hydraulic cylinder; 703. Positioning plate; 704. Auxiliary rod; 705. Buffer spring; 706. Second stop block. Detailed Implementation

[0022] 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, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0023] Please see Figure 1-5 This utility model provides a technical solution: a feeding mechanism for a sheet metal bending machine, including a frame 1, an adjustable support leg 2 installed at the bottom of the frame 1, a foot pad 3 connected to the bottom of the adjustable support leg 2, a transmission group 4 installed on the surface of the frame 1, a conveyor belt 5 connected to the inner side of the frame 1, a tensioning mechanism 6 provided on the surface of both the frame 1 and the conveyor belt 5, and an anti-deviation mechanism 7 provided on the top of the frame 1;

[0024] The tensioning mechanism 6 includes a positioning disc 601, which is mounted on the side of the frame 1. A shaft 602 is connected through the interior of the positioning disc 601. A first stop block 603 is connected to one end of the shaft 602. A tensioning wheel 604 is sleeved on the outer side of the shaft 602. A threaded post 605 is provided at the other end of the shaft 602. A fixing disc 606 is mounted on the other side of the frame 1. A threaded groove 607 is provided on the inner wall of the fixing disc 606. Positioning holes 608 are provided on the surfaces of both the positioning disc 601 and the fixing disc 606. A tension spring 609 is connected to the outer side of the positioning hole 608. A pull block 610 is connected to the outer end of the tension spring 609. The inner end of the pull block 610... A positioning rod 611 is connected, with an elastic ball 612 connected to the end of the positioning rod 611 away from the pull block 610. A limiting hole 613 is provided inside the frame 1. Through the tensioning mechanism 6, the positioning disc 601 is first fitted against one side of the frame 1. The pull block 610 is pushed inward, causing the inner end of the pull block 610 to slide along the positioning hole 608 on the surface of the positioning disc 601. This allows the elastic ball 612 at the end of the positioning rod 611 away from the pull block 610 to engage with the corresponding limiting hole 613 on the frame 1. The engagement of the elastic ball 612 with the limiting hole 613 fixes the positioning disc 601 to the side of the frame 1. At this time, the positioning hole... The tension spring 609 connected to the outside of 608 is in a naturally contracted state, providing a continuous inward pulling force to the positioning rod 611, ensuring that the elastic ball 612 is stably stuck in the limiting hole 613, preventing the positioning plate 601 from loosening. Next, the shaft 602 is passed through the pre-set through hole on the surface of the positioning plate 601. The first stop 603 connected to one end of the shaft 602, because its outer diameter is larger than the inner diameter of the through hole, can prevent the shaft 602 from falling off the surface of the positioning plate 601, thus achieving the initial axial limitation of the shaft 602. Subsequently, the tension wheel 604 is sleeved on the outside of the shaft 602, so that the inner wall of the tension wheel 604 is in contact with the surface of the shaft 602, and one side of the tension wheel 604 is in contact with the positioning plate 601. The side wall of the positioning plate 601 contacts the tensioning wheel 604, further restricting its lateral displacement. Then, the fixing plate 606 is fitted and installed on the other side of the frame 1. The threaded post 605 at the other end of the shaft 602 is rotated, so that the threaded post 605 is gradually screwed into the threaded groove 607 on the inner wall of the fixing plate 606. As the thread engagement between the threaded post 605 and the threaded groove 607 deepens, the shaft 602 drives the tensioning wheel 604 to move closer to the fixing plate 606 until the tensioning wheel 604 is tightly fitted against the inner side of the conveyor belt 5. At this time, the conveyor belt 5 forms a preset tension due to the squeezing support of the tensioning wheel 604, completing the installation of the tensioning mechanism 6 and the tensioning of the conveyor belt 5.

[0025] Furthermore, the adjustable support legs 2 are symmetrically arranged at the four corners of the bottom of the frame 1 along the central axis of the frame 1, and each set of adjustable support legs 2 is connected to a foot pad 3 at the bottom. Through the arrangement of the adjustable support legs 2 and the foot pad 3, the symmetrical distribution at the four corners can make the bottom of the frame 1 evenly stressed, preventing the frame 1 from tilting due to uneven placement surface, ensuring that the conveyor belt 5 and the transmission group 4 are always in a horizontal state, and ensuring the stability of the sheet material conveying trajectory. At the same time, by adjusting the height of the adjustable support legs 2, it can be adapted to the feed inlet of sheet bending machines of different heights, enhancing the compatibility between the feeding mechanism and the bending machine. The foot pad 3 can increase the contact area between the adjustable support legs 2 and the ground, reducing the vibration transmission during the operation of the feeding mechanism, preventing the frame 1 from shifting or the sheet material conveying from deviating due to vibration, and further improving the overall stability of the mechanism.

[0026] Furthermore, a sliding bearing is provided at the through connection between the shaft 602 and the positioning disk 601. The inner ring of the sliding bearing is interference-fitted with the shaft 602, and the outer ring of the sliding bearing is interference-fitted with the inner wall of the positioning disk 601. The shaft 602 is rotatably connected to the positioning disk 601 through the sliding bearing. With the positioning disk 601 and the shaft 602, the positioning disk 601 provides stable axial support for the shaft 602, ensuring that the shaft 602 does not radially deviate when driving the tension wheel 604 to move or rotate. The sliding bearing design converts the sliding friction between the shaft 602 and the positioning disk 601 into rolling friction, greatly reducing the friction loss between the two, making the shaft 602 rotate more smoothly when adjusting the position of the tension wheel 604, while reducing the wear of the shaft 602 and the positioning disk 601, extending the service life of the tensioning mechanism 6, and ensuring the convenience and stability of the tension adjustment operation.

[0027] Furthermore, the positioning rod 611 slides in conjunction with the positioning holes 608 on the surfaces of the positioning disk 601 and the fixed disk 606. The positioning holes 608 are symmetrically distributed on the surfaces of the positioning disk 601 and the fixed disk 606. Through the setting of the positioning holes 608, the symmetrically distributed positioning holes 608 can make the locking force of the positioning rod 611 on the positioning disk 601 evenly distributed on both sides of the positioning disk 601, avoiding the tilting of the positioning disk 601 due to uneven force caused by locking on one side, ensuring the stability of the position of the shaft 602 and the tensioning wheel 604. At the same time, the positioning holes 608 provide precise sliding guidance for the positioning rod 611, preventing the positioning rod 611 from deviating during the pulling or resetting process, ensuring that the elastic ball 612 can be embedded in the limiting hole 613 of the frame 1, realizing the reliable locking of the positioning disk 601 and the shaft 602, preventing the tensioning wheel 604 from becoming loose due to the reaction force of the conveyor belt 5, and ensuring the long-term and stable tensioning effect of the tensioning mechanism 6.

[0028] Furthermore, the anti-deviation mechanism 7 includes a fixed plate 701, which is connected to the top of the frame 1. A hydraulic cylinder 702 is installed on the outer center of the fixed plate 701. The output end of the hydraulic cylinder 702 is connected to a positioning plate 703. Auxiliary rods 704 are connected to both sides of the positioning plate 703. One end of the auxiliary rod 704 passes through the fixed plate 701. A buffer spring 705 is connected to the outer side of the auxiliary rod 704. A second stop 706 is connected to the end of the auxiliary rod 704 away from the fixed plate 701. Through the setting of the anti-deviation mechanism 7, before the plate enters the conveyor belt 5 for conveying, the hydraulic cylinder 702 installed on the outer center of the fixed plate 701 is activated according to the width of the plate. The hydraulic cylinder 702 pushes or pulls the positioning plate 703 connected to it to move laterally. If the plate width is large, the hydraulic cylinder 702 pushes the positioning plate 703 away from the fixed plate 701. If the plate width is small, the hydraulic cylinder 702 pulls the positioning plate 703 towards the fixed plate 701 until a suitable gap is left between the inner side of the positioning plate 703 of the two anti-deviation mechanisms 7 and the two side edges of the plate, ensuring that the plate can be smoothly conveyed without lateral deviation. During the movement of the positioning plate 703, the auxiliary rods 704 connected to its two sides slide synchronously along the through holes of the fixed plate 701. The buffer on the outer side of the auxiliary rods 704... Spring 705 undergoes elastic deformation as the auxiliary rod 704 moves, providing stable buffer support for the positioning plate 703 and preventing excessive driving force from the hydraulic cylinder 702, which could cause the positioning plate 703 to instantly impact the plate. Simultaneously, the second stop 706 connected to the end of the auxiliary rod 704 away from the fixed plate 701 prevents the auxiliary rod 704 from falling out of the through hole in the fixed plate 701, ensuring that the auxiliary rod 704 remains stably connected to the positioning plate 703. When the plate is conveyed on the conveyor belt 5, if lateral movement occurs due to vibration of the conveyor belt 5 or shift of the plate's center of gravity, the edge of the plate will contact the inner side of the positioning plate 703. The positioning plate 703 is then... The supporting force of 702 and the elastic reaction force of the buffer spring 705 work together to form a lateral constraint on the plate, preventing further deviation of the plate and ensuring that the plate is stably transported to the bending machine along the center track of the conveyor belt 5. If the plate shakes slightly and generates an instantaneous impact force on the positioning plate 703, the buffer spring 705 will absorb the impact force through its own deformation, avoiding rigid collision that could cause deformation of the plate edge or damage to the positioning plate 703. After the plate is completely transported to the bending machine, the hydraulic cylinder 702 drives the positioning plate 703 to reset, and the auxiliary rod 704 and the buffer spring 705 synchronously return to their initial state, preparing for the anti-deviation operation of the next plate transport.

[0029] Furthermore, two identical sets of auxiliary rods 704 are provided on the surface of the positioning plate 703, and both sets of auxiliary rods 704 are symmetrically distributed about the central axis of the positioning plate 703. Through the setting of auxiliary rods 704, the two sets of symmetrically distributed auxiliary rods 704 can form balanced guiding support from both sides of the positioning plate 703, avoiding tilting or jamming of the positioning plate 703 due to unilateral force when it moves laterally under the drive of the hydraulic cylinder 702, ensuring that the positioning plate 703 always moves smoothly in the horizontal direction. At the same time, the symmetrical structure can evenly transmit the lateral reaction force on the positioning plate 703 to the two sets of auxiliary rods 704, and then distribute it to the fixed plate 701 through the auxiliary rods 704, preventing the positioning plate 703 from deforming due to excessive local force, ensuring the stability of the anti-offset constraint and the service life of the positioning plate 703, and adapting to the anti-offset requirements of plates of different widths.

[0030] Furthermore, the buffer spring 705 is sleeved on the outside of the auxiliary rod 704, with one end abutting against the outside of the fixed plate 701 and the other end abutting against the inside of the second stop 706. The diameter of the second stop 706 is larger than the diameter of the auxiliary rod 704. Through the setting of the buffer spring 705 and the second stop 706, the buffer spring 705 can undergo elastic deformation synchronously when the positioning plate 703 moves through the abutting structure at both ends, providing continuous and uniform buffer force for the positioning plate 703. This prevents the instantaneous impact force when the hydraulic cylinder 702 starts and stops from being directly transmitted to the positioning plate 703 and the plate, preventing the edge of the plate from being damaged by rigid impact. At the same time, because the diameter of the second stop 706 is larger than that of the auxiliary rod 704, it can prevent the auxiliary rod 704 from falling out of the through hole of the fixed plate 701 and provide a stable support end point for the buffer spring 705, ensuring that the buffer spring 705 is always in the preset position outside the auxiliary rod 704, avoiding spring displacement that would cause buffer failure.

[0031] Working Principle: First, the mechanism is installed and debugged. The positioning plate 601 of the tensioning mechanism 6 is fixed to one side of the frame 1 through the positioning rod 611, the elastic ball 612, and the limiting hole 613 of the frame 1. The shaft 602 passes through the positioning plate 601 and is fitted with the tensioning wheel 604. The first stop block 603 prevents it from falling off. Then, the fixing plate 606 is installed on the other side of the frame 1. The threaded post 605 of the shaft 602 is rotated to screw it into the threaded groove 607 of the fixing plate 606, which drives the tensioning wheel 604 to squeeze the inner side of the conveyor belt 5 to form a preset tension. The sliding bearing between the shaft 602 and the positioning plate 601 reduces friction to ensure smooth adjustment. The symmetrical distribution of the positioning holes 608 ensures that the positioning rod 611 is locked and stable. At the same time, the height of the adjustable support legs 2 at the four symmetrical corners of the bottom of the frame 1 is adjusted to keep the conveyor belt 5 and the transmission group 4 horizontal. The foot pads 3 increase the contact area to reduce vibration transmission. After debugging, the hydraulic pressure of the anti-deviation mechanism 7 is activated according to the width of the plate to be conveyed. Cylinder 702 pushes or pulls positioning plate 703 to move laterally. Auxiliary rod 704 slides along fixed plate 701 for guidance. Buffer spring 705 provides buffering. Second stop block 706 prevents auxiliary rod from falling off until a suitable gap is left between positioning plate 703 and the edge of the sheet material. Then, transmission group 4 drives conveyor belt 5 to run. When the sheet material moves on the conveyor belt, tensioning mechanism 6 continuously maintains the tension of the conveyor belt to prevent slippage. Positioning plate 703 of anti-deviation mechanism 7 constrains the lateral deviation of the sheet material under the support force of hydraulic cylinder and the elastic force of buffer spring. If the sheet material generates instantaneous impact force, buffer spring absorbs the impact force through deformation to protect the sheet material and mechanism. After the sheet material is stably conveyed to the bending machine, hydraulic cylinder drives positioning plate 703 to reset. Auxiliary rod and buffer spring synchronously return to their initial state, preparing for the next feeding operation. The whole process achieves accurate, stable and efficient conveying of sheet material through the cooperation of various components. This completes the use process of a feeding mechanism for a sheet metal bending machine.

[0032] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A feeding mechanism for a sheet metal bending machine, comprising a frame (1), characterized in that: The bottom of the frame (1) is equipped with an adjustable support leg (2), and the bottom of the adjustable support leg (2) is connected with a foot pad (3). The surface of the frame (1) is equipped with a transmission assembly (4), and the inner side of the frame (1) is connected with a conveyor belt (5). The surfaces of the frame (1) and the conveyor belt (5) are both provided with a tensioning mechanism (6), and the top of the frame (1) is provided with an anti-deviation mechanism (7). The tensioning mechanism (6) includes a positioning disc (601), which is mounted on the side of the frame (1). A shaft (602) is connected through the interior of the positioning disc (601). One end of the shaft (602) is connected to a first stop (603). A tensioning wheel (604) is sleeved on the outside of the shaft (602). A threaded post (605) is provided at the other end of the shaft (602). A fixing disc (606) is mounted on the other side of the frame (1). The inner wall is provided with a threaded groove (607). The positioning plate (601) and the fixed plate (606) are both provided with positioning holes (608). A tension spring (609) is connected to the outside of the positioning hole (608). A pull block (610) is connected to the outer end of the tension spring (609). A positioning rod (611) is connected to the inner end of the pull block (610). An elastic ball (612) is connected to the end of the positioning rod (611) away from the pull block (610). A limit hole (613) is provided inside the frame (1).

2. The feeding mechanism of a sheet metal bending machine according to claim 1, characterized in that: The adjustable support legs (2) are symmetrically arranged at the four corners of the bottom of the frame (1) along the central axis of the frame (1), and each set of adjustable support legs (2) is connected to a foot pad (3) at the bottom.

3. The feeding mechanism of a sheet metal bending machine according to claim 1, characterized in that: A sliding bearing is provided at the through connection between the shaft (602) and the positioning disk (601). The inner ring of the sliding bearing is interference-fitted with the shaft (602), and the outer ring of the sliding bearing is interference-fitted with the inner wall of the positioning disk (601). The shaft (602) is rotatably connected to the positioning disk (601) through the sliding bearing.

4. The feeding mechanism of a sheet metal bending machine according to claim 1, characterized in that: The positioning rod (611) slides in conjunction with the positioning holes (608) on the surfaces of the positioning disk (601) and the fixed disk (606), and the positioning holes (608) are symmetrically distributed on the surfaces of the positioning disk (601) and the fixed disk (606).

5. The feeding mechanism of a sheet metal bending machine according to claim 1, characterized in that: The anti-deviation mechanism (7) includes a fixed plate (701) connected above the frame (1). A hydraulic cylinder (702) is installed on the middle of the outer side of the fixed plate (701). A positioning plate (703) is connected to the output end of the hydraulic cylinder (702). An auxiliary rod (704) is connected to both sides of the positioning plate (703). One end of the auxiliary rod (704) passes through the fixed plate (701). A buffer spring (705) is connected to the outer side of the auxiliary rod (704). A second stop (706) is connected to the end of the auxiliary rod (704) away from the fixed plate (701).

6. The feeding mechanism of a sheet metal bending machine according to claim 5, characterized in that: The auxiliary rods (704) are provided in two identical sets on the surface of the positioning plate (703), and the two sets of auxiliary rods (704) are symmetrically distributed about the central axis of the positioning plate (703).

7. The feeding mechanism of a sheet metal bending machine according to claim 5, characterized in that: The buffer spring (705) is sleeved on the outside of the auxiliary rod (704), with one end abutting against the outside of the fixing plate (701) and the other end abutting against the inside of the second stop (706), the diameter of the second stop (706) being larger than the diameter of the auxiliary rod (704).

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