An automatic feeding device for PCB micro drill bits

Abstract

This utility model relates to the field of PCB micro drill bit feeding technology, specifically to an automatic PCB micro drill bit feeding device, including a base, a feeding seat installed at one top end of the base, a feeding groove extending into the feeding seat at one top end of the feeding seat, a limiting groove on one side of the feeding groove at the top of the feeding seat, a guide groove near the bottom end of the feeding seat at the top of the base, and a movable discharge mechanism installed on the limiting groove and the feeding seat. The movable discharge mechanism includes an adjusting feeding component and a limiting component. The adjusting feeding component is used to arrange and feed the material, and the limiting component is used to prevent the material from slipping during conveying. This utility model has a simple structure and is easy to operate. The operator can adjust the position of the conveying component according to the model and size of the PCB micro drill bit being conveyed, so that the conveying space in the feeding seat matches the model of the PCB micro drill bit being conveyed, further increasing the flexibility of the device during use.

Description

Technical Field

[0001] This utility model relates to the field of PCB micro drill bit feeding technology, specifically to an automatic PCB micro drill bit feeding device. Background Technology

[0002] PCB micro drills are mainly used in PCB manufacturing: Printed Circuit Boards (PCBs) are composed of several layers of resin materials bonded together, with copper foil traces inside. They are available in 4, 6, and 8-layer configurations. Drilling accounts for 30-40% of the cost of a PCB, and mass production often requires specialized equipment and drill bits. Good PCB drill bits use high-quality carbide materials, possessing excellent characteristics such as high rigidity, high hole position accuracy, good hole wall quality, and long lifespan. PCB micro drills are generally made of stainless steel shanks and tungsten carbide carbide welded together. Because the diameter of the carbide drill bit is much smaller than the diameter of the stainless steel shank, after welding, it forms an asymmetrical, cylindrical shape with a small head and a large root. This results in frequent material jamming when using traditional automatic micro-bar cutting machines, increasing manual maintenance time and impacting production efficiency.

[0003] To address the aforementioned technical issues, Chinese Patent No. CN216188804U discloses an automatic PCB micro drill bit feeding device, comprising: a hopper with an inlet at the top and an outlet at the bottom, for products to be processed to be stacked sequentially along the length direction; and an discharge mechanism fixed below the hopper, having a slit inside for only a single product to be processed to pass through sequentially, with the upper opening of the slit connected to the outlet of the hopper.

[0004] While the existing technical solution described above allows the feeding cam to feed PCB micro drills one by one, PCB micro drills come in different sizes and models. Once the thickness of their tail ends changes, the gap on the feeding cam cannot guarantee that only a single micro drill will be fed each time. This can easily cause multiple sets of micro drills to be fed and slide towards the end of the slit, which can easily cause the multiple sets of micro drills to get stuck at the end of the slit, thus making it less practical. Summary of the Invention

[0005] (1) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide an automatic feeding device for PCB micro drill bits. This device aims to solve the problem that existing PCB micro drills come in different sizes, and when the thickness of their tail ends changes, the gap on the feeding cam cannot guarantee that only a single micro drill will be fed each time. This can easily lead to multiple sets of micro drills being fed and sliding towards the end of the slit, causing them to jam at the end of the slit, thus limiting its practicality.

[0007] (2) Technical solution

[0008] To solve the above-mentioned technical problems, this utility model provides an automatic PCB micro drill bit feeding device, including a base, a feeding seat installed at one top end of the base, a feeding groove extending into the feeding seat at one top end of the feeding seat, a limiting groove on one side of the feeding groove at the top of the feeding seat, a guide groove near the bottom end of the feeding seat at the top of the base, and a movable discharge mechanism installed on the limiting groove and the feeding seat. The movable discharge mechanism includes an adjusting feeding component and a limiting component. The adjusting feeding component is used to arrange and feed the material, and the limiting component is used to prevent the material from slipping during transportation.

[0009] When using the automatic PCB micro drill bit feeding device of this solution, the material can be fed downward through the port of the feeding chute. The first PCB micro drill bit to fall will contact the surface of the conveyor belt and be located between two adjacent sets of partitions. At the same time, the main body of the conveyor will be started to drive the conveyor belt and rubber side plates to rotate and convey the material. The partitions will push the material on the surface of the conveyor belt forward. After it is misaligned with the port formed by the feeding chute and the limiting seat, the material above it will fall downward to the two adjacent sets of partitions on the other side. This is how the material is conveyed sequentially. The structure is simple and the operation is convenient. The operator can adjust the position of the conveying components according to the model and size of the PCB micro drill bit being conveyed, so that the conveying space in the feeding seat matches the model of the PCB micro drill bit being conveyed, which further increases the flexibility of the device during use.

[0010] Preferably, the adjusting feeding assembly includes an extension groove formed on one side of the outer wall of the feeding seat, a closing plate slidably connected to the inner side of the extension groove, a conveyor body installed on one side of the closing plate, a conveyor belt installed on the conveyor body, and rubber side plates installed at both ends of the outer wall of the conveyor belt.

[0011] Furthermore, the surface of the conveyor belt is overlapped with multiple sets of partitions, and each of the two ends of the outer wall of the partition is equipped with an overlap seat. One side of the overlap seat overlaps with the outer wall of the rubber side plate. A sliding groove is provided at one bottom end of the overlap seat. Synchronization grooves are provided on both sides of the inner wall of the sliding groove. A synchronization rod is slidably connected to the inner side of the synchronization groove. A sliding block is installed between the two sets of synchronization rods. The sliding block is slidably connected to the sliding groove. A discharge groove is provided inside the discharge seat near the bottom end, which communicates with the inner side of the feed groove and the guide groove.

[0012] Furthermore, a pressure plate is installed at the bottom of the sliding block, and a rubber pad is installed on the side of the pressure plate near the rubber side plate. A snap-fit ​​groove is opened inside the overlapping seat on one side of the sliding groove. A snap-fit ​​block is slidably connected inside the snap-fit ​​groove. A connecting groove is opened on one side of the snap-fit ​​block. A first spring is installed between the two ends of the inner wall of the connecting groove and the inner wall of the snap-fit ​​groove. A ramp is opened at the opposite ends of the snap-fit ​​block and the sliding block. A positioning groove is opened on one side of the sliding block. The positioning groove is slidably connected to one end of the snap-fit ​​block.

[0013] Furthermore, an operating groove is provided on the outer wall of the connecting seat near the top. A pull rod is installed on the inner wall of the connecting groove between the two sets of first springs. A toggle groove is provided between the operating groove and the snap-fit ​​groove. The toggle groove and the pull rod are slidably connected. The other end of the pull rod extends to the inner side of the operating groove.

[0014] Furthermore, the limiting component includes an adjusting cylinder installed at one end of the top of the feeding seat. An adjusting groove is provided on one side of the adjusting cylinder. A threaded rod is rotatably connected to the inner side of the adjusting groove. An adjusting plate is threadedly connected to the outer side of the threaded rod. A limiting seat is installed at the other end of the adjusting plate. An inclined surface corresponding to the inclined state of the conveyor belt is provided at the bottom end of the limiting seat. A handle is rotatably connected to the top of the adjusting cylinder. One end of the handle extends into the inner side of the adjusting cylinder and is fixedly connected to one end of the threaded rod.

[0015] Furthermore, a fixed seat is installed on the outer wall of the feeding seat below the closing plate. A push-pull groove is opened at the top of the fixed seat. A push-pull plate is slidably connected to the inner side of the push-pull groove. One end of the push-pull plate and the side section of the inner side of the push-pull groove are both T-shaped. The other end of the push-pull plate is fixedly connected to the outer wall of the closing plate. First magnetic components are embedded in both ends of the outer wall of the push-pull plate. Second magnetic components that attract the first magnetic components are embedded in both sides of the inner wall of the drag groove.

[0016] (3) Beneficial effects

[0017] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0018] 1. In this utility model, the material is arranged and fed by adjusting the feeding component, and the limiting component prevents the material from slipping during the conveying process. The structure is simple and easy to operate. The operator can adjust the position of the conveying component according to the model and size of the PCB micro drill bit being conveyed, so that the conveying space in the feeding seat matches the model of the PCB micro drill bit being conveyed, which further increases the flexibility of the device during use.

[0019] 2. In this utility model, the material on the surface of the conveyor belt is pushed forward by the partition. After it is misaligned with the port formed by the feed chute and the limiting seat, the material above it falls down to the two adjacent partitions on the other side, thus realizing sequential conveying. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0021] Figure 2 This is a partial cross-sectional view of the material feeder of this utility model;

[0022] Figure 3 This is a partial three-dimensional structural diagram of the closing plate and fixing seat of this utility model;

[0023] Figure 4 This is a three-dimensional structural diagram of the conveyor and conveyor belt of this utility model;

[0024] Figure 5 This is a partial three-dimensional structural diagram of the rubber side plate and the overlapping seat of this utility model;

[0025] Figure 6 This is a partial cross-sectional view of the lap joint structure of this utility model.

[0026] In the diagram: 1. Base; 2. Feeding seat; 3. Closing plate; 4. Conveyor body; 5. Conveyor belt; 6. Rubber side plate; 7. Partition plate; 8. Overlapping seat; 9. Synchronizing rod; 10. Sliding block; 11. Pressure plate; 12. Rubber pad; 13. Clamping block; 14. First spring; 15. Pull rod; 16. Adjusting cylinder; 17. Threaded rod; 18. Adjusting plate; 19. Discharge chute; 20. Fixed seat; 21. Push-pull plate; 22. First magnetic component; 23. Limiting seat. Detailed Implementation

[0027] This specific embodiment is an automatic PCB micro drill bit feeding device, the structural schematic diagram of which is shown below. Figure 1-6As shown, an automatic PCB micro drill bit feeding device includes a base 1, a feeding seat 2 installed at one top end of the base 1, a feeding groove extending into the feeding seat 2 at one top end of the feeding seat 2, a limiting groove on one side of the feeding groove at the top of the feeding seat 2, a guide groove near the bottom end of the feeding seat 2 at the top of the base 1, and a movable discharge mechanism installed on the limiting groove and the feeding seat 2. The movable discharge mechanism includes an adjusting feeding component and a limiting component. The adjusting feeding component is used to arrange and feed the material, and the limiting component is used to prevent the material from slipping during conveying. In use, the device can arrange and feed the material by adjusting the feeding component and prevent the material from slipping during conveying. The structure is simple and easy to operate. The operator can adjust the position of the conveying component according to the model and size of the PCB micro drill bit being conveyed, so that the conveying space in the feeding seat 2 matches the model of the PCB micro drill bit being conveyed, further increasing the flexibility of the device in use.

[0028] In this embodiment, the adjusting feeding assembly includes an extension groove on one side of the outer wall of the feeding seat 2. A closing plate 3 is slidably connected to the inner side of the extension groove. A conveyor body 4 is installed on one side of the closing plate 3. A conveyor belt 5 is installed on the conveyor body 4. Rubber side plates 6 are installed at both ends of the outer wall of the conveyor belt 5. The conveyor belt 5 can be fed downward through the port of the feeding trough. The PCB micro drill bit that falls first contacts the surface of the conveyor belt 5 and is located between two adjacent sets of partitions 7. At the same time, the conveyor body 4 is started to drive the conveyor belt 5 and the rubber side plates 6 to rotate and convey. The partitions 7 push the material on the surface of the conveyor belt 5 forward. After it is misaligned with the port formed by the feeding trough and the limiting seat 23, the material above it falls downward to the two adjacent sets of partitions 7 on the other side. This is how the sequential conveying is achieved.

[0029] Secondly, in this embodiment, multiple sets of partitions 7 are overlapped on the surface of the conveyor belt 5. Both ends of the outer wall of the partition 7 are equipped with overlapping seats 8. One side of the overlapping seat 8 overlaps with the outer wall of the rubber side plate 6. A sliding groove is opened at the bottom end of the overlapping seat 8. Synchronization grooves are opened on both sides of the inner wall of the sliding groove. Synchronization rods 9 are slidably connected to the inner side of the synchronization groove. A sliding block 10 is installed between the two sets of synchronization rods 9. The sliding block 10 is slidably connected to the sliding groove. A discharge groove 19 is opened near the bottom of the material feeding groove and the inner side of the guide groove. After the conveyor belt 5 and the partitions 7 drive the material to the outermost edge, the PCB micro drill bit can slide down due to its own weight. Finally, it slides along the inclined surface of the inner wall of the feeding groove to the port of the discharge groove 19 and slides down the inner side of the discharge groove 19 to the inner side of the guide groove for discharge.

[0030] Furthermore, in this embodiment, the limiting component includes an adjusting cylinder 16 installed at one end of the top of the feeding seat 2. An adjusting groove is provided on one side of the adjusting cylinder 16, and a threaded rod 17 is rotatably connected to the inner side of the adjusting groove. An adjusting plate 18 is threadedly connected to the outer side of the threaded rod 17. A limiting seat 23 is installed at the other end of the adjusting plate 18. The bottom end of the limiting seat 23 has an inclined surface corresponding to the inclined state of the conveyor belt 5. A handle is rotatably connected to the top of the adjusting cylinder 16, and one end of the handle extends into the inner side of the adjusting cylinder 16 and is fixedly connected to one end of the threaded rod 17. A fixed seat 2 is installed on the outer wall of the feeding seat 2 below the closing plate 3. 0. A push-pull groove is provided at the top of the fixed base 20. A push-pull plate 21 is slidably connected to the inner side of the push-pull groove. One end of the push-pull plate 21 and the side section of the inner side of the push-pull groove are both T-shaped. The other end of the push-pull plate 21 is fixedly connected to the outer wall of the closing plate 3. First magnets 22 are embedded in both ends of the outer wall of the push-pull plate 21. Second magnets that attract the first magnets 22 are embedded in both sides of the inner wall of the drag groove. An operating groove is provided near the top of the outer wall of the overlapping base 8. A pull rod 15 is installed between the two sets of first springs 14 on the inner wall of the connecting groove. A toggle groove is provided between the operating groove and the snap-fit ​​groove. The toggle groove and the pull rod 15 is a sliding connection. The other end of the pull rod 15 extends to the inside of the operating groove. When it is necessary to convey PCB micro drill bits of different sizes, the handle can be held first to rotate the threaded rod 17, so that the adjusting plate 18 slides along the inside of the adjusting groove, causing the limiting seat 23 to slide inside the feed groove, so that the distance between the bottom end of the limiting seat 23 and the surface of the conveyor belt 5 matches the size of the PCB micro drill bit. Then, the push-pull plate 21 can be held to slide inside the push-pull groove, so that one of the first magnetic components 22 and the second magnetic component no longer attract each other, and the conveyor body 4 on the closing plate 3 is brought out together. You can insert your finger into the inside of the operating groove and push the lever 15 upwards, allowing it to slide along the inside of the groove. This causes the locking block 13 to press the two sets of first springs 14 back into the locking groove. At this time, the position of the sliding block 10 is no longer restricted. It can work with the synchronizing rod 9 and the synchronizing groove to move the pressure plate 11 and rubber pad 12 at the bottom of the sliding block 10 away from the surface of the rubber side plate 6. Then, the adjacent partitions 7 can be adjusted to a suitable spacing according to actual needs to adapt to the model and size of the PCB micro drill bit being processed. The number of partitions 7 can be increased or decreased as needed to match the length of the conveyor belt 5 surface.

[0031] Furthermore, in this embodiment, a pressure plate 11 is installed at the bottom of the sliding block 10, and a rubber pad 12 is installed on the side of the pressure plate 11 near the rubber side plate 6. A snap-fit ​​groove is provided inside the overlapping seat 8 on one side of the sliding groove. A snap-fit ​​block 13 is slidably connected inside the snap-fit ​​groove. A connecting groove is provided on one side of the snap-fit ​​block 13. First springs 14 are installed between both ends of the inner wall of the connecting groove and the inner wall of the snap-fit ​​groove. Slopes are provided at the opposite ends of the snap-fit ​​block 13 and the sliding block 10. A positioning groove is provided on one side of the sliding block 10. The positioning groove is slidably connected to one end of the snap-fit ​​block 13. After the partition 7 is moved to a suitable position on the surface of the conveyor belt 5 and the rubber side plate 6, it can be pressed... The pressure plate 11 presses the rubber pad 12 on its surface against the surface of the rubber side plate 6, causing the sliding block 10 to move closer to the locking groove in conjunction with the synchronizing rod 9. When the locking block 13 and the sliding block 10 come into contact, the ramps press against each other, pressing the locking block 13 into the inner side of the locking groove again, and forcing the two sets of first springs 14 to retract until the port of the positioning groove is close to the tip of the locking block 13. Then, the two sets of first springs 14, which are no longer under pressure, can drive the locking block 13 to pop out into the inner side of the positioning groove, thereby completing the locking of the sliding block 10 and the partition 7. Then, the closing plate 3 can be pushed back, allowing the corresponding first magnetic component 22 and second magnetic component to re-attract, so that the conveyor body 4 is in the working position.

[0032] When using the automatic PCB micro drill bit feeding device of this solution, the material can be fed downwards through the port of the feeding chute. The first PCB micro drill bit to fall contacts the surface of the conveyor belt 5 and is located between two adjacent sets of partitions 7. At the same time, the conveyor body 4 is started to drive the conveyor belt 5 and the rubber side plate 6 to rotate and transport the material. The partition 7 pushes the material on the surface of the conveyor belt 5 forward. After it is misaligned with the port formed by the feeding chute and the limiting seat 23, the material above it falls downwards to the two adjacent sets of partitions 7 on the other side. This sequential conveying is achieved. After the conveyor belt 5 and the partition 7 carry the material to the outermost edge, the PCB micro drill bit can slide downwards under its own weight. The material falls and finally slides along the inclined surface of the inner wall of the feed chute to the port of the discharge chute 19, and slides down the inner side of the discharge chute 19 to the inner side of the guide chute for discharge. When it is necessary to transport PCB micro drill bits of different sizes, you can first hold the handle and drive the threaded rod 17 to rotate, so that the adjusting plate 18 slides along the inner side of the adjusting groove, and drive the limiting seat 23 to slide inside the feed chute, so that the distance between the bottom end of the limiting seat 23 and the surface of the conveyor belt 5 matches the size of the PCB micro drill bit. Then you can hold the push-pull plate 21 and drive it to slide inside the push-pull groove, so that one of the first magnetic parts 22 and the second magnetic parts no longer attract each other, and bring out the conveyor body 4 on the closing plate 3 together. Then you can use your fingers to... Insert the lever 15 into the operating groove and push it upwards, allowing it to slide along the inside of the groove. This causes the locking block 13 to compress the two sets of first springs 14 and retract into the locking groove. At this point, the position of the sliding block 10 is no longer restricted, and it can work with the synchronizing rod 9 and the synchronizing groove to move the pressure plate 11 and rubber pad 12 at the bottom of the sliding block 10 away from the surface of the rubber side plate 6. Then, the adjacent partitions 7 can be adjusted to a suitable spacing according to actual needs to accommodate the model and size of the PCB micro drill bits being processed. The number of partitions 7 can be increased or decreased as needed to match the length of the conveyor belt 5. After the partitions 7 are moved to a suitable position on the surface of the conveyor belt 5 and the rubber side plate 6, Press down on the pressure plate 11 so that the rubber pad 12 on its surface is pressed tightly against the surface of the rubber side plate 6, so that the sliding block 10, together with the synchronous rod 9, moves closer to the locking groove. When the locking block 13 and the sliding block 10 come into contact, the ramps press against each other, pressing the locking block 13 into the locking groove again, and forcing the two sets of first springs 14 to retract until the port of the positioning groove is close to the tip of the locking block 13. Then, the two sets of first springs 14, which are no longer under pressure, can drive the locking block 13 to pop out into the positioning groove, thereby completing the locking of the sliding block 10 and the partition 7. Then, the closing plate 3 can be pushed back to allow the corresponding first magnetic component 22 and second magnetic component to re-adhere, so that the conveyor body 4 is in the working position.

[0033] The control method of this utility model is through a controller. The control circuit of the controller can be implemented by simple programming by those skilled in the art. The power supply is also common knowledge in the field. Since this utility model is used to protect mechanical devices, the control method and circuit connection will not be explained in detail.

[0034] The above embodiments are preferred implementations of this utility model. In addition, this utility model can also be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this utility model.

Claims

1. An automatic PCB micro drill bit feeding device, comprising a base (1), characterized in that: A feeding seat (2) is installed at one top end of the base (1). A feeding groove extending into the interior of the feeding seat (2) is opened at one top end of the feeding seat (2). A limiting groove is opened on one side of the feeding groove at the top of the feeding seat (2). A guide groove is opened at the bottom end of the feeding seat (2) near the top of the base (1). A movable discharge mechanism is installed on the limiting groove and the feeding seat (2). The movable discharge mechanism includes an adjusting feeding component and a limiting component. The adjusting feeding component is used to arrange and discharge the material. The limiting component is used to prevent the material from slipping during transportation.

2. The PCB micro drill bit automatic feeding device according to claim 1, characterized in that: The adjusting feeding assembly includes an extension groove opened on one side of the outer wall of the feeding seat (2), a closing plate (3) is slidably connected to the inner side of the extension groove, a conveyor body (4) is installed on one side of the closing plate (3), a conveyor belt (5) is installed on the conveyor body (4), and rubber side plates (6) are installed at both ends of the outer wall of the conveyor belt (5).

3. The PCB micro drill bit automatic feeding device according to claim 2, characterized in that: The surface of the conveyor belt (5) is covered with multiple sets of partitions (7). Both ends of the outer wall of the partition (7) are equipped with overlapping seats (8). One side of the overlapping seat (8) overlaps with the outer wall of the rubber side plate (6). A sliding groove is opened at one end of the bottom of the overlapping seat (8). Synchronization grooves are opened on both sides of the inner wall of the sliding groove. Synchronization rods (9) are slidably connected to the inner side of the synchronization groove. A sliding block (10) is installed between the two sets of synchronization rods (9). The sliding block (10) is slidably connected to the sliding groove. A discharge groove (19) is opened near the bottom of the discharge seat (2) and communicates with the inner side of the feed groove and the guide groove.

4. The PCB micro drill bit automatic feeding device according to claim 3, characterized in that: A pressure plate (11) is installed at the bottom of the sliding block (10). A rubber pad (12) is installed on the side of the pressure plate (11) near the rubber side plate (6). A snap-fit ​​groove is opened inside the overlapping seat (8) on one side of the sliding groove. A snap-fit ​​block (13) is slidably connected inside the snap-fit ​​groove. A connecting groove is opened on one side of the snap-fit ​​block (13). A first spring (14) is installed between the two ends of the inner wall of the connecting groove and the inner wall of the snap-fit ​​groove. A ramp is opened at the opposite ends of the snap-fit ​​block (13) and the sliding block (10). A positioning groove is opened on one side of the sliding block (10). The positioning groove is slidably connected to one end of the snap-fit ​​block (13).

5. The PCB micro drill bit automatic feeding device according to claim 4, characterized in that: An operating groove is provided on the outer wall of the connecting seat (8) near the top. A pull rod (15) is installed on the inner wall of the connecting groove between two sets of first springs (14). A toggle groove is provided between the operating groove and the snap-fit ​​groove. The toggle groove and the pull rod (15) are slidably connected. The other end of the pull rod (15) extends to the inner side of the operating groove.

6. The PCB micro drill bit automatic feeding device according to claim 5, characterized in that: The limiting component includes an adjusting cylinder (16) installed at one end of the top of the feeding seat (2). An adjusting groove is provided on one side of the adjusting cylinder (16). A threaded rod (17) is rotatably connected to the inner side of the adjusting groove. An adjusting plate (18) is threadedly connected to the outer side of the threaded rod (17). A limiting seat (23) is installed at the other end of the adjusting plate (18). An inclined surface corresponding to the inclined state of the conveyor belt (5) is provided at the bottom end of the limiting seat (23). A handle is rotatably connected to the top of the adjusting cylinder (16). One end of the handle extends to the inner side of the adjusting cylinder (16) and is fixedly connected to one end of the threaded rod (17).

7. The PCB micro drill bit automatic feeding device according to claim 6, characterized in that: The outer wall of the feeding seat (2) is located below the closing plate (3) and a fixed seat (20) is installed. The top of the fixed seat (20) is provided with a push-pull groove. A push-pull plate (21) is slidably connected to the inner side of the push-pull groove. One end of the push-pull plate (21) and the side section of the inner side of the push-pull groove are both T-shaped. The other end of the push-pull plate (21) is fixedly connected to the outer wall of the closing plate (3). A first magnetic element (22) is embedded in both ends of the outer wall of the push-pull plate (21). A second magnetic element that attracts the first magnetic element (22) is embedded in both sides of the inner wall of the push-pull groove.

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