Control method and device for preventing collision and falling of mechanical arm of toll station

Abstract

The invention relates to the technical field of card senders, in particular to a toll station mechanical arm anti-collision and anti-falling control method which comprises the following steps that S1, a mechanical arm stretches out, and a vehicle is detected in real time through a first sensor arranged on a card sending part and a second sensor arranged on a moving part; s2, according to the detection conditions of the first sensor and the second sensor in the step S1, it is judged that the corresponding card issuing part falls off or the whole mechanical arm falls off; s3, the collision position of the vehicle and the mechanical arm is detected, and when the speed of the vehicle is high and the first sensor and the second sensor do not respond in time, the collision position is judged through a pressure sensor; s4, the collision impact force on the card issuing part is detected, and whether the whole mechanical arm falls off or the card issuing part falls off is determined according to the pressure detected by a pressure sensor; and S5, the mechanical arm is restored to the initial position through a reset module.

Description

Technical Field

[0001] The present invention relates to the technical field of card issuing machines, and in particular to a method and device for controlling a toll station mechanical arm from collision and falling. Background Art

[0002] While the vehicle identification system in ETC channels boasts high accuracy and sensitivity, it can still fail to detect a vehicle in certain complex environments. For example, if a vehicle is traveling too fast, there's significant signal interference from the vehicle's electronic tag, or there's interference from other metal objects around the vehicle, the system may be unable to promptly and accurately identify the vehicle. In these situations, the card dispenser's robotic arm will extend normally according to its pre-programmed procedure to issue a card. However, because the vehicle hasn't been detected, the arm's extension interferes with the vehicle's normal trajectory, resulting in a collision between the arm and the vehicle.

[0003] In addition to undetected vehicles, special vehicle types with narrow fronts and extra-wide bodies are also a significant factor in collisions with the robotic arm. In real-world traffic, some large trucks, construction vehicles, and other similar vehicles have relatively narrow fronts to facilitate maneuverability in tight spaces, but their bodies often extend beyond the lane width. When such vehicles enter an ETC lane, their narrow fronts may allow them to pass smoothly during vehicle identification system detection. However, as the vehicle continues to move, the wider body of the vehicle gradually approaches the area where the robotic arm is located.

[0004] If the robotic arm fails to detect the approaching vehicle and continues to execute the card-issuing operation according to its original trajectory, it can easily collide with the vehicle. Furthermore, due to the greater weight of the vehicle, the impact force generated by the collision is also greater, causing more serious damage to the robotic arm and even causing it to fall from its mounting position, leading to more serious safety accidents and equipment failures.

[0005] Therefore, the present application has developed a method and device for preventing collision and falling of a toll station robot arm to solve the problems existing in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and device for controlling the collision and falling prevention of a toll station mechanical arm, so as to solve the problem of mechanical arms in card issuing machines being damaged by collision in the prior art.

[0007] The technical solution of the present invention is: a method for controlling a toll booth mechanical arm from collision and falling, using a mechanical arm anti-collision and falling device composed of a mechanical arm and a card issuing machine, the mechanical arm including a card issuing portion and a moving portion, one end of the moving portion being mounted on a base of the card issuing machine by magnetic rotation, and the other end being connected to the card issuing portion by magnetic attraction, the card issuing portion being extended by the rotation of the moving portion, the card issuing portion and the moving portion being respectively provided with a first sensor and a second sensor facing the direction of vehicle entry, and the card issuing portion and the moving portion being further provided with a pressure sensor; The control method is as follows: S1: The robotic arm extends and detects the vehicle in real time through the first sensor on the card issuing part and the second sensor on the moving part; S2: According to the detection results of the first sensor and the second sensor in step S1, it is determined that the corresponding card issuing part is detached or the entire robotic arm is detached; S3: Detecting the collision position between the vehicle and the robotic arm: When the vehicle speed is high and the first sensor and the second sensor fail to respond in time, the collision position is determined by the pressure sensor; S4: Detecting the impact force on the card issuing part: determining whether the entire robot arm falls or the card issuing part falls according to the pressure detected by the pressure sensor; S5: Restore the robotic arm to its initial position through the reset module.

[0008] Preferably, in step S2, the shedding conditions include the following two: a) If the first sensor detects a vehicle but the second sensor does not detect a vehicle, the magnetic attraction between the card issuing portion and the moving portion is disconnected, causing the card issuing portion to fall alone; b) If both the first sensor and the second sensor detect a vehicle, the magnetic attraction between the moving part and the base is disconnected, causing the entire robotic arm to fall.

[0009] Preferably, in step S3, the shedding conditions include the following two: a) If only the pressure sensor on the card issuing part measures the pressure, only the magnetic attraction between the card issuing part and the moving part is cut off, causing the card issuing part to fall alone; b) If the pressure sensors on both the card issuing part and the moving part measure pressure, or if only the pressure sensor on the moving part measures pressure, the magnetic attraction between the moving part and the base is disconnected, causing the entire robotic arm to fall.

[0010] Preferably, in step S4, the shedding conditions include the following two: a) If the pressure sensor detects that the pressure value is less than the threshold, only the magnetic attraction between the card issuing part and the moving part is cut off, causing the card issuing part to fall alone; b) If the pressure sensor detects a pressure value greater than a threshold, the magnetic attraction between the moving part and the base is disconnected, causing the entire robotic arm to fall.

[0011] Preferably, the magnetic attraction between the hairpin portion and the moving portion is smaller than the magnetic attraction between the moving portion and the base.

[0012] A toll station mechanical arm anti-collision and falling device, comprising: A card issuing machine, wherein the card issuing machine has a base; A robotic arm, comprising a clipping portion and a moving portion, wherein one end of the moving portion is magnetically connected to a base and rotates around the center of the base, and the other end of the moving portion is magnetically connected to the clipping portion; A reset module is located in the card issuing machine, and includes two driving devices and two traction parts. One end of each traction part is connected to the corresponding driving device, and the other end is connected to the moving part and the card issuing part. When the driving device rotates, the moving part and the card issuing part are tightened by the traction part. The detection module includes a first sensor, a second sensor and a pair of pressure sensors. The first sensor and the second sensor are respectively installed on the sides of the moving part and the card-issuing part facing the vehicle, with the transmitting end facing the vehicle, and the pair of pressure sensors are installed on the sides.

[0013] Preferably, the driving device includes a driving mechanism and a rotating wheel, the driving shaft of the driving mechanism is inserted in the center of the rotating wheel, so that the rotating wheel rotates together with the driving shaft, and one end of the traction part is fixed to the outer wall surface of the rotating wheel.

[0014] Preferably, the surfaces of the base and the hairpin portion are symmetrically provided with magnetic portions with opposite magnetism, and correspondingly, the two end faces of the moving portion corresponding to the magnetic portions exhibit symmetrical and opposite magnetism.

[0015] Compared with the prior art, the advantages of the present invention are: (1) The first sensor and the second sensor detect the vehicle. Based on the detection results, the control system cuts off the magnetic attraction between the card issuing part and the moving part, causing the card issuing part to fall alone, or cuts off the magnetic attraction between the card issuing part and the moving part, and between the moving part and the base, causing the entire robotic arm to fall, thereby reducing the degree of damage to key components caused by the collision; (2) After the anti-collision and drop operation is completed, the driving shaft of the driving device is reliably connected to the rotating wheel, and one end of the traction part is fixedly connected to the outer wall of the rotating wheel. When the driving mechanism moves, the traction part can rotate around the rotating wheel and wrap around it, pulling the robotic arm back to its initial position; (3) The magnetic attraction force between the clipping part and the moving part is smaller than the magnetic attraction force between the moving part and the base. The clipping part can be quickly disconnected at the early stage of the collision, preventing the impact force from being transmitted to the moving part and the base, limiting the damage to the clipping part, reducing maintenance costs, and minimizing the risk of damage to the robotic arm. (4) Magnetic parts with opposite magnetism are symmetrically arranged on the surfaces of the base and the hairpin part. The two end faces where the moving part is connected to the base and the hairpin part present symmetrical and opposite magnetism. This ensures that after the hairpin part and the moving part, and the moving part and the base are magnetically re-attached, there is only one installation position, eliminating the possibility of sensor deviation and ensuring that the sensor is oriented correctly after the robot arm returns to its initial position, thereby ensuring the accuracy of subsequent detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flow chart of a method for controlling the collision and falling prevention of a toll station mechanical arm according to the present invention; Figure 2 This is a three-dimensional diagram of a toll station mechanical arm anti-collision and fall device according to the present invention; Figure 3 This is a three-dimensional view of the toll station mechanical arm anti-collision and fall device according to the present invention from another direction; Figure 4 for Figure 3 A is an enlarged schematic diagram; Figure 5 This is a cross-sectional view of a toll station mechanical arm anti-collision and fall device according to the present invention; Figure 6 for Figure 5 A magnified schematic diagram of B.

[0017] Among them: 1. Card issuing machine; 11. Base; 2. Robotic arm; 21. Card issuing part; 22. Moving part; 3. Reset module; 31. Driving device; 311. Driving mechanism; 312. Rotating wheel; 32. Traction part; 4. Detection module; 41. First sensor; 42. Second sensor; 43. Pressure sensor. DETAILED DESCRIPTION

[0018] The present invention will be described in further detail below with reference to specific embodiments: like Figure 1-Figure 4 As shown, a toll station mechanical arm anti-collision and falling control method includes the following steps: S1: When the card issuing machine 1 at the toll station receives the card issuing instruction, the robotic arm 2 starts to extend. On the robotic arm 2, a first sensor 41 and a second sensor 42 are respectively provided on the card issuing part 21 and the moving part 22. The card issuing part 21 is the part of the robotic arm 2 that directly interacts with the vehicle and is used to deliver the pass card; the moving part 22 is responsible for driving the card issuing part 21 to complete various movement movements. Electromagnets are provided at the connection positions of the moving part 22 and the base 11 and the card issuing part 21, and the moving part 22 can rotate around the center of the base 11 driven by the motor.

[0019] While robotic arm 2 is extending, first sensor 41 and second sensor 42 continue to operate, detecting vehicles in real time. Both first and second sensors 41 and 42 are infrared sensors that transmit and receive infrared signals. When robotic arm 2 stops moving, the infrared sensors, located on the robotic arm and not extending beyond it, receive signals, indicating a collision with a vehicle is imminent.

[0020] S2: According to the detection conditions of the first sensor 41 and the second sensor 42 in step S1, it is determined that the corresponding card issuing portion 21 is detached or the entire robot arm 2 is detached.

[0021] If the first sensor 41 detects a vehicle but the second sensor 42 does not, the vehicle may only be at risk of colliding with the card issuing unit 21, while the moving unit 22 is relatively safe. In this case, the control system will immediately cut off the power, thereby breaking the magnetic attraction between the card issuing unit 21 and the moving unit 22. Once the magnetic attraction is broken, the card issuing unit 21 will fall independently under its own weight, thus avoiding a collision that could cause more serious damage to the card issuing unit 21 or the robotic arm 2. If both first sensor 41 and second sensor 42 detect a vehicle, this indicates an impending collision between the vehicle and the motion unit 22. Simply disconnecting the release unit 21 will not effectively prevent damage from the collision. Therefore, the control system immediately shuts off power, quickly breaking the magnetic attraction between the motion unit 22 and the base 11, allowing the entire robotic arm 2 to fall from the base 11, minimizing damage to key components of the robotic arm 2.

[0022] S3: In actual operation, the vehicle is traveling normally, but the ETC system does not detect it and the vehicle shows no sign of stopping. At this time, the robotic arm 2 is extending or has just reached the card issuing position, causing the first sensor 41 and the second sensor 42 to fail to respond in time. The detection information is sent to the control system, which controls the power supply and causes the card issuing unit 21 or the robotic arm 2 to fall off. To cope with this unexpected situation, pressure sensors 43 are installed on both the card issuing unit 21 and the moving unit 22. When the vehicle collides with the robotic arm 2, the pressure sensors 43 can promptly detect the pressure generated by the collision. If pressure is present, a collision has occurred; if no pressure is present, no collision has occurred.

[0023] If only the pressure sensor 43 on the card issuing portion 21 detects pressure, this indicates that the collision occurred on the card issuing portion 21, and the moving portion 22 was not directly impacted. In this case, the control system will only disconnect the magnetic attraction between the card issuing portion 21 and the moving portion 22, allowing the card issuing portion 21 to fall alone. This protects the moving portion 22 and other key components from damage and prevents the card issuing portion 21 from being continuously impacted, which could cause damage to the card issuing portion 21. If the pressure sensors 43 on both the card issuing portion 21 and the moving portion 22 detect pressure, or if only the pressure sensor 43 on the moving portion 22 detects pressure, this indicates that the collision has affected the entire structure of the robotic arm 2. The control system will immediately disconnect the magnetic attraction between the moving portion 22 and the base 11, causing the robotic arm 2 to fall as a whole, preventing further collisions.

[0024] S4: When only the card issuing part 21 collides, the impact force on the card issuing part 21 is different due to the different speeds of the vehicles. In order to prevent the vehicle speed from being too fast and the impact force from being too large, relying solely on the gravity of the card issuing part 21 itself, its falling speed cannot completely avoid the impact force. Therefore, it is necessary to determine the falling mode of the robot arm 2 based on the pressure detected by the pressure sensor 43, that is, to set a threshold value based on different regions and the gravity of the card issuing part 21, and the two pressure sensors 43 are located adjacent to the first sensor 41 and the second sensor 42 respectively.

[0025] When the pressure sensor 43 detects pressure, it transmits the detected pressure value to the control system, which compares it with a preset threshold. If the pressure value detected by the pressure sensor 43 is less than the threshold, it indicates that the impact force generated by the collision is relatively small, and the card issuing portion 21 can fall quickly due to its own gravity without being damaged by further collision. In this case, the control system only disconnects the magnetic attraction between the card issuing portion 21 and the moving portion 22, allowing the card issuing portion 21 to fall alone, thus preventing the entire robot arm 2 from falling unnecessarily. If the pressure sensor 43 detects a pressure value greater than the threshold, this indicates that the impact force generated by the collision is large, and it can be judged that the vehicle speed at this time is fast. In order to prevent damage to the card issuing part 21, the control system will disconnect the magnetic attraction between the moving part 22 and the base 11, causing the robotic arm 2 to fall as a whole, increasing the gravity of the moving part 22, and accelerating the falling speed, thereby avoiding damage to the card issuing part 21.

[0026] S5: After completing the aforementioned anti-collision and drop operation, in order for the toll station card issuing machine 1 to resume normal operation as quickly as possible, the reset module 3 is used to restore the robotic arm 2 to its initial position. The reset module 3 controls the various components of the robotic arm 2 to reassemble and reposition them according to a pre-set program, ensuring that the robotic arm 2 can accurately and stably perform subsequent card issuing tasks.

[0027] Furthermore, the magnetic attraction force generated between the card issuing portion 21 and the moving portion 22 is smaller than the magnetic attraction force generated between the moving portion 22 and the base 11. When an abnormal situation such as a collision occurs, the order in which different parts of the robotic arm 2 fall off can be accurately controlled according to the preset logic. The card issuing portion 21 can be quickly disconnected at the initial stage of the collision to prevent the impact force from being transmitted to the upper arm and the base 11, limiting the damage to the forearm, reducing maintenance costs, and minimizing the risk of damage to the robotic arm 2.

[0028] like Figure 2-Figure 4 As shown, a toll station robot arm anti-collision and falling device includes a card issuing machine 1, a robot arm 2, a reset module 3 and a detection module 4, wherein the card issuing machine 1 is the main bearing structure of the device, equipped with a base 11, providing physical support for the stable operation of the robot arm 2, the robot arm 2 includes a card issuing part 21 and a moving part 22, one end of the moving part 22 is connected to the base 11 by a magnetic connection, and has the function of rotating around the center of the base 11, and the rotation angle range should meet the toll station card issuing operation, and the other end of the moving part 22 is also connected to the base 11 by a magnetic connection. The connection method is connected to the card issuing part 21, and the connection of each structure can be controlled by powering on and off through magnetic attraction; the reset module 3 is arranged inside the card issuing machine 1, and includes two driving devices 31 and two traction parts 32. One end of the two traction parts 32 is respectively connected to the corresponding driving device 31, and the other end is respectively connected to the moving part 22 and the card issuing part 21. When the driving device 31 rotates, the pulling force generated by the traction part 32 will tighten the moving part 22 or the card issuing part 21 that falls due to the collision to the initial position, and continue the card issuing action.

[0029] like Figure 4As shown, the detection module 4 includes a first sensor 41, a second sensor 42, and a pair of pressure sensors 43. The first sensor 41 and the second sensor 42 are respectively installed on the sides of the moving part 22 and the card issuing part 21 facing the vehicle, with the transmitting end facing the vehicle to ensure accurate detection of the vehicle. The first sensor 41 is located at the end of the card issuing part 21 away from the card issuing machine 1, and the second sensor 42 is located at the end of the moving part 22 away from the card issuing machine 1. The arrangement of these positions can ensure the timeliness and accuracy of vehicle entry detection without detection blind spots. A pair of pressure sensors 43 are also installed on these sides to accurately transmit pressure signals to the control system.

[0030] Specifically, such as Figure 5-Figure 6 As shown, the drive device 31 includes a drive mechanism 311 and a rotating wheel 312, which work together to achieve the reset of the robot arm 2. The drive shaft of the drive mechanism 311 and the center hole of the rotating wheel 312 are assembled using an interference fit or key connection method, ensuring sufficient connection strength and transmission accuracy between the drive shaft and the rotating wheel 312, so that the rotating wheel 312 can rotate synchronously and stably with the drive shaft. One end of the traction part 32 is fixedly connected to the outer wall surface of the rotating wheel 312 by a reliable fastening method such as welding or bolt connection. When the drive mechanism 311 moves, the traction part 32 can rotate around the rotating wheel 312, thereby winding around the rotating wheel 312 and pulling the robot arm 2 back to its initial position.

[0031] In order to prevent the orientation of the corresponding sensor from changing after the robotic arm 2 returns to the initial position, magnetic parts with opposite magnetism are symmetrically arranged on the surfaces of the base 11 and the card part 21. Correspondingly, the two end faces of the moving part 22 connected to the base 11 and the card part 21 exhibit symmetrical and opposite magnetism corresponding to the above-mentioned magnetic parts. The magnetic strength of the end face of the moving part 22 matches the magnetic strength of the magnetic parts on the surface of the base 11 and the card part 21, so that after the card part 21 and the moving part 22 are magnetically re-attracted, and the moving part 22 and the base 11 are magnetically re-attracted, there is only one installation position, which eliminates the possibility of sensor deviation. When the robotic arm 2 is pulled back to the initial position, the magnetic attraction direction of the corresponding moving part 22 or the card part 21 changes, repulsion will be generated on the adjacent surfaces and offset will occur until the two mutually attractive magnetic surfaces are opposite, thereby connecting to form a complete robotic arm 2.

[0032] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they are not intended to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention.

Claims

1. A toll station robot arm anti-collision and fall control method, characterized in that: A mechanical arm (2) anti-collision and falling device is provided, which is composed of a mechanical arm (2) and a card issuing machine (1). The mechanical arm (2) includes a card issuing part (21) and a moving part (22). One end of the moving part (22) is mounted on a base (11) of the card issuing machine (1) by magnetic attraction and rotation, and the other end is connected to the card issuing part (21) by magnetic attraction. The card issuing part (21) is extended by the rotation of the moving part (22). The card issuing part (21) and the moving part (22) are respectively provided with a first sensor (41) and a second sensor (42) facing the direction of vehicle entry, and the card issuing part (21) and the moving part (22) are also provided with a pressure sensor (43). The control method is as follows: S1: The robotic arm (2) extends and detects the vehicle in real time through a first sensor (41) provided on the card issuing portion (21) and a second sensor (42) provided on the moving portion (22); S2: Based on the detection results of the first sensor (41) and the second sensor (42) in step S1, it is determined whether the corresponding card issuing portion (21) has fallen off or the entire robotic arm (2) has fallen off; S3: Detecting the position where the vehicle collides with the robotic arm (2): When the vehicle is moving at a high speed, causing the first sensor (41) and the second sensor (42) to fail to respond in time, the collision position is determined by the pressure sensor (43); S4: Detecting the magnitude of the collision impact force on the card issuing portion (21): determining whether the entire robot arm (2) falls or the card issuing portion (21) falls based on the magnitude of the pressure detected by the pressure sensor (43); S5: The robot arm (2) is restored to its initial position through the reset module (3).

2. A toll booth robot arm anti-collision and fall control method according to claim 1, characterized in that: In step S2, the shedding conditions include the following two: a) if the first sensor (41) detects a vehicle and the second sensor (42) does not detect a vehicle, the magnetic attraction between the card issuing portion (21) and the moving portion (22) is disconnected, causing the card issuing portion (21) to fall alone; b) If both the first sensor (41) and the second sensor (42) detect a vehicle, the magnetic attraction between the moving part (22) and the base (11) is disconnected, causing the entire robotic arm (2) to fall.

3. The method for controlling a toll booth robot arm against collision and falling according to claim 1, characterized in that: In step S3, the shedding conditions include the following two: a) If only the pressure sensor (43) on the card issuing portion (21) measures the pressure, only the magnetic attraction between the card issuing portion (21) and the moving portion (22) is disconnected, causing the card issuing portion (21) to fall alone; b) If the pressure sensors (43) on both the card issuing portion (21) and the moving portion (22) measure pressure, or if only the pressure sensor (43) on the moving portion (22) measures pressure, the magnetic attraction between the moving portion (22) and the base (11) is disconnected, causing the robotic arm (2) to fall as a whole.

4. The method for controlling a toll booth robot arm against collision and falling according to claim 1, characterized in that: In step S4, the shedding conditions include the following two: a) If the pressure sensor (43) detects a pressure value less than a threshold value, only the magnetic attraction between the card issuing portion (21) and the moving portion (22) is disconnected, causing the card issuing portion (21) to fall alone; b) If the pressure sensor (43) detects a pressure value greater than a threshold value, the magnetic attraction between the moving part (22) and the base (11) is disconnected, causing the entire robotic arm (2) to fall.

5. The method for preventing collision and falling of a toll booth mechanical arm according to claim 1, characterized in that: The magnetic attraction between the card-issuing portion (21) and the moving portion (22) is smaller than the magnetic attraction between the moving portion (22) and the base (11).

6. A toll station robot arm anti-collision and fall device, controlled by a toll station robot arm (2) anti-collision and fall control method according to any one of claims 1 to 5, characterized in that: include: A card issuing machine (1), wherein the card issuing machine (1) has a base (11); A robotic arm (2), the robotic arm (2) comprising a card-isolating portion (21) and a moving portion (22), one end of the moving portion (22) being connected to the base (11) by magnetic attraction and rotating around the center of the base (11), and the other end of the moving portion (22) being connected to the card-isolating portion (21) by magnetic attraction; A reset module (3) is located in the card issuing machine (1), and the reset module (3) includes two driving devices (31) and two traction parts (32). One end of the two traction parts (32) is respectively connected to the corresponding driving device (31), and the other end is respectively connected to the moving part (22) and the card issuing part (21). When the driving device (31) rotates, the moving part (22) and the card issuing part (21) are tightened by the traction parts (32); A detection module (4), the detection module (4) comprising a first sensor (41), a second sensor (42) and a pair of pressure sensors (43), the first sensor (41) and the second sensor (42) being respectively mounted on the sides of the moving portion (22) and the card issuing portion (21) facing the vehicle, with the transmitting end facing the vehicle, and the pair of pressure sensors (43) being mounted on the sides.

7. The toll booth mechanical arm anti-collision and fall device according to claim 6, characterized in that: The driving device (31) comprises a driving mechanism (311) and a rotating wheel (312). The driving shaft of the driving mechanism (311) is inserted into the center of the rotating wheel (312), so that the rotating wheel (312) rotates together with the driving shaft. One end of the traction portion (32) is fixed to the outer wall surface of the rotating wheel (312).

8. The toll booth mechanical arm anti-collision and fall device according to claim 6, characterized in that: The surfaces of the base (11) and the hairpin portion (21) are both symmetrically provided with magnetic portions having opposite magnetic properties, and correspondingly, the two end faces of the moving portion (22) corresponding to the magnetic portions exhibit symmetrical and opposite magnetic properties.

Images