Lifting clutch of crane

Abstract

According to the crane lifting clutch applied to the technical field of cranes, the moving assembly and the clutch assembly are arranged, hydraulic oil is introduced to extrude a piston to move, the piston moves to extrude a plurality of steel sheets and friction sheets, stable rotation is achieved, the protection assembly is arranged, and when the no-load condition occurs, the clutch assembly is not damaged. A swing plate rotates under the action of centrifugal force to drive a pressing plate to extrude an emergency stop switch to achieve emergency stop, when the overload condition occurs, an inductor detects that the rotating speed of an output shaft is too low, an electromagnetic ring II is started to attract a magnetic block to drive the swing plate to rotate, and the pressing plate extrudes the emergency stop switch to achieve emergency stop; during sudden stop, the electromagnetic valve is powered on to be opened to discharge hydraulic oil, the first electromagnetic ring is powered on to attract the permanent magnet ring to accelerate movement of the piston, and therefore the piston is accelerated to leave the clutch assembly, and faster sudden stop is achieved.

Description

Technical Field

[0001] This application relates to the technical field of cranes, and particularly to a lifting clutch of a crane. Background Art

[0002] Cranes are mainly used for the loading and unloading of goods. They can quickly and accurately unload the goods on the ship to the dock, or load the goods on the dock onto the ship. Cranes can complete a large number of loading and unloading operations in a very short time, improving the transportation efficiency of the port. Since cranes are involved in the loading, unloading and handling of a large amount of goods, after long-term or frequent use, the fatigue strength of the sling on the crane will be damaged. In this case, if the goods fall due to the sling breakage during handling, or the goods are not lifted, at this time, the gravity of the lifting end of the crane suddenly disappears, while the output power of the motor remains unchanged. In this way, the lifting end will rise rapidly, and the output shaft of the clutch will also rotate very fast, which is likely to cause damage to the device. In addition, when the goods being handled exceed the rated load of the crane, at this time, the crane will work overloaded. This will not only damage the fatigue strength of the sling, shorten the service life of the sling and the crane, but also the rotation speed of the lifting end and the output shaft of the clutch of the crane will be greatly reduced, while the output power of the motor remains unchanged. In this way, the motor will heat up and burn out, causing damage to the device.

[0003] Therefore, we propose a lifting clutch of a crane to solve the above problems. Summary of the Invention

[0004] 1. Technical Problems to be Solved

[0005] This application aims to solve the technical problem that in the prior art, when the crane is in a no-load or over-load situation, the rotation speeds of the lifting end and the output shaft of the lifting clutch are too fast or too slow, while the output power of the motor remains unchanged. In this way, the motor will heat up and burn out, causing damage to the device. Compared with the prior art, a lifting clutch of a crane is provided. By setting a moving component and a clutch component, hydraulic oil is introduced to squeeze the piston to move. Through the movement of the piston, multiple steel sheets and friction sheets are squeezed to achieve stable rotation. By setting a protection component, in the case of no-load and over-load, emergency stop can be realized to protect the device and avoid device damage.

[0006] 2. Technical Solutions

[0007] To solve the above technical problems, the present invention adopts the following technical solutions.

[0008] A crane lifting clutch, comprising an input shaft, an output shaft and a protective housing. The input shaft and the output shaft are respectively rotatably connected to both sides of the protective housing. A moving component, a clutch component and a protection component are arranged inside the protective housing. An input transmission shaft is fixedly connected to the input shaft, and an output transmission shaft is fixedly connected to the output shaft. An oil chamber and a moving chamber are formed inside the input transmission shaft.

[0009] Furthermore, the input shaft and the input transmission shaft are integrally formed, and the output shaft and the output transmission shaft are integrally formed.

[0010] Furthermore, an oil inlet hole and an oil drain hole are formed on the input shaft. An electromagnetic valve is arranged inside the oil drain hole. An oil inlet channel and an oil drain channel are formed inside the input shaft. The oil inlet hole is communicated with the oil inlet channel, and the oil drain hole is communicated with the oil drain channel.

[0011] Furthermore, the moving component includes a piston, a mounting seat and a pulling-back spring;

[0012] The piston is slidably connected to the outer wall of the input shaft, and the outer wall of the piston is hermetically and slidably connected to the inner wall of the oil chamber. The mounting seat is snap-connected to the end of the input shaft. A groove is formed on one side of the piston close to the output shaft. The pulling-back spring is fixedly connected between the groove and the mounting seat.

[0013] Furthermore, the clutch component includes steel sheets, friction plates and a limiting plate;

[0014] The steel sheets are slidably connected to the inner wall of the moving chamber. The friction plates are slidably connected to the outer wall of the output transmission shaft. A plurality of steel sheets and friction plates are provided and arranged at intervals. The limiting plate is fixedly connected to one end of the moving chamber close to the output shaft.

[0015] Furthermore, the protection component includes a mounting ring, a mounting bracket, a rotating shaft, a swinging plate, a pressing plate, a reset spring, an emergency stop switch, an electromagnetic ring I, a permanent magnet ring, a magnetic block, an electromagnetic ring II and an inductor;

[0016] The mounting ring is fixedly connected to the outer wall of the output shaft. The mounting bracket is fixedly connected to the mounting ring. The rotating shaft is rotatably connected to the mounting bracket. The swinging plate is fixedly connected to one side of the rotating shaft. The pressing plate is fixedly connected to the other side of the rotating shaft. The reset spring is fixedly connected between the mounting ring and the swinging plate. The emergency stop switch is arranged on the mounting ring and is located below the pressing plate. The volume and mass of the pressing plate are much smaller than those of the swinging plate.

[0017] Furthermore, the electromagnetic ring I is fixedly connected to the inner wall of the input transmission shaft by inlaying, and the permanent magnet ring is fixedly connected to the piston by inlaying. When the electromagnetic ring I is energized, its magnetism is opposite to that of the permanent magnet ring.

[0018] Further, the magnetic block is fixedly connected to the swing plate, the second electromagnetic ring is fixedly connected to the inner wall of the protective housing, the magnetism of the second electromagnetic ring when energized is opposite to that of the magnetic block, the inductor is arranged on the inner wall of the protective housing, and a reflective strip is attached to the side wall of the mounting bracket close to the inductor.

[0019] Compared with the prior art, the advantages of the present application are as follows:

[0020] (1) By setting the protection component, when there is an empty load, the rotation speed of the output shaft suddenly becomes faster, the swing plate rotates upward under the action of centrifugal force, and the pressing plate moves downward to squeeze the emergency stop switch to achieve emergency stop. When there is an overload, the rotation speed of the output shaft becomes slower or stops, lower than the standard speed. When the time for the inductor to sense the reflective strip exceeds the standard time, the system controls the second electromagnetic ring to start. The second electromagnetic ring is energized and attracts the magnetic block to drive the swing plate to rotate upward, thereby driving the pressing plate to rotate downward to squeeze the emergency stop switch to achieve emergency stop.

[0021] (2) By setting the first electromagnetic ring and the permanent magnetic ring, after the emergency stop switch is pressed, the solenoid valve and the first electromagnetic ring are energized. The solenoid valve is energized to open and connect the oil discharge hole with the oil chamber, so that the hydraulic oil is discharged through the oil discharge hole and the oil discharge channel. The first electromagnetic ring is energized and attracts the permanent magnetic ring to accelerate the movement of the piston, making the piston reset more quickly, so as to achieve emergency stop faster.

[0022] (3) By setting the volume and mass of the pressing plate to be much smaller than that of the swing plate, the centrifugal force received by the swing plate during rotation can be made larger than that of the pressing plate, realizing the pressing action of the pressing plate.

[0023] (4) By setting the moving component, the hydraulic oil enters the oil chamber through the oil inlet channel and the oil inlet hole, can squeeze the piston to move. The piston moves to squeeze the pull-back spring to compress it. At the same time, the piston moves to squeeze the clutch component to realize the rotation of the output shaft.

[0024] (5) By setting the pull-back spring, on the one hand, it can help the piston to reset, and on the other hand, it can enhance the stability of the piston, making the clutch drive more stable.

[0025] (6) By setting the clutch component, when the piston moves, it squeezes the steel sheet and the friction plate, driving the steel sheet and the friction plate to move on the surface of the moving cavity and the output transmission shaft respectively, so that the steel sheet and the friction plate are squeezed and pressed tightly. Thus, the input transmission shaft can drive the output transmission shaft to rotate through the pressed steel sheet and friction plate, realizing the stable rotation of the input shaft driving the output shaft, and further realizing the loading and unloading and handling of goods.

[0026] (7) By setting the friction plate, the surface of the friction plate is rough, which can increase the resistance between the steel sheet and the friction plate.

[0027] (8) By arranging multiple steel sheets and friction plates at intervals, the friction between the multiple steel sheets and friction plates can be superimposed, increasing the overall frictional resistance between the steel sheets and friction plates, making the transmission connection more stable.

[0028] (9) By integrally forming the input shaft and the input transmission shaft, and integrally forming the output shaft and the output transmission shaft, the connection strength between the input shaft and the input transmission shaft and between the output shaft and the output transmission shaft can be enhanced, thereby improving the stability of the clutch transmission.

[0029] (10) By setting an electromagnetic valve to block the oil drain hole, which is not opened during normal operation and is opened when the device operates abnormally to timely drain the hydraulic oil in the oil chamber through the oil drain hole, achieving an emergency stop more quickly. Description of the Drawings

[0030] Figure 1 is the overall structural schematic diagram of the present application;

[0031] Figure 2 is the structural schematic diagram of the fitting state of the steel sheet and the friction plate in the present application;

[0032] Figure 3 is Figure 2 the enlarged partial structural view of part A in

[0033] Figure 4 is Figure 2 the enlarged partial structural view of part B in

[0034] Figure 5 is the structural schematic diagram of the separated state of the steel sheet and the friction plate in the present application;

[0035] Figure 6 is Figure 5 the enlarged partial structural view of part C in

[0036] Explanation of the reference numerals in the drawings:

[0037] 1. Input shaft; 2. Output shaft; 3. Protective housing; 4. Moving component; 401. Piston; 402. Mounting seat; 403. Pull-back spring; 5. Clutch component; 501. Steel sheet; 502. Friction plate; 503. Limiting plate; 6. Protection component; 601. Mounting ring; 602. Mounting bracket; 603. Rotating shaft; 604. Swing plate; 605. Pressing plate; 606. Reset spring; 607. Emergency stop switch; 608. Electromagnetic ring I; 609. Permanent magnet ring; 610. Magnetic block; 611. Electromagnetic ring II; 612. Inductor; 7. Input transmission shaft; 701. Oil chamber; 702. Moving chamber; 703. Oil inlet hole; 704. Oil drain hole; 705. Oil inlet channel; 706. Oil drain channel; 8. Output transmission shaft; 9. Electromagnetic valve. Detailed Description of the Invention

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0039] Embodiment 1:

[0040] The present invention provides a crane lifting clutch. Please refer to Figure 1 , Figure 2 and Figure 5 . A crane lifting clutch includes an input shaft 1, an output shaft 2 and a protective housing 3. The input shaft 1 and the output shaft 2 are respectively rotatably connected to both sides of the protective housing 3. A moving component 4, a clutch component 5 and a protection component 6 are arranged inside the protective housing 3. An input transmission shaft 7 is fixedly connected to the input shaft 1, and an output transmission shaft 8 is fixedly connected to the output shaft 2. An oil chamber 701 and a moving chamber 702 are formed inside the input transmission shaft 7. The input shaft 1 and the input transmission shaft 7 are integrally formed, and the output shaft 2 and the output transmission shaft 8 are integrally formed, which can enhance the connection strength between the input shaft 1 and the input transmission shaft 7 and between the output shaft 2 and the output transmission shaft 8, thereby improving the stability of the clutch transmission.

[0041] An oil inlet hole 703 and an oil drain hole 704 are formed on the input shaft 1. A solenoid valve 9 is arranged in the oil drain hole 704. The solenoid valve 9 blocks the oil drain hole 704 and is not opened during normal operation. When the device malfunctions, it is opened to drain the hydraulic oil in the oil chamber 701 through the oil drain hole 704 in a timely manner, so as to achieve an emergency stop more quickly. An oil inlet channel 705 and an oil drain channel 706 are formed inside the input shaft 1. The oil inlet hole 703 is communicated with the oil inlet channel 705, and the oil drain hole 704 is communicated with the oil drain channel 706.

[0042] Please refer to Figure 2 and Figure 5 . The moving component 4 includes a piston 401, a mounting seat 402 and a pulling spring 403. The piston 401 is slidably connected to the outer wall of the input shaft 1, and the outer wall of the piston 401 is slidably connected to the inner wall of the oil chamber 701 in a sealed manner. The mounting seat 402 is clamped at the end of the input shaft 1. A groove is formed on one side of the piston 401 close to the output shaft 2. The pulling spring 403 is fixedly connected between the groove and the mounting seat 402. On the one hand, the pulling spring 403 can help the piston 401 to reset, and on the other hand, it can enhance the stability of the piston 401, making the clutch transmission more stable.

[0043] Specifically, the hydraulic oil enters the oil chamber 701 through the oil inlet passage 705 and the oil inlet hole 703, squeezes the piston 401 to move, the piston 401 moves to squeeze the pull-back spring 403 to compress it, and at the same time the piston 401 moves to squeeze the clutch assembly 5 to realize the rotation of the output shaft 2.

[0044] Please refer to Figure 2 and Figures 4 - 6 , the clutch assembly 5 includes a steel sheet 501, a friction plate 502 and a limiting plate 503; the steel sheet 501 is slidably connected to the inner wall of the moving chamber 702, the friction plate 502 is slidably connected to the outer wall of the output transmission shaft 8, and the surface of the friction plate 502 is rough, which can increase the resistance between the steel sheet 501 and the friction plate 502. There are multiple steel sheets 501 and friction plates 502 and they are arranged at intervals. The multiple steel sheets 501 and friction plates 502 arranged at intervals can make the friction between the multiple steel sheets 501 and friction plates 502 superimposed, increasing the overall frictional resistance between the steel sheet 501 and the friction plate 502, making the transmission connection more stable. The limiting plate 503 is fixedly connected to one end of the moving chamber 702 close to the output shaft 2, and the limiting plate 503 limits the movement of the steel sheet 501 and the friction plate 502.

[0045] Specifically, when the piston 401 moves, it squeezes the steel sheet 501 and the friction plate 502, driving the steel sheet 501 and the friction plate 502 to move in the moving chamber 702 and on the surface of the output transmission shaft 8 respectively, so that the steel sheet 501 and the friction plate 502 are squeezed and pressed together. Thus, the input transmission shaft 7 can drive the output transmission shaft 8 to rotate through the pressed steel sheet 501 and friction plate 502, so as to realize the stable rotation of the input shaft 1 driving the output shaft 2, and further realize the loading, unloading and handling of goods.

[0046] Please refer to Figures 2 - 3 and Figure 5, the protection component 6 includes an installation ring 601, an installation frame 602, a rotating shaft 603, a swing plate 604, a pressing plate 605, a return spring 606, an emergency stop switch 607, an electromagnetic ring 608, a permanent magnet ring 609, a magnetic block 610, an electromagnetic ring 611 and a sensor 612; the installation ring 601 is fixedly connected to the outer wall of the output shaft 2, the installation frame 602 is fixedly connected to the installation ring 601, the rotating shaft 603 is rotatably connected to the installation frame 602, the swing plate 604 is fixedly connected to one side of the rotating shaft 603, the pressing plate 605 is fixedly connected to the other side of the rotating shaft 603, the swing plate 604 rotates together with the output shaft 2, and the centrifugal force during rotation drives the swing plate 604 to rotate upward, and the pressing plate 605 moves downward to squeeze the emergency stop switch 607 to achieve emergency stop during no-load operation. The return spring 606 is fixedly connected between the installation ring 601 and the swing plate 604. The emergency stop switch 607 is arranged on the installation ring 601 and is located below the pressing plate 605. The volume and mass of the pressing plate 605 are much smaller than those of the swing plate 604, so that the centrifugal force received by the swing plate 604 during rotation is greater than that of the pressing plate 605, realizing the pressing action of the pressing plate 605.

[0047] The electromagnetic ring 608 is inlaid and fixedly connected to the inner wall of the input transmission shaft 7, the permanent magnet ring 609 is inlaid and fixedly connected to the piston 401. The magnetic property of the electromagnetic ring 608 when energized is opposite to that of the permanent magnet ring 609. When the electromagnetic ring 608 is energized, it attracts the permanent magnet ring 609, which can accelerate the movement of the piston 401 and make the piston 401 reset more quickly.

[0048] The magnetic block 610 is fixedly connected to the swing plate 604, the electromagnetic ring 611 is fixedly connected to the inner wall of the protective housing 3. The magnetic property of the electromagnetic ring 611 when energized is opposite to that of the magnetic block 610. When the electromagnetic ring 611 is energized, it attracts the magnetic block 610, which can drive the swing plate 604 to rotate upward, thereby driving the pressing plate 605 to rotate downward to squeeze the emergency stop switch 607 to achieve emergency stop during overload. The sensor 612 is arranged on the inner wall of the protective housing 3, and a reflective strip is pasted on the side wall of the installation frame 602 close to the sensor 612.

[0049] Specifically, when the no-load situation occurs, the rotation speed of the output shaft 2 suddenly increases. The swing plate 604 rotates upward under the action of centrifugal force, causing the pressing plate 605 to move downward and squeeze the emergency stop switch 607. When the overloading situation occurs, the rotation speed of the output shaft 2 slows down or stops, being lower than the standard speed. When the time for the sensor 612 to sense the reflective strip exceeds the standard time, the system controls the second electromagnetic ring 611 to start. The second electromagnetic ring 611 is energized and attracted to the magnet block 610, driving the swing plate 604 to rotate upward, thereby driving the pressing plate 605 to rotate downward and squeeze the emergency stop switch 607. After the emergency stop switch 607 is pressed, the solenoid valve 9 and the first electromagnetic ring 608 are energized. The solenoid valve 9 is energized to open, connecting the oil discharge hole 704 with the oil chamber 701, enabling the hydraulic oil to be discharged through the oil discharge hole 704 and the oil discharge channel 706. The first electromagnetic ring 608 is energized and attracted to the permanent magnet ring 609, accelerating the movement of the piston 401, enabling the piston 401 to reset more quickly, and thus achieving emergency stop more rapidly.

[0050] Working principle: When the crane is working normally, the hydraulic oil enters the oil chamber 701 through the oil inlet channel 705 and the oil inlet hole 703, squeezing the piston 401 to move. The piston 401 moves to squeeze the pull-back spring 403 to compress it. At the same time, when the piston 401 moves, it squeezes the steel sheet 501 and the friction plate 502, driving the steel sheet 501 and the friction plate 502 to move in the moving chamber 702 and on the surface of the output transmission shaft 8 respectively, making the steel sheet 501 and the friction plate 502 be squeezed and pressed tightly. Thus, the input transmission shaft 7 and the output transmission shaft 8 can rotate through the tightly pressed steel sheet 501 and friction plate 502, thereby realizing the stable rotation of the input shaft 1 driving the output shaft 2, and further realizing the loading, unloading and handling of goods.

[0051] When the no-load situation occurs, the rotation speed of the output shaft 2 suddenly increases. The swing plate 604 rotates upward under the action of centrifugal force, causing the pressing plate 605 to move downward and squeeze the emergency stop switch 607, achieving emergency stop.

[0052] When the overloading situation occurs, the rotation speed of the output shaft 2 slows down or stops, being lower than the standard speed. When the time for the sensor 612 to sense the reflective strip exceeds the standard time, the system controls the second electromagnetic ring 611 to start. The second electromagnetic ring 611 is energized and attracted to the magnet block 610, driving the swing plate 604 to rotate upward, thereby driving the pressing plate 605 to rotate downward and squeeze the emergency stop switch 607, achieving emergency stop.

[0053] When the emergency stop switch 607 is pressed, the solenoid valve 9 and the first electromagnetic ring 608 are energized. The energized solenoid valve 9 opens to connect the oil drain hole 704 with the oil chamber 701, allowing the hydraulic oil to be discharged through the oil drain hole 704 and the oil drain channel 706. The energized first electromagnetic ring 608 attracts the permanent magnet ring 609, accelerating the movement of the piston 401 and enabling the piston 401 to reset more quickly. After the piston 401 resets and leaves the steel sheet 501, there is no longer any extrusion between the steel sheet 501 and the friction plate 502, and the two separate from each other. The output transmission shaft 8 and the input transmission shaft 7 lose the transmission relationship, and the output shaft 2 stops rotating, thus achieving emergency stop more quickly.

[0054] As described above, it is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application, according to the technical solution and its improved concept of the present application, makes equivalent substitutions or changes, and should be covered by the protection scope of the present application.

Claims

1. A crane lifting clutch, comprising an input shaft (1), an output shaft (2) and a protective housing (3), characterized in that, The input shaft (1) and the output shaft (2) are respectively rotatably connected to both sides of the protective housing (3). A moving component (4), a clutch component (5) and a protection component (6) are arranged inside the protective housing (3). An input transmission shaft (7) is fixedly connected to the input shaft (1), and an output transmission shaft (8) is fixedly connected to the output shaft (2). An oil chamber (701) and a moving chamber (702) are formed inside the input transmission shaft (7).

2. The lifting clutch of a crane according to claim 1, characterized in that, The input shaft (1) and the input transmission shaft (7) are integrally formed, and the output shaft (2) and the output transmission shaft (8) are integrally formed.

3. A crane lifting clutch according to claim 1, characterized in that, An oil inlet hole (703) and an oil drain hole (704) are formed on the input shaft (1). A solenoid valve (9) is arranged inside the oil drain hole (704). An oil inlet channel (705) and an oil drain channel (706) are formed inside the input shaft (1). The oil inlet hole (703) communicates with the oil inlet channel (705), and the oil drain hole (704) communicates with the oil drain channel (706).

4. A crane lifting clutch according to claim 1, characterized in that, The moving component (4) includes a piston (401), a mounting seat (402) and a pulling-back spring (403); The piston (401) is slidably connected to the outer wall of the input shaft (1), and the outer wall of the piston (401) is sealingly and slidably connected to the inner wall of the oil chamber (701). The mounting seat (402) is snap-connected to the end of the input shaft (1). A groove is formed on one side of the piston (401) close to the output shaft (2). The pulling-back spring (403) is fixedly connected between the groove and the mounting seat (402).

5. A crane lifting clutch according to claim 1, characterized in that, The clutch component (5) includes steel sheets (501), friction plates (502) and a limiting plate (503); The steel sheets (501) are slidably connected to the inner wall of the moving chamber (702), the friction plates (502) are slidably connected to the outer wall of the output transmission shaft (8). A plurality of the steel sheets (501) and the friction plates (502) are provided and arranged at intervals. The limiting plate (503) is fixedly connected to one end of the moving chamber (702) close to the output shaft (2).

6. The lifting clutch of a crane according to claim 1, characterized in that, The protection component (6) includes a mounting ring (601), a mounting bracket (602), a rotating shaft (603), a swinging plate (604), a pressing plate (605), a reset spring (606), an emergency stop switch (607), an electromagnetic ring I (608), a permanent magnet ring (609), a magnetic block (610), an electromagnetic ring II (611) and a sensor (612); The mounting ring (601) is fixedly connected to the outer wall of the output shaft (2), the mounting bracket (602) is fixedly connected to the mounting ring (601), the rotating shaft (603) is rotatably connected to the mounting bracket (602). The swinging plate (604) is fixedly connected to one side of the rotating shaft (603), the pressing plate (605) is fixedly connected to the other side of the rotating shaft (603). The reset spring (606) is fixedly connected between the mounting ring (601) and the swinging plate (604). The emergency stop switch (607) is arranged on the mounting ring (601) and is located below the pressing plate (605). The volume and mass of the pressing plate (605) are much smaller than those of the swinging plate (604).

7. A crane lifting clutch according to claim 6, characterized in that, The electromagnetic ring 1 (608) is inlaid and fixedly connected to the inner wall of the input transmission shaft (7). The permanent magnet ring (609) is inlaid and fixedly connected to the piston (401). When the electromagnetic ring 1 (608) is energized, its magnetism is opposite to that of the permanent magnet ring (609).

8. A lifting clutch of a crane according to claim 6, characterized in that, The magnetic block (610) is fixedly connected to the swing plate (604). The electromagnetic ring 2 (611) is fixedly connected to the inner wall of the protective housing (3). When the electromagnetic ring 2 (611) is energized, its magnetism is opposite to that of the magnetic block (610). The inductor (612) is arranged on the inner wall of the protective housing (3). A reflective strip is attached to the side wall of the mounting bracket (602) close to the inductor (612).

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