Automatic ball receiving and sending device for pigging

Abstract

The invention belongs to the technical field of oil and gas pipeline maintenance, and discloses an automatic ball receiving and sending device for pigging, which comprises an automatic ball sending assembly and an automatic ball receiving assembly, the automatic ball serving assembly and the automatic ball collecting assembly each comprise a ball direction switching mechanism and a ball pushing mechanism, the ball direction switching mechanism in the automatic ball serving assembly is provided with a ball storage pipe, and the ball direction switching mechanism in the automatic ball collecting assembly is provided with a collecting box. By the adoption of the scheme, automatic sending and recycling of the spherical pig can be achieved, remote operation is facilitated, the working intensity of workers is reduced, the pipeline cleaning efficiency is improved, meanwhile, safety risks are avoided, in addition, a detector in the spherical pig is matched, a pipeline can be detected to a certain degree, two effects can be achieved through one procedure, and the requirement for safe, green and energy-saving construction operation is better met.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline maintenance technology, specifically relating to an automatic pig launching and receiving device for pipeline cleaning. Background Technology

[0002] In the maintenance of oil and gas gathering and transportation pipelines, pipeline cleaning has always been a crucial step in ensuring the efficient and safe operation of the pipelines. Traditional pipeline cleaning operations rely heavily on manual labor, which has many drawbacks. On the one hand, manual operation is tedious and labor-intensive, requiring a large investment of manpower and is prone to operational risks due to human error, especially when dealing with pipelines containing toxic or hazardous media, posing a serious threat to the safety of operators.

[0003] On the other hand, traditional equipment has a low degree of automation and cannot meet the high-pressure and complex operating conditions required for modern oil and gas pipeline cleaning. Its cleaning efficiency is also insufficient to meet the requirements of daily pipeline maintenance. Although some automated cleaning devices have been proposed in the prior art, such as the patent with patent number "202110630729.7" entitled "A Fully Automatic Cleaning Ball Launching Device and Its Usage Method", which mainly achieves circumferential cleaning through a ball-changing mechanism and automatic cleaning operation through valve control, the applicant found in the research that the reliability of the circumferential cleaning mechanism is relatively poor, which reduces the overall practicality and the complex structure directly increases the implementation cost.

[0004] In addition, existing pipeline cleaning operations mainly involve cleaning the deposits on the inner wall of the pipeline, which has a relatively simple function and relatively high construction or cost, and does not meet the development needs of green and energy-saving operations. Summary of the Invention

[0005] In view of this, the present invention provides an automatic pig launching and receiving device for pipeline cleaning, so as to solve the problems of cumbersome, inefficient, and high operational intensity and safety risks in existing pipeline cleaning operations.

[0006] The technical solution is as follows:

[0007] An automatic ball-launching and ball-retrieving device for cleaning pipes includes an automatic ball-launching component and an automatic ball-retrieving component; both the automatic ball-launching component and the automatic ball-retrieving component include a ball-direction switching mechanism and a ball-pushing mechanism, wherein the ball-direction switching mechanism in the automatic ball-launching component is equipped with a ball storage tube, and the ball-direction switching mechanism in the automatic ball-retrieving component is equipped with a collection box.

[0008] By adopting the above solutions, automated pipe cleaning operations can be achieved, allowing personnel to be relatively far away from the site, thereby improving safety and cleaning efficiency.

[0009] Preferably, the ball-direction switching mechanism includes a housing with two orthogonally arranged channels, channel A and channel B. A switch ball is positioned at the orthogonal point of each channel within the housing, and the switch ball has a connecting cavity adapted to the channel. The housing has a drive mechanism for controlling the switch ball's 90-degree forward and reverse rotation. The drive mechanism drives the switch ball to rotate, enabling either the two ends of channel A or the two ends of channel B to connect. The channels are adapted to the pigging pig. The ball-direction switching mechanism adopts a structure similar to a ball valve, utilizing ball rotation to connect different channels, thereby achieving the functions of pig delivery and reception as well as channel sealing. The design is ingenious and easy to implement. Furthermore, the drive mechanism can directly adopt an electrically controlled ball valve structure, further reducing implementation difficulty.

[0010] Preferably, one end of the communicating cavity has a stop structure. This design primarily serves to stop the incoming pig, preventing it from detaching from the other end and improving reliability.

[0011] Preferably, the stop structure is detachably installed within the communicating cavity. This design improves its practicality.

[0012] Preferably, both the automatic ball-serving assembly and the automatic ball-retrieving assembly are equipped with a negative pressure device. By employing this solution and utilizing the negative pressure device, gas leakage during the ball-serving and ball-retrieving processes can be prevented or reduced, further improving safety.

[0013] Preferably, the suction and discharge ends of the negative pressure device are both located at the top of the corresponding pipeline. This design ensures proper operation and avoids interference with liquid transport.

[0014] Preferably, a pigging ball is configured with a design compatible with the internal communication cavity and storage tube of the switching ball. The pigging ball contains a detector, which includes a cylinder and an integrated microprocessor, ultrasonic thickness measurement module, positioning module, communication module, and power supply. With this design, the detector operates synchronously during the pigging process, allowing for inspection of the pipeline's inner wall. This facilitates monitoring of the pipeline's condition without requiring separate pipeline inspections or reducing the frequency of inspections, thus enhancing the effectiveness of the pigging operation and improving pipeline maintenance.

[0015] Preferably, the ball-pushing mechanism is an electric push rod. This design facilitates automated control, improves operational efficiency, and allows for direct procurement.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] The automatic pig launching and receiving device for pipeline cleaning provided by this invention, with the automatic launching component and the automatic receiving component working together, can realize the automatic launching and receiving of the pig, which is convenient for remote operation, thereby reducing the labor intensity of personnel, improving the efficiency of pipeline cleaning, and avoiding safety risks. In addition, with the detector inside the pig, the pipeline can be inspected to a certain extent. One process achieves two functions, which better meets the needs of safe, green and energy-saving construction operations. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention;

[0019] Figure 2 for Figure 1 Top view;

[0020] Figure 3 This is a schematic diagram of the ball direction switching mechanism in the automatic ball serving assembly;

[0021] Figure 4 for Figure 3 Sectional view;

[0022] Figure 5 This is a schematic diagram of the ball direction switching mechanism in the automatic ball recovery assembly;

[0023] Figure 6 for Figure 5 Sectional view;

[0024] Figure 7 Schematic diagram of the negative pressure device

[0025] Figure 8 This is a schematic diagram of the pigging system.

[0026] Figure 9 Diagram showing detector installation;

[0027] Figure 10 This is a schematic diagram of the internal circuit module of the detector;

[0028] Figure 11 This is a diagram showing the microprocessor connections;

[0029] Figure 12 Schematic diagram of GNSS module;

[0030] Figure 13 This is a schematic diagram of a USB communication interface;

[0031] Figure 14 This is a schematic diagram of the power module;

[0032] Figure 15 This is a schematic diagram of a wireless communication module. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings.

[0034] refer to Figures 1 to 15 The automatic ball-launching and receiving device for cleaning pipes shown includes an automatic ball-launching component and an automatic ball-receiving component. Both the automatic ball-launching component and the automatic ball-receiving component include a ball-direction switching mechanism 400 and a ball-pushing mechanism 700. The ball-direction switching mechanism 400 in the automatic ball-launching component is equipped with a ball storage tube 410, and the ball-direction switching mechanism 400 in the automatic ball-receiving component is equipped with a collection box 420. The following mainly focuses on its installation and use.

[0035] During installation, the starting end of the gathering and transportation pipeline 600 is connected to the launching pipe section 200, and the ending end of the gathering and transportation pipeline 600 is connected to the receiving pipe section 300. The automatic launching assembly and the automatic receiving assembly are respectively installed on the launching pipe section 200 and the receiving pipe section 300. The automatic launching assembly sends the pig into the starting end of the gathering and transportation pipeline 600, and uses fluid to push the pig to complete the pig cleaning operation of the gathering and transportation pipeline 600. Finally, the pig is recovered at the ending end of the gathering and transportation pipeline 600 by the automatic receiving assembly.

[0036] In this embodiment, the ball orientation switching mechanism 400 is mainly used to adjust the direction of the pigging ball to realize the ball launching and collecting operations. The ball orientation switching mechanism 400 in the automatic ball launching assembly and the automatic ball collecting assembly has a basically the same structure, as shown in the figure. Both include a housing 430. The housing 430 has two orthogonally arranged channels, namely channel A431 and channel B432. A switch ball 440 is provided in the housing 430 corresponding to the orthogonal part of the two channels. The switch ball 440 has a connecting cavity 441 adapted to the channel. The housing 430 has a drive mechanism 450 for controlling the switch ball 440 to rotate 90 degrees forward and backward. The drive mechanism 450 drives the switch ball 440 to rotate, which can connect the two ends of channel A431 or the two ends of channel B432. The channel is adapted to the pigging ball and can allow the pigging ball to pass through.

[0037] In practice, the drive mechanism 450 can adopt a structure similar to an electric ball valve and be equipped with a manually operated turntable.

[0038] refer to Figures 1 to 6The housing 430 mainly includes a hollow body 433. The body 433 has two orthogonally arranged through holes. Limiting plugs 434 are provided at both ends of the two through holes. The four limiting plugs 434 together form the rotation space of the switch ball 440. The inner end of the limiting plug 434 is provided with a sealing structure 435. The sealing structure 435 is annular and contacts the surface of the switch ball 440 to achieve a seal. The outer end of the limiting plug 434 has a flange connecting seat 436. The flange connecting seat 436 is fixed to the limiting plug 434 and the body 433 by bolts. Sealing gaskets are provided between the end face of the flange connecting seat 436 and the end face of the limiting plug 434, and between the end face of the through hole of the body 433.

[0039] It should be noted that, for ease of connection and use, the ball direction switching mechanism 400 in the automatic ball serving assembly and the automatic ball receiving assembly are slightly different. In the ball direction switching mechanism 400 of the automatic ball serving assembly, one of the limit plugs 434 has a blind plate 437 directly mounted at its end, and the corresponding flange connection seat 436 is used to install the ball storage tube 410. In the ball direction switching mechanism 400 of the automatic ball receiving assembly, the limit plugs 434 are all connected to the flange connection seat 436.

[0040] To ensure that the pig can only exit from one end after entering the connecting cavity 441, a stop structure 442 is provided at one end of the connecting cavity 411. The stop structure 442 has a through hole in the middle, and both ends of the through hole are rounded and chamfered to allow the ball pushing mechanism 700 to extend into it for ball pushing operation and to prevent jamming. The stop structure 442 can be integrally formed with the switch ball 440 or installed separately. In this embodiment, the stop structure 442 is generally annular and is installed by threaded connection, so that stop structures with different through hole sizes can be installed as needed.

[0041] During installation, the launching pipe section 200 is connected to the gathering and transportation pipe 600 in a T-shape, while the receiving pipe section 300 is connected to the gathering and transportation pipe 600 in a cross shape, as shown in the figure. In this embodiment, the pushing mechanism 700 adopts an electric push rod structure. The diameter of the push rod is smaller than the diameter of the through hole in the middle of the stop structure 442, and the front end of the push rod is concave or a connector with a concave structure is fixedly installed. This can better push the cleaning ball and prevent slippage.

[0042] To enable more automated ball launching and retrieval and improve operational safety, a first electric gate valve 610 and a second electric gate valve 620 are installed on the gathering and transportation pipeline 600, as shown in the figure. The first electric gate valve 610 is located upstream of the launching pipe section 200 and near the connection between the launching pipe section 200 and the gathering and transportation pipeline 600. Correspondingly, the second electric gate valve 620 is located upstream of the retrieval pipe section 300 and near the automatic ball retrieval assembly.

[0043] In the initial state:

[0044] In the automatic ball-launching assembly: the connecting cavity 441 of the switch ball 440 in the ball-direction switching mechanism 400 is in a vertical position, and the stop structure 442 is located below. The ball storage pipe 410 is set vertically, and the top of the gas pipe has a removable sealing plate. The pigging ball inside can fall into the connecting cavity 441. The design should be uniformly designed according to the inner diameter of the gathering and transportation pipeline 600 to ensure that only one pigging ball can be accommodated in the connecting cavity 441 at this time.

[0045] In the automatic ball receiving assembly: the connecting cavity 441 of the switch ball 440 in the ball direction switching mechanism 400 is in a horizontal position, the channel A431 is connected to the collection and transportation pipeline 600, the stop structure 442 in the switch ball 440 is located at the end away from the automatic ball launching assembly, and the corresponding ball pushing mechanism 700 and collection box 420 are set at both ends of the channel B432, as shown in the figure. The ball pushing mechanism 700 and collection box 420 are located on both sides of the collection and transportation pipeline 600.

[0046] To avoid or reduce gas leakage during ball serving or retrieval, both the automatic ball serving assembly and the automatic ball retrieval assembly are equipped with a negative pressure device 500. (Reference) Figure 1 and Figure 7 In this embodiment, the negative pressure device 500 adopts an exhaust fan structure, mainly including an exhaust pipe 510. An impeller is rotatably installed inside the exhaust pipe 510. A motor 520 for driving the impeller to rotate is provided outside the exhaust pipe 510. It should be noted that the motor 520 and the impeller adopt a sealed transmission method, such as gear box transmission, or a sealing cover is set outside the exhaust pipe 510 corresponding to the motor 520. The motor adopts an external method, which is relatively safer and can extend the service life.

[0047] In addition, both ends of the exhaust pipe 510 are flanges 530 for quick assembly and disassembly. As shown in the figure, the launching pipe section 200 has a tee connector A210, and the collecting and transporting pipe 600 is provided with tee connectors B630 and C640 in sequence at the positions corresponding to the launching pipe section 200. Tee connector C640 is located downstream of tee connector B630. The flanges 530 at both ends of the exhaust pipe 510 are connected to the bypass ports of tee connectors A210 and C640 respectively. When installing, pay attention to the direction of negative pressure to ensure that when the motor is working, the gas in tee connector A210 can be drawn into tee connector C640.

[0048] The negative pressure device 500 on the ball receiving pipe section 300 is installed in a similar manner, as shown in the figure. One end of the ball direction switching mechanism 400 in the automatic ball receiving assembly is connected to a tee connector D310, and the collection box can be installed and fixed on the tee connector D310. A tee connector E650 is provided on the collection and transportation pipeline 600 downstream of the channel A431. The two ends of the exhaust pipe 510 of the corresponding negative pressure device 500 are connected to the bypass ports of the tee connector D310 and the tee connector E650, respectively, to draw the gas in the tee connector D310 into the tee connector E650.

[0049] In practice, the suction end and the discharge end of the negative pressure device 500 are both located at the top of the corresponding pipes to achieve a better suction effect.

[0050] In another embodiment, to further improve operational safety, electrically controlled gate valves (not shown in the figure) can be installed at both ends of the exhaust pipe 510. This can reduce the sealing requirements of the motor drive. During normal conveying, the two ends are sealed by the electrically controlled gate valves to prevent gas from entering the exhaust pipe 510 or passing through the exhaust pipe 510, effectively eliminating leakage problems during normal conveying.

[0051] It should be noted that the pigging gantry used with the pig-direction switching mechanism 400 in this application is equipped with a detector 110, as detailed in the reference below. Figures 8 to 15 The pigging sphere mainly includes a sphere 100 and a detector 110 installed inside the sphere 100. The detector 110 mainly includes a cylinder 111, and a microprocessor 112, an ultrasonic thickness measurement module 113, a positioning module 114, a communication module 115, and a power supply 116 that supplies power to all components. The power supply 116 has a corresponding power supply circuit.

[0052] The sphere 100 has a mounting hole 120 that is compatible with the detector 110. The detector 110 is detachably installed in the mounting hole 120, usually by threaded installation. In addition, there is a gap between the detector 110 and the outer end of the corresponding mounting hole 120. The ultrasonic thickness measuring module 113 mainly consists of an ultrasonic pulse probe and a corresponding thickness measuring circuit. Its specific principle can be found in patent number 202211296407.4, entitled "An Ultrasonic Thickness Gauge", which will not be elaborated here. In order to improve the detection accuracy of the ultrasonic thickness measuring module 113, the ultrasonic thickness measuring module 113 is located near the outer end of the mounting hole 120, that is, the ultrasonic pulse probe is located at the outermost end.

[0053] During the cleaning process in the gathering and transportation pipeline, the pig mainly rolls and slides. In order to avoid the ultrasonic pulse probe always pointing towards the axis of the pipeline, which would make it impossible to accurately detect the condition of the pipe wall, at least three mounting holes 120 are provided on the sphere 100. The three mounting holes 120 are in the same plane and are distributed at an angle of 120°. Each mounting hole 120 is equipped with a detector 110 in a detachable manner.

[0054] like Figures 10 to 15 In specific implementation, the microprocessor 112 adopts a C8051F340 / 341 / 344 / 345 microcontroller and is electrically connected to the thickness measurement circuit. The communication module 115 can be a Bluetooth module, a WiFi module, or a GSM module. In this embodiment, an ESP-07WIFI wireless communication module is used. The positioning module 114 adopts a GNSS module. The microprocessor is connected to the GNSS module through two pins, P1.6 and P1.7, to obtain positioning data. The GNSS module adopts a NEO-M8U navigation module, which supports GPS / GLONASS and Beidou satellite signals to achieve global coverage and high-precision positioning. It has a built-in inertial navigation unit (IMU) to maintain continuous positioning when satellite signals are interrupted. It can achieve more accurate positioning in the pipeline, avoid the loss of position information, and is more conducive to the one-to-one correspondence between thickness measurement data and positioning data.

[0055] In addition, the detector in this application is also equipped with a storage device 117 (SST25VF064), which is mainly used to store the received microprocessor data. In this embodiment, a FLASH storage chip or a memory card is used, and the data can be read through a USB communication interface and a wireless communication module.

[0056] The outer surface of the cylinder 111 is equipped with a power module switch and a USB communication interface. The switch is used to control the power module's rechargeable battery to supply power to the microprocessor, other chips, and circuit lights. The USB communication interface can be connected to an external charging power supply (not shown). The external charging power supply can charge the power module's rechargeable battery through the USB communication interface. The USB communication interface charges the rechargeable battery through the TP4056 module. In addition, data in the storage device can be read through the USB communication interface.

[0057] In practice, to further improve the service life of the pigging ball, the ball 100 is made of carbon fiber reinforced silicon carbide ceramic matrix composite material.

[0058] refer to Figures 1 to 15 The automatic ball launching and receiving device for pipeline cleaning shown is used as follows:

[0059] S1. In the initial state, multiple cleaning balls are pre-stored in the ball storage tube 410. The number is determined according to the cleaning needs. When the cleaning ball is put in, the detector 110 inside the cleaning ball is activated. In the ball direction switching mechanism 400 of the automatic ball launching component, the connecting cavity 441 of the switch ball 440 is connected to the ball storage tube 410. There is only one cleaning ball in the connecting cavity 441. The first electric gate valve 610 and the second electric gate valve 620 are in the open state.

[0060] S2. After starting the cleaning process, first close the first electric gate valve 610 and the second electric gate valve 620. Then, open the electrically controlled gate valves at both ends of the negative pressure device 500 on the launching pipe section 200. The negative pressure device will start working and maintain a negative pressure state.

[0061] S3, in the ball direction switching mechanism 400 of the automatic ball serving assembly, the switch ball 440 rotates 90 degrees (e.g., Figure 4 The switch ball is driven to rotate vertically counterclockwise by 90° through the drive mechanism, so that the connecting cavity 441 is connected to the channel B432, and the stop structure 442 is relatively close to the ball pushing mechanism. Then, the corresponding ball pushing mechanism 700 pushes the pigging ball into the gathering and transportation pipeline 600. Then the automatic ball launching component and the corresponding ball pushing mechanism 700 are reset, and the corresponding negative pressure device 500 is turned off at the same time.

[0062] S4. Open the first electric gate valve 610 and the second electric gate valve 620. Use fluid to push the cleaning ball to perform cleaning operations. During the cleaning operation, the cleaning ball also performs pipeline inspection. The cleaning ball cleans the inner wall, while the detector works to detect the pipeline wall thickness and match the wall thickness data with the position data. The detection results are stored for subsequent reading and analysis.

[0063] S5. When the pig reaches the automatic pig recovery assembly, it is blocked by the stop structure 442 and stops in the communication cavity of the corresponding switch ball. At this time, the first electric gate valve 610 and the second electric gate valve 620 are closed, and the automatic pig recovery assembly is used to recover the pig. In specific operation, the corresponding negative pressure device 500 is activated first, the ball direction switching mechanism of the automatic pig recovery assembly works, and the inlet end of the switch ball (the end near the second electric gate valve 620) rotates counterclockwise towards the port where the tee connector D310 is located. During the process, the switch ball can be rotated slowly. When the switch ball rotates 45°, channels A431 and B432 can be temporarily connected through the connecting cavity. At this time, the pressure in the pipeline can be discharged through channel B432, thereby achieving the purpose of pressure relief. Until the connecting cavity is aligned with the tee connector D310, that is, the connecting cavity and channel B432 are completely aligned, the corresponding push ball mechanism 700 pushes the pig in the connecting cavity out and falls into the collection box 420. The collection box 420 has multiple arc-shaped sinks, which can be used to place the pig.

[0064] In the actual implementation process, the pipeline cleaning system is used in conjunction with the background PLC control system. The first electric gate valve 610, the second electric gate valve 620, the two ball direction switching mechanisms 400, the two negative pressure devices 500, and the ball pushing mechanism 700 can all be remotely controlled through the background. Of course, in actual operation, pressure sensors and position sensors can also be installed on the gathering and transportation pipeline to achieve better pipeline cleaning control. The fully automated operation greatly reduces labor intensity. After the pipeline cleaning is completed, the detector inside the cleaning ball can be removed and the internal data can be read through the USB interface (or it can be read directly through wireless communication without removing it) to quickly understand the pipeline condition. In specific implementation, the data from multiple detectors can be comprehensively analyzed to obtain more accurate pipe wall information, which is conducive to reducing or preventing pipeline safety accidents.

[0065] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. An automatic ball launching and receiving device for pipeline cleaning, characterized in that: Includes an automatic ball-serving component and an automatic ball-collecting component; Both the automatic ball-serving assembly and the automatic ball-collecting assembly include a ball-direction switching mechanism (400) and a ball-pushing mechanism (700). The ball-direction switching mechanism (400) in the automatic ball-serving assembly is equipped with a ball storage tube (410), and the ball-direction switching mechanism (400) in the automatic ball-collecting assembly is equipped with a collection box (420).

2. The automatic ball launching and receiving device for pipeline cleaning according to claim 1, characterized in that: The ball-direction switching mechanism (400) includes a housing (430), which has two orthogonally arranged channels, namely channel A (431) and channel B (432). A switch ball (440) is provided in the housing (430) at the orthogonal position of the two channels. The switch ball (440) has a communication cavity (441) adapted to the channel. The housing (430) has a drive mechanism (450) for controlling the switch ball (440) to rotate 90 degrees forward and backward. The drive mechanism (450) drives the switch ball (440) to rotate, which can connect the two ends of channel A (431) or the two ends of channel B (432).

3. The automatic ball launching and receiving device for pipeline cleaning according to claim 2, characterized in that: One end of the communicating cavity (441) has a stop structure (442).

4. The automatic ball launching and receiving device for pipeline cleaning according to claim 3, characterized in that: The stop structure (442) is detachably installed in the communicating cavity (441).

5. The automatic ball launching and receiving device for pipeline cleaning according to any one of claims 2 to 4, characterized in that: Both the automatic ball-serving assembly and the automatic ball-retrieving assembly are equipped with a negative pressure device (500).

6. The automatic ball launching and receiving device for pipeline cleaning according to claim 5, characterized in that: The suction end and discharge end of the negative pressure device (500) are both located at the top of the corresponding pipe.

7. The automatic ball launching and receiving device for pipeline cleaning according to any one of claims 2 to 4, characterized in that: A cleaning ball is configured to be compatible with the internal cavity of the switch ball (440) and the ball storage tube (410). The cleaning ball is equipped with a detector (110). The detector (110) includes a cylinder (111) and a microprocessor (112), an ultrasonic thickness measurement module (113), a positioning module (114), a communication module (115) and a power supply (116) integrated and installed in the cylinder (111).

8. The automatic ball launching and receiving device for pipeline cleaning according to any one of claims 1 to 4, characterized in that: The ball-pushing mechanism (700) is an electric push rod.

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