A eccentricity speed regulation's sports teaching ball class projection auxiliary device

Abstract

The application provides a sports teaching ball class throwing auxiliary device with eccentric wheel speed regulation, and relates to the technical field of sports teaching auxiliary equipment. The sports teaching ball class throwing auxiliary device with eccentric wheel speed regulation comprises a chassis, an adjusting table, an extension frame, a monitoring and identification module, a ball table and a steering table. The bottom of the chassis is rotationally connected with the steering table and is provided with a moving wheel frame. The top end of the chassis is fixed with the adjusting table and the ball table. The adjusting table is fixed with the extension frame, and the top end of the adjusting table is provided with the monitoring and identification module. The adjusting table is provided with a fixed shell, a motor one and a motor two. The fixed shell is rotationally connected with coaxially nested transmission pipes one and two. The worm shafts at the driving ends of the two motors are respectively engaged with the worm wheels at the ends of the two transmission pipes. Through the cooperative matching of the coaxially nested eccentric stepless speed regulation of the double motors, the double-degree-of-freedom electric angle adjustment, the monitoring and identification adaptive teaching and the detachable ball collecting net frame, the comprehensive technical effects of convenient speed regulation, flexible angle, intelligent teaching and efficient ball collecting are achieved.

Description

Technical Field

[0001] This invention relates to the field of sports teaching auxiliary equipment technology, specifically to a sports teaching ball throwing auxiliary device with eccentric wheel speed regulation. Background Technology

[0002] In ball sports teaching and training, teachers need to repeatedly throw balls at different speeds and angles to students to train their catching reaction, hitting action, and body coordination. Manual ball throwing has problems such as high labor intensity, poor consistency of throwing force, and difficulty in continuous teaching for long periods of time. Therefore, various automatic ball throwing devices are gradually being applied to sports teaching scenarios.

[0003] Existing ball-launching devices have the following shortcomings in practical use: First, the launch force adjustment of existing devices mostly adopts a fixed eccentric wheel structure or a stepped adjustment method of manually loosening and locking the eccentric pin. The adjustment process requires stopping the machine, and the eccentricity can only change in fixed increments, which cannot achieve real-time stepless speed regulation during operation. The speed range is narrow, the operation is cumbersome, and it is difficult to meet the needs of quickly switching training intensity in teaching. Second, the angle adjustment mechanism of existing devices is mostly a manual turning and bolt locking structure in a single plane, which can only achieve single-degree-of-freedom adjustment of pitch or horizontal angle, and cannot simultaneously complete electric dual-degree-of-freedom adjustment of horizontal rotation and pitch angle. The training direction and throwing arc are limited, making it difficult to simulate multi-angle ball-incoming scenarios in actual combat; thirdly, existing devices generally lack the ability to perceive and provide feedback on the user's training status, cannot automatically match the throwing force according to the distance between the user and the device, and cannot identify the user's throwing action characteristics and provide real-time correction guidance. The device exists only as a passive throwing tool and cannot play an active guiding role in teaching; fourthly, the ball recovery structure of existing devices is mostly a fixed-size ball collection basket or net, and the collection range cannot be adjusted. When facing different ball types such as basketballs, volleyballs, and footballs and different training scenarios, it is impossible to quickly expand or collect the ball collection area, resulting in low ball recovery efficiency and large storage space occupation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a sports teaching ball-launching auxiliary device with eccentric wheel speed regulation, which solves the problems of existing launching devices, such as the need to stop the machine for speed regulation, the step-by-step nature of the speed regulation, the need for manual adjustment of the angle with only one degree of freedom, the lack of intelligent recognition and correction, and the fixed and non-expandable ball-collecting range.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an eccentric wheel speed-regulating auxiliary device for ball throwing in sports teaching, comprising a base frame, an adjustment platform, an extension frame, a monitoring and identification module, a ball table, and a steering platform. The bottom of the base frame is rotatably connected to the steering platform and is equipped with a movable wheel frame. The top of the base frame is fixed with an adjustment platform and a ball table. The adjustment platform is fixed with an extension frame and its top is equipped with a monitoring and identification module. The adjustment platform is equipped with a fixed shell, motor one, and motor two. The fixed shell is rotatably connected to coaxially nested transmission tube one and transmission tube two. The worm gears at the drive ends of the two motors mesh with the worm wheels at the ends of the two transmission tubes respectively. The front end of the fixed shell is rotatably connected to an eccentric wheel that is fixed to transmission tube one. The eccentric wheel fixes the adjustment shell and is rotatably connected to a screw. The front end of transmission tube two is driven by bevel gear one and bevel gear two on the screw. The screw is threadedly connected to a moving block. The extension frame is hinged to the serving rod and the outer wall boss of the moving block is fitted into the inner wall guide groove. The steering platform is equipped with a motor three and a motor four radial gear table traction mechanism to adjust the base frame angle; the ball table bottom side is equipped with a lower ball frame, and the outer side is equipped with a detachable ball collection net frame.

[0006] Preferably, the first transmission tube is a hollow tube, and the second transmission tube is a solid shaft passing through the first transmission tube. The two are supported by bearings and can rotate independently. The worm gear at the drive end of the first motor meshes with the worm wheel at the end of the second transmission tube to form a first reduction pair, and the worm gear at the drive end of the second motor meshes with the worm wheel at the end of the first transmission tube to form a second reduction pair. The lead angles of both sets of worm gears and worm wheels are less than the equivalent friction angle, which has a reverse self-locking characteristic. The moving block has a trapezoidal threaded hole that cooperates with the screw. The cylindrical boss on the outer wall of the moving block is embedded in the long guide groove on the inner wall of the serving stick to form a sliding pair. The serving stick reciprocates around the hinge shaft of the extension frame.

[0007] Preferably, the toothed platform is a disc-shaped component with a toothed ring machined on the outside. The left end of the toothed platform is fixedly connected to a mounting block, and the right end of the mounting block is rotatably connected to a half-tooth plate via a hinge shaft. The half-tooth plate is a sector gear. A square sliding hole is machined in the center of the toothed platform, and a toothed ring rod slides through the square sliding hole. The toothed ring rod is composed of multiple toothed rings stacked and welded axially. The fourth drive end of the motor is fixedly connected to a second transmission gear, which meshes with the outer toothed ring of the toothed ring rod. A traction rod is fixedly connected to the right side of the half-tooth plate. The end of the traction rod is embedded in a sliding groove frame fixedly connected below the base frame to form a sliding pair. The sliding groove frame is an arc-shaped long groove. The top end of the toothed ring rod is connected to a sliding groove shell via a hinge shaft, and the top end of the sliding groove shell is connected to the bottom end of the base frame via a hinge shaft.

[0008] Preferably, the third drive end of the motor is fixedly connected to the first transmission gear. The outer side of the first transmission gear meshes with the outer gear ring of the gear face platform. The third motor drives the first transmission gear to rotate the gear face platform around the central axis of the steering platform. The gear face platform drives the base frame to rotate horizontally via the mounting block, the half-tooth plate, the gear ring rod, and the slide box to achieve flat angle adjustment. The fourth motor drives the second transmission gear to move the gear ring rod axially upward along the central hole of the gear face platform. The outer gear ring of the gear ring rod meshes with the half-tooth plate, causing the half-tooth plate to rotate around the hinge axis of the mounting block. The half-tooth plate drives the traction rod to move in an arc within the arc groove of the slide box. The traction rod pulls the base frame to pitch around the hinge point of the steering platform via the slide box to achieve pitch angle adjustment.

[0009] Preferably, insertion holes are machined at the four corners of the outer side of the table tennis table, and a retaining plate is fixedly installed at the bottom of the connecting rod. Adjacent retaining plates are fixedly connected by springs. After pressing the retaining plate to retract the spring, the connecting rod is inserted into the insertion hole of the table tennis table. When the retaining plate is released, it is locked into the hole wall by the restoring force of the spring. The four connecting rods and the net bags fixedly connected to the adjacent rods together form a detachable ball collection net frame. After the net frame is unfolded, it covers the outer area of ​​the table tennis table to collect the balls after they have been launched.

[0010] Preferably, the monitoring and recognition module includes a depth sensing unit, an image acquisition unit, a posture analysis unit, a motion analysis unit, a main control decision unit, an electrical drive interface unit, a voice teaching unit, a display unit, a parameter storage unit, and a power management unit. Each unit is connected in a star topology with the main control decision unit at its core. The depth sensing unit is connected to the main control decision unit via a UART serial port; the image acquisition unit is connected to the main control decision unit via a USB interface; the posture analysis unit is connected to the main control decision unit via an SPI bus; the motion analysis unit is connected to the main control decision unit via an I2C bus; the parameter storage unit is bidirectionally connected to the main control decision unit via an SPI bus; the voice teaching unit is connected to the main control decision unit via a UART serial port; the display unit is connected to the main control decision unit via an SPI bus; and the power management unit provides three DC power supplies (5V, 3.3V, and 12V) for the entire module.

[0011] Preferably, the electrical drive interface unit includes three opto-isolated output channels: a speed channel, an eccentricity channel, and an elevation channel. The input terminal of the speed channel is connected to the PWM port of the main control decision unit, and the output terminal outputs a 0 to 10V analog voltage via a PWM to DAC circuit to connect to the frequency conversion speed control circuit of the second motor to adjust the swing frequency of the serve stick. The input terminal of the eccentricity channel is connected to the pulse output port of the main control decision unit, and the output terminal outputs a step pulse sequence via a stepper drive circuit to connect to the first motor to drive the screw to rotate and change the eccentricity of the moving block. The input terminal of the elevation channel is connected to the PWM port of the main control decision unit, and the output terminal outputs a drive current via an H-bridge drive circuit to connect to the third and fourth motors to realize electric angle adjustment. The elevation channel connects to an angle sensor to feed back the current angle to the ADC port of the main control decision unit to form closed-loop control.

[0012] A method for assisting in ball throwing in sports teaching with eccentric wheel speed regulation includes the following steps: Step S1: Place the ball into the table. The ball rolls along the edge of the lower rack to the front of the service stick to be hit. Start the second motor and drive the first transmission tube to rotate via the worm gear. The first transmission tube drives the eccentric wheel to rotate. The eccentric wheel and the moving block form an eccentric transmission, which causes the service stick to reciprocate to flick the ball to complete the launch. In step S2, when the launch speed needs to be adjusted, the starter motor drives the transmission tube 2 to rotate via the worm gear. The transmission tube 2 drives the screw to rotate via the meshing of bevel gear 1 and bevel gear 2. The screw drives the moving block to change the distance between the moving block and the center of the eccentric wheel along the displacement of the adjustment shell, thereby changing the swing amplitude and flicking speed of the launcher. Step S3: When the launch angle needs to be adjusted, the motor starts the third transmission gear one to drive the toothed table to rotate to adjust the horizontal angle of the base frame. The motor starts the fourth transmission gear two to drive the toothed ring rod to move axially upward. The toothed ring rod meshes with the half toothed plate, causing the half toothed plate to drive the traction rod to move in the slide frame. The traction rod pulls the base frame to pitch and rotate through the slide shell to adjust the elevation angle. In step S4, the depth perception unit of the monitoring and recognition module detects the user's distance, the image acquisition unit acquires the user's throwing action and extracts the joint coordinates through the posture analysis unit, the action analysis unit determines the throwing method and generates a defect label, and the main control decision unit integrates the distance and action data to generate control commands and adjusts the operating parameters of motor 1, motor 2, motor 3 and motor 4 through the electrical drive interface unit. At the same time, the voice teaching unit broadcasts correction guidance. In step S5, the parameter storage unit records the distance, motion parameters, and adjustment instructions for each throw, and the display unit displays the training parameters in real time, completing the adaptive throwing teaching cycle.

[0013] Preferably, in step S2, the adjustment range of the center distance between the moving block and the eccentric wheel is 0 to 80 mm, corresponding to the continuous change of the swing amplitude of the serving stick from 0 to the maximum. During the displacement of the moving block, the second motor runs continuously without stopping. The screw and the moving block have a self-locking characteristic to keep the eccentric distance stable after adjustment. The reverse self-locking characteristic of the worm gear prevents the transmission tube one and the transmission tube two from reversing under load.

[0014] Preferably, in step S4, the main control decision unit calculates the target launch speed and elevation angle according to the distance value detected by the depth perception unit and a preset mapping table, automatically matches the launch seat elevation angle according to the throwing method identified by the action analysis unit, lowers the elevation angle when an underhand throw is detected, raises the elevation angle when an overhand throw is detected, and broadcasts the corresponding correction instruction when a motion defect is detected and adjusts the next ball launch parameters to guide the user to correct the motion. The angle sensor feeds back the elevation angle value to the main control decision unit in real time, compares it with the target value, and then corrects the motor's four outputs to form a closed loop.

[0015] Working principle: When the device is running, after the ball is placed on the table, it rolls along the edge of the lower rack to the striking position at the front of the serve stick. Motor 2, after being reduced in speed by a worm gear, drives transmission tube 1 to rotate. Transmission tube 1 drives the eccentric wheel to rotate synchronously. The moving block inside the adjusting housing at the front of the eccentric wheel moves in a circular motion with the eccentric wheel. The cylindrical boss on the outer wall of the moving block slides in the long guide groove on the inner wall of the serve stick, thereby driving the serve stick to reciprocate around the extension frame hinge point. The front of the serve stick continuously flicks the ball in the striking position to launch it. When the launch speed needs to be adjusted, motor 1, after being reduced in speed by a worm gear, drives transmission tube 2 to rotate. Transmission tube 2... The bevel gear one at the front end meshes with the bevel gear two on the screw, driving the screw to rotate. The screw drives the moving block to move along the inner wall of the adjusting shell through the threaded transmission. The change in the distance between the moving block and the center of the eccentric wheel changes the equivalent eccentricity. The swing amplitude and flicking speed of the serving stick change continuously accordingly. Both sets of worm gears and screw threads have reverse self-locking characteristics. After adjustment, the eccentricity is automatically locked and will not drift due to vibration. When it is necessary to adjust the launching direction, the motor three drives the face gear table to rotate around the central axis of the steering table through the transmission gear one, driving the entire base frame and the upper mechanism to rotate horizontally to achieve flat angle adjustment. The motor drives the gear ring rod to move axially upward along the center hole of the gear platform. The stacked gear rings on the outside of the gear ring rod mesh with the half-tooth plate, causing the half-tooth plate to rotate around the hinge point of the mounting block. The half-tooth plate drives the traction rod to move in an arc within the slide frame. The top of the traction rod pulls the front end of the base frame through the slide shell to rotate around the hinge point of the steering table to achieve pitch adjustment. When the monitoring and recognition module is running, the depth perception unit continuously detects the horizontal distance between the user and the device, the image acquisition unit continuously acquires images of the user's upper body movements, the posture analysis unit extracts the coordinates of key joints such as the shoulder, elbow, wrist, hip, knee, and ankle from the image frames, and the motion analysis unit analyzes the joint timing. The system analyzes and determines the throwing method and identifies action defects. The main control decision unit calculates the target launch speed and elevation angle by integrating distance data and action analysis results. The adjustment signals are then output to motors 1, 2, 3, and 4 through the three opto-isolated channels of the electrical drive interface unit. At the same time, the voice teaching unit broadcasts action correction guidance, the display unit shows real-time training parameters, and the parameter storage unit records training data. This forms a complete closed loop of distance perception, action recognition, intelligent decision-making, electrical execution, voice feedback, and data recording, enabling the device to dynamically adjust the throwing parameters and provide immediate teaching guidance according to the user's training status.

[0016] This invention provides an eccentric wheel speed-regulating auxiliary device for ball throwing in sports teaching. It has the following beneficial effects: 1. This invention uses motor one and motor two to drive coaxially nested transmission tube two and transmission tube one respectively, and cooperates with bevel gear screw transmission to change the eccentricity of the moving block, so as to achieve the effect of real-time stepless speed regulation during operation and self-locking stability after adjustment.

[0017] 2. This invention achieves horizontal rotation through a three-drive gear table driven by a motor, and completes the electric adjustment of the pitch angle through a transmission via a semi-tooth plate traction rod slide frame driven by a four-drive gear ring rod driven by a motor, thus achieving the effect of electric adjustment of the angle with two degrees of freedom.

[0018] 3. This invention uses a monitoring and recognition module to sense the user's distance and throwing action characteristics, and coordinates with the electrical drive interface unit to adjust the parameters of four motors in a 3-channel linkage, thereby achieving the effect of adaptive throwing force and angle matching and real-time voice correction teaching.

[0019] 4. This invention uses a connecting rod and a net bag to form a detachable ball-collecting net frame, and with the help of a locking plate and spring quick-locking structure, it achieves the effect of quickly expanding and storing the ball collection range. Attached Figure Description

[0020] Figure 1 The three-dimensional representation of the present invention Figure 1 ; Figure 2 The three-dimensional representation of the present invention Figure 2 ; Figure 3 This is a half-sectional view of the base frame of the present invention; Figure 4 This is a half-sectional view of the adjustment platform of the present invention; Figure 5 This is a half-sectional view of the fixed shell of the present invention; Figure 6 This is a half-sectional view of the steering platform of the present invention; Figure 7 This is a half-sectional view of the face tooth platform of the present invention; Figure 8 This is a schematic diagram of the net structure of the present invention; Figure 9 This is a half-sectional view of the table tennis table of the present invention.

[0021] The components are as follows: 1. Base frame; 2. Adjustment platform; 3. Extension frame; 4. Monitoring and identification module; 5. Table tennis table; 6. Turning platform; 7. Eccentric wheel; 8. Connecting rod; 9. Net; 10. Fixed shell; 11. Adjustment shell; 12. Screw; 13. Serve stick; 14. Motor 1; 15. Motor 2; 16. Transmission tube 1; 17. Spring; 18. Moving block; 19. Transmission tube 2; 20. Motor 3; 21. Face gear platform; 22. Motor 4; 23. Transmission gear 1; 24. Mounting block; 25. Half tooth plate; 26. Traction rod; 27. Slide frame; 28. Transmission gear 2; 29. ​​Gear ring rod; 30. Slide shell; 31. Lower ball frame; 32. Clamping plate. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example: like Figure 1-9 As shown, this embodiment of the invention provides a sports teaching ball launching auxiliary device with eccentric wheel speed regulation, including a base frame 1, an adjustment platform 2, an extension frame 3, a monitoring and identification module 4, a ball table 5, and a steering platform 6. The bottom of the base frame 1 is rotatably connected to the steering platform 6 and is equipped with a movable wheel frame. The adjustment platform 2 and the ball table 5 are fixed at the top of the base frame 1. The extension frame 3 is fixed to the adjustment platform 2 and the monitoring and identification module 4 is provided at its top. Insertion holes are machined at the four corners of the outer side of the ball table 5. The bottom of the connecting rod 8 is fixedly equipped with a clamping plate 32. Adjacent clamping plates 32 are fixedly connected by springs 17. After pressing the clamping plate 32 to retract the spring 17, the connecting rod 8 is inserted into the insertion hole of the ball table 5. When the clamping plate 32 is released, it is clamped to the hole wall under the restoring force of the spring 17 to achieve fixation. The four connecting rods 8 and the net bag 9 fixedly connected between adjacent rods together form a detachable ball collection net frame. After the net frame is unfolded, it covers the outer area of ​​the ball table 5 to collect the launched balls. The adjusting platform 2 is equipped with a fixed shell 10, a first motor 14, and a second motor 15. The fixed shell 10 contains two coaxially nested transmission tubes 16 and 19. The worm gears at the drive ends of the two motors mesh with the worm wheels at the ends of the two transmission tubes. An eccentric wheel 7 is rotatably connected to the front end of the fixed shell 10, which is fixed to the first transmission tube 16. The eccentric wheel 7 fixes the adjusting shell 11 and is rotatably connected to a screw 12. The front end of the second transmission tube 19 is driven by a bevel gear 1 meshing with a bevel gear 2 on the screw 12. The screw 12 is threadedly connected to a moving block 18. The extension frame 3 is hinged to the serving rod 13, and the outer wall boss of the moving block 18 fits into its inner wall guide groove. The first transmission tube 16 is empty. The core tube and the transmission tube 2 19 are solid shafts that pass through the inside of the transmission tube 1 16. They are supported by bearings and can rotate independently. The worm at the drive end of the motor 1 14 meshes with the worm wheel at the end of the transmission tube 2 19 to form a first reduction pair. The worm at the drive end of the motor 2 15 meshes with the worm wheel at the end of the transmission tube 16 to form a second reduction pair. The lead angle of both sets of worms and worm wheels is less than the equivalent friction angle and has a reverse self-locking characteristic. The moving block 18 has a trapezoidal threaded hole that cooperates with the screw 12. The cylindrical boss on the outer wall of the moving block 18 is embedded in the long guide groove on the inner wall of the serving stick 13 to form a sliding pair. The serving stick 13 reciprocates with the hinge shaft of the extension frame 3 as the fulcrum. The steering platform 6 is equipped with motors 3 (20) and 4 (22) for adjusting the angle of the base frame 1 via a traction mechanism on the gear face platform 21. The ball table 5 has a lower ball frame 31 on its bottom side and a detachable ball-collecting net frame on its outer side. The gear face platform 21 is a disc-shaped component with a gear ring machined on its outer side. A mounting block 24 is fixedly connected to the left end of the gear face platform 21, and a half-gear plate 25, a sector gear, is rotatably connected to the right end of the mounting block 24 via a hinge shaft. A square sliding hole is machined in the center of the gear face platform 21, and a gear ring rod 29 slides through this hole. The rod 29 is composed of multiple toothed rings stacked and welded along the axial direction. The drive end of the motor 4 22 is fixedly connected to the transmission gear 28. The transmission gear 28 meshes with the outer toothed ring of the toothed rod 29. The right side of the half toothed plate 25 is fixedly connected to the traction rod 26. The end of the traction rod 26 is embedded in the slide frame 27 fixedly connected below the base frame 1 to form a sliding pair. The slide frame 27 is an arc-shaped long groove. The top of the toothed rod 29 is connected to the slide shell 30 through a hinge shaft. The top of the slide shell 30 is connected to the bottom of the base frame 1 through a hinge shaft. Motor 3 20 is fixedly connected to transmission gear 1 23 at its drive end. The outer side of transmission gear 1 23 meshes with the outer gear ring of face gear platform 21. Motor 3 20 drives transmission gear 1 23 to rotate face gear platform 21 around the central axis of steering platform 6. Face gear platform 21 drives base frame 1 to rotate horizontally via mounting block 24, half tooth plate 25, tooth ring rod 29, and slide box 30 to achieve flat angle adjustment. Motor 4 22 drives transmission gear 2 28 to move tooth ring rod 29 axially upward along the central hole of face gear platform 21. The outer tooth ring of tooth ring rod 29 meshes with half tooth plate 25 to rotate half tooth plate 25 around the hinge axis of mounting block 24. Half tooth plate 25 drives traction rod 26 to move in an arc within the arc groove of slide box 27. Traction rod 26 pulls base frame 1 around the hinge point of steering platform 6 via slide box 30 to achieve pitch angle adjustment.

[0024] The monitoring and recognition module 4 includes a depth sensing unit, an image acquisition unit, a posture analysis unit, a motion analysis unit, a main control decision unit, an electrical drive interface unit, a voice teaching unit, a display unit, a parameter storage unit, and a power management unit. All units are connected in a star topology with the main control decision unit at its core. The depth sensing unit is connected to the main control decision unit via a UART serial port; the image acquisition unit is connected via a USB interface; the posture analysis unit is connected via an SPI bus; the motion analysis unit is connected via an I2C bus; the parameter storage unit is bidirectionally connected to the main control decision unit via an SPI bus; the voice teaching unit is connected via a UART serial port; the display unit is connected via an SPI bus; and the power management unit provides 5V, 3.3V, and 12V to the entire module. The three-channel DC power supply and electrical drive interface unit include three opto-isolated output channels: speed channel, eccentricity channel, and elevation channel. The speed channel input is connected to the PWM port of the main control decision unit, and the output is connected to the frequency converter speed control circuit of motor 2 15 to adjust the swing frequency of the serving stick 13 via the PWM to DAC circuit. The eccentricity channel input is connected to the pulse output port of the main control decision unit, and the output is connected to the stepper drive circuit to output a stepping pulse sequence to drive the screw 12 of motor 1 14 to rotate and change the eccentricity of the moving block 18. The elevation channel input is connected to the PWM port of the main control decision unit, and the output is connected to the H-bridge drive circuit to output drive current to motor 3 20 and motor 4 22 to realize electric angle adjustment. The elevation channel is connected to the angle sensor to feed back the current angle to the ADC port of the main control decision unit to form closed-loop control.

[0025] A method for assisting in ball throwing in sports teaching with eccentric wheel speed regulation includes the following steps: Step S1: Place the ball into the table 5. The ball rolls along the edge of the lower ball rack 31 to the front end of the serving stick 13 to wait for the shot. Start the motor 2 15 to drive the transmission tube 16 to rotate via the worm gear. The transmission tube 16 drives the eccentric wheel 7 to rotate. The eccentric wheel 7 and the moving block 18 form an eccentric transmission, which makes the serving stick 13 reciprocate to flick the ball to complete the launch. In step S2, when the launching speed needs to be adjusted, the starting motor 14 drives the transmission tube 19 to rotate via the worm gear. The transmission tube 19 drives the screw 12 to rotate via the meshing of bevel gear 1 and bevel gear 2. The screw 12 drives the moving block 18 to move along the adjustment shell 11, changing the distance between the moving block 18 and the center of the eccentric wheel 7, thereby changing the swing amplitude and flicking speed of the serving stick 13. The adjustment range of the center distance between the moving block 18 and the eccentric wheel 7 is 0 to 80 mm, corresponding to the continuous change of the swing amplitude of the serving stick 13 from 0 to the maximum. During the displacement of the moving block 18, the motor 15 continues to run without stopping. The screw 12 and the moving block 18 have a self-locking characteristic to keep the eccentric distance stable after adjustment. The reverse self-locking characteristic of the worm gear prevents the transmission tube 16 and the transmission tube 19 from reversing under load. In step S3, when the launch angle needs to be adjusted, the start motor 3 20 drives the gear table 21 to rotate via the transmission gear 1 23 to adjust the horizontal angle of the base frame 1. The start motor 4 22 drives the gear ring rod 29 to move axially upward via the transmission gear 28. The gear ring rod 29 meshes with the half-tooth plate 25, causing the half-tooth plate 25 to drive the traction rod 26 to move within the slide frame 27. The traction rod 26 pulls the base frame 1 to rotate through the slide shell 30 to adjust the elevation angle. In step S4, the depth perception unit of the monitoring and recognition module 4 detects the user's distance, the image acquisition unit acquires the user's throwing action and extracts the joint coordinates through the posture analysis unit, the action analysis unit determines the throwing method and generates a defect label, the main control decision unit integrates the distance and action data to generate control commands and adjusts the operating parameters of motor 14, motor 25, motor 320 and motor 42 through the electrical drive interface unit, and at the same time, the voice teaching unit broadcasts correction instructions. The main control decision unit calculates the target launch speed and elevation angle according to the distance value detected by the depth perception unit according to the preset mapping table, and automatically matches the launch seat elevation angle according to the throwing method identified by the action analysis unit. When an underhand throw is detected, the elevation angle is lowered and when an overhand throw is detected, the elevation angle is raised. When an action defect is detected, the voice teaching unit broadcasts the corresponding correction command and adjusts the next ball launch parameters to guide the user to correct the action. The angle sensor feeds back the elevation angle value to the main control decision unit in real time. After comparing it with the target value, the output of motor 422 is corrected to form a closed loop. In step S5, the parameter storage unit records the distance, motion parameters, and adjustment instructions for each throw, and the display unit displays the training parameters in real time, completing the adaptive throwing teaching cycle.

[0026] Example 1 This embodiment provides a ball-throwing auxiliary device for sports teaching with eccentric wheel speed regulation. The base frame 1 is a rectangular frame welded from 50×50×3mm square tubing. The bottom center is rotatably connected to the steering platform 6 via a thrust bearing. Each set of movable wheel frames, including two omnidirectional casters, is installed on both the front and rear of the steering platform 6, facilitating movement and positioning of the device on a basketball court. The top left side of the base frame 1 is bolted to the adjustment platform 2, and the top right side is bolted to the ball table 5. An extension frame 3 is welded to the left end of the adjustment platform 2. The extension frame 3 extends upward and then bends to the left, with the housing of the monitoring and identification module 4 mounted on its top with screws. The monitoring and identification module 4 houses the main control circuit board and various functional units. The front end of the inner wall of the adjustment platform 2 is bolted to the fixing shell 10, which is a cast iron shell. Motor 14 is mounted on the left outer wall, and Motor 2 15 is mounted on the right outer wall. Both motors are DC geared motors with a rated voltage of 24V. The inner wall of the fixed shell 10 rotatably supports the transmission tube 16 via two deep groove ball bearings. The transmission tube 16 is a hollow steel tube, and its inner wall further supports the transmission tube 19 via two deep groove ball bearings. The transmission tube 19 is a solid shaft that passes through the interior of the transmission tube 16. The two are coaxially nested and can rotate independently. The drive end of the motor 14 is fixedly connected to a worm gear, which meshes with the worm wheel fixedly connected to the end of the transmission tube 19 to form the first worm gear reduction pair. The drive end of the motor 15 is fixedly connected to a worm gear, which meshes with the worm wheel fixedly connected to the end of the transmission tube 16 to form the second worm gear reduction pair. The lead angle of both sets of worm gears is less than the equivalent friction angle, and they have reverse self-locking capability. The front end of the fixed shell 10 is rotatably connected to the eccentric wheel 7 via a bearing. The front end of the transmission tube 16 passes through the front wall of the fixed shell 10 and is fixedly connected to the rear end of the eccentric wheel 7 via a flat key. The front end of the eccentric wheel 7 is fixedly connected to the adjusting shell 11 via bolts. The adjusting shell 11 is a rectangular shell, and the two ends of the inner wall are supported by the screw 12 via bearing seats. The front end of the transmission tube 19 passes through the inner hole of the transmission tube 16 and the center hole of the eccentric wheel 7 in sequence. Its end is fixedly connected to the bevel gear 1. The middle part of the screw 12 is fixedly connected to the bevel gear 2 via a flat key. The bevel gear 1 and the bevel gear 2 mesh perpendicularly. The outer wall of the screw 12 is threadedly connected to the moving block 18. The moving block 18 is a rectangular slider with a trapezoidal threaded hole inside. The outer wall of the moving block 18 is provided with a cylindrical boss. The boss is embedded in the long guide groove of the inner wall of the serve stick 13. The middle part of the serve stick 13 is rotatably connected to the left inner wall of the extension frame 3 via a hinge shaft. The front end of the serve stick 13 is provided with a hitting plate.Motor 3 20 is installed on the right end of the steering platform 6, and motor 4 22 is installed at the front end. The steering platform 6 is rotatably connected to the gear face plate 21 through a thrust bearing in the middle. The gear face plate 21 is a disc-shaped component with a gear ring machined on the outside. The left end is welded to the mounting block 24. The right end of the mounting block 24 is rotatably connected to the half gear plate 25 through a hinge shaft. The half gear plate 25 is a sector gear. The center of the gear face plate 21 is machined with a square sliding hole. The gear ring rod 29 slides through the square sliding hole. The gear ring rod 29 is composed of multiple gear rings stacked and welded along the axial direction. The drive end of motor 4 22 is fixedly connected to the transmission gear 28. The transmission gear 28 meshes with the outer gear ring of the gear ring rod 29. The right side of the half gear plate 25 is welded to the traction rod 26. The traction rod 26 is a round rod with its end embedded in the slide groove frame 27 welded below the base frame 1. The slide groove frame 27 is an arc-shaped long groove. The top end of the gear ring rod 29 is connected to the slide groove shell 30 through a hinge shaft. The top end of the slide groove shell 30 is connected to the bottom end of the base frame 1 through a hinge shaft. The drive end of motor 320 is fixedly connected to transmission gear 123, which meshes with the outer gear ring of the face gear platform 21. The table 5 is a funnel-shaped box with an opening at the top. A lower ball rack 31 is set on the bottom side. The lower ball rack 31 is an arc-shaped guide groove that guides the ball to roll to the front end of the serving stick 13. Insertion holes are machined at the four corners of the outer side of the table 5. The bottom of the connecting rod 8 is equipped with a clamping plate 32. Adjacent clamping plates 32 are connected by springs 17. After pressing the clamping plate 32 to compress the spring 17, the connecting rod 8 is inserted into the insertion hole. After releasing, the clamping plate 32 is clamped to the hole wall by the restoring force of the spring 17 to achieve fixation. The four connecting rods 8 and the net bag 9 between the adjacent rods form a detachable ball collection net frame. The monitoring and identification module 4 is centered around a main control decision unit. The depth perception unit uses an infrared depth sensor connected to the main control decision unit via a serial port. The image acquisition unit uses a wide-angle camera connected to the main control decision unit via USB. The posture analysis unit uses an embedded vision processing chip connected to the main control decision unit via SPI. The motion analysis unit uses a microcontroller connected to the main control decision unit via I2C. The electrical drive interface unit includes three opto-isolated channels that connect to the frequency converter circuits of motor 1 (14) and motor 2 (15), and the drive circuits of motor 3 (20) and motor 4 (22), respectively. The voice teaching unit uses a voice synthesis chip and a speaker connected to the main control decision unit via a serial port. The display unit uses a TFT LCD screen connected to the main control decision unit via SPI. The parameter storage unit uses a Flash chip bidirectionally connected to the main control decision unit via SPI. The power management unit uses a switching power supply to convert AC220V to 5V, 3.3V, and 12V DC for powering the entire module. When used for basketball teaching in this embodiment, the table 5 can hold 8 to 12 standard basketballs, with a launch speed adjustment range of 3m / s to 15m / s, a horizontal angle adjustment range of 0° to 360°, and an elevation angle adjustment range of 15° to 60°.

[0027] Example 2 The difference between this embodiment and Embodiment 1 is as follows: the capacity of the table 5 is changed to accommodate 15 to 20 standard volleyballs; the cross-sectional dimensions of the lower ball frame 31 are correspondingly reduced; the front striking plate of the serve stick 13 is replaced with a wide-angle plate adapted to volleyballs; the maximum eccentricity of the moving block 18 is adjusted to 80mm; the power of motor 14 and motor 2 15 is adjusted to 120W; and the field of view of the image acquisition unit of the monitoring and recognition module 4 is adjusted to cover a training distance of 3m to 8m. The remaining structure is exactly the same as in Embodiment 1. This embodiment is used for volleyball passing and spiking training, with a launch speed range of 5m / s to 18m / s.

[0028] Example 3 The difference between this embodiment and Embodiment 1 is as follows: the capacity of the table 5 is increased to accommodate 10 to 15 standard soccer balls; the radius of the arc guide groove of the lower ball rack 31 is increased; the front striking plate of the serving stick 13 is replaced with an arc-shaped plate adapted to the soccer ball; the maximum eccentricity of the moving block 18 is adjusted to 70mm; the power of motor 14 and motor 2 15 is adjusted to 150W; and the mesh size of the net bag 9 of the ball collection net frame is increased to accommodate the diameter of the soccer ball. The rest of the structure is exactly the same as in Embodiment 1. This embodiment is used for soccer ball stopping and heading training, with a launch speed range of 4m / s to 16m / s.

[0029] Comparative Example 1 The same base frame 1, steering table 6, ball table 5, ball collection net frame, and monitoring and identification module 4 as in Example 1 are used, but the eccentric wheel 7 has a fixed eccentricity structure, and the center distance between the moving block 18 and the eccentric wheel 7 is fixed at 40mm and cannot be adjusted. The launching speed is adjusted only by changing the rotation speed of the motor 15 via frequency conversion. Comparative test results: In Comparative Example 1, the launching speed adjustment range is 5m / s to 12m / s within the range of motor speed from 500 to 1400 r / min. Below 5m / s, the motor torque is insufficient, causing the serving stick 13 to vibrate. Above 12m / s, it cannot be reached due to the maximum speed limit of the motor. In Example 1, the eccentricity of the moving block 18 is changed by the screw 12 driven by the motor 14. At an eccentricity of 20mm and a low speed, a gentle launch of 3m / s with stable movement is achieved. At an eccentricity of 80mm and a high speed, a high-speed launch of 18m / s is achieved. The speed adjustment range is about 120% wider than that of Comparative Example 1, and the motor 15 continues to run without stopping during the adjustment process.

[0030] Comparative Example 2 Using the same main structure as Example 1, but with the angle adjustment changed to a single-degree-of-freedom structure where the bolt is locked after manual rotation, it can only adjust the elevation angle and cannot rotate horizontally. Furthermore, each adjustment requires loosening the locking bolt, manually rotating the machine, and then locking it again. Comparative test results: Example 2 takes an average of 15 seconds to complete one elevation angle adjustment, and cannot adjust horizontally, requiring manual steering. Example 1 uses motor 3 (20) for electric horizontal angle adjustment and motor 4 (22) for electric elevation angle adjustment, with an average adjustment time of 2 seconds per cycle. It can also automatically complete dual-degree-of-freedom linkage adjustment under the control of the monitoring and identification module 4, improving adjustment efficiency by approximately 7.5 times.

[0031] Comparative Example 3 Using the same mechanical structure as Example 1, but without the monitoring and recognition module 4, all parameters must be manually set by the teacher. Comparative test results: Example 3 could not automatically match throwing parameters based on user distance, could not recognize the user's throwing motion, lacked voice correction feedback during training, and student errors could not be corrected immediately; Example 1, with the help of the monitoring and recognition module 4, achieved distance-adaptive speed adjustment, motion recognition matching elevation angle, and real-time voice correction. Within the same training time, the student's motion accuracy improved by approximately 40%, and the number of teacher interventions decreased by approximately 60%.

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

Claims

1. A ball-throwing auxiliary device for sports teaching with eccentric wheel speed regulation, comprising a base frame (1), an adjustment platform (2), an extension frame (3), a monitoring and identification module (4), a ball table (5), and a turning platform (6), characterized in that: The bottom of the base frame (1) is rotatably connected to the steering platform (6) and is provided with a moving wheel frame. The top of the base frame (1) is fixed with an adjustment platform (2) and a ball table (5). The adjustment platform (2) is fixed with an extension frame (3) and is provided with a monitoring and identification module (4) at its top. The adjustment platform (2) is provided with a fixed shell (10), a motor one (14), and a motor two (15). The fixed shell (10) is rotatably connected to a coaxially nested transmission tube one (16) and a transmission tube two (19). The worm gears at the drive ends of the two motors mesh with the worm wheels at the ends of the two transmission tubes respectively. The front end of the fixed shell (10) is rotatably connected to an eccentric wheel (7) which is fixed to the transmission tube one (16). The eccentric wheel (7) fixes the adjustment shell (11) and is rotatably connected to a screw (12). The front end of the transmission tube two (19) meshes with the bevel gear two on the screw (12) via a bevel gear one. The screw (12) is threadedly connected to a moving block (18). The extension frame (3) is hinged to a serving rod (13), and the outer wall boss of the moving block (18) is fitted into its inner wall guide groove. The steering table (6) is equipped with motor three (20) and motor four (22) to adjust the angle of the base frame (1) via the traction mechanism of the face gear table (21); the ball table (5) is equipped with a lower ball frame (31) on the bottom side and a detachable ball collection net frame on the outside.

2. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 1, characterized in that: The first transmission tube (16) is a hollow tube, and the second transmission tube (19) is a solid shaft that passes through the first transmission tube (16). The two are supported by bearings and can rotate independently. The worm at the drive end of the first motor (14) meshes with the worm wheel at the end of the second transmission tube (19) to form a first reduction pair. The worm at the drive end of the second motor (15) meshes with the worm wheel at the end of the first transmission tube (16) to form a second reduction pair. The lead angle of both sets of worms and worm wheels is less than the equivalent friction angle and has a reverse self-locking characteristic. The moving block (18) is provided with a trapezoidal threaded hole that cooperates with the screw (12). The cylindrical boss on the outer wall of the moving block (18) is embedded in the long guide groove on the inner wall of the serving stick (13) to form a sliding pair. The serving stick (13) swings back and forth with the hinge shaft of the extension frame (3) as the fulcrum.

3. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 1, characterized in that: The face gear platform (21) is a disc-shaped component with a gear ring machined on the outside. The left end of the face gear platform (21) is fixedly connected to the mounting block (24), and the right end of the mounting block (24) is rotatably connected to the half gear plate (25) through a hinge shaft. The half gear plate (25) is a sector gear. The center of the face gear platform (21) is machined with a square sliding hole, and the gear ring rod (29) slides through the square sliding hole. The gear ring rod (29) is composed of multiple gear rings stacked and welded along the axial direction. The drive end of the motor (22) is fixedly connected to the transmission. Gear 2 (28), the transmission gear 2 (28) meshes with the outer tooth ring of the tooth ring rod (29), the right side of the half tooth plate (25) is fixedly connected to the traction rod (26), the end of the traction rod (26) is embedded in the slide frame (27) fixedly connected below the base frame (1) to form a sliding pair, the slide frame (27) is an arc-shaped long groove, the top end of the tooth ring rod (29) is connected to the slide shell (30) through a hinge shaft, and the top end of the slide shell (30) is connected to the bottom end of the base frame (1) through a hinge shaft.

4. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 1, characterized in that: The drive end of the third motor (20) is fixedly connected to the first transmission gear (23). The outer side of the first transmission gear (23) meshes with the outer gear ring of the face gear platform (21). The third motor (20) drives the first transmission gear (23) to rotate the face gear platform (21) around the central axis of the steering platform (6). The face gear platform (21) drives the base frame (1) to rotate horizontally through the mounting block (24), the half tooth plate (25), the tooth ring rod (29), and the slide box (30) to achieve flat angle adjustment. The fourth motor (22) drives the transmission gear platform (23) to rotate horizontally. The transmission gear 2 (28) drives the gear ring rod (29) to move upward along the central hole of the face tooth platform (21). The outer gear ring of the gear ring rod (29) meshes with the half tooth plate (25) to drive the half tooth plate (25) to rotate around the hinge axis of the mounting block (24). The half tooth plate (25) drives the traction rod (26) to move in an arc in the arc groove of the slide frame (27). The traction rod (26) pulls the base frame (1) through the slide shell (30) to pitch and rotate around the hinge point of the steering table (6) to achieve pitch angle adjustment.

5. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 1, characterized in that: Insertion holes are machined at the four corners of the outer side of the table (5). The bottom of the connecting rod (8) is fixedly equipped with a clamping plate (32). The adjacent clamping plates (32) are fixedly connected by a spring (17). After pressing the clamping plate (32) to retract the spring (17), the connecting rod (8) is inserted into the insertion hole of the table (5). When the clamping plate (32) is released, it is clamped to the hole wall under the restoring force of the spring (17) to achieve fixation. The four connecting rods (8) and the net bag (9) fixedly connected between the adjacent rods together form a detachable ball collection net frame. After the net frame is unfolded, it covers the outer area of ​​the table (5) to collect the balls after launch.

6. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 1, characterized in that: The monitoring and recognition module (4) includes a depth sensing unit, an image acquisition unit, a posture analysis unit, a motion analysis unit, a main control decision unit, an electrical drive interface unit, a voice teaching unit, a display unit, a parameter storage unit, and a power management unit. Each unit is connected in a star topology with the main control decision unit as the core. The depth sensing unit is connected to the main control decision unit via a UART serial port. The image acquisition unit is connected to the main control decision unit via a USB interface. The posture analysis unit is connected to the main control decision unit via an SPI bus. The motion analysis unit is connected to the main control decision unit via an I2C bus. The parameter storage unit is bidirectionally connected to the main control decision unit via an SPI bus. The voice teaching unit is connected to the main control decision unit via a UART serial port. The display unit is connected to the main control decision unit via an SPI bus. The power management unit provides three DC power supplies of 5V, 3.3V, and 12V for the entire module.

7. The eccentric wheel speed-regulating auxiliary device for ball launching in sports teaching according to claim 6, characterized in that: The electrical drive interface unit includes three opto-isolated output channels: speed channel, eccentricity channel, and elevation channel. The input end of the speed channel is connected to the PWM port of the main control decision unit, and the output end outputs a 0 to 10V analog voltage through the PWM to DAC circuit to connect to the variable frequency speed control circuit of the second motor (15) to adjust the swing frequency of the serving rod (13). The input end of the eccentricity channel is connected to the pulse output port of the main control decision unit, and the output end outputs a step pulse sequence through the stepper drive circuit to connect to the first motor (14) to drive the screw (12) to rotate and change the eccentricity of the moving block (18). The input end of the elevation channel is connected to the PWM port of the main control decision unit, and the output end outputs a drive current through the H-bridge drive circuit to connect to the third motor (20) and the fourth motor (22) to realize electric angle adjustment. The elevation channel is connected to the angle sensor to feed back the current angle to the ADC port of the main control decision unit to form closed-loop control.

8. A method for assisting in the throwing of balls in physical education using an eccentric wheel speed-regulating device, comprising the eccentric wheel speed-regulating device for assisting in the throwing of balls in physical education as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step S1: Place the ball into the table (5). The ball rolls along the edge of the lower ball rack (31) to the front end of the serving stick (13) to wait for the shot. Start the second motor (15) to drive the first transmission tube (16) to rotate via the worm gear. The first transmission tube (16) drives the eccentric wheel (7) to rotate. The eccentric wheel (7) and the moving block (18) form an eccentric transmission, causing the serving stick (13) to reciprocate to flick the ball to complete the launch. In step S2, when the launching speed needs to be adjusted, the starting motor (14) drives the transmission tube (19) to rotate via the worm gear. The transmission tube (19) drives the screw (12) to rotate via the meshing of the bevel gear (1) and the bevel gear (2). The screw (12) drives the moving block (18) to move along the adjustment shell (11) to change the distance between the moving block (18) and the center of the eccentric wheel (7), thereby changing the swing amplitude and flicking speed of the serving stick (13). In step S3, when the launch angle needs to be adjusted, the start motor three (20) drives the gear table (21) to rotate via the transmission gear one (23) to adjust the horizontal angle of the base frame (1). The start motor four (22) drives the gear ring rod (29) to move axially upward via the transmission gear two (28). The gear ring rod (29) meshes with the half-tooth plate (25) so that the half-tooth plate (25) drives the traction rod (26) to move within the slide frame (27). The traction rod (26) pulls the base frame (1) to pitch and rotate via the slide shell (30) to adjust the elevation angle. In step S4, the depth perception unit of the monitoring and recognition module (4) detects the user distance, the image acquisition unit collects the user's throwing action and extracts the joint coordinates through the posture analysis unit, the action analysis unit determines the throwing method and generates a defect label, the main control decision unit integrates the distance and action data to generate control commands and adjusts the operating parameters of motor one (14), motor two (15), motor three (20) and motor four (22) through the electrical drive interface unit, while the voice teaching unit broadcasts correction guidance; In step S5, the parameter storage unit records the distance, motion parameters, and adjustment instructions for each throw, and the display unit displays the training parameters in real time, completing the adaptive throwing teaching cycle.

9. A method for assisting in the throwing of a ball in sports teaching using eccentric wheel speed regulation as described in claim 8, characterized in that: In step S2, the adjustment range of the center distance between the moving block (18) and the eccentric wheel (7) is 0 to 80 mm, which corresponds to the continuous change of the swing amplitude of the serving stick (13) from 0 to the maximum. During the displacement of the moving block (18), the second motor (15) runs continuously without stopping. The screw (12) and the moving block (18) have a self-locking characteristic to keep the eccentric distance stable after adjustment. The reverse self-locking characteristic of the worm gear prevents the transmission tube one (16) and the transmission tube two (19) from reversing under load.

10. A method for assisting in the throwing of a ball in sports teaching with eccentric wheel speed regulation according to claim 8, characterized in that: In step S4, the main control decision unit calculates the target launch speed and elevation angle according to the distance value detected by the depth perception unit and the preset mapping table. It automatically matches the launch seat elevation angle according to the ball throwing method identified by the action analysis unit. When the ball is thrown from below, the elevation angle is lowered; when the ball is thrown from above, the elevation angle is raised. When a defect in the action is detected, the voice teaching unit broadcasts the corresponding correction instruction and adjusts the next ball launch parameters to guide the user to correct the action. The angle sensor feeds back the elevation angle value to the main control decision unit in real time. After comparing it with the target value, the motor four (22) outputs to form a closed loop.

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