An automatic retractable landing gear device for a tethered drone and its control method

Abstract

The present invention discloses a tethered drone landing gear automatic retraction device and its control method. The system includes a landing gear retraction unit and a controller. Among them, the number of landing gear retraction units is four. The landing gear retraction unit includes an ultrasonic sensor, a buffer base, and an electro-mechanical actuator. The controller communicates bidirectionally with the drone flight control system and controls the main motors and standby motors of the four landing gear retraction units. The controller also receives the signal data sent by the ultrasonic sensor and the pressure sensor respectively. In the present invention, two sets of control devices, namely the main and standby ones, are used, which improves the stability and safety margin of the electro-mechanical actuator retraction of the drone.

Description

Technical Field

[0001] The invention belongs to the technical field of tethered unmanned aerial vehicle landing gear retraction and extension, and in particular relates to a tethered unmanned aerial vehicle landing gear automatic retraction and extension device and a control method thereof. Background Art

[0002] UAV is the abbreviation of Unmanned Aerial Vehicle, which is the product of the rapid development of high-tech in the 21st century. It has the advantages of small size, simple structure, low cost, easy control, and can work in complex and dangerous environments. With the development of science and technology and the needs of production and life, UAVs are widely used in fields such as power inspection, disaster prevention and rescue, tunnel exploration, etc. to perform complex tasks. However, due to the limitations of energy problems and wireless interference, UAVs cannot stay in the air for a long time and cannot carry high-power equipment. When wireless data transmission equipment is interfered with, the wireless data transmission speed is limited, which is easy to cause emergencies. In order to solve the above problems, tethered drones came into being.

[0003] Tethered drones are a special form of multi-rotor drones. They use ground power transmitted by tethered cables as a power source to replace traditional lithium batteries. They are characterized by long operating time and good communication stability. Tethered drones are composed of a ground high-voltage DC voltage stabilization system, a cable releaser, a synchronous winding wheel, a tethered cable, an aerial voltage stabilization module, and a backup battery. The high-voltage DC voltage stabilization system and the synchronous winding wheel are installed on the cable releaser. The tethered cable is connected to the voltage stabilization module and the backup battery, which effectively solves the long flight time and high load problems faced by drones. However, due to the complex working environment of tethered drones, it is impossible to always ensure the flatness of the landing surface, which greatly reduces the safety and stability of drone lifting and lowering. In addition, the landing gear of the tethered drone will inevitably conflict with the tethered cable in space, resulting in the failure of the landing gear to be retracted and extended. Therefore, designing a tethered drone landing gear automatic retraction and extension device and method to achieve horizontal landing on a complex landing surface and avoid the conflict between the tethered cable and the landing gear as much as possible is an important research content to ensure the safe and stable landing of the tethered drone.

[0004] The existing tethered UAV landing gear retraction and deployment systems mainly have the following problems:

[0005] 1. The landing gear retraction unit contains only one set of working motors. Failure of the working motor will cause failure of the landing gear retraction system, and the safety margin is low.

[0006] 2. The working environment of tethered drones is complex, and the landing surface cannot always be guaranteed to be flat, and the safety and stability of drone ascent and descent are low.

[0007] 3. There is a spatial conflict between the landing gear and the mooring cables, which may cause the landing gear to be entangled by the mooring cables and cause the retraction and extension to fail. Summary of the Invention

[0008] Aiming at the deficiencies of the above-mentioned existing technologies, the purpose of the present invention is to provide a tethered UAV landing gear automatic retraction device and its control method, so as to solve the problems of low safety margin caused by only one set of working motors in the landing gear retraction unit of the existing tethered UAV and low lifting and lowering stability of the tethered UAV on uneven ground.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] An automatic retraction device for the landing gear of a tethered UAV of the present invention includes: a landing gear retraction unit and a controller; the number of the landing gear retraction units is four;

[0011] The landing gear retraction unit includes an ultrasonic sensor, a buffer base and an electro-mechanical actuator cylinder; the ultrasonic sensor is installed on the outer wall of the electro-mechanical actuator cylinder, and is used to collect the distance between each electro-mechanical actuator cylinder and the ground, and transmit the distance data to the controller; the buffer base is arranged at the bottom of the electro-mechanical actuator cylinder, and is used for buffering when the UAV contacts the ground; the electro-mechanical actuator cylinder is arranged under the UAV body, and is used to drive the retraction and extension of the buffer base; the electro-mechanical actuator cylinder is composed of a lower connection mechanism, a main motor, a backup motor, a main reducer, a backup reducer, an upper connection mechanism, a piston cylinder, a piston rod, a position detection device, a ball screw mechanism and a gear transmission mechanism; the main motor, the backup motor, the main reducer and the backup reducer are fixed on the outside of the piston cylinder, the output end of the main motor is connected to the main reducer, and the output end of the backup motor is connected to the backup reducer, wherein the main motor and the backup motor have exactly the same model and are both equipped with optical-electronic speed sensors; the lower connection mechanism and the upper connection mechanism are respectively located below and above the piston cylinder, the lower connection mechanism is connected to the buffer base, and the upper connection mechanism is connected to the UAV body; the piston rod, the ball screw mechanism and the gear transmission mechanism are installed inside the piston cylinder, the lower end of the piston rod is fixedly connected to the lower connection mechanism, and the upper end of the piston rod is connected to the front end of the nut in the ball screw mechanism; the screw of the ball screw mechanism is combined with the lower end of the gear transmission mechanism, and is used to convert the rotational motion of the gear transmission mechanism into a linear motion to drive the retraction and extension of the piston rod; the position detection device is composed of a pressure sensor and a fixed bracket, the pressure sensor is installed inside the piston cylinder through the fixed bracket, and when the piston rod is in the initial position, the rear end of the nut of the ball screw mechanism contacts the pressure sensor; the upper end of the gear transmission mechanism is respectively connected to the gears in the main reducer and the backup reducer, and is used to transmit the mechanical energy of the reducer to the ball screw mechanism;

[0012] The controller communicates bidirectionally with the UAV flight control system and controls the main motors and backup motors of the four landing gear retraction units, and the controller also receives the signal data sent by the ultrasonic sensor and the pressure sensor respectively.

[0013] Further, the ball screw mechanism includes: a lead screw, a nut, balls, and a ball return pipe; the gear transmission mechanism is connected to the lead screw in the ball screw mechanism and drives the lead screw to rotate. The lead screw and the semi-circular spiral groove on the nut form a spiral raceway with a circular cross-section, and the balls are located in this spiral raceway; when the lead screw rotates, the balls roll in the spiral raceway, driving the nut to move linearly, thereby realizing the telescopic movement of the piston rod.

[0014] Further, one end of the lead screw is arranged in the piston rod, and the two slide relative to each other.

[0015] Further, the main motor, the standby motor, the main reducer, and the standby reducer are fixed to the outside of the piston cylinder by screws.

[0016] Further, the lower end of the piston rod is fixedly connected to the lower connection mechanism by screws.

[0017] A control method for the automatic retracting and deploying device of the landing gear of a tethered drone according to the present invention, based on the above device, the steps are as follows:

[0018] When the tethered drone is in the takeoff state:

[0019] 1) After the flight control system of the drone receives the takeoff command sent by the ground station, the drone enters the takeoff state, and the controller calculates the working time of each fly-by-wire actuator.

[0020] 2) When the drone reaches a certain distance from the ground, the controller sends control commands to each main motor respectively, and each main motor drives the corresponding fly-by-wire actuator to complete the retracting action; when the main motor fails, the controller sends a control command to the standby motor, and the standby motor drives the fly-by-wire actuator to achieve the retracting action.

[0021] 3) When a certain fly-by-wire actuator is completely retracted, the corresponding pressure sensor sends a completion retraction signal to the controller, and the controller controls the motor corresponding to the fly-by-wire actuator to stop working.

[0022] When the tethered drone is in the landing state:

[0023] 4) After the flight control system of the drone receives the landing command sent by the ground station, the drone enters the landing state, and the controller calculates the working time of each fly-by-wire actuator.

[0024] 5) When the drone reaches a certain distance from the ground, the controller sends control commands to the main motors corresponding to each fly-by-wire actuator respectively, and the main motors drive the fly-by-wire actuators to complete the deploying action; when the main motor fails, the controller sends a control command to the standby motor, and the standby motor drives the fly-by-wire actuator to achieve the deploying action.

[0025] 6) The main motors corresponding to each fly-by-wire actuator work for Tj iAfter a certain period of time, the piston rod extends to the specified position, and the controller controls the motor corresponding to the electro-mechanical actuator to stop working, and the release process of the electro-mechanical actuator ends.

[0026] Further, in the step 1), the working time Tq of each electro-mechanical actuator during the take-off process of the UAV i is related to whether there was a previous landing process of the UAV. The calculation formula of Tq i is as follows:

[0027]

[0028] Further, in the step 2), when the UAV takes off and reaches a certain distance from the ground, the controller sends control signals with a duration of Tq i to each main motor respectively. Each main motor rotates reversely, drives the gear transmission mechanism to rotate reversely through the main speed reducer, and thus drives the ball screw mechanism and the piston rod to retract inward; if the main motor corresponding to a certain electro-mechanical actuator has a shutdown failure, the optoelectronic speed sensor inside the main motor will send a fault signal to the controller; after receiving the main motor fault signal, the controller sends a control signal to the standby motor corresponding to the electro-mechanical actuator to continue to complete the inward retraction of the electro-mechanical actuator.

[0029] Further, in the step 4), during the landing process of the UAV, the controller calculates the working time Tj of each electro-mechanical actuator through the following steps i , and the specific calculation steps are as follows:

[0030] 41) Calculate the maximum ground clearance D of each electro-mechanical actuator. The calculation formula is as follows:

[0031] D = max(D1, D2, D3, D4)

[0032] where D1, D2, D3, D4 represent the ground clearances of each electro-mechanical actuator;

[0033] 42) Calculate the gap d between the ground clearance D of each electro-mechanical actuator i and the maximum ground clearance D: i :

[0034] d i = D - D i i = 1, 2, 3, 4

[0035] 43) Calculate the extended length X of each electro-mechanical actuator i :

[0036] X i = L - d i i = 1, 2, 3, 4

[0037] Among them, L represents the length of the piston rod of the electro-mechanical actuator from the initial position to full extension;

[0038] 44) The controller converts the length X of each electro-mechanical actuator extending i into the working time T of the corresponding motor of each electro-mechanical actuator i , and the conversion formula is as follows:

[0039]

[0040] Among them, k1 represents the conversion coefficient between the motor speed and the reducer speed, k2 represents the conversion coefficient between the lead screw speed and the nut horizontal displacement speed in the lead screw structure, and V i represents the working speed of the motor;

[0041] 45) Store the working time Tj of each electro-mechanical actuator i for reading during the takeoff process of the UAV.

[0042] Furthermore, in step 2), when the UAV descends to a certain distance from the ground, the controller sends Tj to the main motors corresponding to each electro-mechanical actuator respectively i duration of the control signal, each main motor rotates forward, drives the gear transmission mechanism to rotate forward after passing through the main reducer, thereby driving the ball screw mechanism and the piston rod to extend outwards; if the main motor corresponding to a certain electro-mechanical actuator has a shutdown failure, the optical rotation speed sensor inside the main motor sends a failure signal to the controller; after receiving the main motor failure signal, the controller sends a control signal to the standby motor corresponding to the electro-mechanical actuator to continue to complete the outward extension of the electro-mechanical actuator.

[0043] Advantages of the present invention:

[0044] The device of the present invention can be automatically retracted and extended, reducing the operation difficulty of the operator to control the takeoff and landing of the UAV; it can adjust the extended length of the electro-mechanical actuator in real time according to the ground flatness, realizing the horizontal landing of the UAV on a complex landing surface; the vertically automatically retractable and extendable electro-mechanical actuator can effectively avoid the entanglement of the electro-mechanical actuator and the tether cable.

[0045] In addition, the present invention uses two sets of main and standby control devices, improving the stability and safety margin of the retraction and extension of the electro-mechanical actuator of the UAV. Brief Description of the Drawings

[0046] Figure 1 is a schematic structural diagram of the device of the present invention.

[0047] Figure 2 is a schematic structural diagram of the landing gear retraction and extension unit in the present invention.

[0048] Figure 3This is the structural sectional view of the electro-mechanical actuator in the present invention.

[0049] Figure 4 This is the schematic diagram of the ball screw mechanism in the present invention.

[0050] Figure 5 This is the schematic diagram of the method of the present invention. Detailed implementation manners

[0051] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with embodiments and the accompanying drawings. The content mentioned in the implementation manners does not limit the present invention.

[0052] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0053] Referring to Figures 1 - 4 As shown, a tethered UAV landing gear automatic retraction device of the present invention includes: a landing gear retraction unit and a controller; wherein the number of the landing gear retraction units is four;

[0054] The landing gear retraction and extension unit includes an ultrasonic sensor 1, a buffer base 2, and an electro-mechanical actuator 3. The ultrasonic sensor 1 is installed on the outer wall of the electro-mechanical actuator 3 and is used to collect the distance between each electro-mechanical actuator and the ground and transmit the distance data to the controller. The buffer base 2 is arranged at the bottom of the electro-mechanical actuator 3 and is used for buffering when the UAV contacts the ground. The electro-mechanical actuator 3 is arranged below the UAV body and is used to drive the retraction and extension of the buffer base 2. The electro-mechanical actuator 3 is composed of a lower connecting mechanism 8, a main motor 5, a backup motor 7, a main reducer 4, a backup reducer 6, an upper connecting mechanism 14, a piston cylinder 9, a piston rod 10, a position detection device 11, a ball screw mechanism 12, and a gear transmission mechanism 13. The main motor 5, the backup motor 7, the main reducer 4, and the backup reducer 6 are fixed on the outside of the piston cylinder 9. The output end of the main motor 5 is connected to the main reducer 4, and the output end of the backup motor 7 is connected to the backup reducer 6. The main motor 5 and the backup motor 6 have exactly the same model and are both equipped with optical speed sensors. The lower connecting mechanism 8 and the upper connecting mechanism 14 are respectively located below and above the piston cylinder 9. The lower connecting mechanism 8 is connected to the buffer base 2, and the upper connecting mechanism 14 is connected to the UAV body. The piston rod 10, the ball screw mechanism 12, and the gear transmission mechanism 13 are installed inside the piston cylinder 9. The lower end of the piston rod 10 is fixedly connected to the lower connecting mechanism 8, and the upper end of the piston rod 10 is connected to the front end of the nut in the ball screw mechanism 12. The screw of the ball screw mechanism 12 is combined with the lower end of the gear transmission mechanism 13 and is used to convert the rotational motion of the gear transmission mechanism 13 into a linear motion to drive the retraction and extension of the piston rod 10. The position detection device 11 is composed of a pressure sensor and a fixed bracket. The pressure sensor is installed inside the piston cylinder 9 through the fixed bracket. When the piston rod 10 is in the initial position, the rear end of the nut in the ball screw mechanism 12 contacts the pressure sensor. The upper end of the gear transmission mechanism is respectively connected to the gears in the main reducer 4 and the backup reducer 6 and is used to transmit the mechanical energy of the reducer to the ball screw mechanism 12.

[0055] The controller communicates bidirectionally with the UAV flight control system and controls the main motors and backup motors of the four landing gear retraction and extension units. The controller also receives the signal data sent by the ultrasonic sensor 1 and the pressure sensor respectively.

[0056] Specifically, the ball screw mechanism 12 includes a screw 15, a nut 16, balls 17, and a ball return pipe 18. The gear transmission mechanism 13 is connected to the screw 15 in the ball screw mechanism 12 and drives the screw 15 to rotate. The screw 15 and the semi-circular spiral groove on the nut 16 form a circular spiral raceway, and the balls 17 are located in this spiral raceway. When the screw 15 rotates, the balls 17 roll in the spiral raceway, driving the nut 16 to move linearly, thereby realizing the telescopic movement of the piston rod 10.

[0057] One end of the lead screw 15 is arranged in the piston rod 10, and the two slide relative to each other.

[0058] The main motor 5, standby motor 7, main speed reducer 4, and standby speed reducer 6 are fixed to the outside of the piston cylinder 9 by screws.

[0059] The lower end of the piston rod 10 is fixedly connected to the lower connecting mechanism 8 by screws.

[0060] The buffer base 2 can absorb the impact force during the landing and docking process of the unmanned aerial vehicle, protect the mechanical equipment, and can also increase the contact area between the landing gear and the ground, improving the stability of the unmanned aerial vehicle when docking on the ground.

[0061] Refer to Figure 5 As shown, the present invention also provides a control method for the automatic retracting and extending device of the tethered unmanned aerial vehicle landing gear. Based on the above device, the steps are as follows:

[0062] When the tethered unmanned aerial vehicle is in the takeoff state:

[0063] 1) After the flight control system of the unmanned aerial vehicle receives the takeoff instruction sent by the ground station, the unmanned aerial vehicle enters the takeoff state, and the controller calculates the working time of each fly-by-wire actuator.

[0064] 2) When the unmanned aerial vehicle reaches a certain distance from the ground, the controller sends control instructions to each main motor respectively, and each main motor drives the corresponding fly-by-wire actuator to complete the retracting action; when the main motor fails, the controller sends a control instruction to the standby motor, and the standby motor drives the fly-by-wire actuator to achieve the retracting action.

[0065] 3) When a certain fly-by-wire actuator is completely retracted, the corresponding pressure sensor sends a completion signal to the controller, and the controller controls the motor corresponding to the fly-by-wire actuator to stop working.

[0066] Specifically, in step 1), during the takeoff process of the unmanned aerial vehicle, the working time Tq of each fly-by-wire actuator i is related to whether there was a previous landing process of the unmanned aerial vehicle. Tq i The calculation formula is as follows:

[0067]

[0068] Specifically, in step 2), when the unmanned aerial vehicle takes off and reaches a certain distance from the ground, the controller sends Tq to each main motor respectively iThe control signal of the duration, each main motor rotates reversely, drives the gear transmission mechanism to rotate reversely after passing through the main speed reducer, thereby driving the ball screw mechanism and the piston rod to retract inward; if the main motor corresponding to a certain electro-hydraulic actuator has a shutdown fault, the photoelectric speed sensor inside the main motor will send a fault signal to the controller; after receiving the main motor fault signal, the controller sends a control signal to the standby motor corresponding to the electro-hydraulic actuator to continue to complete the inward retraction of the electro-hydraulic actuator.

[0069] In the landing state of the tethered drone:

[0070] 4) After the drone flight control system receives the landing command sent by the ground station, the drone enters the landing state, and the controller calculates the working time of each electro-hydraulic actuator.

[0071] 5) When the drone reaches a certain distance from the ground, the controller sends control commands to the main motors corresponding to each electro-hydraulic actuator respectively, and the main motors drive the electro-hydraulic actuators to complete the release action; when the main motor fails, the controller will send a control command to the standby motor, and the standby motor drives the electro-hydraulic actuator to achieve the release action.

[0072] 6) After the main motors corresponding to each electro-hydraulic actuator work for a duration of Tj i the piston rod extends to the specified position, and the controller controls the motors corresponding to the electro-hydraulic actuators to stop working, and the release process of the electro-hydraulic actuator ends.

[0073] Specifically, in step 4), during the landing process of the drone, the controller calculates the working time Tj of each electro-hydraulic actuator through the following steps i , and the specific calculation steps are as follows:

[0074] 41) Calculate the maximum distance from the ground D of each electro-hydraulic actuator, and the calculation formula is as follows:

[0075] D = max(D1, D2, D3, D4)

[0076] where D1, D2, D3, D4 represent the distances from the ground of each electro-hydraulic actuator;

[0077] 42) Calculate the gap d between the distance from the ground D of each electro-hydraulic actuator i and the maximum distance from the ground D: i :

[0078] d i = D - D i i = 1, 2, 3, 4

[0079] 43) Calculate the extended length X of each electro-hydraulic actuator i :

[0080] Xi =Ld i i=1,2,3,4

[0081] Wherein, L represents the length of the piston rod in the electric actuator cylinder from the initial position to the fully extended position;

[0082] 44) The controller extends each electric actuator cylinder to a length X i Transformed into the working time T of each electric actuator cylinder corresponding to the motor i , the conversion formula is as follows:

[0083]

[0084] Among them, k1 represents the conversion coefficient between the motor speed and the reducer speed, k2 represents the conversion coefficient between the screw speed and the horizontal displacement speed of the nut in the screw structure, V i Indicates the operating speed of the motor;

[0085] 45) Working time Tj of each telex actuator i Store and read during the drone takeoff process.

[0086] In addition, in step 2), when the drone lands and reaches a certain distance from the ground, the controller sends Tj to the main motor corresponding to each electromechanical actuator. i The control signal of the time length causes each main motor to rotate forward, and after passing through the main reducer, it drives the gear transmission mechanism to rotate forward, thereby driving the ball screw mechanism and the piston rod to extend outward; if the main motor corresponding to a certain electric actuator cylinder stops functioning, the photoelectric speed sensor inside the main motor sends a fault signal to the controller; after receiving the main motor fault signal, the controller sends a control signal to the standby motor corresponding to the electric actuator cylinder to continue to complete the extension of the electric actuator cylinder.

[0087] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. An automatic retractable landing gear device for a tethered drone, characterized in that, Including: A landing gear retraction unit and a controller; the number of the landing gear retraction units is four; The landing gear retraction unit includes an ultrasonic sensor, a buffer base, and an electro-mechanical actuator; the ultrasonic sensor is installed on the outer wall of the electro-mechanical actuator to collect the distance between each electro-mechanical actuator and the ground and transmit the distance data to the controller; the buffer base is arranged at the bottom of the electro-mechanical actuator for buffering when the drone contacts the ground; the electro-mechanical actuator is arranged below the drone body to drive the retraction and extension of the buffer base; the electro-mechanical actuator is composed of a lower connecting mechanism, a main motor, a standby motor, a main reducer, a standby reducer, an upper connecting mechanism, a piston cylinder, a piston rod, a position detection device, a ball screw mechanism, and a gear transmission mechanism; the main motor, the standby motor, the main reducer, and the standby reducer are fixed on the outside of the piston cylinder, the output end of the main motor is connected to the main reducer, and the output end of the standby motor is connected to the standby reducer, where the main motor and the standby motor have the same model and are both equipped with photoelectric speed sensors; the lower connecting mechanism and the upper connecting mechanism are respectively located below and above the piston cylinder, the lower connecting mechanism is connected to the buffer base, and the upper connecting mechanism is connected to the drone body; the piston rod, the ball screw mechanism, and the gear transmission mechanism are installed inside the piston cylinder, the lower end of the piston rod is fixedly connected to the lower connecting mechanism, and the upper end of the piston rod is connected to the front end of the nut in the ball screw mechanism; the screw of the ball screw mechanism is combined with the lower end of the gear transmission mechanism to convert the rotational motion of the gear transmission mechanism into a linear motion to drive the retraction and extension of the piston rod; the position detection device is composed of a pressure sensor and a fixed bracket, the pressure sensor is installed inside the piston cylinder through the fixed bracket, and when the piston rod is in the initial position, the rear end of the nut in the ball screw mechanism contacts the pressure sensor; the upper end of the gear transmission mechanism is respectively connected to the gears in the main reducer and the standby reducer to transmit the mechanical energy of the reducer to the ball screw mechanism; The controller communicates bidirectionally with the drone flight control system and controls the main motors and standby motors of the four landing gear retraction units, and the controller also receives the signal data sent by the ultrasonic sensor and the pressure sensor respectively.

2. The automatic retractable device for the landing gear of a tethered drone according to claim 1, characterized in that, The ball screw mechanism includes: a screw, a nut, balls, and a ball return pipe; the gear transmission mechanism is connected to the screw in the ball screw mechanism and drives the screw to rotate, the screw and the semi-circular spiral groove on the nut form a circular spiral raceway, and the balls are located in the spiral raceway; when the screw rotates, the balls roll in the spiral raceway to drive the nut to move linearly, so as to realize the telescopic movement of the piston rod.

3. The automatic retractable device for the landing gear of the tethered drone according to claim 1, wherein, One end of the screw is arranged in the piston rod, and the two slide relative to each other.

4. The automatic retractable device for the landing gear of a tethered unmanned aerial vehicle according to claim 1, wherein The main motor, the standby motor, the main reducer, and the standby reducer are fixed on the outside of the piston cylinder by screws.

5. The automatic retractable device for the landing gear of the tethered drone according to claim 1, wherein, The lower end of the piston rod is fixedly connected to the lower connecting mechanism by screws.

6. A control method for an automatic retractable landing gear device of a tethered drone, based on the device described in any one of claims 1-5, characterized in that, The steps are as follows: In the takeoff state of the tethered drone: 1) After the drone flight control system receives the takeoff command sent by the ground station, the drone enters the takeoff state, and the controller calculates the working time of each electro-mechanical actuator; 2) After the UAV reaches a certain distance from the ground, the controller sends control commands to each main motor respectively, and each main motor drives the corresponding fly-by-wire actuator to complete the retraction action; when a main motor fails, the controller sends a control command to the standby motor, and the standby motor drives the fly-by-wire actuator to achieve the retraction action; 3) When a certain fly-by-wire actuator is fully retracted, the corresponding pressure sensor sends a completion retraction signal to the controller, and the controller controls the motor corresponding to the fly-by-wire actuator to stop working; In the landing state of the tethered UAV: 4) After the UAV flight control system receives the landing command sent by the ground station, the UAV enters the landing state, and the controller calculates the working time of each fly-by-wire actuator; 5) After the UAV reaches a certain distance from the ground, the controller sends control commands to the main motors corresponding to each fly-by-wire actuator respectively, and the main motors drive the fly-by-wire actuators to complete the extension action; when a main motor fails, the controller sends a control command to the standby motor, and the standby motor drives the fly-by-wire actuator to achieve the extension action; 6) The working time Tj of the main motor corresponding to each electro-mechanical actuator i After a certain period of time, the piston rod extends to the specified position, and the controller controls the motor corresponding to the electro-mechanical actuator to stop working, and the release process of the electro-mechanical actuator ends.

7. The control method of the tethered UAV landing gear automatic retraction device according to claim 6, characterized in that, In the step 1), the working time Tq of each fly-by-wire actuator during the take-off process of the unmanned aerial vehicle i is related to whether there was a previous landing process of the unmanned aerial vehicle, and Tq i is calculated according to the following formula:

8. The control method of the tethered UAV landing gear automatic retraction device according to claim 7, characterized in that, In step 2), after the UAV takes off and reaches a certain distance from the ground, the controller sends Tq i control signals with a duration of i to each main motor. Each main motor rotates reversely, drives the gear transmission mechanism to rotate reversely through the main speed reducer, and then drives the ball screw mechanism and the piston rod to retract inward. If the main motor corresponding to a certain electro-hydraulic actuator fails to stop, the photoelectric speed sensor inside the main motor will send a fault signal to the controller. After receiving the main motor fault signal, the controller sends a control signal to the standby motor corresponding to the electro-hydraulic actuator to continue to complete the inward retraction of the electro-hydraulic actuator.

9. The control method of the tethered UAV landing gear automatic retraction device according to claim 8, characterized in that, In step 4), during the landing process of the UAV, the controller calculates the working time Tj of each fly-by-wire actuator through the following steps i , and the specific calculation steps are as follows: 41) Calculate the maximum ground distance D of each fly-by-wire actuator, and the calculation formula is as follows: D = max(D1, D2, D3, D4) where D1, D2, D3, D4 represent the ground distances of each fly-by-wire actuator; 42) Calculate the distance D from the ground of each teletype actuator i The difference d between the maximum distance D from the ground i : d i = D - D i i = 1, 2, 3, 4 43) Calculate the length X that each telecontrol actuator extends i : X i = L - d i i = 1, 2, 3, 4 where L represents the length of the piston rod in the fly-by-wire actuator from the initial position to the fully extended position; 44) The controller converts the extended length X of each fly-by-wire actuator i into the operating time T of the corresponding motor of each fly-by-wire actuator i , and the conversion formula is as follows: Among them, k1 represents the conversion coefficient between the motor speed and the reducer speed, k2 represents the conversion coefficient between the lead screw speed and the nut horizontal displacement speed in the lead screw structure, and V i represents the operating speed of the motor; 45) Store the working time Tj of each electro-mechanical actuator for reading during the takeoff process of the UAV. i ​ 10. The control method of the tethered UAV landing gear automatic retraction device according to claim 9, characterized in that, In step 2), when the UAV descends to a certain distance from the ground, the controller sends a control signal with a duration of Tj to the main motors corresponding to each fly-by-wire actuator. Each main motor rotates forward. After passing through the main reducer, it drives the gear transmission mechanism to rotate forward, thereby driving the ball screw mechanism and the piston rod to extend outwards. i When the UAV descends to a certain distance from the ground in step 2), the controller sends a control signal with a duration of Tj to the main motors corresponding to each fly-by-wire actuator. Each main motor rotates forward. After passing through the main reducer, it drives the gear transmission mechanism to rotate forward, thereby driving the ball screw mechanism and the piston rod to extend outwards. If the main motor corresponding to a certain fly-by-wire actuator has a shutdown fault, the optical-electrical speed sensor inside the main motor sends a fault signal to the controller; after receiving the main motor fault signal, the controller sends a control signal to the standby motor corresponding to the fly-by-wire actuator to continue to complete the outward extension of the fly-by-wire actuator.

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