Hydraulic multi-leg unmanned aerial vehicle landing gear control method adaptive to uneven ground conditions

Abstract

The application provides a hydraulic multi-leg unmanned aerial vehicle landing gear control method suitable for uneven conditions, and the specific steps are as follows: a real-time inclination angle of an unmanned aerial vehicle collected by a pose sensor is subtracted from a target inclination angle of the unmanned aerial vehicle when the unmanned aerial vehicle is inclined, so that a control signal of a servo valve on a front landing gear is obtained; a real-time position collected by a position sensor installed on a rear landing gear is subtracted from a target position of a hydraulic cylinder on the rear landing gear obtained according to a target inclination angle of the unmanned aerial vehicle, so that a first difference value is obtained; a real-time force collected by a force sensor installed on the rear landing gear is subtracted from a target force of the hydraulic cylinder on the rear landing gear obtained according to the target inclination angle of the unmanned aerial vehicle, and the difference value is subjected to a second-order impedance control function to obtain a second difference value; and a control signal of a servo valve on the rear landing gear for controlling movement of the rear landing gear is obtained. Through double closed-loop control, the unmanned aerial vehicle can be precisely inclined at any angle front and back under uneven conditions, and the angle of the unmanned aerial vehicle when adjusting loading and unloading of goods according to the needs of the goods is ensured.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) landing gear control, and in particular to a hydraulic multi-leg UAV landing gear control method adapted to uneven working conditions. Background Technology

[0002] Unmanned aerial vehicles (UAVs) are unmanned aircraft controlled by radio remote control equipment and their own program control devices, or by an onboard computer, either completely or intermittently. Large UAVs are generally divided into two types: helicopter UAVs and glider UAVs. The latter can be further divided into fixed and retractable types based on the type of landing gear.

[0003] Large transport drones have wide applications in military reconnaissance, disaster relief, and other fields. Due to their large weight, the landing gear needs to have a large support capacity, while the load-bearing capacity of electric and pneumatic cylinders is limited and insufficient to meet the needs of large transport drones. At the same time, existing drone landing gear is mostly a fixed rigid structure that cannot actively adjust according to the environment. When the drone encounters uneven road conditions or uneven cargo loading, the drone may tilt or even tip over.

[0004] To address this problem, this invention presents a hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions. By collecting the tilt angle signal from an attitude sensor and subtracting it from a given target angle, the controller calculates the difference and transmits the electrical signal to a first servo valve amplifier. The first servo valve amplifier then transmits a modulated signal to a first servo valve, controlling high-pressure hydraulic fluid to enter a first hydraulic cylinder, achieving closed-loop angle control of the front landing gear. Furthermore, by converting the position signal collected by a second position sensor, the adjustment position value obtained by the second hydraulic cylinder based on the tilt angle, and the difference obtained through a second-order impedance control function into a control electrical signal, the controller transmits this signal to a second servo valve amplifier. The second servo valve amplifier then transmits a modulated voltage signal to a second servo valve, controlling high-pressure hydraulic fluid to enter a second hydraulic cylinder, achieving closed-loop position control of the rear landing gear. This dual closed-loop control enables the UAV to precisely tilt at any angle forward or backward under uneven working conditions, ensuring that the UAV adjusts its angle for loading and unloading cargo according to cargo requirements. This allows the UAV to carry more diverse cargo, avoids tilting, and ultimately reduces the risk of tipping over.

[0006] This invention provides a hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions, the specific implementation steps of which are as follows:

[0007] S1. Based on the UAV structural parameters, the fuselage hydraulic pump power system, the servo valve control cylinder system of the front landing gear, the servo valve control cylinder system of the rear landing gear, the number of rear landing gears, and the spacing between adjacent rear landing gears are obtained. An attitude sensor is installed on the fuselage of the UAV. The specific components of the servo valve control cylinder system of the front landing gear and the servo valve control cylinder system of the rear landing gear are as follows:

[0008] The servo valve control system of the front landing gear includes a first safety valve, a first servo valve, a first servo valve amplifier, a first hydraulic cylinder, a first position sensor, and a first force sensor. The output end of the first safety valve is connected to the first end of the first servo valve. The second and third ends of the first servo valve are respectively connected to the first hydraulic cylinder. The first and second control ends of the first hydraulic cylinder are respectively connected to the acquisition ends of the first position sensor and the first force sensor. The control end of the first servo valve is connected to the output end of the controller through the first servo valve amplifier. The oil discharge end of the first servo valve and the first end of the overflow valve are connected in parallel and then connected to the second end of the hydraulic oil tank through an air cooler.

[0009] The servo valve control system of the rear landing gear includes a second safety valve, a second servo valve, a second servo valve amplifier, a second hydraulic cylinder, a second position sensor, and a second force sensor. The output end of the second safety valve is connected to the first end of the second servo valve. The second and third ends of the second servo valve are respectively connected to the second hydraulic cylinder. The first and second control ends of the second hydraulic cylinder are respectively connected to the acquisition ends of the second position sensor and the second force sensor. The control end of the second servo valve is connected to the output end of the controller through the second servo valve amplifier. The oil discharge end of the second servo valve and the first end of the overflow valve are connected in parallel and then connected to the second end of the hydraulic oil tank through an air cooler.

[0010] S2. The difference between the real-time tilt angle of the UAV collected by the attitude sensor and the target tilt angle when the UAV tilts is obtained. The control signal of the servo valve on the front landing gear is obtained by PID calculation to control the movement of the front landing gear.

[0011] S3. Based on the stroke of the hydraulic cylinder measured by the position sensor installed on the rear landing gear in step S1, obtain the extension length of the hydraulic cylinder corresponding to different tilt angles of the rear landing gear.

[0012] S4. Based on step S3, the real-time position collected by the position sensor installed on the rear landing gear is subtracted from the target position of the hydraulic cylinder on the rear landing gear obtained according to the target tilt angle of the UAV, and the first difference value is obtained.

[0013] S5. The real-time force collected by the force sensor installed on the rear landing gear is subtracted from the target force of the hydraulic cylinder on the rear landing gear obtained according to the target tilt angle of the UAV. The difference is then passed through a second-order impedance control function to obtain a second difference value.

[0014] S6. The difference between steps S4 and S5 is used to calculate the control signal of the servo valve on the rear landing gear that controls the movement of the rear landing gear through PID calculation.

[0015] Preferably, in step S1, the number of servo valve control cylinder systems of the front landing gear is one, and the number of servo valve control cylinder systems of the rear landing gear is greater than or equal to one.

[0016] Preferably, in step S1, the information collected by the first position sensor and the first force sensor is transmitted to the input terminal of the controller, and the information collected by the second position sensor and the second force sensor is transmitted to the input terminal of the controller. The controller is used to adjust the changes of the hydraulic cylinders in the servo valve control system of the front landing gear and the servo valve control system of the rear landing gear, so that the UAV can adapt to uneven working conditions.

[0017] Preferably, in step S3, the expression for the extension length of the hydraulic cylinder corresponding to different tilt angles of the rear landing gear is:

[0018]

[0019] Where D is the distance between the left and right landing gears of the UAV, β is the tilt angle of the UAV, Δx is the extension length of the hydraulic cylinder, and ± is the sign for determining the angular direction of the UAV.

[0020] Preferably, in step S5, the expression for the second-order impedance control function is:

[0021]

[0022] Where M is the overall mass of the UAV and landing gear, B is the damping of the compliant control, and K is the stiffness of the compliant control.

[0023] Preferably, in step S1, the fuselage hydraulic pump power system includes a hydraulic oil tank, a shut-off valve, a fixed displacement pump, a motor, a filter, an overflow valve, a pressure gauge, a check valve, an accumulator, and an air cooler. The first end of the hydraulic oil tank is connected to the first end of the fixed displacement pump via a first shut-off valve. The output end of the motor is connected to the second end of the fixed displacement pump. The first end of the overflow valve is connected to the second end of the hydraulic oil tank via an air cooler. The pressure gauge is connected in parallel with the second end of the overflow valve via a second shut-off valve to form a parallel terminal. The parallel terminal is connected in parallel with the third end of the fixed displacement pump and then connected to the first end of the filter. The second end of the filter is connected to the first end of the check valve. The first branch of the first end of the check valve is connected to the accumulator via a third shut-off valve. The second branch of the first end of the check valve is connected to the safety valves in the servo valve control cylinder system of the front landing gear and the servo valve control cylinder system of the rear landing gear, respectively.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The control method of this invention uses a hydraulic servo valve-controlled landing gear to achieve the large load capacity of the UAV. At the same time, the servo valve-controlled system, together with the front landing gear angle closed loop and the rear landing gear position closed loop, enables the UAV to tilt precisely at any angle forward or backward. This ensures that the UAV can adjust the angle when loading and unloading cargo according to cargo requirements, and enables the UAV to carry more diverse cargo.

[0026] 2. The rear landing gear in the control method of this invention adopts an impedance control method, which improves the compliance effect of the rear landing gear. Relying on the closed-loop adjustment of the front landing gear angle and the compliance follow-up effect of the rear landing gear, it ensures that all landing gear support points can generate support force and maintain the corresponding angle on uneven road surfaces, enabling the UAV to adapt to a wider range of terrains. Attached Figure Description

[0027] Figure 1 This is a flowchart of the control method for the hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions according to the present invention.

[0028] Figure 2 Hydraulic schematic diagram of the hydraulic system of the hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions of the present invention;

[0029] Figure 3 This is a schematic diagram of the movement of the hydraulic cylinder of the UAV landing gear used in an example of the hydraulic multi-leg UAV landing gear control method for adapting to uneven working conditions according to the present invention.

[0030] Figure 4 This is a schematic diagram of the UAV landing gear structure used in an example of the hydraulic multi-leg UAV landing gear control method for adapting to uneven working conditions according to the present invention.

[0031] Key reference numerals:

[0032] Hydraulic oil tank 1, first shut-off valve 21, second shut-off valve 22, third shut-off valve 23, fixed displacement pump 3, motor 4, filter 5, relief valve 6, pressure gauge 7, check valve 8, accumulator 9, first safety valve 101, second safety valve 102, first servo valve 111, second servo valve 112, first servo valve amplifier 121, second servo valve amplifier 122, first hydraulic cylinder 131, second hydraulic cylinder 132, first position sensor 141, second position sensor 142, first force sensor 151, second force sensor 152, pose sensor 16, controller 17, air cooler 18. Detailed Implementation

[0033] To fully describe the technical content, structural features, objectives, and effects of this invention, a detailed description will be provided below in conjunction with the accompanying drawings.

[0034] A hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions is proposed. This method employs position-based closed-loop control of the second hydraulic cylinder 132 on each rear landing gear to achieve basic movement. The front landing gear uses angle control to move the UAV to the required angle, while the rear landing gear achieves follow-up movement through compliant control. By introducing force interference signals and roll angle signals, the aircraft's attitude on uneven surfaces is adjusted to ensure that all wheels of the rear landing gear maintain contact and bear force even when the ground is uneven. This enables the UAV to adapt to uneven surfaces, allowing large multi-legged UAVs to land and move smoothly on uneven terrain, and also enabling them to smoothly load and unload cargo. Specific implementation steps are as follows: Figure 1 As shown:

[0035] S1. Based on the UAV structural parameters, obtain the fuselage hydraulic pump source system, the servo valve control cylinder system of the front landing gear, the servo valve control cylinder system of the rear landing gear, the number of rear landing gears and the spacing between adjacent landing gears in the rear landing gear, and install attitude sensor 16 on the fuselage of the UAV.

[0036] Specifically, there is no limit to the number of landing gear legs for drones, and multiple options can be selected based on the actual size of the drone and requirements. The landing gear structure is not limited to tricycle or tailwheel landing gear, and can be set according to the actual aircraft conditions.

[0037] In a preferred embodiment of the present invention, the number of servo valve control cylinder systems of the front landing gear is one, and the number of servo valve control cylinder systems of the rear landing gear is greater than or equal to one.

[0038] The servo valve cylinder control system of the front landing gear includes a first safety valve 101, a first servo valve 111, a first servo valve amplifier 121, a first hydraulic cylinder 131, a first position sensor 141, and a first force sensor 151. The output end of the first safety valve 101 is connected to the first end of the first servo valve 111. The second and third ends of the first servo valve 111 are respectively connected to the first hydraulic cylinder 131. The first and second control ends of the first hydraulic cylinder 131 are respectively connected to the acquisition ends of the first position sensor 141 and the first force sensor 151. The control end of the first servo valve 111 is connected to the output end of the controller 17 through the first servo valve amplifier 121. The information acquired by the first position sensor 141 and the first force sensor 151 is transmitted to the input end of the controller 17. The oil discharge end of the first servo valve 111 and the first end of the overflow valve 6 are connected in parallel and then connected to the second end of the hydraulic oil tank 1 through the air cooler 18.

[0039] The servo valve control system of the rear landing gear includes a second safety valve 102, a second servo valve 112, a second servo valve amplifier 122, a second hydraulic cylinder 132, a second position sensor 142, and a second force sensor 152. The output end of the second safety valve 102 is connected to the first end of the second servo valve 112. The second and third ends of the second servo valve 112 are respectively connected to the second hydraulic cylinder 132. The first and second control ends of the second hydraulic cylinder 132 are respectively connected to the acquisition ends of the second position sensor 142 and the second force sensor 152. The control end of the second servo valve 112 is connected to the output end of the controller 17 through the second servo valve amplifier 122. The information acquired by the second position sensor 142 and the second force sensor 152 is transmitted to the input end of the controller 17. The oil discharge end of the second servo valve 112 and the first end of the overflow valve 6 are connected in parallel and then connected to the second end of the hydraulic oil tank 1 through the air cooler 18.

[0040] The fuselage hydraulic pump power system, such as Figure 2 As shown, the system includes a hydraulic oil tank 1, a shut-off valve, a fixed displacement pump 3, a motor 4, a filter 5, a relief valve 6, a pressure gauge 7, a check valve 8, an accumulator 9, and an air cooler 18. The relief valve 6 is used to set the maximum pressure of the entire system, the pressure gauge 7 is used to observe the system pressure, the accumulator 9 plays a role in stabilizing the circuit, the air cooler 18 is used to cool the system, and the safety valve plays a role in protecting the circuit.

[0041] The first end of the hydraulic oil tank 1 is connected to the first end of the fixed displacement pump 3 through the first shut-off valve 21. The output end of the motor 4 is connected to the second end of the fixed displacement pump 3. The first end of the relief valve 6 is connected to the second end of the hydraulic oil tank 1 through the air cooler 18. The pressure gauge 7 is connected in parallel with the second end of the relief valve 6 through the second shut-off valve 22 to form a parallel end. The parallel end is connected in parallel with the third end of the fixed displacement pump 3 and then connected to the first end of the filter 5. The second end of the filter 5 is connected to the first end of the check valve 8. The first branch of the first end of the check valve 8 is connected to the accumulator 9 through the third shut-off valve 23. The second branch of the first end of the check valve 8 is connected to the safety valve in the servo valve control cylinder system of the front landing gear and the safety valve in the servo valve control cylinder system of the rear landing gear, respectively.

[0042] S2. The attitude sensor 16 collects the required forward tilt and roll angle signals of the UAV. The difference between the real-time tilt angle of the UAV collected by the attitude sensor 16 and the target tilt angle when the UAV tilts is obtained. The control signal of the first servo valve 101 on the front landing gear is obtained by PID calculation to control the movement of the front landing gear. The first hydraulic cylinder 131 on the front landing gear is controlled to realize the angle closed loop.

[0043] S3. Based on the stroke of the second hydraulic cylinder 132 measured by the second position sensor 142 installed on the rear landing gear in step S1, the extension length of the second hydraulic cylinder 132 corresponding to different tilt angles of the rear landing gear is obtained.

[0044] Specifically, the expression for the extension length of the second hydraulic cylinder 132 at different tilt angles of the rear landing gear is as follows:

[0045]

[0046] Where D is the distance between the left and right landing gears of the UAV, β is the tilt angle of the UAV, Δx is the extension length of the second hydraulic cylinder 132, and ± is the determination symbol for the angular direction of the UAV.

[0047] S4. Based on step S3, the real-time position collected by the second position sensor 142 installed on the rear landing gear is compared with the target position of the second hydraulic cylinder 132 on the rear landing gear obtained according to the target tilt angle of the UAV, and the first difference value is obtained.

[0048] S5. The real-time force collected by the second force sensor 152 installed on the rear landing gear is subtracted from the target force of the second hydraulic cylinder 132 on the rear landing gear obtained according to the target tilt angle of the UAV. The difference is then passed through a second-order impedance control function to obtain a second difference value.

[0049] Specifically, the expression for the second-order impedance control function is:

[0050]

[0051] Where M is the overall mass of the UAV and landing gear, B is the damping of the compliant control, and K is the stiffness of the compliant control.

[0052] S6. The difference between steps S4 and S5 is used to calculate the control signal of the servo valve on the rear landing gear that controls the movement of the rear landing gear through PID calculation.

[0053] The following describes in further detail a hydraulic multi-legged UAV landing gear control method adapted to uneven working conditions, based on specific embodiments:

[0054] When uneven ground or slight changes in angle cause a change in the position of the front landing gear, and the force sensor value of the rear landing gear changes, the control method of this invention changes the extension length of the hydraulic cylinders on the front and rear landing gear to maintain a supported state.

[0055] In this specific implementation, there is one front landing gear and six rear landing gears, arranged in pairs in three rows. The specific installation structure is as follows: Figure 4 As shown, force sensors are installed at the top of the hydraulic cylinder rods on the front and rear landing gears to detect the force on the hydraulic cylinders and send the signals collected by the force sensors to the controller 17. Position sensors are installed at the parallel positions of the cylinder rods on the front and rear landing gears to detect the extension length of the cylinder rods and send the signals collected by the position sensors to the controller 17. An attitude sensor 16 is installed on the fuselage of the UAV to collect the real-time attitude of the UAV and transmit the UAV's tilt and roll angle signals to the controller 17. The signals collected by the sensors are filtered to obtain stable real-time signals from the sensors. The controller 17 uses the excitation signal calculated based on the force, position, and angle signals to control the valve core opening of the servo valve, thereby controlling the stroke of the hydraulic cylinders on the front and rear landing gears. In this invention, the front landing gear adopts angle closed-loop control to control the forward tilt angle of the UAV, and the rear landing gear adopts position control. The required extension length of each hydraulic cylinder of the rear landing gear is calculated by kinematics. By introducing a compliant control link into the rear landing gear, after reaching the target position, the rear landing gear is adjusted according to the actual angle and road conditions to achieve arbitrary angle tilt control of the UAV landing gear and uniform and stable support of each hydraulic cylinder on uneven road surfaces.

[0056] The method of this invention determines the landing gear structure based on the UAV parameter requirements and calculates the relationship between the extension length of the hydraulic cylinders on each landing gear and the UAV's tilt angle. The front landing gear employs angle control, using attitude sensor 16 to collect the UAV's forward tilt angle and roll angle. The difference between the expected value and the collected values ​​is used for PID control calculations to control the servo valve core position, achieving closed-loop angle control of the front landing gear. The rear landing gear employs position compliant closed-loop control with the introduction of external disturbance forces. Real-time force is collected using a force sensor, and the external disturbance force on the hydraulic cylinders is calculated. This force is introduced into the position closed loop through a second-order impedance control function, achieving compliant closed-loop control of the rear landing gear and enabling the UAV to maintain angle control on uneven surfaces. The specific implementation steps are as follows:

[0057] S1. Based on the UAV structural parameters, obtain the fuselage hydraulic pump source system, the servo valve control cylinder system of the front landing gear, the servo valve control cylinder system of the rear landing gear, the number of rear landing gears and the spacing between adjacent landing gears in the rear landing gear, and install attitude sensor 16 on the fuselage of the UAV, requiring the front landing gear to be able to extend forward.

[0058] S2. Given the required forward tilt angle of 4° for the UAV, calculate the difference between the current tilt angle and the target tilt angle. Through PID calculation, generate the control signal for the first servo valve 111 and output it to the first servo valve 111 of the front landing gear to realize the angle closed-loop control of the front landing gear.

[0059] S3. Based on the stroke of the second hydraulic cylinder 132 measured by the second position sensor 142 installed on the rear landing gear in step S1, the extension length of the second hydraulic cylinder 132 corresponding to different tilt angles of the rear landing gear is obtained.

[0060] In this embodiment, the hydraulic cylinders on the front and rear landing gear move as follows: Figure 3 As shown, the UAV is tilted at a 4-degree angle. The position values ​​X1, X2, and X3 of each hydraulic cylinder of the rear landing gear are obtained through kinematic calculations.

[0061] The specific calculation process for the kinematics of the rear landing gear is as follows. Since the hydraulic cylinder is rigidly fixed to the UAV platform, the angle of the hydraulic cylinder is always perpendicular to the UAV platform. This calculation process assumes that the second hydraulic cylinder 132 of the second set of rear landing gear does not extend or retract. When the UAV platform tilts from a horizontal state to α, the extension amount produced by the second hydraulic cylinders 132 of the first set of rear landing gear and the second hydraulic cylinders 132 of the third set of rear landing gear is as follows:

[0062] The initial length OC0 of the second hydraulic cylinder 132 of the first rear landing gear is 247mm, and X1 is the extension and retraction of the second hydraulic cylinder 132 of the first rear landing gear. Therefore, the total length OC of the second hydraulic cylinder 132 of the first rear landing gear during movement is: OC = 247 - X1.

[0063] The longitudinal displacement ΔCE of the first rear landing gear during motion, characterized using the law of cosines, is:

[0064]

[0065] ∠3=90-α-∠1-∠2

[0066] ∠4 = ∠3 + 40.77°

[0067] ΔCE=CD·sin∠4-CE.

[0068] In the formula, the letters and subscripts represent points on the rear landing gear and their corresponding angles. Specifically, point O is the connection between the landing gear hydraulic cylinder barrel and the fuselage; point A is the connection between the cylinder barrel and the frame connecting rod; point B is the connection between the frame connecting rod and the wheel connecting rod; point C is the connection between the cylinder rod and the wheel connecting rod; and point D is the wheel axle center. A horizontal line is drawn through point D, and the perpendicular distance from point C to this horizontal line is point E. The angle between lines AC and OC is ∠1; the angle between AC and BC is ∠2; the angle between BC and the horizontal line is ∠3; the angle between CD and BD is ∠4; the angle between BD and the horizontal line is ∠5; and the angle between AO and OC is ∠6.

[0069] The longitudinal displacement generated by the unmanned aerial vehicle platform during its movement can be decomposed into: Figure 3 The expressions for the longitudinal displacement h1 produced by the rotation about point O and the longitudinal displacement h2 produced by the rotation about point D are as follows:

[0070] h1=L·sinα

[0071] h2=OE·(1-cosα)

[0072] Where L is the distance between the two landing gears in the first set of rear landing gears.

[0073] Therefore, the retraction amount X1 of the second hydraulic cylinder 132 of the first rear landing gear is:

[0074]

[0075] The initial length OC0 of the second hydraulic cylinder 132 of the third rear landing gear is 247mm. X3 is the extension and retraction of the second hydraulic cylinder 132 of the third rear landing gear. Therefore, the total length OC of the second hydraulic cylinder 132 of the third rear landing gear during movement is: OC = 247 + X3.

[0076] The longitudinal displacement ΔCE of the third rear landing gear during motion, characterized using the law of cosines, is:

[0077]

[0078] ∠3=90-α-∠1-∠2

[0079] ∠4 = ∠3 + 40.77°

[0080] ΔCE=CD·sin∠4-CE.

[0081] The longitudinal displacement generated by the unmanned aerial vehicle platform during its movement can be decomposed into: Figure 3 The expressions for the longitudinal displacement h1 produced by the rotation about point O and the longitudinal displacement h2 produced by the rotation about point D are as follows:

[0082] h1=L·sinα

[0083] h2=OE·(1-cosα)

[0084] Where L is the distance between the two landing gears in the first set of rear landing gears.

[0085] Therefore, the extension amount X3 of the second hydraulic cylinder 132 of the third rear landing gear is:

[0086]

[0087] S4. Using the roll angle of the UAV collected by the attitude sensor 16, the lateral attitude of the UAV is adjusted, and the position values ​​of each hydraulic cylinder on the rear landing gear are obtained through kinematic calculations. The initial position value of the rear landing gear is obtained by subtracting the position values ​​X1, X2, and X3 of each hydraulic cylinder on the rear landing gear.

[0088] The specific calculation process is as follows:

[0089] When the distance between the left and right sides of the drone's rear landing gear is D, and the drone's roll angle is β, according to the formula...

[0090]

[0091] The calculated adjustment values ​​for the left side of the three sets of rear landing gear on the drone are as follows:

[0092]

[0093] The adjustment values ​​for the right side of the three sets of rear landing gear on the drone are as follows:

[0094]

[0095] The initial position values ​​of the three sets of rear landing gear on the UAV are as follows:

[0096] X 1左 =X1-X1 1

[0097] X1右 =X1-X1 2

[0098] X 2左 =X2-X2 1

[0099] X 2右 =X2-X2 2

[0100] X 3左 =X3-X3 1

[0101] X 3右 =X3-X3 2 .

[0102] S5. The expected output force of the rear landing gear at the current position is calculated by dynamic calculation, and the difference is made with the actual output force collected. After passing through the second-order impedance control function, the difference is made with the position difference of each hydraulic cylinder of the rear landing gear. In the impedance control function, M is based on the actual mass input of the UAV, and the damping and stiffness are adjusted according to the actual feedback effect of the force sensor on the rear landing gear.

[0103] S6. The difference is converted into a servo valve voltage signal and output to the servo valve of the rear landing gear hydraulic cylinder to control the movement of the servo valve core, thereby moving the hydraulic cylinder and realizing the smooth control of the UAV's rear landing gear.

[0104] In this specific implementation of the control method, when the landing gear is running, the first shut-off valve 21, the second shut-off valve 22, and the third shut-off valve 23 are all in the open state. The motor 4 works, driving the metering pump 3 to rotate, causing high-pressure oil to form at the rear end of the metering pump 3. The high-pressure oil is supplied to the safety valves and servo valves in the front and rear landing gears through the filter 5 and the one-way valve 8. After inputting the target angle, the target displacement of the hydraulic cylinders on each rear landing gear is calculated, and the values ​​of the position sensors installed on the hydraulic cylinders on each rear landing gear are collected. At the same time, the roll angle of the UAV is collected by the attitude sensor 16, and the values ​​of the hydraulic cylinders on each rear landing gear are calculated through kinematics. The position value needs to be adjusted from the initial position. The values ​​from the force sensors mounted on the hydraulic cylinders of each rear landing gear are collected, and the force signals are converted into impedance interference position signals through impedance control calculation. The controller calculates the difference between the collected position signal, the position to be adjusted, the impedance interference position, and the target displacement of each hydraulic cylinder on the rear landing gear. The position signal is converted into a control electrical signal by controller 17 and transmitted to the servo valve amplifier. The servo valve amplifier transmits the modulated voltage signal to the servo valve, causing the valve core to move accordingly, controlling the high-pressure oil to enter the cavity of the hydraulic cylinder, extending the hydraulic cylinder to the designated position, thus achieving a closed-loop position for the rear landing gear. The forward tilt angle signal from the attitude sensor 16 is collected and calculated by controller 17 with a given target angle. After calculation, the controller 17 transmits the electrical signal to the first servo valve amplifier 121. The first servo valve amplifier 121 transmits the modulated signal to the first servo valve 111, causing the valve core of the first servo valve 111 to move accordingly, controlling the high-pressure oil to enter the first hydraulic cylinder 131, thus achieving a closed-loop angle for the front landing gear. This allows the hydraulic cylinders to be controlled via a dual closed-loop system to drive the wheels of the landing gear.

[0105] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for controlling the landing gear of a hydraulic multi-legged unmanned aerial vehicle (UAV) adapted to uneven working conditions, characterized in that, The specific implementation steps are as follows: S1. Based on the UAV structural parameters, the fuselage hydraulic pump source system, the servo valve control cylinder system of the front landing gear, the servo valve control cylinder system of the rear landing gear, the number of rear landing gears, and the spacing between adjacent rear landing gears are obtained respectively. An attitude sensor is installed on the fuselage of the UAV. The specific components of the servo valve control cylinder system of the front landing gear and the servo valve control cylinder system of the rear landing gear are as follows: The servo valve control system of the front landing gear includes a first safety valve, a first servo valve, a first servo valve amplifier, a first hydraulic cylinder, a first position sensor, and a first force sensor. The output end of the first safety valve is connected to the first end of the first servo valve. The second and third ends of the first servo valve are respectively connected to the first hydraulic cylinder. The first and second control ends of the first hydraulic cylinder are respectively connected to the acquisition ends of the first position sensor and the first force sensor. The control end of the first servo valve is connected to the output end of the controller through the first servo valve amplifier. The oil discharge end of the first servo valve and the first end of the overflow valve are connected in parallel and then connected to the second end of the hydraulic oil tank through an air cooler. The servo valve control system of the rear landing gear includes a second safety valve, a second servo valve, a second servo valve amplifier, a second hydraulic cylinder, a second position sensor, and a second force sensor. The output end of the second safety valve is connected to the first end of the second servo valve. The second and third ends of the second servo valve are respectively connected to the second hydraulic cylinder. The first and second control ends of the second hydraulic cylinder are respectively connected to the acquisition ends of the second position sensor and the second force sensor. The control end of the second servo valve is connected to the output end of the controller through the second servo valve amplifier. The oil discharge end of the second servo valve and the first end of the overflow valve are connected in parallel and then connected to the second end of the hydraulic oil tank through an air cooler. S2. The difference between the real-time tilt angle of the UAV collected by the attitude sensor and the target tilt angle when the UAV tilts is obtained. The control signal of the first servo valve on the front landing gear is obtained by PID calculation to control the movement of the front landing gear. S3. Based on the stroke of the second hydraulic cylinder measured by the second position sensor installed on the rear landing gear in step S1, obtain the extension length of the second hydraulic cylinder corresponding to different tilt angles of the rear landing gear. S4. Based on step S3, the real-time position collected by the second position sensor installed on the rear landing gear is subtracted from the target position of the second hydraulic cylinder on the rear landing gear obtained according to the target tilt angle of the UAV, and the first difference value is obtained. S5. The real-time force collected by the second force sensor installed on the rear landing gear is subtracted from the target force of the second hydraulic cylinder on the rear landing gear obtained according to the target tilt angle of the UAV, and the difference is obtained by passing the difference through a second-order impedance control function to obtain the second difference value. S6. The difference between steps S4 and S5 is used to calculate the control signal of the second servo valve on the rear landing gear that controls the movement of the rear landing gear through PID calculation.

2. The hydraulic multi-legged UAV landing gear control method for adapting to uneven working conditions according to claim 1, characterized in that, In step S1, the number of servo valve control cylinder systems of the front landing gear is one, and the number of servo valve control cylinder systems of the rear landing gear is greater than or equal to one.

3. The hydraulic multi-legged UAV landing gear control method for adapting to uneven working conditions according to claim 1 or 2, characterized in that, In step S1, the information collected by the first position sensor and the first force sensor is transmitted to the input terminal of the controller, and the information collected by the second position sensor and the second force sensor is transmitted to the input terminal of the controller. The controller adjusts the changes of the hydraulic cylinders in the servo valve control system of the front landing gear and the servo valve control system of the rear landing gear respectively, so that the UAV can adapt to uneven working conditions.

4. The hydraulic multi-legged UAV landing gear control method for adapting to uneven working conditions according to claim 1, characterized in that, In step S3, the expression for the extension length of the second hydraulic cylinder at different tilt angles of the rear landing gear is: ； Where D represents the distance between the left and right landing gears of the drone. The tilt angle of the drone. denoted as the extension length of the hydraulic cylinder, and ± as the angular direction determination symbol for the UAV.

5. The hydraulic multi-legged UAV landing gear control method for adapting to uneven working conditions according to claim 1, characterized in that, In step S5, the expression for the second-order impedance control function is: ； Where M is the overall mass of the UAV and landing gear, B is the damping of the compliant control, and K is the stiffness of the compliant control.

6. The hydraulic multi-legged UAV landing gear control method for adapting to uneven working conditions according to claim 1, characterized in that, In step S1, the fuselage hydraulic pump power system includes a hydraulic oil tank, a shut-off valve, a fixed displacement pump, a motor, a filter, an overflow valve, a pressure gauge, a check valve, an accumulator, and an air cooler. The first end of the hydraulic oil tank is connected to the first end of the fixed displacement pump through a first shut-off valve. The output end of the motor is connected to the second end of the fixed displacement pump. The first end of the overflow valve is connected to the second end of the hydraulic oil tank through an air cooler. The pressure gauge is connected in parallel with the second end of the overflow valve through a second shut-off valve to form a parallel terminal. The parallel terminal is connected in parallel with the third end of the fixed displacement pump and then connected to the first end of the filter. The second end of the filter is connected to the first end of the check valve. The first branch of the first end of the check valve is connected to the accumulator through a third shut-off valve. The second branch of the first end of the check valve is connected to the first safety valve in the servo valve control cylinder system of the front landing gear and the second safety valve in the servo valve control cylinder system of the rear landing gear, respectively.

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