Foldable cross-medium unmanned aerial vehicle and medium-dividing control method thereof

Abstract

The application provides a foldable cross-medium unmanned aerial vehicle and a cross-medium control method thereof, and relates to the technical field of cross-medium unmanned aerial vehicles. The cross-medium unmanned aerial vehicle comprises a rotary sealed main shell, four arms, a four-rotor system, a synchronous folding mechanism and a flight control system. The synchronous folding mechanism is arranged in the middle section of the fuselage and comprises an axial stepping motor, a screw rod, an annular slider and four groups of transmission rods, so that the single axial displacement of the annular slider can be accurately and synchronously converted into the linkage action of the four arms. The flight control system is electrically connected with the four-rotor system and the stepping motor, receives feedback and performs safety interlocking and limitation when the four-rotor system and the stepping motor are not in place or not stopped. Through the deep cooperation of the single-shaft driving multi-rod synchronous mechanism and the threshold safety interlocking logic, the application effectively solves the problems of the out-of-sync arm unfolding and the sensor false triggering during the cross-medium conversion process of the existing equipment, which leads to the system instability or damage, and significantly improves the water conversion stability and the repeated cross-medium task execution capability of the equipment.

Description

Technical Field

[0001] This application relates to the field of cross-medium unmanned aerial vehicle (UAV) technology, and more particularly to a foldable cross-medium UAV and its media-specific control method. Background Technology

[0002] Cross-medium drones need to operate in environments with significantly different physical properties, namely air and water. They typically need to balance a low-drag underwater form factor with a multi-rotor lift architecture in the air. In existing technologies, to achieve the switching between these two forms, multiple independent arm control units are usually set around the drone body to realize the folding and unfolding of the arms, and conventional water immersion sensors or depth gauges are used to determine the medium in which the device is located.

[0003] However, existing cross-medium UAVs have significant technical shortcomings in practical operations. Due to their distributed multi-drive mechanism (i.e., each arm is equipped with an independent folding motor), inconsistent extension or retraction speeds of the arms are highly likely to occur in complex underwater fluid damping environments. This asynchrony can cause the UAV to generate extremely large yaw or roll moments when entering or leaving the water. Furthermore, existing solutions often lack strict hardware and software interlocks between the folding mechanism and the rotor speed, and single-medium sensors (such as those relying solely on water immersion contacts) are prone to false alarms when waves splash or the propellers spray water. Ultimately, this could result in the rotor starting at full speed before the arms are fully locked or the medium condition is fully confirmed, leading to propeller breakage from water impact, capsizing, or even structural damage. Summary of the Invention

[0004] To address the issues of asynchronous arm folding and easy instability and damage during air-water medium switching in existing cross-medium UAVs, this application provides a foldable cross-medium UAV and its medium-separated control method.

[0005] Firstly, this application provides a foldable, cross-medium unmanned aerial vehicle (UAV) that adopts the following technical solution: A foldable cross-medium drone, comprising: The rotary sealed main housing, including the fairing, mid-fuselage section and lower fuselage section, is used to provide a low-drag underwater profile; Four arms are distributed circumferentially along the middle section of the fuselage; A quadcopter system is installed at the outer end of the arm; A synchronous folding mechanism, located in the middle section of the fuselage, is used to drive the arm to extend or retract. The synchronous folding mechanism includes: A stepper motor is arranged along the axial direction of the rotary sealed main housing; The lead screw is connected to the stepper motor via a drive. An annular slider, threadedly sleeved on the outer circumference of the screw rod; and Four sets of transmission rods are connected between the annular slider and the root of the four arms, which are used to synchronously convert the single axial displacement of the annular slider into the linkage action of the four arms. The flight control system is electrically connected to the quadcopter system and the stepper motor. It is used to receive the arm positioning feedback and locking feedback, and to prevent the quadcopter system from entering takeoff speed when any arm is not deployed or the locking feedback is invalid, and to prevent the arm from retracting when the quadcopter system is not stopped.

[0006] Furthermore, the transmission rod includes: The extension rod, with its first end fixed to the annular slider; and The pull rod has one end hinged to the second end of the extension rod and the other end hinged to the root of the arm; The drone also includes a section located at the rear of the lower fuselage: The tail assembly includes a canard, horizontal tail, and vertical tail, all deflected by a waterproof servo; and The underwater propulsion assembly includes two tail propellers arranged side by side and with independent speed regulation.

[0007] Furthermore, it also includes: A pull-out equipment rack is inserted into a sealed compartment inside the rotary sealed main housing, and the pull-out equipment rack is divided along the axial direction into: The control layer, located near the center of gravity of the entire aircraft, is equipped with a low-voltage control module, including the flight control system. A power layer, located on one side of the control layer, is equipped with an ESC and a power distribution board; and The energy layer, located on the side away from the fairing, is equipped with battery modules to keep the center of gravity of the entire aircraft below the center of buoyancy. The sealed chamber is equipped with a water leakage detection module at its lower position, and the outer wall of the sealed chamber is equipped with a depth sensor interface that communicates with external water pressure.

[0008] Secondly, this application provides a media-specific control method for a foldable cross-medium UAV, based on the aforementioned foldable cross-medium UAV, comprising: In underwater cruising mode, the arms are kept retracted, and navigation control is performed by the tail thruster and tail fin assembly located at the rear of the lower section of the fuselage. When the drone receives the water exit command and approaches the water surface, it acquires depth and attitude parameters. When the depth and attitude parameters reach a preset threshold, it enters the water exit preparation state. The synchronous folding mechanism is controlled to unfold the arm, and after receiving a feedback signal that all parts are in place and locked continuously and effectively, the quadcopter system is controlled to pre-rotate. The quadcopter system is controlled to increase total thrust by using a thrust ramp to enter the water lift-off state, and after detecting a valid water-triggered dry-out signal, it switches to air control state. After the drone touches the water during the water entry mission, the quadcopter system is controlled to slow down and stop rotating, the synchronous folding mechanism is controlled to retract the arms, and the tail propeller is switched to take over.

[0009] Furthermore, in the water preparation state, when the external water depth is no greater than 0.30m, the buoyancy speed is no greater than 0.15m / s, the roll angle and pitch angle are both no greater than 8° and the angular velocity is no greater than 20° / s, the arm deployment action is permitted. During the arm's deployment process, if the deployment time exceeds a preset time threshold, or if the stepper motor current exceeds a preset ratio of the normal deployment current, the deployment action will stop and the system will enter a safety protection state.

[0010] Furthermore, the pre-rotation stage logic of the quadcopter system includes: controlling the target rotation speed of the rotor propeller to 10%-20% of the takeoff speed, and monitoring the current of the four rotor motors. When the current deviation is no greater than 15%, the system is allowed to enter the water-lifting state. The logic for the water-lifting phase includes increasing the total thrust according to the slope ascent rate within a time interval of 0.8-1.5s.

[0011] Furthermore, the dual-redundancy logic for determining the water-triggered drying signal and the water-contact signal is as follows: Simultaneously acquire the output voltage of the water immersion contact and the absolute underwater depth; The water-contact state is determined only when the output voltage of the water immersion contact reaches the water immersion threshold and the output underwater absolute depth reaches the depth threshold and is maintained continuously for no less than 200ms. The water-triggered drying signal is considered valid only when the output voltage of the water immersion contact is lower than the reset threshold and the output underwater absolute depth returns to near zero depth and remains there for at least 200ms.

[0012] Furthermore, the navigation control in the underwater cruise state adopts a hierarchical cascaded PID architecture, including: The outer depth control layer uses the error between the desired depth and the measured depth as input to calculate the desired longitudinal velocity; The mid-level underwater velocity control layer uses the error between the desired longitudinal velocity and the measured longitudinal velocity as input to calculate a common reference thrust output to the tail thruster. The intermediate heading control layer uses the error between the desired heading angle and the measured heading angle as input to calculate the differential thrust output to the tail thruster; and The inner attitude damping layer, taking the comprehensive attitude error as input, calculates the tail fin deflection angle and outputs it to the tail fin assembly.

[0013] Furthermore, the flight control in the air control state adopts a three-layer cascaded PID control architecture, including: The outer ring of the position is used to calculate the expected speed based on the error between the desired and actual positions. In the speed loop, based on the error between the desired and actual speeds, the desired roll angle, desired pitch angle, and total lift are calculated; and The attitude inner loop calculates the three-axis control torque based on the error between the desired attitude angle and the actual attitude angle, as well as the angular velocity error, and distributes the total lift to the four rotor motors via the quadcopter hybrid control of the quadcopter system.

[0014] Furthermore, the media-specific control method also includes abnormal interlocking logic: When it is detected that the arm is not locked or folding. When any of the following is triggered: timeout, abnormal rotor motor current, tail propeller failure, tail fin jamming, or water leakage, the system enters a safety protection state. When in the aforementioned safety protection state, based on the current medium properties of the UAV, the corresponding operation among prohibiting leaving the water, maintaining a fixed depth, controlled ascent, hovering in the air, or controlled landing is forcibly executed.

[0015] In summary, this application includes at least one of the following beneficial technical effects: 1. By setting up a synchronous folding mechanism consisting of a single axial stepper motor, a screw screw, and a ring slider to pull four sets of transmission rods, the single-axis linear displacement is forcibly converted into the synchronous action of the four arms, thereby achieving perfect physical synchronization of the quadcopter architecture and improving the asynchronous jamming and overturning problems caused by uneven water flow damping of the distributed independent motors in the existing technology. 2. By introducing dual-redundant logic that synchronously detects water immersion contact voltage and absolute water depth and applies a continuous confirmation time window of no less than 200ms, the system's determination of the medium state does not depend on a single instantaneous sensing, thereby achieving effective filtering of high-frequency pseudo signals such as wave splash and blade water ejection, and significantly solving the potential for aircraft crashes caused by false triggering at cross-medium critical points. 3. By establishing an interlocking algorithm in the flight control system for pre-takeoff current consistency verification, deployment action timeout / overload power cut-off, and thrust ramp increase of 0.8-1.5s during takeoff and climb phase, the rotor power output is matched with the water film separation time, thereby achieving deep collaboration between mechanical hardware and control software and effectively solving the problem of instantaneous attitude instability caused by large thrust step. 4. By arranging the pull-out equipment rack into control, power, and energy layers, and placing the heavy battery modules in the energy layer (away from the fairing and in a low position), the overall center of gravity of the UAV is always lower than the center of buoyancy, thereby achieving passive static self-alignment and improving the adaptability and reliability of the equipment on wavy water. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application; Figure 2 This is a partial cross-sectional structural diagram of an embodiment of this application; Figure 3 This is a front view of the folded state of an embodiment of this application; Figure 4 This is a side view of the folded state of an embodiment of this application; Figure 5 This is a top view of the folded state of an embodiment of this application; Figure 6 This is the main view of the unfolded state of the embodiments of this application; Figure 7 This is a side view of the unfolded state of an embodiment of this application; Figure 8 This is a top view of the unfolded state of an embodiment of this application; Figure 9 This is a schematic diagram of the unfolding of the synchronous folding mechanism according to an embodiment of this application; Figure 10 This is a schematic diagram of the modular fairing structure according to an embodiment of this application; Figure 11 This is a schematic diagram of the structure of the pull-out equipment rack according to an embodiment of this application; Figure 12 This is a tree diagram of the cross-media navigation process in an embodiment of this application.

[0018] Figure label: 1. Fairing; 2. Mid-fuselage section; 3. Lower fuselage section; 4. Arm; 5. Rotor motor; 6. Rotor propeller; 7. Canard; 8. Horizontal tail; 9. Vertical tail; 10. Tail thruster; 11. Lever; 12. Small float; 13. Sealed compartment; 14. Pull-out equipment rack; 15. Stepper motor; 16. Servo; 17. Lead screw; 18. Extension rod; 19. Annular slider. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] Reference Figures 1-12 This application discloses a foldable cross-medium unmanned aerial vehicle, which includes: The rotary sealed main housing includes a fairing 1, a mid-fuselage section 2, and a lower fuselage section 3, which are used to provide a low-drag underwater profile.

[0021] Four arms 4 are distributed circumferentially along the middle section 2 of the fuselage.

[0022] The quadcopter system, installed at the outer end of arm 4, includes four sets of rotor propellers 6 and rotor motors 5.

[0023] The synchronous folding mechanism, located within the middle section 2 of the fuselage, is used to drive the arm 4 to extend or retract. The synchronous folding mechanism includes: Stepper motor 15 is arranged along the axial direction of the rotary sealing main housing; The screw 17 is connected to the stepper motor 15 and is rotatably supported in the middle section 2 of the machine body; The annular slider 19 is threaded onto the outer circumference of the screw rod 17; and Four sets of transmission rods are connected between the annular slider 19 and the roots of the four robotic arms 4, used to synchronously convert the single axial displacement of the annular slider 19 into the linked action of the four robotic arms 4. When the stepper motor 15 rotates forward, the screw 17 drives the annular slider 19 to move in the unfolding direction, and the four sets of transmission rods simultaneously push the four robotic arms 4 to extend outward; when the stepper motor 15 rotates in reverse, the annular slider 19 moves in the retracting direction, and the four sets of transmission rods simultaneously pull the four robotic arms 4 to retract towards the main housing.

[0024] In addition, the cross-media UAV of this application also includes a flight control system electrically connected to the quadcopter system and the stepper motor 15. This system receives positioning and locking feedback from the arms 4, and prevents the quadcopter system from reaching takeoff speed if any arm 4 is not fully deployed or if the locking feedback is invalid. It also prevents the arms 4 from retracting if the quadcopter system is not stopped. This ensures that the deployment and retraction of the arms 4 are protected by necessary safety interlocks, preventing interference between the blades and the casing or arms 4 due to unreliable deployment, and preventing mechanical damage during folding due to the rotor blades 6 not stopping.

[0025] Therefore, the folding or unfolding commands issued by the flight control system directly act on a single stepper motor 15. The rotational motion of the stepper motor 15 is converted into the pure axial linear motion of the annular slider 19 through the lead screw 17. Since the four sets of transmission links are spatially connected in parallel to the same annular slider 19, the four arms 4 are forced to open and close with completely consistent angular velocities and strokes. At the same time, the flight control system establishes a deadlock condition between the rotor speed 6 and the folding feedback at the software level. Thus, from both the physical structure and control logic levels, attitude instability caused by asynchronous actions of the various arms 4 is completely avoided, effectively addressing the cross-medium damage issue raised in the background technology.

[0026] In one specific control sequence for the deployment maneuver, the flight control system first confirms that the rotor blade 6 is not at its operating speed, then drives the stepper motor 15 to deploy, while simultaneously monitoring the deployment time, the current of the stepper motor 15, and the positioning feedback of the four arms 4. After the positioning feedback remains continuously valid for a preset duration, a lockout is confirmed, and only then is the rotor blade 6 allowed to pre-rotate. If the deployment time exceeds a preset threshold, any positioning feedback becomes invalid, or the current of the stepper motor 15 suddenly exceeds a preset proportion of the normal deployment current, deployment immediately stops and enters a safety protection state. For example, the deployment time threshold can be set to 2.5 seconds, the continuous valid positioning feedback time can be set to 300 milliseconds, and the abnormal proportion of the stepper motor 15 current can be set to 150% of the normal deployment current.

[0027] During the retraction process, the flight control system confirms that the water-trigger signal is valid and the depth has reached a preset threshold, and confirms that the rotor speed 6 has dropped to below a preset percentage of the takeoff speed. Then, it releases the lock and drives the stepper motor 15 to retract the rotor. After retraction, the underwater propulsion assembly takes over the depth and orientation control. For example, the water contact depth can be set to no less than 0.10m, and the rotor speed 6 can be reduced to less than 5% of the takeoff speed.

[0028] Specifically, regarding the mechanical structure of the aforementioned transmission rods, refer to... Figure 2 and Figure 9 The transmission components include an extension rod 18 and a pull rod 11. The first end of the extension rod 18 is fixed to an annular slider 19; one end of the pull rod 11 is hinged to the second end of the extension rod 18, and the other end is hinged to the root of the arm 4. It should be understood that by setting the hinged relationship, when the annular slider 19 is pushed or pulled axially, the pull rod 11 can use a lever principle to drive the arm 4 to fold or unfold around its root rotation axis. Thus, a single axial displacement of the annular slider 19 is synchronously converted into the coordinated action of the four arms 4, resulting in high synchronicity in the unfolding and retraction of the four arms 4, reducing attitude deviations caused by asynchronous arm movements, and balancing the requirements of low drag underwater and aerial flight.

[0029] In order to form a complete hydro-aerodynamic closed loop, refer to Figure 1 , Figure 3 and Figure 4 The cross-medium UAV of this application also includes a tail assembly and an underwater propulsion assembly located at the rear of the lower fuselage section 3. The tail assembly includes a canard 7, a horizontal tail 8, and a vertical tail 9, all driven and deflected by a waterproof servo motor 16. The underwater propulsion assembly includes two tail-thrust propellers 10 arranged side-by-side and with independently adjustable speeds. Thus, in the underwater state with the arms 4 folded, the UAV can achieve efficient cruising entirely by relying on the differential motion of the tail-thrust propellers 10 and the deflection of the tail assembly.

[0030] Furthermore, in order to solve the problem of arranging and dissipating heat from the complex electronic components inside the drone, in some embodiments, reference is made to... Figure 2 and Figure 11 The UAV also includes a pull-out equipment rack 14 inserted into a sealed compartment 13 inside the rotary sealed main shell. Specifically, the pull-out equipment rack 14 is strictly divided into three layers along the axial direction: the control layer is located close to the overall center of gravity, reducing the impact of vibration and rotational motion on attitude measurement and control accuracy. This layer houses low-voltage control modules, including the flight control system, to minimize interference from the rotational arm on inertial measurements. It can also house an inertial measurement unit, barometric pressure / altitude sensors, and communication modules. The power layer is located on one side of the control layer and houses an ESC, power distribution board, relays, fuses, and waterproof connectors. The ESC is connected to the shell or heat sink via a thermal pad. The energy layer is located on the side away from the fairing 1 and houses a battery module and battery management module. It can also be equipped with counterweights to lower the overall center of gravity below the center of buoyancy.

[0031] Furthermore, a leakage detection module electrically connected to the flight control system is located at the lower part of the sealed chamber 13. When leakage is detected, the flight control system shuts down unnecessary loads and triggers ascent or return. The outer wall of the sealed chamber 13 is equipped with a depth sensor interface connected to external water pressure, allowing the water trigger signal and the depth sensor signal to be used together to determine water contact and immersion, avoiding false judgments from a single contact point. Preferably, the heat-generating devices in the power layer can be attached to the inner wall of the main housing via thermal pads, utilizing external water for efficient passive heat dissipation. Thus, this layered design not only meets the electromagnetic isolation and heat dissipation requirements of each functional module, but also statically endows the equipment with a natural self-righting ability after immersion in water.

[0032] It is worth noting that the locking feedback structure of arm 4 must be clearly defined here. In some embodiments, the locking feedback can be achieved by a mechanical limit switch located at the end of the slider stroke and the self-locking torque of the stepper motor 15; or by an independent electromagnetic latch at the root of arm 4 providing a feedback signal, thereby providing a reliable logical judgment basis for the flight control system. Those skilled in the art can use conventional waterproof sensors to achieve the above-mentioned detection of positioning and locking, which is entirely feasible and requires no further explanation.

[0033] In a more specific embodiment, reference is made to... Figure 1 , Figure 3 and Figure 7 Small buoyancy tanks 12 are also arranged on the surface of the lower section 3 of the fuselage. The small buoyancy tanks 12 are coordinated with the center of gravity arrangement of the energy layer in the pull-out equipment frame 14 so that the center of gravity of the whole machine is lower than the center of buoyancy. After entering the water, it can naturally recover to a smaller roll angle and pitch angle, thereby improving the attitude stability during the preparation for water exit and the water entry and connection stage.

[0034] This application also discloses a media-specific control method for a foldable cross-media UAV, applied to the aforementioned foldable cross-media UAV, employing the following technical solution: A media-specific control method for a foldable, cross-media UAV, referring to... Figure 1 , Figure 2 and Figure 12 ,include: In underwater cruising mode, keep the arms 4 retracted and perform navigation control through the tail thruster 10 located at the tail of the lower section 3 of the fuselage and the tail assembly. When the drone receives the command to exit the water and approaches the water surface, it acquires depth and attitude parameters. When the depth and attitude parameters reach the preset threshold, it enters the water exit preparation state. The synchronous folding mechanism is controlled to unfold arm 4, and after receiving feedback signals that all arms are in position and locked continuously and effectively, the quadcopter system is controlled to pre-rotate. The quadcopter system is controlled to increase total thrust by using a thrust ramp to enter the water-lift climb state, and switches to air control state when a valid water-triggered dry signal is detected. After the drone touches the water during the water entry mission, the quadcopter system is controlled to slow down and stop rotating, the synchronous folding mechanism is controlled to retract the arm 4, and the tail propeller 10 takes over.

[0035] To cope with complex wave disturbances on the water surface, in some embodiments, the flight control system sets stringent kinematic thresholds during the water-emergence preparation state: The deployment of arm 4 is permitted only when the external water depth is no greater than 0.30m, the buoyancy is no greater than 0.15m / s, the roll and pitch angles are both no greater than 8°, and the angular velocity is no greater than 20° / s.

[0036] Furthermore, during the deployment of the robotic arm 4, if the deployment time exceeds a preset time threshold or the current of the stepper motor 15 exceeds a preset ratio of the normal deployment current, the deployment action will stop and enter a safety protection state, thereby effectively preventing underwater foreign objects from getting stuck and causing the stepper motor 15 to overload and burn out.

[0037] In other embodiments, the pre-rotation phase logic of the quadcopter system includes: The target rotational speed of the rotor propeller 6 is controlled to be 10%-20% of the takeoff speed, and the current of the four rotor motors 5 is monitored. When the current deviation is not greater than 15%, the water lift-off state is allowed.

[0038] The logic for the water lift-off phase includes increasing the total thrust according to the slope rise rate within a time interval of 0.8-1.5s.

[0039] It should be noted that the 0.8-1.5s thrust ramp design is the key to overcoming the shortcomings of existing technology: it avoids the huge transient torque caused by direct full-power takeoff, provides buffer time for the water film to detach from the fuselage and for the release of residual water resistance, and significantly reduces the attitude impact at the moment of water exit.

[0040] It is important to emphasize here that, because a single sensor is highly susceptible to being misled by waves, the dual-redundancy logic for determining the water-triggered drying signal and the water-contact signal is as follows: The flight control system simultaneously reads the water immersion contact output voltage Uw and the depth sensor output depth h, forming the water immersion contact Boolean quantity Sw and the depth Boolean quantity Sh respectively, and uses the combination result of Sw and Sh as the water trigger Boolean quantity W.

[0041] W is updated from dry state to wet state only when Uw reaches the immersion threshold and h reaches the depth threshold and remains there for at least 200 ms.

[0042] W is updated from wet to dry only when Uw is below the reset threshold and h returns to near-zero depth and remains there for at least 200 ms.

[0043] Splashing waves, short-term contact conduction, or instantaneous spikes in the depth sensor are only recorded as candidate signals and do not trigger medium switching.

[0044] The principle of the aforementioned dual-redundant water-triggered logic lies in cross-checking the contact-type water immersion signal with the continuous depth signal and filtering out high-frequency disturbances through time confirmation. This effectively prevents the UAV from misjudging water entry or exit when it is close to the water surface, when the propellers are splashing water, or when waves are surging, thus ensuring that arm 4 deployment, rotor pre-rotation 6, rotor 6 shutdown, and tail thruster 10 connection all occur in a stable medium. Compared to existing technologies that rely solely on switching based on a single water contact point or a single depth threshold, this logic simultaneously improves resistance to false triggering and the reliability of water entry / exit status identification, making it particularly suitable for cross-medium UAVs repeatedly traversing wavy water surfaces.

[0045] For example, the double redundancy judgment logic is as follows:

[0046] in, A Boolean value triggered by water. The output voltage is for the water-immersed contact. To output the absolute underwater depth, the update only occurs after the condition is met continuously for 200ms. Wave splashing does not trigger medium switching when a single contact is activated.

[0047] In some embodiments, for the specific control algorithm closed loops in the underwater and air modes, the navigation control in the underwater cruise state adopts a hierarchical cascaded PID architecture, from the outside to the inside as follows: The expected longitudinal velocity is calculated based on the error between the expected depth of the outer layer and the measured depth. The common reference thrust is calculated based on the expected and measured longitudinal velocity error and output to the tail thruster propeller; The differential thrust is calculated based on the heading angle error and output to the tail thruster propeller; The tail fin deflection angle is calculated based on the overall attitude error and output to the tail fin assembly.

[0048] In the air control state, it switches to a three-layer cascade PID control architecture: the outer position loop calculates the desired speed, the middle speed loop calculates the desired attitude and total lift, and the inner attitude loop finally calculates the three-axis control torque and distributes it to the rotor motor 5 through quadcopter hybrid control.

[0049] For example, underwater control uses a hierarchical cascade PID architecture, with the outer loop outputting the inner loop's desired input, and all control cycles... This can be achieved through the following formula: Outermost ring depth control layer: For depth, error calculation .

[0050] Longitudinal speed command

[0051] .

[0052] Mid-level underwater velocity control layer: For longitudinal velocity, error calculation .

[0053] Common reference thrust

[0054] .

[0055] Mid-level heading control layer: For the heading angle, error calculation .

[0056] Differential thrust

[0057] .

[0058] Innermost ring attitude damping layer: For the tail fin deflection angle, The underwater roll angle, This refers to the underwater yaw angle. Pitch error Roll error Overall attitude error

[0059] .

[0060] Among them, subscript The expected instruction, subscript For real-time measurement feedback, For error, This is the proportionality coefficient. The integral coefficient is... The differential coefficients are... for A limiting function that immediately clamps the boundary value if the range is exceeded. For discrete integral terms, the discrete form is: For the differential term, the discrete difference is... .

[0061] The principle of this underwater control logic is based on generating the desired velocity from the outer depth loop, generating the propulsion reference quantity and differential quantity from the middle velocity and heading loops respectively, and then suppressing roll, pitch, and yaw oscillations from the inner attitude damping loop, so that the tail thruster 10 and the tail fin respectively undertake the functions of propulsion, steering, and damping correction. Its effect is that it can still achieve constant speed, constant depth, and directional navigation when the arms 4 are retracted to form a low-drag shape, and reduces energy consumption and attitude oscillations caused by frequent and large tail fin deflections. Compared with existing technologies that only provide underwater thruster speed adjustment or simple mode switching solutions, this embodiment discloses the input quantities, output quantities, error calculation directions, and actuator allocation relationships of each control layer, which can demonstrate the synergistic advantages between cross-medium UAV underwater control and the folding low-drag configuration.

[0062] Furthermore, upon approaching the water surface, the flight control system reduces the thrust of the tail thruster 10 to below 30% of the cruise thrust and maintains attitude via the tail fin. The aircraft is only permitted to enter the surface preparation state when the depth is no greater than 0.30 m, the ascent speed is no greater than 0.15 m / s, the roll and pitch angles are both no greater than 8°, and the angular velocity is no greater than 20° / s.

[0063] For example, the air control is a three-layer cascade attitude / position control, with the outer loop outputting the desired input to the inner loop, and the attitude inner loop control cycle... Position outer loop control cycle This can be achieved through the following formula: Location: Outer Ring Road For the desired speed, For the desired position, This is the actual position, with an error. .

[0064] Desired vertical velocity ; Expected velocities in the X and Y directions .

[0065] .

[0066] Speed ​​Central Ring: take over Output the desired roll angle Desired pitch angle Total lift ; Triaxial speed error , , , ;

[0067]

[0068] .

[0069] Inner ring of posture: Input desired angle actual angle angular velocity ; error , , ;

[0070]

[0071] .

[0072] The quadrotor hybrid control allocation equation is: .

[0073] in, Wheelbase For single rotor torque coefficient, For tensile force coefficient, subscript The expected instruction, subscript For real-time measurement feedback, For error, This is the proportionality coefficient. The integral coefficient is... The differential coefficients are... This is a limiting function; it immediately clamps the boundary value if the value exceeds the interval. For discrete integral terms, the discrete form is: , For the differential term, the discrete difference is... .

[0074] The principle of this airborne control logic is to prevent position errors from directly affecting the rotor motor 5, instead converting them layer by layer into speed, attitude, and torque commands. This disperses the large disturbances after water exit across different media into control loops at different time scales. The effect is that during the water exit climb phase, it maintains stable attitude even when water film detachment, residual water resistance, and blade water ejection coexist. It also quickly takes over airborne quadcopter control after confirming the water trigger signal has dried. Compared to existing technologies that only vaguely describe the airborne mode or directly use ordinary quadcopter controllers, this embodiment clearly defines the input-output relationships and mixed control distribution paths of the outer, middle, and inner loops. This allows the control method to coordinate with water exit pre-rotation, current consistency detection, and thrust ramp logic, enhancing the executability of repeated water exit takeoffs.

[0075] Regarding the media switching and security protection logic, refer to... Figure 11After the mission is initiated, the flight control system first performs a self-check: the battery SOC is not lower than 35%, the water leakage detection is dry for 5 consecutive seconds, the inertial measurement unit, depth sensor, barometric pressure / altitude sensor and communication link are effective, and the no-load current of the folding mechanism does not exceed 30% of the rated value. After passing the self-check, it enters underwater cruise.

[0076] The water exit process consists of underwater cruising, near-surface water exit preparation, deployment of arm 4 and pre-rotation of rotor 6, and water exit climb. The switching conditions for water exit climb are that the water trigger signal dries out or the altitude is not less than 0.50 m for 0.5 s, while the attitude error is not greater than 5°. Once these conditions are met, the tail thruster 10 stops outputting thrust or maintains the minimum safe thrust, and the air control logic takes over.

[0077] The water entry procedure is as follows: in-flight mission, water entry preparation, water contact take-off and landing arm 4 retraction. During water entry preparation, the descent speed is controlled at 0.2-0.5 m / s, the horizontal speed is no greater than 0.8 m / s, and the roll and pitch angles are both no greater than 8°. After water contact and a depth of no less than 0.10 m, the rotor blade 6 reduces its speed to below 5% of takeoff speed within 1.5 seconds. Then, the folding mechanism retracts landing arm 4, and the tail thruster 10 takes over depth and orientation control within 0.5 seconds.

[0078] During medium switching, the water-triggered Boolean value W, depth h, altitude, attitude angle, angular velocity, arm position feedback, and motor current feedback together constitute the state machine's transition conditions. Underwater, hierarchical cascaded PID control is prioritized; in aerial mode, three-layer cascaded attitude / position control is prioritized; and during the water exit and entry transitions, control is transferred based on the stable update of W and the rotor speed threshold. Therefore, underwater control, water exit detection, and aerial control are not isolated conventional algorithms, but rather form a continuous control logic around the foldable cross-medium configuration.

[0079] The effects of the aforementioned continuous control logic are: maintaining low drag and low energy consumption during underwater navigation, suppressing false triggering during the near-surface phase, smoothly establishing lift during the lift-up phase, and reducing the risk to the rotor propeller 6 before the tail thruster propeller 10 takes over during the water entry phase. Compared to existing technologies that describe underwater navigation, folding motion, and aerial flight in segments, this embodiment links structural motion, media identification, and actuator control through a unified state machine and hierarchical control laws, highlighting the stability, reliability, and engineering feasibility advantages of this invention in repetitive cross-media tasks.

[0080] In addition, the safety protection logic covers all main process states, such as the flight control system detecting any abnormality such as arm 4 not locking, folding action timeout, rotor motor 5 abnormal current, tail thruster 10 failure, tail fin jamming, water leakage, attitude exceeding limits, insufficient power or communication interruption. Safety protection can be triggered in all states. Underwater malfunctions prioritize depth holding or controlled ascent; in-flight malfunctions prioritize hovering, returning to base, or controlled landing; a state of charge (SOC) below 25% triggers a return to base, and below 18% triggers a landing at the nearest landing site or water recovery. In this way, even in the face of complex or abnormal conditions, the flight control system can make the most suitable protective actions for the current physical environment.

[0081] The implementation principle of a foldable cross-medium UAV according to an embodiment of this application is as follows: When the cross-medium UAV of this application is in operation, if the device is initially underwater performing a cruise mission, the four arms 4 are retracted close to the main shell, and the flight control system only uses the tail propeller 10 and tail assembly for heading and depth adjustment. When the cross-medium water-emergence command is triggered, the UAV is controlled to rise to a preset depth (e.g., within 0.3m) and enters an attitude stabilization waiting period. Once the attitude angle and angular velocity meet the low disturbance threshold, the flight control system drives the stepper motor 15, which drives the ring slider 19 to push and pull the rod 11 forward through the lead screw, so that the four arms 4 extend outward at the same speed. After the arms 4 are fully extended and the mechanical and logical double locking is confirmed, the four rotor propellers 6 pre-rotate at 10%-20% speed to verify current consistency. Subsequently, the total thrust increases smoothly in a ramp of 0.8-1.5 seconds, and the UAV overcomes the water film tension to leave the water. At this time, after the dual-redundant logic based on the combination of water immersion contact and depth gauge confirms that the equipment has truly "dried" (for more than 200ms), the flight control system completely transfers the takeover authority to the three-layer PID architecture in the air.

[0082] When returning to the water, after triggering the exact water entry threshold, the four rotor propellers 6 are forced to stop first, then the stepper motor 15 is started to retract the arm 4, and finally the tail propulsion system takes over, forming a complete, interlocked, and highly robust cross-medium working closed loop.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A foldable, cross-medium unmanned aerial vehicle, characterized in that, include: The rotary sealed main housing, including the fairing, mid-fuselage section and lower fuselage section, is used to provide a low-drag underwater profile; Four arms are distributed circumferentially along the middle section of the fuselage; A quadcopter system is installed at the outer end of the arm; A synchronous folding mechanism, located in the middle section of the fuselage, is used to drive the arm to extend or retract. The synchronous folding mechanism includes: A stepper motor is arranged along the axial direction of the rotary sealed main housing; The lead screw is connected to the stepper motor via a drive. An annular slider, threadedly sleeved on the outer circumference of the screw rod; and Four sets of transmission rods are connected between the annular slider and the root of the four arms, which are used to synchronously convert the single axial displacement of the annular slider into the linkage action of the four arms. The flight control system is electrically connected to the quadcopter system and the stepper motor. It is used to receive the arm positioning feedback and locking feedback, and to prevent the quadcopter system from entering takeoff speed when any arm is not deployed or the locking feedback is invalid, and to prevent the arm from retracting when the quadcopter system is not stopped.

2. The foldable cross-medium drone according to claim 1, characterized in that, The transmission rod includes: The extension rod, with its first end fixed to the annular slider; and The pull rod has one end hinged to the second end of the extension rod and the other end hinged to the root of the arm; The drone also includes a section located at the rear of the lower fuselage: The tail assembly includes a canard, horizontal tail, and vertical tail, all deflected by a waterproof servo; and The underwater propulsion assembly includes two tail propellers arranged side by side and with independent speed regulation.

3. A foldable cross-medium drone according to claim 1, characterized in that, Also includes: A pull-out equipment rack is inserted into a sealed compartment inside the rotary sealed main housing, and the pull-out equipment rack is divided along the axial direction into: The control layer, located near the center of gravity of the entire aircraft, is equipped with a low-voltage control module, including the flight control system. A power layer, located on one side of the control layer, is equipped with an ESC and a power distribution board; and The energy layer, located on the side away from the fairing, is equipped with battery modules to keep the center of gravity of the entire aircraft below the center of buoyancy. The sealed chamber is equipped with a water leakage detection module at its lower position, and the outer wall of the sealed chamber is equipped with a depth sensor interface that communicates with external water pressure.

4. A media-splitting control method for a foldable cross-media UAV, applied to a foldable cross-media UAV as described in any one of claims 1-3, characterized in that, include: In underwater cruising mode, the arms are kept retracted, and navigation control is performed by the tail thruster and tail fin assembly located at the rear of the lower section of the fuselage. When the drone receives the water exit command and approaches the water surface, it acquires depth and attitude parameters. When the depth and attitude parameters reach a preset threshold, it enters the water exit preparation state. The synchronous folding mechanism is controlled to unfold the arm, and after receiving a feedback signal that all parts are in place and locked continuously and effectively, the quadcopter system is controlled to pre-rotate. The quadcopter system is controlled to increase total thrust by using a thrust ramp to enter the water lift-off state, and after detecting a valid water-triggered dry-out signal, it switches to air control state. After the drone touches the water during the water entry mission, the quadcopter system is controlled to slow down and stop rotating, the synchronous folding mechanism is controlled to retract the arms, and the tail propeller is switched to take over.

5. The media-specific control method for a foldable cross-media UAV according to claim 4, characterized in that, In the water preparation state, when the external water depth is no greater than 0.30m, the buoyancy is no greater than 0.15m / s, the roll angle and pitch angle are both no greater than 8° and the angular velocity is no greater than 20° / s, the arm deployment action is allowed to be performed. During the arm's deployment process, if the deployment time exceeds a preset time threshold, or if the stepper motor current exceeds a preset ratio of the normal deployment current, the deployment action will stop and the system will enter a safety protection state.

6. The media-specific control method for a foldable cross-media UAV according to claim 4, characterized in that, The pre-rotor system's pre-rotation phase logic includes: controlling the target rotation speed of the rotor propeller to 10%-20% of the takeoff speed, and monitoring the current of the four rotor motors. When the current deviation is no greater than 15%, it is allowed to enter the water-lifting state. The logic for the water-lifting phase includes increasing the total thrust according to the slope ascent rate within a time interval of 0.8-1.5s.

7. The media-specific control method for a foldable cross-media UAV according to claim 4, characterized in that, The dual-redundancy logic for determining the water-triggered drying signal and the water-contact signal is as follows: Simultaneously acquire the output voltage of the water immersion contact and the absolute underwater depth; The water-contact state is determined only when the output voltage of the water immersion contact reaches the water immersion threshold and the output underwater absolute depth reaches the depth threshold and is maintained continuously for no less than 200ms. The water-triggered drying signal is considered valid only when the output voltage of the water immersion contact is lower than the reset threshold and the output underwater absolute depth returns to near zero depth and remains there for at least 200ms.

8. The media-specific control method for a foldable cross-media UAV according to claim 4, characterized in that, The navigation control in the underwater cruise state adopts a hierarchical cascaded PID architecture, including: The outer depth control layer uses the error between the desired depth and the measured depth as input to calculate the desired longitudinal velocity; The mid-level underwater velocity control layer uses the error between the desired longitudinal velocity and the measured longitudinal velocity as input to calculate a common reference thrust output to the tail thruster. The intermediate heading control layer uses the error between the desired heading angle and the measured heading angle as input to calculate the differential thrust output to the tail thruster; and The inner attitude damping layer, taking the comprehensive attitude error as input, calculates the tail fin deflection angle and outputs it to the tail fin assembly.

9. A media-specific control method for a foldable cross-media UAV according to claim 4, characterized in that, The flight control in the air control state adopts a three-layer cascade PID control architecture, including: The outer ring of the position is used to calculate the desired speed based on the error between the desired and actual positions. In the speed loop, based on the error between the desired and actual speeds, the desired roll angle, desired pitch angle, and total lift are calculated; and The attitude inner loop calculates the three-axis control torque based on the error between the desired attitude angle and the actual attitude angle, as well as the angular velocity error, and distributes the total lift to the four rotor motors via the quadcopter hybrid control of the quadcopter system.

10. A media-splitting control method for a foldable cross-media UAV according to claim 4, characterized in that, The media-based control method also includes abnormal interlocking logic: When it is detected that the arm is not locked or folding. When any of the following is triggered: timeout, abnormal rotor motor current, tail propeller failure, tail fin jamming, or water leakage, the system enters a safety protection state. When in the aforementioned safety protection state, based on the current medium properties of the UAV, the corresponding operation among prohibiting leaving the water, maintaining a fixed depth, controlled ascent, hovering in the air, or controlled landing is forcibly executed.

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