An in-out water control method of a longitudinal configuration cross-medium unmanned aerial vehicle based on a switching system

Abstract

The application belongs to the technical field of aircraft control, and particularly relates to a water-entry and exit control method for a longitudinal configuration cross-medium unmanned aerial vehicle based on a switching system, comprising the following steps: step 1) respectively establishing dynamic models of a water-air cross-medium unmanned aerial vehicle in different flight stages; step 2) designing a sliding mode controller for the unmanned aerial vehicle in different flight stages according to the dynamic models of the water-air cross-medium unmanned aerial vehicle; and step 3) using software to perform simulation experiments on the water-air cross-medium unmanned aerial vehicle repeatedly crossing the medium. The unmanned aerial vehicle in different flight stages is regarded as different systems, and a controller is designed separately to control. Through the simulation experiments, it is shown that the control method can effectively control the position and attitude stability of the unmanned aerial vehicle in the water-entry and exit process, and can well cope with external environmental disturbances, and has good robustness.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft control, and in particular relates to a method for controlling entry and exit of a tandem-configured cross-medium UAV into and out of water based on a switching system. Background Art

[0002] While research on unmanned aerial vehicles (UAVs) has seen significant progress in both structural design and control technology, their operational scope is limited to a single medium. Research on amphibious underwater vehicles (HAUVs) is still in its infancy. HAUVs offer the advantages of unmanned aerial vehicles (UAVs), such as rapid deployment and high maneuverability, combined with the rapid cruising capabilities of unmanned surface vessels (USVs) and the high concealment of unmanned underwater vehicles (UUVs). Therefore, they hold broad application prospects in both military and civilian fields. As a new type of aircraft, HAUVs have airborne, underwater, and medium-crossing phases. Their dynamic characteristics differ significantly from those of traditional single-medium aircraft, making it challenging to simultaneously operate in both air and water environments. HAUVs can be categorized as biomimetic, fixed-wing or multirotor, and multimodal. The tandem twin-rotor water-air cross-medium UAV targeted by this invention is a completely new type of multimodal cross-medium UAV. Its design and actuator configuration differ significantly from existing water-air cross-medium UAVs. It possesses functions such as hovering, vertical takeoff and landing, and rapid maneuvering. It also boasts high aerodynamic efficiency, low hovering power requirements, and a wide range of center-of-gravity movement. Currently, no research has been conducted on methods for controlling entry and exit from the water for this type of aircraft. Regarding control, since this tandem water-air cross-medium UAV utilizes two different actuators in the air and underwater, and is underactuated during airborne flight, the same controller cannot be used to control both phases of flight. Summary of the Invention

[0003] The present invention aims to provide a method for controlling the entry and exit of a tandem-configured cross-medium UAV in water based on a switching system, so as to solve the technical problem that a tandem twin-rotor cross-medium UAV cannot be operated by the same controller in different flight phases.

[0004] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0005] In some embodiments of the present application, a method for controlling entry and exit of a tandem-configured cross-medium UAV based on a switching system is provided, comprising the following steps:

[0006] Step 1) establishing dynamic models of the tandem-configured water-air cross-medium UAV at different flight stages;

[0007] Step 2) Based on the dynamic model of the water-air cross-medium UAV, a sliding membrane controller is designed for the UAV in different flight phases;

[0008] Step 3) Use software to conduct a simulation experiment of the water-air cross-medium drone repeatedly crossing the medium.

[0009] In some embodiments of the present application, step 1 includes:

[0010] Step 1.1) Build the kinematic model of the drone:

[0011]

[0012]

[0013] Where ξ1 = [xyz] T , Respectively represent the position and direction of the UAV relative to the inertial coordinate system, V = [uvw] T ,W=[pqr] T They represent the components of the linear velocity and angular velocity of the UAV in the inertial coordinate system in the body coordinate system;

[0014] in, is the rotation matrix from the body coordinate system to the ground coordinate system, and T is the conversion matrix from the angular velocity to the Euler angular velocity in the body coordinate system. The specific expression is as follows:

[0015]

[0016]

[0017] Where c*, s* represent cos*, sin* respectively;

[0018] Step 1.2) Based on the system parameter matrix, a dynamic model of the cross-medium UAV in the air and underwater flight states is constructed;

[0019]

[0020] In the formula, η=[ξ1 T ξ2 T ] T ,v=[V T W T ] T , is the inertia matrix including the additional underwater mass, is the centripetal force matrix caused by the drone and the additional mass, is the hydraulic and torque damping matrix caused by the first-order and second-order velocities, where v ris the speed of the UAV relative to the water flow, and its expression is:

[0021]

[0022] v w is the water flow velocity, are the restoring forces and moments due to gravity and buoyancy, The thrust and torque matrix provided to the propulsion device, is the interference matrix caused by model uncertainty and external disturbances.

[0023] In some embodiments of the present application, designing a sliding membrane controller includes:

[0024] Step 2.1) Design the underwater sliding mold controller:

[0025] Define the sliding surface s as

[0026]

[0027] In the formula is the sliding surface coefficient, is the error between the actual position and attitude of the cross-medium UAV and the expected value, is the error between the actual velocity, angular velocity and the expected value;

[0028] in,

[0029]

[0030] Taking the derivative of (7), we get the reaching law :

[0031]

[0032] For the underwater sliding mode controller, we get:

[0033]

[0034] Where u is the controller output signal, which can be obtained by inverse solution through the reaching law;

[0035] Step 2.2) Design the air slide controller:

[0036] The translational dynamic equation in the z direction is:

[0037]

[0038] Design virtual input u z ,

[0039]

[0040] get,

[0041]

[0042] u1 is the control force of the z axis, and u2, u3, and u4 are the control torques of the x, y, and z axes respectively. Since this cross-medium UAV is an underactuated system in the air cruise phase, it is not easy to control the translation of the x, y, and z directions using only u1. Therefore, a virtual control variable u is introduced in the x and y directions. x ,u y , the translational dynamic equations of x and y are as follows:

[0043]

[0044] Let the virtual control quantity u x 、u y for

[0045]

[0046] At this time, feedback linearization can also be done in the x and y directions. On the basis that u1 is determined by z, u is designed. x ,u y Make x,y achieve the control target; according to the cross-medium UAV to achieve air trajectory tracking, give a fixed reference trajectory (x d ,y d ,z d ,ψ d ), at this time, the expected roll angle and pitch angle φ of the corresponding trajectory tracking are solved by the inverse solution module d ,θ d ,Right now

[0047] φ d =arcsin(u x sinψ d -u y cosψ d )(twenty two);

[0048]

[0049] In order to realize trajectory tracking, the controller is designed according to the given reference trajectory, and sliding mode control is adopted in the three directions of x, y, and z. From equations (10) and (15), we can get

[0050]

[0051] Substituting equation (24) into equations (17) and (20) yields u1, ux, and uy.

[0052]

[0053] by u x ,u y Inversely solve the desired roll angle and pitch angle φ d ,θ d ;

[0054] Among them, the three Euler angles are also controlled by sliding mode controller.

[0055]

[0056] In formula (24-26), λ and ε are the sliding surface coefficient and reaching law coefficient respectively, and the subscript 1 represents the air controller parameter;

[0057] Step 2.3) Switching rule design

[0058] The cross-medium UAV is regarded as a point mass, and the height position z of the UAV is used as the switching variable. When z < 0, the UAV is regarded as being in the underwater diving stage, and the underwater sliding mode controller and UUV dynamic model are adopted; when z ≥ 0, the UAV is regarded as being in the air cruising stage, and the air sliding mode controller and UAV dynamic model are adopted.

[0059] In some embodiments of the present application, the convergence law is

[0060]

[0061]

[0062] In the formula is the reaching law coefficient, subscript 2 indicates the underwater controller parameter;

[0063] In the actual control process, the use of sgn function will cause the controller output to change suddenly, which will cause oscillation. The hyperbolic tangent function is used to replace the sgn function.

[0064]

[0065] By changing the coefficient κ, tanh is made to fit the sgn function. The smaller the coefficient κ, the steeper the curve, and the closer tanh is to the sgn function.

[0066] So the reaching law becomes

[0067]

[0068] Combining equations (11) and (15), the expression of the underwater controller output u is:

[0069]

[0070] Compared with existing technologies, this invention offers the advantage of addressing the water entry and exit control issues of a tandem twin-rotor water-to-air cross-medium UAV, which faces multiple systems and uncertain external interference. By treating each UAV in different flight phases as a distinct system and designing separate controllers to control each system, the invention demonstrates that this control method effectively stabilizes the UAV's position and attitude during water entry and exit, effectively responding to external environmental interference (such as water flow disturbances and crosswind interference), and exhibiting excellent robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0072] Figure 1 A schematic diagram of a tandem-configured water-air cross-medium UAV provided in an embodiment of the present invention;

[0073] Figure 2 A schematic diagram of the overall control block of the water-air cross-medium UAV provided in an embodiment of the present invention;

[0074] Figure 3 A schematic diagram of a sliding mode control block provided in an embodiment of the present invention;

[0075] Figure 4 Schematic diagram of the inner and outer ring control blocks of the water-air cross-medium UAV provided in an embodiment of the present invention;

[0076] Figure 5 A schematic diagram of a position tracking curve for a water-air cross-medium UAV provided in an embodiment of the present invention;

[0077] Figure 6 A schematic diagram of a height error curve provided by an embodiment of the present invention;

[0078] Figure 7 A schematic diagram of a roll angle curve of a cross-medium UAV provided by an embodiment of the present invention;

[0079] Figure 8 A schematic diagram of a pitch angle curve of a cross-medium drone provided by an embodiment of the present invention;

[0080] Figure 9 A schematic diagram of a yaw angle curve of a cross-medium drone provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0081] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0082] In order to better understand the purpose, structure and function of the present application, the present application is further described in detail below in combination with the drawings.

[0083] Referring to the drawings Figure 1-9 According to some embodiments of the present application, the following steps are included:

[0084] Step 1) respectively establish the dynamic model of the water-air cross-medium unmanned aerial vehicle in different flight stages in the longitudinal configuration;

[0085] Step 2) design the sliding mode controller of the unmanned aerial vehicle in different flight stages for the dynamic model of the water-air cross-medium unmanned aerial vehicle;

[0086] Step 3) use software to simulate the repeated cross-medium simulation experiment of the water-air cross-medium unmanned aerial vehicle.

[0087] In the present application, the sliding mode controller, switching rule, actuator and dynamic model of the longitudinal configuration cross-medium unmanned aerial vehicle are composed, the error signal is obtained by subtracting the actual position and posture of the unmanned aerial vehicle from the expected position and posture, and the height signal of the unmanned aerial vehicle is transmitted to the switching rule module to determine the direction of error signal transmission. The error signal is given to the sliding mode controller to obtain the control signal, the control signal enters the distribution module, the distribution module obtains the rotor speed and rudder angle signal to the actuator to obtain the control force and control moment, and finally input to the dynamic model of the cross-medium unmanned aerial vehicle to calculate the position and attitude of the unmanned aerial vehicle.

[0088] Specific implementation steps are as follows.

[0089] Step 1) establish the dynamic model of the water-air cross-medium unmanned aerial vehicle in the longitudinal configuration

[0090] The object of the present application is shown in Figure 1 The kinematic model of the unmanned aerial vehicle is:

[0091]

[0092]

[0093] In the formula respectively represent the position and direction of the unmanned aerial vehicle relative to the inertial coordinate system, V = [u v w] T , W = [p q r] T respectively represent the linear velocity and angular velocity of the unmanned aerial vehicle in the body coordinate system. is the rotation matrix from the body coordinate to the ground coordinate, T is the conversion matrix of the angular velocity in the body coordinate to the Euler angle velocity, and their specific expressions are as follows:

[0094]

[0095]

[0096] Where c*, s* represent cos*, sin* respectively;

[0097] The configuration, propulsion system, and force conditions of a cross-medium UAV differ in different flight phases (cruising in the air and diving underwater), and their dynamic models are also different. When flying in the air, the cross-medium UAV can be regarded as a helicopter with a tandem twin-rotor configuration, whose position and attitude are controlled by two rotors and two servos, making it an underactuated system. When diving underwater, it can be regarded as an unmanned underwater vehicle, whose position and attitude are controlled by five underwater thrusters and a tail rudder. For ease of writing and analysis, the dynamic models of the cross-medium UAV in both flight states are now written in the following unified form:

[0098]

[0099] In the formula v=[V T W T ] T , is the inertia matrix including the additional underwater mass, is the Coriolis centripetal force (torque) matrix caused by the UAV and the additional mass, is the hydraulic and torque damping matrix caused by the first-order and second-order velocities, where v r is the speed of the UAV relative to the water flow, and its expression is:

[0100]

[0101] v w is the water flow velocity, are the restoring forces and moments due to gravity and buoyancy, The thrust and torque matrix provided to the propulsion device, is the interference matrix caused by model uncertainty and external disturbances.

[0102] For the dynamic model (5), when i=1, the UAV is in the air flight stage; when i=2, the UAV is in the underwater diving stage; when in different flight stages, C i (v),D i (v r ),g i (η), The matrices are not the same. The specific system parameter matrix is:

[0103] 1) Air system parameter matrix

[0104]

[0105] Where m is the mass of the UAV, I xx ,I yy ,I zz For drones about x B ,y B ,z B The moment of inertia of the three axes.

[0106]

[0107]

[0108] S2=O 3×3 (A4)

[0109]

[0110] D 1 (v r )=O 6×6 (A6)

[0111]

[0112]

[0113] Where, η f ,η r are the tilt angles of the front and rear rotors of the UAV, Ω f ,Ω r are the rotation speeds of the front and rear rotors of the UAV, c T is the lift coefficient of the rotor.

[0114]

[0115] Where, are the disturbance force and disturbance torque respectively.

[0116] 2) Underwater system parameter matrix

[0117]

[0118] In the above formula, the expression of the additional mass (moment of inertia) coefficient is as follows.

[0119] Added mass / moment of inertia expression

[0120]

[0121] Among them, B is the width of the body, H is the height of the body, L is the length of the body, and K is the corresponding additional mass of the ellipsoid, which can be obtained by looking up the table.

[0122]

[0123]

[0124]

[0125]

[0126]

[0127] Where, X u ,X u|u| They represent the linear and quadratic hydrodynamic viscosity coefficients in the x direction, Y v ,Y v|v| They represent the linear and quadratic hydrodynamic viscosity coefficients in the y direction, Z w ,Z w|w| are the linear and quadratic hydrodynamic viscosity coefficients in the z direction, M q ,M w Represents the viscosity coefficient of the first-order hydrodynamic moment on the y-axis, M w|w| represents the viscosity coefficient of the quadratic hydrodynamic moment, N r ,N v The viscosity coefficient of the first-order hydrodynamic moment about the z-axis, N v|v| represents the viscosity coefficient of the quadratic hydrodynamic moment.

[0128]

[0129] Where, F B is the buoyancy of the drone in water.

[0130]

[0131] B i =[d i r i ×d i ] T (A18);

[0132] In the formula, the action points of each thruster are

[0133] The thrust direction vectors of each thruster are d1=d2=[0 0 -1] T ,d3=[cosδ e sinδ e 0] T ,d4=d5=[0 0 1] T, the control force and control moment generated directly by the propeller are:

[0134]

[0135]

[0136] where, are the disturbance force and disturbance moment, respectively.

[0137] In addition, in order to simplify the dynamics model of the UAV, the following assumptions are considered:

[0138] Assumption 1: The UAV is inertia and hydrodynamic symmetric in the (x B , y B , z B ) plane.

[0139] Assumption 2: The origin O B of the body coordinate system is also the center of gravity of the UAV, and the center of buoyancy z b is located above the center of gravity in the z B axis.

[0140] Assumption 3: When the trans-media UAV is located underwater, the roll angular velocity is 0, which means

[0141] Assumption 4: Because the inertia product of the UAV is much smaller than the main diagonal elements of the inertia matrix, it can be ignored.

[0142] Step 2) Controller design

[0143] According to the trans-media UAV dynamics model established above and the control requirements, the sliding mode control method with strong robustness is selected, which can overcome system uncertainties and external disturbances. The control purpose to be achieved is to make the UAV realize trajectory tracking from underwater z = -1 m to vertical take-off in the air z = 1 m at a speed of 0.1 m / s, hover for a period of time, and then return to the original point at the same speed, while keeping the attitude of the trans-media UAV stable (i.e., the attitude angles θ, ψ → 0). Next, the controller design and switching rules will be introduced in detail, and the control block diagram of the entire control system is shown in Figure 2 .

[0144] Step 2.1) Design of underwater sliding mode controller

[0145] Define the sliding surface s as

[0146] where is the sliding surface coefficient, which is a positive definite matrix, is the error quantity of the actual position and attitude of the trans-media UAV and the expected value. is the error between the actual velocity and angular velocity and the expected value.

[0147]

[0148]

[0149] Taking the derivative of (7), we get the reaching law

[0150] For underwater sliding mold controller, there are also,

[0151] Where u is the controller output signal, and u can be obtained by selecting a suitable reaching law. In this application, the reaching law is selected as

[0152]

[0153] In the formula is the reaching law coefficient, and the subscript 2 represents the underwater controller parameter.

[0154] In the actual control process, the use of the sgn function will cause the controller output to change suddenly, which will cause oscillation and have a great impact on the control effect. In order to reduce this effect, the hyperbolic tangent function is used to replace the sgn function.

[0155]

[0156] By changing the coefficient κ, tanh can be made to fit the sgn function more closely. The smaller the coefficient κ, the steeper the curve, and the closer tanh is to the sgn function.

[0157] So the reaching law becomes,

[0158] Combining equations (11) and (15), the expression of the underwater controller output u is:

[0159]

[0160] The control block diagram of the sliding mode controller is as follows: Figure 3 shown.

[0161] Step 2.2) Design of air sliding mode controller

[0162] Because the movement of cross-media drones in the air is strongly coupled, the control system is usually designed based on the idea of ​​layered design of inner and outer loops. Among the six state quantities of cross-media drones, the x and y position states are not directly related to the control input. The control input directly acts on the attitude channel, but the change of x and y positions depends on the change of attitude. The attitude quantity can be used as an actuator to achieve the desired state of the position quantity. In terms of structure, the position can be used as the outer loop and the attitude as the inner loop. The inner and outer loop control structure is as follows: Figure 4 shown.

[0163] Figure 4 Where u1 is the control force of the z-axis, which is obtained through feedback linearization.

[0164] The translational dynamic equation in the z direction is:

[0165] Design virtual input u z ,

[0166] So we can get,

[0167] u2, u3, and u4 are the control torques on the x, y, and z axes respectively.

[0168] Since the cross-medium UAV is an underactuated system in the air cruise phase, it is not easy to control the x, y, and z directions with only the control quantity u1. Therefore, a virtual control quantity u is introduced in the x and y directions. x ,u y .

[0169]

[0170] Let the virtual control quantity u x 、u y for

[0171]

[0172] At this time, feedback linearization can also be performed in the x and y directions. Based on the determination of u1 by z, design u x ,u y In general, cross-medium UAVs can realize aerial trajectory tracking by giving a reference trajectory (x d ,y d ,z d ,ψ d At this time, the inverse solution module is used to solve the desired roll angle and pitch angle φ to achieve the corresponding trajectory tracking. d ,θ d ,Right now

[0173] φd =arcsin(u x sinψ d -u y cosψ d ) (twenty two);

[0174]

[0175] In order to realize trajectory tracking, a reference trajectory can be given to design a controller, and sliding mode control is adopted in the three directions of x, y, and z. From equations (10) and (15), we can get

[0176]

[0177] Substituting equation (24) into equations (17) and (20) yields u1, ux, and uy.

[0178]

[0179] by u x ,u y Inversely solve the desired roll angle and pitch angle φ d ,θ d ,The three Euler angles are also controlled using sliding mode controller.

[0180]

[0181] In formula (24-26), λ and ε are the sliding surface coefficient and reaching law coefficient respectively, and the subscript 1 represents the air controller parameter.

[0182] Step 2.3) Switching rule design

[0183] The cross-medium UAV is regarded as a point mass, and the height position z of the UAV is used as the switching variable. When z < 0, the UAV is regarded as being in the underwater diving stage, and the underwater sliding mode controller and UUV dynamic model are adopted; when z ≥ 0, the UAV is regarded as being in the air cruising stage, and the air sliding mode controller and UAV dynamic model are adopted.

[0184] Step 3) System simulation experiment and analysis

[0185] Using Matlab / Simulink software, we simulated a water-to-air cross-medium drone repeatedly crossing a medium. The drone took off vertically from underwater at a speed of 0.1 m / s to a certain altitude in the air, hovered for 10 seconds, and then plummeted back into the water at the same speed. The initial altitude was z = -1 m underwater, the desired altitude was z = 1 m in the air, and it finally returned to its origin at z = -1 m.

[0186] Considering that drones are subject to external interference during flight (such as water flow disturbances and crosswind disturbances), we applied random noise disturbances while the drone was underwater and a crosswind disturbance at t = 20 seconds (when the cross-medium drone was hovering in the air). This is more consistent with actual flight conditions. The calculation of crosswind is related to the wind force level and wind direction angle α. Each wind force level has a corresponding wind pressure. The specific calculation method is as follows.

[0187] F di =PA i cosσ i ,(i=x,y,z)(27)

[0188] Where, F di is wind disturbance force, P is wind pressure, A i is the frontal area, cosσ i It is related to the wind direction angle and the drone's own attitude.

[0189] Let the unit vector of the wind direction angle be Q and the normal vector of the body coordinate system be B x ,B y ,B z

[0190] Q=[0-sinα-cosα] T (28)

[0191]

[0192]

[0193] In order to verify the effectiveness and robustness of the control method proposed in this application, we selected

[0194] The most significant impact on the cross-media drone is crosswinds perpendicular to the side of the fuselage, i.e., α = 90. Repeated experimental testing has shown that the cross-media drone can withstand winds up to force 6, corresponding to a wind pressure of approximately 119 Pa.

[0195] The simulation results are as follows Figure 5-9 shown. Figure 5 Middle z d is the desired altitude. As can be seen in the figure, the drone tracks the desired trajectory well. During both the water-to-air and air-to-water crossings, the drone maintains stable tracking with no significant positional deviation. Furthermore, at t = 20 seconds, the y position shifted by 0.4 meters. This was due to a 1-second-long crosswind disturbance while crossing the medium. However, the drone was able to stabilize its y position within 3 seconds, while its x and z positions remained largely unaffected. Figure 6 The height error curve shows that the maximum height error does not exceed 0.1m, which also indicates that the cross-medium drone tracks the expected height well.

[0196] Figure 7 This is the roll angle curve of the cross-medium UAV. The roll angle changes significantly at t=10s and t=20s. The former is because the cross-medium UAV is in the water-to-air crossing stage, and the latter is because the UAV is disturbed by crosswind. However, the roll angle can return to stability in a very short time and remain near 0. Figure 8 , Figure 9 They are the pitch angle curve and the yaw angle curve, respectively. Figure 8-9 It can be seen that the pitch angle and yaw angle can be basically maintained near 0 during the entire process of cross-medium drone flight. Figure 7-9 It shows that the cross-medium UAV can cope well with the influence of random water flow interference and crosswind interference force under the control of the sliding mode control algorithm based on the switching system proposed in this application, ensuring the stability of the UAV posture.

[0197] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0198] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0199] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0200] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0201] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling entry and exit of a tandem-configured cross-medium UAV based on a switching system, characterized in that: The following steps are involved: Step 1) establishing dynamic models of the tandem-configured water-air cross-medium UAV at different flight stages; Step 2) Designing a sliding mode controller for the UAV in different flight phases based on the dynamic model of the UAV. The design of the sliding mode controller includes: Step 2.1) Design the underwater sliding mold controller: Define the sliding surface s as In the formula is the sliding surface coefficient, is the error between the actual position and attitude of the cross-medium UAV and the expected value, is the error between the actual velocity, angular velocity and the expected value; in, Taking the derivative of (7), we get the reaching law For the underwater sliding mode controller, we get: Where u is the controller output signal, which can be obtained by inverse solution through the reaching law; Step 2.2) Design the air sliding mode controller: The translational dynamic equation in the z direction is: Where m is the mass of the drone and g is the acceleration due to gravity; Design virtual input u z , get, u1 is the control force of the z-axis, u2, u3, and u4 are the control torques of the x-, y-, and z-axes respectively; Introduce virtual control quantity u in the x and y directions x ,u y , Let u x = cosψsinθcosφ + sinφsinψ(20); Let u y = sinψsinθcosφ - sinφcosψ (21); At this time, feedback linearization can also be done in the x and y directions. On the basis that u1 is determined by z, u is designed. x ,u y Make x,y achieve the control target; according to the cross-medium UAV to achieve air trajectory tracking, give a fixed reference trajectory (x d ,y d ,z d ,ψ d ), at this time, the expected roll angle and pitch angle φ of the corresponding trajectory tracking are solved by the inverse solution module d ,θ d ,Right now f d =arcsin(u x sinψ d -u y cosψ d (22); In order to realize trajectory tracking, a controller is designed based on a given reference trajectory, and sliding mode control is adopted in the three directions of x, y, and z. k is the gain coefficient of the sliding mode controller; byu x ,u y Inversely solve the desired roll angle and pitch angle φ d ,θ d ; Among them, the three Euler angles are also controlled by sliding mode controller. In formula (24-27), λ and ε are the sliding surface coefficient and reaching law coefficient respectively, and the subscript 1 represents the air controller parameter; Step 2.3) Switching rule design The cross-medium UAV is regarded as a mass point, and the height position z of the UAV is used as the switching variable. When z < 0, the UAV is regarded as being in the underwater diving stage, and the underwater sliding mode controller and UUV dynamics model are adopted; when z ≥ 0, the UAV is regarded as being in the air cruising stage, and the air sliding mode controller and UAV dynamics model are adopted. Step 3) Use software to conduct a simulation experiment of the water-air cross-medium drone repeatedly crossing the medium.

2. The method for controlling entry and exit of a tandem-type cross-medium UAV based on a switching system according to claim 1, characterized in that: The step 1 includes: Step 1.1) Build the kinematic model of the drone: In the formula Represent the position and direction of the UAV relative to the inertial coordinate system, respectively, where is the roll angle, θ is the pitch angle, ψ is the yaw angle, V=[uvw] T ,W=[pqr] T Respectively represent the components of the linear velocity and angular velocity of the drone in the inertial coordinate system in the body coordinate system, where u represents the linear velocity component along the x-axis of the body, v represents the linear velocity component along the y-axis of the body, and w represents the linear velocity component along the z-axis of the body; p represents the angular velocity of the body rotating around the x-axis, q represents the angular velocity of the body rotating around the y-axis, and r represents the angular velocity of the body rotating around the z-axis; in, is the rotation matrix from the body coordinate system to the ground coordinate system, and T is the conversion matrix from the angular velocity to the Euler angular velocity in the body coordinate system. The specific expression is as follows: Where c*, s* represent cos*, sin* respectively; Step 1.2) Based on the system parameter matrix, a dynamic model of the cross-medium UAV in the air and underwater flight states is constructed; In the formula v=[V T W T ] T , is the inertia matrix including the additional underwater mass, is the centripetal force matrix caused by the drone and the additional mass, is the hydraulic and torque damping matrix caused by the first-order and second-order velocities, where v r is the speed of the UAV relative to the water flow, and its expression is: For the kinetic model (5), When i=1, the UAV is in the air flight phase; When i=2, the UAV is in the underwater diving stage; v w is the water flow velocity, are the restoring forces and moments due to gravity and buoyancy, The thrust and torque matrix provided to the propulsion device, is the interference matrix caused by model uncertainty and external disturbances.

3. The method for controlling entry and exit of a tandem-type cross-medium UAV based on a switching system according to claim 1, characterized in that: The reaching law is In the formula is the reaching law coefficient, subscript 2 indicates the underwater controller parameter; In the actual control process, the use of sgn function will cause the controller output to change suddenly, which will cause oscillation. The hyperbolic tangent function is used to replace the sgn function. By changing the coefficient κ, tanh is made to fit the sgn function. The smaller the coefficient κ, the steeper the curve, and the closer tanh is to the sgn function. So the reaching law becomes Combining equations (11) and (15), the expression of the underwater controller output u is:

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