Underwater robot attitude control method and system for adjusting buoyancy center and umbilical cable

Abstract

The invention provides an underwater robot attitude control method and system for adjusting a buoyancy center and an umbilical cable. The method comprises the following steps: S1, constructing a hydrodynamic mathematical model and a control model of a remote control underwater robot system with a cable; the hydrodynamic mathematical model comprises a first mathematical model used for simulating the dynamic response caused by the underwater robot main body in the operation movement process and a second mathematical model used for simulating the dynamic effect of the umbilical cable on the underwater robot main body. The control model comprises a first control module used for controlling the given length of the umbilical cable and a second control module used for controlling the rotating speed of the ducted propeller. S2, constructing a hydrodynamic force and control model; and S3, establishing a time domain calculation numerical solution module, and performing numerical simulation and result output in the module. According to the invention, attitude control of the underwater robot can be realized by utilizing a combined control mode of retracting and releasing the umbilical cable and adjusting the buoyancy center, the attitude control is rapid and effective, and the response speed, the control precision and the stability of the attitude control are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater robot attitude control, and particularly relates to an underwater robot attitude control method and system for adjusting the center of buoyancy and umbilical cable. Background Art

[0002] In the application of underwater robots, attitude control is a key technology to ensure their stable operation and task completion. At present, in the prior art, the attitude adjustment of underwater robots is generally achieved through buoyancy adjustment devices such as buoyancy sliders. This method has obvious deficiencies:

[0003] When solely relying on the buoyancy adjustment device to adjust the attitude, the adjustment speed is slow, the dynamic response is poor, it is difficult to achieve rapid attitude correction, and the collaborative influence of the umbilical cable on the underwater robot attitude is not considered, resulting in low attitude correction efficiency and limited control effect. In addition, most of the prior art does not have specific control algorithms, resulting in the accuracy and response speed of attitude control being unable to meet actual requirements. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an underwater robot attitude control method and system for adjusting the center of buoyancy and umbilical cable. By jointly controlling the umbilical cable retraction and the position of the center of buoyancy, and combining with a control algorithm, rapid and precise attitude control of the underwater robot is achieved, and the problems existing when solely relying on the buoyancy adjustment device to adjust the attitude are solved.

[0005] In order to solve the above technical problems, the technical solution used in the present invention is:

[0006] An underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable according to the present invention includes the following steps:

[0007] S1. Construct a hydrodynamic mathematical model and a control model of the tethered remotely operated underwater vehicle system;

[0008] The tethered remotely operated underwater vehicle system includes the underwater robot main body, a center of buoyancy adjustment device for adjusting the center of buoyancy position of the underwater robot main body, an umbilical cable connected to the underwater robot main body, and a ducted propeller for providing propulsion force;

[0009] The hydrodynamic mathematical model includes a first mathematical model and a second mathematical model. The first mathematical model is used to simulate the dynamic response caused by the underwater robot main body during the maneuvering motion, and the second mathematical model is used to simulate the dynamic effect of the umbilical cable on the underwater robot main body;

[0010] The control model includes a first control module and a second control module. The first control module is used to control the given length L of the umbilical cable K, the second control module is used to control the rotation speed R of the ducted propeller K , and both the first control module and the second control module use the difference between the actual trim angle and the preset trim angle of the underwater robot body as the calculation input quantity;

[0011] S2. Add the control model to the hydrodynamic mathematical model to construct a hydrodynamic and control model;

[0012] S3. According to the hydrodynamic and control model, establish a time-domain calculation numerical solution module, and numerically simulate the hydrodynamic and control characteristics of the tethered remotely operated underwater vehicle system under the action of the control mechanism including the umbilical cable and the ducted propeller in the numerical solution module, and output the simulation results.

[0013] Preferably, the first mathematical model is the six-degree-of-freedom motion equation of a submarine, which is expressed in the local coordinate system of the underwater robot body as:

[0014]

[0015] The left-hand terms of equations (1-1) to (1-6) are the inertial forces and moments of the underwater robot body, and the right-hand terms are the external forces and external torques acting on the underwater robot body, and their symbols are marked according to the international standard method;

[0016] The external force acting on the underwater robot body is F0 = (X, Y, Z) T and the external torque is M0 = (K, M, N) T .

[0017] Further preferably, it is assumed that the external force F0 and the external torque M0 are composed of components such as hydrostatic restoring force, umbilical cable tension, hydrodynamic force acting on the underwater robot body due to ocean current and the underwater robot's own underwater movement, thrust of the ducted propeller being controlled and its corresponding torque, etc., so there are:

[0018] F0 = F W + F T + F H + F TH (1-7)

[0019] M0 = M W + M T + M H + M TH (1-8)

[0020] In equations (1-7) and (1-8), the subscript W represents the hydrostatic restoring force, T represents the umbilical cable tension, H represents the hydrodynamic force acting on the underwater robot body including the ocean current factor, and TH represents the thrust of the ducted propeller.

[0021] Preferably, the second mathematical model is a catenary equation, and the catenary equation is a quasi-steady elastic umbilical cable equation.

[0022] More preferably, the catenary equation is expressed as:

[0023]

[0024] In the formula, m0 is the mass per unit length of the umbilical cable, k is the stiffness of the umbilical cable, L r is the slack length of the umbilical cable, α and β are integral constants related to the positions of both ends of the umbilical cable and the total mass of the umbilical cable, and the curve parameter λ is related to the tangential angle at the point on the umbilical cable:

[0025]

[0026] P1 is the upper end point of the umbilical cable defined in the moving coordinate system of the mother ship, and P2 is the lower end point of the umbilical cable defined in the moving coordinate system of the underwater robot. That is, the two ends of the umbilical cable are P1 point and P2 point respectively. Then, when there is no relative movement between the mother ship and the underwater robot, the acting forces at the two end points P1 and P2 of the umbilical cable are:

[0027] F 1，x = c, F 1，y = csinh(λ1) (1-24)

[0028] F 2，x = -c, F 2，y = -csinh(λ2) (1-25)

[0029] In equations (1-24) and (1-25), F 1，x 、F 1，y are the forces at the upper end point of the umbilical cable, and F 2，x 、F 2，y are the tensions acting on the underwater robot body at the lower end point of the umbilical cable. The resultant force T of the tensions at the lower end point of the umbilical cable is:

[0030]

[0031] The resultant force T of the tension in equation (1-26) is a value in the local coordinate system of the umbilical cable.

[0032] Preferably, the buoyancy center adjustment device includes a floating block that can move longitudinally. The distance L b from the buoyancy center F of the floating block to the center of gravity of the underwater robotB0 The control expression is:

[0033] L b = L B0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 27)

[0034] Wherein, L b is the distance from the center of the floating block to the center of gravity of the underwater robot, L B0 is the initial distance from the center F of the floating block b to the center of gravity of the underwater robot, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ae(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

[0035] Further preferably, the control expression of the first control module is:

[0036] L K = L0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 28)

[0037] Wherein, L K is the length of the umbilical cable, L0 is the initial length of the umbilical cable, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ze(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

[0038] Further preferably, the control expression of the second control module is:

[0039] R K = R0 + K P [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)](1 - 29)

[0040] Wherein, R KLet \(n\) be the rotational speed of the ducted propeller during each adjustment, \(R_0\) be the initial rotational speed of the ducted propeller, \(Ae(n)\) be the difference between the actual trim angle and the preset trim angle at the \(n\)th step, \(Ae(n - 1)\) be the difference between the actual trim angle and the preset trim angle at the \((n - 1)\)th step, and \(Ae(n - 2)\) be the difference between the actual trim angle and the preset trim angle at the \((n - 2)\)th step.

[0041] Preferably, the algorithm adopted by the control model is an incremental PID control algorithm, or a sliding mode control algorithm, or a neural network control algorithm, or a fuzzy logic control algorithm;

[0042] And / or, the numerical solution module includes a main program sub-module, a CFD sub-module, and a control sub-module;

[0043] The calculation steps of the numerical solution module are as follows:

[0044] (1) Input the geometric and physical parameters of the cable-controlled underwater robot system;

[0045] (2) The main program sub-module calculates the steady-state stable solution of the cable-controlled underwater robot system;

[0046] (3) Introduce the motion speed of the workboat at the \((n + 1)\)th time step;

[0047] (4) Use the main program sub-module to calculate the dynamic parameters of the cable-controlled underwater robot system at the \((n + 1)\)th time step;

[0048] (5) If the numerical simulation is not completed, let \(n=n + 1\) and go to step 6; otherwise, the numerical simulation ends and all calculation results are output;

[0049] (6) The main program sub-module outputs the motion parameters of the underwater robot required for the CFD sub-module to calculate at the \(n\)th

[0050] time step;

[0051] (7) Introduce the control action on the underwater robot at the \(n\)th time step;

[0052] (8) According to the motion parameters and the control action of the underwater robot in steps (6) and (7), use the CFD sub-module to calculate the hydrodynamic load acting on the underwater robot at the \(n\)th time step and the control force of the control mechanism Interpolate the values at the \(n\)th and \((n - 1)\)th time steps to obtain the and values at the next time step, which are the dynamic parameters required for the calculation in step (4) using the main program sub-module;

[0053] Proceed to step (3).

[0054] Another object of the present invention is to provide an underwater robot attitude control system for adjusting the center of buoyancy and umbilical cable, comprising a center of buoyancy adjusting device, an umbilical cable retracting and releasing device, a controller and an underwater robot main body;

[0055] The controller is electrically connected to the center of buoyancy adjusting device and the umbilical cable retracting and releasing device, and the controller stores a program of the aforementioned underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable;

[0056] The center of buoyancy adjusting device includes a floating block that can move longitudinally, a bearing, a servo motor and a screw rod. The floating block is sleeved on the screw rod and is threadedly connected to the screw rod. Both ends of the screw rod are respectively rotationally connected to the bearing and the servo motor. The servo motor drives the screw rod to rotate to drive the floating block to move along the screw rod so as to adjust the center of buoyancy position of the underwater robot main body;

[0057] The umbilical cable retracting and releasing device is used to adjust the length of the umbilical cable according to the first control instruction of the controller;

[0058] A ducted propeller is arranged at the stern of the underwater robot main body, and the ducted propeller can adjust the rotation speed of the ducted propeller according to the second control instruction of the controller.

[0059] The beneficial effects of the underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable according to the present invention compared with the prior art are mainly reflected in:

[0060] By constructing a hydrodynamic mathematical model and a control model and performing numerical simulation in the numerical solution module, the present invention can use the combined manipulation method of umbilical cable retracting and releasing and center of buoyancy adjustment to realize the attitude control of the underwater robot, can quickly and effectively realize the attitude control of the underwater robot, significantly improves the response speed, control accuracy and stability of the attitude control, solves the problems of slow adjustment speed and limited control effect of the traditional single adjustment method, and compared with the prior art, this method can not only maintain a specified trim angle, but also realize dynamic trim angle tracking according to the control instruction, and can quickly and effectively solve the problem of underwater robot attitude control.

[0061] The beneficial effects of the underwater robot attitude control system for adjusting the center of buoyancy and umbilical cable according to the present invention compared with the prior art are mainly reflected in:

[0062] The system of the present invention is configured with the above-mentioned underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable, which can realize the attitude control of the underwater robot by means of the combined operation of umbilical cable retraction and center of buoyancy adjustment, and has a fast response speed, high control accuracy and stability. It can not only maintain a specified trim angle, but also track the dynamic trim angle according to the control command. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The above and other objects, features and advantages of the present invention will become more apparent from the preferred embodiments of the present invention shown in the accompanying drawings. The same reference numerals in all the drawings indicate the same parts, and the drawings are not deliberately drawn to scale in actual size, and the focus is on showing the gist of the present invention.

[0064] Figure 1 It is a schematic flow chart of an underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable provided by an embodiment of the present invention;

[0065] Figure 2 It is a schematic diagram of the force at the end of the umbilical cable;

[0066] Figure 3 It is the trim correction of the underwater robot controlled by the floating block;

[0067] Figure 4 It is a calculation block diagram of the hydrodynamic and control model numerical solution module;

[0068] Figure 5 It is a calculation and analysis flow chart of the hydrodynamic and control model numerical solution module provided by an embodiment of the present invention;

[0069] Figure 6 It is a schematic diagram of the center of buoyancy adjustment device provided by an embodiment of the present invention Figure 1 ;

[0070] Figure 7 It is a schematic diagram of the center of buoyancy adjustment device provided by an embodiment of the present invention Figure 2 ;

[0071] Reference numerals: underwater robot main body 1, ducted propeller 2, umbilical cable 3, center of buoyancy adjustment device 4, floating block 401, bearing 402, servo motor 403, screw 404, moving channel 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0072] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. However, the embodiments cited do not limit the present invention. In this embodiment, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention.

[0073] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element and integrated with it, or there may be an intermediate element at the same time. The terms "installation", "one end", "the other end" and similar expressions used in the present invention are only for the purpose of illustration.

[0074] This embodiment provides an underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable, as Figures 1 to 5 shown, including the following steps:

[0075] S1. Construct a hydrodynamic mathematical model and a control model of the tethered remotely operated underwater vehicle system;

[0076] The tethered remotely operated underwater vehicle system includes an underwater robot body, a center of buoyancy adjustment device for adjusting the center of buoyancy position of the underwater robot body, an umbilical cable connected to the underwater robot body, and a ducted propeller for providing propulsion force;

[0077] The hydrodynamic mathematical model includes a first mathematical model and a second mathematical model. The first mathematical model is used to simulate the dynamic response caused by the underwater robot body during the maneuvering motion, and the second mathematical model is used to simulate the dynamic effect of the umbilical cable on the underwater robot body;

[0078] The control model includes a first control module and a second control module. The first control module is used to control the given length L K of the umbilical cable, and the second control module is used to control the rotational speed R K of the ducted propeller, and both the first control module and the second control module use the difference between the actual trim angle and the preset trim angle of the underwater robot body as the calculation input quantity;

[0079] S2. Add the control model to the hydrodynamic mathematical model to construct a hydrodynamic and control model;

[0080] That is, after the establishment of the hydrodynamic mathematical model of the tethered remotely operated underwater vehicle (ROV) system, an appropriate control algorithm is adopted to add a control model designed according to the requirements of the manipulation instructions to the established hydrodynamic mathematical model, thereby constituting the hydrodynamic and control model of the tethered ROV system.

[0081] S3. According to the hydrodynamic and control model, a numerical solution module for time-domain calculation is established. In the numerical solution module, the hydrodynamic and control characteristics of the tethered ROV system under the action of control mechanisms including the umbilical cable and the ducted propeller are numerically simulated, and the simulation results are output. The simulation results mainly include: mechanical parameters such as the three-dimensional spatial coordinates of the characteristic points of the underwater robot (such as the center of gravity of the underwater robot body, the connection point between the underwater robot body and the umbilical cable, etc.) and the Euler angles of the underwater robot, as well as geometric parameters such as the spatial coordinates of the umbilical cable.

[0082] In this embodiment, by constructing a hydrodynamic mathematical model and a control model and performing numerical simulation in the numerical solution module, the attitude control of the underwater robot can be realized by using the combined manipulation method of umbilical cable retraction and buoyancy center adjustment. It can quickly and effectively achieve the attitude control of the underwater robot, significantly improve the response speed, control accuracy and stability of the attitude control, solve the problems of slow adjustment speed and limited control effect of the traditional single adjustment method, and compared with the existing technology, this method can not only maintain the specified trim angle, but also realize the real-time tracking of the dynamic trim angle according to the control instructions, and can quickly and effectively solve the problem of underwater robot attitude control.

[0083] In a preferred embodiment, the first mathematical model is the six-degree-of-freedom motion equation of a submarine, which is expressed in the local coordinate system of the underwater robot body as:

[0084]

[0085]

[0086] The left-hand terms of equations (1-1) to (1-6) are the inertial forces and moments of the underwater robot body, and the right-hand terms are the external forces and external moments acting on the underwater robot body. Their symbols can be marked according to the international standard method and will not be elaborated here;

[0087] The external force acting on the underwater robot body is F0 = (X, Y, Z) T and the external moment is M0 = (K, M, N) T .

[0088] In a further preferred embodiment, the external force F0 and the external torque M0 are assumed to be composed of components such as the hydrostatic restoring force, the umbilical cable tension, the hydrodynamic force acting on the underwater robot body due to ocean currents and the underwater movement of the underwater robot itself, the thrust of the control duct propeller, and its corresponding torque. Therefore, we have:

[0089] F0 = F W + F T + F H + F TH (1-7)

[0090] M0 = M W + M T + M H + M TH (1-8)

[0091] In equations (1-7) and (1-8), the subscript W represents the hydrostatic restoring force, T represents the umbilical cable tension, H represents the hydrodynamic force acting on the underwater robot body including ocean current factors, and TH represents the thrust of the duct propeller.

[0092] Specifically, in equation (1-7), the resultant thrust F TH of the duct propeller is obtained by superimposing the thrusts F THi generated by each attitude control duct propeller on the underwater robot. F TH is a function of factors such as the duct propeller rotation speed and the duct propeller advance speed considering the influence of the underwater robot body on the flow field around the duct propeller.

[0093] F TH = ΣF THi (1-9)

[0094] In equation (1-9), the subscript i represents the serial number of the duct propeller, i = 1, 2,..., N TH , N TH is the total number of operating duct propellers installed on the underwater robot, and the value of F THi is expressed in the local coordinate system fixed on the robot body. Correspondingly, the torque M THi generated by the control duct propeller force F THi is given by the following equation:

[0095] M THi = r i × F THi (1-10)

[0096] where is the coordinate of the dynamic action point of the control duct propeller thrust expressed in the local coordinate system of the underwater robot.

[0097] ri = (x i , y i , z i ) (i = 1, 2, …, N TH ) (1 - 11)

[0098] Therefore, M in equation (1 - 8) TH is determined by the following equation:

[0099] M TH = ΣM THi (1 - 12)

[0100] The umbilical cable tension T acting on the robot body is determined by the catenary equation, and it is converted into the umbilical cable tension F T and moment M T in the local coordinate system of the robot as

[0101] F T = -[E][D]T (1 - 13)

[0102] M T = r T ×F T (1 - 14)

[0103] In equation (1 - 13), [E] is the transformation matrix between the relative coordinates and the absolute coordinates of the underwater robot body, and [D] is the transformation matrix between the relative coordinates and the absolute coordinates of the umbilical cable;

[0104] Substituting equations (1 - 9), (1 - 12) - (1 - 14) into (1 - 7) - (1 - 8), the umbilical cable tension at each time step, the hydrodynamic force acting on the robot body caused by the ocean current and the robot's own underwater movement, the thrust of the control duct propeller, and the corresponding moment in the corresponding external force terms in equations (1 - 1) - (1 - 6) can be determined.

[0105] The hydrostatic restoring force F W and moment M W in the right - hand side terms of equations (1 - 7) - (1 - 8) are obtained by converting the hydrostatic restoring force and moment composed of gravity W and buoyancy B in the fixed inertial coordinate system (X, Y, Z) into the hydrostatic restoring force F W and moment M W in the local coordinate system (x, y, z) of the robot body through the transformation matrix [E]. The expressions of the components of F W and M W in the right - hand side terms of equations (1 - 1) - (1 - 6) are:

[0106] X W = -(W - B)sinθ (1 - 15)

[0107] Y W =(W - B)cosθsinφ (1 - 16)

[0108] Z W =(W - B)cosθcosφ (1 - 17)

[0109] K W =(y G W - y B B)cosθcosφ - (z G W - Z B B)cosθsinφ (1 - 18)

[0110] M W =-(x G W - x B B)cosθcosφ - (z G W - z B B)sinθ (1 - 19)

[0111] N W =(x G W - x B B)cosθsinφ+(y G W - y B B)sinθ (1 - 20)

[0112] In equations (1 - 15) to (1 - 20), θ, φ, and ψ are respectively the pitch angle, roll angle, and yaw angle during the movement of the underwater robot in the fixed inertial coordinate system; (x G , y G , z G ) and (x B , y B , z B ) are respectively the center - of - gravity coordinates and center - of - buoyancy coordinates of the robot body in its local coordinate system.

[0113] Substituting equations (1 - 15) to (1 - 20) into equations (1 - 7) to (1 - 8) can determine the hydrostatic restoring force F W and moment M W .

[0114] The hydrodynamic loads F H , M H acting on the underwater robot in equations (1 - 7) and (1 - 8), the umbilical cable tension loads F T , M T as well as the control forces F TH , M THTheir numerical solutions can be obtained by means of computational fluid dynamics, that is, they can be directly solved by CFD software.

[0115] In another preferred embodiment, the second mathematical model is the catenary equation, which is a quasi-steady-state elastic umbilical cable equation. That is, in the treatment of the catenary, the direct action of the fluid force on the umbilical cable is ignored.

[0116] Furthermore, the catenary equation is expressed as:

[0117]

[0118] In the formula, m0 is the mass per unit length of the umbilical cable, k is the stiffness of the umbilical cable, L r is the slack length of the umbilical cable, α and β are integral constants related to the positions of both ends of the umbilical cable and the total mass of the umbilical cable, and the curve parameter λ is related to the tangential angle at the point on the umbilical cable:

[0119]

[0120] As Figure 2 shown, P1 is the upper endpoint of the umbilical cable 3 defined in the moving coordinate system of the mother ship, and P2 is the lower endpoint of the umbilical cable 3 defined in the moving coordinate system of the underwater robot. That is, the two ends of the umbilical cable 3 are the P1 point and the P2 point respectively. Then, when there is no relative motion between the mother ship and the underwater robot, the forces at the two endpoints P1 and P2 of the umbilical cable 3 are respectively:

[0121] F 1，x = c, F 1，y = csinh(λ1) (1-24)

[0122] F 2，x = -c, F 2，y = -csinh(λ2) (1-25)

[0123] In equations (1-24) and (1-25), F 1，x 、F 1，y are the forces at the upper endpoint of the umbilical cable, and F 2，x 、F 2，y are the tensions acting on the main body 1 of the underwater robot at the lower endpoint of the umbilical cable. The resultant force T of the tensions at the lower endpoint of the umbilical cable is:

[0124]

[0125] The resultant force T of the tension in equation (1-26) is a quantity in the local coordinate system of the umbilical cable.

[0126] Using Equation (1-26), the umbilical cable tension T expressed in the local coordinate system of the umbilical cable can be determined at each time step. It should be noted that substituting the umbilical cable tension T into Equations (1-13) to (1-14) can be converted into the umbilical cable tension F acting on the local coordinate system of the robot. T and the moment M T , and finally substituting them into Equations (1-7) to (1-8), the tension and moment generated by the umbilical cable tension T at each time step can be determined.

[0127] In actual implementation, first use modeling software to establish a three-dimensional geometric model of the underwater robot including the duct propeller, then import the geometric model into computational fluid dynamics software, and simplify and simulate the umbilical cable tension acting on the robot body in the form of a catenary. The overlapping grid and sliding combination method is used to solve the hydrodynamic control equations in the flow field where the underwater robot body, duct propeller, and umbilical cable are located. Thus, the hydrodynamic load acting on the underwater robot body and the thrust and torque generated by the duct propeller can be obtained, and the umbilical cable tension acting on the robot can be calculated by the catenary equation.

[0128] It should be noted that the algorithm adopted by the control model can be an incremental PID control algorithm, a sliding mode control algorithm, a neural network control algorithm, a fuzzy logic control algorithm, or various control algorithms that can be used for the trajectory and attitude manipulation of underwater robots. In the embodiments of this specification, the incremental PID control algorithm is mainly used to construct the required control module as follows.

[0129] In another preferred embodiment, the buoyancy center adjustment device includes a floating block 401 that can move longitudinally. The distance L between the buoyancy center F of the floating block 401 and the center of gravity of the underwater robot body b has a control expression of: B0

[0130] L b = L B0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1-27)

[0131] In the formula, as Figure 3 shown, L b is the distance between the center of the floating block 401 and the center of gravity of the underwater robot, and L B0 is the center of the floating block F bThe initial distance from the center of gravity of the underwater robot, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ae(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

[0132] In a further preferred embodiment, the control expression of the first control module is:

[0133] L K = L0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 28)

[0134] In the formula, L K is the length of the umbilical cable, L0 is the initial length of the umbilical cable, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ze(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

[0135] In another further preferred embodiment, the control expression of the second control module is:

[0136] R K = R0 + K P [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 29)

[0137] In the formula, R K is the rotational speed of the ducted propeller during each adjustment, R0 is the initial rotational speed of the ducted propeller, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ae(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

[0138] In another preferred embodiment, in step S3, the calculation block diagram of the numerical solution module of the hydrodynamic force and control model is as Figure 4 shown, where the numerical solution module includes a main program sub-module, a CFD sub-module, and a control sub-module;

[0139] After the hydrodynamic and control model is constructed, in step S3, a certain numerical method can be used to discretize the hydrodynamic and control model, so as to numerically simulate and completely determine the hydrodynamic and control response characteristics of the tethered remotely operated underwater vehicle system under certain maneuvering control actions. In such a hydrodynamic and control model, the input parameters are the motion parameters (such as the speed and displacement values at the connection point) of the umbilical cable at the upper end of the water surface and the connection point with the surface workboat at each time step, and the control sub-module issues commands to make the control mechanism execute corresponding control actions; through the operation of the CFD sub-module, the manipulation force issued by the control mechanism and the hydrodynamic force acting on the robot body under such control actions are predicted.

[0140] The above main program sub-module solves the hydrodynamic mathematical model and discretizes it into a numerical calculation model;

[0141] The above CFD sub-module is used to determine the hydrodynamic load acting on the underwater robot body and the control force of the control mechanism by using CFD technology at each time step;

[0142] The above control sub-module is used to issue manipulation commands to the underwater robot control mechanism according to the manipulation task requirements.

[0143] It should be noted that in the above embodiment, when the first mathematical model and the second mathematical model are superimposed, that is, at each time step of the maneuvering motion, the hydrodynamic load acting on the underwater robot body and the manipulation force issued by the control mechanism belonging to the main body (such as the ducted propeller 2, the robot buoyancy adjustment device 4, etc.) are calculated by the CFD sub-module, and this is used as the input of the external force and external torque on the right side of the submarine six-degree-of-freedom motion equation; after the tension force of the umbilical cable on the robot body is determined by the catenary equation, it is also superimposed on the right side of the submarine six-degree-of-freedom motion equation in the form of external force and external torque.

[0144] After constructing the hydrodynamic mathematical model and control model of the underwater robot, the CFD sub-module used to determine the hydrodynamic load acting on the underwater robot body and the manipulation force of the control mechanism is coupled into these model frameworks, and the incremental PID technology is used as the core algorithm of the control sub-module.

[0145] As Figure 5 shown, the calculation steps of the above numerical solution module are as follows:

[0146] (1) Input the geometric and physical parameters of the tethered remotely operated underwater vehicle system including the umbilical cable and the underwater robot body;

[0147] (2) The main program sub-module calculates the steady-state stable solution of the tethered remotely operated underwater vehicle system;

[0148] (3) Introduce the motion speed of the workboat at the n + 1 time step;

[0149] (4) Use the main program to calculate the dynamic parameters of the tethered remotely operated underwater vehicle system at the n+1 time step in modules;

[0150] (5) If the numerical simulation has not been completed, let n = n+1 and go to step 6; otherwise, the numerical simulation ends and all calculation results are output;

[0151] (6) The main program outputs the motion parameters of the underwater vehicle at the n time step required for the CFD module calculation in modules (such as the three-dimensional velocity components of the underwater vehicle and its attitude (Euler angles), etc.);

[0152] (7) Introduce the control actions on the underwater vehicle at the n time step. These control actions can be the pay-in and pay-out of the umbilical cable, the rotation speed of the ducted propeller, the steering, etc.;

[0153] (8) According to the motion parameters and control actions of the underwater vehicle in steps (6) and (7), use the CFD module to calculate the hydrodynamic loads acting on the underwater vehicle in the n time step equation and the control force of the control mechanism Interpolate through the values of time steps n and n-1 to obtain the next time step's and values, which are the dynamic parameters required for the calculation using the main program in modules in step (4);

[0154] (9) Go to step (3).

[0155] Based on the above embodiments, an underwater vehicle attitude control system for adjusting the center of buoyancy and umbilical cable is further provided, including a center of buoyancy adjustment device 4, an umbilical cable pay-in and pay-out device (not shown in the figure), a controller, and an underwater vehicle body 1;

[0156] The controller is electrically connected to the center of buoyancy adjustment device 4 and the umbilical cable 3 pay-in and pay-out device. The controller stores the program of an underwater vehicle attitude control method for adjusting the center of buoyancy and umbilical cable as described above; the controller runs the above method program and controls the operation of the center of buoyancy adjustment device 4 and the pay-in and pay-out of the umbilical cable 3;

[0157] The center of buoyancy adjustment device 4 includes a longitudinally movable floating block 401, a bearing 402, a servo motor 403, and a screw 404. The floating block 401 is arranged at the same height as the center of buoyancy of the underwater vehicle. The floating block 401 is sleeved on the screw 404 and is threadedly connected to the screw 404. Both ends of the screw 404 are rotatably connected to the bearing 402 and the servo motor 403 respectively. The servo motor 403 drives the screw 404 to rotate to drive the floating block 401 to move along the screw 404 to change the center of buoyancy position of the underwater vehicle body 1;

[0158] Such as Figure 6 and7 As shown, in this embodiment, the underwater robot is provided with a longitudinally movable floating block 401 at the same height as the center of buoyancy of the robot, which is used to adjust the longitudinal inclination angle of the underwater robot. The rotation of the screw 404 is driven by the servo motor 403 to drive the movement of the floating block 401, thereby changing the position of the center of buoyancy of the underwater robot. The underwater robot body 1 is provided with an immersed moving channel 5 for the floating block 401 to move back and forth. When the floating block 401 is in front of the center of gravity of the underwater robot, the buoyancy F generated by the floating block 401 b forms an induced longitudinal inclination moment M at the center of gravity of the underwater robot, causing the underwater robot to lift its head and be positively correlated with the distance L b from the center of gravity of the underwater robot b to the center of buoyancy F b . As Figure 3 shown, the more forward the floating block 401 is, the larger L b is, and the greater the tendency of the underwater robot to lift its head. When the floating block 401 is behind the center of gravity of the underwater robot, the situation is exactly the opposite. Therefore, by adjusting the distance L b between the floating block 401 and the center of gravity of the underwater robot, the correction of the longitudinal inclination angle of the underwater robot can be realized.

[0159] The umbilical cable retracting and releasing device is used to adjust the length of the umbilical cable 3 according to the first control instruction of the controller.

[0160] A ducted propeller 2 is provided at the stern of the underwater robot body 1, and the ducted propeller 2 can adjust the rotation speed of the ducted propeller 2 according to the second control instruction of the controller.

[0161] The system of the present invention is configured with the above-mentioned underwater robot attitude control method for adjusting the center of buoyancy and the umbilical cable, which can realize the attitude control of the underwater robot by using the combined operation mode of umbilical cable retracting and releasing and center of buoyancy adjustment, and has a fast response speed, high control accuracy and stability. It can not only maintain a specified longitudinal inclination angle, but also realize dynamic longitudinal inclination angle tracking according to the control instruction.

[0162] As an example, the umbilical cable retracting and releasing device can adopt a winch structure, and the control accuracy error of the umbilical cable 3 retracting and releasing is controlled by the servo motor 403 to be as small as possible. In a further preferred embodiment, the umbilical cable retracting and releasing device has an automatic locking function. When the length of the umbilical cable 3 reaches the preset value or the attitude control reaches a stable state, the umbilical cable 3 is automatically locked to prevent unnecessary movement due to external interference.

[0163] Preferably, the underwater robot attitude control system is also equipped with a data storage module for recording historical data such as the attitude parameters, floating block position, umbilical cable length, and control parameters of the underwater robot, so as to analyze and optimize the control strategy later.

[0164] In this specification, unless otherwise clearly specified or limited, a first feature being "on" or "under" a second feature may mean that the first and second features are in direct contact, or the first and second features are indirectly in contact via an intermediate medium. Also, a first feature being "above", "over" and "on top of" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the horizontal height of the first feature is higher than that of the second feature. A first feature being "under", "below" and "beneath" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the horizontal height of the first feature is less than that of the second feature.

[0165] In the description of this specification, the description with reference to terms such as "preferred embodiment", "further embodiment", "other embodiments" or "specific examples", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0166] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present application.

Claims

1. An underwater robot attitude control method for adjusting the center of buoyancy and umbilical cable, characterized in that, It includes the following steps: S1. Construct a hydrodynamic mathematical model and a control model of the cable - deployed remotely - operated underwater vehicle (ROV) system; The cable - deployed remotely - operated underwater vehicle system includes the underwater vehicle body, a buoyancy center adjustment device for adjusting the buoyancy center position of the underwater vehicle body, an umbilical cable connected to the underwater vehicle body, and a ducted propeller for providing propulsion force; The hydrodynamic mathematical model includes a first mathematical model and a second mathematical model. The first mathematical model is used to simulate the dynamic response caused by the underwater vehicle body during the maneuvering motion, and the second mathematical model is used to simulate the dynamic effect of the umbilical cable on the underwater vehicle body; The control model includes a first control module and a second control module. The first control module is used to control the given length L of the umbilical cable K , and the second control module is used to control the rotation speed R of the duct propeller K , and both the first control module and the second control module use the difference between the actual pitch angle and the preset pitch angle of the underwater robot body as the calculation input quantity; S2. Incorporate the control model into the hydrodynamic mathematical model to construct a hydrodynamic and control model; S3. According to the hydrodynamic and control model, establish a time - domain calculation numerical solution module, and numerically simulate the hydrodynamic and control characteristics of the cable - deployed remotely - operated underwater vehicle system under the action of a control mechanism including the umbilical cable and the ducted propeller in the numerical solution module, and output the simulation results.

2. The underwater robot attitude control method according to claim 1, characterized in that: The first mathematical model is the six - degree - of - freedom motion equation of a submarine, expressed in the local coordinate system of the underwater vehicle body as: The left - hand terms of equations (1 - 1) to (1 - 6) are the inertial forces and moments of the underwater vehicle body, and the right - hand terms are the external forces and external moments acting on the underwater vehicle body, and their symbols are marked according to the international standard method; The external force acting on the underwater robot body is F0 = (X, Y, Z) T and the external torque is M0 = (K, M, N) T .

3. According to the underwater vehicle attitude control method described in claim 2, wherein: The external force F0 and the external moment M0 are assumed to be composed of components such as hydrostatic restoring force, umbilical cable tension, hydrodynamic force acting on the underwater vehicle body due to ocean current and the underwater vehicle's own underwater motion, the thrust of the ducted propeller and its corresponding moment, etc. Therefore, there are: F0 = F W + F T + F H + F TH (1 - 7) M0 = M W + M T + M H + M TH (1 - 8) In equations (1 - 7) and (1 - 8), the subscript W represents the hydrostatic restoring force, T represents the umbilical cable tension, H represents the hydrodynamic force acting on the underwater vehicle body including ocean current factors, and TH represents the thrust of the ducted propeller.

4. The underwater robot attitude control method according to claim 1, characterized in that: The second mathematical model is the catenary equation, and the catenary equation is a quasi - steady - state elastic umbilical cable equation.

5. The underwater robot attitude control method according to claim 4, characterized in that, The catenary equation is expressed as: where \(m_0\) is the mass of the umbilical cable per unit length, \(k\) is the stiffness of the umbilical cable, \(L\) r is the slack length of the umbilical cable, \(\alpha\) and \(\beta\) are integral constants related to the positions of both ends of the umbilical cable and the total mass of the umbilical cable, and the curve parameter \(\lambda\) is related to the tangential angle at the point on the umbilical cable: P1 is the upper endpoint of the umbilical cable defined in the motion coordinate system of the mother ship, and P2 is the lower endpoint of the umbilical cable defined in the motion coordinate system of the underwater vehicle, that is, the two ends of the umbilical cable are point P1 and point P2 respectively. Then, when there is no relative motion between the mother ship and the underwater vehicle, the acting forces at the two endpoints P1 and P2 of the umbilical cable are: F 1，x = c, F 1，y = c sinh(λ1) (1-24) F 2，x = -c, F 2，y = -c sinh(λ2) (1 - 25) In Equations (1-24) and (1-25), F 1，x and F 1，y are the forces at the upper endpoint of the umbilical cable, and F 2，x and F 2，y are the tensions exerted by the lower endpoint of the umbilical cable on the underwater robot body. The resultant force T of the tensions at the lower endpoint of the umbilical cable is: The resultant tension T in equation (1 - 26) is a quantity value in the local coordinate system of the umbilical cable.

6. The underwater robot attitude control method according to claim 1, characterized in that: The buoyancy center adjustment device includes a floating block that can move longitudinally, and the distance L from the buoyancy center F of the floating block to the center of gravity of the underwater robot b is expressed by the control formula as follows: B0 The control expression of L b = L B0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 27) Wherein, L b is the distance between the center of the floating block and the center of gravity of the underwater robot, and L B0 is the initial distance between the center F b of the floating block and the center of gravity of the underwater robot. Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ae(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

7. The underwater robot attitude control method according to claim 6, characterized in that The control expression of the first control module is: L K = L0 + K p [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 28) Where L K is the length of the umbilical cable, L0 is the initial length of the umbilical cable, Ae(n) is the difference between the actual longitudinal inclination angle and the preset longitudinal inclination angle at the nth step, Ae(n - 1) is the difference between the actual longitudinal inclination angle and the preset longitudinal inclination angle at the (n - 1)th step, and Ze(n - 2) is the difference between the actual longitudinal inclination angle and the preset longitudinal inclination angle at the (n - 2)th step.

8. The underwater robot attitude control method according to claim 6, wherein: The control expression of the second control module is: R K = R0 + K P [Ae(n) - Ae(n - 1)] + K I Ae(n) + K D [Ae(n) - 2Ae(n - 1) + Ae(n - 2)] (1 - 29) where, R K is the rotational speed of the ducted propeller at each adjustment, R0 is the initial rotational speed of the ducted propeller, Ae(n) is the difference between the actual trim angle and the preset trim angle at the nth step, Ae(n - 1) is the difference between the actual trim angle and the preset trim angle at the (n - 1)th step, and Ae(n - 2) is the difference between the actual trim angle and the preset trim angle at the (n - 2)th step.

9. The underwater robot attitude control method according to claim 1, wherein: The algorithm adopted by the control model is an incremental PID control algorithm, or a sliding - mode control algorithm, or a neural network control algorithm, or a fuzzy logic control algorithm; And / or, the numerical solution module includes a main program sub - module, a CFD sub - module, and a control sub - module; The calculation steps of the numerical solution module are as follows: (1) Input the geometric and physical parameters of the cable - remote - operated underwater vehicle system; (2) Calculate the steady - state stable solutions of the cable - remote - operated underwater vehicle system by sub - modules of the main program; (3) Introduce the motion speed of the workboat at the (n + 1)-th time step; (4) Calculate the dynamic parameters of the cable - remote - operated underwater vehicle system at the (n + 1)-th time step by using sub - modules of the main program; (5) If the numerical simulation has not been completed, let n=n + 1 and go to step 6; otherwise, the numerical simulation ends and all calculation results are output; (6) Output the motion parameters of the underwater vehicle at the n - th time step required for the CFD sub - module calculation by sub - modules of the main program; (7) Introduce the control action on the underwater vehicle at the n - th time step; (8) Based on the motion parameters and control actions of the underwater robot in steps (6) and (7), use the CFD sub-module to calculate the hydrodynamic loads acting on the underwater robot by the n-time-step equation and the control force of the control mechanism Interpolate through the values of time steps n and n - 1 to obtain the and values, which are the dynamic parameters required to be provided for the calculation by the main program sub-module in step (4); (9) Go to step (3).

10. An underwater robot attitude control system for adjusting the center of buoyancy and umbilical cable, characterized in that: It includes a buoyancy - center adjustment device, an umbilical cable retracting and releasing device, a controller, and an underwater vehicle body; The controller is electrically connected to the buoyancy - center adjustment device and the umbilical cable retracting and releasing device, and the controller stores a program of an underwater vehicle attitude control method for adjusting the buoyancy center and umbilical cable according to any one of claims 1 to 9; The buoyancy - center adjustment device includes a longitudinally movable floating block, a bearing, a servo - motor, and a screw rod. The floating block is sleeved on the screw rod and is threadedly connected to the screw rod. The two ends of the screw rod are respectively rotationally connected to the bearing and the servo - motor. The servo - motor drives the screw rod to rotate to drive the floating block to move along the screw rod so as to adjust the buoyancy - center position of the underwater vehicle body; The umbilical cable retracting and releasing device is used to adjust the length of the umbilical cable according to the first control instruction of the controller; A ducted propeller is arranged at the stern of the underwater vehicle body, and the rotational speed of the ducted propeller can be adjusted according to the second control instruction of the controller.

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