A dual-closed-loop attitude control system for underwater towed fish based on tail fin angle of attack position feedback.

Abstract

This invention relates to a dual-closed-loop attitude control system for underwater towed fish based on tail fin angle-of-attack position feedback, belonging to the field of underwater vehicle motion control and marine engineering equipment technology. The system includes an underwater towed platform, an attitude sensing unit, a tail fin angle-of-attack feedback unit, a dual-closed-loop controller, and an electric servo actuator. The system calculates the deviation between the desired and actual attitude angles, outputs the desired tail fin angle-of-attack command via a PID control algorithm, and provides angle limiting protection for the command. It then uses a shaft encoder to obtain real-time tail fin angle-of-attack feedback, inputs the tail fin angle-of-attack deviation into a servo amplifier, and drives a DC motor and gearbox to precisely adjust the deflection angle of the horizontal tail fin, achieving closed-loop correction of the towed fish's attitude. This invention, through the combination of cascade PID control strategy and physical feedback of tail fin angle-of-attack position, features fast response speed, high control accuracy, strong robustness, and excellent anti-interference capability, making it suitable for underwater towed detection and operation equipment in complex sea conditions.

Description

Technical Field

[0001] This invention relates to the field of marine engineering equipment and underwater vehicle control technology, and in particular to a dual closed-loop control system for the attitude of an underwater towed body (towed fish) based on tail fin angle of attack position feedback and cascade PID algorithm. Background Technology

[0002] In existing technologies, underwater towed systems are widely used in marine geological surveys, underwater search and rescue, and military reconnaissance. The towed body (commonly known as a "towed fish") is connected to the mother ship via armored cables, and its attitude stability is crucial to ensuring the quality of sonar imaging and the accuracy of sensor data. However, in actual operations, the towed fish faces a complex disturbance environment: on the one hand, the heave motion of the mother ship on the sea surface is transmitted to the towed fish through the tow cable, causing severe attitude fluctuations; on the other hand, complex ocean currents and depth-changing maneuvers can alter the hydrodynamic characteristics of the towed fish, leading to nonlinear attitude responses.

[0003] Traditional towed fish attitude control methods typically employ a single-loop PID control strategy, directly calculating the servo's control voltage or PWM signal based on the attitude angle deviation. This approach implicitly assumes that the servo's actions are instantaneous and precise. However, in engineering practice, servo actuators inherently possess mechanical backlash, frictional resistance, and response lag. Furthermore, under the impact of high-pressure water flow, the servo surface often struggles to precisely achieve the commanded angle. This discrepancy between "command and execution" can lead to overshoot oscillations, large steady-state deviations, and even instability and divergence in the control system.

[0004] Furthermore, existing control schemes often neglect the coupling effects of hydrodynamics, meaning they fail to fully consider the nonlinear relationship in the physical chain of tail fin angle-of-attack changes and the lift / torque generated by the angle of attack. Without feedback on the physical position of the tail fin angle of attack, the controller cannot perceive the true state of the control surfaces, limiting control accuracy and making it prone to stall or mechanical damage due to the tail fin reaching its maximum angle of attack. Therefore, achieving high-fidelity closed-loop control of "perception-decision-execution" in environments with strong interference is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a dual-closed-loop control system for underwater towed fish attitude based on tail fin angle-of-attack position feedback. This system aims to solve the problems of traditional single-loop control, such as neglecting actuator characteristics, poor anti-interference capability, and susceptibility to mechanical damage. By utilizing the cascade architecture of the attitude outer loop and the tail fin angle-of-attack inner loop, combined with physical position feedback and hydrodynamic characteristics, this invention effectively solves the problems of actuator response lag and nonlinearity in traditional single-loop control, achieving high-precision, high-dynamic-response control of the underwater towed fish attitude.

[0006] The technical solution adopted in this invention is: an underwater towed fish attitude dual closed-loop control system based on tail fin angle of attack position feedback, comprising the following steps:

[0007] S1. By using the attitude sensing unit mounted inside the towed fish, the actual attitude angle information of the towed fish during its underwater movement is collected in real time, including pitch angle, roll angle and heading angle.

[0008] S2. Construct the outer loop of attitude control: Compare the set desired attitude angle with the actual attitude angle obtained in step S1, calculate the attitude deviation, and the control unit calculates the desired tail wing angle of attack command for attitude correction using the PID control algorithm based on the deviation.

[0009] S3. Perform safety limiting processing on the desired tail wing angle of attack command output in step S2 to ensure that the output command value is within the effective stroke range of the mechanical structure.

[0010] S4. Construct the inner loop control loop for tail wing angle of attack: The current actual tail wing angle of attack of the control surface is obtained in real time by the angle sensor in the execution unit. The expected tail wing angle of attack after step S3 is compared with the current actual tail wing angle of attack, and the tail wing angle of attack deviation is calculated.

[0011] S5. Based on the tail fin angle of attack deviation, the servo actuator drives the towed fish tail fin to deflect to the target tail fin angle of attack, changing the effective angle of attack of the tail fin relative to the water flow. This generates lift and pitching torque through hydrodynamic effects. This torque overcomes external disturbance torque and drives the towed fish to rotate around the center of mass, thereby correcting the actual attitude angle of the towed fish. This forms a physical and logical coupling closed loop of tail fin angle of attack position feedback and attitude angle feedback until the actual attitude angle is consistent with the desired attitude angle.

[0012] The dual closed-loop control system achieves attitude stabilization through an electromechanical-fluid coupling mechanism: the PID parameters of the control unit are set based on the hydrodynamic derivative of the towed fish, which includes the slope of the lift curve. and the slope of the moment curve The coupling mechanism is that the output of the outer attitude loop determines the desired hydrodynamic angle of attack of the tail fin, while the execution accuracy of the inner tail fin angle of attack loop determines the accuracy of the actual hydrodynamic angle of attack. By changing the nonlinear hydrodynamic torque caused by the tail fin deflection, the physical variable of the tail fin angle of attack position is mapped in real time to the spatial variable of the towed fish attitude, realizing bidirectional coupling control between inner loop execution and outer loop perception.

[0013] Furthermore, the system adopts a two-stage towing physical architecture, including a main towing cable, a ballast, and a secondary towing cable. The ballast is used to isolate the heave disturbance transmitted by the mother ship through the main towing cable, and the secondary towing cable enables flexible traction of the towed fish, thus achieving interference decoupling at the physical level.

[0014] Furthermore, the attitude sensing unit is a vertical gyroscope, used to provide real-time feedback on the pitch angle of the towed fish. The PID control algorithm includes proportional, integral, and derivative components, used to calculate the theoretical tail fin angle of attack required to eliminate attitude deviations.

[0015] Furthermore, the safety limiting process in step S3 sets the tail fin angle of attack threshold range to be... This prevents the tail fin from experiencing hydrodynamic stall or jamming of the mechanical transmission mechanism at high angles of attack.

[0016] Furthermore, the inner ring of the tail fin angle of attack utilizes a shaft encoder as a feedback element, and the servo amplifier adjusts the tail fin angle of attack position deviation accordingly. Driven by a DC motor and gearbox, it achieves rapid, zero-static-error tracking of the desired tail fin angle of attack.

[0017] The beneficial effects of this invention are as follows: Compared with traditional single-loop control, this system adds an inner loop for tail fin angle of attack position feedback. This inner loop can effectively suppress the dead zone, friction, and nonlinear characteristics of the servo motor, ensuring that the actuator can reproduce the control algorithm's instructions 1:1, greatly improving the system's execution accuracy and response speed. This invention fully utilizes the electromechanical-fluid coupling mechanism. By precisely controlling the tail fin angle of attack position, the hydrodynamic angle of attack of the tail fin is directly and accurately controlled. Utilizing the physical characteristics of the lift curve slope and torque curve slope, the minute control surface deflection is efficiently converted into hydrodynamic torque to restore the towed fish's attitude, achieving high-fidelity control at the physical level. This invention introduces an intermediate-level tail fin angle of attack limiting protection circuit. While ensuring control effect, it physically limits the maximum deflection angle of the control surface at the algorithm level, effectively preventing overload burnout of the servo motor or breakage of mechanical linkages due to sudden changes in sea state, significantly improving the system's reliability and safety. This invention adopts a two-stage towing physical design, combined with a dual closed-loop control algorithm, achieving dual protection of physical vibration reduction and algorithmic attitude stabilization. The ballast isolates most of the high-frequency cable tension interference, allowing the attitude control of the towed fish to only deal with low-frequency residual disturbances, significantly reducing control difficulty and improving steady-state accuracy. From an engineering perspective, this invention bridges the gap between digital commands and physical execution, solving the control model mismatch problem caused by large variations in hydrodynamic loads in underwater equipment. It is suitable for underwater towed exploration, topographic mapping, and intelligence gathering tasks under various complex sea conditions, and has significant engineering application value. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below:

[0019] Figure 1 This is a schematic diagram of the overall structure of an underwater two-stage towing system based on tail fin angle of attack position feedback, as described in an embodiment of the present invention.

[0020] Figure 2 This is a top view schematic diagram of the internal hardware layout and sensor distribution of the underwater towed fish described in an embodiment of the present invention.

[0021] Figure 3 This is a logic flowchart of the dual closed-loop (cascaded PID) control method for towing fish posture described in an embodiment of the present invention.

[0022] The reference numerals in the attached drawings are explained as follows: 1-Towing mother ship; 2-Host computer; 3-Windlock; 4-Main towing cable; 5-Ballast; 6-Pulley; 7-Secondary towing cable; 8-Towing point; 9-Underwater towed fish; 10-Vertical tail fin; 11-Horizontal tail fin; 12-Depth / velocity sensor; 13-PID controller; 14-Vertical gyroscope; 15-Power conversion unit; 16-Servo motor; 17-Tail fin angle of attack feedback unit. Detailed Implementation

[0023] Example 1

[0024] To make the technical solution of the present invention clearer, the following description, in conjunction with specific examples and accompanying drawings, further illustrates an underwater towed fish attitude dual-closed-loop control system based on tail fin angle of attack position feedback. This embodiment is only used to illustrate the technical solution of the present invention and is not intended to limit it.

[0025] This embodiment provides a high-fidelity, interference-resistant underwater towing control system, applicable to deep-sea topographic mapping, underwater target search, and marine environmental monitoring. The system isolates interference from the mother ship through a two-stage towing physical architecture and utilizes a dual-closed-loop coupling mechanism of inner-ring tail fin angle-of-attack position feedback and outer-ring attitude perception to achieve attitude stability of the towed fish in complex hydrodynamic environments.

[0026] like Figure 1 as well as Figure 2 As shown, the system described in this embodiment includes a surface unit, a connection unit, and an underwater unit.

[0027] 1. Surface Unit: Includes towing mother ship 1, host computer 2, and winch 3. Host computer 2 is used to send top-level commands (such as depth, altitude, or attitude control modes) and monitor the underwater status in real time.

[0028] 2. Connection Unit: A two-stage towing method is adopted. The main towing cable 4 connects the mother ship to the heavy ballast 5. The ballast 5 acts as a "low-pass filter", using its large mass and inertia to suppress the heave motion of the mother ship caused by wind and waves. The auxiliary towing cable 7 connects the ballast 5 to the towing point 8 of the towing platform 9 through the pulley 6 to achieve flexible traction.

[0029] 3. Underwater unit (fish tow): such as Figure 2As shown, the towed platform 9 is equipped with core control components.

[0030] (1) Sensing layer: The vertical gyroscope 14 is installed near the center of gravity of the towed fish to measure the real-time pitch angle. Depth / velocity sensor 12 is used for navigation assistance.

[0031] (2) Decision layer: PID controller 13 (which can be an embedded ARM or FPGA chip) is responsible for solving the control law.

[0032] (3) Execution layer: Servo motor 16 is connected to a gearbox to drive the horizontal tail fin 11 to deflect. The key is that the execution layer integrates a tail fin angle of attack feedback unit 17 to form an inner loop feedback.

[0033] (4) Feedback layer: The tail wing angle of attack feedback unit 17 is installed at the connection shaft between the servo motor 16 and the horizontal tail wing 11. This unit directly monitors the physical deflection state of the tail wing. Compared with the traditional motor rear encoder, it eliminates the measurement deviation caused by the gearbox backlash and can more realistically reflect the fluid angle of attack of the tail wing.

[0034] like Figure 3 As shown, the control method in this embodiment adopts a cascade control strategy of attitude outer loop and tail fin angle of attack inner loop, which operates based on electromechanical-fluid coupling mechanism, and specifically includes the following steps:

[0035] S1. After the system is powered on, the vertical gyroscope 14 acquires the current pitch angle of the towed fish at a high frequency (e.g., 50Hz-100Hz). The host computer or internal task planner sets the target desired attitude angle. (For example, keep it horizontal, i.e.) ).

[0036] S2, PID controller 13 calculates attitude deviation Based on this deviation, the outer loop controller calculates "the angle the tail fin should theoretically deflect to eliminate this attitude deviation," which is the desired tail fin angle of attack. The calculation formula is:

[0037]

[0038] in, For the proportional, integral, and differential coefficients of the attitude loop.

[0039] S3. To prevent mechanical damage or fluid stall caused by drastic control, the system... Logical limiting is applied. In this embodiment, the physical limit of the tail fin's angle of attack is set to... If the solution is... Then output This step ensures that subsequent actuators always operate within a safe and linear lift range.

[0040] S4. The desired tail fin angle of attack output in step S3. As the input to the inner loop, the tail fin angle of attack feedback unit 17 collects the current geometric angle of attack of the tail fin in real time. Since this unit is directly coupled to the tail rotor shaft, its feedback value directly represents the effective physical parameters involved in the hydrodynamic calculations. Servo amplifier comparison. and The tail fin angle of attack deviation was obtained. Generate driving voltage Drive the DC motor to rotate until Approaching zero. The presence of this inner ring eliminates the obstruction of gearbox backlash and water flow load torque on the control surface, ensuring that the tail fin truly rotates to the angle desired by the control algorithm.

[0041] S5. This embodiment achieves the final attitude correction through the coupling of physical parameters. When the tail fin accurately deflects to... At that time, the effective angle of attack of the tail fin relative to the incoming airflow was changed. According to hydrodynamic principles (cited from the design basis of this case), the lift generated by the tail fin... With torque The following coupling relationship applies:

[0042]

[0043]

[0044] in, The slope of the lift curve. This represents the slope of the torque curve. The high-precision feedback from the tail fin angle-of-attack feedback unit 17 ensures the tail fin angle of attack. The accuracy of the angle of attack is thus guaranteed. The accuracy of the above formula and the restoring torque generated It can precisely overcome external disturbance torques, drive the towed fish to rotate around its center of mass, and thus achieve its actual posture. Quickly return to .

[0045] The above embodiments are only used to illustrate the present invention. Any equivalent transformations and improvements made on the basis of the technical solutions of the present invention (such as replacing the PID algorithm with the ADRC active disturbance rejection control algorithm, or replacing the vertical gyroscope with the fiber optic inertial navigation system) should not be excluded from the protection scope of the present invention.

Claims

1. A dual-closed-loop control system for underwater towed fish attitude based on tail fin angle of attack position feedback, characterized in that, The system includes a towing mother ship, a secondary towing connection mechanism, and an underwater towed fish. The underwater towed fish is internally equipped with an attitude sensing unit, a control unit, a tail fin angle-of-attack feedback unit, and a servo execution unit. The control method of the control system includes the following steps: S1. By using the attitude sensing unit mounted inside the underwater towed fish, the actual attitude angle information of the towed fish during its underwater movement is collected in real time, including pitch angle, roll angle and heading angle. S2. Construct the outer loop of attitude control: Compare the set desired attitude angle with the actual attitude angle obtained in step S1, calculate the attitude deviation, and the control unit calculates the desired tail wing angle of attack command for attitude correction using the PID control algorithm based on the deviation. S3. Perform safety limiting processing on the desired tail wing angle of attack command output in step S2 to ensure that the output command value is within the effective stroke range of the mechanical structure. S4. Construct the inner loop control loop for tail fin angle of attack: The tail fin angle of attack feedback unit is collected in real time relative to the towed fish axis. The expected tail fin angle of attack after step S3 is compared with the current feedback geometric angle of attack, and the tail fin angle of attack deviation is calculated. S5. Based on the tail fin angle of attack deviation, the servo execution unit drives the towed fish tail fin to deflect to the target tail fin angle of attack, changes the effective angle of attack of the tail fin relative to the water flow, and then generates lift and pitching moment through hydrodynamic effect. This moment overcomes the external disturbance moment and drives the towed fish to rotate around the center of mass, thereby correcting the actual attitude angle of the towed fish, forming a physical and logical coupling closed loop of tail fin angle of attack position feedback and attitude angle feedback, until the actual attitude angle is consistent with the desired attitude angle. The dual closed-loop control system achieves attitude stabilization through an electromechanical-fluid coupling mechanism: the PID parameters of the control unit are set based on the hydrodynamic derivative of the towed fish, which includes the slope of the lift curve. and the slope of the moment curve The coupling mechanism is that the output of the outer attitude loop determines the desired fluid angle of attack of the tail fin, while the execution accuracy of the inner tail fin angle of attack loop determines the accuracy of the actual fluid angle of attack. By changing the nonlinear hydrodynamic torque caused by the tail fin deflection, the physical variable of the tail fin angle of attack position is mapped in real time to the spatial variable of the towed fish attitude, realizing the bidirectional coupling control of inner loop execution and outer loop perception. The secondary towing connection mechanism includes a main towing cable, a ballast, and an auxiliary towing cable. One end of the main towing cable is connected to the winch of the towing mother ship, and the other end is connected to the ballast. One end of the auxiliary towing cable is connected to the ballast, and the other end is connected to the towing point of the underwater towed fish. The ballast is used to isolate the heave disturbance transmitted by the mother ship through the main towing cable, and the auxiliary towing cable enables flexible traction of the towed fish. The attitude sensing unit is a vertical gyroscope, used to provide real-time feedback on the pitch angle of the towed fish. The specific formula for the PID control algorithm in step S2 is as follows: ； in, To achieve the desired angle of attack of the tail fin, Desired attitude angle Compared with actual attitude angle The difference, , , These are the proportional, integral, and differential coefficients, respectively.

2. The system according to claim 1, characterized in that, The safety limiting process in step S3 specifically involves: setting the tail fin angle of attack threshold range. If the desired tail fin angle of attack calculated by the PID exceeds this range, the output is forced to be a boundary value; the threshold range is set as follows. .

3. The system according to claim 1, characterized in that, The execution unit includes a servo amplifier, a DC motor, and a gearbox; the tail fin angle-of-attack feedback unit is a high-precision absolute encoder or a rotary transformer, which is coaxially mounted on the shaft of the horizontal tail fin to provide real-time feedback of the actual physical angle-of-attack signal of the tail fin to the servo amplifier; the specific process of the tail fin angle-of-attack inner loop control in step S4 is as follows: the shaft encoder collects the actual deflection angle of the tail fin in real time. And this feedback is sent to the front end of the servo amplifier; the servo amplifier receives the desired tail fin angle of attack. Compared to the actual tail fin angle of attack The difference The difference signal is amplified and used to drive a DC motor to rotate; the DC motor increases the torque through a reduction gearbox and then drives the horizontal tail fin to rotate until the difference is reached. Approaching zero.

4. The system according to claim 1, characterized in that, The underwater towed fish includes a streamlined hull, a vertical tail fin, and a horizontal tail fin. The horizontal tail fin is symmetrically installed on both sides of the tail of the hull and is driven by two independent servo actuators. It controls the pitch attitude of the towed fish by deflecting in the same direction, or controls the roll attitude of the towed fish by deflecting in a differential direction.

5. The system according to claim 1, characterized in that, The underwater towed fish also integrates a power conversion unit, a depth sensor, and a speed sensor; the power conversion unit is used to convert the high-voltage electricity transmitted through the tow cable into low-voltage DC electricity required by the control unit and the execution unit; the depth sensor is used to assist in depth control.

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