ROV tow cable configuration perception system based on distributed grating fiber and imu array

Abstract

The ROV tow cable form perception system based on distributed grating fiber and IMU array belongs to the technical field of underwater engineering, ocean measurement and ocean equipment. Through the cooperation of four modules, high-precision real-time perception of the tow cable form in complex underwater environment is realized: the grating fiber module collects cable curvature data for form reconstruction; the ROV actuation module realizes dynamic movement by pulling the tow cable, so that the cable produces measurable physical form and can simulate the cable state under different operating conditions; the IMU array module is used to accurately collect the attitude information of each node, and the curvature data of the grating fiber are fused to calculate the three-dimensional space form of the tow cable in real time; the ultra-short baseline module provides a stable spatial reference and correction data for cable form reconstruction. The system can realize high-precision and real-time perception and analysis of the tow cable form in complex underwater environment, and is suitable for ROV underwater operation, tow cable monitoring and form research. It has strong anti-interference ability, high data precision and is suitable for various water depths and operating scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to underwater operation technology and intelligent sensing technology, in particular to a system and method for underwater remotely operated vehicle (ROV) tow cable form perception, belonging to the technical field of underwater engineering, ocean measurement and ocean equipment. BACKGROUND

[0002] The remotely operated vehicle (ROV) is widely used in ocean engineering, seabed exploration, ocean resource survey, cable operation and underwater robot operation. When performing tasks such as tow cable operation, pipeline laying and deep sea observation, the tow cable pulled by the ROV is usually affected by factors such as water flow, wave, pulling force and the flexible characteristics of the cable itself, resulting in complex three-dimensional form changes. The cable form directly affects the safety of the tow cable, the operation accuracy and the motion control of the ROV. Therefore, accurately obtaining the form information of the tow cable underwater is of great significance to ensure the safety of underwater operation, improve operation efficiency and realize precise navigation control.

[0003] At present, the traditional tow cable monitoring methods mainly include mechanical model calculation, tow cable tension measurement and a small number of discrete sensor monitoring methods. The mechanical model calculation depends on the cable material parameters, fluid mechanics model and initial boundary conditions, and is greatly affected by the uncertainty of the underwater environment, making it difficult to realize real-time high-precision form reconstruction. The tow cable tension measurement can only obtain limited overall force information and cannot reflect the local curvature and attitude changes of the tow cable at each node. Although a small number of discrete sensors can obtain local information, they are limited by the number and density of sensors, making it difficult to realize continuous form perception of the entire tow cable. In addition, the existing methods have limited adaptability to underwater disturbances and environmental changes, making it difficult to meet the needs of high-precision, real-time monitoring in deep sea and complex environments.

[0004] In order to solve the above problems, in recent years, distributed fiber grating sensing technology has been applied to tow cable form monitoring. FBG sensors can be continuously laid along the cable to realize distributed measurement of cable curvature, strain and deflection, and have the advantages of anti-electromagnetic interference, remote transmission and real-time acquisition. However, relying solely on optical fiber sensing cannot directly obtain accurate attitude information of the cable nodes, especially in complex three-dimensional motion states, there is a certain calculation error.

[0005] In the aspect of underwater environment monitoring, in order to meet the scientific observation and operation requirements, various environmental sensors can be arranged on the cable for collecting water temperature, pressure, salinity, flow rate, chemical composition and other environmental parameters. These environmental information can not only assist in the reconstruction of the shape and motion analysis of the towed cable, but also provide data support for ocean engineering, environmental monitoring, marine ecological research and underwater task decision-making. However, the existing towed cable system has limited real-time acquisition capability of environmental data, and lacks a fusion method with the shape perception module.

[0006] Therefore, the prior art still has deficiencies in the continuity, accuracy, real-time performance of the towed cable shape perception and the collection of environmental information, and it is difficult to meet the requirements of high-precision towed cable operation in deep sea and complex water areas. SUMMARY

[0007] The present application proposes a ROV towed cable shape perception and environment monitoring system based on distributed fiber grating and IMU array to solve the problems of low accuracy, poor continuity, insufficient real-time performance and limited environmental information acquisition in the existing underwater towed cable shape perception technology. The system realizes high-precision three-dimensional shape reconstruction of the towed cable in complex underwater environment through the cooperative work of multiple sensors, and can simultaneously collect water environment data to provide reliable data support for underwater operation.

[0008] The system realizes real-time perception and reconstruction of the three-dimensional shape and attitude of the towed cable in complex underwater environment through the cooperative work of distributed fiber grating sensor, inertial measurement unit array, ROV actuator and ultra-short baseline positioning module. At the same time, the system can arrange various environmental sensors on the towed cable for monitoring the environmental data of the water area where the towed cable is located, including but not limited to temperature, pressure, salinity, flow rate, etc., to provide high-precision shape data and environmental information support for underwater towed cable operation, cable laying operation, seabed observation and underwater robot operation.

[0009] The present application belongs to the technical field of underwater towed cable shape perception and environment monitoring system, and also relates to multiple sensor fusion, curve reconstruction, underwater motion control and underwater environmental data acquisition and other related technologies.

[0010] The system includes a grating fiber module, an ROV actuator module, an IMU array module, an ultra-short baseline module and an environmental sensor module arranged along the towed cable.

[0011] In the system, the ROV actuation module plays a key role in actively towing the cable. By adjusting the towing speed, direction and attitude, it realizes the controllable movement of the cable in different operating states. Further, the ROV actuation module can automatically adjust the towing strategy according to the real-time feedback of the shape, so that the cable can maintain the required shape in complex underwater environment while avoiding excessive bending or uneven stress. This module not only provides dynamic operating conditions for the data collected by the fiber grating and IMU, but also forms a closed-loop control system with the ultra-short baseline module, so that the three-dimensional shape reconstruction results can reflect the real movement state of the cable in the actual underwater space. Through the active control of the ROV actuation module, the system can accurately arrange the cable shape in a specific task area, providing controllable and reliable operating conditions for underwater engineering operations, cable laying operations and environmental monitoring.

[0012] The grating fiber module continuously measures the curvature and torsion of each sensor node on the cable through distributed fiber grating sensors, thereby obtaining the local shape information of the cable at different positions.

[0013] Further, to realize continuous shape reconstruction, the discrete curvature and torsion data measured by the fiber grating are fitted into continuous functions using cubic spline interpolation or linear interpolation method, obtaining the curvature function and the torsion function along the length direction of the cable. On this basis, by constructing the Frenet-Serret frame, the interpolated curvature and torsion functions are substituted into the differential equation

[0014]

[0015] where, , and are the unit tangent vector, normal vector and binormal vector respectively, s represents the arc length parameter along the cable, and by giving the initial boundary conditions , and , the unit tangent vector along the cable can be integrated. Subsequently, the spatial curve shape is calculated according to the tangent vector.

[0016]

[0017] where, is the starting position of the cable, which is generally set as the coordinate origin. Through the above steps, continuous shape reconstruction of the cable in three-dimensional space can be realized.

[0018] Further, the IMU array module is installed on the ROV and the key nodes of the tow cable, which can collect the acceleration, angular velocity and attitude information of the nodes in real time, and provide the tangent vector of the specific node, which is used to correct the cumulative error of the tangent vector at each node derived based on the Frenet-Serret frame, correct the direction of the tangent vector, fuse the curvature data measured by the grating fiber, optimize the curve reconstruction result through multi-sensor data processing, and improve the shape reconstruction accuracy and anti-interference ability. The ROV actuation module is used to actively pull the tow cable, so that the cable forms a controllable shape under different operation states, and the traction strategy can be automatically adjusted according to the real-time shape feedback, thereby enhancing the closed-loop control ability of the system, and making the tow cable maintain the required shape in complex water areas.

[0019] Further, the ultra-short baseline module obtains the three-dimensional absolute position reference information of the ROV relative to the mother ship through acoustic positioning technology, and provides a global spatial reference for shape reconstruction. Combined with the USBL positioning result, the system can globally correct the tow cable curve calculated by the Frenet-Serret frame, so that the three-dimensional reconstruction not only accurately reflects the local shape of the cable, but also ensures the absolute position accuracy of the cable in the actual underwater coordinate system. In other words, the ultra-short baseline positioning provides a spatial reference for the cable shape reconstruction, avoids the cumulative error that may be caused by relying only on fiber and IMU data, and realizes global consistency and high-precision positioning of the shape reconstruction.

[0020] Further, the environmental sensor module is arranged along the tow cable, which is used to collect parameters such as temperature, pressure, salinity, flow rate and chemical composition of the water area. The collected environmental data can not only assist in tow cable shape analysis and task decision-making, but also realize real-time monitoring of the underwater environment, and provide reliable information for marine engineering, environmental monitoring and scientific research.

[0021] Through the above algorithm and the cooperative work of each module, the present application can realize high-precision three-dimensional shape perception, global spatial correction and environmental information acquisition of the tow cable in complex underwater environment. Compared with the prior art, the present system has the advantages of high shape reconstruction accuracy, accurate global position, strong real-time performance, high anti-interference ability and flexible deployment, and provides comprehensive data support for underwater tow cable operation, cable laying operation, seabed observation and underwater robot operation.

[0022] The effective gain of the application: compared with the existing technology of only relying on Frenet-Serret equation to integrate the curvature of the towed cable to realize the geometric shape recovery, the application introduces distributed grating fiber, IMU array, ultra-short baseline positioning and ROV actuation module to construct a towed cable shape sensing system with multi-source information perception, fusion calculation and active actuation cooperation. The system takes advantage of the continuous distribution of distributed grating fiber along the towed cable to obtain the shape parameters such as curvature and torsion of the cable at each position in real time, and combines with the attitude angle, angular velocity and direction information provided by the IMU array at the key nodes of the towed cable to introduce discrete but high-precision attitude constraints for the shape reconstruction process, effectively correcting the direction drift and error accumulation caused by only based on curvature integration, and the IMU also provides the initial direction for the Frenet-Serret equation, thereby significantly improving the accuracy, stability and robustness of the three-dimensional shape reconstruction of the towed cable in complex underwater environment.

[0023] At the same time, the three-dimensional absolute position information of the ROV relative to the mother ship is obtained in real time through the ultra-short baseline positioning module, and the position information is used as the global spatial reference for the shape reconstruction of the towed cable, and the shape of the towed cable calculated based on the fiber and IMU data is corrected as a whole, so that the reconstruction result not only reflects the relative geometric shape of the towed cable, but also can be accurately mapped into the actual underwater spatial coordinate system, avoiding the overall deviation problem caused by uncertain initial conditions or cumulative errors.

[0024] Further, the ROV actuation module is introduced to construct a closed-loop cooperation mechanism of shape sensing and active actuation based on the real-time shape reconstruction result, so that the system can not only passively monitor the shape of the towed cable, but also dynamically adjust the traction direction, propulsion force and motion trajectory according to the shape state of different specified operation areas or functional sections, realize the regional monitoring and differential regulation of the shape of the towed cable, thereby effectively reduce the risk of local excessive bending, stress concentration or cable instability, and improve the safety and controllability of underwater operation.

[0025] In addition, the system further fuses the environmental data such as water temperature, pressure, salinity and flow rate collected by the environmental sensor to realize the cooperative processing of towed cable shape sensing and underwater environment monitoring, and provides environmental information support for towed cable shape analysis, operation strategy adjustment and task evaluation, so that the application not only has high-precision shape sensing capability, but also has comprehensive perception and decision support capability for actual engineering application, has significant engineering practical value and popularization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions, the following drawings will briefly introduce the drawings needed in the existing description.

[0027] Figure 1 is a schematic diagram of the system.

[0028] Figure 2 is a workflow diagram of the system. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application will be further described in conjunction with the accompanying drawings. The present application is specifically described by way of examples, and it is necessary to point out here that the following examples are only used to further illustrate the present application, but not limited thereto, unless otherwise stated.

[0030] An integrated system capable of combining fiber-optic distributed sensing, IMU node pose measurement, ROV active actuation, ultra-short baseline positioning, and environmental sensor monitoring, realizes high-precision real-time reconstruction of the towed cable shape and acquisition of underwater environmental information, to improve the safety, accuracy, and data integrity of underwater operations.

[0031] To further improve the reconstruction accuracy of the towed cable shape, introducing an array of inertial measurement units (IMU) has become an effective means. IMU can measure acceleration, angular velocity, and attitude angle, and can be deployed at key nodes of the cable to achieve high-frequency sampling of node pose and provide discrete pose constraints for three-dimensional shape reconstruction of the towed cable. By fusing fiber-optic sensing data with IMU node information, the accuracy and real-time performance of the towed cable shape reconstruction can be greatly improved, and the robustness of the system to underwater disturbances can be enhanced.

[0032] In addition, the motion state of the ROV directly affects the shape of the towed cable, so the ROV actuation module is introduced to actively control the motion of the towed cable, which can adjust the traction force, heading angle, propulsion speed, and attitude to achieve controllable shape of the cable under specific operation modes. This method of closed-loop actuation combined with shape feedback makes the towed cable shape monitoring and control more closely, meeting the fine needs under different tasks.

[0033] Ultra-short baseline (USBL) positioning technology can provide a reference position for the ROV to realize spatial correction and global coordinate reference for the towed cable shape reconstruction, further ensuring the accuracy of three-dimensional shape reconstruction. Combined with grating fiber, IMU, and ROV actuation module, a complete multi-sensor cooperative system is formed, which can realize high-precision and continuous towed cable shape sensing in complex underwater environments.

[0034] The specific steps of the system in operation are as follows:

[0035] S1, system initialization: start and parameter configuration of the distributed grating fiber module, IMU series module, ultra-short baseline positioning module, ROV actuation module, and environmental sensor module.

[0036] S2, data acquisition: the distributed grating fiber module collects continuous curvature, torsion and strain information along the tow cable, and transmits to the data processing unit;

[0037] S3, the IMU array module collects the posture, angular velocity and acceleration information of the key nodes of the tow cable and the ROV;

[0038] S4, the environmental sensor module collects environmental parameters such as water temperature, pressure, salinity and flow rate.

[0039] S5, data preprocessing: time synchronization and preprocessing are performed on grating fiber data, IMU data, environmental data and ultra-short baseline positioning data.

[0040] S6, initial three-dimensional shape reconstruction of the tow cable, according to the data collected by the grating fiber, the continuous curvature function of the tow cable along the arc length direction is constructed, and the initial three-dimensional shape reconstruction of the tow cable is carried out based on the Frenet-Serret frame.

[0041] S7, shape correction and calibration: fusion of the node posture information of the IMU array, correction of the shape of the tow cable, improvement of the shape reconstruction accuracy and stability;

[0042] S8, the ultra-short baseline positioning module obtains the absolute spatial position of the ROV, and corrects the global coordinate of the tow cable shape reconstruction result.

[0043] S9, shape state analysis, analysis and discrimination of the shape state of different specified regions of the tow cable.

[0044] S10, closed-loop control: generating ROV actuation control instructions according to the shape analysis result, adjusting the propulsion force, traction direction and motion posture, realizing the closed-loop control of shape sensing and active actuation.

[0045] S11, information display and storage: display and storage of the three-dimensional shape of the tow cable, the position of the ROV and the environmental information.

[0046] The following will describe the specific embodiments of the present application in detail in combination with the technical solutions: Embodiment 1

[0047] This embodiment takes underwater ROV tow cable operation as the object, and uses the tow cable shape sensing and environmental monitoring system based on distributed grating fiber and IMU array proposed by the present application to perform three-dimensional shape reconstruction and environmental data acquisition on the underwater tow cable.

[0048] The system comprises a grating optical fiber module, an ROV actuation module, an IMU array module, an ultra-short baseline module and an environmental sensor module arranged along the tow cable. The grating optical fiber module adopts a three-core distributed fiber grating sensor and is arranged continuously along the tow cable to measure the curvature and flexure of each node in real time. The total length of the tow cable is 500 meters, and the IMU array module is installed at key positions on the tow cable with one node arranged every 20 meters, each node containing a three-axis accelerometer and a gyroscope to collect acceleration, angular velocity and attitude information. The ROV actuation module is composed of a motor drive device and a control unit, which can adjust the pulling speed and direction to realize the dynamic movement of the cable. The ultra-short baseline module is arranged on the working mother ship using acoustic positioning technology to obtain the three-dimensional absolute position of the ROV relative to the mother ship in real time. The environmental sensor module is arranged along the tow cable to collect parameters such as water temperature, pressure, salinity and flow rate.

[0049] In actual operation, first, the grating optical fiber module and the IMU array module are started to obtain the curvature, flexure and attitude data of each node. Then, the discrete curvature and bending direction data are fitted into continuous functions by cubic spline interpolation and , and the unit tangent vector and the spatial curve along the cable are calculated in the Frenet-Serret frame to complete the three-dimensional shape reconstruction of the tow cable. The data collected by the IMU and the fiber curvature data are fused to further optimize the shape reconstruction accuracy and reduce the influence of local disturbance and measurement error.

[0050] On this basis, the ROV actuation module adjusts the pulling strategy according to the real-time shape feedback to form the required operation shape of the tow cable underwater while keeping the cable force uniform and avoiding local excessive bending. The ultra-short baseline module provides real-time absolute position reference of the ROV, so that the reconstructed cable curve has spatial correction capability in the global coordinate system, improving the absolute accuracy of the three-dimensional shape. The environmental sensor module synchronously collects data such as water temperature, salinity, pressure and flow rate and transmits the data to the main control unit for display and storage for subsequent analysis and underwater operation decision-making.

[0051] Through the above embodiment, high-precision continuous three-dimensional shape perception of the tow cable in complex underwater environment can be realized, and underwater environmental data can be obtained to realize synchronous monitoring of shape and environmental information. The embodiment verifies the reliability, real-time performance and high-precision characteristics of the system in actual operation, which can be widely applied to underwater tow cable operation, cable laying operation and seabed observation tasks.

[0052] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A ROV tow cable conformation sensing system based on distributed grating fiber and IMU array, characterized in that, The system comprises a grating fiber module, an ROV actuation module, an IMU array module, an ultra-short baseline module, and an environmental sensor module, which work together to realize high-precision form perception and analysis of the tow cable in complex underwater environments. The grating fiber module is used to distribute the distributed fiber grating sensors along the tow cable, to continuously monitor the curvature, flexural rate, and strain of each section of the cable body through the fiber grating sensors distributed along the cable, and to transmit the distributed optical data obtained by the fiber grating sensors to the data processing unit in real time for analysis and form estimation. The ROV actuation module is used to pull the tow cable to realize dynamic movement, so that the cable reaches a specific area for operation. It comprises a propeller driving device, a posture and depth control unit, and a control interface for communication with the mother ship, which is used to adjust the propelling speed, heading angle, pitch angle, and pulling direction of the ROV, so that the tow cable obtains a controllable spatial form distribution in different operation scenarios. The IMU array module is installed on the ROV and key nodes of the tow cable, and is used to sample the linear acceleration, angular velocity, attitude angle, and direction change of the ROV and key nodes of the tow cable, to provide attitude constraint information at the discrete nodes for cable form reconstruction, and to fuse with the curvature data of the grating fiber to calculate the three-dimensional form of the tow cable. The ultra-short baseline module is used to obtain the reference position information of the ROV relative to the mother ship, to provide spatial reference for cable form reconstruction. It uses acoustic ultra-short baseline positioning technology to measure the acoustic round-trip time and azimuth angle of the ROV through the underwater acoustic array arranged on the mother ship, to obtain the absolute coordinate position of the ROV in three-dimensional space, and to provide global coordinate constraints for tow cable form reconstruction. The environmental sensor module is arranged along the tow cable, and is used to monitor the environmental parameters of the water area where the cable is located, including temperature, electromagnetic field, salinity, and flow rate. The multi-source sensing data output by the grating fiber module and the IMU array module are processed through a unified data fusion algorithm, to comprehensively estimate the local curvature, direction vector, and node attitude of the tow cable, so as to realize continuous and real-time reconstruction of the three-dimensional form of the tow cable. The data fusion algorithm comprises Kalman filtering, multi-sensor cooperative optimization, rotation matrix solving, coordinate system transformation and curve reconstruction algorithm based on Frenet-Serret framework; wherein the FS framework describes the change relationship of tangent vector normal vector and binormal vector of the spatial curve of the streamer through the following matrix differential equation: ； wherein, is the curvature, is the torsion, the distributed curvature information collected by the grating fiber and the IMU node attitude information are combined to solve the above equation; The spatial curve form is calculated according to the tangent vector. ； wherein, is the start position of the streamer, and the continuous shape reconstruction of the streamer in three-dimensional space is realized.

2. The system of claim 1, wherein: The IMU array module comprises a plurality of three-axis accelerometers and three-axis gyroscopes. Alternatively, it also comprises a three-axis magnetometer.

3. The system of claim 1, wherein: The ROV actuation module automatically adjusts the pulling strategy through closed-loop control based on the real-time form reconstruction results of the tow cable, including adjusting the pulling angle, propelling force, and movement trajectory, to meet the required form change and attitude control of the tow cable in a specific task mode.

4. The system of claim 1, wherein: The system further comprises a display and storage module, which is used to visually display the three-dimensional form of the reconstructed tow cable, the position of the ROV, and the state of the sensors in real time, and to store the historical data in a classified manner, to support operation evaluation, fault diagnosis, and subsequent trajectory analysis.

5. The system of claim 1, wherein: The data collected by the environmental sensor module are jointly processed with the data of the grating fiber module and the IMU module, to provide environmental information assistance for tow cable form reconstruction, and to realize real-time monitoring of the underwater environment.

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