Conventional Autonomous Underwater Vehicles Research Articles

Parent-child underwater robot-based manipulation system for underwater structure maintenance

This study proposes a parent–child robot-based underwater manipulation system for underwater structure maintenance comprising two underwater vehicles with split roles. The larger autonomous underwater vehicle (AUV) acts as the base to transport and control a tethered child robot that is deployed to perform actual manipulation tasks. Conventional AUVs face several challenges when performing manipulation missions because of their large and massive body and the complexity of dynamic control with a rigid arm manipulator in the precise hovering state. To address this problem, we proposed an underwater manipulation system that uses a large parent AUV with high-performance sensors to navigate to the desired location and a child robot with high mobility to perform manipulation tasks. In this study, a parent–child robot-based manipulation system was developed and mathematically modeled considering hydrodynamics. Based on the system model, a nonlinear time delay (TD) controller was applied to the child robot to ensure robustness of the movement, and complementary sensing methods were proposed according to the observation distance. Subsequently, we detailed the mission process such that the manipulation tasks could be performed autonomously. To implement and verify the proposed method, we conducted three-dimensional (3D) simulations, water tank experiments, and sea trials. In the 3D simulation and water tank experiments, we evaluated the position control using a TD controller during a specific disturbance and performed an operational evaluation of the parent–child system. In the water tank, we performed the operation of the child robot with the tether length adjustment of the winch system and the manipulation task. In the sea trial, the predefined mission was successfully completed, which demonstrated the feasibility of properly operating both the robots. The results of the experiments demonstrated the high potential and capabilities of the proposed manipulation system.

Microstructure Turbulence Measurement in the Northern South China Sea from a Long-Range Hybrid AUV.

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10-10 to 4.18 × 10-7 W·kg-1. In the surface mixed layer, high values of ε (10-9∼10-8 W·kg-1) were observed toward the water surface. In the thermocline, ε was 10-9.5∼10-9 W·kg-1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations.

Stabilizer design for an under-actuated autonomous underwater vehicle in a descriptor model under unknown time delay and uncertainty

This paper focuses on autonomous underwater vehicle (AUV) stabilization in the nonlinear descriptor model, as well as some AUV limitations such as model uncertainty, singularity, saturation constraint, and time delay. The capability of the descriptor model to show the real model is more reasonable than the standard state-space model. Based on the constructed Lyapunov function method and applying the bilinear matrix inequalities technique, all of the constraints are handled by introducing the new theorem. This theorem aims to design a state feedback with the intent that the closed-loop system be admissible. Here, the results are less conservative than other approaches. This issue has not yet been fully addressed in the literature, especially on AUVs. Theorem achievement is implemented on new AUV descriptor model that is obtained and introduced here. This method covers both neutral and descriptor systems. Also, it can be generalized and applied to conventional AUVs or similar dynamics. Examples and simulation results illustrate the effectiveness of the proposed approach.

The future of autonomous underwater vehicle control

The future of autonomous underwater vehicle control

Admissibility analysis for autonomous underwater vehicle based on descriptor model with time-varying delay

This article investigates an enhanced optimal robust time-delay stabilizer for an autonomous underwater vehicle in the descriptor model. Time-delay, model uncertainty, and actuator saturation constraint are some practical challenges in autonomous underwater vehicle controller design. In this regard, an appropriate autonomous underwater vehicle descriptor model is obtained, and sufficient stabilization conditions are determined in the terms of linear matrix inequality. The obtained criterion guarantees the system to be regular, impulse-free, and stable. Meanwhile, the delay-dependent and rate-dependent conditions are taken into account. Furthermore, uncertainty and time-delay are time-variant. This method includes a tuning factor for practical design aspects and tradeoff among desired requirements. Also, as an essential general requirement in non-linear systems, the maximal estimate of the attraction domain is proposed as an optimization problem. Numerical examples and simulations illustrate that the proposed methods are effective and useful in less conservative results. The technique can be generalized and applied to the most conventional autonomous underwater vehicles.

A practical feedforward speed control system for autonomous underwater vehicles

The autonomy of any airborne, land borne or waterborne vehicle starts with controlling its speed. To achieve cruise speed control, the conventional approach is to use closed-loop feedback control systems that require high precision sensors. Underwater sensors are expensive due to harsh environment and corrosive properties of seawater. In this study, we propose a speed control system for autonomous underwater vehicles (AUVs) that closes the control loop via a feedforward mechanism, eliminating the need for these expensive sensors. The feedforward control is based on the recently developed self-propulsion estimation model which can accurately predict propeller rotation rate for conventional AUV forms. The model is first validated by comparing the predicted resistance and propeller rotation rate of DARPA Suboff with the experimental and numerical results published in the literature. After observing a good match, the feedforward control system is used to ensure that the AUV reaches a predetermined surge speed. Two different underwater vehicles are considered in presenting the results of this study: the DARPA Suboff and the Gavia AUV, which has real time measurements available in the literature. The feedforward control system developed in this study achieves the desired speed with negligible errors. Transient response analysis shows that the computer simulation results are in good agreement with experimental results for the Gavia AUV.

AUV Docking Method in a Confined Reservoir with Good Visibility

Underwater docking technology enables autonomous underwater vehicles (AUVs) to execute long-term observation missions by periodically recovering and recharging AUVs. The conventional AUV homing and docking operations utilize acoustic and optical sensors at different ranges relative to the docking station. However, this method cannot perform perfectly in confined water regions because of the acoustic reflection and multipath effect. Thus, this paper proposes a novel navigation system, which fuses downward-looking visual odometry and model-based velocity for homing, and recognizes and tracks the light marker for terminal docking, in order to overcome the defects of the conventional navigation method. The reservoir experiment result verifies the effectiveness of the proposed method and shows good potential to extended applications in underwater routine cruise.

Advantages of aquatic animals as models for bio-inspired drones over present AUV technology

Robotic systems are becoming more ubiquitous, whether on land, in the air, or in water. In the aquatic realm, aquatic drones including ROVs (remotely operated vehicles) and AUVs (autonomous underwater vehicles) have opened new opportunities to investigate the ocean depths. However, these technologies have limitations related to shipboard support, programing, and functionality in complex marine environments. A new form of AUV is being developed to become operational. These drones are based on animal designs and capabilities. Biological AUVs (BAUVs) promise to improve performance in the varied environments of the ocean. Comparison of animal swimming performance with conventional AUVs and BAUVs demonstrates that natural systems still have swimming capabilities beyond the current state of AUV technology. However, the performances of aquatic animals with respect to swimming speed, efficiency, maneuverability, and stealth can serve as benchmarks to direct the development of bio-inspired AUV technology with enhanced capabilities.

An Underwater Quadrotor Control with Wave-disturbance Compensation by a UKF

Abstract This paper proposes an unscented Kalman filter (UKF) with disturbance estimation for an underwater quadrotor control system by utilizing backstepping control. Autonomous underwater vehicles (AUVs) have been attracted attention to scientific and commercial applications. The tasks in those applications are such as surveys and inspections for various objects underwater in narrow space. In this study, a quadrotor type robot, in which high-performance results are obtained for aerial application, is regarded as AUVs. The quadrotor robot is a smaller system than general AUVs and has suitable merits for work in a narrow place. On the other hand, since the quadrotor system is small and light in weight, it is more susceptible to underwater waves than conventional AUVs. Therefore, consideration of a technique to suppress or to reject the influences of the waves in the control systems is a must. This paper proposes a UKF system including a second-order model of input disturbance for estimating the influence of waves and an accurate quadrotor state simultaneously. Additionally, the disturbance estimation performance assists in make robustness as its estimated disturbance is rejected to actual disturbance. Finally, the usefulness of the proposed system is shown via simulations of position control for the underwater quadrotor affected by a wave effect model.

Study on Maneuvering Motion Modeling of Small AUV

The maneuvering motion equations of AUVs (Autonomous Underwater Vehicles) are mostly appropriated and constructed from the field measurement on maneuverability in marine engineering. The applicability of the equations of motions applied to the conventional AUVs was confirmed for the NMRI small cruising AUV “mini-AUV” with 1.8m length developed at National Maritime Research Institute (NMRI) in Japan.

Creation of 3D Print Gel Actuator

United Nations set the goal to maintain the richness of the sea in SDGs. In Japan, they are aiming for broad spectrum and real time of ocean information collection. Various kinds of underwater exploration techniques have been developed. For instance, submersible research vehicles and autonomous underwater vehicle (AUV) have been used for observation of underwater conditions, in addition to the technique of fixed-point observation. However, such research vehicles and conventional AUV are difficult to control, are expensive, and are usually made with non-biodegradable materials such as metals. For this problem, we came up with the robot composed by only organic material. This idea realizes the recycling society. Jellyfish is the most efficient swimmers, traveling for long distance with saving energy by drifting in the ocean, its body can be decomposed after death, and safe for surrounding creatures. Therefore, we are developing the jellyfish-mimic AUV using a hydrogel. For designing a Jellyfish-mimic AUV robot, it is preferable to introduce a soft actuator driven by water pressure, as it requires low electric power and it is eco-friendly. Here, we report a 3D printing hydrogel hydraulically-driven soft actuator that can make a bending motion of umbrella-shaped bell of artificial Jellyfish. We utilized the Pneunets Bending Actuator for designing the actuator, and the detailed information of this actuator is shown in the website of Soft Robotics Toolkit (see https://softroboticstoolkit.com/book/pneunets-bending-actuator). We changed the parameters of 3D print speed and UV light power gel concentration when we make some gel actuators. In addition, we measured and evaluated these performances. Finally, we are making the robot to use it and be composed by only organic materials so that we can release many robots at the same time.

관성 항법 센서와 도킹 유도 센서를 융합한 무인잠수정의 도킹 유도 항법 알고리즘에 대한 연구

This paper describes a docking guidance navigation algorithm for autonomous underwater vehicles (AUVs). To dock an AUV to a docking station installed underwater, a set of inertial navigation sensors used for conventional AUV navigation and a set of docking guidance sensors for docking missions are used. A docking guidance sensor typically measures the relative distance and attitude between the AUV and the docking station. As many different sensors are used, a precise position and attitude estimation technique, considering both types of sensors, is needed. Therefore, we designed a serial filter chain for estimating the orientation, position, and relative distance. Considering the non-holonomic characteristics of an AUV in the underwater environment, we first estimated the attitude by separating the position and the attitude. Then, the position of the AUV was estimated on the basis of the estimated attitude. Finally, we estimated the relative distance from the docking station to the estimated AUV position. This paper contributes to the following topics: i) position and attitude estimation considering non-holonomic characteristics of AUVs: and ii) precision estimation algorithm for docking guidance using docking guidance sensors.

Diving Adaptive Position Tracking Control for Underwater Vehicles

This paper presents a robust position tracking control scheme for underwater vehicles moving in a vertical plane. The idea comes from the demand of underwater position tracking control for the newly borne Trans-media Aerial Underwater Vehicle (TMAUV). Although position control of a TMAUV is still within the scope of autonomous underwater vehicles (AUVs) control, it has new features. An underwater reference path for the TMAUV could be characterized by a strong maneuver that many assumptions in the conventional AUV controller design could not be employed. In this paper, a Lyapunov-based backstepping controller is developed for a nonlinear coupled input system releasing all constraints on the pitch angle, heave velocity, and angular velocity. Furthermore, neural networks and parameter estimation are employed to develop a robust controller in the presence of model uncertainties, parameter uncertainties, and external disturbances. This paper also solves the problem of adaptive estimation for the system parameters under the coupled input condition. Simulations are presented to demonstrate the feasibility and effectiveness.

A novel vectored thruster based on 3-RPS parallel manipulator for autonomous underwater vehicles

Autonomous underwater vehicles (AUVs), which serve as main tool platforms, have played an important role in underwater surveys in scientific, military, and commercial applications. However, conventional AUVs are unable to perform missions at zero or low forward speeds because the control surfaces are ineffective in this regime.This paper presents novel vectored-thruster AUVs based on a 3-RPS parallel manipulator; the performance of the AUVs at zero and low forward speeds is found to be effectively improved. The 3-RPS parallel manipulator used for the thrust-vectoring mechanism provides certain advantages, including high positioning accuracy, fast response and compact structure. Additionally, studies of the kinematics and dynamics of the thrust-vectoring mechanism have been performed through a theoretical analysis and numerical simulation. Meanwhile, a simplified kinematics method for the 3-RPS parallel manipulator is presented and verified in MATLAB. The analysis and numerical simulation of the thrust-vectoring mechanism prove the feasibility of the design. Using this novel thrust-vectoring mechanism based on the 3-RPS parallel manipulator, the AUVs obtain the ability to provide the motion required for thrust-vectoring propulsion effectively and efficiently.

Creation and Drive Evaluation of Jellyfish Type Autonomous Unmanned Submersible

Submersible research vehicles and autonomous underwater vehicle (AUV) have been used for observation of underwater conditions, in addition to the technique of fixed-point observation. However, such research vehicles and conventional AUV are difficult to control, are expensive, and are usually made with nonbiodegradable materials such as metals. In contrast, jellyfish is the most efficient swimmers, traveling for long distance with saving energy by drifting in the ocean, its body can be decomposed after death, and safe for surrounding creatures. Therefore, we are developing the jellyfish-mimic AUV. In this study, we report a silicone-based hydraulically-driven soft actuator that can make a bending motion of umbrella-shaped bell of artificial Jellyfish. The behavior of the actuator in salt water was evaluated by image analysis, and the shrinkage factors of gel robots were compared with that of real jellyfish. Consequently, we have concluded there is a possibility that this actuator can reproduce jellyfish movement.

3D Gel Printing for Jellyfish-Mimic Robot

Various kinds of underwater exploration techniques have been developed. For instance, submersible research vehicles and autonomous underwater vehicle (AUV) have been used for observation of underwater conditions, in addition to the technique of fixed-point observation. However, such research vehicles and conventional AUV are difficult to control, are expensive, and are usually made with non-biodegradable materials such as metals. In contrast, jellyfish is the most efficient swimmers, traveling for long distance with saving energy by drifting in the ocean, its body can be decomposed after death, and safe for surrounding creatures. Therefore, we are developing the jellyfish-mimic AUV using a hydrogel. For designing a Jellyfish-mimic AUV robot, it is preferable to introduce a soft actuator driven by water pressure, as it requires low electric power and it is eco-friendly. In this study, we prototyped a Jellyfish-AUV robot using a soft material and a soft actuator. While it is ideal to make a robot body with hydrogel it is difficult to make the actuator with hydrogel. Here, we report a silicone-based hydraulically-driven soft actuator that can make a bending motion of umbrella-shaped bell of artificial Jellyfish. We utilized the Pneunets Bending Actuator for designing the actuator, and the detailed information of this actuator is shown in the website of Soft Robotics Toolkit (see https://softroboticstoolkit.com/book/pneunets-bending-actuator). The actuator is composed of inflation parts, basis, and copy paper placed between them. We poured into the 3D printed mold made with polylactic acid (PLA) and preserved at room temperature for 4 h to cure the silicone parts (inflation parts and basis). Copy paper was sandwiched between inflation parts and basis. The size of copy paper was 30 mm × 5 mm. Then, we poured additional silicone resin to combine the parts. By inserting a toothpick into the mold, we made the insertion port of the silicon tube. Before curing, we removed the air bubbles for 20 minutes with a vacuum de-foaming device. Finally, we inserted a silicon tube into the fuselage and attached a syringe for air supply. The behavior of the actuator in salt water was evaluated by image analysis, and the shrinkage factors of gel robots were compared with that of real jellyfish. The results were obtained as shown in Figs.1, 2 and 3. The shrinkage ratio of the jellyfish robot was 46.4 % at the maximum in the case of air injection of 2.8 cm³. The ratio did not reach 56.3 % at the maximum shrinkage ratio of the real jellyfish. To achieve the 56.3 % shrinkage ratio, we have to improve the maximum volume of injection air. Consequently, we have concluded there is a possibility that this actuator can reproduce jellyfish movement.

An autonomous underwater vehicle as an underwater glider and its depth control

To provide a conventional autonomous underwater vehicle with gliding capability, we assume a moving battery and a buoyancy bag installed in a torpedo shaped autonomous underwater vehicle. We develop a mathematical model for the underwater vehicle and derive a stable gliding condition for it. Then an LQR controller is designed to control the zigzag depth of the vehicle, where the derived gliding condition is used as set-points of the control system. For control efforts in the gliding movement, the changes in the center of gravity and the net buoyancy are used, but neither thruster nor rudders are used. By using the gliding capability, the underwater vehicle can move to a farther location silently with less energy consumption and then start operating as a normal autonomous underwater vehicle. We show the feasibility of the proposed method by simulations using Matlab/Simulink.

A hybrid-driven underwater glider model, hydrodynamics estimation, and an analysis of the motion control

An autonomous hybrid-driven glider is a new class of autonomous underwater glider that integrates the concept of a buoyancy-driven underwater glider and a conventional autonomous underwater vehicle (AUV). This glider has multi-functionality that enables it to overcome the speed and maneuverability limitations of buoyancy-driven gliders. Thus, this paper presents a mathematical model of the hybrid-driven glider, an estimation of the hydrodynamics and an analysis of the motion control. A Newtonian approach has been used to model the glider under the influence of water current. In addition, the hydrodynamics were estimated by using a Strip theory and a computational fluid dynamic (CFD). In order to analyze the motion of the glider, a Neural Network Predictive Control (NNPC) has been designed and its performance has been compared with the Model Predictive Control (MPC) and Linear Quadratic Regulator (LQR). The simulation results demonstrated that the Neural Network Predictive Control (NNPC) produced better control performance than the performance of the MPC and LQR when dealing with disturbances. In addition, the results also demonstrate the hydrodynamic response of the glider over the velocity, angle of attack and sideslip angle.

Motion Analysis of a Manta Robot for Underwater Exploration by Propulsive Experiments and the Design of Central Pattern Generator

Although, Autonomous Underwater Vehicles (AUVs) used for investigating underwater ecology have attracted the attention of underwater researchers, conventional AUVs moved underwater by screw propellers generate loud noise thatmay disturb the underwater environments and inhabitants to be observed. This paper discusses the development of an AUV that mimics the manta ray. Central Pattern Generators (CPGs) are also proposed to generate the motion of pectoral fins for Manta robot. The practicality of the robot is checked in underwater propulsion experiments, and the effectiveness of the proposed motion generation method is demonstrated in numerical simulations.

Armless underwater manipulation using a small deployable agent vehicle connected by a smart cable

Conventional underwater manipulation is performed by a remotely operated vehicle (ROV) equipped with a rigidly connected multi-link arm. However, accurate manipulation requires the ROV to have excellent maneuverability, which limits the design flexibility and capabilities of the vehicle. This paper instead proposes the use of a small, deployable, and highly maneuverable agent ROV as an end effector, which is connected to the main vehicle by a flexible smart cable. This cable tracks the relative position of the agent, thus eliminating the need for additional positioning sensors and allowing significant size reduction for the agent. In addition, to compensate for the limited lifting capability of the small agent, it is equipped with active buoyancy control. The proposed system can be applied to common autonomous underwater vehicles (AUVs) with minimal modification for coarse station-keeping. The whole system is operated as a conventional AUV under normal operating conditions, but the agent is deployed when manipulation or precise monitoring is necessary. Numerical simulations were performed for dynamic analysis and prototype design of the agent vehicle, and this design was implemented as a model-scale system for experiments in a test tank. This implementation confirmed the feasibility and potential capabilities of the proposed manipulation system concept.