Underwater Manipulator System Research Articles

The Adaptive Bilateral Control of Underwater Manipulator Teleoperation System with Uncertain Parameters and External Disturbance

A novel self-adaptive bilateral control strategy is introduced to manage uncertainties inherent in the teleoperation of an underwater manipulator system effectively. In response to uncertainties stemming from both the mathematical model and external disturbances, our approach offers innovative solutions. Firstly, to address uncertainties in the master model parameters, we propose a reference adaptive impedance control based on a nominal model. This control strategy dynamically adjusts the reference position of the desired model, leveraging adaptive control laws to compensate for model uncertainties. Additionally, to tackle uncertainties specific to the slave manipulator, we employ adaptive compensation using radial basis function (RBF) networks. Our unique combination of sliding mode variable structure controllers and robust adaptive controllers aims to mitigate approximation errors, ensuring precise tracking of the master manipulator’s position by the slave manipulator. By employing Lyapunov function analysis, we demonstrate the system’s superior tracking performance and global stability, with assured asymptotic convergence for force–position tracking. Through comprehensive experimentation, our results showcase the exceptional force–position tracking capabilities of the overall control system, even under challenging conditions of model uncertainties and external disturbances. Moreover, our system exhibits remarkable stability, reliability, and robustness, underscoring the effectiveness of our proposed adaptive control approach.

Underwater manipulator that imitates the movements of the human arm

In this paper, the design of a five degrees of freedom (5DoF) underwater manipulator system is presented and discussed. The forward and inverse kinematics problem are solved and shown. Additionally, a system that mimics the human arm movements using a manipulator is proposed. In order to imitate the movement of the human arm, the layout diagram of the IMU sensors and the method of first calibration were presented. The work also presents a device with a simple haptic feedback used to facilitate control of the gripper. The presented approach to the design of a robot control system is dedicated to an underwater robot with the main assumption of reducing the complexity of the system. Taking into account the authors’ knowledge, this approach distinguishes the presented system from solutions known from the literature.

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.

Research on Underwater Manipulator Control Based on HJI Theory and RBF Neural Network

Aiming at the influence of the underwater complex working environment on the control performance of the manipulator, and the traditional manipulator control method is not effective, a new method based on HJI (Hamilton-Jacobi Inequality) theory and RBF (radial basis function) neural network is proposed. The intelligent controller to realize the stable control of the underwater manipulator. Considering the influence of various additional forces on the manipulator in the underwater environment, the Lagrange method is used to establish the dynamic model of the underwater manipulator. Then the robust conditions of HJI differential inequality are used to ensure the stability of the control system, and the stability of the underwater manipulator system is verified by the Lyapunov stability theory. Finally, MATLAB/Simulink is used to simulate the control of the manipulator. The simulation results verify the effectiveness of the method and can realize the stable control of the underwater manipulator system.

Kinematics Model of the 6-DOF Underwater Manipulator and Control System Design Based on PLC Technology

The paper introduces kinematics analysis for a kind of 6 degrees of freedom underwater manipulator. Firstly, kinematics model was established based on D-H principle; The solving process of kinematics direct solution and inverse solution of manipulator was presented. Secondly, Numerical simulation is performed based on ADAMS software, every joint speed and acceleration curve is obtained. The working principals and control requirement of underwater manipulator are illustrated; Based on kinematics modeling, the control system of manipulator was designed based on PLC and carried out the control the function of the manipulator.

A nonregressor nonlinear disturbance observer-based adaptive control scheme for an underwater manipulator

A new nonlinear disturbance observer-based tracking control scheme for an underwater manipulator is presented in this paper. This observer overcomes the disadvantages of existing disturbance observers, which are designed or analyzed by the linear system techniques. It can be applied in underwater manipulator systems for various purposes such as payload compensation, interaction effects compensation, underwater current or external disturbance compensation, and independent system control. The performance of the proposed tracking control scheme is demonstrated numerically by the payload compensation and interaction effects compensation for a two degrees of freedom vertical underwater manipulator.

Manipulation in the Seabed: A New Underwater Manipulation System for Shallow Water Intervention

In this paper the hardware architecture of a new Underwater Manipulation System is presented, which includes details about the design of the mechanical components, as well as the electronics that control the manipulation tasks, such as the PC104 ROS (Robotic Operating System) enabled server, an Arduino manager of the power consumption of the arm, and an underwater camera included in the visual servoing loop for manipulation.The manipulation system is integrated into the Girona 500 AUV, providing a complete system that can be operated via a network from the ground base station. The paper describes this system architecture, which is the purpose of the ongoing FP7 TRIDENT project. Further work will focus of extending the experiments to a more realistic scenario in the sea. At the moment of writing the scientific team is performing this integration in the northern coast of Spain.

Positioning of a Flexible Rotating Arm in Water using Sliding Mode Control and Optimal Control.

A controller for the manipulator of an underwater robot must position it speedily and accurately, even when it grips an unknown body. In addition, an underwater manipulator system is nonlinear. Therefore, a sliding mode control is suitable, because it has robustness and is able to deal with nonlinear systems. However, chatter due to switching delay of input is a serious problem. In this study, a discrete-time sliding mode control, which is able to suppress the chatter, is applied to the positioning controller of a flexible rotating arm in water driven by a thruster. However, it is found that stable equivalent control cannot be obtained. Therefore a positioning controller is developed using a combination of discrete-time sliding mode control and optimal control. The hyperplane is defined by the feedback gain of optimal control, and the equivalent control is replaced by the optimal control. Then, positioning experiments are carrried out. The performance of the developed controller is confirmed.

Design issues for underwater manipulator systems

Underwater manipulators have developed from the crude grabbers first fitted to submersibles in the 1970s to become advanced systems capable of a diverse range of tasks, operating dependably in a hostile and unstructured environment. However, many difficulties still exist in this field and new manipulators with enhanced capabilities, particularly in terms of intelligent control, will be required within the next few years if the efforts to replace the diver are to continue to advance. The wide range of technologies embodied in manipulator systems, together with inherent non-quantifiable and human factors considerations, necessitates a mechatronics approach to design for all but the crudest of arms. Many of the design criteria for underwater systems contrast sharply with those in the better known industrial robotics context. This paper provides an overview of underwater manipulator technology, and discusses the broad range of design problems associated with subsea operation which must be considered for any new design.