Underwater Robotic Manipulator Research Articles

Trajectory control and optimization of PID controller parameters for dual-arms with a single-link underwater robot manipulator

ABSTRACT This paper focuses on the modeling, simulation, and control of the trajectories of a dual-arm single-link underwater robot manipulator (DS-URM), having dual arms (left and right) with a single link each. The dynamic coupling between the base and the dual arms makes trajectory control of the end effector difficult. This study attempts to simulate and control dual arms with a single-link underwater robotic manipulator using a hybrid controller. To reduce the error for a sinusoidal wave and a cycloid trajectory, a hybrid controller is the combination of the Proportional-Integral-Derivative (PID) controller and overwhelm controller. The underwater dynamic’s buoyancy, gravity, and hydrostatic forces acting on the underwater robot are modeled in an integrated SIMULINK model, including the DS-URM. The DS-URM has been investigated, revealing some significant trajectories of the left and right tips. Effective tuning methods include Ziegler-Nicholas (Z-N), genetic algorithms, Ant Colony Optimization (ACO), and Particle Swarm Optimization (PSO). The Integral of Time multiplied by Absolute Error (ITAE) criteria has been used to improve trajectory tracking via particle swarm optimization. Results show significant improvements in trajectory tracking, with ITAE error reduction by 96.44% and 98.6% for left and right arms, respectively, achieving stability in 0.000645s.

Uncertainty and velocity observer-based predefined-time nonsingular terminal sliding mode control of the underwater robot manipulators

This paper introduces an observer-based predefined-time nonsingular terminal sliding mode control to the position tracking control of the n-degree-of-freedoms underwater robot manipulators subject to the uncertainty compensation and sensor reduction. The proposed sliding surface has only the sliding phase, while the reaching phase is eliminated using a continuous augmented function. Besides, the sliding phase is predefined-time, where it is independent of the initial conditions and control parameters. As a result, it has led to the development of a predefined-time control scheme, in which not only its convergence time is fast, but also (due to the elimination of the reaching phase) the effect of uncertainties in this phase is eliminated. Naturally, there is a wide range of uncertainties such as structured-unstructured uncertainties and/or un-modeled dynamics, ocean current, waves, etc., in the underwater robot manipulators and underwater conditions. Therefore, the proposed predefined-time nonsingular terminal sliding mode control is combined with a finite-time observer to estimate the underwater robot manipulator's joint velocity and eliminate the destructive effect of existing uncertainties. Under this combination, the stability analysis could guarantee predefined-time global asymptotic stability of the system in the presence of existing uncertainties. Simulation results are conducted on a 2-link underwater robot manipulator to validate the proposal.

Enhancing Underwater Robot Manipulators with a Hybrid Sliding Mode Controller and Neural-Fuzzy Algorithm

The sliding mode controller stands out for its exceptional stability, even when the system experiences noise or undergoes time-varying parameter changes. However, designing a sliding mode controller necessitates precise knowledge of the object’s exact model, which is often unattainable in practical scenarios. Furthermore, if the sliding control law’s amplitude becomes excessive, it can lead to undesirable chattering phenomena near the sliding surface. This article presents a new method that uses a special kind of computer program (Radial Basis Function Neural Network) to quickly calculate complex relationships in a robot’s control system. This calculation is combined with a technique called Sliding Mode Control, and Fuzzy Logic is used to measure the size of the control action, all while making sure the system stays stable using Lyapunov stability theory. We tested this new method on a robot arm that can move in three different ways at the same time, showing that it can handle complex, multiple-input, multiple-output systems. In addition, applying LPV combined with Kalman helps reduce noise and the system operates more stably. The manipulator’s response under this controller exhibits controlled overshoot (Rad), with a rise time of approximately 5 ± 3% seconds and a settling error of around 1%. These control results are rigorously validated through simulations conducted using MATLAB/Simulink software version 2022b. This research contributes to the advancement of control strategies for robotic manipulators, offering improved stability and adaptability in scenarios where precise system modeling is challenging.

Application of Adaptive and Switching Control for Contact Maintenance of a Robotic Vehicle-Manipulator System for Underwater Asset Inspection.

The aim of this study is to design an adaptive controller for the hard contact interaction problem of underwater vehicle-manipulator systems (UVMS) to realize asset inspection through physical interaction. The proposed approach consists of a force and position controller in the operational space of the end effector of the robot manipulator mounted on an underwater vehicle. The force tracking algorithm keeps the end effector perpendicular to the unknown surface of the asset and the position tracking algorithm makes it follow a desired trajectory on the surface. The challenging problem in such a system is to maintain the end effector of the manipulator in continuous and stable contact with the unknown surface in the presence of disturbances and reaction forces that constantly move the floating robot base in an unexpected manner. The main contribution of the proposed controller is the development of the adaptive force tracking control algorithm based on switching actions between contact and noncontact states. When the end effector loses contact with the surface, a velocity feed-forward augmented impedance controller is activated to rapidly regain contact interaction by generating a desired position profile whose speed is adjusted depending on the time and the point where the contact was lost. Once the contact interaction is reestablished, a dynamic adaptive damping-based admittance controller is operated for fast adaptation and continuous stable force tracking. To validate the proposed controller, we conducted experiments with a land robotic setup composed of a 6 degrees of freedom (DOF) Stewart Platform imitating an underwater vehicle and a 7 DOF KUKA IIWA robotic arm imitating the underwater robot manipulator attached to the vehicle. The proposed scheme significantly increases the contact time under realistic disturbances, in comparison to our former controllers without an adaptive control scheme. We have demonstrated the superior performance of the current controller with experiments and quantified measures.

An adaptive data-driven controller for underwater manipulators with variable payload

The underwater environment poses a complex problem for developing control systems for underwater manipulators. Modeling the system is a complicated and costly process due to the highly nonlinear dynamics and the presence of unknown hydrodynamical effects. Furthermore, manipulators are usually deployed on Autonomous Underwater Vehicles (AUVs) which further influence and change the dynamics of the arm. This is aggravated in underwater operations where manipulating different objects is necessary. These diverse manipulation tasks introduce external disturbances to the system and can lead to a fast degradation of the control system performance. In this article, we propose a novel adaptive controller for underwater robot manipulators that have to handle varying payloads with different masses, geometries, and buoyant forces. The proposed control strategy utilizes a data-driven model of the system in an optimal control formulation based on neural networks. Moreover, we developed an online tuning strategy, based on the adaptive interaction theory, which allows the gains of the controller to be updated online with respect to a set of performance metrics. Experiments were performed with the robotic arm manipulating a variety of payloads while mounted on both a fixed base and a free-floating vehicle. We present a number of simulated and experimental results that illustrate the benefits of the proposed strategy. In addition, a comparative study against a classical Model Predictive Control (MPC) demonstrates the benefits of our adaptive proposal.

A Novel Continuous Nonsingular Finite–Time Control for Underwater Robot Manipulators

In this paper, the tracking control problem of underwater robot manipulators is investigated under the influence of the lumped disturbances, including unknown ocean current disturbances and parameter uncertainties. The proposed novel continuous nonsingular finite–time (CNFT) control method is twofold. Firstly, the modified adaptive super–twisting algorithm (ASTA) is proposed with a nonsingular fast terminal sliding mode (NFTSM) manifold to guarantee the finite–time convergence both in the sliding mode phase and the reaching phase. Secondly, a higher–order super–twisting disturbance observer (HOSTDO) is exploited to attenuate the effects of the lumped disturbances. Considering the time–varying gain matrix of the closed–loop control system, the bounded stability is strictly proved via the Lyapunov theory. Hence, the superiority of the proposed controller is singularity–free, fast convergence, chattering–free, high steady–state tracking performance, and good robustness by resorting to the methods of CNFT control and ASTA in combination with a disturbance observer. Finally, numerical simulations are conducted on a two degree–of–freedom (DOF) underwater robot manipulator to demonstrate the effectiveness and high tracking performance of the designed controller.

A novel U-shaped piezoelectric actuator for underwater robotic finger

In order to reduce the structural complexity of underwater robotic manipulators using electric and hydraulic driving techniques, a novel U-shaped piezoelectric actuator is proposed for underwater robotic finger in this study. Without complicated equipment to protect the piezoelectric actuators from water ingress, the robotic finger can adopt an open configuration in underwater environment, effectively reducing structural complexity. Firstly, the elitist non-dominated sorting genetic algorithm II is used to determine the geometric parameters of the U-shaped piezoelectric actuator, to satisfy a tradeoff between the frequency difference of two operation modes and amplitudes of the piezoelectric actuator. Then prototypes of the U-shaped piezoelectric actuator are manufactured and articulated to construct a robotic finger. Finally, experimental investigation is carried out to evaluate mechanical performances of the robotic finger prototype. Experimental results indicate that the angular velocity and stalling torque of the finger prototype in water are 304 deg s−1 and 13.9 mN · m under an excitation voltage of 500 Vpp, respectively.

An Underwater Robotic Manipulator with Soft Bladders and Compact Depth-Independent Actuation.

An underwater manipulator is essential for underwater robotic sampling and other service operations. Conventional rigid body underwater manipulators generally required substantial size and weight, leading to hindered general applications. Pioneering soft robotic underwater manipulators have defied this by offering dexterous and lightweight arms and grippers, but still requiring substantial actuation and control components to withstand the water pressure and achieving the desired dynamic performance. In this work, we propose a novel approach to underwater manipulator design and control, exploiting the unique characteristics of soft robots, with a hybrid structure (rigid frame+soft actuator) for improved rigidity and force output, a uniform actuator design allowing one compact hydraulic actuation system to drive all actuators, and a novel fully customizable soft bladder design that improves performances in multiple areas: (1) force output of the actuator is decoupled from the working depth, enabling wide working ranges; (2) all actuators are connected to the main hydraulic line without actuator-specific control loop, resulting in a very compact actuation system especially for high-dexterity cases; (3) dynamic responses were improved significantly compared with the counter system without bladder. A prototype soft manipulator with 4-DOFs, dual bladders, and 15 N payload was developed; the entire system (including actuation, control, and batteries) could be mounted onto a consumer-grade remotely operated vehicle, with depth-independent performances validated by various laboratory and field test results across various climatic and hydrographic conditions. Analytical models and validations of the proposed soft bladder design were also presented as a guideline for other applications.

Design and Implementation of Low Cost Manipulator Robot for Underwater Object Grasping Process

Various developments in the technologies over the industrial sectors, Robots are implemented to perform the several processes like picking and placing objects by using a human hand like structures. These robotic manipulators are mainly employed in the areas which are radioactive or hazardous or the place not accessible by the humans. It uses both direct pneumatics and inverse pneumatics. Underwater object or material grasping is a challenging task in these days. Here we are going to design and implement the robot manipulator at low-cost for object grasping process. The 3 DOF underwater robot manipulator can be developed by using the servo motors embedded in a mechanical setup. A camera based system is used to identify the objects to be grasped. These whole processes can be controlled by using Raspberry pi 3 as a central processor. The movement of the robot manipulator is controlled by using position control joystick through Internet of Things (IoT).

Adaptive Neural Network Control of Underwater Robotic Manipulators Tuned by a Genetic Algorithm

This paper describes a novel approach for the control of underwater robots that can handle uncertainties and disturbance problems, which are commonly met in underwater environments. The considered system is an underwater manipulator with n-degrees of freedom. The approximation capability of an adaptive neural network is exploited to estimate uncertainties in system dynamics. Drag and lift forces are considered as an external disturbance, and a disturbance observer approach which has been proved to be effective with on-land robotic systems, is applied to compensate for it. The objective of the controller designed is to track a desired trajectory. To find the optimal gain parameters of this controller, a classical Genetic Algorithm is employed. Extensive simulation studies carried out on a two degrees of freedom manipulator indicate the efficacy of the proposed approach, proving that the disturbance observer originally developed for on-land systems can also be used effectively for underwater robotic systems. Finally, the performance of the proposed controller, tuned by the Genetic Algorithm is compared with that of a controller, tuned manually. The results show that the reliance on a well-known classic Genetic Algorithm for the tuning of the controller parameters not only saves time, but also provides better values of the parameters.

A hybrid impedance control scheme for underwater welding robots with a passive foundation in the controller domain

A hybrid impedance control scheme for the force and position control of an end-effector is presented in this paper. The interaction of the end-effector is controlled using a passive foundation with compensation gain. For obtaining the steady state, a proportional–integral–derivative controller is tuned with an impedance controller. The hybrid impedance controller is implemented on a terrestrial (ground) single-arm robot manipulator. The modeling is done by creating a bond graph model and efficacy is substantiated through simulation results. Further, the hybrid impedance control scheme is applied on a two-link flexible arm underwater robot manipulator for welding applications. Underwater conditions, such as hydrodynamic forces, buoyancy forces, and other disturbances, are considered in the modeling. During interaction, the minimum distance from the virtual wall is maintained. A simulation study is carried out, which reveals some effective stability of the system.

Recent Developments in Modeling and Control of Underwater Robot Manipulator: A Review

Objective: The ocean resources and scientific related research is an attractive research topic. To witness a significant development of an intelligent robotic underwater work system, it is necessary to present various technological advancements in this area in form of technical review. Methods/Statistical Analysis: In this direction, authors provide a comprehensive assessment of recent developments of underwater robots and their various control strategies. This review highlights the different control techniques of underwater robots, which have been investigated for overall control of underwater robots. These controls include motion control, trajectory control of end-effect or for the underwater robot manipulators, thrust control and force control. Finding: Various control strategies have been developed and employed by researchers such as adaptive control, PID control, Sliding Mode Control (SMC), robust/optimal control, and robust overwhelming control. The literature survey has further emphasized the use of such controllers for motion, thrust and force control in underwater robotic conditions. Application: This article will be beneficial for researchers in this area to understand various applications of underwater robots. Another focus of this paper is to provide a candid commentary on modeling and simulation techniques adopted by various researchers in the area of underwater robots.

Some Considerations on an Underwater Robotic Manipulator Subjected to the Environmental Disturbances Caused by Water Current

Abstract The objective of this paper is to discuss some of the issues associated with environmental load on the three-link serial manipulator caused by underwater current. We have conducted CFD simulations to investigate hydrodynamic effects induced by changing current direction and changing with time current speed in order to better understand the physics of the problem. The results are presented in terms of moments of hydrodynamic forces plotted against relative position of the current and the robotic arm. Time history of hydrodynamic loads according to periodically changing current speed is presented and discussed.

Preliminary Study of Hydrodynamic Load on an Underwater Robotic Manipulator

Preliminary Study of Hydrodynamic Load on an Underwater Robotic Manipulator

Design of an underwater robot manipulator for a telerobotic system

SUMMARYThis paper describes a telerobotic system used for manipulation tasks in underwater environments. The telerobotic system is composed of a robotic arm of 3 degrees of freedom. This robotic arm has been designed to support corrosion environments such as seawater or freshwater. The prototype is designed to support several types of perturbations such as ocean currents and high pressures. The main objective is to efficiently control a teleoperation task considering common perturbations present in deep water. Finally, this paper presents the design, modelling and experiments of the underwater telerobotic system.

Adaptive VSS Control with Deformable Sliding Surfaces for Underwater Robot Manipulator Drives

the paper is devoted to new adaptive variable-structure system (VSS) control algorithms and their applications in underwater robotics. Variable-structure systems (VSS) are known as a class of nonlinear systems with discontinuous control. One of the most attractive features of VSS is availability of sliding mode. System dynamics in sliding mode can be robust to parametric uncertainties. Adaptive control is also available in VSS. Simulations of underwater robot drives control with derived adaptive VSS algorithms confirmed their high efficiency.

Optimal Trajectory of Underwater Manipulator Using Adjoint Variable Method for Reducing Drag

In order to decrease the fluid drag on an underwater robot manipulator, an optimal trajectory method based on the variational method is presented. By introducing the adjoint variables, which are Lagrange multipliers, we formulate a Lagrange function under certain constraints related to the target angle, target angular velocity, and dynamic equation of the robot manipulator. The state equation (the partial differentiation of the Lagrange function with respect to the state variables), adjoint equation (the partial differentiation of the Lagrange function with respect to the adjoint variables), and sensitivity equation (the partial differentiation of the Lagrange function with respect to torques) can be derived from the stationary conditions of the Lagrange function. Using the state equation, we can calculate the state variables (angles, angular velocities, and angular acceleration) at every time step in the forward time direction. These state variables are stored as data at every time step. Next, by using the adjoint equation, we can calculate the adjoint variables by using these state variables at every time step in the backward time direction. These adjoint variables are stored as data at every time step. Third, the sensitivity equation is calculated by using both the state variables and the adjoint variables. Finally, the optimal trajectory of the manipulator is obtained using the sensitivities. The proposed method is applied to the problem of two-link manipulators. It can obtain the optimal drag reduction trajectory of the manipulator under the constraints mentioned above.

A Potential 4-D Fingertip Force Sensor for an Underwater Robot Manipulator

The latest generation of underwater robots employ manipulators without force sensors. Accordingly, this paper presents a novel 4-D fingertip force sensor based on an E-type membrane for underwater robot manipulators. Specifically, this sensor is aimed at obtaining the accurate interaction force between underwater robot manipulators and other objects. Moreover, a seal technique and natural pressure compensation for the sensor are also described. The experimental results demonstrate strong linearity, high sensitivity, and weak couplings.

SYMBOLIC SYNTHESIS OF CONTROL LAWS FOR UNDERWATER VEHICLE AND ROBOT MANIPULATOR

This paper deals with the problem of the automation of design procedures for nonlinear control systems. As an example the procedure has been realized for the well-known technique consisting of the exact linearization via nonlinear feedback. The developed software achieves the synthesis of control laws in symbolical form that is convenient for further analysis, modeling, and practical implementation of the system. Examples of the software application to underwater vehicle and robot manipulator are given and discussed.

2P1-2F-A7 水中ロボットマニピュレータの学習制御と時間軸変換を利用した運動計画の実現方法

水中では複雑な構造体の動力学パラメータを推定して, 運動計画を行なうことが一般的に困難である。本研究では, 学習制御と時間軸変換を行なうことで, 水中ロボットマニピュレータの複雑な動力学を推定することなく, 適切な運動計画と入力トルクの生成を実現する手法について考察する。