Control Of Underwater Vehicle-manipulator Systems Research Articles

Model-free control of underwater vehicle-manipulator system interacting with unknown environments

The underwater vehicle-manipulator (UVM) interaction tasks require that UVM can adapt to different environments and have good stability properties. However, the complicated structures of UVM and uncertainties of the environment lead to poor interaction. In addition, transient performance related to overshoot and convergence is required during the interaction to ensure the safety of the UVM and environment. In this paper, an inner-loop/outer-loop control formulation is developed for underwater vehicle-manipulator interacting with environment, subject to unknown system and environment dynamic. For the inner-loop, an approximation-free state feedback controller is designed for UVM system without a prior knowledge of dynamics, capable of guaranteeing trajectory tracking with prescribed performance. A prescribed function is constructed, which allows the convergence time and convergence accuracy to be predetermined. Moreover, it is independent of the initial conditions. For the outer-loop, an off-policy reinforcement learning algorithm is presented to optimize the parameters of the admittance model without requiring the information of environment dynamic. The proposed admittance optimization is feasible for arbitrary desired trajectory. Finally, simulation and experimental results validate the effectiveness of the proposed model-free tracking controller.

Adaptive sliding mode tracking control of underwater vehicle-manipulator systems considering dynamic disturbance

This paper proposes an adaptive sliding mode tracking control method with a nonlinear disturbance observer (NDO-ASMTC) to solve the trajectory tracking problem of the underwater vehicle-manipulator system (UVMS) in the presence of large dynamic uncertainties and severe external disturbances. The proposed NDO-ASMTC method employs an adaptive control law, an improved fractional-order sliding mode, and a nonlinear disturbance observer to achieve excellent tracking performance of the UVMS. To obtain a fast response speed in the sliding mode phase and eliminate static error in the reaching phase, a modified fractional-order sliding mode control scheme is proposed. An adaptive auto-tuning law of switching gains is presented to overcome the problem that the fixed switching gain may lead to obvious tracking performance degradation under lumped uncertainty. In addition, a nonlinear disturbance observer is implemented to maintain the robustness and stability of the control scheme under severe disturbances. Moreover, the proposed adaptive control scheme has been proved to be stable using the Lyapunov theorem. Simulations and experiments show that the proposed control scheme can meet the design requirements of the UVMS in terms of tracking accuracy, system stability, and interference attenuation under the application of external disturbances.

Cooperative Control of Underwater Vehicle-Manipulator Systems Based on the SDC Method.

The paper considers the problem of cooperative control synthesis for a complex of underwater vehicle–manipulator systems (UVMS) to perform the work of moving a cargo along a given trajectory. Here, we used the approach based on the representation of nonlinear dynamics models in the form of state space with state-dependent coefficients (SDC-form). That allowed us to apply methods of suboptimal control with feedback based on the state-dependent differential Riccati equation (SDDRE) solution at a finite time interval, providing the change in control intensity with the transient effect of the system matrices in SDC form. The paper reveals two approaches to system implementation: a general controller for the whole system and a set of independent subcontrollers for UVMSs. The results of both approaches are similar; however, for the systems with a small number of manipulators, the common structure is recommended, and for the systems with a large number of manipulators, the approach with independent subcontrollers may be more acceptable. The proposed method of cooperative control was tested on the task of cooperative control for two UVMSs with six-link manipulators Orion 7R. The simulation results are presented in the article and show the effectiveness of the proposed method.

Evaluation of Dynamic Coupling Intensity and Passive Attitude Control of Underwater Vehicle-Manipulator Systems

In the future, underwater manipulation tasks are intended to be performed by moving base robots, namely Underwater Vehicle-Manipulator Systems (UVMSs). However, the manipulation task induces reaction forces and torques on the underwater vehicle, affecting its positioning. Therefore, it is necessary to compensate for these disturbances to perform the coordinated control of the UVMS or the station keeping of the underwater vehicle. For this sake, this paper presents a new methodology to evaluate the intensity of the dynamic coupling as a function of the working frequency of the manipulator. With such information will be possible to predict the frequency range in which the dynamic coupling is significant. Also, this approach could be used on the task planning level to produce dynamically feasible reference trajectories, improving the control performance. Beyond the identification of a safe frequency range, the obtained results also provide interesting insights about the dynamic coupling influence for the attitude Degrees of Freedom (DoFs) of the underwater vehicle, which can be related to results reported in previous works. Moreover, motivated by the results obtained here and the originality of this application, a passive control is synthesized for the attitude of UVMSs. The simulation results show good attenuation for the pitch oscillations with the proposed control.

Motion Planning and Coordinated Control of Underwater Vehicle-Manipulator Systems with Inertial Delay Control and Fuzzy Compensator

This paper presents new motion planning and robust coordinated control schemes for trajectory tracking of the underwater vehicle-manipulator system (UVMS) subjected to model uncertainties, time-varying external disturbances, payload and sensory noises. A redundancy resolution technique with a new secondary task and nonlinear function is proposed to generate trajectories for the vehicle and manipulator. In this way, the vehicle attitude and manipulator position are aligned in such a way that the interactive forces are reduced. To resist sensory measurement noises, an extended Kalman filter (EKF) is utilized to estimate the UVMS states. Using these estimates, a tracking controller based on feedback Linearization with both the joint-space and task-space tracking errors is proposed. Moreover, the inertial delay control (IDC) is incorporated in the proposed control scheme to estimate the lumped uncertainties and disturbances. In addition, a fuzzy compensator based on these estimates via IDC is introduced for reducing the undesired effects of perturbations. Trajectory tracking tasks on a five-degrees-of-freedom (5-DOF) underwater vehicle equipped with a 3-DOF manipulator are numerically simulated. The comparative results demonstrate the performance of the proposed controller in terms of tracking errors, energy consumption and robustness against uncertainties and disturbances.

Model reference sliding mode control of underwater vehicle-manipulator systems

UVMS consisting of the underwater vehicle and underwater manipulator is a dynamically coupled system. The movement of the underwater manipulator has a great impact on the stability of the underwater vehicle. A control scheme combining robust feedback control of the vehicle and feed forward compensation of the manipulator is proposed. First, the dynamic modelling of UVMS by Newton-Euler method is presented and used to obtain compensation. And then, we designed a sliding mode controller with the compensation. Finally, computer physics simulations are performed to investigate the effectiveness of this scheme in stability.

Joint space tracking control of underwater vehicle-manipulator systems using continuous nonsingular fast terminal sliding mode

To ensure satisfactory control performance for the underwater vehicle-manipulator systems, a novel continuous nonsingular fast terminal sliding mode controller is proposed and investigated using time delay estimation in this article. Complex lumped unknown dynamics including the strong nonlinear couplings and external disturbance are properly compensated with time delay estimation, which are mainly based on the time-delayed signals of underwater vehicle-manipulator systems and can provide with a fascinating model-free feature. Afterwards, the satisfactory tracking control performance and good robustness under heavy lumped uncertainties are ensured using the continuous nonsingular fast terminal sliding mode term with a fast terminal sliding mode–type reaching law. Therefore, the proposed controller is easy to use thanks to time delay estimation, and can ensure good control performance owing to continuous nonsingular fast terminal sliding mode. Stability of the closed-loop control system is analyzed using Lyapunov stability theory, and theoretical tracking errors are calculated and presented. Finally, the effectiveness and advantages of the proposed controller are demonstrated through comparative 7-degree-of-freedom pool experiments.

Adaptive control of underwater vehicle-manipulator systems using radial basis function networks

This paper deals with a control scheme for underwater vehicle-manipulator systems with the dynamics of thrusters in the presence of uncertainties in system parameters. We have developed two controllers that overcome thruster nonlinearities, which cause an uncontrollable system: one is a regressor-based adaptive controller and the other is a robust controller. However, the structure of the adaptive controller is very complex due to the feedforward terms including the regressors of dynamic system models, and the error feedback gains of the robust controller with a good control performance are excessively high due to the lack of feedforward terms. In this paper we develop an adaptive controller that uses radial basis function networks instead of the feedforward terms. The replacement leads to a moderately high gain controller whose structure is simpler than that of the regressor-based adaptive controller.

On the inverse kinematics of an underwater vehicle-manipulator system

The inverse kinematics plays an important role in the trajectory planning and the control of underwater vehicle-manipulator system. The solutions of this problem have an important influence on the motion quality of end-effectors. This paper presents an improved method based on the Jacobian matrix and the error feedback. By using this method, the accuracy of the solution of inverse kinematics for the vehicle-manipulator system is improved. In addition, one of the advantages of a redundant system is exploited to avoid impact on joint limitations. Numerical simulations in software Matlab are carried out to verify the efficiencies of the proposed method.

Neuro-fuzzy control of underwater vehicle-manipulator systems

This paper presents an intelligent controller for underwater vehicle-manipulator systems (UVMS) based on the neuro-fuzzy approach. The controller is composed of fuzzy PD control with membership function tuning by linguistic hedge. A neural network compensator approximates the dynamics of the UVMS in decentralized form. The new controller has the advantages of simplicity of implementation due to decentralized design, precision, and robustness to payload variations and hydrodynamic disturbances. It has significantly low energy consumption compared to both the conventional PD and conventional fuzzy control methods. The effectiveness of the proposed controller is illustrated by results of simulations for a six degrees of freedom autonomous underwater vehicle with a three degrees of freedom on-board manipulator.

Underwater Robots: Motion and Force Control of Vehicle-Manipulator Systems (G. Antonelli; 2006) [Book Review

This book covers the area of robot control while addressing the additional challenges of a mobile platform (the underwater vehicle) and considers the difficulties and adversity related to the underwater environment. Some of the topics covered include: a discussion on the state of underwater vehicle technology; modeling of underwater vehicle/manipulator systems (UVMs); a survey of existing control algorithms for autonomous underwater vehicles (AUVs); fault detection and tolerance strategies for underwater vehicles; experimental results on both control and fault tolerance to thruster faults; the kinematics, dynamics, and interaction control for UVMs; and coordinated control of a platoon of AUVs. This book does an excellent job presenting many of the issues related to the modeling and control of UVMs. The number of references is impressive, and most of the work in the field that any researcher would need to consult for a deeper understanding of the state of the art is included.

Motion Control of underwater vehicle-manipulator systems using feedback linearization

In this paper control of underwater vehicle-manipulator systems using feedback linearization has been studied. Performance, robustness and energy consumption of the system depend on the choice of output variables, these output variables can be chosen in several ways. In this paper two alternatives have been analysed by simulations, decoupling of the manipulator end-effector velocities from the -vehicle velocities and from the -total system momentum. The performance is almost the same for the two choices of decoupling schemes while robustness and energy consumption of the system depend on the accuracy of the dynamic model.