Santhakumar Mohan

Task space-based control of an underwater robotic system for position keeping in ocean currents

For an underwater vehicle-manipulator system, which consists of an underwater vehicle equipped with a manipulator, it is important to regulate the position of the manipulator’s end-effector with respect to a given target position in many interactive operations. This paper presents a task space-based approach for designing a controller that ensures that the end-effector of an underwater vehicle-manipulator system maintains its position in the presence of unknown ocean currents and uncertainties without the explicit use of a disturbance observer. A feedback linearizing control in task coordinates is used, and an extended Kalman filter (EKF) is employed as a state observer. The proposed approach can also be applied to dynamic positioning or controlled weathervaning of a surface ship whose motion is affected by environmental disturbances. To demonstrate the validity and effectiveness of the proposed approach, numerical simulations and experimental tests were carried out and their results are shown. Graphical Abstract

Disturbance observer based terminal sliding mode control of an underwater manipulator

This paper addresses the issue of developing a robust and efficient controller for a manipulator for underwater applications by proposing a terminal sliding mode control scheme along with a disturbance observer and incorporating the same for 3-RRR serial spatial manipulator to ensure finite time convergence as asymptotic convergence in undesirable in underwater tasks like positioning and tracking of a trajectory. The performance of the proposed scheme is studied using extensive numerical simulations depicting practical circumstances with external disturbances and parameter uncertainties within the system. The capability of the control scheme to overcome hydrodynamic forces and moments including added mass effects, damping effects are extensively studied and validated for the control scheme. The dynamic modelling is done using the Euler-Lagrangian approach involving the energy associated with the system. The results are presented after analyzing the trajectory tracking capabilities of the manipulator in the presence of external disturbances and model uncertainties.

Dynamic Modelling, Simulation and Spatial Control of an Underwater Robot Equipped with a Planar Manipulator

This paper describes the dynamic modelling, simulation and control of an underwater vehicle equipped with two degrees of freedom (DOF) planar underwater manipulator with all its joints revolute. Performance analysis of underwater vehicle and manipulator tracking control in spatial co-ordinates are done using numerical simulations. A PID controller based feedback linearization control design is developed for the underwater vehicle and manipulator. Controlled movement in surge (x-direction), sway (y-direction) and heave (z-direction) directions is achieved for the underwater vehicle and controlled movement in x-z (global) plane is achieved for the underwater manipulator, both with respect to inertial frame of reference. Simulation of tracking control of the robot using cubic polynomial equation based trajectory planning is done.

Task space position tracking control of an autonomous underwater vehicle with four tilting thrusters

Underwater vehicles are usually designed with additional degrees of freedom than those required to accomplish given manipulator tasks. A robot platform should be effective to maintain its position and orientation in order to attain diverse underwater tasks. This study addresses the dynamic modeling of an autonomous underwater vehicle (AUV) which consists of tilting thrusters for hovering motion to oppose reaction force of the manipulator and ocean current. The suggested system consists of four tilting thrusters with six degrees-of-freedom (DOF). The tilting movements of the thrusters make the system unstable due to complex coupling. A robust position tracking controller is designed based on redundancy resolution scheme has been posited. The trajectory tracking potentiality of the manipulator has been analyzed. The numerical results of the proposed redundancy resolution scheme indicate that this approach shows a significantly revamped outcome when compared with the conventional counterpart.

Relative analysis of controller effectiveness for vertical plane control of an autonomous underwater vehicle

Control and guidance of Autonomous Underwater Vehicle (AUV) is tedious process as it is an underactuated model where the numbers of inputs to the actuator are less than the number of degrees-of-freedom to be controlled; also the dynamics of AUV is affected by internal interruptions like sensor noise and exterior distractions namely hydrodynamic effects and ocean current. The difficulty of uncertainty in the vehicle dynamics can be handled by adaptive control, chosen based on its clarity using conventional controller like Proportional-Integral-Derivative (PID) and also by intelligent Fuzzy Logic Control (FLC). To increase the quality of these autonomous systems, model-based control strategies such as Internal Model Control (IMC) and Model Predictive Control (MPC) has been focused in this paper. The control operation includes motion planning and trajectory generation tasks which provide the desired vehicle depth location as a function of time and subsequently the controller determines required stern angle position, based on the sensor measurements. The comparative result shows that Model based control strategies exhibits better performance than the classical controls.

Robust PID control for position tracking of an underwater manipulator

This article investigates a new robust nonlinear proportional integral derivative (PID) position tracking control applied on a serial underwater spatial manipulator with three degrees of freedom. The proposed controller integrates the known approximated inverse dynamic model output as a model-base portion of the controller. It uses a feed forward term to enhance the control activity with indulgence from known desired acceleration vector. The proposed control scheme carries an estimated perturbed term to compensate for the unknown effects namely external disturbances and unmodelled dynamics. Finally, it has a decoupled nonlinear PID controller as a feedback portion to enhance closed-loop stability and account for the estimation error of uncertainties. The usefulness and competency of the proposed approach are demonstrated with the help of numerical simulations.

Design Optimization and Accuracy Analysis of a Planar 2PRP-PRR Parallel Manipulator

This paper addresses the dimensional synthesis and design optimization of a three-degree-of-freedom planar U-shape fixed base 2PRP-PRR parallel manipulator to maximize its workspace. Two kinematic design solutions are proposed and their link parameters are optimized to maximize the workspace. Furthermore, accuracy analysis of the optimized manipulator configurations for the actuator inaccuracies is performed and the results are compared with the well-known planar 3PRP and 2PRP-PPR parallel configurations.

Prediction of Torque Variations in a Pipe Inspection Robot through Computational Fluid Dynamics

Several designs of In-pipe inspection robots (IPIR) have been proposed in the literature to solve the problems related with inspection of these complicated internal geometries. Designing of an in-pipe inspection robot (IPIR) is a difficult task and hence the designer must take care of the design issues. Authors have already proposed a new design for in pipe inspection robot. This research work presents investigations into driving torque variation during its use in a full running pipe to overcome the drag caused by the flowing viscous fluid. This proposed model is a screw driver type wall press adaptable wheeled In-pipe inspection robot. It is able to move through vertical, inclined and horizontal pipes and it can easily pass through elbow of a pipe line. This model comprises of three modules- rotor, stator and control unit. The Rotor module has three wheels mounted on the outer periphery with a helix angle of 18°. Wheels of rotor follow the helical path on the internal surface of pipe line and move in the longitudinal direction inside the pipe. A mathematical model is proposed to estimate the driving torque required by the proposed robot. Driving torque is a function of forces coming on the robot due its motion inside the pipe and drag force generated due to flowing media. The torque on motor varies with change in viscosity of flowing fluid inside the pipe, speed of fluid and pipe inclination. The form and skin drag forces are predicted using computational fluid dynamic approach through ANSYS fluent software and robot driving torque variation is studied under full running pipe.

Dual-Loop Motion Control for Geometric Errors and Joint Clearances Compensation of a Planar 2- P RP+1- P PR Manipulator

The existence of geometric errors (misalignment and kinematic errors) and joint clearances is an inherent problem in manipulators. In addition, friction between surfaces and gear backlash errors are unavoidable factors in manipulators using geared motors as their joint actuators. This paper presents a potential solution for the above issues through the application of a dual-loop control scheme. The proposed control scheme uses a redundant feedback strategy, i.e., individual joint displacements (at the joint space level) and, end-effector positions and orientation (at the task space level) are obtained as a feedback signal using appropriate sensors. Using this redundant feedback information, the actual error of the joint displacements are computed and rectified the desired joint space trajectory in joint-space trajectory tracking control to achieve the desired task space trajectory. To demonstrate the effectiveness and show overall performance of the controllers, real-time experiments are performed on an in-house fabricated 2-PRP+1-PPR planar parallel manipulator. The experiment results show that the manipulator tracking performance is significantly improved with the proposed dual-loop control scheme. In addition, the controller parameter sensitivity and robustness analyses are performed.

Development of a Planar 3PRP Parallel Manipulator using Shape Memory Alloy Spring based Actuators

This paper presents the development of a SMA (shape memory alloy) spring actuation based 3-dof (three degree of freedom) 3PRP (prismatic-rotary-prismatic) planar parallel manipulator where each limb (3 stands for three limbs) of the manipulator having PRP joint arrangement. The active prismatic actuators are made of SMA springs. This 3PRP planar parallel manipulator has a parallel structure including a fixed base and a moving platform (end-effector) and placed in xy plane. Base and the end-effector of the manipulator are linked together by three limbs consisting of prismatic-revolute-prismatic (PRP) joint arrangement in which each limb has one active prismatic joint made of SMA springs. Forward and inverse kinematic analysis of the 3PRP planar parallel manipulator has been studied. Suitability and usage of SMA spring based actuators replacing highly bulky prismatic actuators has been investigated. In addition, the detailed study of the actuation or deflection of the SMA springs in the application of driving the manipulator has been presented experimentally. From the experimental results, it is observed that the 3PRP manipulator associated with SMA spring based actuators has larger workspace to total area required ratio as all the three active prismatic actuators actuates properly and in same time. In overall, this paper shows the 3PRP planar parallel manipulator associated with SMA spring actuators is superior alternatives to conventional motion stages for high precise micro-positioning and tracking applications.