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

Abstract

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.

A Robotic Experimental Setup with a Stewart Platform to Emulate Underwater Vehicle-Manipulator Systems

“…The experimental setup was evaluated with the force/position hybrid control architectures of [ 4 , 5 ] for the contact management. The aim of the force controller is to ensure that the end-effector of the robot manipulator is in contact with the environment perpendicularly via applying a linear reference force in the z translational direction (a dynamically changing direction always perpendicular to the unknown surface) and a zero torque in roll ( ) and pitch ( ) rotational directions in the local (tool) frame.…”

“…The control strategy in [ 4 ] is for fixed-based robot manipulators where a standard proportional (P) controller was used to control perpendicular force interaction and surface trajectory tracking. In [ 5 ], taking into account the unknown disturbance effect of the floating base vehicle to the position of the robot manipulator, the control architecture is enhanced via an admittance control approach.…”

“…As a result, a simulation environment and a physical experimental setup have been developed to interact with each other to replicate a UVMS in order to test and validate the controllers in a dry-lab environment. A force/position control method is adapted from our earlier studies [ 4 ] and an admittance based controller [ 5 ] that applies virtual dynamics at the manipulator end-effector for perpendicular force interaction with the unknown surface is implemented in this study. This admittance controller does not require knowledge of the vehicle position/velocity, the stiffness of the environment or manipulator base disturbance effects.…”

Manipulation at optimum locations for maximum force transmission with mobile robots under environmental disturbances

“…Thereby, the reference force/torque can be denoted as f r = 0 0 f z r 0 0 0 , which implies that the force controller makes an effort to apply constant force, f z r , in z direction and zero torque in x and y directions to prevent misalignment at the tool frame. To eliminate force components affecting in other directions, calculated v f will be multiplied with a task matrix = diag 0, 0, 1, 1, 1, 0 before using in the manipulator control algorithm as in Moura et al (2018), Cetin et al (2021).…”

Sliding Mode Controller for Positioning of an Underwater Vehicle Subject to Disturbances and Time Delays

“…In [6] a decoupled PD controller has been proposed as a motion control algorithm. To cope with the translational and turbulence force impacts on a rigid body moving in a fluid, adaptive control methods have been developed as well, see for instance [7], [8], [9], [10], [11], to improve the tracking performance of the UUVs. An Extended Kalman Filter (EKF) adaptive controller utilizing feedback linearization control method has been implemented to a UUV with a manipulator in [10].…”