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.