A unified autonomous underwater vehicle-manipulator system

Abstract

With the increasing interest in underwater exploration and intervention, there is a need for vehicles that can perform complex mission tasks involving autonomous manipulation. This brought about the conceptualization of the underwater vehicle-manipulator system (UVMS), which has been a topic of theoretical interest, but with little support for actual development. This research focuses on a kinematically unified formulation for a UVMS in order to coordinate the motion of the components, for the purpose of physical implementation in an actual system. The combination of a manipulator with any number of degrees of freedom (DOF) with an underwater vehicle, which itself has 6 DOF, results in a redundant system in terms of the desired task, usually the pose of the end effector. To resolve the redundancy, this effort proposes a task prioritized approach, so that the motion of the vehicle is performed with a lower priority than that of the manipulator, just as a human would do while writing completely across a large chalkboard, for example. However, this prioritization generates algorithmic problems, when one task conflicts with another, in addition to kinematic singularities where the manipulator exists in an unfavorable configuration. This is addressed by a novel approach that reconstructs the multiple prioritized tasks, simultaneously considering the singularities and joint limits in a least-squares manner. The proposed topics are demonstrated through illustrative simulations to detail the effectiveness of each approach. Then, the theoretically viable concepts are verified through empirical application with an existing UVMS by performing autonomous manipulation tasks in the subsea environment, requiring completely coordinated motions with no human interaction.