Unified Dynamics-based Motion Planning Algorithm for Autonomous Underwater Vehicle-Manipulator Systems (UVMS)

Among the underwater robotic systems that are currently available, remotely operated vehicles (ROVs) are the most commonly used underwater robotic systems. A ROV is an underwater vehicle that is controlled from a mother-ship by human operators. Sometimes a ROV is equipped with one or more robotic manipulators to perform underwater tasks. These robotic manipulators are also controlled by human operators from a remote site (e.g., mother-ship) and are known as tele-manipulators. Although the impact of ROVs with telemanipulators is significant, they suffer from high operating cost because of the need for a mother-ship and experienced crews, operator fatigue and high energy consumption because of the drag generated by the tether by which the ROV is connected to the ship. The performance of such a system is limited by the skills, coordination and endurance of the operators. Not only that, communication delays between the master and the slave site (i.e., the mother-ship and the ROV) can severely degrade the performance. In order to overcome some of the above-mentioned problems, autonomous underwater vehicles (AUVs) are developed. However, an AUV alone cannot interact with the environment. It requires autonomous robotic manipulator(s) attached to it so that the combined system can perform some useful underwater tasks that require physical contact with the environment. Such a system, where one or more arms are mounted on an AUV, is called an autonomous underwater vehicle-manipulator system (UVMS). One of the main research problems in underwater robotics is how to design an autonomous controller for a UVMS. Since there is no human operator involved in the control of a UVMS, the task planning has become an important aspect for smooth operation of such a system. Task planning implies the design of strategies for task execution. In other words, a task planning algorithm provides a set of desired (i.e., reference) trajectories for the position and force variables, which are used by the controller to execute a given task. Task planning can be divided into motion planning and force planning. In this research, we focus on the design of motion planning algorithms for a UVMS. The motion planning of a UVMS is a difficult problem because of several reasons. First, a UVMS is a kinematically redundant system. A kinematically redundant system is one which has more than 6 degrees-of-freedom (DOF) in a 3-D space. Commonly, in a UVMS, the AUV has 6 DOF. Therefore, the introduction of a manipulator, which can have n DOF, makes the