| Underwater robots with manipulators are a key resource for marine exploration, particularly for tasks involving intervention with the environment. For missions where small vehicles equipped with manipulators are required, there can be significant dynamic coupling between the arm and the vehicle, causing the vehicle to “swim” whenever the manipulator is actuated. This interaction affects the robot's ability to achieve precise end-point placement for intervention tasks, as well as the control performance of the system as a whole.; Two issues that are affected by this complex interaction have been addressed in this research. First, a new model for the drag forces on a two-link underwater swinging manipulator has been developed. This model adds three newly-defined drag coefficients that are functions of the arm configuration. Joint torque predictions calculated using the new model show significant improvement over existing models in the literature for multiple-link manipulators, which assume that the links translate only. These improvements have been demonstrated for torque predictions on a fixed-base manipulator, as well as for a control scheme for hovering the OTTER experimental vehicle during manipulation maneuvers.; Second, a new analytic tool called a Dynamic Disturbance Map has been developed. This tool is a graphical representation of the coupling characteristics of an underwater arm-vehicle system and can be used for arm-joint path analysis and planning. This work captures the benefits of a similar tool developed for space-based systems, where there is only inertial coupling, allowing the extension of planning techniques for underwater systems to include hydrodynamics terms and unconstrained end-effector paths. Arm motions planned to minimize vehicle motion were demonstrated experimentally on the OTTER arm-vehicle system with significant improvements. |
