Model development of an underwater manipulator for coordinated arm-vehicle control

This paper presents research on the hydrodynamic modeling of a manipulator for an autonomous underwater scientific vehicle. The focus is on improving the modeling accuracy of the in-line hydrodynamic coupling between a two-link manipulator and a small, free-floating vehicle in order to achieve better control for coordinated motion of the combined system. Loads predicted using existing models for underwater arms were determined to be off by as much as 25% when applied to a real, two-link arm in a test tank. In this new approach, an experimentally-determined model has been developed that takes into account the 3D flow effects that have previously not been included. The end result is a model that provides accurate predictions for the joint torques of a two-link arm in a form simple enough to be implemented in algorithms for precision planning and control. This project is part of a joint program between the Aerospace Robotics Laboratory at Stanford University and the Monterey Bay Aquarium Research Institute.