Control of a compact, tetherless ROV for in-contact inspection of complex underwater structures

In this paper we present the dynamic modeling and control of EVIE (Ellipsoidal Vehicle for Inspection and Exploration), an underwater surface contact ROV (Remotely Operated Vehicle) for inspection and exploration. Underwater surface inspection is a challenging and hazardous task that demands sophisticated automation - as in boiling water nuclear reactors, water pipeline, submarine hull and oil pipelines inspection. EVIE is inspired by its predecessor, the Omni Submersible, in its ellipsoidal, streamlined, and appendage free shape. The objective for the robot is to carry inspection sensors - magnetic, acoustics or visual - to determine cracks on submerged surfaces. Unlike a robot moving in a practically boundless fluid, contact forces complicate the dynamics by bringing in normal and frictional forces, both of which are highly non linear in nature. This makes the modeling much more challenging and the development of an integrated controller more difficult. In this paper we will discuss the preliminary design and hydrodynamic modeling of such a robot. We analyze in detail the controls for one of the many transitional states of this robot. Eventually all transitional states need to be integrated to develop a hybrid dynamical system which shall use a controller that can adapt to its different states.