| A fish caudal fin has three advantages over propeller, (1) stealthiness, (2) high efficiency and (3) maneuverability. Therefore, we devise an oscillating foil to mimic fish caudal fins. The objective of this thesis is to provide practical maneuvering control of an aquatic vehicle (AV) using an oscillating foil as a propulsor and rudder. The AV is an under-actuated system with non-minimum phase property, therefore, a single standard control methodology (e.g., input-output feedback linearization) cannot be directly applied. We propose combinations of an off-line motion planning and on-line tracking control to achieve arbitrary maneuvers. To be practical, we utilize optimal control techniques to compute a repertoire of time-scalable and concatenable motion primitives. The complete motion planning is generated by concatenating time-scaled copies of these primitives. In order for the AV to track the planned motion, combinations of finite-time optimal control and input-output feedback linearization control strategies are implemented. To avoid solving Riccati equation for finite-time optimal control for every maneuver, we develop time-scaled optimal control. Sliding mode control strategy is also integrated to improve the system performance. Finally the presented methodology is experimentally verifying. Experiments are conducted on a two-dimensional, two degrees of freedom planar AV. We divided our experiments into two parts, namely laterally constrained and unconstrained motions. The laterally constrained experiments are for conceptual verification while the unconstrained experiments are for demonstrating abilities to achieve both longitudinal and lateral motions tracking in the same time. |
