Controlling a Robotic Fish to Swim Along a Wall Using Hydrodynamic Pressure Feedback

This paper presents a method to control a robotic fish to swim along a straight wall by measuring nearby hydrodynamic pressure variations. This robotic fish is built for exhibiting in a museum, and is expected to swim back and forth along the boundary of an aquarium. Transparent glass walls of the aquarium are not easy to detect for the robotic fish using the optical camera. In nature, fish can detect pressure variations around their bodies to extract near-field information. This concept is adopted for a fish-like swimming mechanism. In this study, the tail of the robot is modeled as an oscillating dipole in a 2-D potential flow, and the wall effect is described by an image dipole on the opposite side of the wall. Based on this model, the distance and angle of the robot with respect to the wall are derived from the magnitudes and ratios of pressure variations measured by pressure sensors distributed on the head and the body of the robot. The pressure information is then fed back to control the orientation of the robot. Experimental results show that the robotic fish is able to swim with a distance-to-wall/tail-span ratio of 1-1.33 beside a wall. The wall effect decreases as the ratio increases. The proposed technique can be used to navigate a robotic fish with a close distance along a wall.