Hover kinematics and distributed pressure sensing for force control of biorobotic fins

A comprehensive understanding of the ways in which fish create and control forces is fundamental to engineering underwater vehicles that maneuver with the agility of fish. In this study the sunfish was selected as a biological model from which to understand pectoral fin motions and forces during hover. The kinematic patterns of the biological fin were identified and implemented on a biorobotic model of the fin. The effects of fin patterns and mechanical properties on force were evaluated. Pressure was measured at multiple points on the fin´s surface and assessed for use in the closed loop control of fin force. The study revealed that a wide range of motions are used during hover, and that forces are significantly different from those found previously for steady swimming. However as fin speeds increase, the fin´s dynamic motions, and the magnitude and direction of the forces become more similar to those of steady swimming. Collective measures of pressure over the fin´s surface exhibited trends that correlated well with fin forces in relative magnitudes and directions. Results strongly suggest that distributed measures of pressure are useful for force prediction and control.