Initial implementation of basic actuated unit of a flexible pectoral fin driven by SMA

Fish are capable of remarkable locomotor performance through the complex 3D motions and the cooperation of different fins. Specially, pectoral fins play an important role to provide thrust, maneuverability and balance ability. In this paper, a novel design of a flexible pectoral fin capable of 3D motions actuated by Shape Memory Alloy (SMA) is proposed. The flexible pectoral fin can perform five basic gestures of real pectoral fins: Relaxed, Expansion, Bending, Cupping and Undulation. First, we present the mechanical design of the flexible pectoral fin, and then put forward two effective designs (Plate Mode and Wire Embedded Mode) of fin ray, the basic actuated unit of the pectoral fin, capable of bending in two mutually orthogonal directions. Second, we conduct theoretical analysis of the SMA fin ray respectively based on the two designs. Finally, a series of experiments are conducted to investigate the performance of the two designs, meanwhile, the comparison between the two is given out.