Preliminary study of flexible pectoral fin capable of 3D motions actuated by Shape Memory Alloy

Fish are noted for their excellent performances to cruise efficiently, to maneuver and to position themselves accurately. These performances are the result of complex 3D motion and the cooperation of different fins of fish. In this paper, we focus on the research of the pectoral fin, and present a novel mechanical design of flexible pectoral fin capable of 3D undulation, actuated by shape memory alloy (SMA). First, we implement a detailed design of flexible pectoral fin which is composed of a series of SMA fin rays. Each fin ray consists of two serial installed SMA plate couples and is capable of bending in two mutually orthogonal directions. Second, we analyze the energy distribution of the response process of the SMA plate couple from the aspect of thermodynamics, meanwhile, we conduct a thermodynamics simulation to research the response process. Third, the control system is designed to obtain the accurate control of the locomotion of the fin ray. Finally, we conduct experiments to investigate the performance of the SMA fin ray and attain the following results: (a) relationship between temperature and actuation time; (b) relationship between angular displacement and time; (c) relationship between torque and current. The experimental results show that SMA driven fin ray has a good performance and that the SMA driven flexible pectoral fin can be well achieved.