Embedded SMA wire actuated biomimetic fin: a module for biomimetic underwaterpropulsion

Abstract

An embedded shape memory alloy (SMA) wire actuated biomimetic fin is presented, andbased on this module for biomimetic underwater propulsion, a micro robot fish (146 mm inlength, 30 g in weight) and a robot squid (242 mm in length, 360 g in weight) were developed.Fish swim by undulating their body and/or fins. Squid and cuttlefish can alsoswim by undulating their fins. To simplify engineering modeling, the undulatingswimming movement is assumed to be the integration of the movements of manyflexible bending segments connected in parallel or in series. According to this idea,a biomimetic fin which can bend flexibly was developed. The musculature ofa cuttlefish fin was investigated to aid the design of the biomimetic fin. SMAwires act as ‘muscle fibers’ to drive the biomimetic fin just like the transversemuscles of the cuttlefish fin. During the bending phase, elastic energy is storedin the elastic substrate and skin, and during the return phase, elastic energy isreleased to power the return movement. Theorem analysis of the bending angle wasperformed to estimate the bending performance of the biomimetic fin. Experimentswere carried out on single-face fins with latex rubber skin and silicone skin (SF-Land SF-S) to compare the bending angle, return time, elastic energy storage andreliability. Silicone was found to be the better skin. A dual-face fin with silicone skin(DF-S) was tested in water to evaluate the actuating performance and to validatethe reliability. Thermal analysis of the SMA temperature was performed to aidthe control strategy. The micro robot fish and robot squid employ one and tenDF-S, respectively. Swimming experiments with different actuation frequencieswere carried out. The speed and steering radius of the micro robot fish reached112 mm s−1 and 136 mm, respectively, and the speed and rotary speed of the robot squid reached40 mm s−1 and 22° s−1, respectively.