Bio-inspired Robotic Cownose Ray Propelled by Electroactive Polymer Pectoral Fin

The cownose ray (Rhinoptera bonasus) demonstrates excellent swimming capabilities; generating highly efficient thrust via flapping of dorsally flattened pectoral fins. In this paper, we present a bio-inspired and free swimming robot that mimics the swimming behavior of the cownose ray. The robot has two artificial pectoral fins to generate thrust through a twisted flapping motion. Each artificial pectoral fin consists of one ionic polymermetal composite (IPMC) as artificial muscle in the leading edge and a passive PDMS membrane in the trailing edge. By applying voltage signal to the IPMC, the passive PDMS membrane follows the bending of IPMC with a phase delay, which leads to a twist angle on the fin. The characterization results have shown that the pectoral fin was able to generate up to 40% tip deflection and 10o twist angle with less than 1 Watt power consumption. A bio-inspired rigid body was designed using Computerized Axial Tomography (CT Scan) data of the cownose ray body and printed using a 3-dimensional printer. A light and compact on-board control unit with a lithium ion polymer battery has been developed for the free swimming robot. Experimental results have shown that the robot swam at 0.034 BL/S. ∗Address all correspondence to this author. INTRODUCTION The cownose ray (Rhinoptera bonasus, shown in Fig. 1) demonstrates excellent swimming capabilities; generating highly efficient thrust via flapping of dorsally flattened pectoral fins [1]. Many efforts have been directed towards building a bio-inspired pectoral fin structure to mimic the swimming behavior of the ray, such as electric motor actuated rigid plates [2] and tensegrity structures [3]. Due to size limitations of the electric motors and tensegrity structures, they are not suitable for small scale robots (on the order of 5-10 cm) [4–6]. A bio-inspired actuating material, which is lightweight, compliant, resilient, and capable of generating 3D deformation with low power consumption, is highly desirable in constructing a free swimming and small scale robotic cownose ray. Electroactive polymers (EAPs), also known as artificial muscles, can generate large deflections under electrical stimulus [7]. Ionic polymer-metal composites (IPMCs) are one category of ionic EAPs [8], which can work well under a low actuation voltage (1 to 2 Volts) in a sodium salt water environment. An IPMC consists of one ion exchange membrane, such as Nafion (DuPont), coated with two novel metal electrodes [9]. When the IPMC is hydrated, the positive ions in the Nafion polymer, such 1 Copyright c © 2011 by ASME Proceedings of the ASME 2011 International Mechanical Engineering Congress & Exposition IMECE2011 November 11-17, 2011, Denver, Colorado, USA