Artificial Pectoral Fins Research Articles

Development of an Unmanned Hybrid Vehicle Using Artificial Pectoral Fins

AbstractAn unmanned vehicle has been developed for dual use as both an aircraft and a submersible. To achieve long-range emplacement of a highly maneuverable underwater asset to a target environment, the Flimmer (Flying-Swimmer) vehicle is designed for both high-speed flight and low-speed swimming. Building on previous research in bioinspired propulsion and control systems, the vehicle employs a unique set of artificial flapping fins for underwater maneuvering, which must be considered when evaluating the flight and water landing capabilities. This paper describes the computational analysis and experimental results for all three phases of vehicle operation—flight, landing, and swimming. Computational fluid dynamics simulation results predict aero- and hydrodynamic characteristics and demonstrate landing loads on and trajectory of the vehicle. Experimental data demonstrate flight and swimming performance and validate the computational results, and experimental testing of water landing provides a comparison with computations. Results and analyses of the Flimmer vehicle performance demonstrate the operational capabilities of an unmanned hybrid vehicle for long-range flight and low-speed swimming.

Bio-inspired robotic manta ray powered by ionic polymer–metal composite artificial muscles

The manta ray (Manta birostris) is the largest species of rays that demonstrates excellent swimming capabilities via large-amplitude flapping of its pectoral fins. In this article, we present a bio-inspired robotic manta ray using ionic polymer–metal composite (IPMC) as artificial muscles to mimic the swimming behavior of the manta ray. The robot utilizes two artificial pectoral fins to generate undulatory flapping motions, which produce thrust for the robot. Each pectoral fin consists of an IPMC muscle in the leading edge and a passive polydimethylsiloxane membrane in the trailing edge. When the IPMC is actuated, the passive polydimethylsiloxane membrane follows the bending of the leading edge with a phase delay, which leads to an undulatory flapping motion on the fin. Characterization of the pectoral fin has shown that the fin can generate flapping motions with up to 100% tip deflection and 40° twist angle. To test the free-swimming performance of the robot, a light and compact on-board control unit with a lithium ion polymer battery has been developed. The experimental results have shown that the robot can swim at 0.067 BL/s with portable power consumption of under 2.5 W.

Analytical predictions, optimization, and design of a tensegrity-based artificial pectoral fin

For millions of years, aquatic species have utilized the principles of unsteady hydrodynamics to perform efficient, highly maneuverable and silent swimming motions. The manta ray, Manta birostris, has been identified as one such high performance species due to their ability to migrate long distances with low energy consumption, maneuver in spaces the size of their tip-to-tip wing span, produce enough thrust to leap out of the water and attain sustained swimming speeds of 2.8 m/s with low flapping frequencies. These characteristics make the manta ray an ideal candidate to emulate in the design of a bio-inspired autonomous underwater vehicle. The enlarged pectoral fins of the manta ray undergo complex motions that couple a curved spanwise deformation with a chordwise traveling wave to produce thrust and to maneuver. To produce an artificial pectoral fin that achieves this compound deformation while supporting large force generation, a tensegrity-based solution is developed. Various actuation strategies that are capable of matching these key kinematic features are explored and compared. Analytical solutions for active planar tensegrity beam structures are derived. These solutions allow for the direct calculation of optimal parameter values without the need to perform an exhaustive parametric study using a numerical solution. Moreover, the analytical solutions provide physical insight into the mechanics of tensegrity beams. Building on previous studies of active tensegrity structures, the loading response of different actuation strategies has been investigated analytically and is validated by a nonlinear numerical model and experiments. Optimal stiffness-to-mass and strength-to-mass strategies have been identified. Utilizing the analytical predictions for the optimal solution, an example design of a tensegrity-based artificial pectoral fin is shown. Structural performance metrics were calculated showing that the fin structure can closely match the kinematics of the manta ray, under external loading, using open-loop actuation of four actuators remotely located outside of the active structure. This approach costs minimal power consumption and shows the simple design of a high performance tensegrity-based artificial pectoral fin.

A novel fabrication of ionic polymer–metal composite membrane actuator capable of 3-dimensional kinematic motions

Abstract Ionic polymer–metal composites (IPMCs) are one type of wet electroactive polymers that show promising actuating properties in many bio-inspiring underwater robotic applications. In these applications, 3-dimensional kinematic motions are desirable to generate high efficient thrust and maneuverability. However, traditional IPMCs are limited in being only able to generate bending motion. In this paper, a novel synthesis technique is developed to fabricate a hybrid IPMC membrane actuator capable of generating 3-dimensional (3D) kinematic motions. The actuator consists of separated IPMC beams bonded with a soft polydimethylsiloxane (PDMS) membrane. By controlling each individual IPMC beams, we can generate complex 3D motions such as oscillation and undulation. IPMC beams are cut from one sheet of IPMC, which is fabricated through chemically plating platinum electrodes on a Nafion film. A multiple plating process is used to enhance the conductivity of the electrodes, which leads to better actuation performance of IPMC. An assembly based fabrication process is adopted to bond the IPMC actuators with PDMS gel using two CNC-machined molds. Then the PDMS is cured at room temperature to form an actuating membrane. Overall this novel synthesis technique is cost effective and less time-consuming compared to existing strategies. The characterization of the actuating membrane has shown that the maximum twist angle can reach up to 15°, the flapping deflection can reach up to 25% of spanwise length, the tip force can reach up to 0.5 g force, and the power consumption is below 0.5 W. The first application of this novel membrane actuator is in the design of a free-swimming robotic batoid ray. The robot consists of two membranes functioning as artificial pectoral fins. Experimental results show that the robot is capable of free swimming with low power consumption.

Monolithic fabrication of ionic polymer–metal composite actuators capable of complex deformation

Ionic polymer–metal composites (IPMCs) are soft actuation materials with promising applications in robotics and biomedical devices. However, traditional IPMC actuators can generate the bending motion only. In this paper, a lithography-based approach is presented for monolithic, batch-fabrication of IPMC actuators that are capable of complex deformation. Such an actuator consists of multiple, individually controlled IPMC regions that are mechanically coupled through compliant, passive regions. Two novel techniques have been introduced to overcome challenges in fabrication of patterned IPMCs: (1) selectively thinning down Nafion using reactive ion etch, to make the passive areas thin and compliant, and (2) modulating the stiffness and swellability of Nafion with ion-exchange. Ion-exchanged Nafion shows almost 300% increase in stiffness, and over 94% reduction in swellability in water and acetone, which facilitates lithography and other critical fabrication steps. Prototypes of artificial pectoral fins have been fabricated with the proposed method, and sophisticated deformation modes, including bending, twisting, and cupping, have been demonstrated. For example, a peak-to-peak twisting angle of 16 ° is achieved under 3 V, 0.3 Hz actuation voltages, showing the promise of the fabricated device in robotic fish applications.