Macro-Fiber Composite Actuated Piezoelectric Robotic Fish

Abstract

This chapter is centered on fish-like aquatic robotics using flexible bimorphs made from Macro-Fiber Composite (MFC) piezoelectric laminates. Bimorph propulsors employing MFCs offer a balance between the actuation force and velocity response for performance enhancement in bio-inspired swimming, in addition to noiseless and efficient actuation over a range of frequencies, geometric scalability, and simple design. The experimental component of this work first explores the effect of a passive substrate fin extension on the thrust frequency response of MFCs bimorphs in quiescent water along with measurement procedures. Specifically, it is shown that broadband thrust generation can be achieved in the presence of a passive substrate extension. The second part of the experiments is focused on the characterization of an elastically constrained uniform MFC bimorph propulsor (in-air and underwater) as well as the development of a robotic fish prototype combining a microcontroller and a printed circuit board amplifier to generate high actuation voltage for untethered locomotion. A distributed-parameter electroelastic model including the hydrodynamic effects and actuator dynamics is coupled with the elongated-body theory for estimating the mean thrust in quiescent water. For electroelastically nonlinear actuation levels, experimentally obtained underwater vibration response is coupled with the elongated-body theory to predict the thrust output. The measured mean thrust levels in quiescent water (on the order of ~10 mN) compare favorably with thrust levels of biological fish. An untethered robotic fish prototype that employs a single bimorph fin for straight swimming and turning motions is developed and tested in free locomotion. A swimming speed of 0.3 body length/s (7.5 cm/s swimming speed for 24.3 cm body length) is reported at 5 Hz for a nonoptimized main body-propulsor bimorph combination under a moderate actuation voltage level.