Research Background of the Project:
Fish and other aquatic organisms propel themselves by performing various types of flapping foil routines. Be it the tail or lateral fins, the overarching principle of aquatic propulsion entails the oscillation of a plate at a prescribed frequency in order to obtain a certain swimming speed. Similarly, aquatic organisms such as squids and octopuses perform oscillations of a hollow, flexible chamber of their body in order to recursively ingest and expel fluid and in this way perform a pulsed-jetting locomotion routine. In order to enhance swimming efficiency, many aquatic organisms exploit resonance-based phenomena where activation frequency and natural frequency of the system (combined fluid and body) are matched.
This project aims to study the use of Variable Stiffness Actuators (VSA) embedded in aquatic propulsors with the aim of actively selecting the degree of flexibility of the system and in this way exploit resonance-aided actuation over a continuous spectrum of frequencies. The purpose of this is to enable an underwater vehicle endowed with such VSA apparatus to always operate near the resonance regime and in this way benefit of persistent maximum efficiency over a broad range of swimming speeds.
A VSA is a mechanism which exploits the differential arrangement of elastic components in order to actively modify the overall rigidity of an end-effector. VSAs have been commonly employed in the design of cybernetic arms and other manipulators. Here we intend to exploit the benefit of stiffness control in the frame of aquatic propulsion. Our system will be able to control both the natural frequency and actuation frequency of the system, ideally demonstrating how persistent operation within the resonance regime can be achieved for the purpose of efficient aquatic propulsion.
Weblinks: Adam Stokes’ Soft Robotics Research Group http://stokesresearchgroup.com/
1) F Giorgio-Serchi, A Lidtke, G Weymouth, (2018), A soft aquatic actuator for unsteady peak power amplification, IEEE/ASME Transactions on Mechatronics, DOI: 10.1109/ TMECH.2018.2873253
2) S. Wolf et al., "Variable Stiffness Actuators: Review on Design and Components," in IEEE/ASME Transactions on Mechatronics, vol. 21, no. 5, pp. 2418-2430, Oct. 2016. doi: 10.1109/TMECH.2015.2501019
3) F. Giorgio-Serchi, Arienti, A., & Laschi, C. (2016). Underwater soft-bodied pulsed-jet thrusters: actuator modeling and performance profiling. The International Journal of Robotics Research, 35(11), 1-22. DOI: 10.1177/ 0278364915622569