Ribbon Fin Swimming Robot Driven by Twisted and Coiled Polymer Actuators

Abstract

Gymnotiform swimming, also known as ribbon fin swimming, is an unconventional swimming mechanism in nature and in robotics that excels in both agility and manoeuvrability. This swimming mode provides a solution that addresses the limitations of commercial underwater vehicles nowadays, such as manoeuvrability in tight spaces and disturbance to the surroundings by the propellers. With the emergence of soft robotics, the potential of realising a realistic ribbon fin robot akin to that of a gymnotiform by utilising novel soft actuators is becoming increasingly feasible.

This thesis explores the development of a ribbon fin robot driven by twisted and coiled polymer (TCP) actuators. It starts with a literature review covering contemporary marine robots and their limitations, soft robotics focusing on soft actuators, ribbon fin robots, and TCP actuators.

Following the literature review, TCP actuator fabrication and characterisation processes are discussed in detail, from building devices to fabricate TCPs to analysing the characterisation results. Four types of conductive TCP actuators were fabricated and examined. Additionally, a study on slowing down the degradation process of conductive TCP actuators in water was conducted, and based on the findings, a method that significantly reduced the degradation rate using zinc is introduced.

Building on the actuator characterisation, a TCP-driven caudal fin robotic fish is developed as the first attempt to produce an undulating motion, which is critical for the ribbon fin swimming mode, with TCP actuators. The robot has a caudal fin driven by a TCP-spring antagonistic muscle system. Its actuation achieved the highest reported locomotion speed for a TCP-driven robot, to the author's knowledge, before the ribbon fin robot was developed.

Based on the success of the caudal fin robotic fish, a ribbon fin robot is developed. It consists of five fin rays, each controlled by antagonistic TCP actuator muscles. The robot superseded the caudal fin robotic fish and demonstrated the highest reported locomotion speed for a TCP-driven robot, showcasing the potential of ribbon fin swimming powered by TCP actuators.

This research project compared various types of electro-thermal TCP actuators and proposed a novel method that effectively slows down the degradation of a TCP actuator in water. It also demonstrated the potential of TCP actuators in underwater locomotion by developing two swimming robots with distinct propulsion mechanisms. Both robots achieved record-high actuation frequencies and swimming speed for TCP applications. These promising results showcase the capability of TCP actuator-driven systems for higher-frequency operations, broadening the actuator's range of applications. Furthermore, by introducing the first reported soft-actuator-driven ribbon fin robot, the project paves the way for developing a realistic, flexible ribbon fin robot for underwater navigation.

Date of Award	5 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jonathan M Rossiter (Supervisor) & Hemma Philamore (Supervisor)