A novel biomimetic torsional actuator design using twisted polymer actuators

Michael W. Shafer, Heidi P Feigenbaum, Diego Ricardo Higueras Ruiz

Research output: Chapter in Book/Report/Conference proceedingConference contribution

7 Scopus citations


Artificial muscle systems have the potential to impact many technologies ranging from advanced prosthesis to miniature robotics. Recently, it has been shown that twisting drawn polymer monofilaments, such as nylon fishing line or sewing thread, can result in a biomimetic thermally activated torsional actuator. The actuation phenomenon in these twisted polymer actuators (TPAs) is thought to be a result of an untwisting that occurs about the fiber's axis due to an anisotropic thermal expansion. Before being twisted, the precursor fibers are comprised of polymer chains that are aligned axially. During fabrication of TPAs, the polymer chains reorient as the precursor fiber is twisted about the central axis of the monofilament. At the end of the fabrication process, the TPA is annealed in order to relieve internal stresses and to keep the fiber in the twisted configuration. The mechanism of untwisting actuation is generally thought to be a result of radial expansion and axial contraction. After being twisted, these radial and axial expansion relationships remain relatively unchanged, but the polymer chain direction is no longer axially aligned. Thus, upon heating the twisted fibers of the TPA, the fibers untwist and torsional actuation occurs. This actuation phenomenon has been used in the past to create linear actuators, but can also be use directly as a torsional actuator. Compared to other torsional actuators TPAs are low cost, lightweight, and can actuate reasonably high torques per unit volume. However, because TPAs are thermally activated, they may not be suitable for all applications. In this work, we present a novel TPA design for use as a torsional actuator for miniature actuation and artificial muscle applications. Our design bundles twisted monofilaments to increase the torque. Both fabrication and testing methods of the new design are presented. Results for temperature versus torsional displacement under various loads give insights as to how these actuators may be used and the reversibility of the actuation process under different fabrication loads. Additionally, comparisons are made between these bundled actuators and similarly loaded single TPA monofilament actuation.

Original languageEnglish (US)
Title of host publicationDevelopment and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies
PublisherAmerican Society of Mechanical Engineers
ISBN (Electronic)9780791858257
StatePublished - 2017
EventASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2017 - Snowbird, United States
Duration: Sep 18 2017Sep 20 2017

Publication series

NameASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2017


OtherASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2017
Country/TerritoryUnited States

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Civil and Structural Engineering
  • Building and Construction
  • Mechanics of Materials


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