Jammkle: Fibre jamming 3D printed multi-material tendons and their application in a robotic ankle

TL;DR

This research presents a novel, modular, multi-material, 3D printed, fibre jamming tendon unit for use in a stiffness-tunable compliant robotic ankle, or Jammkle, which outperforms comparative leg structures in terms of compliance, damping, and slip prevention.

Abstract

Fibre jamming is a relatively new and understudied soft robotic mechanism that has previously found success when used in stiffness-tuneable arms and fingers. However, to date researchers have not fully taken advantage of the freedom offered by contemporary fabrication techniques including multi-material 3D printing in the creation of fibre jamming structures. In this research, we present a novel, modular, multi-material, 3D printed, fibre jamming tendon unit for use in a stiffness-tuneable compliant robotic ankle, or Jammkle. We describe the design and fabrication of the Jammkle and highlight its advantages compared to examples from modern literature. We develop a multiphysics model of the tendon unit, showing good agreement with experimental data. Finally, we demonstrate a practical application by integrating multiple tendon units into a robotic ankle and perform extensive testing and characterisation. We show that the Jammkle outperforms comparative leg structures in terms of compliance, damping, and slip prevention.

Figures (10)

• Figure 1: Four tendon units integrated into a robotic ankle, showing compliance over rough terrain.
• Figure 2: Modular Design of Jamming Tendons: A) Jamming tendon showing cross-sections of three regions along its length. Short Shore A-30 fibres (red) connect to longer Shore A-85 fibres (blue). B) When stretched, extension occurs mainly in the softer Agilus30 fibres. C) The tendon is designed to be generically applicable and stabilise similarly to organic tendons; they can be modularly applied to joints including knees and ankles. D) Mechanical implementation of bio-inspired jamming ankle (Jammkle) and conceptual knee mechanism.
• Figure 3: Test setup used for characterisation of a single Tendon unit. Left panel shows unjammed, unstretched tendon. Right panel shows jammed, stretched tendon.
• Figure 4: Experimental Force vs Displacement curves of multimaterial tendon. The effective stiffness of the tendon is able to be controlled by vacuum pressure. Five repeats of each test are shown.
• Figure 5: Force-displacement curves showing modelled and experimental behaviour of the jamming tendon during elongation: (a) unjammed, (b) jammed.