Owl-Neck-Spine-Inspired, Additively Manufactured, Joint Assemblies with Shape Memory Alloy Wire Actuators

Abstract

Nature provides a considerable number of good examples for simple and very efficient joint assemblies. One example is the enormously flexible cervical spine of American barn owls, which consists of 14 cervical vertebrae. Each pair of vertebrae produces a comparatively small individual movement in order to provide a large overall movement of the entire cervical spine. The biomimetic replication of such joints is difficult due to the delicate and geometric unrestricted joint shapes as well as the muscles that have to be mimicked. Using X-ray as well as micro-computed tomography images and with the utilisation of additive manufacturing, it was possible to produce the owl neck vertebrae in scaled-up form, to analyse them and then to transfer them into technically usable joint assemblies. The muscle substitution of these joints was realised by smart materials actuators in the form of shape memory alloy wire actuators. This actuator technology is outstanding for its muscle-like movement and for its high-energy density. The disadvantage of this wire actuator technology is the low rate of contraction, which means that a large length of wire has to be installed to generate adequate movement. For this reason, the actuator wires were integrated into additively manufactured carrier components to mimic biological joints. This resulted in joint designs that compensate for the disadvantages of the small contraction of the actuators by intelligently installing large wire lengths on comparatively small installation spaces, while also providing a sufficient force output. With the help of a test rig, the developed technical joint variants are examined and evaluated. This demonstrated the technical applicability of this biomimetic joints.

Processing of shape memory alloys research, applications and opportunities: a review

“…The austenite-to-martensite transformation temperature (Ms) and the martensite-to-austenite transformation temperature (As) are the two distinct phase transformation temperatures for SMAs. The resistive heating effect of SMAs is utilised during electrical activation [188]. The SMA experiences resistive heating as an electrical current is conducted across it, raising its temperature over the transition temperature.…”

Test Rig for Investigating the Functional and Structural Fatigue of Shape Memory Alloy Wires Based on Different Activation Profiles

“…The requirements are divided into three requirement categories (concept, product life phases, and planning) and assigned main features that must be fulfilled. As part of the idea generation process, the existing test benches in the research group and those presented in the literature were considered [ 63 , 64 , 65 , 66 , 67 , 68 ].…”

A review of shape memory alloy artificial muscles in bionic applications

“…In addition, Löffler et al proposed a prototype inspired by owl neck, where integrated SMA wire actuators were utilized as muscle substitutes. Ultimately, this prototype achieved the fundamental capability of flexible movement by employing 23 rotational joints (figure 11(c)) [120].…”

“…Reprinted from[113], Copyright © 2009 Elsevier Ltd. All rights reserved. (c) A prototype mimicking owl neck[120]. Reproduced from[120].…”