3D-Printed Ready-To-Use Variable-Stiffness Structures

Majid Taghavi,Tim Helps,Boxiong Huang,Jonathan Rossiter

doi:10.1109/lra.2018.2812917

Majid Taghavi, Tim Helps + Show 2 more

Open Access

https://doi.org/10.1109/lra.2018.2812917

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Abstract

Various physical phenomena have been used to develop variable-stiffness (VS) materials and structures, but all have involved some elements of manual fabrication, which limits their applications. In contrast, here we show fully three-dimensional (3D) printed monolithic VS structures that can be used directly from the printer. Thermally responsive polylactic acid (PLA) and conductive graphene PLA (GPLA) are combined in-printer to deliver a new framework for the temperature-controlled 3D VS structures. The embedded GPLA acts as a heating element, and both it and the surrounding PLA can be transitioned from rigid to soft using simple Joule heating because of the glass transition behavior of PLA. The mechanical and electrical properties of printed composite VS structures are studied. The great potential of this technology is demonstrated in a prototype variable-stiffness orthotic for foot drop.

Highlights

R ECENTLY, variable-stiffness (VS) materials and structures have been demonstrated as a means of shape adaption [1] and transitioning between soft and rigid states [2]
We present a totally 3D-printable VS structure based on thermally responsive graphene polylactic acid (PLA) (GPLA) which acts as the heating element and is printed at the same time as, and in composition with, non-conductive PLA by means of multi-material 3D printer
To obtain a reliable connection between wires and conductive PLA, the connections were made to copper tape, which was clamped against the ends of the VS structure by acrylic clips

Summary

INTRODUCTION

R ECENTLY, variable-stiffness (VS) materials and structures have been demonstrated as a means of shape adaption [1] and transitioning between soft and rigid states [2] They have a broad range of applications in robotics, where compliant and safe motion are needed, ranging from robotic manipulation [3] to human-robot interactions [4], prosthetics [5] orthotics [6], and wearable [7] robots. The stiffness is changed by environmental or direct Joule heating, and results in transition between solid and liquid phases, encapsulation is required [14] These thermoactivated VS materials have low bandwidth and need sufficient time to transfer thermal energy into, and out of, the structure. Engineering and Physical Sciences Research Council under Grants EP/M020460/1 and EP/M026388/1. (Corresponding author: Jonathan Rossiter.)

Design

Fabrication

RESULTS AND DISCUSSION

Variation of Electrical Resistance With Temperature

CONCLUSION