3D Printed Actuators: Reversibility, Relaxation and Ratcheting

TL;DR

This paper introduces a novel 3D printed hybrid actuator using thermoplast/conductor bilayers that can perform reversible and irreversible deformations, enabling scalable, integrated 4D printing and actuation of complex structures.

Contribution

It demonstrates a new method for 3D printing functional actuators with reversible and ratcheting capabilities using thermoplastic/conductor bilayers.

Findings

Actuators can propel structures under step-wise voltages.

Strong driving causes irreversible deformations, enabling 4D printing.

Ratcheting allows large deformations through cyclic thermoplastic relaxation.

Abstract

Additive manufacturing strives to combine any combination of materials into three dimensional functional structures and devices, ultimately opening up the possibility of 3D printed machines. It remains difficult to actuate such devices, thus limiting the scope of 3D printed machines to passive devices or necessitating the incorporation of external actuators that are manufactured differently. Here we explore 3D printed hybrid thermoplast/conducter bilayers, that can be actuated by differential heating caused by externally controllable currents flowing through their conducting faces. We uncover the functionality of such actuators and show that they allow to 3D print, in one pass, simple flexible robotic structures that propel forward under step-wise applied voltages. Moreover, exploiting the thermoplasticity of the non-conducting plastic parts at elevated temperatures, we show how strong driving leads to irreversible deformations - a form of 4D printing - which also enlarges the range of linear response of the actuators. Finally, we show how to leverage such thermoplastic relaxations to accumulate plastic deformations and obtain very large deformations by alternatively driving both layers of a bilayer; we call this ratcheting. Our strategy is scalable and widely applicable, and opens up a new approach to reversible actuation and irreversible 4D printing of arbitrary structures and machines.