Highly Dynamic Shape Memory Alloy Actuator for Fast Moving Soft Robots

TLDR

Shape memory alloys are favored actuators for soft bioinspired robots because of their compliance, high work density, and compatibility with miniature electronics, yet their bandwidth is limited by the slow cooling required to return to shape. The study aims to overcome this limitation by building SMA actuators from thermally conductive elastomers and investigating how electrical current and actuation frequency affect blocking force, bending amplitude, and operating temperature. The actuator consists of a U‑shaped SMA wire sandwiched between layers of stretched and unstretched thermally conductive elastomer. The resulting actuator weighs 3.7 g, delivers ≈0.2 N of force, bends with a curvature change of ≈60 m⁻¹ in 0.15 s, and can be driven at frequencies above 0.3 Hz using two 3.7 V Li‑polymer batteries, enabling its use as an artificial muscle for fast dynamic soft‑robotic locomotion.

Abstract

Abstract Shape memory alloys (SMAs) are popular as actuators for soft bioinspired robots because they are naturally compliant, have high work density, and can be operated using miniaturized on‐board electronics for power and control. However, SMA actuators typically exhibit limited bandwidth due to the long duration of time required for the alloy to cool down and return to its natural shape and compliance following electrical actuation. This challenge is addressed by constructing SMA‐based actuators out of thermally conductive elastomers and examining the influence of electrical current and actuation frequency on blocking force, bending amplitude, and operating temperature. The actuator is composed of a U‐shape SMA wire that is sandwiched between layers of stretched and unstretched thermal elastomer. Based on the studies, the ability is demonstrated to create a highly dynamic soft actuator that weighs 3.7 g, generates a force of ≈0.2 N, bends with curvature change of ≈60 m −1 in 0.15 s, and can be activated with a frequency above 0.3 Hz with a pair of miniature 3.7 V lithium–polymer batteries. Together, these properties allow the actuator to be used as an “artificial muscle” for a variety of tethered and untethered soft robotic systems capable of fast dynamic locomotion.