Thin-film NiTi Microactuator With A Magnetic Spring For A Tiny Launcher Mechanism

In this work, we present a thin-film shape memory alloy microactuator with a magnetic spring. This novel actuator design utilizes two permanent magnets and 3D-printed magnet holders to effectively apply a tensile strain on the NiTi thin-film. This actuator is expected to generate 8.7 mN of blocking force, and a free displacement of 30 µm is experimentally characterized. The actuator leverages bare NiTi film (∼ 1 µm thick) for actuation, enabling a high actuator bandwidth up to 50 Hz. A comprehensive analytical model is also studied, which was then validated by comparing to the experimental results. A launcher mechanism was designed and integrated with the NiTi actuator, and this mechanism was used to launch a microscale projectile (a salt grain) thereby demonstrating the relative high power actuation achievable with thin-film NiTi.

I. INTRODUCTION

Microactuators capable of providing a large amount of mechanical work are necessary for small-scale robotic systems due to limitations in size and mass. Among various microactuation methods, shape memory alloy (SMA) is an attractive actuation option for microrobots, as it can take advantage of high-work density materials such as NiTi (∼ 1 J/g) to provide a high force and a large displacement. NiTi thin films (< 5 µm) can also be microfabricated using sputter deposition processes for microscale applications [1] – [4].