Abstract
We present the design, fabrication, and characterization of single and antagonistic SMA microactuators allowing for uni- and bi-directional self-folding of origami-inspired devices, respectively. Test devices consist of two triangular tiles that are interconnected by double-beam-shaped SMA microactuators fabricated from thin SMA foils of 20 µm thickness with memory shapes set to a 180° folding angle. Bi-directional self-folding is achieved by combining two counteracting SMA microactuators. We present a macromodel to describe the engineering stress–strain characteristics of the SMA foil and to perform FEM simulations on the characteristics of self-folding and the corresponding local evolution of phase transformation. Experiments on single-SMA microactuators demonstrate the uni-directional self-folding and tunability of bending angles up to 180°. The finite element simulations qualitatively describe the main features of the observed torque-folding angle characteristics and provide further insights into the angular dependence of the local profiles of the stress and martensite phase fraction. The first antagonistic SMA microactuators reveal bi-directional self-folding in the range of −44° to +40°, which remains well below the predicted limit of ±100°.
Highlights
The increasing demand on the functionality of microsystems requires new approaches for active control of mechanical, optical, and fluidic components
Fabrication, and characterization of uni- and bi-directi origami-inspired self-folding microactuators based on micromachined shape memory alloys (SMAs) foils
Basic design consists of two triangular tiles that are interconnected by double-be
Summary
The increasing demand on the functionality of microsystems requires new approaches for active control of mechanical, optical, and fluidic components. Most microactuator concepts are limited to one- or two-dimensional workspaces. The concept presented here uses the technique of self-folding, following the ancient art of paper folding, known as origami, by which flat sheets transform into numerous three-dimensional (3D) shapes. The advantage of origamiinspired designs in engineering is their compact and deployable setup, which has proven its versatility in various macroscopic applications, e.g., airbags [4], wings [5], or tools for minimally invasive surgery [6]. The actual 3D function could be assigned after the fabrication of the initially flat 2D structures. An overview of the designs and mechanisms of self-folding structures can be found in recent reviews, e.g., [7,8,9]
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