Self-folding origami requires a low-profile actuator to be embedded in a sheet of paper-like planar material. Various actuation methods have been employed to actively fold such sheets. This paper presents a torsion shape-memory alloy (SMA) wire actuator embedded in patterned origami structures that actively folds the origami by twisting the SMA wire. A simple wire is aligned with the fold line, and each end is fixed to a facet. The twisting of the wire directly rotates the facets. This method has the advantage of using an easily available wire SMA and the advantage of a flat form factor similar to that of sheet SMA. Generally, SMA wire is used in a linear manner or as a spring. The torsion SMA wire presented in this paper is trained to generate torsional force when heated. The amount of rotation depends on the length of the wire; a 200-μm-diameter SMA wire 12 mm in length can induce 540° rotation. SMA wires are arranged in pairs side by side to rotate the facets in both directions. Maximum torque of 70 mNcm is generated in this antagonistic arrangement. The torsion SMA wire actuators enable a novel design for a programmable folding sheet that is easily manufactured and exhibits fast folding and unfolding.

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