A bending microactuator with large angular range for origami-inspired bidirectional folding

Abstract A bending microactuator with large angular range is presented consisting of a novel antagonistic design of cascaded shape memory alloy (SMA) hinges. The antagonistic design comprises two counteracting hinges with double-bridge design to enable bidirectional folding of a pair of rigid tiles serving as a building block of an origami-inspired microsystem. Additional connection of the hinges in series results in a cascaded design to enhance the bidirectional folding angle. A microfabrication process is developed using a combination of magnetron sputtering of TiNiCu films and UV photolithography. The strongly coupled thermo-mechanical properties of the SMA hinges are taken into account in finite element simulations to determine optimized hinge geometries, which allow for selective shape setting at either maximum or minimum bending angle to functionalize their performance as protagonists or antagonists. Thus, localized Joule heating enables folding and unfolding to discrete angles ensuring reversible and programmable folding motions. The bidirectional folding angles of the bending microactuators cover the range of about ±105°, which is more than a factor of two compared to microactuators with single hinge design.