A Bistable Actuator Based on Antagonistic Buckling SMA Beams

Abstract:
We present the design, fabrication and characterization of a miniature-scale bistable actuator consisting of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to be opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snapping motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography and systems integration. Selective heating is accomplished via heat transfer by direct mechanical contact of the SMA beams to a low-grade heat source. The force-displacement characteristics of single SMA beams and bistable SMA actuators as well as their dynamic performance are characterized with respect to the influence of geometrical parameters and heat source temperature. For heat source temperatures in the range of 160-180 °C, the bistable SMA actuator generates a large stroke of 1.7 mm at frequencies near 1 Hz.