Fast Thermal Actuators for Soft Robotics

Thermal actuation is a common actuation method for soft robots. However, a major limitation is the relatively slow actuation speed. Here we report significant increase in the actuation speed of a bimorph thermal actuator by harnessing the snap-through instability. The actuator is made of silver nanowire/polydimethylsiloxane composite. The snap-through instability is enabled by simply applying an offset displacement to part of the actuator structure. The effects of thermal conductivity of the composite, offset displacement, and actuation frequency on the actuator speed are investigated using both experiments and finite element analysis. The actuator yields a bending speed as high as 28.7 cm^-1/s, 10 times that without the snap-through instability. A fast crawling robot with locomotion speed of 1.04 body length per second and a biomimetic Venus flytrap were demonstrated to illustrate the promising potential of the fast bimorph thermal actuators for soft robotic applications.