Researchers from North Carolina State University have developed a new thermal actuator that provides soft robots with a boost in speed. Thermal actuation is common in soft robots, which creates motion by turning energy into work, and while it's efficient for locomotion, it lacks speed.
"Using thermal actuation is not new for soft robots, but the biggest challenge for soft thermal actuators was that they were relatively slow – and we've made them fast," states Yong Zhu, professor of Mechanical and Aerospace Engineering at NC State.
The new thermal actuator works by implementing a bi-stable design. Think of it like a snap hair clip, which is stable until pressure is introduced and snaps it into a different shape. It's that bi-stable design that gives the actuator increased speed. It functions by layering two materials on top of each other with silver nanowires sandwiched in the middle. Both materials have different heat coefficients of thermal expansion, meaning they expand at different rates when heated. In other words, the materials bend when heat energy is introduced.
Actuation occurs when the materials are shaped into a design that gives them a default curvature in one direction. When voltage is applied to the silver nanowires, the material heats up, bending them in the opposite direction. Once a specific temperature is reached, the material snaps into its new default shape, curving up rapidly. When the voltage is removed, the temperature goes back down. Once it cools past another critical temperature, the material snaps back to its previous default shape, curving down rapidly.
The researchers created two robotic prototypes to demonstrate the new type of actuation, including a Venus Flytrap and a crawler that can move more than one body length per second. As it stands, the actuators are controlled manually, but the team hopes to integrate sensors and mechanisms to automate them fully.