New Design for Thermal Actuators Developed by Team at NC State University

A team of researchers from NC State University have developed a new design for thermal actuators that can be used to induce rapid movements in soft robotic devices.

NC State Ph.D. student Shuang Wu, former NC State graduate student Langston Baker, NC State associate professor of mechanical and aerospace engineering Jie Yin, and NC State Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering Yong Zhu published a new paper titled “Fast Thermal Actuators for Soft Robotics,” Dec. 7 in Soft Robotics, which describes the new thermal actuator design.

“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,” Zhu said about the team’s research.

Actuation refers to the process by which a device creates motion from energy. The part of a device that completes this function is an actuator. In the case of the team’s new thermal actuators, soft robotic devices can rapidly produce motions by being heated to specific temperatures.

“What makes this new actuator design work is a structure with a bi-stable design,” Wu said. “Think of a snap hair clip. It’s stable until you apply a certain amount of energy (by bending it over), and then it snaps into a different shape – which is also stable.”

Instead of being bent by one’s fingers like a hair clip, the new thermal actuators “snap” into specific positions that correspond with the actuator being heated to specific temperatures.

To create rapid movements in soft robots, the researchers applied voltage to silver nanowires that run between layered materials bent in one specific direction, and when the nanowires successfully heat the layered materials, it quickly bends in the other direction. The temperature that induces this motion is referred to as the critical temperature. When the voltage is removed from the nanowires, the materials cool to another critical temperature, causing it to bend in the same direction that it started.

The team created two prototypes to demonstrate the use of these new thermal actuators, one of which “snaps” like a Venus flytrap, while the other is a “crawler” capable of moving more than one body length per second.

“Potential applications range from biomedical applications to prosthetic devices to high-end manufacturing,” Zhu says. “Any application in which you’d want to be able to move quickly, but also want to avoid rigid materials and conventional robotics.”

The team hopes to develop sensor and control mechanisms that could more fully automate the actuation process and allow the devices to operate without manual control. According to Zhu, the team also hopes to explore the use of other materials in the thermal actuation process, which would allow them to specifically tailor the speed and force of the motion.


Image credit: Shuang Wu.

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