Soft robots are made of pliant, supple materials, such as silicone. Some can squeeze through tiny spaces or travel over broken ground — tasks that stymie rigid robots. The field of soft robotics is still in the early stages of development, but it offers remarkable potential. One day soon, soft robots may be used in applications as diverse as searching collapsed buildings or as exosuits that facilitate recovery from injuries or strokes.
But soft robots need soft circuits that can bend and stretch with the devices they inhabit. “Regular circuit boards are too rigid,” said Callen Votzke, a doctoral candidate in robotics and electrical and computer engineering, and a graduate fellow with the Semiconductor Research Corporation. His research has been devoted largely to developing circuits for soft robots and other stretchable electronics.
A crucial component of those circuits is liquid metal made of gallium, indium, and tin, mixed with nickel microparticles, whose consistency resembles that of toothpaste. It’s used to connect microchips or sensors to create fully functional circuits, all encapsulated in channels within the silicone.
The possibilities seem endless. For example, stretchable electronics could be used in physical therapy. “Imagine a silicone exosuit that makes sure rehab patients are doing their exercises correctly, and even assists their movements,” Votzke said. “As the liquid metal wires stretch and contract with the exosuit, their electrical resistance changes, and that information can be used to measure motion.” Using an early prototype, Votzke successfully demonstrated the idea’s feasibility.
He’s also made important progress toward the development of a soft robotic gripper, which will be studded with dozens of microprocessors and sensors, all networked with liquid metal connections. (Rigid microprocessors and sensors are so small nowadays that many of them can be embedded in a soft robot without compromising mobility.) Ideally, it will use only tactile feedback for determining the position and shape of objects and for grasping. “That would be a huge improvement on many current grasping technologies, which rely a lot on visual input,” Votzke said.
Votzke and his colleagues in the lab of Matthew Johnston, associate professor of electrical and computer engineering, meet regularly with another group of Oregon State researchers, led by Joe Davidson, assistant professor of robotics, whose goal is to build robotic grippers capable of picking fruits and vegetables. “Replicating that action with robotics is extremely challenging, but we’re getting closer,” Votzke said.
Votzke says he feels lucky to attend Oregon State University for his doctorate. “The faculty have given me a tremendous amount of latitude, but also welcome guidance, to explore this field and to build things that almost nobody else in the world is building,” he said. “And I’ve developed industry connections that have given me a sense of where I can fit in after I leave the university to further develop my work.”