Soft robots given more agility

Led by Kirstin Petersen, assistant professor of electrical and computer engineering at Cornell University, the team took advantage of a property of liquids and gasses that had previously hindered the movement of fluid-driven soft robots. The team’s paper - Harnessing Nonuniform Pressure Distributions in Soft Robotic Actuators – has been published in Advanced Intelligent Systems.

“Soft robots have a very simple structure, but can have much more flexible functionality than their rigid cousins. They’re sort of the ultimate embodied intelligent robot,” Petersen said in a statement. “Most soft robots these days are fluid-driven. In the past, most people have looked at how we could get extra bang for our bucks by embedding functionality into the robot material, like the elastomer. Instead, we asked ourselves how we could do more with less by utilising how the fluid interacts with that material.”

Petersen’s team connected a series of elastomer bellows with slender tubes, a configuration that allows for antagonistic motions of pulling and pushing. The tubes induce viscosity, causing the pressure to be distributed unevenly. That would normally be a problem, but the team found a way to utilise it.

The researchers developed a full descriptive model that could predict the actuator’s possible motions with a single fluid input. That resulted in an actuator that can achieve far more complex motions, but without the multiple inputs and complex feedback control that previous methods required.

To demonstrate the technology, the team built a six-legged soft robot, with two syringe pumps on top, that walks at 0.05 body lengths per second, and can crouch.

“We detailed the full complement of methods by which you can design these actuators for future applications,” Petersen said. “For example, when the actuators are used as legs, we show that just by crossing over one set of tubes, you can go from an ostrich-like gait, that has a really wide stance, to an elephant-like trot.”

The new fluid-driven actuator could be used for different types of devices, such as robot arms, and Petersen is interested in exploring how placing bellows in 3D configurations will result in even more useful motion patterns.

“This is basically a whole new subfield of soft robotics,” she said. “Exploring that space will be super interesting.”