A team of US researchers has developed a soft robot that can navigate through mazes and traverse sandy surfaces, without any programming or outside energy source.
The robot is a twisted strip of polymers, which looks rather like a long piece of pasta.
“These soft robots demonstrate a concept called ‘physical intelligence’, meaning that structural design and smart materials are what allow the soft robot to navigate various situations, as opposed to computational intelligence,” says Jie Yin, an associate professor of mechanical and aerospace engineering at North Carolina State University, US, and co-author of a paper describing the research, published in PNAS.
The robots are made from a substance called liquid crystal elastomer, or LCE. LCEs are made from long molecular chains, cross-linked in a way that makes them flexible like rubber, but with some of the physical and molecular properties of liquid crystals.
The robots are twisted like rotini pasta. When placed on a warm surface, the base of the ribbon contracts while the top doesn’t. This causes the ribbon to roll.
“This has been done before with smooth-sided rods, but that shape has a drawback – when it encounters an object, it simply spins in place,” says Yin.
“The soft robot we’ve made in a twisted ribbon shape is capable of negotiating these obstacles with no human or computer intervention whatsoever.”
The ribbon has two tricks for avoiding obstacles. It can rotate slightly, allowing it to roll its way out. Or it can snap under the pressure (sort of). As it deforms on a warm surface, the robot stores up energy. Once it can’t move, this energy can be released quickly, allowing the robot to snap backwards.
“The two actions, rotating and snapping, that allow the robot to negotiate obstacles operate on a gradient,” says first author Dr Yao Zhao, a researcher also at North Carolina State University.
“The most powerful snap occurs if an object touches the centre of the ribbon. But the ribbon will still snap if an object touches the ribbon away from the centre, it’s just less powerful. And the further you are from the centre, the less pronounced the snap, until you reach the last fifth of the ribbon’s length which does not produce a snap at all.”
Because the snap changes its orientation, the robot will eventually find its way around an obstacle – but it might take a few tries.
“In this sense, it’s much like the robotic vacuums that many people use in their homes,” says Yin.
“Except the soft robot we’ve created draws energy from its environment and operates without any computer programming.”
The researchers have trialled their robot in a variety of lab-based environments – across sand, on slopes, and around several different obstacles.
“This is interesting and fun to look at, but more importantly it provides new insights into how we can design soft robots that are capable of harvesting heat energy from natural environments and autonomously negotiating complex, unstructured settings such as roads and harsh deserts,” says Yin.
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