Researchers at North Carolina State University have discovered a new law of physics that should have major implications for the field of robotic technologies. The new law helps solve some of the issues surrounding a robot’s grip, which is usually relied on in many different fields. These robots struggle with accounting for the friction that takes place when gripping objects, especially in wet environments.
Lilian Hsiao is an assistant professor of chemical and biomolecular engineering at North Carolina State University and corresponding author of the paper. The new principle was developed by Hsiao and graduate student Yunhu Peng, who is first author.
“Our work here opens the door to creating more reliable and functional haptic and robotic devices in applications such as telesurgery and manufacturing,” Hsiao says.
The major issue in this area is elastohydrodynamic lubrication (EHL) friction. EHL friction takes place when two solid surfaces come into contact with a thin layer of fluid that is between them. This often takes place when two fingertips are rubbed together, which in this case the fluid is the thin layer of naturally occurring oil.
EHL friction could also take place when a robotic claw lifts an oil-coated object or a surgical device that is being used inside the body. Friction is what enables us to grasp and hold things without dropping them.
“Understanding friction is intuitive for humans — even when we’re handling soapy dishes,” Hsiao says. “But it is extremely difficult to account for EHL friction when developing materials that controls grasping capabilities in robots.”
Engineers need a framework capable of being applied uniformly to different patterns, materials, and dynamic operating conditions if they want to control EHL friction to some extent.
“This law can be used to account for EHL friction, and can be applied to many different soft systems — as long as the surfaces of the objects are patterned,” Hsiao says.
Surface patterns include the slightly raised surfaces on the tips of our fingers, or the grooves that are present in the surface of a robotic tool.
The new principle relies on four equations to account for all of the physical forces present in EHL friction. The research team demonstrated three systems including human fingers, a bio-inspired robotic fingertip, and a tribo-rheometer tool, which can measure frictional forces.
“These results are very useful in robotic hands that have more nuanced controls for reliably handling manufacturing processes,” Hsiao says. “And it has obvious applications in the realm of telesurgery, in which surgeons remotely control robotic devices to perform surgical procedures. We view this as a fundamental advancement for understanding touch and for controlling touch in synthetic systems.”
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