Physics of Slippery When Wet

Scientists have now explained a new law of physics that accounts for elastohydrodynamic lubrication (EHL) friction, which should really progress a large variety of robotic systems. EHL friction takes place when two strong surfaces arrive into get hold of with a skinny layer of fluid concerning them. Credit score: Lilian Hsiao

Despite the fact that robotic products are used in every thing from assembly strains to medicine, engineers have a tough time accounting for the friction that takes place when those robots grip objects — specifically in moist environments. Scientists have now identified a new regulation of physics that accounts for this variety of friction, which ought to progress a huge assortment of robotic systems.

“Our get the job done right here opens the door to producing a lot more dependable and useful haptic and robotic units in purposes these kinds of as telesurgery and production,” claims Lilian Hsiao, an assistant professor of chemical and biomolecular engineering at North Carolina Condition University and corresponding creator of a paper on the do the job.

At situation is something called elastohydrodynamic lubrication (EHL) friction, which is the friction that takes place when two stable surfaces come into get in touch with with a skinny layer of fluid amongst them. This would involve the friction that occurs when you rub your fingertips with each other, with the fluid getting the slim layer of by natural means taking place oil on your skin. But it could also use to a robotic claw lifting an object that has been coated with oil, or to a surgical device that is getting utilised inside of the human system.

A person motive friction is vital is mainly because it helps us hold things without having dropping them.

“Understanding friction is intuitive for human beings — even when we’re dealing with soapy dishes,” Hsiao claims. “But it is extremely challenging to account for EHL friction when establishing materials that controls grasping abilities in robots.”

To create resources that assistance management EHL friction, engineers would want a framework that can be used uniformly to a extensive wide range of designs, components and dynamic operating problems. And that is particularly what the researchers have discovered.

“This regulation can be made use of to account for EHL friction, and can be utilized to many different tender programs — as long as the surfaces of the objects are patterned,” Hsiao says.

In this context, surface styles could be anything from the a little bit raised surfaces on the recommendations of our fingers to grooves in the area of a robotic device.

The new physical principle, produced jointly by Hsiao and her graduate pupil Yunhu Peng, helps make use of four equations to account for all of the actual physical forces at participate in in knowledge EHL friction. In the paper, the exploration workforce demonstrated the law in 3 techniques: human fingers a bio-inspired robotic fingertip and a resource referred to as a tribo-rheometer, which is used to measure frictional forces. Peng is initially creator of the paper.

“These outcomes are very helpful in robotic palms that have additional nuanced controls for reliably handling production processes,” Hsiao says. “And it has evident purposes in the realm of telesurgery, in which surgeons remotely command robotic gadgets to carry out surgical treatments. We look at this as a essential improvement for understanding contact and for controlling touch in synthetic programs.”

Reference: “Elastohydrodynamic friction of robotic and human fingers on gentle micropatterned substrates” by Yunhu Peng, Christopher M. Serfass, Anzu Kawazoe, Yitian Shao, Kenneth Gutierrez, Catherine N. Hill, Veronica J. Santos, Yon Visell and Lilian C. Hsiao, 29 April 2021, Mother nature Materials.
DOI: 10.1038/s41563-021-00990-9

The paper was co-authored by Christopher Serfass, a Ph.D. student at NC Point out Catherine Hill, an undergraduate scholar at NC State Anzu Kawazoe, Yitian Shao and Yon Visell of the College of California-Santa Barbara and Kenneth Gutierrez and Veronica J. Santos of the University of California-Los Angeles.

The get the job done was carried out with assistance from the AAAS Marion Milligan Mason Award and from the Nationwide Science Foundation, below grant amount CBET-2042635.