If grabbing an object, adapting to its texture and its viscosity so that it does not escape your hands seems intuitive to us, the laws that govern this touch are far from being. In particular, when programming robotic devices loaded with meticulous operations, evaluating the friction that occurs when these devices pick up objects remains difficult, especially in the presence of humid environments. Researchers at the University of North Carolina have succeeded in modeling this type of contact and creating a “new law of physics”, which should allow advances in robotics. The results of their research have been published in the journal Nature Materials this April 29, 2021.
Haptics are to touch what acoustics are to hearing
The source of their research is elastohydrodynamic lubricated friction (EHD), or the frictional contact of two solid surfaces between which there is a thin layer of fluid which lubricates the contact. This can include hand rubbing during washing, where the soap acts as a fluid layer between the two hands, but also when a robotic hand lifts an object coated with oil, or even a surgical tool that operates on it. interior of the human body.
This friction is very important because it is what allows us to hold objects without them slipping between our hands. “Understand the friction is intuitive to humans – like holding utensils full of soap “ says Hsiao, assistant professor of chemical and biomolecular engineering at North Carolina State University, who participated in the research. “But take into account the EHD is extremely difficult when developings materials that control this gripping ability of robots “. Indeed, to perfectly model the contact by friction between two objects requires a multiphysical coupling between the deformation of solids and the dissipation of fluids.
“Our work opens doors to create more reliable and applicable haptic and robotic devices in fields such as telesurgery and precision manufacturing,” said Lilian Hsiao. Developing materials that control this type of contact would require a reference system that can be applied uniformly to a wide variety of materials, surfaces, and operating conditions. And that’s exactly what the researchers achieved.
Udo law for many applications
Using a system of four equations, they established a new physical principle which takes into account all the forces brought into play during an elastohydrodynamic contact. By varying the geometry and elasticity of materials and the properties of fluids, the team succeeded in modeling all types of elastohydrodynamic lubricated friction. Their model was tested on a bio-inspired robotic finger and on human fingers: the predictions were compared to a friction measurement by a tribo-rheometer, and the results agreed.
“This law can be used to take into account the friction EHD, and applied to many different systems, as long as the surfaces of the objects are modeled “, Hsiao said. In this context, these “models” can range from slightly raised surfaces like fingertips, to grooves in the surface of a robotic tool. This research could open new doors in the design of robotic hands or grippers under realistic conditions, especially in telesurgery where precision is the key word.
“VSThis will have obvious applications in the field of telesurgery, where surgeons remotely control robotic devices to perform surgical procedures. We see this as ae advanceée fundamentale to understand touch and to control touch in synthetic systems “, declares Hsiao