Reviewed by Alex SmithApr 7 2022
Machines can beat even the greatest of chess players in a game, but robots cannot hold a chess piece quite as well. Artificial grippers lack the precise tactile sense of the human fingertip, which is utilized to guide our hands as we pick up and handle items. This is what ultimately results in their lack of dexterity.
Robotic hand with a 3D-printed tactile fingertip on the little (pinky) finger. The white rigid back to the fingertip is covered with the black flexible 3D-printed skin. Image Credit: University of Bristol.
The first in-depth evaluation of an artificial fingertip with brain recordings of the human sensation of touch is described in two publications published in the Journal of the Royal Society Interface. Nathan Lepora, a Professor of Robotics and AI (Artificial Intelligence) at the University of Bristol’s Department of Engineering Maths and the Bristol Robotics Laboratory, led the study.
Our work helps uncover how the complex internal structure of human skin creates our human sense of touch. This is an exciting development in the field of soft robotics - being able to 3D-print tactile skin could create robots that are more dexterous or significantly improve the performance of prosthetic hands by giving them an in-built sense of touch.
Nathan Lepora, Professor, Robotics & AI, Department of Engineering Maths, Bristol Robotics Laboratory, University of Bristol
Professor Lepora and coworkers used a 3D-printed mesh of pin-like papillae on the underside of the compliant skin to simulate the dermal papillae located between the outer epidermal and inner dermal layers of human tactile skin to establish the feeling of touch in the artificial fingertip. The papillae are created using powerful 3D printers that can combine soft and hard materials to form complex biological structures.
We found our 3D-printed tactile fingertip can produce artificial nerve signals that look like recordings from real, tactile neurons. Human tactile nerves transmit signals from various nerve endings called mechanoreceptors, which can signal the pressure and shape of a contact.
Nathan Lepora, Professor, Robotics & AI, Department of Engineering Maths, Bristol Robotics Laboratory, University of Bristol
“Classic work by Phillips and Johnson in 1981 first plotted electrical recordings from these nerves to study ‘tactile spatial resolution’ using a set of standard ridged shapes used by psychologists. In our work, we tested our 3D-printed artificial fingertip as it ‘felt’ those same ridged shapes and discovered a startlingly close match to the neural data,” added Professor Lepora.
Professor Lepora also stated, “For me, the most exciting moment was when we looked at our artificial nerve recordings from the 3D-printed fingertip and they looked like the real recordings from over 40 years ago! Those recordings are very complex with hills and dips over edges and ridges, and we saw the same pattern in our artificial tactile data.”
While the mechanical fingertip and human nerve impulses were found to be astonishingly similar, the artificial fingertip was not as sensitive to fine detail. Professor Lepora believes this is because 3D-printed skin is thicker than real skin, and his team is currently investigating ways to 3D-print structures on a tiny size similar to that of human skin.
“Our aim is to make artificial skin as good—or even better—than real skin,” said Professor Lepora.
What is tactile robotics?
Video Credit: University of Bristol.
Journal Reference:
Pestell, N., et al. (2022) Artificial SA-I and RA-I afferents for tactile sensing of ridges and gratings. Journal of the Royal Society Interface. doi.org/10.1098/rsif.2021.0822.