PREVIEW

Swiss scientists have created a robot that can mimic the texture of a marshmallow, fruit or flesh.
Although it may seem an odd task to assign to technology, their breakthrough has huge implications for the future of medicine, agriculture, and even space travel.
The perception of softness is something that comes naturally to humans - we can judge the ripeness of an avocado or feel the welcome touch of a loved one.
Understanding and reproducing softness perception has proved more of a challenge to robots, however, because it involves so many sensory and cognitive processes.
Researchers at the École polytechnique fédérale de Lausanne (EPFL) have tried to address this challenge with haptic devices, but previous attempts have not distinguished between two primary elements of softness perception: cutaneous cues (sensory feedback from the skin of the fingertip), and kinesthetic cues (feedback about the amount of force on the finger joint).
“If you press on a marshmallow with your fingertip, it’s easy to tell that it’s soft. But if you place a hard biscuit on top of that marshmallow and press again, you can still tell that the soft marshmallow is underneath, even though your fingertip is touching a hard surface,” explains Mustafa Mete, a PhD student in the Reconfigurable Robotics Lab (RRL) in EPFL's School of Engineering. “We wanted to see if we could create a robotic platform that can do the same.”
With SORI (Softness Rendering Interface), the RRL, led by Jamie Paik, has achieved just that. By decoupling cutaneous and kinesthetic cues, SORI faithfully recreate the softness of a range of real materials.
Mete explains that neuroscientific and psychological studies show that cutaneous cues are largely based on how much skin is in contact with a surface, which is often related in part to the deformation of the object. In other words, a surface that envelopes a greater area of your fingertip will be perceived as softer.
“We realised that the softness I feel may not be the same as the softness you feel, because of our different finger shapes,” he adds. “So, for our study, we first had to develop parameters for the geometries of a fingertip and its contact surface in order to estimate the softness cues for that fingertip.”
The researchers extracted the softness parameters from a range of different materials, and mapped both sets of parameters onto the SORI device.
SORI is equipped with motor-driven origami joints that can be modulated to become stiffer or more supple. Perched atop the joints is a dimpled silicone membrane. A flow of air inflates the membrane to varying degrees, to envelop a fingertip placed at its centre.
SORI succeeded in recreating the softness of a range of materials – including beef, salmon, and marshmallow, over the course of several experiments with two human volunteers.
It also mimicked materials with both soft and firm attributes - such as a biscuit on top of a marshmallow, or a leather-bound book.
In one virtual experiment, SORI even reproduced the sensation of a beating heart, to demonstrate its efficacy at rendering soft materials in motion.
Mete says SORI will also be able to transmit the softness of materials to humans far away - meaning you could even use it to hug a loved one from afar by working out their softness and then mimicking them.
“This is not intended to act as a softness sensor for robots, but to transfer the feeling of ‘touch’ digitally, just like sending photos or music,” he summarises.
The more practical applications for the technology are endless - but the primary one will be medicine. It can be used to train medical students to detect cancerous tumours, or to provide crucial sensory feedback to surgeons using robots to perform operations.
Other applications include robot-assisted exploration of space or the deep ocean, where the device could enable scientists to feel the softness of an extra-terrestrial object or organic material at the bottom of the sea.
SORI is also a potential answer to one of the biggest challenges in robot-assisted agriculture - harvesting tender fruits and vegetables without crushing them.
At the moment, although robots can be used for many agricultural tasks, it’s often humans who still have to sift through or pick fruit to check it’s fully ripe and fresh.
The research appears in the Proceedings of the National Academy of Science (PNAS).