The perception of softness may be taken for granted, but it plays an important role in many actions and interactions, from judging the ripeness of an avocado to performing a health check to holding a loved one's hand. However, understanding and reproducing softness perception is difficult because it involves so many sensory and cognitive processes.
Robotics researchers have attempted to solve this problem using haptic devices, but previous attempts have failed to address the two fundamental components of softness perception: cutaneous signals (sensory feedback from the skin at the fingertip) and kinesthetic signals (sensory feedback about the amount of force at the fingertip). feedback) could not be distinguished. finger joints).
“If you press a marshmallow with your fingertip, you can easily tell that it's soft. But if you put a hard biscuit on top of that marshmallow and press it again, even with your fingertip, you can tell that there's a soft marshmallow underneath. You're touching a hard surface.” Mustafa Mete, a PhD student in the School of Engineering's Reconfigurable Robotics Lab, explains. “We wanted to see if we could create a robotic platform that could perform the same task.”
RRL, led by Jamie Paik, has achieved just that with SORI (Softness Rendering Interface). By separating skin signals from kinesthetic signals, SORI fills a gap in robotics that faithfully reproduces the softness of a variety of real-world materials, enabling a variety of applications where the sense of softness is important, from deep-sea exploration to robot-assisted surgery.
The study Publications of the National Academy of Science (PNAS).
Softness feels different for each person.
Mete explains that neuroscientific and psychological research shows that skin signals are largely determined by how much skin is in contact with a surface, which is often partially related to the object's deformation. This means that surfaces that cover a larger area of the fingertip are perceived as smoother. However, because human fingertips vary greatly in size and firmness, one finger may have more contact with a given surface than another.
“We realized that the softness I feel may be different from the softness you feel due to different finger shapes. So for our research, we first had to develop parameters for the geometry and contact surface of the fingertip. “It’s about estimating the smoothness signal,” explains Mete. The researchers then extracted softness parameters from various materials and mapped both sets of parameters to the SORI device.
Based on RRL's trademark origami robotics research that promoted spinoffs for reconfigurable environments and haptic joysticks, SORI features motorized origami joints that can be adjusted to be stiffer or more flexible. A dimpled silicone membrane sits over the joint. The flow of air causes the membrane to expand at various angles, wrapping around the fingertip in the center of the membrane.
With the new separation of kinesthetic and skin functions, SORI succeeded in replicating the softness of a variety of ingredients, including beef, salmon, and marshmallows, across multiple experiments with two volunteers. We also imitate materials that have both soft and sturdy properties (e.g. biscuits on top of marshmallows, leather-bound books). In one virtual experiment, SORI even recreated the feeling of a heartbeat to demonstrate the effect of moving soft materials.
Medicine is therefore a major field where this technology can be applied. For example, training medical students to spot cancerous tumors or using robots to perform surgeries, providing important sensory feedback to surgeons.
Other applications include robotic space exploration or deep-sea exploration, where the device allows scientists to feel the softness of discovered objects from remote locations. SORI is also a potential answer to one of the biggest challenges of robot-assisted agriculture: harvesting soft fruits and vegetables without crushing them.
“It is not intended to act as a softness sensor for the robot, but to digitally convey the feeling of ‘touch’, like sending a photo or music,” Mete summarizes.