Innovative haptic device enables robots to perfect soft touch abilities

That is exactly what a team of researchers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland has accomplished with SORI (Softness Rendering Interface).

According to the team, SORI closes a gap in the robotics field by accurately simulating the softness of various genuine materials by disentangling cutaneous and kinesthetic inputs. This allows for various applications where softness sensation is crucial, including deep-sea research and robot-assisted surgery.

Customizable softness for individual fingertips

In various research works in neuroscience and psychology, cutaneous cues are primarily determined by the amount of skin in touch with a surface, which is frequently influenced by the object’s deformation. Put otherwise, a surface covering a larger portion of your fingertip will be considered softer. However, because human fingertips vary widely in size and firmness, one finger may make greater contact with a given surface than another.

“We realized that the softness I feel may not be the same as the softness you feel because of our different finger shapes. So, for our study, we first had to develop parameters for the geometries of a fingertip and its contact surface to estimate the softness cues for that fingertip, said Mustafa Mete, a Ph.D. student in the Reconfigurable Robotics Lab (RRL) in the School of Engineering at EPFL, in a statement.

The Softness Rendering Interface (SORI) can recreate the softness of a range of materials. Credit: Jamani Caillet

Expanding upon the RRL’s well-known research on origami robots, which has sparked spinoffs for haptic joysticks and changeable settings, SORI has motor-driven origami joints tunable to become more flexible or stiff. A silicone membrane with dimples sits atop the joints. The membrane expands to different degrees as air passes, encircling a fingertip inserted in the middle.

Encouraging results opens up diverse applications

Through tests with two human volunteers, SORI could replicate the softness of various foods, including marshmallows, salmon, and beef, thanks to this new decoupling of kinesthetic and cutaneous functions. Researchers highlight that it also imitated stiff and soft textures (like a leather-bound book or a biscuit on top of a marshmallow). To show how effective SORI is in animating soft materials, one virtual experiment even replicated the feeling of a beating heart.

According to the team, one of the main fields in which this technology may be used is medicine; for instance, to teach medical students how to identify malignant tumors or give vital sensory feedback to surgeons who use robotics to do surgeries.

Additional uses for the gadget would be robot-assisted space or deepwater exploration, allowing researchers to feel an object’s softness from a distance. One of the main problems in robot-assisted agriculture is collecting delicate fruits and vegetables without crushing them; SORI may be able to solve this issue, claims the team.

“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,” said Mete.

The details of the team’s research were published in the journal Proceedings of the National Academy of Sciences.

Abstract

Tactile perception of softness serves a critical role in the survival, well-being, and social interaction among various species, including humans. This perception informs activities from food selection in animals to medical palpation for disease detection in humans. Despite its fundamental importance, a comprehensive understanding of how softness is neurologically and cognitively processed remains elusive. Previous research has demonstrated that the somatosensory system leverages both cutaneous and kinesthetic cues for the sensation of softness. Factors such as contact area, depth, and force play a particularly critical role in sensations experienced at the fingertips. Yet, existing haptic technologies designed to explore this phenomenon are limited, as they often couple force and contact area, failing to provide a real-world experience of softness perception. Our research introduces the softness-rendering interface (SORI), a haptic softness display designed to bridge this knowledge gap. Unlike its predecessors, SORI has the unique ability to decouple contact area and force, thereby allowing for a quantitative representation of softness sensations at the fingertips. Furthermore, SORI incorporates individual physical fingertip properties and model-based softness cue estimation and mapping to provide a highly personalized experience. Utilizing this method, SORI quantitatively replicates the sensation of softness on stationary, dynamic, homogeneous, and heterogeneous surfaces. We demonstrate that SORI accurately renders the surfaces of both virtual and daily objects, thereby presenting opportunities across a range of fields, from teleoperation to medical technology. Finally, our proposed method and SORI will expedite psychological and neuroscience research to unlock the nature of softness perception.