The novel skin described in a paper titled “Closed-Loop Haptic Feedback Control Using a Self-Sensing Soft Pneumatic Actuator Skin” in the journal of Soft Robotics consists of a stretchable 500μm thin Soft Pneumatic Actuator (SPA) integrating an array of stretchable thin-metal film strain sensors. When inflated with air, the actuator changes shape (it can be controlled at up to 100Hz to deliver an output forces up to 1N) and creates strain which is detected in real time. But this platform can be used bidirectionally, that is to produce a force-tunable vibratory feedback for a person wearing SPAs at the fingertips, for example to get feedback from a remotely controlled robotic hand manipulating objects, or to establish virtual hand contact with another user connected via a virtual reality scenario.
Such flexible sensors with closed-loop haptic feedback could ensure that users get a consistent feedback when interacting with a virtual environment. They were jointly developed by the Reconfigurable Robotics Lab (RRL) led by Prof. Jamie Paik and the Laboratory for Soft Bioelectronics Interfaces (LSBI) led by Prof. Stéphanie Lacour at EPFL.
The soft skin, made out of silicone, hosts soft strain sensors filled with a mix of solid and liquid metal (gallium) that continuously measure its deformation. This way, the vibration can be tuned in real time in response to the actual deformation that it is causing in the material, and thus to the feeling it is transmitting to the user.
“For the first time, we have an entirely soft wearable interface consisting of integrated sensors and actuators, that produces a consistent tactile feedback with high fidelity” explains Harshal Sonar, a researcher in Paik’s lab and the first author of the paper. “This opens the door for various applications and new research, from bidirectional communication with humans or machines to more precise, quantitative experiments on somatosensory feedback in humans”.
Next, the researchers aim to develop a fully wearable prototype for applications in rehabilitation, virtual and augmented reality. The haptic sensors could also be used in neuroscientific studies, to accurately stimulate the human body while studying dynamic brain activity in magnetic resonance experiments, note the authors.