N. Sanchez-Tamayo, Z. Yoder, P. Rothemund, G. Ballardini, C. Keplinger, K. J. Kuchenbecker, Cutaneous Electrohydraulic (CUTE) Wearable Devices for Pleasant Broad-Bandwidth Haptic Cues. Adv. Sci. 2024, 2402461. https://doi.org/10.1002/advs.202402461
Recent demos of our CUTE devices
IEEE Haptic Symposium 2024, Long Beach, CA, USA
IEEE Robosoft 2024, San Diego, CA, USA
EuroEAP 2024, Stuttgart, Germany
Motivation
Audio and visual communication currently dominate our interactions with the digital world, while feedback which activates our sense of touch is largely ignored. Yet the human skin can feel a wide range of sensations, presenting an opportunity for rich communication. Currently haptic devices generally provide only vibrotactile feedback at particular frequencies, while devices which aim to deliver more expressive feedback are typically heavy and bulky, or are designed for the fingertips which encumber the hands of the user. There is therefore a need for wearable devices that provide wide-ranging, controllable haptic feedback, and are designed for use off of the fingertips, on the less sensitive, hairy skin.
Approach
HASEL actuators are lightweight, have wide bandwidth including constant displacements, can produce high forces and don’t heat up during operation – making these actuators interesting candidates for driving wearable haptic devices. But current materials systems have prevented them from having small footprints while retaining high performance, have limited their maximum actuation frequencies at small scales, and the exposed high-voltage electrodes presents challenges for use in close contact with the skin.
We developed a new materials system for HASEL actuators which enabled them to be downscaled to a 14 x 14 mm footprint while retaining high output forces and high-frequency operation, and made them safe to touch and to operate in close contact with the skin.
Our approach enables not only broad-bandwidth vibrotactile cues, but also a completely new range of haptic sensations including making and breaking contact with the skin, constant pressure, independent frequency and amplitude control, and multi-frequency patterns – all through a soft contact area with the skin. Here are some examples of the wide variety of cues our device can deliver.
Although HASEL actuators are actuated using high-voltage, our CUTE devices are completely safe and comfortable to wear. We implemented multiple layers of insulation and safety components, and analyzed the risks posed by the un-insulated actuators. We found that the actuators draw such low currents and store so little energy, that even without insulation they are not considered a hazard based on international standards and guidelines.
User study
We carried out a psychophysical study where participants felt a wide variety of haptic cues delivered by a wrist-wearable CUTE device. The performed a cue recognition task, achieving nearly 98% overall accuracy, as well as a description task, where they rated all cues except the pure-tone vibration as pleasant.
I developed the full stack for the program used for our user study. The user interfaced with the program for the entire test, and progressed through multiple phases, including familiarization (free-play), training and testing. In each phase, certain cues were delivered to the user and their responses were recorded.
The program was designed for robust operation, and included rapid device failure detection and shut-off (using an accompanying electrical circuit and high-voltage relay). This meant that when a device would wear out after many users, we could easily replace the device without causing substantial testing interruptions.
Featured photo in Der Spiegel
