Wearable soft artificial skin for hand motion detection with embedded microfluidic strain sensing

Abstract

This paper describes the design and manufacturing of soft artificial skin with an array of embedded soft strain sensors for detecting various hand gestures by measuring joint motions of five fingers. The proposed skin was made of a hyperelastic elastomer material with embedded microchannels filled with two different liquid conductors, an ionic liquid and a liquid metal. The ionic liquid microchannels were used to detect the mechanical strain changes of the sensing material, and the liquid metal microchannels were used as flexible and stretchable electrical wires for connecting the sensors to an external control circuit. The two heterogeneous liquid conductors were electrically interfaced through flexible conductive threads to prevent the two liquid from being intermixed. The skin device was connected to a computer through a microcontroller instrumentation circuit for reconstructing the 3-D hand motions graphically. The paper also presents preliminary calibration and experimental results.

Design and functional evaluation of an epidermal strain sensing system for hand tracking

“…Overall, the thickness and mechanical stiffness of these sensors mimic the physical properties of the stratum corneum, the outermost layer of the skin (10 µm to 40 µm in thickness and Young's modulus of 6 MPa) [16]. Compared to solutions based on micro-channels filled with conductive liquids, our proposed gauges are one to two orders of magnitude thinner [11], [14]. Their form factor makes them unobtrusive when worn on the skin.…”

“…Designs including thin films with high strain sensitivity [10], highly resistive ionic liquids [11], and highly resistive composites [12] have been reported. Another approach consists in translating the design of traditional foil strain gauges to elastic carrier substrates, and preparing the sensitive meanders with stretchable conductive materials [13], [14].…”

Assessment of hand kinematics and interactions with the environment

“…State-of-the-art sensing modalities within this field can be found in biological sensors, e.g. strain sensors based on carbon nanotubes' [222] and microfluidic strain sensing [31]. Electromagnetic acoustic and optical transceiver systems belong to the second category.…”

“…Not only the reduction of sensors, but also minimizing the dimensions of sensors does increase the unobtrusiveness and eases the embodiment of sensors in garment [8,31,118]. Still, the challenge will be in the definition, and eventual estimation, of effective metrics such that relevant questions can be answered within devised protocols.…”

“…It is questionable whether the silicon material used could accommodate for such adaptions, or that a sensor made from a different material, possible with fewer sensitive measurement directions, would be more suitable. Many groups already investigate potential materials to estimate interaction forces or, rather, pressure from changes in material properties [8,31,109,157]. Different kinds of stretchable sensors emerge from the development of smart garments applicable for the assessment of clinal outcomes in daily life [188,205] or for physical assistance during the rehabilitation of a particular disorder [148].…”