Soft tactile sensors for human-machine interaction

Abstract

With many upcoming aging societies, the demand for automated assembly lines, the need for surgery robots in hospitals, and the growing popularity of personal products with touch interfaces, more advanced and reliable soft tactile sensing techniques are required for human-machine interaction. Soft tactile interface will enable new generations of touch-sensitive health-care robots to attend the old and the disabled, pressure-sensing shoes and garment to collect human physiological signals for health monitoring, and many others in various fields including biomedical, agriculture, and food processing. In the past decade, substantial effort has been made toward soft tactile sensors for smart skin that emulates the human skin, where four different types of touch receptors are embedded in a viscoelastic media, dermis. Current tactile sensing techniques include capacitive, piezoelectric, conductive elastomeric, optical, and conductive liquid types. Although each has its merits and limitations, many extreme tactile sensors have been developed: some can detect a pressure of 13 mPa; some show a sensitivity of 8.4 kPa-1 in the low-pressure regime; some tolerate a 300 % stretch; some measure three-dimensional forces; and some remain stable after 100,000 repetitive loadings. Nevertheless, no single sensing technology provides sensors on a par with human skin in all technical aspects, including sensitivity, hysteresis, response time, spatial resolution, flexibility, and stretchability. Fortunately, it is viable to emulate a subgroup of the four human force receptors. Future directions of soft tactile sensors are task-centered design, nano-material, micro-fabrication and replication techniques, as well as more soft, elastic, and dynamic tactile sensing. Future development of soft tactile sensing solutions for human-machine interface shall reasonably bring more surprises to our life.