Meter-scale flexible touch sensor using projection capacitive measurement technique and fabric electrode for human position detection

Abstract

We developed a meter-scale large-area bendable touch sensor that utilizes a 1-m-wide fabric electrode and a projection capacitance measurement method. This sensor is used to detect human position on floors or soft beds. A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is coated on hundred-meter-long nylon fibers through a die coating technique, and the resultant fibers are woven in a weft and warp pattern with a 1-m-wide automatic looming machine, forming a 1-m-wide fabric sensor. The mechanism of sensing human position is based on the detection of the capacitance change between a conductive polymer-coated sensing fiber and a human foot. A change of approximately 3.3 pF is measured when the fabric sensor is pushed with a human-foot-sized electrode, i.e., 6.3 cm, under an average foot pressure of 2.6 N/cm2, which is large enough to detect with conventional capacitance measurement circuits in microcontroller units (MCUs). The sensing fibers have high mechanical flexibility as they withstand tens of thousands of bending tests at a bending radius of 10 mm. Finally, a 1 × 1 m2 fabric sensor is connected to capacitance measurement circuits and personal computers (PCs) to construct a human position sensor system. The fabric touch sensor system demonstrates the capability to detect human positions not only on the flat surface of a floor but also on the bendable surface of a soft bed. This technology should lead to bed and floor sensors that monitor elderly people in nursing homes and hospitals.