Warp-Knitted Textile as a Strain Sensor: Characterization Procedure and Application in a Comfortable Wearable Goniometer

Long-term and minimally invasive joint angular measurements are required for monitoring everyday activities, motor rehabilitation sessions, and sport training. In this paper, we designed an innovative wearable device composed of a light, comfortable, and low-cost textile strain-resistance sensor. First, we proposed a methodology to characterize and to calibrate a commercial knitted textile. This characterization procedure represents an interesting result per se. It has been conducted on a single material, but its general characteristics make it suitable for analyzing the behavior of any conductive and stretchable fabrics. Second, we developed a wearable sensor (a goniometer) and we validated it using the humanoid robot SABIAN. Dynamic tests demonstrated that our wearable device is suitable for scenarios, where the accuracy of measurements is less relevant than the ability to continuously track joint movements in a not-obtrusive way.