Printable Skin Adhesive Stretch Sensor for Measuring Multi-Axis Human Joint Angles

This paper presents a printable skin adhesive stretch sensor to estimate rotation angles of multi-axis joint for biomedical engineering applications, such as gait analysis, gesture recognition, and motion monitoring. Silicone rubber mixed with multiwall carbon nanotube composites were fabricated to make a highly stretchable (up to 120%) strain sensors. Embedding liquid state composites to the fabric leaded to enhance the adhesive force between the composites and fabric. The skin adhesive sensor system could be used to estimate rotation angles of the multi-axis joints while providing comfortable physical interfaces. To reduce misalignment to the axis of rotation, a calibration method was formulated based on geometrical relationship between the sensor axes and the joint angle. In order to validate the estimation performance of the sensor in multi-axis joint, shoulder flexion/extension and abduction/adduction angles were estimated. The results showed the system could estimate the rotation angles of the shoulder enough to identify motion intentions of the user. In the future, the proposed system can be applied to the motion monitoring system by direct attachment to skin without discomfort to the user in daily life.