Integrated Force Sensing Technology for Twisted String Actuation Using Conductive Yarns

Abstract:
Twisted String Actuators (TSA) are compact, lightweight, and low-cost mechanical devices. They can be used in robotics to convert rotary motion into linear tensile force. It is often necessary to measure the tensile force of TSAs. However, these measurements are currently performed using external force sensors in TSA systems, which are bulky and expensive. We propose to use conductive yarns as integrated force sensors to eliminate the need for external sensors, thus saving space and cost. Our approach calculates the applied force from the change in resistance of the conductive yarns, which changes with the angle of rotation and the applied force. To verify this approach, a mathematical model is developed and experiments are carried out on a TSA test rig using silver-coated conductive yarns as strings. The results show that the resistance decreases with increasing angle of rotation and force. However, for reliable and robust measurements, issues such as wear, standard deviation of resistance measurements, and yarn properties need to be addressed. Despite these challenges, the use of conductive yarns for TSA force sensors is promising, provided that improvements in yarn properties and contact friction are achieved.