Cable-Integrated Single-Axis Load Cell for Tendon-Driven Robotic Actuation Enabled by Thin-Film Soft Sensor

Abstract

Cable-driven force transmission is one of the most widely used actuation mechanisms in robotics, finding applications in robotic arms, grippers, and wearable robots. However, measuring cable tension directly is challenging due to limited space and difficulties in attaching sensors to flexible cables. In this paper, we propose a single-axis load cell designed for direct integration into a high-strength woven cable, enabling tension measurement. A small portion of the cable becomes slightly stretchable by infusing an uncured polymer into its weaving pattern, and a liquid-metal thin-film soft sensor is affixed externally. As the cable experiences axial strain, the thin-film soft sensor stretches and changes its electrical resistance, providing real-time tension information. To mitigate the hysteresis and the nonlinearity caused by the viscoelastic effect of the cable and tendon materials, a metal spring casing surrounds the sensor, making the behavior of the sensor governed by that of the spring. The proposed sensor is experimentally characterized, and the result shows a linearity in the range of 5 N to 100 N with negligible hysteresis. It is tested with a twisted-string actuator to control the axial force generated by the actuator through a closed-loop control as an application.