Force-Sensor-Integrated Buckle for Wearable Robots

Wearable robots require compact sensing interfaces to monitor the forces transmitted through attachment straps. This study aims to combine strap fastening and force measurement in a lightweight buckle, enabling the magnitude and direction of strap loading to be monitored at the attachment interface. The proposed buckle incorporates two capacitive sensing cells and a flexure structure that converts applied loads into measurable capacitance changes. Their combined responses provide dual-axis force sensing within the buckle body. The complete device measures 64×45×10mm and weighs 34g, including its sensing and signal-processing electronics. Its force and angle ranges are 0–200N and ±8°, respectively. The average capacitance sensitivity was 1.33fF/N, and the force linearity error was 6.96% of full scale of output (FSO). Force root-mean-square error (RMSE) was 7.34% of FSO without initial preload and 1.21–1.76% of FSO with approximately 18N preload in the respective tests. The validation angle RMSE was 1.67% of FSO. Force hysteresis and repeatability were 8.88% and 0.51% of FSO, respectively. The force and angle FSO values were 200N and 16°. The estimated −3dB bandwidth was 2.7Hz. The proposed design provides a compact sensing interface for strap-based wearable robots.