Real-Time 3D Proprioception for Soft Robots Using a Single Capacitive Bend Sensor

Soft robots enable safe human-robot interaction, but their continuous deformation complicates real-time state estimation, particularly under open-loop control. This paper presents a lightweight proprioceptive approach for reconstructing the 3D pose of a cable-driven soft actuator using a single commercial capacitive bend sensor. The sensor measures net tip bending, which is mapped to the full actuator shape using a Piecewise Constant Curvature model, avoiding complex processing and data-driven training. Experiments on a spiral-inspired actuator show accurate, low-latency pose reconstruction that significantly outperforms open-loop motor-based estimation and remains robust to cable slack and hysteresis, achieving millimeter-level accuracy suitable for wearable and real-time soft robotic applications.