A Low Cost Multi Degree of Freedom Capacitive Soft Sensor

Abstract

Embeddable strain sensors are typically deployed to measure a single mode of deformation and thus require additional sensor units for multiple degree of freedom (DOF) sensing. In this work, a low-cost capacitive-based soft sensor capable of multi DOF sensing is developed for soft robotic systems and wearable applications. The single-common double-capacitor (SCDC) sensor can measure linear stretching, bending, and twisting action with only three conductive elements, by simultaneously measuring the capacitance across different electrode pairs. Analytical models of deformation in each DOF closely match experimental measurements, showing how the sensor can measure simultaneous stretching and bending or simultaneous stretching and twisting. Experimental results show high sensor response linearity for stretching and bending (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ≥ 0.99) and twisting (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ≥ 0.91). The sensor was embedded within a fluidic elastomer actuator to measure curvature without affecting actuation performance and is demonstrated as a lightweight wearable sensor to measure finger joint angles. The dimensional scalability and ease of fabrication of the SCDC sensor make it well suited to emerging applications in wearable posture and motion sensing, soft robotic manipulation, and locomotion.