Highly Stretchable Strain Sensor With Spiral Fiber for Curvature Sensing of a Soft Pneumatic Gripper

This paper proposes a flexible strain sensor based on the principle of resistance sensing to estimate the curvature information of the soft pneumatic gripper. The proposed sensor mainly includes a spiral conductive fiber and a central elastic base pillar. The conductive fiber is made of the stretchable elastomer DragonSkin-30 and multi-walled carbon nanotubes (MWCNTs) mixture, and a customized platform is designed to perform extrusion for fabrication. Three essential factors of the substrate, the fiber diameter, and the mixing ratio of MWCNTs have been investigated to improve the sensitivity and strain range of the sensor. Ecoflex-10 with excellent tensile properties has been selected to make the elastic base pillar. The stretchability, linearity, and service life of the sensor were improved by optimizing the spiral arrangement of conductive fibers through experiments. The proposed approach for manufacturing and assembly offers the advantages of easy implementation, convenient integration, and low cost. The electrical performances of the prototyped spiral sensor have been characterized, and it can reach an excellent strain range of up to 400% with linearity of 98%. The prototype has been integrated on the outer surface of a soft pneumatic gripper and well reflected the diameters of the unknown objects with an error of 3.99% through calibration and grasp-release experiments.