Super-elastic ultrasoft natural rubber-based piezoresistive sensors for active sensing interface embedded on soft robotic actuator

Abstract

Piezoresistive soft composites are ubiquitous in strain sensing that manifests in a dramatic increment of electrical resistivity upon elongation. A piezoresistive strain sensor embedded-soft robotic arm has been a challenging task in terms of surface compatibility, shape and dynamics of the soft robotic components. We present a super-elastic, ultrasoft natural rubber composite containing multiwalled carbon nanotubes in presence of a hydrofinished oil-based softener. The resulting conducting elastomer offered a line-up of compelling characteristics such as low electrical percolation (<2 vol%), ultra-softness (Shore A harness ∼19), elastic modulus in the kPa range (∼350 kPa at 100% elongation), ultra-stretchability (∼800%) and high tensile strength (∼10.5 MPa). In addition, the sensor exhibited low hysteresis (3.5%), high piezoresistive sensitivity (gage factor≈472) and switching response over wide strain range (70%) and stable sensing performance for multiple test cycles (>1000). On account of the excellent responses mentioned, the sensor could detect human motion and has also been demonstrated in this paper. Furthermore, the sensing strip embedded on a soft robotic pneumatic actuator mounted on a test rig showed excellent movement detection response upon actuation. This proof-of-concept sensor-integrated soft robotic interface could be instrumental in the future development of proprioceptive sensing robots and soft robotic segments.