Stretchable Liquid Metal E-skin for Soft Robot Proprioceptive Vibration Sensing

Vibration perception can help robots recognize their dynamic states to explore the surrounding environment. However, the intrinsic stretchability of soft robots poses challenges to integrating vibration sensors. This study introduces an innovative stretchable electronic skin (e-skin) that facilitates vibration proprioception in soft robots. Constructed with a thickness of approximately 0.1 mm, this ultra-thin e-skin is produced using a screen-printing technique with liquid metal particles, incorporating a kirigami design for seamless integration. The e-skin works by the triboelectric nanogenerator-based sensing mechanism, which transduces mechanical vibration into an electrical signal without an external power source. By analyzing the vibration signals generated by the dynamic motions of soft robots, the e-skin shows a wide range of applications. From the vibration signal of the soft robotic finger's sliding motion, 17 different textures can be distinguished with 99% accuracy. Furthermore, analysis of the vibration signal from a soft robotic gripper's swinging motion enables the estimation of both the type and weight of grains inside the container it grips, achieving accuracies of 97.7% and 95.3%, respectively. As such, this work presents a new approach to realizing the vibration proprioception of soft robots, thereby broadening the applications of dynamic proprioception in soft robotics.