Highly sensitive capacitive flexible 3D-force tactile sensors for robotic grasping and manipulation

Highly sensitive flexible three-dimensional (3D) force tactile sensors with synergistic normal and tangential force perception are urgently required for emerging electronic skin (e-skin) applications. Herein, for the first time we report a new type of capacitive 3D-force tactile sensor with high sensitivity (1.08 and 1.20 N−1 corresponding to respective normal and tangential force range of 0.7 and 0.6 N) and flexibility, rapid dynamic response (response/recovery time of ∼40/∼100 ms) and low hysteresis (5.93%) based on a U-shaped groove structure. These are developed by a low-cost, practical and efficient 3D printing technique along with a layer-by-layer assembly method. The theoretical mechanism is established to elaborate the corresponding working principle and sensing performance, which is further complementarily verified by finite element modeling (FEM). The results of theoretical calculation, FEM simulation and experimental measurements are in good agreement, consolidating the effectiveness of the developed devices as flexible 3D-force tactile sensors. Importantly, the proposed theoretical model provides constructive and general guidance for capacitive sensors. The capability of our 3D-force tactile sensor used as a flexible e-skin for tactile sensing is confirmed by gripping and slipping detection, as well as rocker movement detection. The developed flexible 3D-force tactile sensors are promising candidates for a wide range of applications, e.g. artificial skins, soft robots, intelligent prosthesis, and human–machine interface systems.