Development of flexible tactile sensing arrays for hardness recognition

Hardness sensation is an essential function of human skin, which is significant for enhancing the objects perception ability of intelligent manipulators in various scenarios. Although progress has been made in mimicking this function of human hands, the hardness identification still remains a great challenge. In this study, inspired by the Hertz model and the static pressure response of Merkel cells (SA-I) mechanoreceptors, we develop a membrane-like piezoresistive flexible tactile sensor array (PFTSA) that consists of a flexible electrode array layer and a sensitive material layer with a micropyramidal structure, which can effectively identify the hardness values of different objects. The sensor can be a part of the manipulator's system due to its conformal ability and large deformation, which shows high pressure response sensitivity (4.432 mA/N in the 0–1 N pressure range) and good cycling stability (2100 cycles at 5 N), enabling the consistent and precise detection of external information. As a proof-of-concept illustration, we integrate the PFTSA on a finger of the manipulator to discriminate six objects with different hardness values. The results demonstrate the great potential of PFTSA in the application of human-machine interactions, paving the way for the development of robotic diagnostics, mechanical sorting operations and virtual reality technology.