Highly sensitive flexible three-axis tactile sensors based on the interface contact resistance of microstructured graphene.

The lack of high-performance tactile sensors, especially for pressure/force, is a huge obstacle for the widespread application of intelligent robots. Current pressure sensors are often operated in the high range of pressure and normal direction, showing a little ability in the low range of pressure and three-axis direction simultaneously. Herein, a highly sensitive flexible tactile sensor with three-axis force sensing capacity is presented by combining microstructured polydimethylsiloxane (PDMS) arrays and a reduced graphene oxide (rGO) film. The deformation of microstructured rGO/PDMS results in a change in the contact area between the rGO film and electrode, leading to a high sensitivity of -1.71 kPa-1 in the low range pressure of 0-225 Pa with a fast response time of 6 ms at a large feature size of 100 μm. To realize three-axis sensing, a sensing unit was built up, which was composed of the adjacent four parts of patterns and electrodes underneath a bump. A mechanical model of the exerted spatial force was established to calculate each axis force component via the deformation of the rGO/PDMS pattern. The experimental results show that the current difference between the adjacent two parts has a strong relationship with the applied force. As a proof of concept, we have demonstrated a 3 × 3 array sensor for arbitrary force sensing. Our tactile sensor would be used in transmitting information from a gentle spatial force and would exhibit broad applications as e-skin in integrated robots.