Deformable fingertip with a friction reduction system based on lubricating effect for smooth operation under both dry and wet conditions

For stable robotic grasping, a surface with high friction is required; thus, a soft surface is preferable. In contrast, a slippery surface is preferable for inserting fingers into a narrow space or placing a grasped object on a table. Additionally, in an environment involving humans, such operations are performed under dry and wet conditions. Hence, this study aims at developing a soft robotic fingertip with a friction control system in which the surface friction is actively controllable under dry and wet conditions, whereas the external effects on friction, such as wetness, are minimized. The basic concept involves achieving high friction under both conditions by using a slit surface texture, while friction is reduced with a lubricating system by utilizing capillary action. The experimental validation shows that the proposed lubricating system embedded in a robotic finger surface successfully reduces friction under both conditions. The releasing and grasping operations reveal the efficacy of the proposed system in an actual situation. Additionally, the mechanism of the lubricating method is confirmed by introducing the spreading coefficient.