Surface Texture of Deformable Robotic Fingertips for a Stable Grasp Under Both Dry and Wet Conditions

This letter investigates the effect of the surface texture of soft deformable fingertips on the maximum resistible force under dry and wet conditions, and proposes a new hybrid structure that provides a stable grasp under both conditions. One definition of stable grasp is the capability of balancing a large external force or moment while grasping. For soft fingertips, both the friction and surface deformation contribute to the stability. Therefore, we investigate the maximum resistible force, which is defined as the maximum tangential force at which the fingertip can maintain contact when applying and increasing the tangential/shear force. We investigate the slit textures with primitive patterns and demonstrate that the nonpattern performs the best under dry conditions, whereas the horizontal slit pattern performs the best under wet (oily) conditions. Based on this, a concentric hybrid texture of the two patterns is proposed, and its effectiveness is verified by a grasping test.