Soft grasping with wet adhesion: Preliminary evaluation

Locking two surfaces with minimum normal force may result in safe grasping of objects in soft robotic hands. This paper presents a preliminary approach on design and analysis of a bio-inspired soft pad that enhances the adhesion with the environment by morphological design of its surface at micro-scale. The design principle is originated from the biological wet attachment of a tree-frog toes with the surrounding environment, caused by capillary force and surface tension of a secretion film between the toe and the surface. Especially, the tree-frog's toe has a network of polygonal cells (or blocks) with grooves among them, which act as liquid reservoirs and capillary tubes. We conducted some analysis on this wet adhesion principle, showing that total normal force increases with the grooved pattern compared to the that of the flat one in wet condition. We then fabricated a micro-patterned mold, using e-beam technology, for casting grooved surface onto a silicon substrate. We also conducted preliminary investigation of the adhesion strength of the fabricated soft pad with measurement of normal force under wet and dry condition. This is the first time wet adhesion was considered in soft robotic grasping, and this research is expected to be applied in wet and high-moisture environment.