Grasping Interface With Wet Adhesion and Patterned Morphology: Case of Thin Shell

Abstract

In this letter, we present an analytical method for studying the role of the micropatterned morphology of soft fingers with wet adhesion in grasping a deformable thin shell. This letter originated from a project on a robotic platform for autonomous attachment and removal of a soft contact lens in a “human eye” under a wet environment. In this scenario, a contact lens (hemispherical thin shell) was gripped by a soft-fingered hand in three conditions: inside/outside a liquid environment and when the contact lens was in contact with a convex curved substrate (as an eye). Two fingertip surfaces were compared: a flat surface, and a micropatterned surface inspired by the adhesion mechanism of a tree-frog's toes. The pattern of the latter comprised 3600 square cells, each of size 85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m × 85 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m interspaced by 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. A proposed analytical model was utilized to evaluate the grasp forces in both types of fingertip surface. The forces were subsequently verified by application in grasping a contact lens. The experimental results showed good agreement with the analysis as the micropattern pad decreased the preload and deformation of the shell 1.1–2× lower than that of the flat surface. This letter could be extended to model grasping interfaces with deformable curvature objects in wet and high moisture content environments.