An insect-inspired wall-climbing robot using capillary adhesion

This paper describes an insect-scale wall-climbing robot that can move on vertical and inverted surfaces using capillary adhesion. The adhesive mechanism of the robot is designed based on the attachment organs of ants, which utilizes surface tension and viscosity of secreted mucus for adhesion. In this study, we focused on the surface tension and utilize the capillary force of a water droplet confined between two surfaces. We installed two adhesive glass pads on the robot and provided water droplets on the pads. The robot is propelled using two wheels to stabilize the adhesive contact. Since the friction force between the pad and the surface is much smaller than the normal adhesion force, the robot can move smoothly by the wheels with the adhesive pads sliding on the surface. To evaluate the adhesive properties of the pad, the normal capillary force and the tangential friction force were measured. It was found that the adhesion force reached a maximum value when a 5 μl\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu \mathrm{l}$$\end{document} water droplet was supplied to the pad, and the friction force increases with increasing both positive and negative normal load. Two non-tethered robots with different weights and gear ratios were fabricated. Results of the climbing tests show that the robot weighing 10.2 g can successfully move on a vertical acrylic surface at a speed of 12.3 mm/s. The other robot weighing 14.3 g can climb 500 mm on a vertical surface, and 190 mm on an inverted surface.