Electroadhesion Design for Microrobotic Locomotion on Diverse Surfaces

Abstract

Small bioinspired insect-scale microrobots have the potential to someday be useful for exploration or inspection tasks, with their small size allowing for access to confined spaces. However, real-world inspection tasks often involve surfaces of variable inclines and finishes, highlighting the need for small-scale robust climbing options that are adaptable to diverse terrains. In this work we examine development of the Harvard Ambulatory Microrobot (HAMR), a 4.5 cm, 1.5 g microrobot. Improvements to the fabrication process for more robust manufacturing are made, with demonstration of an even smaller scaled (22.5 mm, 320 mg) HAMR-JR robot. Electroadhesion improvements and robot capabilities are further explored for the purposes of enhancing locomotion and payload capacity over a diversity of pristine, rough, and inclined terrains. On pristine, smooth, flat terrains, improvements using thinner dielectric layers enable fabrication of electroadhesive pads capable of 60 g of shear force (roughly 40 times the weight of a robot). On these smooth terrains, large simple circular foot pads exhibit the greatest shear forces. However, on rougher inclined surfaces, pads which adjusted the width, length, and number of spoke-like features provide greater compliance and achieve more consistent shear adhesion forces. The improved adhesion capabilities of a compliant spoked foot pad are demonstrated with enhanced robot locomotion over steeper 37 degree inclines on a rough (75 µm vertical and 1 mm horizontal spatial roughness) conductive surface. Further design explorations of various compliant kirigami geometries are conducted to consider spoke, serpentine, and fractal patterns, with a simple model developed for spoke design parameters. Serpentine designs are found to most enhance compliance and shear adhesion capability on rough surfaces (up to twice the adhesion force of circular designs). Several demonstrations of the robot using compliant electroadhesive pads illustrate the potential of the robot to be used in industrial environments, with simple manipulation and locomotion tasks over a variety of conductive rough, inclined, and curved terrains.