# Strong and Agile Wall-Climbing Robots Capable of Traversing Obstacles via Anisotropic Acoustic Adhesion

## TL;DR

This paper introduces a small, agile climbing robot that uses sound-based adhesion to climb walls and ceilings, carrying a heavy payload while navigating complex environments.

## Contribution

The novel contribution is the development of a compact climbing robot using anisotropic acoustic adhesion for strong normal adhesion and minimal tangential resistance.

## Key findings

- The robot can climb vertical and inverted surfaces at 70 mm/s while carrying a 70-g payload.
- Acoustic adhesion is achieved through a vibrating flexible disk that creates a thin air layer with negative pressure.
- The robot demonstrates agile mobility in 3D mazes and retired aircraft engines for damage inspection.

## Abstract

Small inspection robots are highly desirable for inspecting complex machinery and detecting damage in confined spaces. However, common climbing robots that rely on vacuum suction or bioinspired dry adhesion often suffer from bulky sizes or slow locomotion speeds. Developing compact yet intelligent wall-climbing robots that mimic the agility and payload capacity of geckos remains an important challenge. In this work, we design a 20-g, 10-cm artificial intelligence (AI)-integrated robot capable of carrying a 70-g payload while climbing on vertical and inverted surfaces at a speed of 70 mm/s. Acoustic adhesion is generated by vibrating a flexible annular disk on smooth surfaces, where air is periodically absorbed and expelled, resulting in negative pressure. The thin air layer with negative pressure indicates anisotropic performance, characterized by strong normal adhesion and negligible tangential resistance, making it highly suitable for designing small, yet strong, climbing robots. The theoretical model and laser surface morphology measurements reveal the thickness-dependent adhesion of a thin air layer beneath the disk. A servo-spring system is designed to meet the stringent requirements of a thin air layer thickness, yielding robust normal adhesion. Resonance analysis and the use of proper spring material stiffness further enhance adhesion performance. Therefore, combining this innovative acoustic adhesion with optimized structural design, our robot achieves gecko-like mobility and payload capacity. Additionally, integrated AI techniques simplify robot control, allowing voice-commanded operation and autonomous task execution. We demonstrate the functions of these climbing robots through agile inspections in a 3-dimensional maze and retired aircraft engines. This work presents the design of small, strong, and agile climbing robots that utilize anisotropic acoustic adhesions, demonstrating agile mobility across gaps, right corners, and discontinuous curved surfaces. It offers potential solutions for in situ damage detection in aero-engines and other complex equipment cavities.