Design of a Small Unmanned Aircraft System for Bridge Inspections

Abstract

Bridge inspections are an important procedure for maintaining the infrastructure vital to our economy and well-being. The current methodology of utilizing specialized equipment such as snooper trucks and scaffolding to support manned-inspections poses a significant financial cost, disrupts traffic, and is dangerous to the inspectors and public. The advent of unmanned aerial systems (UAS), more commonly called drones, presents a practical solution that promises reduced cost, enhanced safety, and is significantly less intrusive than previous methodologies. Current limitations in the implementation of UAS include the reliance on a skilled operator and/or the requirement for a UAS to operate in a cluttered, GPS-denied environment. A solution to these challenges is presented in this paper by utilizing commercial off-the-shelf (COTS) hardware including laser rangefinders, optical flow sensors, and live video telemetry. Included in the system is the obstacle avoidance equipped drone and a ground station intended to be manned by a pilot and bridge inspector. The proposed custom-fabricated UAS was implemented during eight inspections of Florida Department of Transportation (FDOT) bridges. The UAS was able to navigate under GPS-denied and obstacle-laden bridge decks with position-hold performance comparable to, if not better than, a COTS unit in an unobstructed environment. The position hold capability maintained an altitude of ±12.8 cm with a horizontal hold of ±435 cm. Details of the hardware, algorithm development, and suggestions for future research are discussed in this paper.

User requirements for an automated bridge inspection system

“…The current UAS implementation has challenges, such as the need for a trained operator and/or the need for a UAS to function in a crowded, GPS-denied environment. A solution to these challenges was presented by Whitley et al (2020) using commercial off-the-shelf (COTS) gear such as laser rangefinders, optical flow sensors, and live video telemetry. The system includes a drone with obstacle avoidance capabilities and a ground station manned by a pilot and bridge inspector.…”

Impact of UAV Hardware Options on Bridge Inspection Mission Capabilities

“…Custom-made UAVs have gained considerable attention to address the current limitations of off-the-shelf vehicles. Whitley et al (2020) [17] presented a solution to the current limitations in the implementation of UAVs which are reliance on a skilled operator and/or the requirement for a UAV to operate in a cluttered, GPS-denied environment. They utilized commercial off-the-shelf hardware, including laser rangefinders, optical flow sensors, and live video telemetry.…”

“…UAVs have emerged as a viable and promising option to facilitate and expand bridge inspection activity and overcome the challenges of conventional bridge inspection [17][18][19][20][21]. Their use can both expedite current visual-based inspections and enable more advanced multi-sensor approaches [22].…”

Localization System for Lightweight Unmanned Aerial Vehicles in Inspection Tasks

“…There are popular SLAM ( Self Localization And Mapping ) solutions, such as VSLAM [ 19 ], LOAM [ 20 ], or ORB-SLAM [ 21 ], which aim to solve the localization problem, using onboard sensors. UAV localization in GNSS-denied environments has also been approached by using algorithms based on optical flow and rangefinder sensors [ 22 ]. Unlike LIDARs, cameras can offer a more lightweight solution than most mechanical and solid-state LIDARs, which have a weight that is one or even two orders of magnitude greater.…”