Techniques for contact-based structural health monitoring with multirotor unmanned aerial vehicles

Use of Unmanned Aerial Vehicles (UAVs) for Structural Health Monitoring (SHM) has become commonplace across civil and energy generation applications with hazardous or time-consuming inspection processes. Expanding upon surface screening offered by non-contact remote visual inspection UAVs, systems are now beginning to incorporate contact-based Non-Destructive Evaluation (NDE) transducers to detect and monitor incipient sub-surface flaws. However, challenges to environmental interaction using conventional multirotor platform dynamics amid aerodynamic disturbances have frustrated efforts for stable and repeatable sensor placement. Herein, two distinct UAV systems are evaluated as a means to overcome these challenges. The first utilizes vectored thrust with a tri-copter layout. It may dynamically reorient dual-axis tilting propellers to directly effect interaction force and deploy drycoupled ultrasonic thickness measurement across omnidirectional targets. In static point and rolling scan measurement, laboratory tests demonstrate mean absolute error below 0.1 mm and 0.3 mm, respectively. The second UAV uses rigidly affixed multidirectional propellers to reverse and redirect its net thrust. Landing atop cylindrical structures it may crawl around their circumference, supporting itself without magnetic or vacuum adhesion. Arbitrary static position is maintained to within a mean deviation of 0.7 mm. Lastly, comparative discussion of each system informs strategies for further development of contact-based aerial SHM and its adoption to industrial practice.