Implementation and evaluation of an autonomous airborne ultrasound inspection system

Abstract

The mobility of an Unmanned Aerial Vehicle (UAV) offers significant benefits when deploying remote Non-Destructive Testing (NDT) inspections of large-scale assets. Ultrasonic inspection is primarily a contact-based NDT method, that grants the opportunity to remotely monitor the structural health of an industrial asset with enhanced internal integrity information. Presented in this paper is an implementation of an autonomous UAV system, equipped with an ultrasonic thickness measurement payload. This system is designed to conduct ultrasonic inspections of non-magnetic facilities and industrial infrastructure where surface adhesion cannot be achieved magnetically. Operating within a laboratory environment, this system autonomously positioned the transducer on a vertically mounted, unpainted, aluminium sample and completed an ultrasonic thickness measurement without manual intervention. An onboard laser scanner provided instantaneous UAV alignment and standoff error measurements versus the sample's surface normal vector. While inspecting a region of the aluminium sample with 12.92 mm nominal thickness, the UAV system demonstrated a measurement error of 0.03 mm. During this process, the standard deviation of the craft's positional error was recorded to be below 63.26 mm, accompanied by an angular alignment error versus the surface normal vector of below 2.71°. The accuracy of the UAV deployed inspection, including thickness measurement accuracy and positional accuracy, depends on many factors. As such, transducer alignment constraints, electrical noise and UAV stability are investigated and discussed. Findings from this paper may be taken to inform future research regarding autonomous airborne ultrasonic inspection of constructed infrastructure and industrial facilities.

Dry Coupled Ultrasonic Non-Destructive Evaluation Using an Over-Actuated Unmanned Aerial Vehicle

“…Protrusion of the deformable tire beyond the flanking support caps is similarly found to permit acoustic coupling at probe angles within approximately ±10° of surface normal: an improvement over the ±3° alignment tolerance observed using hard-faced probes [39]. These pressure and orientation criteria therefore define the physical interaction necessary for this probe to support ultrasonic measurement.…”

“…All works listed in TABLE VIII conduct static, point thickness ultrasonic measurements. However, many are limited in applicability to single orientation interaction modes: contacting vertically planar walls [37], [39], the underside of horizontally planar ceilings [38], or depositing a sensor package atop horizontal plates and pipes [35]. We show increased applicability to the generic in situ inspection process through the multidirectional target interactions of Section IV by development of a novel thrust vectoring, bi-axial tilting propeller, over-actuated tricopter architecture.…”

“…Comparatively, under-actuated quadrotors with unidirectional thrust, [35], [38], [39], exhibit strong coupling between attitude and translational dynamics. To control interaction forces they must reorientate the full UAV body, potentially incurring ultrasonic probe motion and degrading its measurements.…”

“…Kocer et al demonstrate a proof of concept Dry coupled ultrasonic non-destructive evaluation using an over-actuated unmanned aerial vehicle controller for ultrasonic thickness measurement of the underside of a horizontal acrylic plate using a standard quadcopter [38]. Others conduct ultrasonic measurement via short-duration contact with a vertical plate under autonomous control from a planar lidar sensor [39].…”

Sensor-Enabled Multi-Robot System for Automated Welding and In-Process Ultrasonic NDE

“…One particular challenge with such crawlers is accurately tracking their position, which is achieved through a combination of drive encoders, accelerometers, machine vision and in often cases expensive external measurement systems [ 10 ]. Multirotor aerial vehicles can deliver visual [ 11 ], laser and, more recently, contact ultrasonic [ 12 ] sensors in remote NDE inspection scenarios, where a magnetic crawler could not be deployed. While umbilical/tether cables are used commonly with mobile crawlers, they pose a challenge for the manoeuvrability and range of aerial systems.…”