A Novel Complete-Surface-Finding Algorithm for Online Surface Scanning with Limited View Sensors

Abstract

Robotised Non-Destructive Testing (NDT) has revolutionised the field, increasing the speed of repetitive scanning procedures and ability to reach hazardous environments. Application of robot-assisted NDT within specific industries such as remanufacturing and Aersopace, in which parts are regularly moulded and susceptible to non-critical deformation has however presented drawbacks. In these cases, digital models for robotic path planning are not always available or accurate. Cutting edge methods to counter the limited flexibility of robots require an initial pre-scan using camera-based systems in order to build a CAD model for path planning. This paper has sought to create a novel algorithm that enables robot-assisted ultrasonic testing of unknown surfaces within a single pass. Key to the impact of this article is the enabled autonomous profiling with sensors whose aperture is several orders of magnitude smaller than the target surface, for surfaces of any scale. Potential applications of the algorithm presented include autonomous drone and crawler inspections of large, complex, unknown environments in addition to situations where traditional metrological profiling equipment is not practical, such as in confined spaces. In simulation, the proposed algorithm has completely mapped significantly curved and complex shapes by utilising only local information, outputting a traditional raster pattern when curvature is present only in a single direction. In practical demonstrations, both curved and non-simple surfaces were fully mapped with no required operator intervention. The core limitations of the algorithm in practical cases is the effective range of the applied sensor, and as a stand-alone method it lacks the required knowledge of the environment to prevent collisions. However, since the approach has met success in fully scanning non-obstructive but still significantly complex surfaces, the objectives of this paper have been met. Future work will focus on low-accuracy environmental sensing capabilities to tackle the challenges faced. The method has been designed to allow single-pass scans for Conformable Wedge Probe UT scanning, but may be applied to any surface scans in the case the sensor aperture is significantly smaller than the part.

Autonomous Robotic Sensing for Simultaneous Geometric and Volumetric Inspection of Free-Form Parts

“…Recently, a completely autonomous surface-profiling and part inspection process has been proposed [17]. That enables in-process surface mapping by acquiring the readings of three laser distance sensors conveniently arranged at the end-effector of a robotic arm, which is also equipped with an NDT probe for the volumetric inspection of the sample.…”

“…The robot position is corrected, bringing the NDT probe to a constant standoff and aligning its sampling direction to the surface normal, thus allowing a good NDT signal collection. Autonomous surface exploration is enabled through a generalised Flood Fill Algorithm (FFA) [18], therein named as Complete-Surface Finding Algorithm (CSFA) [17]. Although this system is a significant advancement in autonomous robotic sensing, it has limitations.…”

Robotic Non-Destructive Testing

“…The other two papers on fixed-base robotic arms introduce a novel algorithm for complete-surface-finding [ 4 ] and an automated system for the real-time eddy current inspection of nuclear assets [ 5 ]. The work presented in the first article enables the robot-assisted ultrasonic testing of unknown surfaces within a single pass, a significant advancement toward fully autonomous inspection systems.…”

Robotic path planning using NDT ultrasonic data for autonomous inspection

“…With the rapid development of modern industrial technology, more and more industries require the use of Non-Destructive Testing (NDT) for quality inspection. In order to meet the needs of different NDT applications, the use of automated equipment to replace manual inspection of workpieces offers a more advanced inspection method leading to less operator fatigue, and improvements in repeatability [1]. Robots can be programmed to perform specific operations, thus replacing manual labour for heavy, complex and dangerous inspection tasks.…”