An Optimized Robotic Scanning Scheme for Ultrasonic NDT of Complex Structures

To reduce the inspection time for evaluating defects in geometrically complex structures, this study investigates a more efficient scheme in which the test object is grasped by the robot (TOGR). Compared with the traditional approach in which the ultrasonic probe is grasped by the robot (UPGR), the TOGR solution consumes less time in the inspection of complex specimens because fewer joints are involved in the scanning motion. A six-degrees-of-freedom industrial robot is used to hold the non-destructive testing (NDT) probe normal to the test surface, and ultrasonic time-domain reflectometry (UTDR) is used to identify the flaw echo. The ultrasonic signals are acquired synchronously with positional data regarding the robot. The TOGR solution shows a significant improvement in the positional accuracy of the robotic trajectory. The distribution of defects inferred via ultrasonic C-scan imaging is plausible, as verified by the stable surface echo in the time domain during an experimental test. The TOGR solution is well suited for the high-speed automatic inspection of complex structures, such as turbine blades, milling tools and other test specimens with curved surfaces. Experiments were conducted in which NDT data were acquired at scanning speeds of up to 50 mm/s with a minimum defect resolution of 0.15 mm.