A study on 3D scan-based robot arm control approach for pulse-echo laser ultrasonic testing of curved composite structures

Abstract The increasing use of composite materials in aircraft structures requires efficient non-destructive testing (NDT) to ensure structural integrity. Pulse-echo (PE) laser ultrasonic testing (LUT) is a powerful, contactless, and medium-free NDT technique for detecting subsurface defects. This study proposes a 3D scan-based robot arm control approach that utilizes 3D scanning to create a raster scan path for a robotic PE ultrasonic propagation imaging system. In contrast to existing PE LUT techniques that are typically limited to specific shapes or rely on predefined mathematical models, the proposed approach enables automated path generation directly from 3D scan data, making it suitable for inspecting complex, arbitrarily curved surfaces. Experimental validation on a non-planar carbon fiber-reinforced plastic (CFRP) specimen achieved high mean signal-to-noise ratios with low mean errors, confirming the approach’s ability to maintain a constant standoff distance and ensure a perpendicular incident angle between the sensing laser and the specimen surface. Additionally, the approach was successfully applied to a real aircraft composite structure, further demonstrating its feasibility in practical inspections. By eliminating the need for predefined geometric models and incorporating actual surface data, the proposed approach significantly enhances the flexibility and applicability of robotic PE LUT for inspecting curved composite structures.