Contour Extraction of Curved Metal Component Using Robotic Arm-Assisted Eddy Current Testing System

The design of metal components in industrial equipment is becoming increasingly complex and the manufacturing is more and more precise. As metal components with complex morphologies bear uneven load distribution during service, they are more prone to deformation and wear. Contour extraction is therefore critical for quality assessment. Eddy current testing (ECT) technology offers a nondestructive solution for contour extraction, but its accuracy is hindered by the coupling of liftoff and tilt effects. In this study, a contour extraction method is proposed, which uses a specially designed eddy current (EC) probe and an established robotic arm assisted ECT system. Contour is reconstructed based on tilt angle inversion instead of liftoff measurement, thus avoids the influence of the liftoff-tilt coupling effect. The probe is composed of two coplanar horizontal rectangular coils. It is found that there exists a peak value in the signal of probe response vs. liftoff, and the peak value is only affected by the tilt of the component surface in the direction of the line connecting the coil centers and is independent of the tilt in the orthogonal direction. This characteristic allows to measure the tilt angles of the component surface in different directions individually, which avoids the complicated decoupling of measuring the two tilt angles. The probe, carried by the robotic arm, scans the designated area of a curved metal component (CMC) and obtains the tilt angles at every testing point. The contour of the component is reconstructed by the integration of the surface slopes derived from the tilt angles. An area of a sample surface with 5 mm maximum difference in height is tested, and the average error between the extracted contour and the actual contour in the height direction is 0.03 mm. The proposed method is nondestructive, noncontact, environmentally robust, and highly promising for contour extraction of CMCs.