Hemispherical Multidirectional Eddy Current Array Sensor for Robotic Profiling of Metallic Edge Surfaces

In non-destructive testing (NDT), inspection of complex metallic parts is a challenge. At the moment, the object ' s surface profile is typically obtained from design documents or through separate dedicated measurements such as optical methods. Previously we have used contactless inductive sensing and real time feedback to control a robot to follow unseen complex smooth surfaces in a non-contact autonomous manner. In this work, further progress is made to increase the capacity of the system so that it can transverse a sharp edge. A hemi-spherically-arranged multidirectional eddy current array sensor is devised for this purpose. The array sensor is fixed to the end-effector of a UR5 robotic arm, and its signals are used to control the pose of the robotic arm, keeping its axis perpendicular to the local surface and maintaining a constant lift-off distance when traversing a sharp edge, both for convex and concave ones. The metallic surface profile can then be reconstructed from the scanning trajectory of the robotic arm. The resulting sensor pose is also used to estimate the edge direction, enabling integrated reconstruction of both geometry and orientation. Experiments on copper foil samples with both convex and concave edges at 120°, 90°, and 60° demonstrate accurate reconstruction results. The acquired scanning trajectories closely follow the true surface profiles and exhibit symmetric arc transitions at edge regions. For a 90° edge, the maximum profile measurement error is less than 3 mm, and the estimated edge orientation deviates less than 1°.