Defect imaging curved surface based on flexible eddy current array sensor

Abstract

Due to it is difficult to visually reflect the size, distribution shape and location of the defects in surface quality detection of complex surfaces, the flexible eddy current array (FECA) probe combined with the Cartesian coordinate robot is employed to scan the defects on last stage blades of steam turbine (LSBST) in this paper. The sensor probe is designed to parallel and stagger arrangement and weld onto a flexible printed circuit board (FPCB). The FECA sensor is thin and flexible, and thus it can conform to the surface geometries of the LSBST. To increase the inductance value of the single probe coil, Iron core is added in the middle of the cylindrical coil. In the process of detecting signal, the starting point compensation and lift-off effect compensation are carried out, which improves the resolution of defect detection and realizes the imaging of the natural defects on the surface of LSBST. Finally, the effect of defect imaging on steam turbine blades is verified through conducting experiments. Results demonstrate that the size, location and shape of defects are consistent with the actual situation which verifies the feasibility of the imaging algorithm.