Approach for assessing compressor blade leading edge damage without CAD model reference

A miniaturized fringe projection sensor is being developed as part of a transfer project within the Collaborative Research Centre 871 for the automated inspection of aircraft engines. The sensor is intended for damage assessment on high-pressure compressor (HPC) blades. It features a rigid design and is actuated by a linear and a rotational axis. This article addresses the evaluation of damages on the leading edge of HPC blades. The criteria used to assess the defects are depth, width, and location on the blade. Determining the position of a defect on the blade is challenging because only a partial area of the blade is measured. In this context, the rigid structure of the measuring system is advantageous. The axis kinematics and a hand-eye calibration can be used to estimate the pose of the sensor head. This enables the positioning of individual measurements relative to one another. A second challenge in damage analysis is that a CAD model of the blade is often not available during inspection, leaving no reference for comparing deviations between a CAD model and the measurements. This article proposes an approach for determining the depth of a damage on the blade’s edge. For this purpose, profile sections of the measurements are analyzed. These are used to determine the radius at the blade edge and to generate a reference edge. Deviations between the reference edge and the measurement can then be calculated, from which the values of depth and extent are derived. Based on these three criteria, the condition of the blade can be assessed.