Projection CCD Moiré method for dynamic full-field out-of-plane displacement measurement of aviation propellers

Accurate full-field out-of-plane displacement measurement of high-speed rotating propeller blades is critical for aviation propeller performance evaluation and fault diagnosis. Conventional image-based methods face an inherent accuracy–speed trade-off, as the reduced image resolution at high frame rates degrades measurement precision. This work extends the CCD moiré method from the attached-grating scheme to a projection-based configuration, gaining out-of-plane sensitivity while retaining the period-magnification effect that enables high-precision measurement from low-resolution images. However, projecting the grating rather than attaching it introduces new factors that degrade fringe quality—projector gamma nonlinearity, lens diffraction, and projector–camera temporal mismatch—which are therefore analysed by theoretical modelling and simulation. Binary fringe patterns are shown to be inherently immune to gamma distortion and to be converted by lens diffraction into high-quality sinusoidal moiré. Two projection modes are examined: for periodically refreshed projection, the temporal pitch ratio governs flicker, yielding an integer-ratio criterion for flicker-free imaging; for fixed-pattern projection, no temporal-matching constraint arises, so the frame rate can be chosen freely. A 38.000 mm standard sphere was reconstructed with a fitted diameter of 37.315 mm (relative error 1.80%; MAE 0.084 mm, RMSE 0.098 mm), and calibrated displacements were measured with average MAE and RMSE of 0.083 mm and 0.099 mm—approximately one third of the errors of conventional projection fringe profilometry under identical conditions. This accuracy margin can be traded for resolution and hence frame rate. Experiments on a composite propeller at 172–802 RPM captured full-field displacements and reliably identified an embedded blade defect and mounting-platform looseness.