Accurate calibration method for blade 3D shape metrology system integrated by fringe projection profilometry and conoscopic holography

Blade with complex and thin-walled shape is one of the critical parts in an aircraft engine, and its whole 3D shape should be measured to ensure the efficiency and safety of the engines. But there hardly exist an omnipotent blade 3D measurement method that can simultaneously address accuracy, efficiency and ability of measuring high-reflective surface. To this end, a hybrid 3D metrology method integrated by fringe projection profilomety (FPP) and conoscopic holography (CH) is developed, and FPP is responsible for gaining measurement accuracy and efficiency, while CH scans the high-reflective areas that FPP fails to measure. In this integrated system, the key task involved is calibration of rigid transformation between coordinate systems of inhomogeneous 3D sensors, so an accurate calibration method is proposed. It only requires FPP sensor and CH sensor to measure a planar target at several different poses in the measurement volume, and then the measured space planes can be used to compute rigid transformation. In order to enhance its robustness to noise, a non-linear optimization model that considers signal-to-noise ratio (SNR) of CH sensor is establish for obtaining the optimal calibration results. The simulations and real experiments demonstrate that proposed method can achieve accurate and robust calibration of inhomogeneous 3D sensors for measuring the blade.