Study On Fast Phase Correction Methods Of Gamma Imaging Model In Fringe Projection Profilometry For Blades

The rapid development of aviation industry and air-transport industry in China has deeply promoted the development of civil aviation maintenance.The blades of aviation engine are key components with the characteristics of many types,complex shape,serious dimension polarization and complicated manufacture.In terms of automatic welding repair technology for defect blades,it is the basis of guaranteeing the quality of welding repair for blades to accurately and quickly obtain three-dimensional model of defect blades.However,a mature domestic measuring and welding integration equipment hasn't been made,so it is fundamentally important to study three-dimensional measurement applied to automatic welding repair equipment for defect blades.Three-dimensional optical measurement technique based on fringe projection has been widely applied with its advantages of high-speed,high-accuracy and non-contact.Due to the system gamma effect,it destroys the sinusoidal fringe projected and brings phase error which is inevitable and ultimately influences system measurement accuracy.In order to solve this problem,two kinds of phase correction methods based on a gamma imaging model are presented.A gamma correction method based on step images is presented by establishing a system imaging model and analyzing the relationship between imaging spectrum and the system gamma.It estimates the system gamma by the nature of step images and pre-codes the system gamma into sinusoidal fringe images to offset the distortion caused by the system gamma through the projected fringe pre-deformation.According to the experimental result in the contrast experiment of different projection angles,it proves that this method can not only estimate the system gamma reliably,but improve phase correction speed.Phase correction accuracy to 0.0137 rad with the proposed method can be achieved by obtaining the plane phase error.In the projector calibration experiment,it is necessary to establish the corresponding relationship between camera pixels and projector pixels.The validity of the method can be further verified according to the calibration results before and after phase correction.By comparison with the measurement result of a ball before and after phase correction,it shows that the measurement accuracy of the ball is improved significantly and the relative measurement error is 0.20%.A relationship between phase error and the wrapped phase obtained can be proved by phase error analysis.A phase compensation method based on gamma can be further presented.It generates the artificial phase error by the system gamma obtained and compensates the measured phase.Compared with the proposed gamma correction method,this method has lower phase correction accuracy,but it simplifies the phase correction process and further improves the overall system measurement speed.In order to measure conveniently different dimensions of blades,a fringe projection experimental platform for blade measurement is set up and a blade model is obtained by system calibration.The measurement result of a blade before and after phase correction is compared.It proves that the proposed two phase correction methods can obviously improve the measurement accuracy of a blade.