The Research On Single Period Fringe And Double Four-step Phase Shift Projector Calibration In Fringes Projection 3D Measurement System

With the rapid development of civil aviation industry,the development of aircraft engine maintenance industry is attracting more and more attention in recent years.Aero engine blade is the key spare parts of the aircraft engine,which accounts for nearly half of the total amount of engine maintenance.Most of damage aero engine blades need weld and repair.Automated welding and repair has become the trend of development.In order to ensure the automatic welding and repair tracking precision of the defect aero engine blades,the key step is to obtain the accurate 3-D(three dimensional)shape and size.Non-contact optical 3-D measurement has become the first choice for 3-D measurement of the defect aero engine blades.The DLP(Digital Light Processing)projector with DMD(Digital Micromirror Device)digital micro mirror device as the core is the key component of the grating projection measurement system,which is used for projecting digital structured light fringes.The calibration accuracy is one of the important factors that affect the aero engine blades 3-D precision measurement accuracy.The projector calibration method of establishing the corresponding relationship between the camera and the projector obtaines the phase information by fringe projection method.This projector calibration method is not affected by the camera calibration results and does not exist two error propagation.But the issues of oblique projection and distortion of projector affect the projector calibration accuracy.To improve the calibration method of the projector,a high precision and high efficiency projector calibration method is proposed.The problem of the fringe period and the fringe series change when oblique project multi period fringes,which effect the transform precision between the absolute phase and the pixel coordinates.A projector calibration method is proposed which designing a single period fringe instead of the multi period fringes.Under the premise of ensuring the projector calibration accuracy,the time of the phase extraction and phase unwrapping is greatly shortened.The method of projecting single period grating fringe image improve the projector calibration efficiency.Aiming at the problem that the nonlinear phase error caused by the distortion of the projector can affect the projector calibration accuracy.The double four-step phase shift projector calibration method is proposed.Superposing the phase master diagrams which are obtained by double four-step phase shift.This method only need project twice as much as the traditional single period grating fringe and does not require the projector lens distortion correction error or phase error compensation.This projector calibration method also can weaken the nonlinear phase error that influence the projector calibration accuracy,which have the convenient operation and the simple equipment.The 3DS MAX software simulation and experimental verification proved that the single period fringe and double four-step phase shifting projector calibration method can quickly and accurately obtain the internal parameters and external parameters of the projector.The results satisfy the requirements of the three-dimensional measurement of the aero engine blades.Collecting the point cloud data of aero engine blades one surface,this experiment proof that the generation of the aero engine surface have a good experimental effect.