Research On Fringes Hybrid Coding Method For 3D Measurement

Fringe projection profilometry has been widely studied and used in the commercial and academic fields because of its properties of non-contact,full field measurement and fast data-processing speed.System calibration and fringe projection are two key technologies of fringe projection profilometry,determining some key factors of the system such as system setup,measuring speed,accuracy and robustness.Until now these two technologies still have some limitations in some cases,strict system constraints,slow measuring speed,low accuracy and weak robustness,to name a few.To solve the problems above,key technology of fringe hybrid coding method for 3D measurement has been studied thoroughly.It mainly consists of the following content.1.A calibration method is presented based on pattern geometric constraints.By analyzing the pattern distribution in the image coordinate,this method establishes one-to-one mapping relationship between phase and height directly,and the lens distortion of camera is considered and involved in the mathematical description.An efficient calibration procedure is presented as well.Experiments including error evaluation and robustness evaluation are conducted to verify its accuracy and robustness respectively.2.A calibration model of phase-to-height conversion is presented.By building a virtual camera coordinate system and analyzing the conversion process of fringe patterns between projector coordinate system and camera coordinate system,a one-to-one mapping relationship from phase to height in the camera coordinate system is built and the lens distortion of the camera is included in the PHC model.Plus,we present an effective and efficient calibration method for this model and back-projection process(BPP)is used to optimize the parameters of the camera in calibration process.Experiments are used to verify the feasibility of this model and its calibration procedure.3.Fringe projection system is used to design a volume measurement system.According to the requirement of system parameters,system structure is designed,devices are selected and software is designed.The 3D point cloud of measured object is acquired using fringe projection profilometry.Based on the volume calculating algorithm and the point cloud,the volume of the measured object is acquired.The feasibility of this system is verified by experiments.4.A time-spatial domain hybrid encoding method is presented in this paper.Three frames of sinusoidal two-level patterns are used to achieve 3D measurement in sub-pixel accuracy.Three sinusoidal two-level patterns are projected,image binarization and extracting stripe center method are then introduced to acquire sub-pixel accuracy image coordinates and codewords of the stripes.Simulation and experiments are used to verify the feasibility of this method.