Research On 3D Measurement Technology Of Digital Fringe Projection

Three-dimensional(3D)measurement with digital fringe projection is one of the most representative technologies in the field of optical 3D measurement,and has been increasingly widely used in many fields,such as national defense security,advanced manufacturing,medical diagnosis,cultural education,studio entertainment,and so on,which benefits from its advantages of non-contact,high universality,high resolution,high precision and high speed,etc.This dissertation focuses on the nonlinear response,3D reconstruction efficiency and high-dynamic-range 3D reconstruction in the 3D measurement with digital fringe projection.The goal is to explore a universal nonlinear phase error model and compensation methods,flexible and efficient phase-mappingbased 3D reconstruction method and active light-field 3D reconstruction method with single group of fringe images.In the 3D measurement with digital fringe projection,the nonlinear response between the digital projector and the camera brings a large phase error,which is an important source of error in 3D measurement.The existing nonlinear phase error models and compensation methods are generally applicable only to the 3D measurement with fringe projection of a special phase-shifting step.When changing the phase-shifting step,it is usually necessary to reestablish a phase error model.Aiming at this problem,this dissertation employs the power-law response to derive the nonlinear phase error,and establishes a universal phase error model.The model is suitable for 3D measurement with fringe projection of any phase-shifting step.Based on the model,an active and a passive phase error compensation methods are proposed respectively.Experimental results verified that the two methods can compensate the nonlinear phase error effectively and accurately.In addition,the current nonlinear phase error compensation methods require to utilize some additional auxiliary conditions,such as phase benchmark building,gamma calibration,response curve fitting,and so on,which affects the flexibility and robustness of the methods.This dissertation proposes a nonlinear phase error compensation method based on Hilbert transform,by making use of the property of Hilbert transform that induces a phase shift of ?2 to a signal.The method can adaptively compensate the nonlinear phase error without additional auxiliary conditions.Experimental results demonstrated that the phase error was reduced by 80% in the three-step phase-shifting method,and by more than 95% in four or more step phaseshifting method.There are two major 3D reconstruction methods for 3D measurement with digital fringe projection,phase-height mapping and stereovision.The former can map the phase to the height coordinate efficiently,but its application flexibility is low due to the limitation of system structure.The latter adopts flexible binocular structure,but its efficiency of 3D reconstruction is low causing by the time-consuming process of homogenous point search.This dissertation proves that the phase can be mapped not only to the height coordinate(Z),but also to the transverse coordinates(X,Y),through a strict derivation based on the stereovision model.Then a method of phase-3D mapping with digital fringe projection is proposed,which makes best use of the advantages of the phase-height mapping and stereovision.A two-step calibration approach for determining the phase-3D mapping coefficients is also proposed to achieve flexible and efficient 3D reconstruction.Experimental results showed that the 3D reconstruction efficiency of the proposed method is 80 time of the stereovision method.The methods of high-dynamic-range 3D reconstruction with digital fringe projection generally need to capture multiple groups of fringe images in diverse viewpoints or optical parameters,then reconstruct effective 3D data of high-dymanicrange surface of objects.These methods are cumbersome in experimental operation and complex in data processing.Making use of the light-field imaging property of ray direction recording,this dissertation introduces the light field imaging into the 3D measurement with digital fringe projection to propose a method of active light-filed 3D reconstruction with digital fringe projection.The proposed method realizes multidirectional 3D reconstruction by phase-depth mapping from different ray directions.A flexible ray-based calibration approach is also proposed to determine the mapping coefficients for each ray.As a result,the proposed method can achieve highdynamic-range 3D reconstruction with single group of fringe images.