Research On Structured Light Three-dimensional Scene Reconstruction Using Digital Fringe Projection Technique

Phase-shifting digital fringe projection technique has been playing a prominent role in3D shape measurement for its high resolution,high speed,and non-contact measurement.It gains extensive applications in many areas such as product design and manufacturing,quality inspection and control,biomedicine,virtual reality,and intelligent security.A typical fringe projection vision system is composed of one digital camera and one digital projector.At present,the research work mainly focuses on phase to 3D coordinates mapping,phase unwrapping,system calibration,error compensation,and high-speed measurement.In recent years,large-scale three-dimensional measurement has received considerable attention in the academic community and technology companies.A typical application is safety inspection for human-robot cooperation in industrial automation field.Nowadays,the employment of multi-camera structure can be applied to realize the three-dimensional scene reconstruction for safety inspection,for example,Pilz Safety Eye triple-camera 3D vision system.However,because of it~?s passive measurement property,there exist technical challenges on feature point matching and computational complexity.Considering the digital projector has a large working range,the fringe projection technique can be used on large-scale scene reconstruction for industrial safety inspection.Therefore,the research work of this paper is not limited to the basic technology like setting up phase to 3D coordinates transformation equations,obtaining the surface of the detected objects,analyzing the error sources,or improving the measuring accuracy.Furthermore,the research work is explored that aims to realize large-scale complex scene reconstruction.In order to realize it,creative phase unwrapping method on multiple discontinue objects is proposed,and the technique on depth-of-field extension is also studied in this paper.Firstly,the key technologies on digital fringe projection are presented in this paper.A geometrical model that relaxes the restriction on the camera's and projector's relative alignment is proposed and the mathematical description on phase to absolute 3D coor-dinates is presented.Based on the plane-based system calibration method,important parameters on phase to 3D coordinates transformation are derived.And the absolute phase map is derived by phase unwrapping method.The experimental system with DLP Light Crafter and VC6210nano smart camera is set up that verifies the effectiveness and correctness of the proposed mathematical model and the phase to 3D coordinates mathematical description.In addition,further studies are given on large-scale scene re-construction using fringe projection technique.A fringe-coding method based on the frequency analysis is proposed on deriving the absolute phase map for spatially isolated objects.Furthermore,we extend the depth of field to a large extent with cubic curve fitting depth error compensation method,which makes it possible on large-scale scene reconstruction.This opens enormous potential in a wide range of application areas.The main innovations of this thesis are as follows:1.In the classical geometrical model,rigorous constraints on the optical axes and the optical center of the camera and the projector make the mechanical assembly process demanding,which brings the installation error as a result.In order to reduce the manu-facturing complexity and the installation error,a new geometrical model is proposed that relaxes the restriction on the camera and the projector's relative alignment on parallelism and perpendicularity.And a complete mathematical description on phase to 3D coordi-nates transformation is given.In addition,the measured range can be flexibly adjusted on the basis of the measurement requirements.The complete mathematical description provides a solid theoretical basis for the realization of the 3D scene reconstruction.2.Since phase unwrapping method based on gray-coding is sensitive to the gray information of the measured object and not appropriate for real-time application,a fringe-coding method for absolute phase retrieval on multiple spatially discontinuous objects is presented in this paper.In order to obtain the fringe order information for phase unwrapping,a period-coding cue is embedded into the projected pattern by taking full advantage of the frequency characteristic of the sinusoidal fringe pattern.Unlike the gray-coding phase unwrapping method,the proposed method is insensitive to noise and object texture since there is no gray level information used in the system.Moreover,only one additional fringe pattern is projected for the proposed fringe-coding method,which makes it more suitable for time-critical applications.The proposed fringe-coding method makes it possible for the fast phase unwrapping on multiple spatially discontinuous objects.3.In theory,the three-dimensional measurement can be explored to a large scene reconstruction with geometrical modeling fringe projection technique.However,in fact,the depth measuring range is generally very small since the detected object is required to work at the focus range of the camera and the projector.In this paper,the effect of camera and projectors'lens defocus to three-dimensional measurement is analyzed.The depth of field is extended with cubic curve fitting depth correction method,which makes it possible for large-scale scene reconstruction.This opens enormous potential in a wide range of application areas.