Research On Phase Shifting Profilometry Based Portable Fringe Projection3D Surface Measuring System

With the development of modern industry and the improvement of people’s living standards, the traditional methods and information are unable to meet people’s requirements anymore; therefore, high-precision and multi-information measurement technologies for complex freeform object have become hot issues. Among the existing3D measurement techniques, the visual measurement integrated with phase shifting profilometry has been widely applied, thanks to its characteristics of non-contact, high-speed, high-precision and wide-viewing.In this background, a portable fringe projection3D measuring system is independ-ently designed and established based on the in-depth study of phase shifting profilome-try. In this dissertation, the measuring system is used as an experimental platform, then, related key techniques are fully studied. The main works and contributions are summ-arizeed as follows:1. Aiming at camera calibration, some in-depth researches in feature recognition, edge detection and center location are carried out, such as, a new subpixel edge extraction method based on polynomial fitting is proposed; A robust curcular object recognition method is implemented besed on their geometric characteristics; A new method based on concentric circle pattern is proposed to locate the projection of center precisely using the principles of harmonic conjugate and pole-polar. Then, the camera could be calibarated automatically and precisely by the combination of our algorithms with Zhang’s method. The correctness and accuracy of these algorithms are demonstrat-ed by some experiments.2. A new subpixel positioning method of the absolute phase value is presented in this dissertation for accurate stereo matching. In addition, the factors that influencing the phase value are analyzed carefully, further, a method combining3-step and4-step phase shifting techniques is given to reduce the number of the projection grating, while maintaining the measurement accuracy.3. After the advantages and disadvantages of the existing registration algorithms are analyzed detailed, the method based on circular targets is adopted in our system to transform the points from different views into global coordinate system. Firstly, a more robust stereo matching algorithm for feature object is presented; then,3D registration for two views is performed based on distance invariance under rigid transformation. It is found that the accuracy obtainded only using circular targets can not meet the requirements of our measuring system, so a multi-level enhanced ICP algorithm is proposed to improve the registration accuracy by taking the result of circular targets as initializtion. Experimental result shows that the accuracy is improved by almost three times.4. A simple and efficient method for the estimation of point normals is introduced by considering the characteristics of the data points acquired by our system. The correctness and efficiency of the algorithm is demonstrated by experiments, it gives a favor to user’s visualization and subsequent algorithms run.5. Data fusion is one of the essential key technologies for a measurement system. Taking the noise data and registration errors into account, an adaptive neighborhood clustering fusion method based on the existing algorithm is given. The experimental results show the validity and efficienty of the algorithm. It is concluded that the algorithm can not only obtain the surface data from multi-view redundant points, but also performs fairly well in detail preservation for the sake of iterative optimization.6. A prototype phase shifting surface measuring system is established based on the related theories and key techniques. The overall architecture of the system software is also figured to list the function modules. The accuracy, efficiency and other performance indicators of the prototype system are also given by several experiments which illustrate that the prototype system runs pretty well overall.