High Accuracy Surface Structured Light Projection Three Dimensional Measurement Research

Surface Structured Light Projection Profilometry(SSLPP) is widely used in many fields such as industrial inspection, biomedical applications, reverse engineering, protection of cultural relics etc, due to its advantages of non-contact operation, fast measurement speed and high accuracy. Aim to improve the accuracy of measurement system, this thesis focuses on the researches of image denoising and system calibration with a brief introduction of the surface structured light measurement technology.In the SSLPP, the low noise deformation fringe pattern can reduce the phase error and improves the measuring accuracy of the system. In this thesis, based on the theoretical analysis and experimental study, the Curvelet transform image denoising method is used for the first time in the SSLPP. And the results are compared with Wavelet transform method, which show both Curvelet transform and Wavelet transform have a good effect in image denoising. However, for spatially isolated surfaces, Wavelet method makes the blurring image and changes the edge points, Curvelet method can remove noise while retaining the edges very well. Therefore, the Curvelet transform can well protect the accuracy of phase demodulation and improves the measurement accuracy.The precision of 3D reconstruction is closely related to the accuracy of the system calibration. In the syestm calibartion, the typical SSLPP system has a rigid optical structure with the relative position of the projector, the camera, and the reference plane, such as parallelism, verticality and so on. The accuracy and flexibility of the typical SSLPP could be adversely affected. In order to eliminate these limitations of the SSLPP, we propose an arbitrary arranged SSLPP system to improve the accuracy and flexibility. At same time, we introduce several common system calibration methods, and analyze the advantages and disadvantages of traditional system calibration. Based on the principle of camera calibration technique, for this arbitrary arranged SSLPP system, a flexible and practical system calibration technique is presented to improve the measurement accuracy and reconstruct three-dimensional shape. The 3D gauge block or precise translation stage is not needed throughout the calibration process. The system calibration is easily fulfilled by just using one color printing checkerboard while providing accurate 3D measuring results. The board is placed at several random positions to determine the relationship of phase and height, as well as pixel position and X, Y coordinates.Experimental results show that, the proposed system and the corresponding system calibration technique has great flexibility, practicality and stability. With the curvelet denoising method, the accuracy of SSLPP has been improved significantly, reach up to 20μm.