Research On 3D Imaging System Based On Self-adaptive Structure Light Projection

Due to surface non-contact, large field of view, real-time, high accuracy,3D measurement method based on structured-light projection has been widely used in reverse engineering, industrial components defect detection, biology and medicine, virtual reality, face recognition etc. In recent years, the traditional 3D measurement technology has matured. With the development of science and technology, people also put forward higher requirements on the traditional technology, such as solve the nonlinear problem of projection, phase unwrapping problem and so on. Based on the phase measuring profilometry, this article detailed introduces the principle of 3D measurement based on structured-light projection, focusing on the nonlinear problem of 3D measuring system and the adaptive phase unwrapping problem. The content of the research embraces four principal sections:1) Based on the principle of defocused projection three-dimensional measurement and combined with phase shift method, the phase error of Floyd-Steinberg Dithering algorithm error diffusion asymmetry was analyzed. The phase error under different defocusing amounts, different phase-shifting step numbers and different pitch-width was presented by simulation. It find that the error diffusion asymmetry of Floyd-Steinberg Dithering algorithm will make the binary fringe pattern generated by sinusoidal structured-light loss symmetry. It also affects the phase shift. At the same time, for Floyd-Steinberg Dithering algorithm, the structured-light directions are selective. Experimental tests show that, When the structured-light direction is parallel to the Floyd-Steinberg Dithering algorithm scanning direction, the phase will be more consistent and the phase error will be smaller, even under different defocusing amounts and different phase-shifting step numbers, which confirmed with simulation results.2) Phase-shift method based on domain analysis is not suitable for measuring step-changed object and always causes the accumulation of phase errors. Symmetric and asymmetric dual stair phase structure light coding methods for absolute phase retrieval are presented. By the projection of binary coding structure light patterns, stair phase can be obtained. For the different frequency sine stripes, different phase-shift steps can be choose to achieve adaptive frequency projection of dual-structure light and phase unwrapping. During measurement, on the basis of traditional sinusoidal fringe projection and phase shift method, high-precision wrapped phase is obtained. The stair phase can be used to determine corresponding orders of wrapped phase. According to the order, the absolute phase can be got. Experiments prove that both methods can effectively restore three-dimensional reconstruction for highly step-changed object.3) For the high frequency wrapped-phase, two new dual structure light encoding methods requires a lot of coding image for phase unwrapping. A new improvement of dual structure light encoding method was proposed to solve the problem. This method requires only three pieces of structure light images and will be able to unwrap the higher frequency wrapped phase. For the different frequency sine stripes, it can realize the adaptive frequency binary coding. Experimental results demonstrate the effectiveness of the proposed method.4) Based on the system calibration module of OpenCV and Matlab, the experiment system was built on the optical table. By using this system, the camera and the images were calibrated. The camera intrinsic parameters and external parameters were also calculated.