Research On Some Key Technologies In High-Speed Three-Dimensional Measurement Based On Defocused Fringe Projection

Three-dimensional measurement with fringe projection is a kind of measurement technique based on optical theory, combined with computer vision, image processing, digital signal processing and other disciplines. Because of its non-contact and high precision, it is widely used in aerospace, biomedical, manufacturing industry, conservation and other fields. The technique has very considerable development prospects and high value. With the rapid development of three-dimensional optical measurement technology and manufacturing industry, how to achieve real-time, fast 3D shape measurement becomes particularly important In this thesis, a study on issues related to high-speed three-dimensional measurement based on fringe projection with projector defocusing is carried out. The research is applied in high-speed three-dimensional measurement system we developed. Specific work and innovation are summarized below.(1) We introduce the background and applications of fringe projection three-dimensional measurement technology and current research in high-speed three-dimensional measurement technique. The defocusing principle of DLP projectors and the feasibility in the measurement system is analyzed.(2) Fringe projection technique based on Sierra Lite dithering with projector defocusing is proposed. Projector defocusing technique can eliminate projector nonlinearity in high-speed three-dimensional shape measurement. However, the high frequency harmonics brought by defocusing will weaken the sinusoidal feature of the defocused fringe pattern, which will bring obvious measurement error. The Sierra Lite dithering algorithm using a serpentine raster is proposed to generate binary dithered fringe patterns. This method improves the sinusoidality of the defocused fringe pattern. Absolute phase is retrieved by applying fringe patterns generated by this method in traditional phase-shifting algorithm with projector defocusing. Simulations and experiments are carried out to verify the proposed method. Results show that both the sinusoidality of the defocused fringe pattern and phase quality have been improved greatly. Compared with the fringes generated by Bayer ordered dithering or Floyd-Steinberg dithering, the proposed method achieves higher performance and can generate fringe patterns more sinusoidally, which is more proper for projector defocusing profilometry.(3) We analyze and discuss several hardware key issues on high-speed three-dimensional measurement system based on projector defocusing, including realizing camera and projector synchronization, high-speed fringe projection and GPU parallel computing in high-speed measurement Three schemes are proposed to achieve high-speed camera and projector synchronization:using microcontroller circuit, using FPGA to generate fringe patterns and projection video and using DLP LightCrafter 4500. The advantages, disadvantages and feasibility of each proposal are analyzed. We finally adopt the proposal of using DLP LightCrafter 4500. GPU acceleration for high-speed measurement system to improve the performance is discussed and its feasibility is analyzed. Finally, we describe hardware configuration, software design and implementation of the high-speed three-dimensional measurement system.