Research On The Key Method Of Improving The Measurement Precision Of The Fringe Projection Profilometry

Structured light3D measurement technology is the most widely used non-contact profilometry measurement technology at present, and have very high application value in many areas such as quality control, industrial inspection, computer-aided design, reverse design, heritage preservation, anthropometric, and biological medicine. With the development of digital technology, projector and digital camera are usually taken as the projection and acquisition equipment, they bring a lot of convenience for measurement, But in an oblique-angle projection, due to the Gamma effect of the projector, nonlinear effect of CCD camera and fringe cycle broadening, they bring many errors to the phase measurement, the fringe have a certain degree of distortion, Therefore, in the process of phase calculation, the non-sinusoidal fringe is the main reason for the phase error. How to obtain phase information quickly and accurately is still an important research topic in the field.In order to solve the above problems, this paper studied two works:Firstly, we expounded in detail Fourier transform profilometry, phase calculation method and the problem of frequency overlapping. And the dual-frequency fringe Fourier transform profilometry based on binary fringe defocusing was proposed based on it. Because the fringe generated by this method only have two gray level0and255, so it overcome the Gamma effect of the projector and nonlinear effect of CCD camera, by properly defocusing, the fundamental frequency and the third harmonic components can be preserved, and the proposed dual-frequency fringe was generated. A defocusing optical system acts as a low-pass filter, dumping the noises, also it avoided of frequency overlapping at the same time, it brings many conveniences to the following filter design, single filter, and phase calculation. In addition, The camera and the projector do not need to be strictly synchronous. High-speed and real-time measurements have obvious advantages. The two group experiment results show that the proposed method has higher accuracy than the traditional dual-frequency FTP.Secondly, we expounded in detail the process of fringe non-sinusoidal due to the cycle broadening and Gamma effect of the projector, and analyzed the characteristic of non-sinusoidal fringe by experiment and simulation, and proposed a novel phase error compensation method based on Look-up table (LUT). Firstly, the phase error LUT was generated by the comparing the measured phase with the ideal phase, and find the corresponding phase error according to the phase on the object surface, then compensate to the phase. We also proposed a novel height expression. The algorithm eliminated the Gamma effect and the nonlinear effect of CCD camera effectively, and correct cycle broadening at the same time, and this method could reduce the phase error and prove measurement precision which was proved by experiments.