Study On Dynamic 3D Morphology Measurement Technology Of Color Grating Projection

The grating projection 3D measurement technology describes the spatial distribution of the projected grating field through the phase distribution.It has many characteristics,such as large amount of information,single full-field measurement,high measurement accuracy,fast measurement speed and non-contact measurement,etc.At present,it is widely used in industrial testing,cultural relic protection,medical modeling,virtual reality,reverse design and other fields.In these fields and industries,there is no lack of demand for 3D topography measurement of moving objects.At present,the use of equipment and high development cost for dynamic 3D measurement limit the popularization and use of this technology.This paper focuses on a low-cost dynamic 3D topography measurement technology based on color grating projection.The main research contents include:(1)In view of the phase distribution extraction error existing in the measurement system,the source of the phase distribution error is analyzed and the theoretical model of the error is established.It is divided into two categories: the nonlinear response error of light intensity and the grating period and shape distortion error.The multi-region ? value nonlinear correction technology and the semi-axis feature extraction grating distortion self-correction technology are proposed,which can effectively eliminate the water ripple phenomenon and the surface distortion caused by the full-field nonlinear error and the period extension error.After correction,the standard deviation of measurement error decreases from 3.560 before correction to 0.102 after correction,which is about 34 times.(2)The coding and phase distribution extraction of color grating are further studied,and two solutions based on different color models(RGB model and HSI model)are proposed.The experimental results show that the traditional RGB single-channel nonlinear correction method has limited correction effect and poor phase reconstruction effect.However,the hue-phase mapping correction method proposed based on HSI color model does not need to correct the RGB channel crosstalk.Instead,the RGB images captured by the camera are converted to the HSI model.According to the monotony of the Hue and its similarity to the folded phase,it can be treated as the phase to map with the ideal phase.Set up a query table for phase compensation correction.The experimental results show that the effect of 3D reconstruction is close to that of phase shift method.At the same time,the four-step phase-shifting method was used as the benchmark for phase extraction,and the phase extraction experiment was compared with Fourier transform profilometry based on single frame gray grating reconstruction.The root mean square error of the extraction phase was 0.0512,which was about 2 times lower than that of Fourier transform profilometry.(3)The dynamic three-dimensional topography measurement system based on color grating projection and its supporting software are developed,which is composed of projector,camera,sliding guide and computer.The supporting software of the measuring system was developed using Visual Studio 2017 integrated development environment.After the system calibration,the dynamic three-dimensional measurement of the moving workpiece spoon was carried out.A color grating mask extraction method,which is able to remove the background and defect points,reduce the phase calculation time,and improve the efficiency and quality of phase reconstruction,was proposed.The distributed phase is extracted,the 3D reconstruction is completed and the desired accuracy is achieved.