Research On 3D Measurement Method Of Reflective Object Based On Coded Structured Light

At present,non-contact optical measurement methods have become the most effective method for obtaining three-dimensional information on the surface of an object.Among them,active 3D measurement technology has become an important research direction in the field of visual non-contact 3D measurement due to its many advantages such as low cost,easy implementation,simple operation,and strong practicability.However,for the surface structured light measurement system,if the surface of the object to be measured has a high reflectivity,or has characteristics similar to specular reflection,it is easy to make the image feature information collected by the camera inaccurate,thereby forming a high saturation.Bright areas and dark areas with low saturation will eventually cause phase errors.Therefore,in order to improve the measurement accuracy and efficiency of the surface of reflective objects,the main research contents of this thesis are as follows:(1)Analyze and study the entire components of the coded structured light measurement system,and realize the calibration of the measurement system according to the established camera pinhole model.Explain the principle of camera imaging,extract the corresponding feature points between the two-dimensional image coordinates and the three-dimensional camera coordinates,and use the acquired feature points as the basis for solving the internal and external parameters of the camera.The projector is regarded as a reverse camera,and the ray of the projection point is first obtained.For equations and plane equations,the three-dimensional coordinates of the projection point are obtained by the line-surface intersection method,and then the projector is calibrated using the same method as the camera calibration.By re-projecting the extracted corner points to reduce the calibration error,the calibration results obtained meet the requirements of measurement accuracy.(2)Describes the existing structured light three-dimensional measurement technology and coding method,and analyzes the respective advantages and disadvantages of the Gray code coding and decoding methods and the sinusoidal phase shift coding method.On this basis,the Gray code encoding method and the sine phase shift encoding method are combined to obtain the absolute phase of the sampling point of the entire measurement space.Correction is made for the phenomenon of periodic sudden changes in the process of obtaining the absolute phase.The corrected phase improves the measurement speed and accuracy of subsequent experiments to a certain extent.(3)On the basis of traditional manual exposure methods,an automatic multiple exposure technology is used to extract raster images on reflective objects under different exposure times.The biggest feature of automatic multiple exposure technology is that it can accurately measure the number of exposures required and the actual situation.The exposure time is calculated,and then multiple grating fringe images on the surface of the reflective object are collected according to the number of exposures and different exposure times,and the multiple grating images are fused into an image with a better exposure rate using a mask image sequence.Finally,the traditional exposure method and the improved automatic multiple exposure method are used to reconstruct the three-dimensional surface of the reflective stainless steel mirror spherical surface.The simulation experiment results show that the improved three-dimensional measurement of the coded structured light reflective surface can effectively overcome the problem of overexposure or underexposure on the surface of reflective objects.(4)After obtaining the decoding and calibration data,the camera coordinates is used to calculate the three-dimensional point cloud data of the surface of the target measurement object.Build an experimental three-dimensional measurement platform to reconstruct the topography of the object to be measured with different reflective properties on the surface.By comparing and analyzing the 3D reconstruction renderings obtained by different material objects,it is verified that the method in this thesis can be better applied to the 3D measurement of the surface of reflective objects.