Study And Design Of 3D Measurement System Based On Monocular Fringe Pattern Projection

With the flourishing improvement of social economy and scientific technology,people's demand for acquiring the 3D profile form of objects is also gradually increased,optical 3D measurement technology has been widely used in reverse engineering,equipment manufacturing and quality inspection,information security,medical plastics industry and other fields because of the merits of non-contact,full field and high degree of automation.In recent years,the optical 3D measurement technology based on active grating projection of structural light has been widely researched,there are various types of excellent products based on this.Recently,3D measurement products are expensive,which has significant affects the spread of optical 3D measurement technology.At present,owning to digital projection device phase shift stability,simple operation and other excellent performance,instead of physical grating to produce striped projection structure light.At the same time,the gray response of the measurement system is changed,and nonlinear errors are introduced.The phase needs to be optimized to reduce the influence of errors.The 3D measurement system based on monocular fringe pattern projection has only one camera,the imaging quality of the camera is a guarantee for the normal operation of the followup work.It is necessary to study imaging degradation.For the optical triangulation measurement,the calibration work of the camera and projector is particularly important,and the calibration accuracy directly affects the system accuracy of object shape recovery.In this paper,using structured light 3D measurement technology based on the phase measurement profilometry,drawing on the design ideas and structure of mainstream products,the design and implementation of a set of monocular fringe projection 3D measurement system including software and hardware.After studying the reconstruction principle of the system,after establishing the model of imaging degradation and analyzing the gray-scale response error of the system,the camera and projector are calibrated with high precision,and finally a high-precision,high-density point cloud 3D digital measurement system is realized.In the process of designing and implementing the 3D measurement system,the mainly work and studies are following:1.The image noise level,edge degradation model of the camera imaging process are studied,and based on this model,a sub-pixel edge detection method combining curve fitting and edge gray partial area effect is proposed.Use Gaussian curve fitting for areas with smooth grayscale changes at the edges,and solve the extreme points of the curve as subpixel edges.For areas where the edge gray scale changes drastically,the sub-pixel edge extraction algorithm of the partial area effect of gray scale is used by establishing the quadratic curve equation of the edge.For some low-cost scanning schemes,the camera has high noise and low resolution.The sub-pixel edge extraction algorithm proposed in this paper is especially suitable for the calibration of the camera.There are many points involved in the calculation of the sub-pixel edge extraction process,which has a suppression effect on noise.2.The image characteristics of the circular array calibration plate and the arrangement rule of the marker points are studied.According to the distribution characteristics of the positioning mark points on the calibration board,a method for automatically sorting the camera mark points based on perspective transformation is proposed.With the positioning method of marker points based on morphological operations,the correspondence between the image coordinates of the marker points and the world coordinates is realized.Furthermore,the automatic camera calibration technology based on Zhang's calibration method is realized,and the camera reprojection error is 0.06 pixels.3.Analyze the gray-scale nonlinear response of the system,simulate the phase-shift fringes affected by noise and nonlinearity,and analysis of the phase error of fringes under different phase shift steps.Comparing the spatial unwrapping and the unwrapping in the time domain,the method of multi-frequency phase shift is used to accurately expand the phase of the objects with sharp changes in shape and holes.4.In the calibration of the projector,analyze the phase quality at the center of the mark point.The linear interpolation method based on radial basis and multi-point phase value are used to reduce the influence of phase error and noise,thereby improving the stability of calibration.After obtaining the projector image coordinates of the center point of the positioning mark point,the use of perspective transformation and reverse interpolation gives the projector the ability to take images,which is convenient for observing the relative position of the projector and the calibration board during calibration.The projector reprojection error is 0.12 pixels.5.The monocular fringe projection 3D measurement system was built,and the system calibration software and 3D scanning software were developed.The accuracy of the system is tested,and objects with a distance of one meter are measured,and the standard deviation of the point cloud plane fit is 0.2 mm.Using the system to scan objects and people,the point cloud quality is very good.