Research On Three-dimensional Reconstruction Of Machined Surface Topography Based On Microscopic Image

The machined surface topography is one of the important metrics to measure the machining quality of mechanical parts,not only determines the wear resistance,corrosion resistance,contact stiffness,fatigue resistance and sealing of the surface of parts,but also has an important impact on the matching property of mechanical equipment,the static and dynamic characteristics of the joint,the service life and reliability.By using the existing topography measurement technology to detect the machined surface topography,it is easy to have surface damage,high detection cost,low detection efficiency and poor real-time performance,and which is difficult to meet the requirements of high efficiency,high precision,on-line real-time detection along with the rapid development of automation and intelligence of manufacturing process.For this reason,this paper proposes SFS(Shape from Shading)three-dimensional reconstruction method solves the problem of on-line detection of machined surface topography.A systematic theoretical and experimental study on the surface characteristics,reflection characteristics,illumination model and SFS method in the process of SFS reconstruction of machined surface topography is carried out,which provides a new method for the detection of machined surface topography.The principle of microscopic imaging is analyzed.Aiming at the problem that the way of illumination affects the image quality in the micro imaging system,the SFS reconstruction using the coaxial optical micro image of the cutting surface is determined.Based on the experimental platform of coaxial optical microscopic imaging and topography detection,the data acquisition of the coaxial optical microscopic image and topography of the machined surface is completed.The correlation between the coaxial optical microscopic image and topography of the machined surface is analyzed.The internal relationship between the image grayscale and topography characteristics is obtained,which provides data support for SFS reconstruction of machined surface topography.The normal deviation angle of microfacet is proposed to describe the geometric characteristics of the machined surface topography,and the distribution law of the normal deviation angle of the different machined surfaces topography is studied by using mathematical statistics method,and the statistical characteristics of the geometric distribution of the machined surface topography are obtained.Based on the theory of probability distribution,a mathematical model for the characterization of the machined surface topography is established,which can accurately characterize the geometric characteristics of the machined surface topography.The accuracy of the model is verified by experiments,and provides a mathematical model for the description of the geometric characteristics of the machined surface topography.According to the characteristics of coaxial optical microscopic imaging,a BRDF(Bidirectional Reflection Distribution Function)method for measuring the machined surfaces topography is proposed,and the BRDF measurement data of machined surfaces are obtained.The action mechanism of the machined surface topography on the incident radiation is studied by theory and simulation,and the influencing factors of the reflection characteristics of the machined surface topography are proved.The BRDF parameter model of the machined surface is established,which takes into account the geometrical characteristics,reflectivity and processing methods of the machined surface.The experimental results show that the BRDF parameter model can accurately reflect the reflection characteristics of the machined surface.The principle of the surface brightness transfer of the coaxial optical microscopic imaging system is analyzed,and the influencing factors of the surface brightness are revealed.According to the reflection characteristics of machined surface topography and the statistical distribution law of normal deviation angle,a micro surface illumination model based on lognormal distribution is established to accurately describe the reflected brightness of machined micro surface,and the reliability of the model is verified by experiments,which provides an accurate illumination model for 3D reconstruction of machined micro surface.The principle of SFS reconstruction is analyzed,the geometric correspondence between the grayscale surface and its topography is studied,the constraint relationship between the grayscale gradient and the surface topography gradient is proved,and the SFS analytical reconstruction method based on the gradient consistency constraint is proposed.The image quantization error elimination,the gradient resolution of the reconstructed surface,the correction of the positive and negative singularity of the gradient,and the calculation of the relative height of the surface are systematically studied,and the analytic reconstruction algorithm for machined surface topography is established.The reconstruction experiments of the synthetic image and the coaxial optical image of the machined surface are carried out by using the analytic reconstruction algorithm.The variation of the analytic reconstruction accuracy with the surface roughness,the processing method and the image resolution is obtained,which provides a reliable theoretical and technical support for the accurate and rapid on-line detection of the machined surface topography.