Structured Light Based Large-sized Object Surface Measurement Techniques

With the rapid development of science and technology,modern industry has entered an unprecedented "advanced development stage".The society holds increasingly higher demands for modern manufacturing of industrial products.In this process came the real-time,efficient and accurate three-dimensional entity digital detection technology,which is an essential and tricky part that modern manufacturing industry must tackle.Structured light three-dimensional detection technology is a non-contact three-dimensional detection method based on active vision.It features high accuracy,wide range,satisfactory expansibility,and strong adaptability,and has been widely used in cultural relics protection,industrial automation,reverse engineering and other fields.It has developed into a technology with very promising prospects in the "non-contact three-dimensional detection technology" category.Based on the three-dimensional structured light detection technology,this paper uses a projection grating pattern as structured light to project on the object to be measured before using camera for image formation,and mainly completes the spatial three-dimensional detection model of structured light to solve and obtain three-dimensional point cloud data and points.This paper also involves cloud processing and stitching to fulfill three-dimensional surface detection of large objects.The main research contents of this article are as follows:Based on the analysis of the limitations of classical system detection model for structured light analysis,an improved three-dimensional system detection model is focused on analyzing model calibration techniques based on digital grating projection of structured light.The camera distortion and camera aperture model are described,and the camera calibration method based on the single-plane checkerboard and the system calibration method based on the circle center target are analyzed in detail.The research on image processing technology related to the grating projection structured light detection technology is carried out,including how to correct the non-sinusoid of the projection grating,and the reasons for the non-sinality of the projection grating are analyzed.The trapezoidal correction of grating fringes and the method of grating self-correction based on phase shift are studied.In addition,the image denoising technology related to the digital projection grating structured light image is described.The research finds that the application of cosine similarity improves the non-local mean filtering algorithm to make it have better denoising effect.The research on how to obtain accurate phase is carried out.The multi-frequency heterodyne solution phase technology based on beat frequency principle is studied in detail.For the detection tasks of large-sized objects,relevant point cloud processing technology research was carried out.After point cloud denoising and point cloud smoothing processing,the research on the point cloud registration technology was completed.Thus,surface detection of large objects through the application of grating structured light method is realized.