Research On 3D Imaging System Of Structured Light Based On Telecentric Lens

Fringe projection 3D topography measurement method has become one of the most popular 3D measurement techniques in recent years due to its own advantages,and it is an important method to achieve high precision measurement of objects.However,high precision measurement is urgently needed in many fields such as surface condition analysis,mechanical function testing and quality detection of MEMS.This promotes the development of the technology towards three-dimensional morphological information on the surface of small objects.In this paper,a set of structured light three-dimensional measurement system is built to meet the high precision detection requirements of small objects.It adopts double telecentric lens and shift axis projector to increase the common measurement range of the system,studies the corresponding calibration algorithm according to the characteristics of the imaging model of lens and projector,and then uses beam adjustment to optimize the global parameters of the system.It can obtain high precision 3D imaging results quickly.The main work content of this paper includes three aspects:(1)The appropriate phase extraction algorithm and phase unwrapping algorithm are researched and determined,and the external parameters of the telecentric model are determined with the aid of projector.Then the "inverse camera" principle and phase-coded coordinate mapping method are used to complete the calibration of the pinhole projector,and its accuracy is verified by experiments.(2)In the process of extracting feature points,an improved Canny edge extraction method is used.First,the median filter is used to reduce the impact of image noise,and then the improved Canny algorithm is used to extract the edge information.The calculation results show that the algorithm can effectively reduce the reprojection error and improve the calibration accuracy of the measurement system.(3)For the accuracy of the calibration plate,the beam adjustment algorithm is used to optimize the system.The world coordinates of the feature points are set as a variable,and the known coordinates of the feature points are taken as the initial value,which is modified to a more reliable value,so as to improve the calibration accuracy.Finally,the practical objects were measured to verify the feasibility of the measuring system in this paper.The reconstruction results show that the measuring range of the system is 55.4mm × 43.8mm,the average measuring accuracy of the full field of view is 32μm,and the center of the field of view can reach 10μm within the range of about 20 mm × 20 mm.In addition to ensuring the measurement accuracy of the center of the field of view,it provides as large a measurement range as possible,which can meet the requirements of high precision industrial detection and realize the detection of packaged circuit board defects.