Research On On-Line Measurement For Complex Curved Parts Based On Multi-View Phase Shifting

Complex curved surfaces are widely used in aerospace,automobile,national defense science and technology and other important fields related to the national economy and people's livelihood,such as impellers of aircraft engine,automobile doors,gears,molds,etc,whose processing and manufacturing level reflects the core competitiveness of a country's manufacturing industry.And the full coverage,high efficiency and automatic measurement of complex surface parts is an important prerequisite to ensure the level of manufacturing.In view of the urgent demand of the processing and manufacturing industry for automatic,efficient and full coverage online three-dimensional measurement technology of complex surfaces,this paper focuses on the research of complex system calibration,phase shift method measurement technology and high-reflective object measurement.The main research contents are as follows:(1)A framework model for the overall calibration of the complex system is established,and a method of rotating axis calibration based on adaptive distance weighting is proposed.In order to achieve full coverage of the three-dimensional measurement of the measured object,an online three-dimensional measurement system framework has been established.The system framework involves multiple coordinate systems such as the camera coordinate system,the robot end coordinate system,the robot base coordinate system,and the linear module coordinate system.The transformation relationship between different coordinate systems is established,and the overall calibration scheme of the complex system is designed.The rotation axis calibration method is realized by using a checkerboard calibration board.The weighting coefficient is designed by analyzing the influence of the trajectory center of each corner of the calibration board on the fitting accuracy of the rotation axis,so that the weighting coefficient can be adaptively selected based on the movement distance of the corners.Based on this,the rotating axis can be fitted more accurately;In addition,an error evaluation method is designed to evaluate the calibration accuracy.The experiment proves that the proposed method can improve the calibration accuracy by about 15% compared with the traditional method.(2)The method of complex surface measurement based on multi-view phase shifting is studied.The model of binocular vision and trinocular vision is established based on the principle of multiocular vision.The key steps of binocular vision measurement are introduced,and the differences and connections between binocular vision and trinocular vision are analyzed.Experiments show that trinocular vision can expand the measurement range and reduce the measurement dead Angle.The principle of phase-shifting method is studied,and the advantages and disadvantages of Gray code phase unwrapping method and dual-frequency phase unwrapping method are analyzed.The experiments show that the Gray code method is only suitable for measuring the objects with single surface color and no reflection phenomenon,while the dual-frequency method is widely applicable,but its phase unwrapping accuracy is relatively low.Finally,based on the calibration results of the system,the transformation relationships between the point clouds from different view are deduced to achieve the unification of the point cloud coordinate system,so as to complete the multi-view point cloud splicing.The experimental results prove that the multi-view phase shifting method combined with the multi-view point cloud splicing method can effectively realize the full coverage measurement of the measured object.(3)The highlight region is measured based on the principle of multi-exposure image synthesis.Aiming at the highlight phenomenon that occurs when measuring objects with specular reflection,a multiple exposure method is adopted,and the light intensity of the collected image is changed by adjusting the exposure time of the camera to obtain images under different exposures.Based on this,image synthesis is performed by extracting effective pixels of images under different exposures,and a synthesized image without highlight phenomenon is finally obtained.Multi-exposure composite images were evaluated based on the ratio of effective pixels.The experimental results show that this method can effectively realize the measurement of high-light areas.(4)System hardware and software platform construction and experimental verification.The composition and design of the hardware platform of the measurement system are introduced,and the specifications and functions of each mechanism are described respectively.Analyze the experimental requirements and develop online 3D measurement integration software and multi-view point cloud splicing software.The online measurement software mainly includes camera control module,projector control module,3D reconstruction module and point cloud display processing module,which can meet the needs of all aspects of 3D measurement experiments.The point cloud splicing software encapsulates the multi-view point cloud splicing method,and can splice the multi-view point cloud based on the calibration results and measurement parameters,so as to obtain the complete results of the measured object.Finally,a complex and specular impeller is measured based on the software combined with the hardware platform of the measurement system.The experimental results show that the measurement system can realize the high efficiency,full coverage and automatic measurement of the measured object.