| Metal pipe as an important section of transportation,aerospace,military and others,within the same requirements for anti-bending and twisting strength,pipe can effectively reduce its weight;within the same circumference,pipe can transport more fluid;and when the radial pressure is applied,it is evenly stressed.As an important geometric parameter,the straightness of pipe has a direct impact on its application and equipment safety.In order to detect hole straightness of pipe,off-line contact or non-contact measurement are mainly used at domestic and abroad,however,whose measuring process are complex and low efficiency;Meanwhile,if the straightness does not meet the requirements,the three point pressure correction method is adopted,yet which is difficult to realize precise control of straightening process.In order to realize on-line measurement of pipe and improve measurement efficiency and precision straightening,a new straightening method is proposed in this paper,by using the machine vision measurement method to obtain the deflection information of tube,and then adjust the straightening stroke with straightening theory to guide straightening operation.The main research contents of this paper are as follows:(1)Based on the principle of camera imaging and image processing technology,the characteristics of the end face image of pipe are studied.The gray scale transformation of the face image collected is carried out,and the optimal threshold algorithm is used for threshold segmentation and binarizatio.Then the characteristic parameters of image target area are extracted,including corner coordinates,area of the target region,centroid coordinates and equivalent elliptic attributes value,etc.,which lay the foundation for bending deflection detection.(2)Method of measuring deflection of elbow based on machine vision was proposed.The mathematical model of the characteristic parameters of the target area of the elbow and the deflection and the bending phase angle of the elbow are established.In view of poor identification ability of small deflection elbow Problem,a method of twice-threshold processing for image is proposed,which effectively improves its recognition ability.The feasibility of the measurement method was verified by comparing the deflection value obtained by image processing method with the measured value of displacement sensor.(3)Based on the elastic-plastic theory of metal materials,the straightening force and straightening moment of straightening were calculated,and the straightening curve equation was obtained.The mathematical model of straightening stroke of pipe was established by combining its initial deflection,size parameters of pipe,material parameters and the straightening distance.In order to reduce errors caused by hypothesis condition,the correction coefficient of straightening stroke was proposed,which can effectively improve the straightening efficiency and reduce the residual deflection after straightening.The dynamic simulation analysis of straightening process was carried out by Workbench LS-DYNA,and verified the correctness of the straightening stroke mathematical model.(4)Straightening experiment platform was built and the straightening experiment was carried out.By analyzing parameters such as initial deflection,residual deflection and straightening load,and comparing with theoretical calculation,finite element simulation and experimental data,the correctness of the theoretical model was verified.And the straightening precision satisfies engineering application requirement.In this paper,based on the machine vision bend deflection detection method,to achieve a on-line,non-contact deflection measurement for pipe.And compared with the current common method,it is more economical,convenient and faster,and effectively improve measurement efficiency;The mathematical model of straightening stroke established realizes precise control of straightening precision,which lays the foundation for the study of precision straightening of pipe fittings. |
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