Research On 3D Measurement For Heavy Forging Based On Binocular Vision

Heavy forgings are the key parts of large core equipment which are widely used in the filed of shipbuilding,power,heavy machinery and aerospace.The technological level and prodduction capacity of the forging industry are the important marks of the industrial automation degree and key technical equipment production ability.While the domestic forging industry has developed rapidly in recent years,great gaps still exist in key technologies and the level of industry automation betreen our forging industry and the advanced world level,especially the 3D measurement of large forgings,which mainly relies on manual measurement method to obtain the size of forging,seriously restricts the production efficiency,product precision of forgings and the automation process of domestic forgings industry.Aiming at the urgent demand of the high-precision and reliable non-contact 3D measurementechnology with high accuracy in forging industry,a 3D reconstruction and measurement method based on binocular vision is proposed and applied to 3D measurement of heavy forgings.What's more,a measurement system for heavy forgings with high precision and strong applicability is designed.The main reasearch contents and results are as follows:(1)Overall scheme and platforms of software and hardware are designed.According to the factory environment and specific technical requirements of forging measurement,The overall scheme and measuring process of 3D non-contact measurement system for large forgings based on binocular vision are determined.Then the hardware platform and software framework of the measurement system are designed on basis of overall scheme.(2)3D reconstruction method of heavy forging based on feature curve reconstruction is proposed.Targeting at solving the problem of external surface reconstruction of forging with complex structure,a reconstruction method based on feature curve is proposed.First of all,the principle of curve reconstruction method and the mathematical relationship between the projection curve and the 3D curve to be reconstructed are detailedly explained from multiple view geometry theory.Then,the specific procedure of forging measurement is designed based on 3D curve reconstruction method.The extraction and matching of the center line of the light strip are described in detail based on background difference method and gray-gravity method.After the center line of light is extracted,the parametric equation of it and the corresponding parametric equation of the projection surfaces are obtained with B-Spline fitting method.Further,robust iterative algorisms are developed to get inter-section of corresponding projection surfaces to recover 3D curve.Finally,fit the external surface of forgings with the reconstructed curves and 3D information of the forging is obtained.(3)Method of refraction correction and measurement system calibration are designed.In the measurement process,the CCD cameras are protected by glass shields.The refraction caused by glass shields lead to measurement errors in 3D reconstruction based on traditional single viewpoint model.To solve this problem,a glass refractive correction model is established and the refraction deviation is corrected by modifying the incident path of the projection point.According to the model,the calibration method of camera parameters and refractive parameters is developed.Finally,experiment is carried out and the result shows that the the size error and position deviation of reconstruction respectively decreased from0.413% to 0.169% and from 3.0312 mm to 0.2951 mm after refractive correction.Measuring accuracy and reliability can be greatly improved with the the refractive correction method in 3D reconstruction.(4)The hardware and software platforms of the measurement system are established and the 3D measurement of the models and forgings are relized.After in-depth analysis of the theory and algorithm of binocular visual forging reconstruction based on curve reconstruction and programming in VC++development environment,3D measurement system for heavy forgings is established according to the designed measurement scheme and process.Finally,reconstruction and measurement experiments of cylindrical model,water cup model,axial forging and oblique tee forging are carried out.The results show that the relative error of measurement on key dimensions is no more than 0.5%,and the maximum deviation of cylinder reconstruction is less than 0.588%.The reconstruction reults of the water cup model and the forging external surface can basically restore the real information of the surface.All in all,the measurement system built in this paper can meet the needs of 3D measurement of heavy forgings.