Research On Automated 3D Measurement For Online Inspection Of Hot Forming Parts

Hot die forgings are widely used in power generation,shipbuilding,petrochemical,aerospace,military,and other fields.As important bearing components in high-end equipment,the manufacturing level of hot die forgings is an important indicator to measure a country's industrial strength and military capabilities.The development of online automated three-dimensional measurement technology and equipment for hot forming parts will solve the problem of online acquisition of hot forming parts three-dimensional shape data and can provide important data support for hot die forging process improvement and quality control.Hence,it is of great significance in improving the level of forging manufacturing in China.In recent years,the hot forming parts inspection technology has been continuously improved,and a variety of hot forming parts measurement methods have emerged.Among them,the hot forming parts inspection method based on three-dimensional measurement of surface structured light has the advantages of high speed and dense data and has the potential to be combined with industrial robots to perform multi-view automatic measurement of complex or large and medium-sized forgings and obtain their complete shape data.However,due to the harsh environment of hot forgings production,to apply the existing technologies to the online automated three-dimensional measurement of hot forgings,we still face the following problems: the measurement process is interfered by the vibration of the working forging press,resulting in difficulty in stable acquisition of three-dimensional shape data;measurement viewpoint planning is difficult to implement on site in high temperature and high heat radiation environment;the measurement data background is complex and closely linked to the target data thus it is difficult to extract critical dimensions from it.To this end,this paper conducted research on the above problems,and overcame key technologies such as highspeed projection & vibration compensation method,measurement viewpoint virtual planning method and multi-view data fusion & background removal method,and formed a complete set of online automated three-dimensional measurement technology system for hot forming parts.The specific research work is as follows:Aiming at the problem that the three-dimensional measurement data is difficult to obtain stably due to the vibration of the working forging press in the forging factory,a high-speed projection and vibration compensation method was proposed.By analyzing the limitation of projection and acquisition speed within the framework of multi-frequency phase-shifting method and the Digital Light Processing(DLP)platform,the vibration interference was reduced by increasing the projection speed.A projection acceleration method based on improved frame gray-scale modulation was proposed,which improved the projection and acquisition speed of the measurement device,limited the vibration impact on the device to a small range,and reduced the difficulty of vibration detection and compensation.The influence of vibration caused image sequence misalignment on phase recovery and phase unwrapping process of multi-frequency phase-shifting was analyzed,and the global pixel constraint relationship between multi-frequency phase-shifting images was clarified.The vibration detection method based on the grayscale characteristic difference between images and the vibration compensation method based on homography mapping between images in the case of low parallax were proposed.The proposed high-speed projection and vibration compensation method improved the stability of the measurement equipment under vibration conditions and ensures the acquisition of high-precision three-dimensional shape data.For the forging production environment,high temperature and high heat radiation cause the measurement plan to be difficult to implement on site.To this end,a virtual measurement planning method based on viewpoint generation and reachability verification was proposed.Specifically,for the viewpoint generation process,voxel-based model partition and viewpoint generation methods based on sensor model were proposed,and the evaluation mechanism of viewpoint imaging quality was established,and the measurement viewpoint with the best imaging quality was selected.For the viewpoint accessibility verification process,a sensor-robot unified model was established,and a robot kinematics model incorporating hand-eye relationship was proposed to describe the complex mechanicaloptical system,thus the robot reachability of the viewpoint was directly verified without hand-eye coordinate conversion,which reduced the difficulty of viewpoint accessibility verification and improved the efficiency of measurement planning.The proposed virtual measurement planning method solved the measurement planning problem in the online measurement of hot forgings and avoided manual teaching in a dangerous environment.For the online measurement scene,the background data is closely connected with the target data,and cannot be removed by the point cloud filtering method,which causes difficulty in key dimension extraction.To this end,a multi-view data fusion and background removal method was proposed.Based on the robot reproducible positioning of measurement volumes,multi-view data fusion without external positioning was realized,and the total amount of target data features in the measurement data was improved,which provides a calculation basis for data registration.On this basis,an improved ICP(Iterative Closest Point)method based on the dynamic adaptive threshold was proposed.In the process of iterative registration of the fusion data to the design model,background data was removed from far to near,and most irrelevant background data was removed simultaneously while exact registration was achieved,avoiding the problem of non-convergence of registration in existing ICP methods and the problem of accidental deletion of target data in point cloud filtering methods.The proposed multi-view data fusion and background removal method lays the foundation for subsequent data analysis and size extraction.It has unique advantages in the online automatic 3D measurement scenario of hot forming parts.Based on the above key technologies,through the solving of engineering problems such as long-distance data transmission,thermal protection of measurement equipment etc.,the online automated three-dimensional measurement equipment for hot forming parts were successfully developed,and changed the status that the relevant enterprises could not measure the thermal forgings,and could only perform cold forging sampling,and realized the full inspection and online measurement of the thermal forgings.