Double Precision Method And Data Registration Technology For Three-dimensional Geometric Measurement

Geometric deviation is inevitable due to the machining error,which affects the interchangeability of parts,and the friction,wear,and fatigue strength of a mechanical system.In aerospace engineering,the structure and stress condition of a part is complex,which may cause vibration and stress deformation,it is difficult to ensure the machining precision and quality.Correct measurement and evaluation of geometric variable is important to improve the quality and efficiency of mechanical processing,reduce production costs and promote the development of machining and testing automation in modern aerospace field.Measurements of small geometric features(such as chamfer,transition fillet,edge,etc.)need to focus on local areas,which requires higher measurement accuracy and resolution than global geometric measurement.Therefore,it is still difficult to achieve multi-scale geometric precision measurement through a single measurement instrument.In this study,double precision measurement system and method were proposed for 3D geometric multi-scale measurement.After measurement path analysis and error compensation,global and local geometric information of workpiece were obtained.SAC-IA and ICP algorithm was used for the registration of double precision measurement data,and the error was analyzed to verify the measurement accuracy of the double precision measurement system.The contents and results of this paper can provide process monitoring and evaluation methods for high precision machining of 5-DOF hybrid machining robot developed by the project.It offers a new approach for rapid detection and evaluation of global geometric at millimeter scale and local geometric at micrometer scale,and meets the demands of multi-scale 3D geometric characterization in the fields of machining,aerospace and tool manufacturing.Firstly,a double precision system for 3D geometric measurement was built based on the principle of laser triangulation measurement.Two measurement instruments were selected for global and local geometric measurement,which have different resolution and measurement range.Special fixtures were designed for the integration of measurement instruments and multiaxis precision machining equipment.Static and dynamic analysis were carried out to verify the strength and stiffness of the fixtures under different working conditions,and ensure the precision and stability of the measurement system.Secondly,the changes of the C-axis rotation angle and rotation speed of the robot in the process of global geometric measurement were analyzed based on inverse kinematics solution of hybrid robot,and the motion stability of the robot under line,circle and plane scanning paths was predicted.The feasibility of geometric measurement path for typical parts was analyzed.The accuracy evaluation method for typical geometric measurement was proposed,the measurement and accuracy evaluation experiments were conducted.The results show that,when measuring the plane and its related features,the distance error between each feature plane is less than 0.0300 mm.When the diameter is greater than 80 mm,the diameter error,shape error and normal error are 0.0202 mm,0.0725 mm and 0.1091°,respectively,which are close to the nominal accuracy of the equipment(0.0300 mm).High efficency precision measurement of global geometric features was realized on typical workpiece.Then,precision rotation of line structured light and its error compensation method for local geometric measurement was proposed.The trajectory of line structured light was fitted by image recognition,then the eccentricity error of rotation center of profilometer and rotation stage was calculated.By Matlab and Java programming,3D synthesis and polar processing of point cloud data was processed.The run-out and eccentricity errors of rotation stage,tilt error of line laser profilometer were compensated.The effectiveness of the proposed method was verified by measuring features such as sphere radius,feature width and plane high difference.The measurement error is smaller than 3 μm,which is close to the limit of measurement accuracy of this instrument set.The accuracy of the error compensation model was verified.High precision measurement of typical local geometric was realized on typical workpieces.Finally,double precision method and data registration technology for 3D geometric measurement are studied.Holes with different diameters and machining quality were drilled with three tools on a CFRP workpiece.The global area and local area with hole of CFRP workpiece were measured with double precision measurement system,respectively.3D point cloud data in large scale global geometric and high accuracy local geometric were obtained.SAC-IA and ICP algorithm were used to complete the coarse registration and fine registration of global point cloud and local point cloud data,respectively.The maximum registration RMSE is 0.1612 mm,and the minimum is 0.0923 mm.After registration,the measurement error of hole diameter decreases from 0.1 mm to 0.01 mm.The hole spacing measurement error is reduced from the maximum 0.2506 mm to 0.0535 mm.Data registration of multi-scale 3D geometric measurement was completed.Proposed methods and system is effective for high efficency precision measurement of global geometric while ensuring high precision measurement in target area on the CFRP workpiece.