Research On Geometric Error Identification And Compensation Of Five-axis NC Machine Tool Based On Ballbar Measurement

Five-axis CNC machine tools are used to process a variety of complex curved surfaces and precision components because they can achieve the linkage function between each axis and have high precision.Therefore,they have important applications in aerospace,ships,and military equipment.With the improvement of manufacturing level,the requirements for machine tool machining accuracy are also higher.Machine tools are developing in the direction of high precision,and error compensation is an effective method to improve machine tool machining accuracy.The geometric errors have a great impact on the machining accuracy of the machine tool,and geometric error measurement takes time and effort.Therefore,this paper analyzes the geometric error modeling process,proposes a method for rapid measurement and identification of geometric errors,analyzes the sensitivity of the geometric error during processing,and studies error compensation methods.The main research contents of the paper are as follows:? The geometric error model of a five-axis NC machine tool with double turntable is established based on the screw theory.The screw theory is introduced into the geometric error modeling of machine tools.The exponential matrix is used to represent the motion transformation matrix between rigid bodies,and the exponential product formula representing the kinematics of the machine tool is derived.The geometric error terms of each movement axis of the machine tool are analyzed and the geometric error model is derived.? The geometric errors of the linear and rotary axes of the five-axis CNC machine tool are quickly measured and identified based on the ballbar.Using the double ballbar to the linear axis geometric error measurement,only one measurement in each of the XY,YZ,and ZX planes is needed to identify the 21 geometric error terms of the linear axis.The axial and radial measurement modes of the A and C axes are used to identify the PIGES of the rotation axis,and the deviation of the center of the fitted circle of the ballbar measurement data is related to the geometric error,which overcomes the defect of taking special location points in the measurement results for identification and improvs the identification accuracy.A tapered measurement method is proposed to measure the PDGES of the rotation axis,and the matrix relation formula between the geometric errors and the change in length of the ballbar instrument is derived.Combining the measurement results,the error value can be obtained,making the identification process more efficient.? The sensitivity of the geometric errors to the spatial error during the processing of the conical test piece is analyzed,and the key geometric error terms are identified.Based on the Sobol method,the variance analysis of the geometric error model is carried out,and the calculation formula of the sensitivity coefficient is derived.During the processing of the conical table specimen,several processing position points are taken,and the first-order and global sensitivity coefficients of the geometric error to the spatial position and posture error at the processing point are calculated.The key geometric error terms that affect the spatial error during the processing of the workpiece are identified,which provides a theoretical basis for geometric error compensation? A five-axis CNC machine tool geometric error compensation strategy is proposed.Construct the Jacobian matrix of machine tool position error and attitude error,first compensate the attitude error and then compensate the position error,and calculate the compensation amount of the linear axis and the rotation axis.the geometric error modeling,measurement,identification and compensation methods proposed in this paper are executed on the Huazhong CNC HMU20 five-axis CNC machine tool,and the compensation results are verified.Combined with the results of sensitivity analysis during the processing of the truncated cone test piece,the compensation is focused,and the effect of compensating all errors and only critical errors is compared.According to the compensation effect,correct the error model,simplify the compensation process,and improve the efficiency of modeling and compensation.