Study On Volumetric Error Measurement,Compensation And Dynamic Error Control Of Five-Axis CNC Machine Tools

The equipment manufacturing industry is an important indicator of the degree of industrialization of a country.The CNC machine tool,as the "worker" of the equipment manufacturing industry,is an indispensable "production tool".As a representative of high-end machine tools,the five-axis CNC machine tool has the advantages of better processing flexibility and higher processing efficiency due to its two rotary axes,but at the same time it also introduces more error effects and makes the tool movement more complex.Studying the error behavior of five-axis machine tools,and measuring and compensating the errors,is of great significance for improving the machining accuracy of five-axis machine tools.This dissertation takes the five-axis CNC machine tools as the research target,considering the impact of geometric errors and control errors,carries out related research with error compensation and control as the ultimate goal.The volumetric error model of the five-axis machine tool is established,and the sensitivity analysis and error coupling analysis of geometric errors are carried out.A volumetric error measurement method using optimized measurement points distribution and an adaptive identification method of geometric errors are proposed.The multilateration measurement method is optimized based on the laser tracker distribution and the coordinate selfcalibration.The formation mechanism of tool path error under the influence of tool path acceleration and deceleration is analyzed.A tool path acceleration and deceleration method considering the synchronized movement of tool position and postrure is proposed.A machining test method for evaluating dynamic error is designed.By applying the researches,the error compensation scheme of the machine tool is designed.Then,the application case study is carried out.The main research contents of this dissertation are as follows:(1)The volumetric error model of the five-axis machine tool is established,and the sensitivity analysis and coupling relationship analysis of geometric errors are carried out.Based on the theory of rigid body kinematics,the transfer relationship from geometric error to volumetric error is established.Using error projection and introducing effective cutting length,a single sensitivity index is defined,and then a geometric error sensitivity analysis method that comprehensively considers six tool position and posture errors is proposed to analyze the key geometric errors that have a major impact on tool position and posture errors in the workspace.Based on the analysis of the coupling relationship between geometric errors,the volumetric error model is simplified by the definition of the coordinate system.By considering the coupling relationship of geometric errors in the error measurement and solution,all geometric errors of each rotary axis can be masured through four measurement patterns under two installation positions of the ballbar,and the measurement efficiency is improved.(2)The measurement method of the five-axis machine tool volumetric error considering opitmized selection of measurement points and an adaptive identification method of the geometric error are studied.By describing the geometric error as the Chebyshev polynomial,the identification of the geometric error is transformed into the identification of Chebyshev polynomial coefficients.By defining the observability index based on the transformation matrix from the polynomial coefficients to the volumetric error,a method for selecting the distribution of measurement points is designed,which can reduce the influence of measurement errors on the accuracy of geometric error identification.By comparing with the measurement points random distribution,the proposed measurement point distribution method is validated.A geometric error identification method for adaptively assigning polynomial order is proposed,which optimizes the approximation of geometric error,and then improves the geometric error identification accuracy.The volumetric error of an AC double-swing five-axis machine tool is measured,and then by comparing the prediction accuracy of volumetric error obtained by different geometric error identification methods,the proposed geometric error identification method is applied and validated.(3)The measurement accuracy of the multilateration measurement method is improved by laser tracker distribution and coordinate self-calibration.By establishing the mapping relationship between the coordinates of the laser tracker and the measurement points,a method for selecting laser tracker distribution to reduce the influence of measurement errors and manual placement errors is proposed,which improves the measurement accuracy.By comparing the measurement accuracy of different laser tracker distribution,the proposed laser tracker distribution is validated.The relationship between the coordinate self-calibration error of the laser tracker and the measurement point is established,and the coordinate self-calibration method for solving the coordinate self-calibration error is proposed,which improves the accuracy of the coordinate self-calibration.The proposed coordinate self-calibration method is compared with the traditional one.By comparing the measurement accuracy of different measurement methods,the opimized multilateration is applied and validated.(4)An tool path acceleration and deceleration control method considering the synchronized movement of tool position and posture in the workpice coordinate system is proposed,and a test specimen for evaluating dynamic error is designed.Based on theoretical and graphical analysis,the formation of tool path error under the traditional five-axis tool path acceleration and deceleration control is studied.By accelerating and decelerating the tool position trajectory along the feed direction,and accelerating and decelerating the tool posture trajectory at the same time,and then using inverse kinematics to calculate the command trajectory of each axis.the tool path acceleration and deceleration control method is improved,which eliminates the tool path error caused by the traditional tool path acceleration and deceleration control method.By designing a linear tool path with the rotary axis moving in the opposite direction in the middle position,a straight test piece is proposed,which can significantly reflect the error caused by the tool path acceleration and deceleration control.(5)By applying the researches of this dissertation,a five-axis machine tool error compensation scheme is formed.The volumetric error model is constructed.The measurement method for volumetric error is designed and the geometric errors are identified,and then the volumetric error can be compensated based on the identified geometric errors.The improved tool path acceleration and deceleration method is applied to control the movement of the machine tool,and ultimately reduce the tool path error.Taking an AC double-swing five-axis machine tool as the research target,the application research of error compensation is carried out for the tool path of the S-shaped test piece.