Research On Geometric Error Modeling And Measurement Methods Of Five-axis CNC Machine Tools

Compared with three-axis machine tools,five-axis machine tools can process complex curved surfaces,which has the advantages of efficient processing and convenient clamping.However,the structure of the five-axis machine tool is more complicated,and the two rotary axes introduce additional geometric errors,which greatly affects the accuracy of the machine tool.Therefore,this paper aims to study the geometric errors of five-axis machine tools,build an error model of five-axis machine tools based on the screw theory,and measure the geometric errors of five-axis machine tools by the proposed error measurement method.The main contents of this article are as follows:A five-axis machine tool geometric error model based on the screw theory was established for the DMU 80 T five-axis machine tool.The screw theory can be used to establish five-axis machine tools modeling,and the geometric errors of the machine tools can be modeled by introducing error screw.The machine tool model based on the screw theory is exactly the same as the traditional modeling result obtained by the homogeneous coordinate transformation method,and all the motion matrices are defined in the machine tool coordinate system during the modeling process,and the modeling process is relatively simple.A method for accuracy evaluation of machine tools based on double ballbar(DBB)is proposed.Based on the screw theory,a cradle-type five-axis machine tool was used to study the error modeling.The error model was used to simulate the Position Independent Geometric Errors(PIGEs)of the rotary axis on the DBB measurement trajectory.The trajectories have different geometric characteristics.By comparing the simulated trajectory with the actual measurement trajectory of the DBB,the accuracy of the machine tool under test can be evaluated.This method is suitable for the acceptance test of machine tools and the periodic detection of machine tool accuracy.The error measurement methods for linear and rotary axes of five-axis machine tools are studied,and three error measurement paths based on the DBB for rotary and linear axes are proposed: X-axis and C-axis linkage,Y-axis and C-axis linkage,and Zaxis and B-axis linkage.A mathematical model of constant-speed linkage between the linear axes and the rotary axes was established to ensure that the uniform data collected by the DBB during the measurement process was synchronized with the actual movement.The machine tool error model is used to simulate the influence of PIGEs in the measurement path on the measurement track of the DBB.Calibrate the DBB spindle tool cup and pivot tool cup to improve measurement accuracy.Based on the particle swarm optimization,the data measured by the DBB are decoupled,and six PIGEs in the two axes linkage measurement process are solved.The calculation method of measurement uncertainty is given.Compared with the traditional method of measuring the geometric error of the linear axes or the rotary axes separately,the proposed measurement method can simultaneously obtain the PIGEs of the linear axes and the rotary axes.Combined with the established machine tool error model,the application of error measurement results in machine tool error compensation is studied.By introducing a machine tool error compensation strategy based on the jacobian matrix,an error model combining differential operators and screw theory is established,and the jacobian matrices of the differential motion of each axis of the machine tool are proposed.The pseudo-inverse matrices is used to solve the compensation amount of each movement axis of the machine tool,and then the machine code is corrected.