Geometric Error Measurement And Identification Of Rotary Axis Of NC Machine Tools Based On R-test Instrument

It is crucial to the development of the computer numerical control(CNC)machine tools in the modern manufacturing industry,the CNC's machining accuracy and properties reflects the level of the development in manufacturing.Geometric errors,an important factor to affect the machining accuracy of CNC machine tools,has always been the focus of domestic and foreign scholars.Geometric errors of five-axis machine tools are mainly concentrated in the translational axis and rotation axis,but the geometric errors of rotation axis is difficult to mearsure directly,measuring standards have not been unified,their special measuring instrument is not yet perfect.In this paper,the rotation axis' s geometric errors identification method of CNC machine tool is studied based on the non-contact R-test measuring instrument,which is invented independently by the author's research team,and the main work as follows:In the first part,the paper describes the R-test measuring instrument's structure composition and measuring principle,and analyse the instrument's setting errors,including the R-test mearsuring coordinate system's setting errors relative to machine tool's coordinate system,the R-test mearsuring ball's eccentricity error.For the rotating axis and R-test's mearsuring head on the side of the workbench at the same time,the paper discussed the data conversion analysis in that measurement model.The paper presents a method for mearsurement and identification of the rotation axis structural errors based on the R-test instrument.Firstly,the rotation axis structural errors,which including two displacement errors and two verticality errors of the axis of rotation axis,is analysed.Then,establishing measurement coordinate system under the axis of rotation,selecting points in the coordinate system and using the R-test instrument to mearsure the integrated displacement error values under the rotation angles of the rotation axis.Finally,four structural errors of the rotation axis are obtained by the least square fitting method.Based on the four structural errors of the rotation axis and the R-test instrument,a method for mearsurement and identification of the rotation axis motion errors is carried out.Firstly,analyze the kinematics of five-axis machine tools,each functional unit of the five-axis machine tools could be regard as a multibody system,and establish a coordinate system for the typical body.Through the coordinate system transformation between two adjacent body to describe their mutual movement relationship,and then,the ideal kinematic model about the position relationship between workpiece and tools is obtained.On the basis of the ideal kinematic model,the geometric errors of each motion body of the machine tools is analyzed,and the geometric errors model of the rotary axis is established.Finally,analyze the sensitivity of the geometric errors model of the rotary axis,and thus,it could improve the accuracy of the identification results.In the end,using the self-developed non-contact R-test measuring instrument to mearsure the comprehensive displacement errors of GF UCP800 Duro five-axis CNC machine tool's A and C table rotation axis,based on the method of rotation axis geometric errors identification,A and C table rotation axis' s geometric errors is gotten.Then,compensate the A table rotation axis' s geometric errors and measure again,observe variation of A rotation axis' s comprehensive displacement errors and geometric errors.The experiment results shows that the mearsuring and identification method based on the R-test instrument in this paper could solve the problem of geometric errors identification of rotary axis of CNC machine tools effectively,improve the mearsuring efficiency and the machining accuracy of the CNC machine tools.