Research On Compensation Of Nonlinear Errors In Post-processing Of Five-axis Machine Tool With Dual Rotary Table

The rotary axis of the five-axis CNC machine tool can change the direction of the tool axis according to the processing requirements.This special feature improves the machining efficiency of the machine tool and reduces the number of times the parts are clamped.However,the structure of the five-axis machine tool is complicated,so there are many technical difficulties in actual machining.Based on the nonlinear error generated by five-axis linkage and the structural characteristics analysis of the five-axis machine tool with double turntable,the main research content of this paper is to establish the compensation method and kinematics model of this type of machine tool.The post processing of the five-axis machine tool is a process of converting the tool position file generated by the CAD software into a numerical control code.The variety of machine configurations and types of CNC systems has led to the need for machine tools to be matched with post-processors.The generalization of post-processing is an important means to solve the various problems of the existing post-processing.Therefore,based on the general post-processing technology,this paper derives the kinematics analytical formula of the five-axis machine tool of the double-turn table based on the homogeneous coordinate transformation.However,when the rotary axis moves with the translation axis,the generalized post processing produces a nonlinear error.Therefore,the nonlinear error compensation method is used to predict the error and pre-compensate,so as to reduce the nonlinear error and improve the machining accuracy of the five-axis CNC machine.Firstly,the paper takes the offset vector of the ideal interpolation point and the actual interpolation point as the research object,analyzes its distribution characteristics in the space coordinate system,and constructs the nonlinear error compensation plane.Based on the above plane,the vector of the error is decomposed into a plane error parallel to the plane and a vertical error perpendicular to the plane,so that the vertical error influence coefficient is obtained by using the above-mentioned decomposition error,and provide a basis for the subsequent establishment of the above compensation method and prediction of the error.Secondly,the distribution characteristics of the error are analyzed in depth,and two nonlinear error compensation methods based on the workpiece coordinate systemand the machine coordinate system are proposed,namely the pre-linear error compensation method and the post-linear error compensation method.These two kinds of error nonlinear error compensation methods compensate the error in advance and improve the processing quality of the parts.The pre-linear error compensation method firstly acquires the post-processing points of the machine coordinate system according to the tool position in the known workpiece coordinate system,and simultaneously samples uniformly in the two coordinate systems.Then,the post-processing of the sampling point in the workpiece coordinate system and the sampling point in the machine coordinate system are used to construct a compensation vector,and the error vector is pre-processed and error-calculated to obtain the error of the uniform sampling point.Finally,the pre-linear error compensation method is constructed by sampling points and tool points to predict the ideal tool curve trajectory.The method interpolates the workpiece tool coordinate system with the curve tool path,and then obtains the interpolation point in the machine coordinate system by the classical post processing,thereby reducing the nonlinear error;The post-linear nonlinear error compensation method first selects two points in the tool position file as the tool position for establishing the compensation method,and then establishes the post-linear error compensation method according to the maximum error distribution in the classic post-processing in the middle of the two-tool position.Finally,the analytic function of the compensation method is used to quickly predict the nonlinear error between two adjacent points in the location file,thereby realizing the real-time error compensation of the intermediate interpolation point.Finally,the simulation verification of the pre-linear error compensation method is carried out for the two-tool position.The simulation result reduces the nonlinear error by 98%.The tool position file of an impeller part is generated by 3D design software(UG),and a tool path in the tool position file is simulated by Matlab.The experimental results verify the nonlinear error of the interpolation path using the post-linear error compensation method.Reduced by 95%.