| High precision is the inevitable trend of the development of CNC machine tools.As an effective way to improve the accuracy of CNC machine tools,error compensation technology is great of significance.At present,the compensation of machine tool error mainly focuses on positioning error and straightness error in the field of industry.However,the Abbe error and Bryan error which exist in the measurement process are not taken into account.Similarly,the research of volumetric error does not fully consider the influence of measurement point position and angle error on the error model,which leads to the low accuracy of volumetric error compensation.Focusing on the industry requirement of improving the accuracy of space error compensation for three-axis NC machine tools,this paper studies the theory and method of volumetric error modeling and compensation for three-axis NC machine tools based on screw theory,starting from the study of the influence of Abbe error and Brian error on the position error of the processing point,and taking each link of error compensation as the main line.The main work is summarized as follows:(1)Based on the principle and characteristics of single-axis motion error measurement,the influence of Abbe error and Bryan error on the machining accuracy of machine tools is analyzed,and the formula for calculating tool tip position error is deduced by using rigid body theory.Finally,the design experiment is carried out to verify the formula.(2)Based on the screw theory and the topological structure of three-axis NC machine tools,the volumetric error model of tool tip in the workspace of the machine tool is derived.The model takes into account the influence of the angle error of each axis on the position error of the machine tool.Finally,the calculation process of the workspace error field is given based on the measurement process of uniaxial motion error.(3)The error compensation strategy is optimized,and a volumetric error compensation strategy is designed,which first calculates the volumetric error of the characteristic points of the error field and then predicts the volumetric error of the non-characteristic points.This strategy effectively solves the problem of too much time-consuming for multiple modeling of single error.On this basis,the BP neural network method is used to train the volumetric error field to obtain the error prediction model,which effectively solves the problem of excessive compensation parameters with the increase of measurement points,even exceeding the storage space limitation of the system.Finally,the development of space error compensation module is completed on the domestic CNC system HNC818.(4)A set of software with functions of original error analysis,error modeling,volumetric error field simulation and compensation file generation is developed.Finally,the experiments of measuring,modeling and compensating volumetric errors are carried out on a three-axis NC machine tool.The diagonal positioning errors of PPP,PNP,NPP and NNP after measuring and compensating are reduced by about 70% compared with those before compensating,and the volumetric error compensation accuracy is effectively improved. |
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