Study On Decoupling And Compensation Of Volumetric Error Of CNC Gear Grinding Machine Tool

The worm wheel grinding is the main method of small and medium size gear finishing,and there is a great demand for CNC worm wheel gear grinding machine in the economic development.As a gear finishing machine,CNC worm wheel gear grinding machine must have strict requirements on the machining precision,and volumetric error caused by geometric error elements has a great impact on the accuracy and reliability of the machine,so scholars have pointed to improve the machining precision by using the error compensation technology,and carried out extensive research.In the process of volumetric error compensation of machine tool,due to the presence of the rotation axis of CNC worm wheel grinding machine,volumetric position error is about to the linear axis,the angle of rotation axis is also linked to it,which causes the existence of coupling relationship and makes the computation of compensation movement of various axes of the machine tool difficult through the volumetric error.So we need decoupling the volumetric error to provide a theoretical basis for error compensation technology and achieve effective compensation of the volumetric error.The volumetric error caused by the geometric errors of the machine tool is studied in the paper.Based on the theory of multi-body system,the volumetric error model of machine tool has been established;and based on sensitivity analysis,the main rotational geometric errors element of the machine are found;then a kind of effective decoupling method for volumetric error compensation of machine tool is put forward;finally a double ball bar experiment is done to validate the theory of volumetric error decoupling and compensation.The main contents of this paper are as follows:(1)Volumetric error modeling of the machine tool.Firstly,the definitions of volumetric error and geometric error and theory of multi-body system are introduced;and then analyzing the machining motion and geometric structure of the machine tool to get geometric error elements influencing machining accuracy;finally,based on the multi-body system theory and homogeneous coordinate transformation,transform matrixes of the machine tool bodies have been derived and volumetric error model caused by geometric error elements has been established.(2)Sensitivity analysis of rotational geometric errors elements of machine tools.First introducing the related theory of sensitivity analysis,and then the sensitivity analysis method based on variance is introduced into the error analysis of the machine,and finally the reasonable sampling of the rotational geometric error elements and the working space of machine tool has been done to analyze the main rotational geometric error elements of the machine tool.Rotational geometric error elements of PID errors and angle errors of rotational axes are found as the main rotational geometric error elements.(3)Study on decoupling method of volumetric error of machine tools.This paper firstly analyzes several existing methods of volumetric error decoupling of machine tools,combining characteristics of machine tools,choosing the analytical method based on the simplified model of machine volumetric errors to decouple the volumetric error.Then the sensitivity analysis results is used to simplified volumetric error model and ignore the new errors caused by compensation motions,after that,effective decoupling has been realized through multi-step computation.(4)Experimental verification of volumetric error decoupling method.First selecting the ball bar tests as measurement method of the geometric errors,and then design volumetric error decoupling verification experiments based on the ball bar tests,and the experimental results have proved the correctness and validity of the volumetric error decoupling method.