Analysis Of Thermal Error Mechanism And Real-Time Error Compensation Of Machining Center

This paper is sponsored by the important National Science&Technology Specific Projects and the National Natural Science Funds ofChina. This paper mainly focus on VDM-75three-axis machining center,Thermal error mechanism analysis, the integrated error modeling, errordetection and modeling and error compensation based on virtualinstrument were studied in this paper.The main contents are as follows:1、Build the finite element model of VDM75based on the analysissoftware ANSYS, find out the heat source of the machine tools and thecalculating method of the quantity of heat. Then load the quantity of heaton the model as boundary condition to calculate the temperature field anddeformation field. The result of finite element analysis can be used toguide error compensation. According to the distribution of deformationfield, the structure of the machine tool can be optimal designed based onheat symmetry principle to prevent and reduce the original error of themachine tool.2、Introduce the machining center that studied in this paper, and thenanalyze the error of each moving axis.26error facts of this machiningcenter are confirmed. Using homogeneous coordinate transformation to getthe transformation between the tool coordinate system and the workcoordinate system and build the integrated error model of machiningcenter.3、Give the way to measure positioning error of each axis and thermaldrift error of the spindle, and also introduce the software and hardwareused to gather temperature data. Then take different strategy to build the model of the two kinds of errors. For positioning error, separate it togeometric part and thermal part. The geometric part is related to positionand use polynomial fitting to build the model. The slope of the thermal partis related to temperature. Firstly, use principle component analysis toreduce the temperature variables, then build the model of the slope onreduced temperature variables based on the least squares method. Theintegrated model is the composition of the two parts. For thermal drifterror, use principle component analysis to simplify temperature variablesfirstly, then send the reduced temperature variables and error data to BPNeural Network for training and get the model of thermal drift error.4、A real-time error compensation system based on virtual instrumentis developed, which contains the software and hardware structure. Carry oncompensation experiments based on the principle of extended externalcoordinate excursion function of FUNAC CNC system. The comparisonbetween the error data before and after compensation shows thatcompensation result is satisfactory.