Geometric And Thermal Error Modelling Of CNC Machine Tools And Real-time Compensation Research

With the rapid development of science and technology,as the industrial mother machine of CNC machine tools in the national economic development and manufacturing industry occupies a pivotal position.Today’s manufacturing industry requires higher and higher accuracy of CNC machine tools,while the demand for high-precision CNC machine tools is increasingly diversified,so it is important to improve the machining accuracy of CNC machine tools to achieve the goal of industrialization power.This work takes the XH714 vertical CNC milling machine as the research object,and after fully weighing the relationship between the machining accuracy of the machine and the cost of compensation,the error compensation is carried out for the thermal and geometric errors which occupy about 65% of the total error of the machine.The main elements are as follows:(1)The geometric and thermal errors of CNC machine tools are analysed to determine the 44 error elements that have an impact on the machining accuracy of CNC machine tools.The topology of the machine tool and the error transmission chain are analysed.Based on the multi-body system theory,a spatially integrated error model of the CNC machine tool is constructed using the flush coordinate transformation matrix,and the laser interferometer step-by-step measurement method and the five-point measurement method are proposed to accurately measure the geometric and thermal errors of the CNC machine tool,and finally the least squares modelling method and the BP neural network theory method are proposed for the geometric and thermal errors of the CNC machine tool respectively,providing theoretical support for the subsequent error compensation.(2)The spatially integrated error model is used to analyse 21 geometric error elements,followed by the partial differential method to establish the spatial position sensitivity coefficient matrix of the machine tool,and the error element synthesis assessment method is proposed in conjunction with the actual measured error values of the machine tool’s geometric errors to identify 12 critical geometric error elements.On this basis,the Legendre-based orthogonal polynomial geometric error modelling method is proposed and compared and analysed with the least squares modelling method to provide a theoretical basis for geometric error modelling.(3)Using the machine tool spindle as the research object to establish a thermal error prediction model,firstly,the machine tool thermal error and temperature measurement,based on the basic selection principle of machine tool temperature measurement points,combined with engineering experience,finite element thermal analysis method to determine the machine tool temperature measurement points.A genetic algorithm-based improved K-means cluster analysis method was used to select the machine tool temperature measurement points,reducing 17 temperature measurement points to 5 key temperature measurement points.A genetic algorithm-based improved K-means cluster analysis method was used to screen the key temperature measurement points of the machine tool,and the key temperature sample data and the thermal error sample data obtained from the experiment were used to establish a Logistic-ACO-BP thermal error prediction model,which was also compared and analysed with the traditional BP neural network prediction model,ACO-BP prediction model and LVSSVM prediction model to provide a theoretical basis for thermal error modelling.(4)Taking real-time error compensation technology as a starting point,the geometric error prediction model,the thermal error prediction model and the error parameters are input into the external compensator of the CNC machine tool for compensation experiments,the specific content of the error compensation experimental process is divided into two stages.In the first stage,error compensation experiments were carried out on CNC machine tools under no-load conditions to compare the values of each error element before and after compensation of the machine tools to verify the effectiveness of the compensation method and the prediction model.In the second stage,the dimensions of the keyway machined after and before compensation are measured separately in the actual process of machining the keyway on the XH714 CNC machine tool.By comparing the dimensions of the workpiece before and after compensation,the effectiveness of the error prediction model of the CNC machine tool and the real-time compensation method is further verified,which is of great significance for improving the machining accuracy of the CNC machine tool.