Error Modeling, Measurement And Analysis Of A Heavy Duty CNC Double Column Vertical Lathe

The improvement of machining accuracy of CNC machine tools has a very important significance for the modern manufacturing industry. In this paper, the study focuses on a 7.5m CNC double column vertical lathe. As the mainly finishing equipment in an energy equipment factory, this machine tool exists two error sources: ram deflection and the table lift, which greatly impact the machining accuracy. Based on the systematic and scientific theories, the corresponding solutions and methods are proposed, as well as practiced in field.Error compensation is the effective method to improve machine tool accuracy. The thesis firstly introduces the main parts of error compensation, and makes a review of the status in error modeling and measuring. Finally, the main research procedures and contents are determined as: machine tool error synthesis modeling, error measurement, thermal error modeling and analysis.The error synthesis model is quite necessary to analyze machine tool accuracy and execute error compensation. The paper describes the main kinematical structure of machine tool by multi-body system kinematics theory, and establishes error synthesis model contained the geometric and thermal errors. Considering the actual constructions of machine tool, the different influences to final machining accuracy of all sorts of errors are discussed, and clarify the importance to establish on-line measurement system for the significant angle errors.In order to monitor the status of ram and chuck table, as well as to improve the efficiency of machine tool accuracy measurement and maintenance, an on-line measurement system consisted of eddy current displacement sensor and data acquisition card is established in virtual instrument technology. In section 3, the details of the system development process are discussed: the solution schemes comparison and selection, the hardware construction, the measures to anti-interference and the features of software. In addition, a temperature data acquisition system is established for the chuck table, so the rise displacement and components temperature can be obtained synchronously.At last, the regression analysis is applied in thermal error modeling and the chuck-table fault diagnosis. The paper describes the multivariate regression modeling, stepwise regression analysis, ridge regression analysis, as well as discusses the variable selection and collinearity analysis. On this basis, the"optimal"linear regression model is fitted by the chuck-table rise displacement and temperature data. Then, the relationship between variables and their significance analysis are provided.