Research On Positioning Error Composite Modeling And Compensation Of CNC Machine Tools

Sponsored by the “National Science and Technology Major Project ofthe Ministry of Science and Technology of China”,“National NaturalScience Foundation of China” and “Research Fund for the DoctoralProgram of Higher Education of China”，this paper focuses on VDM75,the vertical machining center of Shanghai Academy of SpaceflightTechnology, and studies its mechanism of positioning errors, precisionmodeling and real-time error compensation.The following main points are studied in this paper:(1) This paper analyzes the causes of positioning errors in themachining center and focuses on the study of positioning errors in theeffect of geometry and temperature. It also analyzes the structure of thefeeding system, which has the greatest influence on the positioningaccuracy, and determines the support mode of ball-screw and thedistribution of the main heat sources.(2) A finite element model of ball-screw is built based on ANSYSand the heat generated by bearings and nut is set as a boundary condition.Load-step and uniform heat loading are adopted to analyze the temperaturefield and thermal deformation field of ball-screw in the steady state andtransient state.(3) Positioning errors and the corresponding temperatures in the machining center are collected by using laser interferometer andtemperature sensors. The positioning errors are divided intoposition-dependent errors and position-independent errors. According tothe full temperature composite modeling theory, longitudinal modeling isadopted to study the positioning errors in a single location, and then therelationship between the machine longitudinal modeling coefficients andlocations is built. Finally, considering the influence of the machinelocations and the temperatures in the machining center, a compositeprediction model of positioning errors is built.(4) The control and implementation strategies of real-time errorcompensation for machine tool are determined and analyzed. Then, anerror compensation software platform based on FANUC CNC machineorigin offset interface is established by VB. Ethernet is adopted to achievethe data communication between the error compensation platform andmachine tools. Finally, experiments in the vertical and horizontalmachining center show that the error compensation platform and the fulltemperature composite prediction model can significantly improve theaccuracy of machine tools and have a high practical value.