Research On Thermal Error Modeling And Compensation Method Of Electric Spindle Under Complex Working Conditions

As the kernel part of CNC machine tools,electric spindle has the merits of high rotating speed,high integration and fast response.When it operates continuously under complex operating conditions,the uneven temperature field is generated due to the action of internal and external heat sources and complex heat transfer,resulting in inconsistent thermal deformation of each component and affecting the machining accuracy of the parts.How to better control the thermalinduced machining error of the electric spindle,even the ordinary CNC machine tools can ensure the processing quality of the parts is the focus of the current research.It is the most economical and feasible method to explore the relationship between temperature field and thermal deformation of electric spindle and to compensate its thermal error.This article takes the electric spindle as the research target and uses the finite element method to investigate its thermal performance.Exploring the influence of the temperature field changes on the thermal deformation of electric spindle from the mechanism.Construct a thermal error prediction model for electric spindle,and develop the thermal error compensation module to compensate the thermal error of electric spindle during operation.The main study contents of this paper are as below:Based on the three-dimensional structure of the electric spindle,clarify the main heat source,heat transfer path and heat dissipation methodes during operation.Calculate the theoretical heat generation of the main heat source(motor,bearing)and the convective heat transfer coefficient of the main heat dissipation surface.Based on the theory of heat transfer and thermoelasticity,the finite element method is adopted to build the thermal-structural coupling simulation model,and the steady-state temperature field and deformation field of the electric spindle under various working conditions and the transient temperature and thermal deformation curves of the key components are solved.Conduct thermal characteristic experiments on the electric spindle under complex operating conditions.Based on the energy conservation theorem and thermoelastic theory,the natural exponential mechanism model of temperature field and deformation field of electric spindle is established.The least square method is adopted to recognize the model coefficients,and the transient variation law of temperature and thermal error of electric spindle is clarified from the mechanism.Based on the heat conduction differential equation of one-dimensional rod,the temperature response and thermal deformation of electric spindle under the action of changing single heat source are derived,and the thermoelastic phenomenon of electric spindle under complex working conditions is revealed.Using Aggregation hierarchical clustering(AGNES)and grey relational analysis(GRA)to select thermal key points.An adaptive segmented thermal error prediction model based on support vector regression(PSO+SVR)optimized by particle swarm optimization is established.Compared with the multiple regression model and the unsegmented PSO+SVR model,the precision and robustness of the model in describing the thermal performance of the electric spindle are verified.Based on the BC five-axis CNC machine tool,the machining errors of each axis are traced.Based on the multi-body system theory,the extension structure of the machine tool is constructed,and the tool pose error model is established by using the homogeneous coordinate transformation principle.The Jacobian matrix is used to complete the compensation decoupling analysis.Based on SIEMENS 840D CNC system,the thermal error compensation scheme is designed by using the origin translation method,and the external thermal error compensation module is developed.The thermal error compensation experiment of electric spindle with multiple models under complex working conditions is carried out to verify the robustness,correctness and practicability of the compensation model,compensation scheme and compensation module.