Thermal Error Modeling And Active Control Method Of Electric Spindle Unit

Electric spindle unit,being a key functional component of precision machine,has the outstanding characteristics such as the high speed,precision,and rigidity.Accuracy and accuracy stability of electric spindle unit directly affects comprehensive quality of precision machining,so it has a significant influence onto the status of advanced manufacturing industry and the ability of international competition of China.Because precision electric spindle unit is generally equipped with the built-in motor,its thermal error caused by the motor and bearing heating at its high rotational speed is the main factor affecting the accuracy of the electric spindle unit.Currently,the traditional open-loop and identical circulating cooling system and strategy,which are commonly applied onto electric spindle units,can partially remove heat generated by endogenous heat source.However,its identical and open-loop temperature control mode cannot adapt to the dynamic changes of the temperature control ability demand,which is caused by the operating condition change of electric spindle unit.This results in the long-time cycle of start-thermal stabilization process,temperature control capability imbalance and other issues of the electric spindle unit,and is adversely affecting the control of comprehensive accuracy of the electric spindle unit.Thermal error compensation of electric spindle unit is one of common methods to improve the accuracy of electric spindle,but it usually only achieve axial thermal elongation compensation.In addition,due to the weak robustness of its compensation model,the discreteness and non-uniformity of its compensation implementation process,its comprehensive compensation effect is difficult to satisfy the needs of precision machining,so thermal error compensation of electric spindle unit has not been widely used in industrial enterprises.To improve and maintain the accuracy and accuracy stability of electric spindle unit,the thermal simulation technique of heat-fluid-solid coupling FEM and analytical modeling method is adopted,and a heat transfer-structural temperature rise-thermal error modeling method of the electric spindle unit is proposed in this dissertation.Based on this method,the mechanism and process of the heat transfer-structural temperature rise-thermal error generating of electric spindle unit has been systematically analyzed.To solve the problems of traditional circulating cooling system and strategy,a prototype of active temperature control equipment is developed,with multi-loops and differentiated dynamic temperature control.Then,the active control method for the thermal errors of electric spindle unit is given,which can decrease five kinds of thermal errors of electric spindle unit and keep stabilization of thermal errors;and two typical active temperature control strategies are studied,including dynamic power matching strategy between heat generating and thermal dissipation,the initial status maintaining strategy of temperature field.Finally,the simulation and experiment results illustrate that the active temperature control strategies,which are based on above-mentioned methods and equipment,can effectively improve the thermal stability of electric spindle unit,so that the accuracy and accuracy stability of electric spindle unit can be obviously improved.For the thermal error modeling of the electric spindle unit,the temperature rise-thermal deformation model of elastic thick-walled ring is constructed,then the temperature rise-relative thermal displacement between bearing inner and outer rings models of two typical electric spindle bearings are built up,including short cylinder rollers bearing and angular ball bearing.On this basis,the combination of the numerical simulation technique of heat-fluid-solid coupling FEM and analytical modeling of thermal error is adopted,and the heat transfer-structural temperature rise-thermal error modeling method of the electric spindle unit is constructed.From the comparison validation experiment between simulation analysis results with the above modeling method and experiment results,it can be demonstrated that this method has evident accuracy in aspects of electric spindle unit temperature,thermal errors and other features prediction,and can provide theoretical supporting and guidance for the design and optimization of thermal balance design and optimization of electric spindle unit.For hardware equipment of the active thermal error control model of electric spindle unit,to meet the requirements of differentiated dynamic temperature control from electric spindle unit and other key functional parts of precision machine tools,a design philosophy and principle of multi-loops differentiated active temperature control system is explored,and a prototype of active temperature control equipment is developed,using the principle and mode of the quantitatively mixing of high and low temperature circulating coolant.And the test platform for testing and control the thermal characteristics of electric spindle unit is built,which provide the hardware and software systems to the studies of active thermal error control strategies of thermal errors of electric spindle unit.For the active thermal error control strategy for electric spindle unit,two typical active temperature control strategies are proposed,including dynamic power matching strategy between heat generating and thermal dissipation,the initial status maintaining strategy of temperature field.The former strategy can be realized with the aid of heat generating power of endogenous heat generating parts and bottom communication technologies with CNC system.The latter strategy is based on the PID control theory with BP neural network.On the one hand,the experiments based on the prototype of active temperature control equipment and the test platform for testing and control the thermal characteristics of electric spindle unit showed that: Compared with the traditional open-loop and identical circulating cooling strategy,the active control strategies of thermal errors can effectively control the thermal errors of electric spindle unit in the whole process.The strategies are benefit to improving the accuracy and accuracy stability of electric spindle unit,and the comprehensive precision of electric spindle unit can be effectively improved.On the other hand,based on heat transfer-structural temperature rise-thermal error modeling method of electric spindle unit,the above strategies can be deeply studied from aspect of mechanism to analyze their advantages and disadvantages for inhibitory effect for thermal errors of electric spindle unit;it can also provide reference for study of active thermal error control strategy for electric spindle unit in the future.The research of thermal error modeling and active control method of the electric spindle unit has important theoretical significance and engineering value for the promotion of electric spindle unit design level in China,and has a positive role in promoting for design and development of intelligent electric spindle product,which has the self-regulating function for thermal characteristics.Meanwhile,it also has reference and experience value for thermal error modeling and active control method of other function components of precision machine tools.