| With the rapid development of high-speed machining technology,the processing speed requirements of Motorized Spindle gradually improve.Studying the dynamic characteristic of bearing-rotor system can avoid the occurrence of spindle resonance.The bearing stiffness of the spindle bearing is an important factor affecting the spindle bearing-rotor system.And the heat generated by high-speed bearing rotation affects the dynamic characteristic of the bearing.Therefore,establishing a bearing-rotor dynamic model considering the heat generation of the bearing and analyzing the frequency reliability under its working speed are of great significance for the optimization design of the motorized spindle and the resonance avoidance.The details are as follows:(1)Diagonal ball bearings dynamic performance is analyzed.According to the force balance equations of all the balls and the force balance equation of the whole inner ring,certain parameters such as force and contact angle of the whole model can be obtained.An example is given to illustrate the relationship between centrifugal force,gyroscopic moment,contact angle and contact load with the rotational speed.The quantitative relationship between the bearing stiffness with rotational speed and preload force is obtained.(2)The empirical formula is used to calculate the frictional heat generating in the contact area of the bearing.The energy balance equation is established using the thermal resistance network to obtain the temperature of each component node and calculate the thermal displacement,taking into account the bearing inner ring centrifugal displacement.On the basis of bearing heat generation,the bearing stiffness analysis model based on the bearing thermal characteristic is studied.The influence of the bearing thermal characteristic and the centrifugal effect of the inner ring on the bearing stiffness are analyzed.The quantitative analysis of the bearing stiffness based on the bearing thermal characteristic is partially solved.(3)The key of dynamic analysis of the spindle system is to study the dynamic characteristic of its internal bearing-rotor system.Based on the analytical model of the bearing stiffness,the bearing-rotor system finite element analysis model is established,and the change law of the natural frequency of the bearing-rotor system is studied.The influence of rotation effect,centrifugal effect of bearing inner ring and bearing thermal effect on the natural frequency of bearing-rotor system are studied,and a reference method is provided to avoid resonance.(4)The main shaft size parameters and bearing stiffness are regarded as the basic variables.Then we use optimal Super Latin hypercube sampling and response surface method to get the explicit function relation between the bearing-rotor natural frequency and each parameter.The AFOSM method is used to analyze the frequency reliability and reliability sensitivity of the spindle-rotor system at operating speed.According to the analysis of bearing characteristic and spindle-rotor dynamic characteristic,it can be seen that the thermal characteristic of bearing during bearing operation have a great influence on bearing stiffness and bearing-rotor dynamic performance.Bearing thermal characteristic should be considered in the analysis.According to the frequency reliability analysis of the motorized spindle,we can see that the rational design of the shaft size and the adjustment of the bearing stiffness can improve the frequency reliability of the motorized spindle. |
