永磁同步型磨削电主轴偏心振动分析及实验*

电主轴是将旋转主轴与电机转子集成为一体的主轴单元,结构复杂,由于加工或装配误差等原因,电主轴转子会存在着一定的偏心量,为探求由于电主轴偏心所导致的转子振动特性,建立了电主轴转子偏心模型,采用Maxwell应力张量法计算了偏心造成的不平衡磁拉力(UMP),将UMP解析式代入Jeffcott转子模型,得到了转子偏心振动方程。以某磨床的永磁同步电主轴为研究对象,利用有限元方法分析了UMP,发现作用于转子的UMP始终指向气隙最小的方向,研究了不同转速下转子在质量偏心离心力和UMP作用下的振动响应。研究结果表明,电主轴在低速运行时,UMP为转子振动的主要来源;随着转速的增加,质量偏心离心力对转子振动的影响更加明显,而UMP大小保持不变,其频率随转速增加而增大,对转子振动的作用随之减弱。对某机床厂所研发永磁同步型磨削电主轴在试运行时产生的振动问题进行了实验,对主轴振动频谱分析后判断实验电主轴存在静态偏心,测得主轴轴心轨迹对前述分析进行了验证。

Eccentric vibration analysis and test of permanent magnet synchronous grinding motorized spindle

The motorized spindle is a spindle unit that integrates the rotating shaft and the rotor of the motor, and its structure is complicated. Due to machining or assembly errors, the rotor of the motorized spindle has a certain amount of eccentricity. In order to explore the vibration characteristics of the rotor caused by the eccentricity of the motorized spindle, the rotor eccentric model of the motorized spindle was established. The unbalanced magnetic pull (UMP) caused by the eccentricity was calculated with Maxwell stress tensor method. The UMP analytical equation was substituted into the Jeffcott rotor model, and the rotor eccentric vibration equation was obtained. Taking the permanent magnet synchronous (PMS) motorized spindle of a certain grinding machine as an example, the UMP was analyzed with FEM, and the UMP characteristic acting on the rotor was obtained. It was found that the UMP is always pointing to the direction of the smallest air gap. The vibration responses of the rotor under the action of the mass eccentric centrifugal force and UMP were studied under different rotational speeds. The research results show that when the motorized spindle is operating at low speed, the UMP is the main source of rotor vibration. With the increasing of the rotational speed, the effect of mass eccentric centrifugal force on the rotor vibration is more obvious. The magnitude of the UMP remains unchanged, and its frequency increases with the rotational speed, while the effect on the rotor vibration is weakened. The vibration issue of the grinding motorized spindle developed by a machine tool factory in trial operation was tested. Through the spindle vibration spectrum analysis it is concluded that the tested spindle has static eccentricity, and the spindle axis trajectory was measured, which verifies the aforementioned analysis.