Ceramic motorized spindle is more suitable for high-precision and high-speed machining because of its material with high stiffness, low deformation, and other excellent characteristics. The ceramic bearing assembly and support location are critical elements influencing the stiffness and dynamic characteristics of ceramic motorized spindle. In order to investigate the influence of bearing assembly on the dynamic characteristics of spindle, the relationship between preload and bearing stiffness is determined and a dynamic model of ceramic motorized spindle bearing rotor system is established taking the comprehensive impact of bearing span and preload into account. The bearing stiffness fluctuation caused by bearing preload and bearing thermal deformation is calculated, and the effect of bearing preload and span on the dynamic characteristics is investigated. The results show that the rotor amplitude firstly decreases with the bearing preload and span vary, and then increases. The best assembly combination of ceramic spindle is a preload of 400 N and a span of 190 mm in the speed of 12,000–18,000 r/min. The vibration experiments are conducted on the ceramic motorized spindle, and the average error between experimental date and calculated date is 2.49%, which verifies the accuracy of the model. This study lays a theoretical foundation for further investigation of the dynamic characteristics of ceramic motorized spindle and its structural optimization.

Full-ceramic motorized spindle is suitable for high-grade CNC machine tool due to its high stiffness and wear resistance, while axial transfer of unbalanced magnetic pull (UMP) caused by reverse magnetic characteristic leads to random vibration at the shaft end. In order to investigate the nonlinear dynamics of full-ceramic motorized spindles under the influence of reverse magnetic, a five-degree-of-freedom dynamic model of bearing-rotor system considering the axial transfer of UMP is constructed. The improved transfer matrix method is proposed to establish the axial transfer model of UMP and the vibration mode of the shaft is obtained. The dynamic characteristics of the bearing-rotor system are analyzed considering the effect of UMP. The magnetic field density and vibration characteristics of the motorized spindle system is studied, and the full-ceramic motorized spindle shaft influence of UMP axial transfer, the vibration of the rotor tends to decrease from inward to outward, while the shaft end vibration also tends to increase gradually with the increase of rotation speed and eccentricity value. The results show that the vibration of ceramic shaft end is 55.4% weaker than that of metal shaft end. It can be seen that under the action of the diamagnetic property, UMP transfer occurs on the ceramic shaft, which reduces the vibration. The experiments show that the average error between the calculated value and the experimental result is 8.5% at the operating speed, which verifies the accuracy of the model developed in this paper.