Abstract: The rotary accuracy is an important performance index of high-speed magnetic levitated cylindrical grinding spindles, usually evaluated through the rotary error, is mainly affected by rotor unbalance forces and bearing characteristics. As the magnetization effect causes ferromagnet bearings to output non-linear forces, in order to achieve high rotary accuracy in engineering applications, the bearing forces are generally linearized by obtaining look-up tables through hardware experiments. However, when bearing design changes, experiments need to be repeated to update the look-up tables, which increases costs and period. If the influence of magnetization effect on the rotary accuracy can be clarified, the experiment might be omitted, and the costs and period can be reduced. Hence, the active magnetic bearing force characteristics of three different magnetization models are compared, such as non-magnetization model, fixed permeability model, and Jiles-Atherton (J-A) transient permeability model. A rigid rotor dynamics spindle system model containing rotor unbalance forces, bearing forces and grinding forces is established. The influence of the magnetization effect on the system closed-loop amplitude-frequency characteristics is investigated through simulation, and it is found that the magnetization effect significantly changes the low and medium frequency system response. The time-domain simulation results show that the magnetization effect increases rotary error. Near the bias current, the output deviation between the fixed permeability model and the transient permeability model is negligible. Using the fixed permeability model for bearing design and the transient permeability model for verification might be an efficient and valuable method to achieve high rotary accuracy for the spindle.

Key words: cylindrical grinding spindle, rotary error, active magnetic bearing, rotor dynamics, magnetization models