Global linearization and microsynthesis for high-speed grinding spindle with active magnetic bearings

Because of the nonlinear relationship between force and current/displacement the performance of active magnetic bearing (AMB) systems based on local linearization varies greatly as the operating point of the spindle changes. However, consistent stiffness and displacement tracking performance are demanded for a grinding spindle with AMBs, especially when noncircular workpieces need grinding. Here, we analyze the influence of changing operating point on performance theoretically and present experimental confirmation of the analysis. Three linear compensation methods-minimum flux (MIF), constant flux sum (CFS), and constant flux product (CFP)-are explained and compared in terms of power loss and dynamic performance. In order to design stiffness easily and to guarantee system performance in the presence of model uncertainties and disturbance force, we adopted a microsynthesis controller. We performed some experiments to compare the dynamic performance of the three linear compensation methods. The results show that CFS and CFP have better dynamic performance than MIF. An AMB system based on global linearization yielded almost the same stiffness and displacement tracking performance, despite the change of operating point.