Magnetically Levitated Spindle for Long Term Testing of Fiber Reinforced Plastic

This article describes a magnetically levitated spindle for long term cyclic fatigue strength testing of cylinders made of fiber reinforced plastic. These cylinders represent the outer-rotor of a kinetic energy storage. The realized spindle design has multiple eigenmodes below the operational speed range, which are described in the first part of this paper. Because the system is operated under vacuum conditions, the second part of this paper focuses on the heat generation and distribution on the rotor during operation. First, transient electromagnetic finite element simulations are described for the active magnetic bearings. These simulations are used to derive power losses of the active components on the rotor. Second, a finite element simulation characterizes the thermal behavior of the rotor and includes thermal radiation and conduction. Using the power losses calculated in the electromagnetic simulation, the thermal simulation provides the temperature of the rotor. Finally, these results are compared with measured data from the spindle. The comparison shows that the losses in the upper bearings are underestimated by the electromagnetic simulation. Nevertheless, the simulations show that the rotor overheats during long term operation, and thus further improvements on the control of the system have to be carried out.