Active Magnetic Bearings: Robust performance against uncertainty in rotational speed

An unbalanced mass on a rotating spindle causes synchronous vibrations. Active magnetic bearings have been successfully used to mitigate these vibrations for a particular operating speed. This is done by placing a notch in the closed-loop at a frequency corresponding to the rotational speed. In applications such as micro-milling the operational speed of the spindle can very well deviate from the desired set point. These deviations in the rotational speed can be regarded as an uncertainty in the disturbance model affecting the plant. The controller synthesis problem for robust performance against uncertainty in the disturbance model is recently shown to be convex. We design and implement such a robust controller on an experimental AMB setup.