Publications

Disturbance Rejection Control of an Electromagnetic Bearing Spindle

Redmond, James M.; Redmond, James M.

The force exerted on the rotor by an active magnetic bearing (AMB) is determined by the current flow in the magnet coils. This force can be controlled very precisely, making magnetic bearings a potential benefit for grinding, where cutting forces act as external disturbances on the shaft, resulting in degraded part finish. It is possible to achieve precise shaft positioning, reduce vibration of the shaft caused by external disturbances, and even damp out resonant modes. Adaptive control is an appealing approach for these systems because the controller can tune itself to account for an unknown periodic disturbance, such as cutting or grinding forces, injected into the system. In this paper the authors show how one adaptive control algorithm can be applied to an AMB system with a periodic disturbance applied to the rotor. An adaptive algorithm was developed and implemented in both simulation and hardware, yielding significant reductions in rotor displacement in the presence of an external excitation. Ultimately, this type of algorithm could be applied to a magnetic bearing grinder to reduce unwanted motion of the spindle which leads to poor part finish and chatter.