Control of Magnetic Bearings with Rotor-Mounted Accelerometers

Mounting MEMS accelerometers inside hollow shaft rotors has been proposed as a novel sensor design for vibra- tion monitoring and control in rotating machinery. The application of this technology to Active Magnetic Bearings (AMB) could allow sensor/actuator collocation. This paper explores the possibility of using rotor-mounted ac- celerometers as standalone sensors for AMB control. The integration of the acceleration signals, after conversion from the rotating to the inertial reference frame, is considered as a means to extract rotor displacement informa- tion. The sensitivity of this method to uncertainty in the measurement of the gravitational component and in the estimation of the initial angular position is studied. The latter produces a steady state error in the rotor position estimation which cannot be measured by the accelerometers. Therefore, a current injection technique has been developed to eliminate this error. The method produces a low-amplitude, high-frequency response in the rotor, which has negligible effect on the rotordynamics, but is easily detected by accelerometers and allows the steady state error to be estimated and reduced. The simulation of a disc being levitated in an AMB system using only internal accelerometers has been undertaken and results are reported.