This paper describes a novel active magnetic bearing with distributed actuation, designed for contact-free support of a thin-walled rotor. A full dynamic analysis, control formulation and experimental evaluation are presented. Important aspects of the bearing operation include vibration excitation of the rotor wall due to asymmetries in manufacture and assembly, and the limits of stable operation with respect to static loading of the bearing. For the proposed design, the vibratory dynamics for flexure of the rotor wall are accounted for explicitly in the actuator coil-winding and driving scheme so that coupling of the levitation control with the wall dynamics is minimized. This enables the selection of control feedback laws based on rigid-body dynamic considerations alone. Dynamic performance is investigated by theoretical and experimental study involving a prototype rotor-bearing system. The operating principles are validated and the dynamic behavior shown to align well with the theoretical predictions.

This paper considers the problem of controlling the vibration of a lightweight thin-walled rotor with a distributed actuation magnetic bearing (DAMB). A theoretical flexible rotor model is developed that shows how multiharmonic vibration arises due to small noncircularity of the rotor cross section. This model predicts a series of resonance conditions that occur when the rotational frequency matches a subharmonic of a system natural frequency. Rotor noncircularity can be measured offline, and the measurement data used to cancel its effect on the position sensor signals used for feedback control. A drawback of this approach is that noncircularity is difficult to measure exactly and may vary over time due to changing thermal or elastic state of the rotor. Moreover, any additional multiharmonic excitation effects will not be compensated. To overcome these issues, a harmonic vibration control algorithm is applied that adaptively modifies the harmonic components of the actuator control currents to match a target vibration control performance, but without affecting the stabilizing feedback control loops. Experimental results for a short thin-walled rotor with a single DAMB are presented, which show the effectiveness of the techniques in preventing resonance during operation. By combining sensor-based noncircularity compensation with harmonic vibration control, a reduction in vibration levels can be achieved without precise knowledge of the rotor shape and with minimal bearing forces.