Tomohiro Sugai

Nonlinear vibration analysis of a rotating shaft supported by a repulsive magnetic bearing and vibration suppression using the axial control

A repulsive magnetic bearing (RMB) supports a rotating shaft without contact by utilizing a magnetic repulsive force between magnets. However, the rotating shaft may contact with a backup bearing during its passage of the critical speed and its vibration may increase due to the small damping and the nonlinearity. A vibration suppression method by controlling the axial displacement of the RMB depending on the rotational speed is proposed. The control of the axial displacement enables it to control the linear and nonlinear stiffness of simultaneously. The main resonance and the nonstationary vibration can be suppressed. These results are validated experimentally.

Contact Whirling Vibration of a Rotating Shaft Supported by a Repulsive Magnetic Bearing and the Influence of the Axial Displacement on Its Suppression

A rotating shaft supported by a repulsive magnetic bearing may contact with a backup bearing during the passage of the critical speed as the damping coefficient of the repulsive magnetic bearing is small. This paper investigates the contact vibration during passage of the critical speed. Particularly, the influence of the axial displacement of the repulsive magnetic bearing on the escape speed from the contact vibration is focused. As a result, it is clarified that the rotational speed of the escapement from the contact vibration decreases as the axial displacement increases. It is explained by the change of both the linear stiffness and nonlinear coefficient in the increase of the axial displacement.© 2011 ASME

Vibration of the Vertical Rigid Rotor Supported by a Repulsive-Type Magnetic Bearing: Effects of Both the Axial Displacement and the Magnetical Anisotropicities of Magnets

Magnetic bearing is considered for the usage in various industries. This paper investigates vibration of the rotating shaft supported passively by a repulsive-type magnetic bearing. The permanent magnet on the market not only has strong nonlinear force characteristics, but also may have a few percents of non-uniform magnetization characteristics. Also nonlinear force characteristics change as axial displacement of the shaft. Restoring force of a repulsive-type magnetic bearing is evaluated numerically considering the effects of both the axial displacement of the shaft and the magnetical anisotropicities of the inner and outer magnets. The occurrences of not only the linear and nonlinear parametric characteristics, but also the excitational forces for each pattern of magnetical anisotropicities are observed and they are evaluated in terms of the axial displacement. Furthermore, the influence of each magnetical anisotropicity pattern on the occurrences of various resonance phenomena is clarified.Copyright