Control of Oscillating Transmitted Forces in Axial-Thrust Bearings with a Secondary Magnetic Bearing

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Abstract
In certain applications, axial pulsating forces in a machine need to be isolated so as to reduce the vibration or transmitted force of the main support. This paper illustrates the trade-offs that must be considered for such vibration isolation. It considers tile use of active feedback control and duly notes the control algorithm difficulties that are anticipated in the use of a magnetic bearing as the means for implementing the isolation. Complete vibration isolation is theoretically possible in a machine over certain frequency ranges for a sinusoidally varying exciting force, but at the cost of large vibration amplitudes of the shaft or very large control forces at low frequencies. Conversely, optimum (reduced) transmitted forces may be determined on the basis of a maximum prescribed amplitude of vibration that is acceptable for a particular machine.