Control of magnetic suspension with elastic ferromagnetic substance for vibration isolation system

抄録

The insertion of elastic ferromagnetic substance into the gap has been proposed to increase the attractive force of a magnetic suspension for vibration isolation system. The vibration isolation system with a series connection of a positive-stiffness and a negative-stiffness suspensions (zero-compliance vibration isolation system) has been studied extensively. In this system, the isolation table does not displace when a static direct disturbance is applied on the table. A negative-stiffness suspension has been achieved by using zero-power control magnetic suspension. To increase the attractive force of the zero-power magnetic suspension system, the insertion of an elastic ferromagnetic substance into the magnetic flux path between an electromagnet and a suspension target has been proposed. The elastic ferromagnetic substance increases the suspension force with higher magnetic permeability than air. However, the zero-power magnetic suspension system with elastic ferromagnetic substance suffers from low-frequency self-oscillation due to friction. The amplitude of the self-oscillation has been halved by adding a dither signal to the control input. To reduce the self-oscillation more, a dead-band element is added in the controller. In addition, the amplitude of the self-oscillation is reduced by increasing the amplitude of negative stiffness. The basic characteristics of reducing the self-oscillation in the negative-stiffness and zero-power control system are studied experimentally in a single-degree-of-freedom magnetic suspension apparatus.