General forms of controller realizing negative stiffness

The zero-power magnetic suspension system behaves as if it has negative stiffness. Suspension with a similar characteristic can be realized by using a linear actuator such as a voice coil motor. The controllers realizing negative stiffness with a linear actuator are compared with zero-power controllers analytically. The analyses show that they have similar structures. It is pointed out that a control technique, which was effective in widening the operation range of zero-power controllers, can be applied to the controllers realizing negative stiffness.