Realization of Indirect Magnetic Suspension with Indirect Sensing through Conductive Wall

Abstract

The magnetic suspension of a ferromagnetic object (floator) across a conductive wall was achieved without directly sensing the displacement of the floator. When a floator is inside a chamber made of conductive material, the cross-wall detection of the motion of the floator is impossible or at least difficult with an eddy-current type displacement sensor. This study discussed two approaches to the problem. In the first approach, an electromagnet directly actuates the floator across the wall. In the second approach, the floator is indirectly actuated through a permanent magnet; such suspension is called as double series magnetic suspension. Because a critical problem due to induced voltage is expected in the former, the latter was focused. In the latter system, the motion of the first floator (permanent magnet) outside the chamber is detected directly. In contrast, the motion of the floator inside the chamber is not detected. Instead, its displacement and velocity are estimated by an observer, which is referred to as indirect sensing. Because the system is controllable and observable even with indirect sensing, the system can be stabilized by feeding back these estimated signals. To demonstrate the validity of such an approach, an experimental apparatus was designed and manufactured. A full-order observer was built for the estimation. The displacement estimated by the observer was compared with the actual displacement. Then, magnetic suspension with indirect sensing was achieved by replacing the sensor signal by the estimated signal.