Force measurement using double series magnetic suspension

Double Series magnetic suspension is applied to force measurement. In a double series magnetic suspension system, two floators are suspended with a single electromagnet. The attractive force of the electromagnet directly acts on the first (upper) floator in which a permanent magnet is installed. The motion of the second (lower) floator is controlled indirectly through the attractive force of the permanent magnet. When PID control is applied to the second floator, the first floator displaces proportionally to external force acting on the second floator. Therefore, the force can be estimated for the displacement of the first floator. When the parameters are set appropriately, even small force leads to large displacement so that the proposed measurement method is suitable for noncontact measurement of micro force. An apparatus was fabricated for experimental study on the proposed measurement method. Its effectiveness was demonstrated experimentally.