This paper demonstrates the idea of magnetic force control in magnetic levitation systems using flux density measurements. A Hall-effect sensor is used to sense the flux density in the airgap. A simple magnetic levitation system is used for the demonstration, consisting of a U-shaped electromagnet and a manipulator. First, the system dynamic model are described in state equations using airgap displacement, manipulator velocity and flux density as state variables. Second, the magnetic levitation system is unstable in nature, so we stabilize it using digital state feedback control. The magnetic force is then regulated using a digital $H_\infty$ controller to achieve robust stability against various modeling uncertainties, disturbance/noise rejection, asymptotic tracking to command signal avoidance of saturation of the actuators. Finally, the system is implemented using a digital signal processor with 16 bit A/D and D/A converters.
