Actuator and sensor modeling for magnetic levitation system

In this paper, we consider the modeling of the sensor and actuator characteristics of a magnetic levitation system. The sensor part consists of an infra-red emitting diode (IRED) and a strip of photo-transistors to widen the control range of the maglev. Actuator is a lab-built electromagnet made of coil. In order to levitate a load through small amount of current, we attach a strong magnet block to the top of the levitated object. The sensor used in this paper has nonlinear characteristics because the photo-transistors are not accurately positioned. Furthermore, the actuator also has some sort of nonlinearity. We propose to use a screw-based height gauge system for modeling the actuator characteristics and the relationship between the height of the levitated object and the sensor output. We adopt two methods to model the sensor and actuator characteristics : look-up table and segmented linear approximation. The merit of the proposed modeling method is that it is very cost-effective because the screw-based measurement system can be built at a reasonable cost. Finally we show the usefulness of the proposed modeling approach through a real control experiment.