Enhanced-Performance Control of an Electromagnetic Solenoid System Using a Digital Controller

Solenoids can be used as linear or incremental motion actuators, most often by coupling the solenoid armature to a linear spring. In this configuration, its limited open-loop stable range (less than one-third of the full range) affects performance and limits applications. The input-output linearization control method is an effective technique to extend the stable range. But in practice, however, the time-delay effect from both measurement and actuation can make the system less damped and therefore more sensitive to disturbances. This effect was analyzed and a digital proportional and integrator controller plus extended state observer (ESO) is proposed to enhance the performance of the electromagnetic actuator. Simulation and experimental tests show that this combined proportional and integral and ESO technique can extend the stable range of motion to 77.6% of full stroke with less sensitivity to external disturbances.