Initial condition-adaptive robust control for a high-speed magnetic actuator

This paper deals with a robust control method for a magnetic actuator for lift motion applications. The actuator is driven by electromagnets positioned around an armature connected to an actuated object. The armature is suspended by springs with a large spring rate, enabling it to move at high speed. A feedback controller has been designed to adjust the magnetic force so as to moderate the speed of the armature when it comes in contact with the magnets, thereby reducing mechanical shock and noise. Difficulties in designing the controller stem from magnetic force properties, such as severe instability and nonlinearity, which prevent push-pull type actuation. To overcome such difficulties with sufficient robustness, an adaptive control scheme has been developed, which varies the control force depending on the initial condition at which the controller is activated.