Robust Control of an Unstable Magnetic-Driven-Type Actuator by Trajectory Changing

Abstract

This paper deals with a robust control method for a magnetic-driven-type actuator. 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, a new control scheme, which is derived from considaration of the armature motional trajectory has been developed. The control sheme is realized as a simple structured controller: a disturbance observer and a pole assignment compensator. The effectiveness of the control scheme is verified by computer simulation results and experimental results using a test rig.