Quasi-Sliding Mode Control of a High-Precision Hybrid Magnetic Suspension Actuator

Abstract

A novel 1-DOF hybrid magnetic suspension actuator for precise motion control is presented. The actuator is designed to achieve sub-micron positioning accuracy over a range of motion in excess of 1000 µm while avoiding large nominal levitation currents and iron core saturation. The proposed passive push-active pull configuration offers precise motion control with moderate actuator effort when a payload is to be accurately suspended over a large range of travel. The proposed actuator can be used modularly to control multiple axes of motion in a multi-DOF positioning application that requires millimeter-range travel with submicron accuracy. A Quasi-Sliding Mode controller (QSM) is presented in which the sliding mode dynamics are directly designed, as opposed to the typical Lyapunov function approach that is solely based on stability. Since full knowledge of the state vector is required, a nonlinear high-gain observer was also designed and implemented. Performance of the QSM algorithm in controlling the proposed actuator is compared to that of a PID controller with standard feedback linearization. Several experiments are conducted to demonstrate both the positioning and tracking capabilities of the proposed actuator. The proposed QSM method shows better transient performance than the standard PID feedback linearization approach. QSM also shows better tracking performance, which is highly desirable in systems in which fast and accurate motion control along a desired path is critical.