Model-Based Commutation of a Long-Stroke Magnetically Levitated Linear Actuator

This paper concerns a commutation and switching algorithm for multi-degree-of-freedom (DOF) moving-magnet actuators with permanent magnets and integrated active magnetic bearing. Because of the integration of long-stroke actuation and an active magnetic bearing, DQ-decomposition cannot be applied. Therefore, these actuators are a special class of synchronous machines. A newly developed model-based commutation algorithm for linear and planar actuators enables long-stroke motion by switching between different sets of coils. Moreover, the ohmic losses in the coils are minimized. Three different versions of the algorithm are compared and successfully implemented on a three-DOF magnetically levitated linear actuator.

I. Introduction

In Recent Years, magnetically levitated planar actuators have been developed as an alternative to -drives constructed of stacked linear actuators. Although the translator of these actuators can move over relatively large distances in the -plane only, it has to be controlled in six degrees-of-freedom (DOFs) because of the active magnetic bearing. These actuators have either moving coils and stationary magnets [1] or moving magnets and stationary coils [2], [3]. The coils in the actuator are simultaneously used for propulsion in the -plane as well as for the four-DOF active magnetic bearing. To integrate the long-stroke propulsion and the active magnetic bearing of a moving-magnet actuator, new design [4] and control methods [5] have been developed.