Magnetic actuators

The subject of magnetic actuators is very broad, and encompasses various te chnologies, as well as a wide range of magnetic circuit topologies and perf ormance characteristics, for an ever-increasing spectrum of applications in all market sectors. Magnetic actuators can be rotary or linear, and can ha ve continuous or limited motion, the basic classes being moving-coil, movin g-iron and moving-magnet. Within these, the airgap length may either remain constant or vary with displacement, and while the majority of such actuato rs have only one degree-of-freedom, systems are emerging which are capable of providing multiple degrees-of-freedom of controlled motion. In view of t he breadth of the subject, the paper focuses on research which is being und ertaken in the Electrical Machines and Drives Group at he University of She ffield on some specific magnetic actuation systems. These include: Aerospace-electromechanical and electro-hydraulic actuators for flight cont rol surfaces, Automotive-short-stroke actuators, for applications such as high-speed dies el fuel injector control valves; active and passive magnetic bearing actuat ion systems for electric vehicle flywheel energy storage units, Industrial-long stroke linear motors for high-speed packaging and manufactu ring applications, Healthcare-reciprocating linear actuators for resonant electro-mechanical s ystems, such as positive-displacement diaphragm air-compressors, Computer-multi-degree-of-freedom spherical actuators for force-feedback joy sticks, manipulators etc. As will be highlighted, much of the research involves the application of hi gh-energy rare-earth permanent magnets, which have facilitated the developm ent of new and improved performance magnetic actuators. (C) 2000 Elsevier S cience S.A. All rights reserved.