Development of a Moving-Coil Linear PM Machine With Improved Thrust Profile Employing a Double-Sided Misaligned Hybrid Topology

High-performance servo instruments, such as mobile platforms of semiconductor lithography and galvo laser scanning systems, generally require high thrust force, low thrust ripple and low system mass of linear PM machines to improve the loading capability, position precision and dynamic performance of these servo instruments. However, most existing technologies of reducing thrust ripple generally result in the decreaseof thrust force. In this paper, a coreless moving-coil linear PM machine with double-sided misaligned hybrid (DSMH) topology consisting of two asymmetric-arranged hybrid magnet patterns is proposed to meet these requirements. The asymmetric combination of double-sided misaligned magnets with unequal width in the topology helps to enhance the air-gap flux density, while achieving approximately sinusoidal air-gap magnetic field and low thrust ripple. Firstly, the schematic structure and working principle of the DSMH linear machine are presented. Secondly, analytical models of air-gap magnetic field and thrust fore considering the irregular boundary condition of the hybrid magnet patterns are formulated. Then, the influence of the structural parameters on the output performance of the moving-coil linear machine is analyzed through the models, and one DSMH linear machine is designed. Thirdly, to confirm the merits of the DSMH machine, the quantitative electromagnetic performance of the proposed linear machine is compared with that of conventional designs typically used in servo instruments. Finally, one research prototype and two test-rigs are developed, and the experimental measurements of air-gap flux density, thrust force and ripple of the prototype are implemented to validate the design concept of the DSMH linear machine well.