| Linear motion is widely used in industry automation. Without special mechanical adjustments, linear motors directly convert electricity into linear moving mechanical power. It provides load thrust with linear motion, and single-direction or double-direction controllable displacement can be gained. With a number of benefits including high speed, high precision, fast response, stiffness, and zero backlashes, linear motor will have wide application prospect.In this paper, the principium, structures, sorts and characters are analyzed and discussed, and especially tubular permanent magnet s linear synchronous motor (PMLSM), which is the most important part of the dissertation, is analyzed particularly. With FEM, effects of different permanent magnet structures on the air gap magnetic field of PMLSM are analyzed. The Halbach array applied to linear motors, the amplitude of the fundamental wave of the air gap flux density can be increased, and the air gap flux density distributes sinusoidally. The effect of Halbach array is contrasted with the effect of tradition permanent magnet structures on the sinusoidal distribution and the fundamental amplitude of the air gap flux density, and the effect on the air gap flux density is also analyzed while the thickness and the width of permanent magnets is changed.The causes of alveolar effect and the advantages of a more poles and fewer slots motor are introduced. PMLSM with different rates of poles and slots, taken for example, by FEM, the effects of the rate on the magnetic field, the winding factor, and the alveolar effect are analyzed. The alveolar effect is also related with the shape of the primary slot. The slot leak reactance of open slot and half-open slot is calculated, and the effects of the slot shape on the air gap magnetic field are discussed.Magnetic field of PMSLM analyzed, some methods are brought to improve the air gap magnetic field, to reduce the alveolar effect and to optimize the motor characters.
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