Field and thrust analysis of linear servo motor with permanent-magnet of different shapes

Thrust ripple, caused by non-sinusoidal magnetic field, always deteriorates the servo characteristics of linear servo system. In this paper the magnetic field and thrust of the double side air-core permanent magnet linear servo motor (DAPMLSM) is analyzed. It mainly analyzed trapezoidal shape permanent magnets motor, including the winding design, to find the key factors which affect the motor performance, and do some optimization. PM height coefficient and air-gap height coefficient should be chosen appropriately to gain larger density amplitude, and PM width coefficient should be between 0.2-0.6 to obtain more sinusoidal flux density distribution. Then it evaluated the flux density and thrust ripple of two different magnet shapes, ordinary rectangular shape and trapezoidal shape. Finite element analysis results shown, PMLSM with optimized trapezoidal shape PM can lower the sinusoidal distortion of magnetic field and thrust ripple efficiently. Finally the design laws of trapezoidal DAPMLSM´s main dimensions, including windings, were given to obtain optimal sinusoidal magnet field and stable thrust.