Precision Tracking Motion Control

Among the electric motor drives, permanent magnet linear motors (PMLM) are probably the most naturally akin to applications involving high speed and high precision motion control. The increasingly widespread industrial applications of PMLM in various semiconductor processes, precision metrology and miniature system assembly are self-evident testimonies of the effectiveness of PMLM in addressing the high requirements associated with these application areas. The main benefits of a PMLM include the high force density achievable, low thermal losses and, most importantly, the high precision and accuracy associated with the simplicity in mechanical structure. PMLM is designed by cutting and unrolling their rotary counterparts, literally similar to the imaginary process of cutting a conventional motor rotary armature and rotary stator along a radial plane and unroll to lay it out flat, as shown in Fig. 2.1. The result is a flat linear motor that produces linear force, as opposed to torque, because the axis of rotation no longer exists. The same forces of electromagnetism that produce torque in a rotary motor are used to produce direct linear force in linear motors.