Magnetic field modeling and force ripple minimization in slotted moving coil type linear motor

Abstract

Recently, there is an increasing requirement for controlled high speed precision linear motion over long strokes. Among the linear actuation technologies, the linear motion actuator consisted of linear PM motor is becoming increasingly popular because of their advantages. The force per ampere capability of linear PM motor is enhanced by using an slotted armature. But, the linear PM motor using slotted armature exhibits force ripple due to the slotting and finite length of armature. Because this force degrades the positioning accuracy and induces fluctuation of speed, the design for force ripple reduction is required for smooth and precise motion of the actuator. The system consisted of linear PM motor and square type air bearing is proposed as a linear motion actuator for the precision positioning system. The system is designed conceptually to have the force ripple reduction method, symmetry and shaped coil winding, and inherently infinite positioning resolution to meet the principles for precision system design. By using the magnetic field of linear PM motor with infinite slotted armature obtained from the finite element analysis, which can describe the flux focusing effect in the tooth, relative permeance function of armature slotting effect is expressed with the function of motor geometric parameters. Relative permeance function of finite slotless armature effect is obtained from numerical anaysis and fitting method. The field distribution of a linear PM motor with finite slotted armature is obtained from the field distribution by infmite slotless annature and relative permeance function of fmite slotted armature. Optimal design is conducted so as to be designed with minimum force ripple under required driving force. In optimal design, field distribution described by relative penneance function is used in calculation of force components. By using the analytic equation of field distribution, optimal design processing is possible in case of system with many de...