Design of high precision linear stage with double-sided multi ...

Mechatronics Journal., Volume 16, Issue6, Pages 303-378 (July 2006)
Design of high precision linear stage with double-sided multi-segmented
trapezoidal magnet array and its compensations for force ripples
By: Moon G. Lee, Young-Man Choi, Sung Q. Lee, Dae-cheol Lim, Dae-Gab Gweon
Abstract
Generally, linear motor is used as actuators for high precision stage which requires long stroke, high
speed and high precision capability. In order to meet the needs of high speed and high precision, it is
important that the motor generates large force and has small size. In this paper we propose a linear motor
with multi-segmented (MST) magnet array to maximize actuating force per unit volume. The MST
magnet array is a modified version of standard Halbach magnet array. Each magnet in the MST magnet
array has various shapes and dimensions while standard Halbach magnet array has identical magnets. In
order to optimize the shapes and dimensions, design optimization of the motor is carried out and its
performance is investigated. We conclude that the linear motor with the MST array can generate more
actuating force per unit volume than the one with conventional magnet array and standard Halbach
magnet array. A high precision stage is constructed using the optimized MST magnet array. Even though
we obtain maximized actuating force, the flux density by the MST array is seriously distorted from ideal
sinusoidal flux density with respect to mover position. This distorted flux density results in force ripples
when we use three phase commutation. And no matter how small force ripples would be, serious tracking

errors occur in high precision linear stages. Thus, force ripple must be compensated. In this paper, we
proposed a simple method to reduce the ripple by current shaping.
Keywords: Multi-segmented trapezoidal magnet array; Halbach magnet array; Linear motor; Force
ripple