A Long-Stroke Planar Actuator with Multiple Degrees of Freedom by Minimum Number of Polyphase Currents

Abstract

There are a large number of drive systems employing numerous actuators in industry. As such, the performances of these actuators require constant improvement in terms of higher speed and precision, miniaturization, and lower energy consumption. In addition, most of these drive systems need a design that permits MDOF (Multi-Degree-Of-Freedom) motion. Motion controls allowing MDOF have been practically realized by using stacked multiple actuators (Ebihara et al., 2005). However, there are problems in attempting to improve the performance of these types of drive systems such as a larger and more complicated structure, fluctuation of the center of gravity, and Abbe errors in position measurement due to the multiple-moving parts. In order to eliminate these problems, MDOF actuators—which have only a single moving part, but are capable of being directly driven with MDOF—are emerging technologies for future applications (Ebihara et al., 2005). Most MDOF actuators can be classified into two prominent types: a planar actuator that can drive in two-degree-of-freedom (2-DOF) translational directions; and, a spherical actuator that can drive in 2-DOF rotational directions. As for forms of the driving forces, electromagnetic, piezoelectric, magnetostrictive, and electrostatic types of MDOF actuators have been proposed (Ueda, 2009). Most models are of the electromagnetic actuator type because of mightiness and good controllability of the driving forces (Ueda, 2009). This study deals with electromagnetic planar actuators, which have a mover capable of traveling over large translational displacements in a plane. The electromagnetic planar actuators that have been proposed can be classified by their drive principle such as stepping, direct-current, induction, and synchronous types. Synchronous planar actuators are expected to offer extremely good controllability of the motion controls, and furthermore in attempting to position a mover precisely, the mover should have no problematic wire in order to avoid heat generation at the mover and tension due to the wire that often deteriorates the drive characteristics. Therefore, synchronous planar actuators with a permanent-magnet mover have been studied actively. However, the movable area tends to be quite narrow due to the use of conventional magnetic circuits for the MDOF drives, which are spatially separated from one another as shown in Fig. 1 (Kim & Trumper, 1998), unless the planar actuator has a large number of armature coils (Jeon et al., 2007). Source: Motion Control, Book edited by: Federico Casolo, ISBN 978-953-7619-55-8, pp. 580, January 2010, INTECH, Croatia, downloaded from SCIYO.COM