A new 3-DOF Z-tilts micropositioning system using electromagnetic actuators and air bearings

A new 3-DOF Z-tilts (z, pitch, and roll motion) micropositioning system has been developed. It uses electromagnetic actuators and air bearings. An ele ctromagnetic actuator produces an attraction force between the air bearing and the base plate. An air bearing has the role of suspension and guidance, with a clearance of several tens of micrometers in the z-direction. Theref ore, this system has design features of guiding 3-DOF XY theta motion witho ut limiting the plane motion and playing the role of a z-directional positi on actuator. With the control of current, the equilibrium position between magnetic attraction force and air bearing thrust force can be controlled wi th inherently infinite resolutions. The theoretical background of an electr omagnetic actuator is explained. Then, an air bearing is analyzed in the po int of z-directional positioning mechanism. The air bearing can be modeled as a second-order system with parameter variation-stiffness and damping var y with respect to the z-directional displacement. Therefore, a simple robus t control algorithm is applied to improve the control performance. With the aid of robust control, this system provides 25 nm positioning resolution o ver the total range of 40 mu m along the z-direction and, accordingly, 0.29 mu rad resolution over the total range of 460 mu rad in pitch and roll mot ion. (C) 2000 Elsevier Science Inc. All rights reserved.