Precision measurement and decoupled control of a planar motion stage

This paper describes the measurement and decoupled control of a surface motor-driven XY planar motion stage. The surface motor is composed of four linear motors placed on the XY-plane in a rectangular shape. The magnetic array and the stator winding of the linear motor are mounted on the platen (the moving element) and the stage base, respectively. The platen can be moved in the X- and Y-directions and rotated about the Z-axis. The XY-positions and the theta-Z rotation of the platen are measured by a three-axis laser interferometer. A decoupled controlling element is employed to reduce the interference errors between the in-plane motions. A cascaded notch compensator is also applied for dealing with the stage resonance. In addition, an effective disturbance observer is implemented to estimate and eliminate the influence of disturbance forces. Experimental results indicate that the developed controller has good dynamic and tracking performances, especially the capability of reducing the interference errors between different drive axes.