This chapter describes a surface motor-driven XYθZ stage system. The surface motor consists of two pairs of linear motors. The magnetic arrays are mounted on the moving element (platen) and the stator windings of the linear motors on the stage base. The platen can be moved in the X and Y directions by the X-linear motors and the Y-linear motors, respectively. It can also be rotated about the Z-axis by a moment generated by the X-or Y-linear motors. In the controller of the stage, a decoupled controlling element is employed to reduce the interference errors between the in-plane motions. A cascaded notch compensator is applied for dealing with the stage resonance. A disturbance observer is implemented to estimate and eliminate the influence of disturbance forces. A surface encoder is also developed to replace the conventional laser interferometers for XYθZ motion measurement.
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