Precision positioning of a five degree-of-freedom planar motion stage

This paper presents the development of a five degree-of-freedom (DOF) planar motion stage with an integrated surface encoder for position detection. The single-level moving element is levitated by three air-bearings without mechanical contact, and is actuated by three linear motors and three piezoelectric transducer (PZT) actuators. The three linear motors are placed on the stage base to generate movement of the stage in the XYθz directions (in-plane motion), while the three PZT actuators move the stage in the Zθxθy directions (out-of-plane motion). A surface encoder composed of three two-dimensional (2D) angle sensors and a 2D angle grid is employed as the position sensor to detect the five DOF position of the stage for feedback control. Experimental results demonstrate that the surface encoder has a resolution of 30 nm and is suitable for sub-micrometer positioning. It is also confirmed experimentally that the stage can be controlled independently in the five DOFs with a positioning resolution of 50 nm and a settling time of 50 ms.