Precision positioning of a Sawyer motor-driven stage by a surface encoder

This paper describes the precision positioning of an XY-planar motion stage driven by a two-axis Sawyer motor. The moving part of the stage is levitated on the stage platen by an air-bearing. The X- and Y-forcers mounted on the moving part generate electromagnetic forces against the platen for the X- and Y-directional motions, respectively. The position of the moving part is feedback-controlled based on the measurement result of a surface encoder, which is composed of a 2-D slope sensor mounted on the stage moving part and an angle grid film stuck on the stage platen. The angle grid film, on which sinusoidal micro-structured surface with 100 nm amplitude and 100 νm wavelength is fabricated by UV replication, is as thin as 100 νm. It is confirmed by experiments that necessary driving performance can be maintained when the forcer moves on the film. Experimental results also indicate that sub-micrometers positioning accuracy can be achieved by closed-loop positioning control based on the surface encoder output.