Multi-axis grating encoders for stage motion measurement

This paper describes an overview of the multi-axis grating encoders developed for measurement of stage motions. Two grating mirrors are employed in the grating encoders. One of the grating mirrors is utilised as the scale grating. The other grating mirror is included in the sensor head as the reference grating. The ±1st order diffracted beams from the two grating mirrors are superimposed to generate interference signals, which have information about not only the Z-directional out-of-plane displacement but also X- or Y-directional in-plane displacement. A prototype two-axis linear grating encoder with a software compensation technique for X- and Z-directional measurement, and a prototype three-axis surface grating encoder with a double Y-PD unit design for X-, Y- and Z-directional measurement are then presented.