A New Optical Configuration for the Surface Encoder with an Expanded Z -Directional Measuring Range

This paper proposes a new optical configuration for a two-axis surface encoder that can measure the in-plane ( -axis) and out-of-plane ( -axis) displacements of a positioning stage. The two-axis surface encoder is composed of a scale grating and a sensor head. A transparent grating is employed in the sensor head for measurement of the -directional displacement of the scale grating based on the Fizeau-type measurement method; a reference beam reflected from the transparent grating and the zeroth-order diffracted beam from the scale grating are superimposed to generate an interference signal. A pair of prisms and a beam splitter are also employed in the sensor head, so that the positive and negative first-order diffracted beams can be superimposed over a long working distance to generate an interference signal for measurement of the -directional displacement of the scale grating. Focusing on the new, extended -directional measurement mechanism, proof-of-principle experiments were carried out to verify the feasibility of the proposed optical configuration for the surface encoder that can measure the uni-directional displacements of a scale grating along the - and -axis. Experimental results from the developed optical configuration demonstrated the achievement of a -directional measuring range of ±1.5 mm.