Encoder apparatus

Abstract

A position measurement encoder apparatus including: a scale including a series of position features which are readable by a readhead; and a readhead including: a polarised light source for emitting polarised light toward the scale; a first sensor configured to sense light filtered along a first polarisation axis, the first sensor being arranged to sense light from the polarised light source that has interacted with the scale; and a polarisation manipulator, located in the optical path between the polarised light source and the first sensor, configured such that regardless of the polarisation state of the light emitted from the polarised light source, light that leaves the polarisation manipulator toward the first sensor will have a polarisation state which is at least partially resolvable along the first polarisation axis.

Dependencies are inferred from the claim text.