US Patent 7473886 Position-measuring device

In a position-measuring device for acquiring the relative position of a scanning unit and a reflection measuring graduation movable relative thereto in at least one measuring direction, the scanning unit includes a light source and a detector arrangement in a detection plane. In a first variant of the scanning unit, at least one optical reflector element is positioned in the scanning beam path which has an optical effect on the scanning beam path to the effect that the distance between a virtual light source and the reflection measuring graduation on one hand, and the distance between the reflection measuring graduation and the detector arrangement/detection plane on the other hand are identical. In a second variant, in the scanning unit at least one optical transmission element is disposed in the scanning beam path which has an optical effect on the scanning beam path to the effect that the distance between the light source and the reflection measuring graduation on one hand, and the distance between the reflection measuring graduation and a detector arrangement in a virtual detection plane on the other hand are identical.