Patent ID: 7227124
Filing Date: 2007-06-05
Classification: G01D

Abstract:
1. A device for measuring the relative displacement between two members, the device comprising: a scale extending along a measuring axis direction; a readhead designed to be positioned at a nominal distance L from the scale to receive operable scale image light from a field of view on the scale and provide an operable image of the scale when the scale is illuminated, the readhead comprising: an imaging portion that provides the operable image of the scale, the imaging portion comprising an imaging lens; and an illumination portion that provides illumination to the field of view, the illumination portion comprising a condenser lens having a focal length f and a light source having an emitting element having a width w, wherein the emitting element is nominally located at the focal length f from condenser lens, wherein: the illumination portion is configured such that the illumination provided to the field of view is approximately uniform across the field of view and at least partially incoherent such that the operable image of the scale does not include self-imaging effects; and the device is configured to fulfill at least one design criterion from a group of design criteria comprising: