Patent ID: 7965393
Filing Date: 2011-06-21
Classification: G01D

Abstract:
1. A fiber optic readhead and scale arrangement for measuring the relative displacement between two members along a measuring axis direction, the fiber optic readhead and scale arrangement comprising a fiber optic reference signal generating configuration usable to provide an indication of a reference position, the fiber optic reference signal generating configuration comprising: at least a portion of a first fiber optic readhead, the at least a portion of a first fiber optic readhead comprising a light source that outputs a first diverging source light, and at least first and second fiber optic reference mark signal receiver channels that are configured to provide respective reference mark signals; and a scale member comprising at least a first scale track extending along a measuring axis direction and arranged to reflect the first diverging source light to provide scale light to the first fiber optic readhead, the first scale track comprising: wherein: the first fiber optic reference mark signal receiver channel comprises a first reference mark signal receiver channel optical fiber and a first reference mark signal receiver channel aperture, the second fiber optic reference mark signal receiver channel comprises a second reference mark signal receiver channel optical fiber and a second reference mark signal receiver channel aperture, and when the first fiber optic readhead is operably positioned relative to the first scale track the boundaries of the first and second reference mark signal receiver channel apertures that are closest to one another are separated by a dimension AR the at least one reference mark portion is configured to such that two reference mark portion boundaries are separated by an edge-to-edge dimension LETOE along the measuring axis direction; and the fiber optic reference signal generating configuration is configured such that: