Patent ID: 7126696
Filing Date: 2006-10-24
Classification: G01D

Abstract:
1. A device for measuring the relative displacement between two members, the device comprising: a scale having a scale grating pattern formed along a measuring axis direction; and a fiber optic readhead arrangement positionable relative to the scale grating pattern to provide an operable interference illumination field arising from light diffracted by the scale grating pattern, wherein the interference illumination field comprises respective light and dark interference fringe zones that extend along a direction approximately perpendicular to the scale grating pattern, the fiber optic readhead arrangement comprising: wherein: the respective receiver channel optical signal light received by the at least one respective receiver channel optical fiber comprises optical signal light collected through the respective receiver channel spatial phase mask portion over a respective collected light area having a collected light area dimension along the measuring axis direction that is at least one full period of the respective receiver channel spatial phase mask portion; when the readhead is operably positioned relative to the scale grating pattern at least first and second respective channels of the plurality of fiber-optic receiver channels spatially filter their respective portions of the light of the operable interference illumination field at the nominal receiver plane to provide at least first and second respective receiver channel optical signals having at least first and second respective signal phases; and the device outputs the at least first and second respective receiver channel optical signals along respective optical fibers to provide relative displacement measurement information in the form of a plurality of respective optical output signals, the respective optical output signals produced without the use of an electronic photodetector element.