Patent ID: 6905258

Claim:
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 to provide an operable image of the scale grating pattern, the fiber optic readhead arrangement comprising: a housing element; a lens; and a plurality of fiber-optic receiver channels, each respective fiber-optic receiver channel comprising: a respective receiver channel spatial phase mask portion having a respective spatial phase and having its light-blocking elements arranged at a pitch that is operable for spatially filtering the operable image of the scale grating pattern, the respective receiver channel spatial phase mask portion generally located at a nominal receiver plane that is operable for spatially filtering the operable image of the scale grating pattern; and at least one respective receiver channel optical fiber having an input end that receives a respective receiver channel optical signal light; 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 operable image of the scale grating pattern 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.