Fountain solution thickness measurement using phase shifted light interference in a digital lithography printing system
AssigneeXerox Corporation
InventorsPaul J. McConville, Chu-heng Liu, Jason M. LeFevre, Seemit Praharaj, Douglas K. Herrmann
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Abstract
According to aspects of the embodiments, there is provided a method of measuring the amount of fountain solution employed in a digital offset lithography printing system. Fountain solution thickness is measured by using phase shifted monochromic light to produce optical path differences through the fountain solution film. The intensity of the reflected light through the fountain solution film is very sensitive due to the phase shifted light so interference fringes are easier to delineate and fountain solution thickness measurement more reliable.
Claims16
A method to measure fountain solution thickness for variable data lithography printing via an imaging member having an arbitrarily reimageable imaging surface for transferring an ink image to a receiving substrate, comprising:
- applying a coating of fountain solution to the imaging member having the arbitrarily reimageable imaging surface via a fountain solution vapor supply;
- transferring a portion of the fountain solution coating on the imaging member onto an optical gating surface of a fountain solution carrier roll as a fountain solution layer;
- radiating with an extended phase shifted monochromatic light source to a measurement point of the optical gating surface of the fountain solution carrier roll, the fountain solution carrier roll being adjacent the imaging member and having the optical gating surface as a noninktransferable optical gating surface, the fountain solution carrier roll being a non ink transfer roll absent ink and saturated with the fountain solution layer;
- receiving reflected light from a top surface of the fountain solution layer and from the measurement point using an optical system, while the light reflected from the measurement point is received after traveling through the fountain solution layer at the optical gating surface;
- wherein the received reflected light forms an interference pattern obtained by an optical path length differences associated with the reflected light from the top surface and the measurement point;
- and
- determining thickness of the fountain solution layer at the optical gating surface based on reflected light intensity at the interference pattern.
An ink-based digital printing system useful for ink printing via an imaging member having an arbitrarily reimageable imaging surface for transferring an ink image to a receiving substrate, comprising:
- a fountain solution carrier roll adjacent the imaging member and having a noninktransferable optical gating surface, the fountain solution carrier roll being a non ink transfer roll absent ink and saturated with a layer of fountain solution;
- a light source for outputting an extended phase shifted monochromatic light source to a measurement point of the optical gating surface under the fountain solution layer;
- an optical subsystem to receive reflected light from a top surface of the fountain solution layer and from the measurement point, while the light reflected from the measurement point is received after traveling through the fountain solution layer at the optical gating surface, the light source including two monochromatic light sources having a constant phase shift modulated via Cos (θ1/2) therebetween;
- wherein the received reflected light forms an interference pattern obtained by an optical path length differences associated with the reflected light from the top surface and the measurement point;
- and
- a controller having
- a storage device coupled to a processor, wherein the storage device comprises instructions which, when executed by the processor, cause the processor to determine fountain solution layer thickness for variable data lithography printing by:
- determining the thickness of the fountain solution layer at the optical gating surface based on reflected light intensity at the interference pattern.
A fountain solution measurement device useful for an ink-based digital printing system used for ink printing via an imaging member having an arbitrarily reimageable imaging surface for transferring an ink image to a receiving substrate, comprising:
- a fountain solution carrier roll adjacent to the imaging member and having a noninktransferable optical gating surface, the fountain solution carrier roll being a non ink transfer roll absent ink and saturated with a layer of fountain solution;
- a light source for outputting an extended phase shifted monochromatic light source to a measurement point of the optical gating surface under the fountain solution layer;
- an optical subsystem to receive reflected light from a top surface of the fountain solution layer and from the measurement point, while the light reflected from the measurement point is received after traveling through the fountain solution layer at the optical gating surface;
- wherein the received reflected light forms an interference pattern obtained by an optical path length differences associated with the reflected light from the top surface and the measurement point;
- and
- a controller configured to determine the thickness of the fountain solution layer at the optical gating surface based on reflected light intensity at the interference pattern, the controller providing input to a fountain solution vapor supply to apply a coating of fountain solution to the imaging member having the arbitrarily reimageable imaging surface, the optical gating surface of the fountain solution carrier roll receiving a portion of the fountain solution coating from the imaging member as the fountain solution layer.
Dependencies are inferred from the claim text.