Fountain solution thickness measurement system and method using ellipsometry

Patent metadata

Field	Value
Publication number	US-11835446-B2
Application number	US-202117355692-A
Country	US
Kind code	B2
Filing date	Jun 23, 2021
Priority date	Jun 23, 2021
Publication date	Dec 5, 2023
Grant date	Dec 5, 2023

Abstract

An optical light reflectance measurement system above an imaging member surface measures fountain solution surface light reflectance interference on reflective substrate portions of the imaging member surface in real-time during a printing operation. The measured light reflectance interference corresponds to a thickness of the fountain solution layer and may be used in a feedback loop to actively control fountain solution layer thickness by adjusting the volumetric feed rate of fountain solution added onto the imaging member surface during a printing operation to reach a desired uniform thickness for the printing. This fountain solution monitoring system may be fully automated.

First claim

What is claimed is:

1. An image forming device for controlling fountain solution thickness on a non-reflective imaging member surface of a rotating imaging member, comprising:
a reflective substrate attached to the non-reflective imaging member surface at non-image forming regions along a first side gutter of the imaging member surface outside a imageable area of the imaging member surface to form a reflective surface on the otherwise non-reflective surface, the imaging member surface having a layer of fountain solution fluid dispensed on both the reflective surface and the non-reflective surface at a fountain solution dispense rate;
a light reflectance detector spatially separate from the imaging member surface forming a gap therebetween, the light reflectance detector configured to measure a light reflectance from the reflective surface with the fountain solution fluid layer thereon; and
a controller in communication with the light reflectance detector and the fountain solution applicator to modify the fountain solution dispense rate based on the measured light reflectance.

2. The image forming device of claim 1 , further comprising a fountain solution applicator configured to apply the fountain solution fluid layer at the fountain solution dispense rate onto the imaging member surface for a printing.

3. The image forming device of claim 2 , the fountain solution applicator configured to apply a subsequent fountain solution layer at the modified fountain solution dispense rate onto the imaging member surface for a subsequent printing.

4. The image forming device of claim 1 , the imageable area defined by regions of the non-reflective imaging member surface that may be imaged by a laser.

5. The image forming device of claim 1 , further comprising a reference mark on the first side gutter used to identify a location of the reflective substrate.

6. The image forming device of claim 1 , further comprising a second reflective substrate attached to the imaging member surface at second non-image forming regions of the imaging member surface outside a imageable area of the imaging member surface at a second side gutter of the imaging member surface opposite the first side gutter.

7. The image forming device of claim 1 , wherein the imaging member is cylindrical and the reflective substrate is shaped in a zig-zag pattern evenly spaced around the non-image forming regions.

8. The image forming device of claim 1 , wherein the light reflectance detector includes a rotational analyzer ellipsometer that measures the amount of light reflectance at a non-normal incidence and at two different polarizations to determine the thickness of the fountain solution, the thickness being determined by interference between light reflecting from the reflective substrate surface and reflective light also traveling through the fountain solution layer.

9. The image forming device of claim 8 , further comprising a light beam emitter producing unpolarized light that is sent through a polarizer, the polarizer allowing light of an electric field orientation to pass, with the polarizer having an axis oriented between p- and s-planes.

10. The image forming device of claim 1 , wherein the fountain solution thickness is determined by an interference between the measured light reflectance and a known input polarization to determine the polarization change caused by the reflection through the fountain solution layer, the interference including amplitude and phase information.

11. The image forming device of claim 1 , the controller being configured to compare the measured light reflectance to a target light reflectance and modify the fountain solution dispense rate based on the comparison.

12. The image forming device of claim 1 , wherein the controller is configured to estimate a thickness of the applied fountain solution fluid layer based on the measured light reflectance and modify the fountain solution dispense rate based on the estimated thickness of the applied fountain solution fluid layer.

13. A method of controlling fountain solution thickness on a non-reflective imaging member surface of a rotating imaging member, comprising:
(a) applying a fountain solution fluid layer at a dispense rate onto the imaging member surface, the imaging member surface being non-reflective with a reflective substrate attached to the non-reflective imaging member surface at non-image forming regions along a gutter of the imaging member surface outside a imageable area of the imaging member surface to form a reflective surface on the otherwise non-reflective surface, the fountain solution fluid layer being dispensed on both the reflective surface and the non-reflective surface at the fountain solution dispense rate with a fountain solution applicator;
(b) measuring a light reflectance from the reflective surface having the fountain solution fluid layer thereon with a light reflectance detector spatially separate from the imaging member surface and forming a gap therebetween; and
(c) modifying the fountain solution dispense rate via controller in communication with the light reflectance detector and the fountain solution applicator based on the measured light reflectance.

14. The method of claim 13 , further comprising attaching the reflective substrate to the non-reflective imaging member surface at the non-image forming regions.

15. The method of claim 13 , further comprising applying a subsequent fountain solution fluid layer at the modified fountain solution dispense rate onto the imaging member surface with the fountain solution applicator for a subsequent printing.

16. The method of claim 13 , the Step (b) further comprising measuring the amount of light reflectance at a non-normal incidence and at two different polarizations with a rotational analyzer ellipsometer to determine the thickness of the fountain solution, the thickness being determined by interference between light reflecting from the reflective substrate surface and reflective light also traveling through the fountain solution layer.

17. The method of claim 16 , the Step (b) further comprising emitting unpolarized light through a polarizer with a light beam emitter, the polarizer allowing light of an electric field orientation to pass, with the polarizer having an axis oriented between p- and s-planes.

18. The method of claim 13 , further comprising determining the fountain solution thickness by an interference between the measured light reflectance and a known input polarization to determine the polarization change caused by the reflection through the fountain solution layer, the interference including amplitude and phase information.

19. The method of claim 13 , the Step (c) further comprising comparing the measured light reflectance to a target light reflectance and modifying the fountain solution dispense rate based on the comparison.

20. An image forming device for controlling a fountain solution dispense rate, comprising
a rotatable imaging member having an imaging member surface that is non-reflective over an imageable area thereon, the imaging member surface including a reflective substrate attached at non-image forming regions thereon along a first side gutter of the imaging member surface outside the imageable area, the imaging member surface having a layer of fountain solution fluid dispensed on portions of both the imageable area and the non-image forming regions at a fountain solution dispense rate;
a light reflectance detector spatially separate from the imaging member surface forming a gap therebetw

Assignees

• Xerox Corp

Inventors

• Thresh Donald
• Ireland Jonathan
• Smith Bruce H
• Soures Michael N
• Vanbortel James D

Classifications

• G01N21/211 Primary

  Ellipsometry (optical thickness measurement G01B11/06) · CPC title

• B41F7/24

  Damping devices · CPC title

• B41N3/08

  Damping; Neutralising or similar differentiation treatments for lithographic printing formes; {Gumming or finishing solutions, fountain solutions, correction or deletion fluids, or on-press development (treatment of materials containing silver salts G03F7/063; developers per se for processing photosensitive materials G03F7/32)} · CPC title

• B41P2233/30

  Measuring or controlling the consumption of ink · CPC title

• B41P2227/70

  Forming the printing surface directly on the form cylinder · CPC title