Fountain solution thickness identification via gloss measurement system and method

A method of controlling fountain solution thickness on an imaging member surface of a rotating imaging member in an image forming device, the image forming device printing a current image onto a print substrate, the printing including applying a fountain solution fluid layer via vapor deposition at a dispense rate onto the imaging member surface, the imaging member surface being a reimageable ink transfer member surface having carbon black therein to absorb laser light, the fountain solution fluid layer having a surface above the imaging member surface and thickness maximum of 100 nm, vaporizing in an image wise fashion a portion of the fountain solution fluid layer to form a latent image, applying ink onto the latent image over the imaging member surface, and transferring the applied ink from the imaging member surface to the print substrate, the method comprising:

• a) measuring a specular reflection of the fountain solution fluid layer surface while the fountain solution layer is steadily decreasing in thickness from at most 100 nm over time due to evaporation thereof on the imaging member surface as a gloss value with a gloss meter spatially separate from the imaging member surface, the measuring including projecting an incident light having a wavelength onto the fountain solution fluid layer surface at an angle offset from the surface perpendicular, and measuring reflection of the incident light as reflected light by the gloss meter at an equal but opposite angle to the surface perpendicular, wherein a difference between the angle and the opposite angle is 85°, the measuring including determining the fountain solution layer thickness by correlating gloss measurements of the fountain solution aver steadily decreasing in thickness using a slope change of measured gloss to fountain solution thickness, wherein a gloss decrease down from 90 GU corresponds to a fountain solution thickness of 4.6 μm minus about 140 nm GU, the measuring of Step a) occurring before applying ink onto the latent image over the imaging member surface;
• b) modifying the fountain solution dispense rate based on the measured gloss value;
• and
• c) printing a subsequent image by the image forming device using the modified fountain solution dispense rate.

An image forming device controlling fountain solution thickness on an imaging member surface of a rotating imaging member, comprising:

• the imaging member surface being a reimageable ink transfer member surface having carbon black therein to absorb laser light;
• a fountain solution applicator configured to apply a fountain solution fluid layer via vapor deposition at a dispense rate onto the imaging member surface for a printing, the fountain solution fluid layer having a surface above the imaging member surface and a thickness maximum of 100 nm;
• a gloss meter spatially separate from the imaging member surface forming a gap therebetween, the gloss meter located between the fountain solution applicator and an inking member and configured to measure a specular reflection of the fountain solution fluid layer surface while the fountain solution layer is steadily decreasing in thickness from at most 100 nm over time due to evaporation the of on the imaging member surface as a gloss value by projecting an incident light having a wavelength onto the fountain solution fluid layer surface at an angle offset from the surface perpendicular, and measuring reflection of the incident light as reflected light by the gloss meter at an equal but opposite angle to the surface perpendicular, wherein a difference between the angle and the opposite angle is 85°, the measuring including determining the fountain solution layer thickness by correlating loss measurements of the fountain solution layer steadily decreasing in thickness using a slope change of measured gloss to fountain solution thickness, wherein a gloss decrease down from 90 GU corresponds to a fountain solution thickness of 4.6 μm about 140 nm per GU;
• an inking apparatus configured to apply ink onto the continuously decreasing fountain solution layer after the measuring;
• and
• a controller in communication with the gloss meter and the fountain solution applicator to modify the fountain solution dispense rate based on the measured gloss value,
• the fountain solution applicator configured to apply a subsequent fountain solution fluid layer at the modified fountain solution dispense rate onto the imaging member surface for a subsequent printing.