Method and apparatus for in-situ digital image forming fountain solution thickness measurement

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 layer at a fountain solution dispense rate onto the imaging member surface, vaporizing in an image wise fashion a portion of the fountain solution layer on the imaging member surface to form a latent image, applying ink onto the latent image, and transferring the applied ink to the print substrate, the method of controlling fountain solution thickness comprising:

• (a) transferring fountain solution from the fountain solution layer dispensed at the fountain solution dispense rate onto the rotating imaging member onto a carrier roll having a surface with a coefficient of friction that varies as a function of fountain solution layer thickness to allow the transferred fountain solution to wet the carrier roll surface and alter the coefficient of friction to a wetted coefficient of friction;
• (b) measuring the wetted coefficient of friction of the wetted carrier roll surface as a measured coefficient of friction;
• and
• (c) modifying the fountain solution dispense rate to a modified fountain solution dispense rate based on the measured coefficient of friction for a subsequent printing of 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:

• a carrier roll having a surface with a coefficient of friction that varies as a function of fountain solution layer thickness;
• a heat source configured to evaporate fountain solution from a fountain solution layer dispensed onto the rotating imaging member at a dispense rate for transfer onto the carrier roll, the transferred fountain solution wetting the carrier roll surface via condensation thereon and altering the coefficient of friction to a wetted coefficient of friction;
• a sensor including a sensor head adjacent the carrier roller and in contact with the transferred fountain solution, the sensor configured to measure the wetted coefficient of friction;
• and
• a controller in communication with the sensor and a fountain solution applicator to modify the dispense rate based on the measured wetted coefficient of friction for a subsequent dispense of a subsequent fountain solution layer at the modified fountain solution dispense rate onto the imaging member surface for an image forming operation thereon.