Method and system for indirect measurement of fountain solution using variable laser power

An apparatus useful in a printing device, comprising:

• a dither circuit coupled to a laser imaging system, said dither circuit operable to generate a variable current signal to perturb the laser imaging system to irradiate a fountain solution layer;
• a spectrometer incorporated in the printing device providing a feedback signal of acquired optical density of halftone or solid patches created by the laser imaging system at each variable current signal;
• and
• a processor coupled to the dither circuit being operational to receive and process the feedback signal to adjust a layer of fountain solution based on a determined fountain solution level, wherein the processor determines the fountain solution level by identifying from the feedback signal a maximum optical sensitivity to current variation (dL/dAmps) and identifying from the feedback signal a minimum current value (KneeCurrent) at which a solid patch is below a threshold value.

A method to determine fountain solution level at an imaging surface in a variable data lithography system, the method comprising:

• applying a layer of fountain solution to the imaging surface at a fountain solution flow rate;
• selectively removing with a patterning subsystem portions of the fountain solution layer so as to produce a latent image thereon;
• dithering a current drive output to the patterning subsystem to selectively remove portions of the fountain solution layer at varying current levels;
• analyzing the removed portions of the fountain solution layer to acquire optical density of halftone or solid patches at the varying current levels;
• identifying from the acquired optical density a maximum optical sensitivity to current variation (dL/dAmps);
• identifying from the acquired optical density a minimum current value (KneeCurrent) at which a solid patch is below a threshold value;
• determining fountain solution level from the maximum optical sensitivity and the minimum current value;
• and
• adjusting the layer of fountain solution based on the determined fountain solution level.